Duplex Stainless Steels
Contents Answers for today s challenges...4 The expert s voice...5 Product positioning...6 Product suitability...8 Chemical composition...9 Mechanical properties...10 Physical properties...13 Corrosion resistance...14 Product assortment...16 Fabrication...17 2
We believe in a world that lasts forever The world needs and deserves innovations that pass the test of time and are able to be recycled and used again at the end of their lifecycle. Outokumpu stainless steel is durable in the most challenging of conditions delivering ever longer project lifecycles. The recycled content of Outokumpu advanced materials varies between 70% and 90% depending on the grade and Outokumpu stainless steel is also fully recyclable. The properties of Outokumpu advanced materials, also make them an economically sustainable solution. Our vision of a world that lasts forever not only reflects these properties but also our ongoing commitment to innovation and the development of lasting customer relationships. Outokumpu Duplex 2205 in Marina Bay bridge, Singapore3
Winning the future useful answers for today s challenges The use of stainless steel is increasing fast due to the material's durability, corrosion resistance and aesthetics. If the right grades are selected, stainless steel lasts hundreds of years. In the long run, stainless steel is also often the least expensive material, thanks to low maintenance costs. Trend 1: Global economics and striving for stability When it comes to costs, all parties seek stability. In large-scale construction projects, the right material choices can multiply savings. Outokumpu Duplex stainless steel has excellent strength, which often means the same structure can be built with less material: for example, tank walls can be considerably thinner. Compared to other grades with comparable corrosion resistance, the nickel content of Outokumpu Duplex is very low. This means greater price stability and easier budgeting. Trend 2: Rising environmental awareness In previous years, temporary structures built for world fairs and events for example, could be demolished after the event. Such a waste of labour and disregard for the environment is simply not acceptable anymore. Environmental responsibility and legislation have an increasing impact on operations in every industry. Proof of responsibility is demanded for the whole life cycle of the product. Those who can offer action instead of words in social and environmental responsibility will be the winners of tomorrow. Outokumpu Duplex is an environmentally sound choice from many different viewpoints: It uses recycled steel as its main raw material and it is 100% recyclable Very low level of metal ion is released into the environment. Less need of hazardous coatings Thanks to high strength, it is possible to reduce the weight of the structures and therefore lower energy consumption in transport, construction and usage Trend 3: Ensuring safety, pleasing the eye In addition to corrosion resistance and durability, constructors face increasing demands for a human approach: it is no longer enough that the tanks, vessels and buildings do their job. They need to be safe for both the builders and the employees and be aesthetically pleasing. In short, Outokumpu Duplex makes it possible to fabricate strong, fascinating structures while reducing the total weight. 4
The expert's voice Duplex stainless steel was developed by Outokumpu more than 80 years ago and since that time we have produced more than half the world s volume of duplex. Our long history with duplex gives us a unique insight into the challenges faced by our customers and the experience and solutions to help them meet these challenges. Today we offer a complete family of duplex grades and we work with our customers to select the grade which provides the most suitable corrosion resistance for its intended use. Duplex grades utilize a more cost-effective alloy composition lower nickel and higher nitrogen content which provides better price stability than austenitic grades. Moreover in addition to great corrosion resistance, duplex grades also offer higher mechanical strength, more than twice as high as standard austenitic stainless steels or carbon steels. The main advantage of this is to save weight in the steel structure by reducing the thickness of the material. This is successfully utilized in applications such as pressure piping in the oil & gas and offshore industries as well as in large pressure vessels and in large stationary storage tanks in the pulp and paper industry. The potential weight saving together with high corrosion resistance, less maintenance and no requirement for protective coatings provides a foundation for more cost effective solutions compared to carbon steel, particularly when the total life cycle cost is considered. Outstanding life cycle performance is a strong factor in the choice of duplex within the building and construction sector where its use is growing due to a combination of advantageous properties: high strength, high durability (i.e high corrosion resistance, high wear and fatigue resistance) and aesthetic surface finishes. The high strength and toughness of duplex delivers high energy absorption capacity which combined with reasonable high temperature properties delivers enhanced fire resistance. This is utilized in blast and fire walls on offshore platforms to provide safety for the platform personnel. These beneficial aspects of duplex are also of great interest for other areas such as evaporator shells in desalination plants, cargo tanks in chemical tankers, in the severe environments of mining and minerals processing and in vehicles and chassis components for rail cars, road tankers and automotive applications. Claes Tigerstrand, Outokumpu Research & Development Duplex applications: Pressure piping systems for seawater, chemicals, oil and gas handling etc. Pressure vessels like digesters, evaporators, fermenters, autoclaves, water heaters, road tankers etc. Storage tanks for pulp, chemicals, biofuels, beverages, grains, ore slurry etc. Structural components for bridges, sluice/flood gates, steel frameworks, rebars for concrete structures etc. Blast and fire walls on off shore platforms Cargo tanks in chemical tankers Evaporators in desalination plants Heat exchangers in petrochemical plants Suction roll shells in paper machines Flue-gas cleaning equipment Rotors, impellers and shafts Vehicle and chassis components 5
More strength less material Put simply, the benefit of Outokumpu Duplex lies in weight reduction. You gain more strength with less material. Below, you can see an example of what happens when standard austenitic steel is substituted with Outokumpu Duplex. General benefits provided by Outokumpu Duplex grades: Thinner gauges due to higher strength weight savings and lower cost Higher durability and reduced maintenance longer service life Cost efficient alloying by lower nickel content lower price volatility Additional benefits - LDX concept: Leaner alloying compared the regular duplex grades (i.e. less nickel and higher nitrogen content) added strength and performance ensuring highest value for money LDX 2101 and LDX 2404 can potentially provide more cost efficient solutions for storage tanks and other structural components Additional benefits - newly launched EDX concept: Enhanced properties of already established grades EDX 2304 is primarily developed for offshore topside applications to provide better corrosion performance than standard 2304 or 316L Additional benefits - newly launched FDX concept: The new FDX TM product family exhibits a unique combination of high strength and substantially improved formability utilizing Transformation Induced Plasticity (TRIP) The increased formability of FDX 25 and FDX 27 allows for utilization of duplex in more complex components such as forming intensive heat exchanger plates Calculate your weight savings on the Internet E-tools at outokumpu.com offers interactive tools for materials selection, rough estimation on wall thickness calculations etc. Less material means benefits in every step of the project With Outokumpu Duplex, you can purchase, transport, weld and assemble less material. When thinking of the cost of labour, savings can be significant. Pipes: reduction in wall thickness and weight between grades 304L and LDX 2101 Design data Pressure = 16 bar Temperature = 50 C OD = 610 mm Required Pipe length = 1000 m Min WT acc to EN 13480-3 Weld factor z = 0.7 304L = 5.8 mm LDX 2101 = 2.9 mm WT = wall thickness OD = outer diameter Grade 304L WT = 6.0 mm Weight = 90 metric tons Grade LDX 2101 WT = 3.0 mm Weight = 45 metric tons 6
Duplex as a substitute for austenitic in storage tanks Strength, R p0.2,[mpa], hot rolled coil 304L 85 metric tons LDX 2101 61 metric tons Required thickness duplex Required thickness austenitic [m] 20 18 16 14 12 10 8 6 600 550 500 450 400 350 300 250 200 150 0 LDX 2404 2207 LDX 2101 EDX 2304 2304 2205 4565 254 SMO 4439 4404 4438 904L 4307 4432 10 20 30 40 50 60 70 80 90 4 Corrosion resistance, CPT typical 2 Duplex Austenitic [mm] 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Figure 1. Great combination of high strength and adequate corrosion resistance. Tank cost example 1: Austenitic steel versus Outokumpu Duplex When the same tank is manufactured from Outokumpu Duplex instead of conventional austenitic steel, the biggest savings are made in manufacturing phase, thanks to less amount of material needed. The tank walls can be significantly thinner, yet safe in use. Table 1 304L LDX 2101 Plate thickness (API 650) 6-14 mm 6-8 mm Material cost* 240 keur 197 keur Welding and assembly cost 81 keur 55 keur Surface treatment cost 55 keur 55 keur Total manufacturing cost 136 keur 110 keur Total initial cost 376 keur 307 keur Potential cost saving ~18% Tank size: diameter 20 m, height 20 m. *Based on typical costs provided by tank manufacturers and sub-suppliers. Tank cost example 2: Carbon steel versus Outokumpu Duplex When the same tank is manufactured from Outokumpu Duplex instead of carbon steel, the biggest savings come in the maintenance phase: carbon steel needs to be properly protected in the manufacturing phase and again after certain periods of usage. All this means extra labour, which can be avoided using Outokumpu Duplex. Table 2 Carbon steel A516-60/S235 LDX 2101 Total initial cost* 366 keur 307 keur Recoating cost 75 Euro/m 2 x 2500 m 2 Elapsed time between maintenance events 15 years Life cycle duration 30 years 30 years Operating cost 125 keur 0 keur No surface protection required! Total life cycle cost 491 keur 307 keur Potential cost saving ~37% Tank size: diameter 20 m, height 20 m. *Based on material, welding, assembly, surface treatment and coating costs. 7
Project checklist when to go with Duplex? Are some of the characteristics listed below relevant for your application? Then Outokumpu Duplex might be your material of choice. Demands for material resistance to uniform corrosion resistance to pitting and crevice corrosion resistance to stress corrosion cracking and corrosion fatigue high mechanical strength good abrasion and erosion resistance good fatigue resistance high energy absorption low thermal expansion 8 good weldability good formability service temperature range within -40 C to 250 C* *maximum allowable design temperature = 325 C in ASME II-D 2013.
The recipe for success: ingredients according to your needs What makes Outokumpu Duplex such a strong material? The secret lies in connecting the best of both microstructures: Combining austenite and ferrite. The result is two crystallographic phases, each with a composition sufficient to make it corrosion resistant. Favorable properties of both phases can be utilised in one alloy. The chemical composition of duplex grades gives good corrosion resistance and desired mechanical and physical properties. Outokumpu can supply you with stainless grades especially designed to meet your needs. Molybdenum improves corrosion resistance Molybdenum improves corrosion resistance in most environments, particularly in acids and chloride containing environments. Alloying elements and their purpose Chromium makes it stainless A minimum of about 11% chromium has to be added to steel to form the passive layer that makes it stainless. Outokumpu Duplex steels have a high chromium level, between 21 and 25%. These contents improve the corrosion resistance. Nickel adds toughness Nickel helps to obtain the desired phase balance and provides toughness. Duplex steels contain a relatively small amount of nickel, between 1.5 and 7%. Nitrogen adds strength and corrosion resistance Nitrogen is a very important addition as it gives a substantial increase in strength and pitting and crevice corrosion resistance. At the same time it strongly stabilises the austenite phase. Furthermore, nitrogen improves welding properties. Outokumpu LDX 2101 in footbridge, Sölvesborg Sweeden 9
Table 3. Chemical composition. Outokumpu steel name International steel No Chemical composition, % by weight Typical values EN ASTM UNS ISO C N Cr Ni Mo Others FDX 25 TM 1.4635 - S82012-0.022 0.23 20.2 1.4 0.4 Mn Cu LDX 2101 1.4162 - S32101 4162-321-01-E 0.03 0.22 21.5 1.5 0.3 5Mn Cu 2304 1.4362 - S32304 4362-323-04-I--- 0.02 0.10 23.0 4.8 0.3 Cu FDX 27 TM 1.4637 - S82031-0.023 0.18 20.1 3.0 1.25 Mn Cu Duplex EDX 2304 TM 1.4362 - S32304 4362-323-04-I 0.02 0.18 23.8 4.3 0.5 Cu LDX 2404 1.4662 - S82441 4662-824-41-X 0.02 0.27 24.0 3.6 1.6 3Mn Cu 2205 1.4462 - S32205 1 4462-318-03-I 0.02 0.17 22.0 5.7 3.1 4501 1.4501 - S32760 4501-327-60-I 0.02 0.27 25.4 6.9 3.8 W Cu 2507 1.4410 - S32750 4410-327-50-E 0.02 0.27 25.0 7.0 4.0 4307 1.4307 304L S30403 4307-304-03-I 0.02 18.1 8.1 Austenitic 4404 1.4404 316L S31603 4404-316-03-I 0.02 17.2 10.1 2.1 904L 1.4539 904L N08904 4539-089-04-I 0.01 20.0 25.0 4.3 1.5Cu 254 SMO 1.4547 - S31254 4547-312-54-I 0.01 0.20 20.0 18.0 6.1 Cu Mechanical properties 1 Also available as S31803 The mechanical and physical properties are beneficial characteristics of Outokumpu Duplex. The mechanical strength is superior compared to austenitic or ferritic stainless steels, and the physical properties offer new possibilities. This is a clear advantage for structural applications, such as pressure vessels and beam constructions. Pressure vessel approvals Outokumpu duplex grades 1.4362 (2304), 1.4462 (2205), 1.4501 (4501) and 1.4410 (2507) are listed in EN 10028-7. European material approval EAM 0045-01:2012/01 for LDX 2101 (1.4162) is available for cold rolled 0.5-6.4 mm and hot rolled 3.0-10.0 mm. (LDX 2101 is partly listed in EN 10088). Work are in progress for European and ASME approvals of LDX 2404. In ASME II-D 2007 (Metric) edition grades S31803 (2205), S32304 (2304) and S32750 (2507) are listed for general use between -30 C to +325 C. Data for LDX 2101 can be found in ASME code case 2418-1. 10
Table 4. Mechanical properties for flat products at room temperature. LDX 2101 Minimum values, according to EN 10088 Outokumpu typical values P H C P (15 mm) H (4 mm) C (1 mm) Proof strength R p0.2 MPa 450 480 530 500 560 610 Tensile strength R m MPa 650 680 700 700 755 810 Elongation A 5 % 30 30 30/20 1 38 35 29 3 Hardness HB 225 235 99 2 2304 Proof strength R p0.2 MPa 400 400 450 450 600 620 Tensile strength R m MPa 630 650 650 670 765 790 Elongation A 5 % 25 20 20/20 1 40 30 26 3 Hardness HB 210 235 99 2 EDX 2304 TM * Proof strength R p0.2 MPa 420* 500* 500* 600 600 Tensile strength R m MPa 630* 690* 690* 750 770 Elongation A 5 % 25* 25* 25* 30 30 Hardness HB 290* 290* 290* LDX 2404 ** Proof strength R p0.2 MPa 480 550 550 520 645 640 Tensile strength R m MPa 680 750 750 750 825 850 Elongation A 5 % 25 25 25/20 1) 33 30 24 3 Hardness HB max 290 290 290 230 250 2205 Proof strength R p0.2 MPa 460 460 500 510 630 690 Tensile strength R m MPa 640 700 700 750 840 880 Elongation A 5 % 25 25 20/20 1 35 30 26 3 Hardness HB 230 250 101 2 2507 Proof strength R p0.2 MPa 530 530 550 580 700 730 Tensile strength R m MPa 730 750 750 830 905 940 Elongation A 5 % 20 20 20/20 1 35 30 24 3 Hardness HB 250 270 103 2 P = hot rolled plate H = hot rolled coil and sheet C = cold rolled coil and sheet *Mechanical properties according to NORSOK Material Data Specification MDS-D35. **Mechanical properties according to next revision of EN 10088-2 (to be published end of 2013). 1 Refers to A80 for gauges less than 3 mm. 2 HRB (Rockwell B-scale). 3 A 80. 11
Temperature and embrittlement Duplex steels are more prone to precipitation of intermetallic phases, nitrides and carbides than corresponding austenitic steels, causing embrittlement and reduced corrosion resistance. The formation of intermetallic phases such as sigma phase occurs in the temperature range 600-950 C and decomposition of ferrite occurs in the range 350-525 C (475 C embrittlement). Exposures at these temperatures should therefore be avoided. In proper welding and heat treatment the risk of embrittlement is low. However, certain risks exist, for example at heat treatment of thick sections, especially if the cooling rate is low. Due to the risk of embrittlement, duplex steels should not be used at temperatures above 250-325 C (See Figure 2). The maximum temperature depends on grade and the design rules being used. High energy absorption The combination of high strength and ductility gives Outokumpu Duplex a very good ability to absorb energy. This makes it a perfect material for applications like blast walls on offshore platforms and car body components. Good fatigue strength of base material The high tensile strength of Outokumpu Duplex also implies high fatigue strength in the base material. The fatigue strength of the duplex steels follows the proof strength of the material. Our technical experts can provide you with more detailed information, if needed. For welds, the benefit of the high fatigue strength of the parent or base material is limited. The fatigue strength is, like other materials, reduced by unfavorable weld geometry, residual stresses, distortions and weld defects. Figure 2. Curves for 50% reduction of impact toughness compared to solution annealed condition. Table 5. Impact toughness. Minimum values according to EN 10028-7 transverse direction for hot rolled plate. Temperature ( C) LDX 2101 * 2304 LDX 2404 ** 2205 2507 1100 1000 2507 20 C 60 (80 1 ) 90 60 100 90-40 C 27 (50 1 ) 40 40 40 40 900 800 700 2205 LDX-2101 2304 *Values from internal standard, AM 611. **Values from internal standard, AM 641. according to internal specification. 1 Value according to EAM-0045-01:2012/01 for thick- 600 nessess up to and including 10mm. 500 400 300 0.01 0.02 1,0 10 100 1000 (36 s) (6 min) Time (h) 12
Physical properties: new opportunities Compatible with carbon steel Outokumpu Duplex grades have a lower thermal expansion ratio (approximately 13 10-6/ C) and higher thermal conductivity than austenitic steels. This means that there are fewer problems with temperature expansions caused by connecting Outokumpu Duplex with carbon steels. Duplex is a good alternative for lining carbon steel vessels operated with large cyclic temperature variations. Magnetic properties Duplex stainless steels are more magnetic than austenitic grades due to higher ferrite content. But for safety reasons magnets shall not be used to lift duplex sheets. Table 6. Physical properties of duplex stainless steels, according to EN 10088. Physical property 20 C 200 C Density [g/cm3] 7.8 - Modulus of elasticity [GPa] 200 186 Poisson ratio [Dimensionless] 0.3 - - 13.5 Thermal conductivity [W/m C] 15 17 Thermal capacity [J/kg C] 500 560 Electric resistivity [μω/m] 0.8 0.9 Linear expansion from 20 C to 200 C (x10-6/ C) Palm oil tank farm in LDX 2101. Photo courtesy of Loders Croklaan. 13
Corrosion resistance in a wide range of environments The corrosion resistance of Outokumpu Duplex is generally very good. The resistance is especially good in environments such as halide containing media, oxidising acids, and hot alkaline solutions. This means that, for example, heat exchangers, water heaters, offshore equipment, storage tanks, sulphate pulp digesters, black liquor evaporators and flue gas cleaning equipment greatly benefit from the material properties of duplex steels. Uniform corrosion The uniform corrosion resistance is generally considered good if the corrosion rate is less than 0.1 mm/year. Thanks to their high chromium content, duplexes offer excellent corrosion resistance in many media, especially in alkaline solutions. Pitting and crevice corrosion: heat exchangers, water heaters, offshore equipment, storage tanks etc. In chloride solutions LDX 2101 has better resistance than 4307 and in some cases as good as 4404. Grade 2304 is in most cases equivalent to 4404, while the other more highly alloyed duplex steels show even better resistance. The resistance to pitting and crevice corrosion is often illustrated by the pitting resistance equivalent (PRE) for the material. The most commonly used formula for PRE is: PRE = %Cr + 3.3 x %Mo + 16 x %N The PRE value can be used for the ranking of different stainless steels, see Table 7. A more in depth way to rank steels is measuring the Critical Pitting corrosion Temperature (CPT). Outokumpu uses an electrochemical method, ASTM G150, based on the in-house developed Avesta Cell, see Figure 3. Chloride and sulphide induced stress corrosion cracking: boreholes and gas wells etc. All duplex grades are much more resistant than the standard austenitic grades to chloride induced stress corrosion cracking (SCC). Thus, the duplex grades can tolerate higher chloride contents at elevated temperatures. In the presence of hydrogen sulphide and chlorides (e.g. sour conditions in bore holes and gas wells) the risk of stress cracking, at low temperatures, increases. In these environments Outokumpu Duplex grades, especially 2205 and 2507, have demonstrated good resistance. Corrosion fatigue and intergranular corrosion The combination of high mechanical strength and very good resistance to corrosion gives duplex steels superior corrosion fatigue strength. Due to the duplex microstructure and low carbon content, the duplex grades have a good resistance to intergranular (intercrystalline) corrosion. Erosion corrosion In general, stainless steel offers good resistance to erosion corrosion. Duplex grades are especially good due to their combination of high surface hardness and good corrosion resistance. Galvanic corrosion Galvanic corrosion may occur when two dissimilar metals are electrically connected (as by welding) in an electrolyte. Stainless steel is in most cases more nobler than other metallic materials. The more noble metal is protected while the less noble metal is more severely attacked by corrosion. The electrolyte, area ratio, and the less noble metal determines the corrosion rate. Stainless steel in contact with carbon 14
steel rebars fully cast in concrete does not cause galvanic corrosion of the carbon steel reinforcement due to the high ph in concrete. Galvanic corrosion does not occur between different grades of stainless steels as long as both grades are in passive state. Atmospheric corrosion Atmospheric corrosion is not a unique form of corrosion, but a collective term to denote the corrosion of surfaces in the atmosphere. When stainless steel is exposed to an aggressive atmosphere it is primarily stained. This is sometimes referred to as tea staining, but it can also be attacked by localised corrosion with time, particularly at high chloride levels as in marine atmospheres. Today there are duplex grades available for any type of atmosphere. The Outokumpu Corrosion Handbook For more information on corrosion and corrosion resistance in different media, see further the Outokumpu Corrosion Handbook. You can obtain your own copy from your local sales office. Table 7. PRE values for different grades. Figure 3. Typical critical pitting corrosion temperatures (CPT) in 1M NaCl measured according to ASTM G150 using the Avesta Cell. Test surfaces wet ground to 320 mesh. CPT varies with product form and surface finish. Outokumpu steel name PRE 4307 18 LDX 2101 26 4404 24 FDX 25 TM 25 2304 26 FDX 27 TM 27 EDX 2304 TM 28 LDX 2404 33 904L 34 2205 35 254 SMO 43 2507 43 CPT, ( C) 100 90 80 70 60 50 40 30 20 * 10 0 4307 LDX 2101 4404 2304 4432 EDX 2304 TM LDX 2404 2205 904L 2507 254 SMO span CPT min. -CPT max. * = Less than 10 C 15
Product assortment and services Outokumpu Duplex is available in various shapes and sizes to suit your needs. Hot rolled quarto plate Hot rolled coil and plate Cold rolled coil and sheet Precision strip Semifinished (bloom, billet, ingot and slab) Bar, wire rod and rebar Welded tube, pipe, fittings and threaded fittings Structural sections, DUPROF TM Fasteners Our added value services ease your project and offer ways to save expenses at critical points Edge preparation Cut to shape Bending Surface finishing: 1D, 2E, 2B, 2R Polishing Construction kits Prefabrication Modified chemical analysis Slit coils Package solutions Welding advice Technical support/project administration 2B surface finish perfect for food & health sectors Surface finish characteristics are not merely a question of appearance. The quality affects the corrosion resistance as well as the cleansability of dirt and bacteria, which is paramount in the food industry and health sector. Outokumpu can additionally offer a 2B surface finish in duplex stainless steels, which most often fulfills the industry surface requirements without any further surface treatment saving both time and money. See our product programme in the online tool Stainless Steel Finder at outokumpu.com 16 Table 8. Surface finishes. Finish Type of process route Surface appearance 1D 2E 2B Hot rolled, heat treated, pickled. Cold rolled, heat treated, mechanically descaled followed by pickling. Cold rolled, heat treated, pickled, skin passed. Skin passing can be done by tension levelling. Standard for most steel types to ensure good corrosion resistance; also common finish for further processing. Rough and dull. Rough and dull. Smooth surface with low lustre. 2R Cold rolled, bright annealed. Smoother and brighter than 2B.
Fabrication Outokumpu Duplex offers excellent opportunities when constructing challenging and durable structures. However, due to the high strength of the material, the working process is somewhat different than with austenitic or ferritic steels. Outokumpu is prepared to assist you with every technical aspect of fabrication. We can provide you with the necessary training, computer simulations and detailed instructions. Welding Outokumpu Duplex can be welded with most of the methods used for austenitic stainless steel: Shielded metal arc welding (SMAW) Gas tungsten arc welding TIG (GTAW) Gas metal arc welding MIG (GMAW) Flux-cored arc welding (FCAW) Plasma arc welding (PAW) Submerged arc welding (SAW) Others: Laser, resistance and high frequency (HF) welding In general, the main issue with welding Outokumpu Duplex is to maintain the phase balance in the heat affected zone without precipitations. The chemical composition balances the microstructure. Therefore, it is important to have the right welding consumable and the right procedure. The following general instructions should be considered: 1. Weld without preheating 2. Allow the material to cool between passes, preferably to below 150 C. For 2507 100 C 3. Duplex filler material is required and recommended with the exception for LDX 2101 which may be welded without filler material in some cases 4. The recommended arc energy should be kept within specified limits 5. The heat input should be adapted to the steel grade and adjusted to the thickness of the welded material 6. Edge preparation angle should be about 10 greater and the land should be somewhat smaller compared to welding standard austenitics 7. If welded with filler, post-weld annealing is not necessary. In cases where heat treatment is considered, e.g. for stress relieving, it should be carried out in accordance with the temperatures stated in Table 9, but with the minimum temperature increased by 30-50 C, to secure full dissolution of intermetallic phase in the weld metal 8. GTAW and PAW methods: addition of nitrogen (1-2%) in the shielding/ purging gas is recommended Table 9. Characteristic heat treatment temperatures, C. LDX 2101 2304 LDX 2404 2205 2507 Hot forming 1100-900 1100-900 1120-900 1150-950 1200-1025 Quench annealing 1020-1080 950-1050 1000-1120 1020-1100 1040-1120 Stress relief annealing 1020-1080 950-1050 1000-1120 1020-1100 1040-1120 17
Table 10. Welding consumables. Steel grade Consumable ISO designation Typical chemical composition, % by wt. C Cr Ni Mo N FDX 25 TM 23 7 NL 0.02 23.5 8.0 0.3 0.14 22 9 3 NL 0.02 22.5 8.5 3.0 0.15 LDX 2101 23 7 NL 0.02 23.5 8.0 0.3 0.14 22 9 3 NL 0.02 22.5 8.5 3.0 0.15 2304 23 7 NL 0.02 23.5 8.0 0.3 0.14 22 9 3 NL 0.02 22.5 8.5 3.0 0.15 FDX 27 TM 22 9 3 NL 0.02 22.5 8.5 3.0 0.15 EDX 2304 TM 23 7 NL 1 0.02 23.5 8.0 0.3 0.14 22 9 3 NL 1 0.02 22.5 8.5 3.0 0.15 LDX 2404 22 9 3 NL 0.02 22.5 8.5 3.0 0.15 2205 22 9 3 NL 0.02 22.5 8.5 3.0 0.15 2507 25 9 4 NL 0.02 25 9.5 3.5 0.25 1 Although both 23 7 NL and 22 9 3 NL welding consumables can be used, it is recommended to use the higher alloyed 22 9 3 NL filler in order to match the higher tensile strength and improved corrosion resistance of the EDX 2304 grade. Welding to other steels including carbon steels Outokumpu Duplex can be easily welded to other steels including carbon steels. The filler type can be duplex. When duplex steels are welded to carbon steels an alternative is to use a filler of 23Cr13Ni2Mo type. In most cases duplex filler offers more strength and better corrosion resistance. When joining duplex to super austenitic steels, please contact Outokumpu for assistance. Filler metals for joining similar duplex steels, see table 10. Post weld treatment In order to restore the stainless steel surface and achieve good corrosion resistance, it is necessary to perform a post weld treatment. There are both mechanical methods (e.g. brushing, blasing, grinding) and chemical methods (e.g. pickling) available. The applicable method depends on the type of imperfections to be removed, as well as corrosion resistance, hygiene and aesthestic requirements. 18
The Outokumpu Welding Handbook For more information on welding and post weld treatment, please see the Outokumpu Welding Handbook. Forming Outokumpu Duplex is suitable for all forming techniques. The higher strength and the lower elongation compared to austenitic stainless steel will however impose some differences in forming behaviour: Generally a higher force is needed. On the other hand, since duplex design often implies downgauging, the force level can be similar to austenitics. If the forming technique is not already decided, we recommend choosing the most appropriate one for duplex stainless steels. FDX 25 and FDX 27 The new FDX product family exhibits substantially improved formaility. The elongation after fracture is typically about 40% compared to about 30% for other duplex grades, which make them more suitable for advanced forming. Machining The high strength will of course effect the machinability, but not as much as expected. Some technical guidance when machining duplex, is given below. See also the duplex machining guidelines for further details. Stable setup Due to the higher strength the cutting forces will be higher, which increases the risk of vibrations. The trick is to have a stable setup. Use the shortest possible tool extension, good and rigid clamping. Sharp tools Use cutting tools with a positive geometry. Duplex grades are prone to work hardening, a dull geometry will generate a hard surface and decrease the tool life. Avoid build up edge Stainless steels have a tendency to stick to the tool. Problems occur when the cutting speed is too low. The main difference between carbon steel and stainless steels when machining is that you face problems if you run too slowly. The result will be poor surface finish and short tool life. The problem is solved by increasing the cutting speed. Table 11. Cutting, shearing Roll bending Break bending Deep drawing Roll forming Tooling use Lubrication Things to consider Maximum thickness for shearing and punching is 80-85% of that of austenitic steel. More bending force will be needed compared to other stainless steels. Through the downgauging, this effect will however be smaller than anticipated. The springback due to the higher strength is large when roll bending. Avoid sharp bending radius. Minimum ratio between inner radius to sheet thickness should not be less than 2. If drawing is dominant, formability is comparable to austenitic stainless steel. If stretching is dominant, formability is closer to ferritic steels. The high strength of the sheet has to be considered in the design of the rolls. If properly designed there are no problems in roll forming Duplex. Strong, durable tools (hardness, HRC larger than 500, Ra-value preferably lower than 0.2 micrometers). Because of the high strength of Outokumpu Duplex and extreme pressure additives are useful in complex forming operations. LDX 2101 The lean duplex grade LDX 2101 has superior machinability compared to other duplex grades. Even if you compare with the low alloyed standard austenitic grades LDX 2101 is easier to machine. 19
1528EN-GB:1. December, 2013. Working towards forever. We work with our customers and partners to create long lasting solutions for the tools of modern life and the world s most critical problems: clean energy, clean water and efficient infrastructure. Because we believe in a world that lasts forever. Information given in this brochure may be subject to alterations without notice. Care has been taken to ensure that the contents of this publication are accurate but Outokumpu and its affiliated companies do not accept responsibility for errors or for information which is found to be misleading. Suggestions for or descriptions of the end use or application of products or methods of working are for information only and Outokumpu and its affiliated companies accept no liability in respect thereof. Before using products supplied or manufactured by the company the customer should satisfy himself of their suitability. outokumpu.com