acom4 – 2011 A corrosion management and applications engineering magazine from Outokumpu Properties of the new duplex grade LDX 2404 ® 600 Hot coil LDX 2404® 2507 550 LDX 2101® 2205 DUPLEX Strength, Rp0.2 [MPa] 500 450 4565 2304 400 350 254 SMO 4439 300 200 150 4404 4436 AUSTENITIC 250 0 4438 904L 4307 10 20 30 40 50 60 70 80 90 Corrosion Resistance, CPT typical Introduction Today there is a large range of duplex stainless steel grades, which all combine good corrosion resistance with a strength which is superior to corresponding austenitic grades. This gives a considerable advantage by allowing a reduction in the gauge thickness needed in order to fulfil a particular requirement. The duplex spectrum starts with LDX 2101® for applications that require moderate corrosion resistance and extends up to the superduplex 2507 for very aggressive environments. However, a vast number of applications of stainless steels grades require neither of these two extremes but instead are focused around the well-established and multipurpose austenitic grade 316L. The new duplex grade LDX 2404® is tailor-made to have corrosion resistance superior to 316L and at the same time have a high strength, above that of 2205. LDX 2404® is an excellent choice in a vast number of applications where 316L is the “standard” option and where 2205 is over-specified in regards to corrosion resistance. The higher strength of LDX 2404® gives an increased possibility for weight savings, thereby reducing materials requirements and ultimately also costs. www.outokumpu.com | acom 4 - 2011 2 Properties of the new duplex grade LDX 2404 ® C. Canderyd, R. Pettersson, M. Johansson, Outokumpu Stainless AB, Avesta Research Centre, Avesta / Sweden Abstract The new duplex grade LDX 2404® (EN 1.4662, UNS S82441) has a property profile designed to fill the gap between the existing duplex grades 2304 and 2205. The higher strength than the other duplex grades, particularly for hot rolled coil, has appreciable advantages in permitting a decrease in wall thickness for constructions such as storage tanks and thereby also weight and cost reduction while maintaining functionality. In this paper the property profile of the new duplex steel LDX 2404® is compared to 316L and 2205 and linked to application examples in which advantages can be gained. The resistance to localized corrosion is illustrated by testing according to ASTM G 48 (pitting and crevice corrosion in ferric chloride), ASTM G 150 (electrochemical testing in NaCl), ASTM G 36 (stress corrosion cracking in MgCl2) and ASTM G 123 (SCC in NaCl) for a variety of product forms. An application in which pitting and crevice corrosion are particularly relevant is in heat exchangers and piping systems for potable or cooling water, and results on the performance in long-term tests in chlorinated water are presented. Corrosion in acid media is critical for the storage and transportation of chemicals, of which sulphuric acid and phosphoric acid are some of the most important. Evaluation has primarily been in terms of the critical temperatures for corrosion, evaluated according to the MTI-1 (ASTM G 157) method as the lowest temperature at which the extrapolated corrosion rate exceeds a 0.127 mm/year. Atmospheric corrosion resistance is important in all structural and architectural use of stainless steels, results show strong differentiation between grades after shorter exposure time than one year on site. Finally no new grade will find its use unless it can be readily welded with good results. LDX 2404® with its lower alloy content is less susceptible to intermetallic phase precipitation than 2205 and also shows excellent austenite reformation, making autogenous welding possible in certain applications. Examples are also given of the properties of various types of welds, including TIG, MMA, MAG, FCAW and SAW with 2209 filler. Keywords: stainless, duplex, properties, corrosion, welding 3 | acom 4 - 2011 Fig. 1 Strength-corrosion resistance profile of a range of stainless steels. In this paper the focus is on LDX 2404® compared to 2205 and 4404/4432. CPT – Critical Pitting Temperature in °C. 600 Hot coil LDX 2404® 2507 550 LDX 2101 ® 2205 DUPLEX Strength, Rp0.2 [MPa] 500 450 4565 2304 400 350 254 SMO 4439 300 AUSTENITIC 250 200 150 4404 4436 0 4438 904L 4307 10 20 30 50 40 60 70 80 90 Corrosion Resistance, CPT typical 1. Introduction Duplex stainless steels possess an attractive combination of mechanical properties and corrosion resistance. These advantages are to a large extent a result of the fine austeniticferritic microstructure, which imparts a higher strength than for the single phase grades and also gives superior resistance to stress corrosion cracking. The lower nickel level in the duplex grades compared to their austenitic counterparts also gives good price stability in times of nickel price volatility. The most widely used duplex stainless steel grade is 2205 (EN 1.4462, UNS S32205) which has been on the market for many years. This was subsequently followed by developments both towards the leaner, lower-alloyed end of the spectrum, as exemplified by 2304 and LDX 2101® and towards superduplex, of which the seawater-service grade 2507 is the most well known. However, a vast number of applications of stainless steels require neither of these two extremes but instead are focused around the well-established multi-purpose grade 316L (EN 1.4404 or 1.4432) with the additional requirement of being able to utilise the strength inherent in the duplex structure in order to achieve weight savings. Hitherto the answer to finding a duplex alternative has often lead to use of 2205, but this may well be over-specified if the corrosion demands are in the 316L range. This driving force has lead to the development of the new duplex grade LDX 2404® (EN 1.4662, UNS S82441). This is alloyed to give a higher strength than 2205 and at the same time a corrosion resistance which is significantly above that of 316L. These two considerations are illustrated in Figure 1, which places the grades in perspective by comparison across the range of austentic and duplex steels. The nominal composition of the steel grades included in this paper is shown in Table 1 together with their PRE-values. Table 1 Chemical composition and PRE-values for tested stainless steel grades. EN ASTM/UNS Outokumpu Cr Ni Mo N Others PRE* 1.4662 S82441 LDX 2404 24 3.6 1.6 0.27 3Mn 33 1.4462 S32205 2205 22 5.7 3.1 0.17 – 35 ® 1.4404 316L 4404 17.2 10.1 2.1 – – 24 1.4432 316L 4432 16.9 10.7 2.6 – – 26 * PRE = Cr + 3.3Mo + 16N 4 | acom 4 - 2011 2. Results and Discussion 2.1 Mechanical properties The tensile properties of LDX 2404® are listed in Table 2, from which it is seen that both yield strength (R p0.2) and tensile strength (Rm) are higher than those for 2205, particularly in the intermediate gauge thickness range which corresponds to hot rolled coil. The elongation (A 5) is maintained at least at the level of 2205. The major advantages are apparent when LDX 2404® is compared to the austenitic grades, which have less than half the tensile strength, albeit coupled to higher ductility. The minimum impact toughness values at room temperature and -40°C are given in Table 3. The same minimum values are applied to LDX 2404® as for the majority of duplex grades, including 2205. Minimum values of room temperature mechanical properties according to EN 10088. P=Hot rolled plate, H= Hot rolled coil, Table 2 C= cold rolled plate and sheet Steel grade P H C LDX 2404 Rp0.2 [MPa] Rm [MPa] A5 [%] 480 680 25 550 750 25 550 750 25/202 2205 Rp0.2 [MPa] Rm [MPa] A5 [%] 460 640 25 460 700 25 500 700 20 4404/4432 Rp0.2 [MPa] Rm [MPa] A5 [%] 220 520 45 220 530/550 40 240 530/550 40 ®1 1. According to internal standard AM641, EN application in progress 2. A80 for gauges less than 3.0 mm Minimum values of impact toughness (J), transverse direction, Table 3 according to EN 10028. Steel grade 20ºC - 40°C LDX 2404 60 40 2205 60 40 4404/4436 60 602 ®1 1. According to internal standard AM641, EN application in progress 2. Austenitic value at -196ºC 2.2 Strength utilisation example A common application for stainless steels is storage tanks, and for larger tanks it is often possible to reduce the wall thickness and thereby decrease costs by selecting a duplex grade instead of an austenitic. For smaller storage tanks, the minimum shell thickness is used in the whole tank, so in order to make such weight savings, the tank has to have either a large diameter or a large height. | acom 4 - 2011 Calculation of weight savings have been carried out as an illustrative example for the cylindrical part of a storage tank with 25 m in diameter and a height of 20 m. The design temperature is room temperature and the design pressure is the hydrostatic pressure from the content. The welding factor is set to 1.0 for the tank according to EN 14015 design rules. The minimum wall thickness specified is 5 mm for EN 14015 for this size of tank. For this example the width of the sheet is 2 m, ten sheets give the height of 20 meters. The content is assumed to have a density of 1000 kg/m3. The thicknesses of the sheets in the cylindrical shell part are presented in Figure 2. The duplex grade, LDX 2404®, gives considerably lower shell thickness, and corresponding lower weight, in the lower part of the tank where the hydrostatic pressure is high, as compared with the standard austenitic grade 4404. The weight saving is approximately 35% in this specific case, when the weight could be reduced from 124 ton for 4404 to 80 ton for LDX 2404®. For this particular application it is seen that the minimum thickness sets a limit to the possible weight saving. Fig. 2 Thicknesses and weight of the cylindrical part of the storage tank according to EN 14015. The calculated design stress used in EN 14015 were 147 MPa for 4404 and 260 MPa (preliminary value) for LDX 2404®. Total weight of cylindrical part: 80 tons LDX 2404@ 20 m (10 sheets x 2 m) 4404/316L 20 m (10 sheets x 2 m) Total weight of cylindrical part: 124 tons 0 5 10 5 2.3 Forming 15 20 Sheet thickness (mm) All forming processes available for stainless steels can also be used for the duplex stainless steels but due to their high proof strength, compared to austenitic stainless steels, are greater working forces necessary. Other differences in forming behaviour could be an increased tendency to springback. The OSU test (Ohio State University) is a stretching procedure used to estimate the formability of a material close to plane strain conditions. The die and the punch are used to form a U-shaped geometry in which fracture occurs along the wall of the specimen, stretching is performed both transverse and longitudinal to the rolling direction and averaged, a schematic sketch is shown in Figure 3. Care is taken to minimize friction and effect of edges. The height is evaluated at fracture and this value can be used to rank the formability of different steel grades. In Figure 3 the data is normalized to the height at fracture of the standard austenitic grade 4301 which has good stretch forming properties. As is seen, the duplex grades generally show lower formability than the standard austenitic grades but LDX 2404® performs better than 2205. Fig. 3 To the left, sketch of the sample setup, testing is carried out in and transverse to the rolling direction on cold rolled 0.8 – 1 mm material. To the right, height at fracture normalised to 4301. 1.0 0.8 Rolling direction Formability in plane strain 0.6 0.4 0.2 0.0 4301 4404 LDX 2404® 2205 | acom 4 - 2011 6 2.4 Pitting and crevice corrosion CPT (°C) There are a number of standardised tests available for ranking the localised corrosion performance of different steel grades in chloride containing environments. The critical pitting temperature, CPT, and the critical crevice corrosion temperature, CCT, have been evaluated according to the ferric chloride immersion test ASTM G 48 method E and F [1], the results presented in Figure 4 and Figure 5 are mean values from a number of samples. The samples were immersed for 24 hours at a constant temperature; the critical temperature is the lowest value where pitting corrosion occurs on the rolled surface. LDX 2404® show somewhat lower CPT than 2205 but more than 10°C higher than for 4432. It should be noticed that this method shows some variability in the results for all tested steel grades. It is sensitive to the product form tested, edge preparation and exactly how the evaluation is carried out. Initiation of pitting corrosion occurs on the most susceptible sites on a sample, which in this case means the edges. Below the CPT, the surface can be cathodically protected by corrosion on the edges and thus remain intact. This test technique thus includes more uncontrolled parameters than method F (crevice corrosion) and the scatter in the results can also be expected to be greater. Crevice corrosion occurs at lower temperatures than pitting and the CCT value for LDX 2404® was 15°C, compared to 20°C for 2205. The test solution is too corrosive for testing of creviced samples of the standard austenitic grades 4404 and 4432. A test solution somewhat closer to service applications is 1M NaCl, which is used as a basis for electrochemical testing Fig. 4 The critical pitting temperature, CPT, according to ASTM G 48 method E. 6% FeCl3 + 1% HCl. at an applied potential of 700 mVSCE in ASTM G 150. This method gives similar ranking to ASTM G 48 method E but 40 the definition of the critical pitting temperature, as the temperature at which a current density of 0.1 mA/cm2 is reached and maintained, leads to higher CPT values. Data is given in 30 Figure 6 and shows that LDX 2404® ranks mid-way between 4432 and 2205. 20 10 0 4404/316L 4432/316L LDX 2404® 2205 Fig. 5 The critical crevice corrosion temperature, CCT, according to ASTM G 48 method F. 6% FeCl3 + 1% HCl. Fig. 6 The critical pitting temperature, CPT, according to ASTM G 150. The light blue bars show the normal variation which is to be expected between different heats and product forms. 60 40 50 30 CPT (°C) CPT (°C) 40 20 30 20 10 10 0 4404/316L 4432/316L LDX 2404® 2205 0 4404/316L 4432/316L LDX 2404® 2205 7 | acom 4 - 2011 2.5 Application in potable and cooling water systems A study has been carried out to investigate the performance of the duplex stainless steel grades LDX 2101® and LDX 2404® in drinking water applications [2]. Welded-, crevicedand plain sheet samples were immersed in 200 and 500 ppm chlorides with different total residual chlorine. Some results from this study are shown in Table 4. The duplex grades LDX 2404® and 2205 showed very good performance at both 30 and 50°C with 1 ppm total residual chlorine, no crevice corrosion could be seen. The standard austenitic grade 4404 was more susceptible to crevice corrosion and suffered from pitting corrosion in the harshest condition. LDX 2404® could be a very good alternative to both 4404 and 2205, especially instead of 4404 in the range of the more severe conditions of this study. Summary of visible pitting and crevice corrosion in this Table 4 investigation from [2]. Test condition Type of specimen Temp. (°C) Chlorides (ppm) TRC* (ppm) 30 200 0.2 P 4404 W C LDX 2404® P W C P 2205 W C 0.5 1.0 30 500 0.2 0.5 1.0 50 200 0.2 0.5 1.0 50 500 0.2 0.5 1.0 *TRC = Total residual chlorine, P = Plain (sheet) sample, W = Welded sample, C = Creviced sample No corrosion Corrosion Not tested in this study 2.6 Stress corrosion cracking Duplex stainless steels show good resistance to stress corrosion cracking and are a good alternative to the standard austenitic grades in those cases where chloride induced stress corrosion cracking could cause problem, i.e. chloride containing environments mainly at elevated temperature. There are a number of standardised tests available which specify loading methods and test environments with varying relevance to real applications. Immersion tests in NaCl and MgCl2 are described in ASTM G 123 och G 36 respectively. MgCl2 is very corrosive, even for the duplex grades, and cracking occurs already after 24 hours, Table 5. In the NaCl environment, no cracking occurs for the duplex grades after immersion for 1000 hours at either low or neutral pH. Another tests that is more relevant to evaporative conditions is ASTM C 692 – commonly denoted Wick testing – in which a dilute chloride solution is allowed to soak into insulation material which is in contact with the resistance heated specimen. This test also shows the superior performance of the duplex grades, Table 5. Interpretation of the results from laboratory stress corrosion cracking test is fraught with a number of pitfalls and can be difficult to correlate to actual service conditions, this issue is discussed in more detail in [3]. | acom 4 - 2011 8 Table 5 Number of cracked U-bend specimens. [3, 4] Test method ASTM G 36 ASTM G 123 Modified ASTM G 123 ASTM C 692 – Wick testing Temp. Salt Others Test period 155°C 45% MgCl2 – 24 h Boiling point 25% NaCl Acidified 1000 h Boiling point 25% NaCl – 1000 h 100°C 1500 ppm ClInsulation 28 days 4404/4432 3 out of 3 4 out of 4* 2 out of 4 4 out of 4 LDX 2404 3 out of 3 0 out of 12 0 out of 12 0 out of 7 3 out of 3 0 out of 4 0 out of 4 1 out of 6** 2205 ® * Cracking after 7 days ** Minor cracking, interpretation complicated by the occurrence of pitting and/or selective corrosion. 2.7 Corrosion in acids Sulphuric acid is used in a large variety of industries from fertilisers to production of other acids, so large amounts of this acid are stored and transported around the world. It can be challenging to choose the appropriate steel grade since the corrosivity of sulphuric acid changes with concentration and temperature. It is also strongly influenced by impurities, so data in corrosion tables and iso-corrosion diagrams based on laboratory testing in pure chemicals must be used with caution. Different steel grades performance can also vary between the test methods and thereby rather reflect the test procedure than the actual performance of the steel grade [5]. Figure 7 shows the results of laboratory tests in 96 and 98% sulphuric acid using the so-called Corrosion Handbook method. This involves three successive immersion periods of 24 hours, 72 hours and 72 hours, with activation in the last period. A commonly used criterion for the corrosion rate is 0.1 mm/y, which means that rates below 0.1 mm/y are often accepted. The standard austenitic grade 4404 showed increased corrosion rate with increased temperature whereas the duplex grades showed similar value of the corrosion rate at 20, 30 and 40°C in 96% sulphuric acid and at 40 and 50°C in 98%. The corrosion rates for LDX 2404® were in the same range as for 2205. Tests have also been carried out according to the MTI-1 method [6], which uses a 96 hour immersion period and a critical temperature is evaluated when the corrosion rate exceeds 0.127 mm/y (5 mpy), the critical temperatures in sulphuric acid and phosphoric acid are shown in Table 6. According to the results in Figure 7 it would seem that this test method is less suitable for the duplex grades in 96% sulphuric acid because of the small temperature dependence of the corrosion rate and thereby difficulties to find a representative critical temperature. However, the individual corrosion rates, in the MTI-1 test method, for LDX 2404® showed a large step from negligible at 20 and 30°C to appreciably higher Table 6. The critical temperatures, a corrosion rate higher than Table 6 0.127 mm/y (5 mpy), evaluated according to MTI-1. [4, 6, 7] Steel grade 96% Sulphuric acid 85% Phosphoric acid 40°C 100°C 2205 25°C 90°C 4432 45°C 95°C LDX 2404 ® | acom 4 - 2011 9 Fig. 7 Corrosion rates in 96 and 98% sulphuric acid tested with the Corrosion Handbook method, three test periods 24, 72 and 72 hours with activation in the third period. [5] 1.0 1.0 96% Sulpuric acid Corrosion rate (mm/y) 0.6 0.4 0.2 LDX 2404® 2205 4404 /316L 0.8 0.6 0.4 0.2 0.0 20°C 30°C 40°C 50°C 40°C 50°C Fig. 8 Corrosion rates evaluted for phosvalues at 35 and 40°C. This demonphoric acid with the Corrosion Handbook strates that under some circumstances method, three test periods 24, 72 and 72 the temperature dependence is actually hours with activation in the third period. quite large. It is not possible to make the same comparison of the individual 0.6 corrosion rates for 2205 since only a Phosphoric acid -100°C few tests have been carried out with 0.5 corrosion rates close to the critical LDX 2404® value. 0.4 2205 4404 /316L Phosphoric acid is not nearly as 0.3 corrosive as sulphuric acid but there are limitations in usage together with 0.2 stainless steels at high temperatures. The results from tests carried out in 0.1 phosphoric acid are shown in Figure 8. The performance of LDX 2404® was 0.0 60% 80% similar to 2205 and both the duplex grades were superior to 4404. The results from the MTI-1 test procedure also confirm the similar performance of the duplex grades even though the value for 2205 seems to be at the lower end, Table 6. The different trends seen in 85% phosphoric acid in MTI-1 and 80% phosphoric acid in the Corrosion Handbook method for 4404 might in some extent be explained by the difference in molybdenum between 4404 and 4432. Another explanation is that the results from the test methods differs due to fundamental aspects of the test technique such as test time, presence of oxygen and activation of the samples. Corrosion rate (mm/y) Corrosion rate (mm/y) 0.8 0.0 0°C 98% Sulpuric acid LDX 2404® 2205 4404 /316L 2.8 Atmospheric corrosion Atmospheric corrosion is the general name for different corrosion forms that occurs when a material is exposed to the atmosphere, for example pitting- and crevice corrosion induced by chlorides. In cases where staining should be avoided, i.e. architectural applications, the choice of surface condition and cleaning procedure can in some extent be equally important as the choice of appropriate steel grade. The appearance of the surface is not nearly as vital for structural applications. LDX 2404® is included in test programmes on the Swedish west coast (Bohus-Malmön) and at a marine test station in Dubai. The samples are still being exposed and it is thereby not possible to investigate them in detail, but photographs of the samples exposed at the different sites can be seen in Figure 9 and Figure 10. 4404 showed much more staining than the duplex grades in both cases. 10 | acom 4 - 2011 Fig. 9 Appearance of specimens after 12 months exposure at Bohus-Malmön, Sweden. LDX 2404® and 2205 have a 2E surface and 4404 has a 2B surface. The blue tint on LDX 2404® and 2205 is due to reflections. LDX 2404@ 2205 4404 Fig. 10 Appearance of specimens after 3 months exposure in Dubai. All steel grades were cold rolled and bright annealed (2R). LDX 2404@ 2205 4404 2.9 Welding and weld properties In order to evaluate weld properties, a variety of different welding methods were applied to various thicknesses of LDX 2404®, ranging from 2 mm cold rolled coil to 30 mm plate, Table 7. In all cases where filler metal was used, this was of 2209-type (Avesta 2205, 22 9 3 N L) All welds were sound and passed both radiographic evaluation and bend testing. Further details of welding and microstructural evaluation are given in [8]. The pitting corrosion resistance of the welds is shown in Figure 11. The values in the ferric chloride immersion test according to ASTM G 48 method E are all above 20°C. This may seem low compared with the average base material CPT of 35°C, but it should Table 7 Welding parameters used for the investigated welds. Weld method t [mm] Joint Weld gas / Purge gas Filler TIG TIG 2 2 I I Ar+2% N2 / N2+10% H2 – Avesta 2205 (W 22 9 3 N L) MMA 3 V – Avesta 2205 (E 22 9 3 N L R) MAG 6 V Mison 2He Avesta 2205 (G 22 9 3 N L) FCAW FCAW 6 10 V X Mison 18 Avesta FCW-2D 2205 (T 22 9 3 N L R) SAW 15 X SAW 15 K Avesta Flux 805 Avesta 2205 (S 22 9 3 N L) SAW 20 X SAW 30 X SAW 30 K Mison 2He = Ar+2% CO2+30% He+0.03% NO, Mison 18 = Ar+18% CO2+0.03% NO 11 | acom 4 - 2011 be realised that the test in itself shows fairly large scatter and lower values can also be measured for base material. This difficulty is illustrated by the results for ASTM G 150 testing in 1M NaCl, which tends to give a more precise critical pitting temperature. In this case it is seen that the values for the TIG, MMA and MAG welds are around the typical lower bound for base material. Impact toughness data for the same welds are given in Figure 12 and show that the heat-affected zone impact toughness, evaluated from K-joints, meets the minimum requirements for base metal according to Table 3. This reflects the good austenite formation in LDX 2404® which is a result of its high nitrogen content. The weld metal impact toughness was generally good, and can probably be improved in marginal cases by careful selection of welding parameters and possibly also filler material. There is also a possibility to increase the weld metal strength by the use of an over alloyed 2507-type filler. Fig. 11 CPT values for welded, shot blasted and pickled samples evaluated according to ASTM G 48 method E and ASTM G 150 compared to the typical values for base material. Values for TIG welds are average of top and root for both welds. 50 G 48 E CPT – Welded specimens 45 G 150 Base material – G150 40 Base material – G48E CPT (°C) 35 30 25 20 15 10 5 0 G TI 2 m m A 3 m m AG M 6 m m AW m m AW FC M M 6 10 m m W SA FC 15 m m W SA 20 m m W SA 30 m m Fig. 12 Impact toughness for welded samples and comparison to average values for 6 mm hot coil and 30 mm plate taken from ASTM A 240 application. Broken lines show minimum values for base material at the two temperatures according to Table 3. * Reduced size rods, to 3/4. 200 +20°C Impact toughness – Welded specimens 180 -40°C 160 140 CV (J) 120 100 80 60 40 20 0 * BM 10 * m m AW FC 10 m m BM 15 m m W SA 15 ) AZ m m W SA 15 m m (H W SA 20 m m W SA 30 ) m AZ m W SA 30 m m (H BM 30 m m | acom 4 - 2011 12 3. Conclusions The new duplex grade LDX 2404® (EN 1.4662, UNS S82441) has a property profile designed to fill the gap between the existing duplex grades 2304 and 2205. The higher strength than the other duplex grades, particularly for hot rolled coil, has appreciable advantages in permitting a decrease in wall thickness for constructions such as storage tanks. The formability of LDX 2404® is intermediate between 2205 and more readily formable 4404. In standard pitting and crevice corrosion tests, the performance of LDX 2404® is below that of 2205 but clearly superior to 4404 and 4432. This is also supported by long-term tests in chlorinated water systems, designed to simulate low chloride cooling water or drinking water. Stress corrosion cracking resistance is good, as is characteristic for duplex grades. Uniform corrosion resistance in sulphuric acid is very similar to that for 2205, which means that in 98% acid it is has a corrosion rate less than half that of 4404 at 50°C. The same type of trend is seen in 60% and 80% phosphoric acid at 100°C. LDX 2404® has shown superior performance to 4404 in atmospheric exposure tests at marine sites in both Sweden and Dubai. LDX 2404® can be welded with a variety of methods. The good austenite reformation facilitates autogenous welding and the use of a standard 2209-type filler has proved to give sound welds using TIG, MMA, MAG, FCAW and SAW. Pitting corrosion resistance and impact toughness of the welds are acceptable for a wide range of applications. The overall conclusion is that the LDX 2404® grade is eminently suitable for structural purposes, which do not require a corrosion resistance at the level of 2205, and is a good all-round performer in the duplex alloy spectrum. 4. Acknowledgments Andreas Persson, Andreas Lundstedt, Hans Groth, Jan Y Jonsson, Eugenia Sundqvist and Maria Lundberg are thanked for provision of data used in various sections of this paper. 5. References [1] ASTM G 48 - 03 (Reapproved 2009) Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution, in, ASTM International, West Conshohocken, 2009. [2] S. Mameng, Localised corrosion of stainless steels depending on chlorine dosage in chlorinated water, Eurocorr, Stockholm, 2011. [3] R. Pettersson, E. Johansson, Stress corrosion resistance of duplex grades, Acom, (2011) 10 – 22. [4] J.-O. Andersson, E. Alfonsson, C. Canderyd, H. Groth, Development and Properties of New Duplex Stainless Steels, Stainless Steel World, SSW, Houston, USA, 2010. [5] C. Canderyd, R. Pettersson, P.-E. Arnvig, Uniform corrosion testing in Sulphuric acid – a critical comparison of methods, Eurocorr, Stockholm, 2011. [6] MTI, MTI-1 Test Method comprises 14 test solutions of various concentrations of HCl, H2SO4, HNO3, H3PO4, acetic acid, formic acid, NaOH, HCl, ferric chloride, and acetic acid and acetic anhydride, 1995. [7] Outokumpu Corrosion Handbook, 10th Edition ed., Outokumpu Oyj, Espoo, 2009. [8] L.-Å. Bylund, M. Johansson, R. Pettersson, Welding of the new duplex grade LDX 2404® with 2209-type filler, SSW, Maastrich, 2011. This article was first published in the Proceedings of the Stainless Steel World Conference & Expo 2011, November 29th – December 1st, 2011, Maastricht, The Netherlands © KCI Publishing, 2011 1498EN-GB Art 58. December 2011 Comments on acom and its articles or suggestions on future articles are appreciated and should be sent to the editor Andreas Persson at
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