Stainless Steel cladding and Weld Overlays (2).pdf

ASM Specialty Handbook: Stainless Steels, 06398GJ.R. Davis, Davis & Associates ladding and Weld Stainless Steel verlays A STAINLESS-STEEL-CLAD metal or alloy is a composite product consisting of a thin layer of stainless steel in the form of a veneer integrally bonded to one or both surfaces of the substrate. The principal object of such a product is to combine, at low cost, the desirable properties of the stainless steel and the backing material for applications where full-gage alloy construction is not required. While the stainless cladding furnishes the necessary resistance to corrosion, abrasion, or oxidation, the backing material contributes structural strength and improves the fabricability and thermal conductivity of the composite. Stainlesssteel-clad metals can be produced in plate, strip, tube, rod, and wire form. The principal cladding techniques include hot roll bonding, cold roll bonding, explosive bonding, centrifugal casting, brazing, and weld overlaying, although adhesive bonding, extrusion, and hot isostatic pressing have also been used to produce clad metals. With casting, brazing, and welding, one of the metals to be joined is molten when a metal-to-metal bond is achieved. With hot/cold roll bonding and explosive bonding, the bond is achieved by forcing clean oxide-free metal surfaces into intimate contact, which causes a sharing of electrons between the metals. Gaseous impurities diffuse into the metals, and nondiffusible impurities consolidate by spheroidization. These non-melting techniques involve some form of deformation to break up surface oxides, to create metal-to-metal contact, and to heat in order to Copyright © 1994 ASM International ® All rights reserved. www.asminternational.org accelerate diffusion. They differ in the amount of deformation and heat used to form the bond and in the method of bringing the metals into intimate contact. This article will review each of the processes commonly associated with stainless-steel-clad metal systems as well as the stainless steels used. Design considerations and the welding of stainless-steel-clad carbon and low-alloy steels are also addressed. Additional information can be found in Ref 1 to 3. Hot Roll Bonding (Ref 3) The hot roll bonding process, which is also called roll welding, is the most important commercially because it is the major production method for stainless-clad steel plates. Hot roll bonding accounts for more than 90% of the clad plate production worldwide (Ref 1). It is known also as the heat and pressure process because the principle involves preparing the carefully cleaned cladding components in the form of a pack or sandwich, heating to the plastic range, and bringing the stainless and backing material into intimate contact, either by pressing or by rolling. A product so formed is integrally bonded at the interface. The clad surface is in all respects (corrosion resistance, physical properties, and mechanical properties) the equal of the parent stainless steel. It can be polished and worked in the same manner as solid stainless steel. Table 1 lists the clad combinations that have been commercially produced on a large scale. As this table indicates, stainless steels can be joined to a variety of ferrous and nonferrous alloys. On a tonnage basis, however, the most common clad systems are carbon or low-alloy steels clad with 300-series austenitic grades. The types of austenitic stainless steel cladding commonly available in plate forms are: .. • .. .. .. .. .. .. • lit lit Type 304 (18-8) Type 304 L (18-8 low carbon) Type 309 (25-12) Type 310 (25-20) Type 316 (17-12Mo) Type 316 Cb (17-12 Nb stabilized) Type 316 L (17-12 Mo low carbon) Type 317 (19-13 Mo) Type 317 L (19-13 Mo low carbon) Type 321 (18-lOTi) Type347(18-11Nb) The carbon or low-alloy steel/stainless steel plate rolling sequence is normally followed by heat treatment, which is usually required to restore the cladding to the solution-annealed condition and to bring the backing material into the correct heat-treatment condition. Table 2 lists typical mill heat treatments. The cladding thickness is normally specified as a percentage of the total thickness of the composite plate. It varies from 5 to 50%, depending on the end use. For most commercial applications in- Table 1 Selected dissimilar metals and alloys that can be roll bonded (hot or cold) into clad-laminate form Weldabililyraliog(a) Base metal No.l/No.2 Ag Al Alfesil Be Carbon steel Cn Mn Ni Nb Stainless steel Steel U Ag D D A B AI D D B B B B B AI alloys Au steel Co Cn Mo C D D B D D C D D A B D D B A D D Carbon A A B Mo·N! Nb Ni B D D PI Stainless steel Steel So Ta Ti U Zr D D D D D D D D C D D A A B D D B B B A B D D D D D D B B B B A B B A (a) A, easy to weld; B, difficult but possible to weld; C. impractical to weld; D, impossible to weld. Source: Ref2 A A D D B B B B D D B B B B B B B B B normalize 870 to 900 °C (1600 to 1650 "F) 1 hr per 25 mm (1 in. Procedure selected will be onefavorable forboth cladding andbacking material. % mm in.. normalize 870 to 900°C A301 (all gages) (1600 to 1650 OF)1 hr per 25 mm (1 in.Source:Ref3 volving carbon or low-alloy steel/stainless steel combinations. 316Cb.) thickness. % Type 434 stainless/5052 40:60 aluminum Thickness mm in. lubricants. 316. and other trim components.5:85:7. 20:60:20. involves three basic steps: " The mating surfaces are cleaned by chemical and/or mechanical means to remove dirt. 321.5 0.41 0. 310.15 0.15% max).008-0. or 2 in. often replacing solid stainless steel or aluminum. drip rails. " The materials are joined in a bonding mill by rolling them together with a thickness reduction that ranges from 50 to 80% in a single pass.76 0. surface oxides. corroding sacrificially to the body sleel. 317L. bond created by the massive cold reduction. niobium (0.03% max). high luster. copper. or green.030 0. 304L. Deviationsmay be madeto meet specific requirements. 0.7-150 0. A201. which is shown schematically in Fig. . A212 (up to 50 mm. 316Cb. The shear strength of the cladding bond can be as high as 400 MPa (58 ksi). The clad material can be worked by any of the traditional processing methods for strip metals. Cold Roll Bonding The cold roll bonding process. 316L. The outer layer of carbon steel cathodically protects the stainless core of the tube. air quench. Used in formed cans for transistor and button cell balleries. rocker panels. and slitting are typically performed to produce the finished strip to specific customer requirements.20-2. the resultant clad material can be treated in the same way as any other conventional monolithic metal. 5). stamped. simultaneously cleaning away surface oxide films and creating a metallic bond.56-0. or 2 in. The resulting bond can exceed the strength of either of the parent materials. or 347 304. high-energy impulse of an explosion to drive two surfaces of metal together. Rolling.095 25-64 1-2.321. Clad steels prepared by this method show substantially the same microstructures as those that have been bonded by hot roll bonding processes. and abrasion and dent resistance.. Source: Ref2 Tensile strength MPa ksl 415(a)· 60(a) Applications Widely used for automotive body moldings. or2 in. 316L. extending its life significantly. gage) Anneal 1065 to 1175 °C (1950 to 2150 oF). Heat treatment(a) A285. and nickel. 304L. Hot roll bonding has also been used to clad high-strength low-alloy (HSLA) steel plate with duplex stainless steels (Ref 4.014 Width Yield strength MPa ksi Elongation.022-0. 309.5 17:66:17. 310. and the aluminum on the inside provides sacrificial protection for the painted auto body steel and for the stainless steel. 317. 2) (Ref 6). Other metals and alloys commonly roll bonded to stainless steels include aluminum. annealing. (b)Stabilized orlow-carbon typesof stainless steelshould beusedwhenthisdouble heattreatment is involved. which is a serious problem in underground installations. air quench A204..006 12. Immediately afterwards. 316L.610 :0. The stainless steel provides resistance to gnawing by rodents. air quench. 321. Stainless steel provides bright appearance. 316. the materials have an incipient. pickling.or347 304L. " The materials then undergo sintering. 316Cb. The microalloyed base metals contain small amounts of copper (0. A212 (over 50mm. 317. the cold bonding process is not practical for producing clad plates of any appreciable size. 1.36 0. and nitrogen (0. replacing teme-coated carbon steel tubing. Diffusion occurs at the atomic level along the interface and results in a Upon completion of this three-step process. Used in hydraulic tubing in vehicles. 317L. Anneal 1065 to 1175 °C (1950 to 2150 oF).004-0. gage). Table 3 lists properties and applications of roll-bonded clad laminates. and any other contaminants. cladding thickness generally falls in the 10 to 20% range.108 / Introduction to Stainless Steels Table 2 Typical mill heattreatments for stainlessclad carbonand low-alloysteels Typeof ASTM-grade backingmaterial Typeof claddingmaterial 304. Anneal 1065 to 1175 °C (1950 to 2150 OF). replacing solid nickel at a lower cost Replaces heavier gapes of copper and bronze in buried communications cable.10-0. The two surfaces do not collide instantaneously but rather progressively over the in- Table 3 Typical properties of roll-bonded stainlesssteel Materialssystem Composite ratio.5-6 (a)20/60/20three-layerlaminate. :0.. 309.5 ksi) and impact values of 60 J (44 ft-lbf) at -60°C (-75 OF). or drawn into the required part. 33:34:33 0. Because of the high power requirement in the initial reduction. The single largest application for cold-rollbonded materials is stainless-steel-clad aluminum for automotive trim (Table 3 and Fig.) thickness.010% max) and have mechanical properties comparable to those of duplex stainless steels. 316Cb. The stainless steel exterior surface provides corrosion resistance. 316L. gage) Anneal 1065 to 1175 °C (1950 to 2150 oF). or2 in. A 302 (up to 50mm.321. or 347 metallurgical bond that is due to a sharing of atoms between the materials.24 395 57 360 52 12 305 12 393 57 195 28 35 310 45 40 275 40 20(a) CI008 steel/type 347 stainless steel/CI008 steel 45:10:45 Nickel201/type 304 stainless steel/nickel 201 Copper 1mOO/type 430 stainless steel/copper 10300 7. Typically these HSLA base metals have yield strengths of 500 MPa (72. airquench(b) (a) Heat treatments listedaregenerallycorrect for the material combinations shown. the hidden aluminum base provides cathodic protection. so that the material can be roll formed. Explosive Bonding (Ref 1) Explosive bonding uses the very-short-duration. gage) air quench A201. A 302 (over 50mm. a heat treatment during which the bond at the interface is completed. air quench(b) A204.or347 304L. with a brazing alloy placed between each pair of surfaces to be bonded. or X65 grades and internal cladding made of type 316L stainless steel.Stainless Steel Cladding and Weld Overlays / 109 Chemical Cleaning CLAPDING METAL (a) Mechanical Cleaning Fig. the temperature of the outer shell is monitored. By controlling these various parameters it is possible to achieve minimum mixing at the interface and maintain homogenous cladding thickness and wall thickness. 2 terface area. Centrifugal Casting (Ref 1) An entirely different approach to clad seamless pipe production uses horizontal centrifugal casting technology. Figure 3 illustrates the wavy interface that characterizes most explosive bonds.~ Sintering I Process steps in cold roll bonding Steel body panel (b) Fig. in their respective final gages. and concentric cylinders.) in diameter. Materials are type 304L stainless steel and medium-carbon steel. where the required bond width does not exceed 20 times the flyer plate thickness. More detailed information on explosive bonding is available in Ref? to 9. X60. (c) Closeup of (b) showing mechanism for jetting away the surface layer from the parent layer per the outer pipe to achieve the required mechanical properties. the surface layers and any contaminating oxides present are removed in the form of a jet projected ahead of the collision front.12 in. 1 Roll Bonding ~ . 4 Parallel-plate explosion welding process.5 in. plate. The more commonly used parallel-plate geometry (Fig. (b) Explosion-cladding assembly during detonation. The energy of bonding typically creates sufficient deformation that flattening or straightening is required prior to further processing. The only metallurgical limitation is sufficient ductility and fracture toughness to undergo the rapid deformation of the process without fracture. The pressure generated at the resulting collision front is extreme and causes plastic deformation of the surface layers. Figure 5 lists the combinations that are useful in industry. and the pouring temperature of the stainless steel are the most important factors in achieving a sound metallurgical bond. Finally. 20x Stainless-steel-c1ad aluminum automotive trim provides sacrificial corrosion protection to the auto body while maintaining a bright corrosion-resistant exterior surface. Brazing In furnace brazing. 3 Bond zone pattern typical of explosion-clad metals. First. wall thickness from 10 to 90 mm (004 to 3. The selection of the flux.) (minimum 3 mm.) in diameter. the stainless steel cladding and the backing material. (a) Explosion-cladding assembly before detonation. Sizes range from 100 to 400 mm (4 to 16 in. cladding). withlongerlengths above 200mm (8 in. or 0. Explosive bonding is an effective joining method for virtually any combination of metals. respectively. Centrifugal casting is followed by heat treatment to solution anneal the cladding and quench and tem- (e) Fig. Angle bonding is normally used for bonding sheet components and tubes. well-refined molten steel is poured into a rotating metal mold with flux. are assembled as a multilayer sandwich. Fig. and lengths typically from 4 to 5 m (13 to 16 ft). At a suitable temperature after solidification the molten stainless steel is introduced. Two basic geometric configurations of the explosive bonding process are commonly used: angle bonding and parallel-plate bonding. Flattening is performed with equipment of the same design used in plate and sheet manufacture. The sandwich is heated under continuous vacuum to a temperature at which . the temperature of the outer shell when the molten stainless steel is introduced. the pipe is machined externally and internally to remove the shallow interdendritic porosity in the bore and achieve the required dimensions and surface finish. This leaves perfectly clean surfaces under pressure to form the bond. Generally accepted limits are 10% and 30 J (22 ft-lbf) minimum. Centrifugal cast pipe is available with the outer steel made of API 5L X52. In this way. 4) is applicable for welding larger flat areas. After casting. whereas the purchaser specifies the sur- .. However. -E '(ij .. 5 CD • Commercially availableexplosion-cladmetal combinations the brazing alloy liquefies and forms an intennetallic alloying zone at the interface of the stainless and backing material (normally carbon steels). buildup alloys. and Dissimilar Metal Joining.. 1J a:: o 'w Z eo '0 Q) 2: 0 Qi . More detailed information on brazing of stainless steels can be found in the article" Brazing. Weld cladding is usually performed using submerged arc welding.2 Q) • • • • Stainless steels ED III ED It III Copper aIIoys III Nickel alloys Titanium ::J a:l CD ED It CD ED III Hastelloy It CD It 4& Tantalum ED III • • Niobium • • Silver Gold • Platinum Stellite 68 Magnesium Zirconium Fig. Q) E Q) Q) (f) • • • • • • • • • • • • • • • • " • • " • • • • • " " • • • • • • • • • • ED CD CD III III 4& It Aluminum >'" . Such materials are also difficult to weld except in the flat position.:. The term buildup refers to the addition of weld metal to a base metal surface for the restoration of the component to the required dimensions. For very large areas. E ::J :. Some alloys exhibit eutectic solidification. its original dimensions. Hardfacing produces a thinner surface coating than a weld cladding and is normally applied for dimensional restoration or wear resistance.. or to provide adequate support for subsequent layers of truehardfacing materials.. It differsfrom buildup in that the primary purpose of buttering is to satisfy some metallurgical consideration.. paper digesters.. impact. An extensive review of the weld processes and materials associated with weld overlays can be found in the article "Hardfacing. erosion. and buttering alloys. nuclear reactor containment vessels. Weld cladding is an excellent way to impart properties to the surface of a substrate that are not available from that of a base metal. Buildup alloys are generally not designed to resist wear.. The cladding material is usually an austenitic stainless steel or a nickel-base alloy. flux-cored arc welding (either self-shielded or gas-shielded).::3 mm.2 c ::J .. galling.. plasma arc welding. In addition. Soldering. Welding position also must be considered when selecting an overlay material and process.. but to return the worn part back to. A weld clad is a relatively thick layer of filler metal applied to a carbon or low-alloy steel base metal for the purpose of providing a corrosion-resistant surface.'" . WeldCladding The term weld cladding usually denotes the application of a relatively thick layer (. 'c C... Figure 6 compares' deposition rates obtainable with different welding processes. Hardfacing is a form of weld surfacing that is applied for the purpose of reducing wear.) of weld metal for the purpose of providing a corrosion-resistant surface. coiled electrode wire.. which leads to large molten pools that solidify instantly.2 E ::J C .. It is used primarily for the joining of dissimilar metal base metals.2 ::J '" '" .. or Ys in. Weld Cladding.E ::J .. '" ::J '" . tubesheets. welding vertically or overhead may be difficult or impossible. and strip electrodes. ~ o z o ~ l'" '" I'"eo i= ~ . A wide range of brazing filler metals can be used to join stainless steels to carbon or low-alloy steels. Typical base metal components that are weld-cladded include the internal surfaces of carbon and low-alloy steel pressure vessels. Certain processes are limited in their availablewelding positions (e. with no "mushy" (liquid plus solid) transition. Several inherent limitations or possible problems must be considered when planning for weld cladding. c .0 '...9! '" 0c co. strip welding with either submerged arc or electro slag techniques is the most economical.g. as described in the section "Welding Austenitic-Stainless-Clad Carbon or Low-Alloy Steels" in this article. or cavitation. and Adhesive Bonding" in this Volume. Table 4 lists some of the filler metals for stainless steel weld claddings. co '" E >. urea reactors. Qi >]. 'fc .. and electroslag welding can also produce weld claddings. when using a highdeposition-rate process that exhibits a large liquid pool. and hydrocrackers.. There are several types of weld overlays: weld claddings...s 0 ..c." in Volume 6 of the ASM Handbook (Ref 10). submerged arc welding can be used only in the flat position).. or to conserve expensive or difficult-to-obtain materials by using only a relatively thin surface layer on a less expensive or abundant base material. The most commonly used are silver-base alloys.Buttering also involves the addition of one or more layers of weld metal to the face of the joint or surface to be welded... DilutionControl. The fabricator selects the filler wire and welding process. abrasion. Filler metals are available as covered electrodes..110 / Introduction to Stainless Steels E E 'c 0 'in ::J ~ N Carbon steels Alloy steels Q) c 01 '" :2: Q) ~ ] (f) '" '" Qi Qi '" . The thickness of the required surface must be less than the maximum thickness of the overlay that can be obtained with the particular'process and filler metal selected. Application Considerations. hardfacing materials. or near. Weld Overlays Weld overlaying refers to the deposition of a filler metal on a base metal (substrate) to impart some desired property to the surface thatis not intrinsic to the underlying base metal.The economics of stainless steel weld cladding are dependent on achieving the specific chemistry at the highest practical deposition rate in a minimum number of layers. (a) Refer tn AWS specification A5. gravity causes the weld pool to run ahead of. four microstructure prediction diagrams have found the widest application. These include the Schaeffler diagram.~. Fig.Stainless Steel Cladding and Weld Overlays /111 mum. If the pool is too far ahead of the arc. and the Welding Research Council (WRC) diagrams (WRC-1988 and WRC-1992).) thick stainlesssteel strip.90 mm strip o 4 8 10 12 14 16 18 20 22 24 26 28 30 32 34 Deposition rate. most welding processes have considerably greater dilution.~. A short electrode extension increases dilution. • Travel speed: A decrease in travel speed decreases the amount of base metal melted and increases proportionally the amount of filler metal melted. thus decreasing dilution.025 in. III Electrode extension: A long electrode extension for consumable electrode processes decreases dilution. less base metal penetration and resulting dilution will occur. remain under.~. such as the proper ferrite level to minimize hot cracking. Alternating CUITent results in a dilution that lies between that provided by DCEN and DCEP. or run behind the arc. kg/h Fig.90 mm strip <>"'>'. During the last two decades. A value between 10 and 15% is generally considered opti- Amperage: Increased amperage (current den- sity) increases dilution. the lower the dilution.~. ABB Combustion Engineering . along with the base metal.]. Courtesy of l. For stainless steel cladding.~."*m~""". The prediction of the microstructures and properties (such as hot cracking and corrosion resistance) for the austenitic stainless steels has been the topic of many studies. The most outstanding difference between welding a joint and depositing an overlay is the percentage of dilution: % dilution =.~. The frequency of oscillation also affects dilution: The higher the frequency of oscillation.. 7 Weld cladding of a 1. Submerged arc .4.. and more base metal melting occurs. which results in less dilution.~.60 mm strip Electroslag . and carbon at a low level to ensure corrosion resistance. absence of martensite at the interface for bond integrity.2.experimenting with the welding parameters can minimize dilution. a fabricator must understand how the dilution of the filler metal with the base metal affects the composition and metallurgical balance. III Oscillation: Greater width of electrode oscillation reduces dilution. Each of these is described in Ref 10 and the article" Welding" in this Volume. Although each weld cladding process has an expected dilutionfactor. the DeLong diagram. Because of the importance of dilution in weld cladding as well as hardfacing applications.. each welding parameter must be carefuIly evaluated and recorded. Many of the parameters that affect dilution in weld cladding applications are not so closely controlled when arc welding is performed: Hot wire GTAW Submerged arc . and greater than 15% increases the cost of the filler metal.120 mm strip Electroslag .~ Spray transfer GMAW """ III ~SUbmergedarc . III Polarity: Direct current electrode negative (DCEN) gives less penetration and resulting lower dilution than direct current electrode positive (DCEP).) wide.~ Pulsed GMAW ~. III Electrode size: The smaller the electrode.9. multiply the metric value by 2.~. To obtain equivalent deposition rates in pounds per hour. it penetrates more deeply.60 mm strip Submerged arc .£ x 100 x+y where x is the amount of base metal melted and y is the amount of filler metal added.8 m (6 ft) inner diameter pressurevesselshell with SO mm (2 in.double wire . (b) Referto AWS specification A5. Less than 10% raises the question of bond integrity.64 mm (0. Source: Ref 1 face chemistry and thickness. 6 Comparison of deposition rates for various weld cladding processes. Barger. If the weld pool stays ahead of or under the arc. 0. Unfortunately. III Welding position: Depending on the welding position or work inclination. the lower the amperage.. there will be insuffi- Table 4 Stainless steel fillermetalsfor weld cladding applications First laxer Weld overlay Subsequentlayers Bare rod or electrodetb) Covered Bare rodor Covered type electrode(a) eleclrode(b) eleelrode(a) 304 304L E309 E309L E309Cb E309Cb E309Cb E309 E310 E309Mo E309MoL E317L E309Mo E317 E309MoL E317L E320 ER309 ER309L E308 E308L ER308 ER308L ER309Cb ER309Cb ER309 ER310 ER309Mo E309MoL ER317L ER309Mo ER317 ER309MoL ER317L ER320 E347 E347 E309 E310 E316 E316L ER347 ER347 ER309 ER310 ER316 ER316L E317 ER317 E317L ER317L E320 ER320 321 347 309 310 316 316L 317 317L 20Cb Note: Colombium (Cb) is also referred to as niobium (Nb). The arc becomes hotter.~. tubular rod Various forrns(b) Bare tubular wire 1-10 1-10 1-10 10-20 15-40 15-40 10-20 10-20 30-60 0. as shown in Fig.025 in. tubular wire Flux-covered cast rod. strip.13 Form of hardfacingalloy Deposition \-32 Y32 Y. single Minimum thickness(a) Weld-metal dilution.9-5 (d) 25-60 25-35 1-15 1-8 1-8 2-12 2-12 (d) 4.) thick stainless steel strip used to clad a 300 mm (12 in.) wide by 0. such as base metal. flux-covered tubular rod Alloy-cored tubular wire Alloy-cored tubular wire Bare cast rod. (d)Varies widely depending on powderfeedrateandlaserinput power . low-alloy steels. wire. 8 Hardfacing materials include a wide variety of alloys.5-4 0. and ferrous alloys (high-chromium white irons. The most popular processes. Hardfacing alloy selection is guided primarily by wear and cost considerations. self-shielded flux-cored arc welding.5-7 0. oxidation. lis %2 3!:l2 Ys Deposit efficiency. and stainless steels). Hardfacingprocess Consumable form Oxyfuel/oxyacetylene (OFW/OAW) Shielded metal arc (SMAW) Bare cast or tubular rod Coated solid or tubular rod (stick electrode) Bare cast or tubular rod Tubular or solid wire Tubular wire (flux cored) Tubular or solid wire Powder Powder Gas-tungsten arc (GTAW) Gas-metal arc (GMAW) Flux -cored open arc Submerged arc (SAW) Plasma transferred arc (PTA) Laser beam Table 5 Characteristics of welding processes used in hardfacing Welding process OAW SMAW Open arc GTAW SAW Modeof application Manual Manual Automatic Manual Semiautomatic Automatic Manual Automatic Automatic. wide beads produced by oscillated multiple-wire systems or strip electrodes have become the means to improve productivity and minimize dilution while offering a uniformly smooth surface.8 0. and combinations of these alloys. Hardfacing alloys usually are available as bare rod. However. and the forms most commonly associated with each process. corrosion. helium.) inner diameter pressure vessel nozzle.5-5 5-11 1-4 1-4 1-15 1-12 5-25 5-25 1-6 1-10 10-25 0.5-4 0. extra-long (2. Courtesy of ).tungsten carbide powder withcastrodorbaretubular wire.5-2 0.4 2.005 95 95 85-95 98-100 98-100 90-95 90-95 85-95 (a)Recommended minimum thickness of deposit. Conventional hardfacing alloys are normally classified as carbides (We-Co). flux-coated rod. austenitic manganese steels. carbides.8 0.2 3. reduces dilution by increasing the total amount of filler metal and reducing the amount of base metal that is melted.% kg/h Ib/h mm in.112/ Introduction to Stainless Steels Hardfacing Alloys Fig. or powders.6 1. • Additionalfillermetal: Extra metal (notincluding the electrode). The following list ranks various shielding mediums in order of decreasing dilution: granular flux without alloy addition (highest). long-length solid wires. gas or flux. % 100 85-95 100 65 80-85 80-85 98-100 98-100 95 wire Automatic. Barger.6 0. added to the weld pool as powder.8 2. other manufacturing and environmental factors must also be considered.).64 mm (0. ABB Combustion Engineering dent melting of the surface of the base metal. carbon dioxide. argon.5-7 0. cobalt-base alloys. nickel-base alloys. also affects dilution. tubular rod Various forrns(b) Alloy-cored tubular wire Alloy-cored tubular wire Powder 15-25 10-25 5-15 5-15 5-15 10-40 10-40 1-10 11-27 11-16 0.4 3. and thermal requirements.2 3. Stainless steel hardfacing alloys include martensitic and austenitic grades.8 3. multi wire Automatic. deposition process. Usually.5-2 0. Bare cast rod. For weld cladding the inside surfaces oflarge pressure vessels. (c) Withor without tungsten carbide granules. (b)Baretubular wire. the latter having high manganese (5 to 10%) and/or silicon (3 to 5%) contents.4 m.5-5 2-11 2-11 0.32 Y I6 1/16 0.4 2.2 Y32 Bare tubular wire Bare tubular wire Powder(c) Bare cast rod.2 2. are: Closeup view of the 25 mm (1 in. seriesarc PAW GMAW Laser Automatic Manual Automatic Semiautomatic Automatic Automatic 3/16 3/16 Y32 %2 3. As will be described below.9-5 0.or8 ft) barecastrod.8 0. • Arc shielding: The shielding medium. and granular flux with alloy addition (lowest). both cobalt-containing and cobalt-free austenitic stainless steel hardfacing alloys have been developed.5-3 0. tubular rod Powder Extra-long bare cast rod. or with flux. and impact. 7 and 8. the hardfacing process dictates the hardfacing or filler metal product form. and coalescence will not occur.4 1. long-length tube wires (with and without flux).8 4. Welding parameters for stainless steel strip weld overlays are described in Ref 10. Y. 01 0.4 2.3 4. and crane wheels. 0.0 2. wt% 0.0 bal Martensitic air-hardening steels (including stainless steels) are metal-to-metalwear alloys that.02Cu. corrosion.9 1.2 5. and L.7 0. thesematerials are commonly referred to as machinery hard/acing alloys.4 1.7 6. and they have a microstructure consisting of an austenitic matrix containing eutectic alloy carbides.12N.05-0.07Co C Mn Si NOREM Ol/Stoody NOREM Ol/Cartech 1.7-1. However. 0.7 1.0 bal produced. or replacement of components.6 0.5 4.3 1.3 0. 0. in a fluid that is moving across the surface of a solid component.6 2. Compositions of these alloys are given in Table 8. These alloys can be deposited successfully on stainless and carbon steel substrates with gas-tungsten arc welding. The stainless steel in this category is AWS ER420.47 2 2.7 0. seat valves.3 2. along with various forms.. Table 6 Galling wear of gas-tungsten arc weld overlays made from cobalt-free NOREM alloys Alloy/form NOREM Ol/solid NOREM Ol/solid NOREM OI/metalcore NOREM Ol/metalcore NOREM OI/metalcore NOREM 04/metalcore Stellite 21/solid Stellite 6/solid Stress. material loss has been found for cobalt-base hardfacings used for control or throttle valves that are exposed to high flow velocities.3 3.ElectricPower Research Institute P .OICo 0.2 2. More detailed information on the selection of hardfacing alloys and processes can be found in Ref 10. which is a strong emitter of gamma radiation.0 24-26 4. Galling wear data for various NOREM and cobalt-base alloys are given in Table 6.1 2.7 0. the Electric Power Research Institute has developed cobalt-free NOREM alloys (U. Nominal compositions of the NOREM alloys are as follows: Element Composition.2 1. deposition rates. which has a hardness value of 24 HRC and the following chemical composition: Element Carbon Chromium Manganese Silicon Nickel Molybdenum Iron Composition. 1989).1 1. Fox Antinit DUR 300 (28 to 32 HRC). Typical examples of applications where buildup alloys are used for wearing surfaces include tractor rails. 0.2 4.Dl5 O. and large slow-speed gear teeth. iron-base hardfacing alloys.0 2. iron-base alloys have been performed since the late 1960s. material loss due to wear.19 NOREMA/Anval 1.13 25.0 nt nt nt 1.15 bal Carbon Chromium Manganese Silicon Nickel Molybdenum Nitrogen Iron NOREM alloys are characterized by high wear resistance and antigalling properties. in any position and with no preheat.068Co 0. steel mill table rolls. The activated particles are incorporated into the oxide layers of primary system components and contribute considerably to the occupational radiation exposure of maintenance personnel during the inspection.029 0.A.9 (a) Single values are maximum values.3 8.7-2. Hence. 7.15 3.E.3 nt 0.4 1.can be applied(withoutcracking)to wearing areas of machinery parts.S.M.3 1. wt% 0.3 1.007Ti.02 0.03Nb. Chemical compositions of the alloys tested are provided in Table 7. austenitic manganese steels are used as wear-resistant materials under mild wear conditions.5 4. and modes of application of hardfacing alloys.5 0.01 2.7 1.0-9. Cobalt-base alloys have been traditionally used for hardfacing nuclear plant valves (check valves.17 12.6 0.S.2 5.0-5. are given in Table 5.6 nt Source: H.4 0. The buildup alloys include low-alloy pearlitic steels.\. Everit 50 (47 to 53 HRC) .9 2.Stainless Steel Cladding and Weld Overlays /113 Typical dilution percentages. Typical applications of this alloy family include undercarriage components of tractors and power shovels.2 1.0 1. and minimum deposit thicknesses for different welding processes. repair.22 7.1 0. Ocken. at indicatedtestsin air 275 (40) 415 (60) 140(20) 275(40) 415 (60) 0.MPa (ksi) tests in water 140 (20) Surface damage. The stainless steel included in this category is AWS EFeMn-Cr.236N. 0. um.(%(a) Cr Ni Mo S Other 0. is AlIoylVendor Nominal composition.3 1.803. or cavities.006 0.22N. and high-manganese austenitic stainless steels. Cobalt-containing austenitic stainless steels have been developed by Hydro-Quebec for the repair of the cavitation erosion damage of its hydraulic turbines. Additional information on these alloys can be found in Refll to 14.0 1. Studies have demonstrated that these alloys have tribological. indicating that this type of alloy has a limited resistance to erosion-corrosion and cavitation attack. The particles are entrained in the coolant flow through the core.4 0.8 0.5 1.0 15.03 NOREM 04/Anval 1. and mechanical properties comparable to those of cobalt-base Stellite 6 (Ref 15).5 15.3 12. compositions. Cavitationrefers to the formation of vapor bubbles.17 25 25. using controlled heat input techniques.E Rueil-Malmaison (France).3 0. railroad rail ends.27 9.5 0.5 1.05Cu.045.8 0.7 1. The NOREM alloys meet or surpass the performance of cobalt alloys with respect to corrosion. Electric PowerResearch Institute Table 7 Chemical compositions of the NOREM hardfacing alloys listed in Table 6 Cobalt-free austenitic stainless steels have been developed to replace cobalt-base hardfacing alloys (Stellite grades) in nuclear power plant applications. and Co60 . Feb.3 0.5 4. Detailed investigations of candidate replacement cobalt-free.009 1.Source:H. wt% 0. and maintenance of the valve's sealing function.0 1. its original dimensions and to provide adequate support for subsequent layers of true hardfacing materials.4 nt 1. steel mill work rolls.5-3.018 0. these alloys are not designed to resist wear but to return a worn part back to.9 2.. Considerable work has also been carried out in Europe on cobalt-free.7 26. because they generally show high corrosion resistance and superior tribological behavior under sliding conditions. and control valves).7 0.81 0. In the U. with care. However. 0. respectively. Vereinigte Edelstahlwerke Kapfenberg (Austria).21 0. Ocken. O. which has a hardness value of 45 HRC and the following chemicalcomposition: Element Carbon Chromium Manganese Silicon Iron Composition. Patent 4.6 0. Additionally. even the (usually low) corrosion and sliding-wear rates of these hardfacings lead to a release of particles with a high cobalt content. or near. austenitic manganese (Hadfield) steels.5 1. and Cenium Z 20 (42 to 48 HRC) are tradenames used by Thyssen Edelstahlwerke Bochum (Germany).0 1.IN 0. For the most part. carbon can be replaced by nitrogen. Source: Ref 18 Studies by Simoneau (Ref 16 and 17) at the Institut de Recherche d'Hydro-Quebec have determined that the elements most favorable to cavitation resistance.301. which are balanced with silicon and chromium to give good corrosion resistance. 9 Effect of carbon plus nitrogen additions on cavitation erosion of cobalt-containing alloys. Source:Ref 15 These vapor bubbles are caused by localized reductions in the dynamic pressures of the fluid. and so on. 10 Effectof cobalt additions on cavitation erosion of austenitic stainless steels.2 0. Thus. In the" incubation" period of the alloy surface under a cavitation condition.5 0. Nickel is detrimental.6L. cobalt. whereas chromium and manganese show a neutral effect within the 8 to 12% Co range. The composition of cobalt-containing austenitic stainless steels provides a balance of elements in such a way that an essentially austenitic yphase with a low stacking fault energy is obtained in an as-welded and solidified weld overlay.5V 8. ship propellers. This metastable face-centered cubic (fcc) y-phase transforms under stress to a body-centered cubic (bee) rx-martensitic phase exhibiting fine deformation twins.6'-----'-_-'-_. This eventually results in serious erosion damage to the metallic surfaces and is a major problem in the efficient operation of hydraulic equipment. carbon.7 0. nickel has been replaced by manganese and cobalt.0. and Fig..5 2.wt % 0. molybdenum) to stabilize the austenite phase at room temperature. In order to increase the ductility and the corrosion resistance. it must be supplemented with manganese. on the steady-state rate of cavitation erosion.1 C + N concentration.3 0.5 NR(b) . in decreasing order. this incubation period is long and high hardness levels (450 HV) are reached in the steady state.4 00 0 Ctp 0 o Cb o 0 goo o 0 --.9 1. Because the twins are relatively small and the metal particles also small.2 17 9. Decreasing the nickel and replacing it with cobalt results in a decrease in yield strength and in an important increase in ultimate tensile strength. The metal loss during this period is generally minimal.(b) NR. runners. which exhibit a transformation from a fcc y-phase to a hexagonal close-packed (hcp) s-phase in addition to twinning. excessive downtime and lost revenue. the result is a uniform and slow degradation of the metal surface. The outstanding cavitation erosion resistance of cobalt-containing austenitic stainless steels comes from a patented chemistry formulated to yield the highest work-hardening rate. reduced operating efficiencies.-----I 0. pumps. the hardness increases as deformation twins form on the surface. manganese) and ferritizer elements (chromium.-_---'-_ _-'-_ _.114 / Introduction to Stainless Steels Table 8 European-developed cobalt-free hardfacing alloys Alloy Everit50 Fox Antinit Dur 300 CeniumZ20 C Mn Si 2.6 ~ 2. and in particular for the cobalt-containing stainless steel. and silicon. This larger strain hardening is as- . nitrogen.L-_--I_ _.5 5. valves.°.---1 ~ o °0 0 d90a 0 moval of small metallic particles from the exposed surface.6 True strain Fig. unspecified other elements .5 0.2 0. which leads to the re- 3 <D 00 0 2. it increases to a very high value at larger strains (up to 1. and shortened equipment service life. The work. 11 Tensile stress-straincurves of 308. such as hydroturbines.0 21.8 o c o 00 010 .26) for cobalt-containing stainless steels. and cobalt-containing stainless steels. The damage caused by cavitation erosion frequently contributes to higher maintenance and repair costs.L-_-'-_---'-_---'-_--IL. 11..0 27 Mo Olher 3.5 9 0.1.1 0. Figure 9 presents the effect of carbon plus nitrogen.' 0. The nominal composition for these alloys is: Element Composition.0 18 2. Although the initial strain-hardening coefficient for these steels is quite similar.wt%(a) Cr Ni 25. Source: Ref 17 Carbon Chromium Manganese Silicon Cobalt Nitrogen Iron 0.. Source: Ref 17 301 304 Fe-18Cr-l0CD O"--_. are carbon. The collapse of these vapor cavities produces extremely high compressive shocks.0 6.2 E ~_ 1. because it only very slightly lowers the martensitic transformation temperature. Unlike the case for other alloys. such as 300-series stainless steels. further cavitation causes damage by initiating fatigue cracks and subsequent detachment of particulates at the intersections of the deformation twins. and the surface is smooth and hardened. ~ 1200 ~c o 'ii) e w o o 0. After the surface is fully hardened. silicon. or nitrogen. Cobalt alone is not sufficient as an austenitizer. % Fig.2 bal 2000 1600 ro a.4 0.°--"----:-0..0 W. These repeated collapses (compressive shocks) in a localized area cause surface tearing or fatigue cracking. and in order to stabilize a fully austenitic structure.::. The phase transformation and twinning absorb the energy of the shock waves generated by the collapsing of the vapor bubbles.or strain-hardening coefficient increases markedly when going from 304 to 301. The main effect of these chemical composition modifications on the mechanical properties of austenitic stainless steels is illustrated by the tensile curves shown in Fig. For the same reason.5 o 0.:.3 0.1 0.5 (a) Singlevaluesaremaximum values. use of replacement power (which is very expensive). 10 presents the effect of cobalt concentration. The combination of carbon and nitrogen has an equivalent effect. These results allow the formulation of alloys with the appropriate amount of austenitizer (carbon.~ w 1..L---'_---'-_-'-_L---l 6 4 8 10 12 14 16 18 20 CDbait concentration.. cobalt. which leads to local elastic and/or plastic deformation of the metallic surfaces.. % Fig. Such behavior is similar to that of cavitation-resistant highcobalt alloys. notreported. with a high interstitial carbon and nitrogen content.12 0. nitrogen.3 .0 NR(b) Chemicalcomposition. as shown in Fig... Cobalt-containing austenitic stainless steels are about ten times more resistant to cavitation erosion than the standard 300-series stainless steels (Fig. whereas substantial strain hardening was measured for austenitic stainless steels and the cobaltbase alloy.) and 1. 12.. 15 Heatexchanger fabricated using clad brazing ("self-brazing") materials . It appears to be not so much the initial hardness or the strain energy (area under the stress-strain curve) that controls cavitation resistance.. in good correlation with their ultimate tensile strength and cavitation resistance. min (a) 400 ~ Stellite-21 .. Additional information on cobalt-containing stainless steel hardfacing alloys can be found in Ref 16 to 23 and in the article "Tribological Properties" in this Volume._'_~.L.Q d ::: 300 d Fe-18Cr-l0Co A > I ~ 0 ss:e«i 200 ~""'--: 301 30B --==-_o . The as-welded hardness is around 25 HRC. 14 "E 308SS Deformation-induced martensitic transformation measured in tensile tests. and the ultimate strength can exceed 1000 MPa (145 ksi)... the less the plastic deformation required to transform the fcc "{-austenitic phase to the bee a'-martensitic phase.jim (b) Fig. but rather the strain-hardening capability under cavitation exposure (Ref 18).. of the less stable austenite phase. comparable to that of type 301 stainless steel.. strength..:::[g-::::I':::=------..~~.) and 4.J o 50 100 150 200 250 300 350 400 450 Depth. 15.045 in.00 s: '§..00 45 0... and cor- SELFBRAZING MATERIAL (CopperClad StaInlessSteel) SELF BRAZINGMATERIAL (Copper Clad StainlessSteel) Fig.) shielded metal arc welding electrodes. fe-15Mn-14Cr Stellile-21 Stellile-6 fe-IOCr-lOCo fe-18Cr-8Co Alloy Fig..Source: Ref 18 Comparison of cavitation erosion rate of various materials.o-1~-'-~l-o.appearance. Designing with Clad Metals (Ref6) The choice of a material for a particular application depends on such factors as cost.. E 20.. The original experimental cobalt-containing stainless steels were named IRECA to denote Improved REsistance to CAvitation.. % 35 40 5.00 5 Ou:. The hardness values measured on the surfaces exposed to cavitation also correspond quite well to values equivalent to their ultimate strength. being somewhat limited by the higher carbon content.l : l . availability.2 mm (0.00 30 25. Figure I3(b) shows that strain hardening is restricted to a very thin surface layer « 50 um).Stainless Steel Cladding and Weld Overlays / 115 35. their ductility is good enough to be welded or cast without cracking.6 mm (1/16 in.-L~-'-.... which is a tradename of Thermodyne Stoody. 'Y~a'. 12 500 Fe-1BCr-l0Co A_ '0 II-- ~ 400 Stellite-21 Ol ~ > I ~300 c {--30B «l s: § 200 ~ o (ID- - - - 1020 (ferrite) 100'----_-'-_---'--_ _'----_-'-_---'--_---' -50 50 100 150 200 250 o Cavitation time..0 mm (5/32 in. the annealed yield strength is around 350 MPa. with work-hardened materials reaching 50 HRC. electrical or thermal properties..-- o 5 10 15 20 25 30 Elongation.L. fabricability.------. which is even thinner for the cobaltcontaining alloys. 13 Source: Ref 18 301SS CA-6NM Cavitation-induced surface (a) and crosssection (b) hardening in various materials.00 ell 304N 304 301N Fe-1BCr-l0Co '§ c 0 '(. The higher the cavitation resistance.. The currently commercially available welding consumables that can be deposited on stainless and carbon steel substrates are 1.00 1020 Fig. Although cobalt-containing stainless steels may become less ductile because of their high work-hardening coefficient. only 5% elongation is required to produce some 25% transformation.. -_ _ o 1020 ""-------XJo---_:>----~~'""t ~ 1OO.00 34 35 30.. Figure I3 presents the actual hardness values reached by the material surface exposed to cavitation.-----. thematerialsareadequateformostapplicationsin flowing river or tap waters.. Source: Ref 18 sociated with a faster initial martensitic transformation..-.....2 mm (1/8 in. The corrosion resistance is fair..) gas-metal arc welding wires and 3..00 e UJ 10. With a tensile elongation between 10 and 55%. Nevertheless. For the cobalt-containing steel. The name for these consumables is Hydroloy HQ9 13.. mechanical properties. 14). Almost no cavitation-deformation hardening could be detected for 1020 carbon steel. These clad metals find various applications in the marine. plate. power. These products are used primarily in highvolume manufacturing operations. and in the polishedand-etched condition (Fig. and motor vehicles. the metallographic structure of the stainless steel is clearly visible. Clad metals of this type are typically used in the form of strip. and tubes and . Figure 17 shows cross sections of this material. The noble metal cladding ranges from commonly used stainless steels. After brazing. and honeycomb structures. steel is frequently chosen as the substrate. such as the production of heat exchangers. The grain structure is analogous to that of annealed stainless steel strip. C12200 copper clad to 3041.). The cladding metal is chosen for its corrosion resistance in a particular environment. A turbulator is brazed to a copperclad stainless steel base and cover. such as Inconel625.. Additional material on clad brazing alloys can be found in Ref 24 and 25. cost. furnace tubes.5/86. sour gas.116/ Introduction to Stainless Steels Table 9 Properties of copper-clad stainless steel brazing alloys Material system Two-layer systems C12200/304LSS CI2200/409SS Layer thickness ratio MP. The use of a self-brazing sheet reduces the total part count. using the cold roll bonding technique. (a) Designing Clad Metals for Corrosion Control (Ref 6) Clad metals designed for corrosion control can be categorized as follows: • • . provide an example of the unique properties designed into a clad material. ksi MP. 17b). and tubing. Properties of two-layer and three-layer brazing strips are listed in Table 9. 16 stainless steel Photomicrograph of typical clad brazing material. 18 Stainless-steel-clad aluminum truck bumper material that combines the corrosion resistance of stainless steel with lightweight aluminum ing. ksi 50mm(2ln. which is important when making a hermetically sealed heat exchanger. and reduces assembly time and. Clad metals provide a means of designing into a composite material specific properties that cannot be obtained in a single material.5 15/85 590 650 400 86 94 58 255 300 215 37 43 31 55 55 36 10/80/10 13n4/13 32/34/32 10/80/10 15/80/5 600 575 380 385 385 87 83 55 56 56 310 290 170 205 205 45 42 25 30 30 55 53 48 37 37 0. the dimensional changes in this part are minimal. Selection of the substrate metal is based on the properties required for a particular application. reaction and pressure vessels. (a)Aspolished. Fig.. such as copper-clad stainless steel (Cu/SS or Cu/SS/Cu). when strength is required. Noble metal clad systems Corrosion barrier systems Sacrificial metal systems Transition metal systems Complex multilayer systems Proper design is essential for providing maximum corrosion resistance with clad metals. and pollution control industries. 300x. One example is type 304 stainless steel on steel. SOOx Aluminum Stainless steel Fig. Figure 16 shows a typical clad brazing strip of copper-clad stainless steel. Self-brazing materials. to high-nickel alloys. (b) Polished and etched. high temperature. 17 Photomicrographs of cross sections of type 304 stainless-steel-clad carbon steel.% 6/94 13. brazed bellows. simplifies the assembly operation (because the brazing filler metal is always present on the core material). A wide range of corrosion-resistant alloys clad to steel substrates have been used in industrial applications. such as seawater. Specific uses include heat exchangers. such as type 304. there is no need for the application of flux or for its subsequent removal. This not only saves the initial purchase cost of the flux. The strips comprise a base metal that is clad with a brazing filler metal on either one or both sides. therefore. The base and cover are formed from a stainless steel strip containing copper braze on one side. chemical process- (b) Fig.2%yield strength Tensile Elongation in Three-layer systems C I2200/304LSS/ CI2200 CI2200/409SS/ C12200 Source:Ref 25 rosion resistance. In addition. For example. Noble metal clad systems are materials having a relatively inexpensive base metal covered with a corrosion-resistant metal. but also the waste-management cost associated with the disposal of the spent material. The uniformity of the bond interface is apparent in Fig. 17(a). Figure 15 depicts an automotive transmission fluid cooler that was assembled using clad brazing materials. This section will discuss the basis for designing clad metals for corrosion resistance. • . Clad brazing materials are produced as strips. In general. but also allows welding techniques to be used when direct joining is not possible. 316. Deposits of type 309. A portion of the stainless steel cladding is removed from the back of the joint. are in the active region of the galvanic series and are extensively used for corrosion protection. or 347 should not be deposited directly on carbon or low-alloy steel. The copper layer on the inside provides the electrode contact surface as well as compatible When the nonstainless portion of the plate is comparatively thick. (b) Carbon-steelclad stainless steel tube elements for boilers. only a thin pore-free layer is required. the second method is often preferred. and aluminum. ill many cases. 18). In environments in which the corrosion rate of copper is high. It not only reduces galvanic corrosion where dissimilar metals are joined. (a) Fig. The stainless steel layer provides strength and resistance to perforation corrosion. Welds made with types 309 and 312 filler metals are partially ferritic and therefore are highly resistant to hot cracking. ill this corrosion barrier system. Sacrificial metals. localized corrosion of the type 304 stainless steel is arrested at the C-276 alloy interface. and carbon or low-alloy steel filler metal is used for the remainder. such as magnesium. Low-carbon steel and stainless steel are susceptible to localized corrosion in chloride-containing environments and may perforate rapidly. the type 302 stainless steel cladding provides a bright corrosion-resistant surface that also resists the mechanical damage (stone impingement) encountered in service. The aluminum provides a substrate with a high strength-to-weight ratio. one side is exposed to one corrosive medium. For example. filler metals of type 308. scrubbers. 20 of carbon steel clad to type 304 stainless steel demonstrates how this combination prevents perforation in seawater. The example shown in Fig. 309Cb. Corrosion Barrier Systems. Thus. (c) Carbonsteel-clad type 304 stainless steel . 2. zinc. or a critical material may be required in large quantity. and stainless steel filler metal is deposited. This material can be used for tubing and for wire in applications requiring strength and corrosion resistance. the differences in the coefficients of thermal expansion of the base plate and the weld should be taken into consideration. type 304 stainless steel that is clad to a thin layer of Hastelloy C-276 provides a substitute for solid Hastelloy C-276. A single material may not be able to meet this requirement. When steel is clad over the stainless steel layer. The location of the sacrificial metal in the galvanic couple is an important consideration in the design of a system. 20 cell chemistry. Carbon steel cannot be used when increased general corrosion resistance of the outer cladding is required. Another group of commonly used noble metal clad metals uses aluminum as a substrate. stainless-steel-clad nickel (Cu/SS/Ni) is used where the external nickel layer provides atmospheric-corrosion resistance and low contact resistance. as described for the stainlesssteel-clad aluminum automotive trim shown in Fig. although type 310 is fully austenitic and is susceptible to hot cracking when there is high restraint in a welded joint. it is more economical to use the first method. (a) Solid carbon steel. depending on plate thickness and service conditions: • The unclad sides of the plate sections are beveled and welded with carbon or low-alloy steel filler metal. stainlessclad plate can be welded by either of the two following methods. Therefore. The procedure most commonly used for making welded joints in stainless-clad carbon or lowalloy steel plate is shown in Fig. In small battery cans and caps. Stainless steel filler metal is deposited only in that portion of the weld where the stainless steel cladding has been removed. the sacrificial metal may be located precisely for efficient cathode protection. 21. materials are exposed to dual environments. All stainless steel deposits on carbon steel should be made with filler metal of sufficiently high alloy content to ensure that normal amounts of dilution by carbon steel will not result in a brittle weld.Stainless Steel Cladding and Weld Overlays / 117 Low-carbon steel (a) Low-carbon steel Stainless steel (b) Fig. while the inner copper layer maintains high electrical conductivity of the shield. A low-grade stainless steel with good resistance to uniform corrosion but poor resistance to localized corrosion can be selected. The most widely used clad metal corrosion barrier material is copper-clad stainless steel (Cu/430 SS/Cu) for telephone and fiber optic cable shielding. Complex Multilayer Systems. When welding components for applications involving elevated or cyclic temperatures. (a) Low-carbon steel. CD The entire thickness of the stainless-clad plate is welded with stainless steel filler metal. The combination of two or more metals to form a corrosion barrier system is most widely used where perforation caused by corrosion must be avoided (Fig. 310. 309L. copper-clad. When the nonstainless portion of the plate is thin. that is. 309Mo. in stainless-steel-clad aluminum truck bumpers (Fig. MA. or 312 are usually acceptable. ill seawater service. 19). Localized corrosion of the stainless steel is prevented: The stainless steel is protected galvanically by the sacrificial corrosion of the steel in the metal laminate. as in most pressure vessel applications. By cladding. Photomicrographs of cross sections of materials after 18 months of immersion in seawater at Duxbury. A clad transitional metal system provides an interface between two incompatible metals. the corrosion barrier mechanism prevents perforation. The backgouged por- (b) (e) Welding Austenitic-Stainless-Clad Carbon or Low-Alloy Steels (Ref 26) To preserve its desirable properties. while solid type 304 stainless steel does not. 19 Illustrations of the corrosion barrier principle. such as acidic or sulfide-containing soils. and the other side is exposed to a different one. (b) Type 304 stainless steel. welds made with type 310 filler metal should be carefully inspected. Transitional Metal Systems. and other systems involved in the production of chemicals. the stainless steel acts as a corrosion barrier and thus prevents perforation. Figure 22 illustrates an alternative method (method A) of welding clad plate. method B). penetration must be held to a minimum. the welding procedure must be carefully controlled to obtain the desired weld metal composition in the outer layers of the weld. are made with stainless steel filler metal. - a(min) ( a) Faces beveled and cladding stripped (b) Filled up (c) Welded from side A. If the cladding is of type 316.5 mm WB in. 3 '<.) from each side of the joint. the first layer must be sufficiently high in alloy content to avoid cracking as a result of normal dilution by the carbon steel base metal. or an inlay of wrought stainless steel can be welded in place (d. This method is more expensive than the method described in Fig. butt and corner joints). . (f) When required for severely corrosive service. weld ground flush an side B (d) Surfaced fromside B ~----------------Methad A . and the joint is fitted up in position for welding. 21f) to ensure uniformity of corrosive resistance. 21 because of the cost of removing a larger portion of the cladding and depositing more stainless steel filler metal. the first layer is deposited with type 309 Mo filler metal and the subsequent layers with type 316. Chemical analysis of sample welds should be made before joining clad plates intended for use under severely corrosive conditions. methods A and B).Carbon steel filler metal is deposited.~3'11fj~~-Cladding SluE B (b) Fitted up (c) Welded from side A. 22 (e) Welded from side B ( f ) Protective plate welded an Fig. The fillet welds joining the protective plate to the cladding should be carefully inspected after deposition.) to the cladding. methods A and B). When the cladding is of type 304L or 347. the first layer of stainless steel weld metal should be of type 309 or 312.. A stringer bead technique should be employed. using stainless steel filler metal exclusively. 23 Procedures for welding V-groove butt and corner joints in stainless-clad carbon or lowalloy steel plate. The same basic welding procedure is followed for both the butt and comer joints shown in Fig. in which a carbon or low-alloy steel weld joins the carbon steel portion of the plate. tion of the stainless steel cladding should be filled with a minimum of two layers of stainless steel filler metal (Fig. 23. if necessary.6 mm (1/16 in. and the root of the weld is ground flush with the underside of the carbon steel plate (c. a narrow protective plate of wrought stainless steel of the same composition as the cladding is welded over the completed weld (Fig. taking care not to penetrate closer than 1. The joint is prepared by beveling side A and removing a portion of the stainless steel cladding from side B to a minimum width of 9.. a protective strip of stainless steel plate may be fillet welded to the cladding to cover the weld zone. using stainless steel filler metal only in portion of joint from which cladding was removed.. In some applications.--------- Weld metal (carbon steel) (b) Fitted up SIDE A (d) Gouged from side B q . Because there is no danger of alloy contamination from the cladding layer.The area from which cladding was removed is surfaced with at least two layers of stainless steel weld metal (d. If the cladding is of type 304 stainless steel. In depositing the stainless steel weld metal. and the use of stainless steel Alternative procedures for joining stainless-clad carbon and low-alloy steel plate involving different techniques for replacing portions of the stainless steel cladding removed before welding the carbon or low-alloy steel side. If the proper weld metal composition is not achieved after the second layer has been deposited. (c) Carbon steel filler metal is deposited from side A (a low-hydrogen filler metal is used for the first pass). (a) and (b) The clad plates are machined for a tight fitup. 23. The clad plates are beveled and fitted up (a and b. before depositing stainless weld metal from the stainless steel side (d. 2Ie). an additional layer is recommended if a high weld reinforcement at the cladding surface can be tolerated. a stainless steel weld is deposited from the carbon steel side. Subsequent layers of weld metal can be oftype 308. of course.118/ Introduction to Stainless Steels ~ D?i. butt and corner joints). After the plate has been beveled and fitted up for welding. (d) Stainless steel cladding on side B is backgouged until sound carbon steel weld metal is reached. 21 Procedure for welding stainless-clad carbon and low-alloy steel.--e. The most common method of joining stainless-steel-clad carbon or low-alloy steel plate with a weld that consists entirely of stainless steel is shown in Fig.. a portion of the second layer should be ground off and additional filler metal should be deposited to obtain the desired composition. filler metal is limited to replacement of the cladding that was removed prior to making the carbon or low-alloy steel weld. such as submerged arc welding. Use of a root gap (not shown) is permissible (a and b.. 22 permits the use of faster welding processes. method A in Fig. This method is most frequently used for joining thin sections of stainlessclad plate. using a filler metal sufficiently high in alloy content to minimize difficulties (such as cracking) resulting from weld dilution and joint restraint. These welds. (e) The backgouged groove is filled with stainless steel weld metal in a minimum of two layers.. in depositing the carbon steel weld. method A). .) above the stainless steel cladding. Figure 22(d) of method B shows an alternative procedure in which the exposed carbon steel weld on side B is covered by welding an inlay of wrought stainless steel to the edges of the cladding. The root of the weld is cleaned and gouged. with the bottom of the weld groove not less than 1.6 mm (1/16 in. weld ground flush on side B (d) Inlaid and welded ~----------------Method B---------------~ Fig. (a) Faces beveled (b) Fitted up (c) Welded from side A (d) Welded from side B Butt joint-------~ (b) Fitted up (a) Faces beveled (c) Welded from side A (d) Welded from side B Corner joint - Fig.. Types 309 and 312 filler metals are suitable for this application. ASM Handbook." The Intemational Nickel Company. Iron-Based HardFacing Alloys. IAHR Symposium (Stirling. United Kingdom). Haynes. 1993. and Soldering. Welding. Vol 6. Welding. Nickel Development Institute. and Soldering. K. Vol6. 1963 H. Field Experience with Ultra-High Cavitation Resistance Alloys in Francis Turbines. Welding. Norway). Norway). and Soldering. Ocken supplied material on cobalt-free NOREM alloys developed at EPRI." Report NP-6466-SD. 4. p 657-665 R Baboian and G. Bemhardsson. ASM International. L." Report NP-5874. Banker and E.. and Coatings. it may be necessary to backgouge before deposition of the final weld metal layers to ensure that the proper weld metal composition is obtained at the surface of the weld. as required. 22. Inc. 1992. J. Wem. Welding. Corrosion. B. Mossoba. Cavitation Erosion and Deformation Mechanisms of Ni and Co Austenitic Stainless Steels." paper presented at Canadian Electrical Association Spring Meeting (Montreal. Ed. and Hydroturbine Cavitation Erosion. ASM Handbook. Oregon). Simoneau. 1993. A New Class of High StrainHardening Austenitic Stainless Steels to Fight 17. Application of Clad Brazing Materials. Ed. "RecentResults Obtained with High Cavitation Resistance Alloys in Hydraulic Turbines. "Stainless Clad Steels. June 1988 R Simoneau and Y. S. Smith. 1993. les editions de physique. Corvin. REFERENCES 1. 1987. or grinding. Electric Power Research Institute. July 1989 "Laboratory Evaluations of Iron-Based HardFacing Alloys-A European Study. 12. Linse. United Kingdom). Laboratory and Field Comparisons of Cavitation Erosion Resistance for Base Materials. l Charles and S. Vibratory. Patterson. p 789-829 "Welding of NOREM Iron-Base Hardfacing Alloy Wire Products-Procedures for Gas Tungsten Arc Welding. 8. Weldability. Fundamentals of Explosion Welding. Electric Power Research Institute. Protheroe. and A. Procedure Development and Process Considerations for Explosion Welding. Charles and S. 10. 2. and Soldering. Brazing. If the cladding is type 316. "Designing with Clad Metals. p 887-890 lG. Meeking. Brazing. p 649-655 J. Proc. IAHR Symposium (Trondheim.M. 1993. Welding. 20. ASM International. Mr. Dunn. Weld Cladding." NiDI Technical Series No. 24. Procedures and Uses. Karavolis. Charles et al.. Welding. 1993. ASM International. ACKNOWLEDGMENTS The editor thanks Howard Ocken. Simoneau contributed material on cobalt-containing IRECA alloys that he developed atIREQ. Jha. June 1991 PA March. Electric Power Research Institute. Sept 1992 "Endurance Tests of Valves with Cobalt-Free Hardfacing Alloys-PWR Phase Final Report. and J.P. Vol 6. 26. Proc. 11. The filler metal composition should correspond to that normally employed to weld the type of stainless steel used for cladding. ASM Handbook. 3. and one or more layers of stainless steel filler metal are deposited (Fig. Vol 13. Heathcock. Malina-Altzinger. M. Cavitation Erosion of Stainless Steels. Omig. and Dissimilar Metal Joining. Jan 1993 "NOREM Wear-Resistant.. The Optimum Protection ofHydraulic Thrbines Against Cavitation Erosion. Sept 1986 R Simoneau. 23c). 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Sept 1984 S.Stainless Steel Cladding and Weld Overlays / 119 After the stainless steel weld has been deposited from the carbon steel side (Fig. 1993. 5.