Lean Duplex Research Articles

XPS analysis of manganese in stainless steel passive films on 1.4432 and the lean duplex 1.4162

Passive films were compared on two stainless steels: the recent lean duplex EN 1.4162 and EN 1.4432 (316L). For alloys with significant amount of manganese and nickel, the Mn 2p 3/2 peak will overlap with the Ni-LMM. To resolve this overlap, Ni 2p 3/2 to Ni-LMM intensity ratios were recorded on 1.4432, compensated for overlayer thickness, and then used to fix the Ni-LMM intensities in the Mn 2p spectra on the duplex material. Manganese was found in oxidation states II and V/VI; its film content was not dependent on the bulk composition.

Experimental and numerical studies of lean duplex stainless steel beams

Stainless steel is well suited to a range of engineering applications owing to its durability and favourable mechanical properties. The most widely used grades of stainless steel are from the austenitic family and typically contain around 18% chromium and 8%–11% nickel — these grades have a relatively high initial material cost, due, in part, to their high nickel content, and a nominal yield strength (in the annealed condition) of around 220 N/mm 2. A new, low nickel grade of stainless steel (UNS 32101/EN 1.4162), commonly referred to as ‘lean duplex’, has been developed, that offers over two times the strength of the familiar austenitic grades and at approximately half the initial cost — this lean duplex stainless steel appears well suited to load-bearing applications in construction. This paper reports material and 3-point bending tests on lean duplex stainless steel hollow sections. The 3-point bending tests were replicated by finite element (FE) analysis and, upon validation of the numerical models, parametric studies were conducted to assess the effect of key parameters such as cross-section aspect ratio, cross-section slenderness and moment gradient on the strength and deformation capacity of lean duplex stainless steel beams. Based on both the experimental and numerical results, appropriate slenderness limits and design rules, suitable for incorporation into structural stainless steel design standards, have been proposed.

Nickel: important part of climate change solution

It is clear that a combination of varied efforts will be required to effectively reduce greenhouse gas emissions on the scale needed to avoid disastrous climate change impacts. A portfolio of technologies now exists to meet the world's energy needs over the next 50 years and limit atmospheric CO2. Many of these technologies pose significant corrosion challenges and as such, will require some use of advanced materials. Nickel containing alloys (ranging from lean duplex to superaustenitic stainless steel grades to the high nickel alloys) are important enabling materials for climate change solutions such as solar energy, ethanol production, and carbon capture and storage.

New Trends Emerge in Thermal Desalination Evaporator Materials

Lessons Learned In the last half of the 20th century, the main evaporator body for an MSF was made of carbon steel of varying thickness, depending on the evaporator component. The general trend was to first establish the evaporator structure’s required thickness and add a corrosion allowance based on an assumption of general uniform corrosion to meet the evaporator’s expected life span. The highest corrosion allowance for an evaporator component was for areas subject to severe corrosion, such as the stage division wall and flashing brine gates deflector, which can reach 25 mm. Because carbon steel corrosion was never uniform, an evaporator was plagued by frequent shutdowns to patch leaks in the evaporator body or water boxes. The immediate impact was higher maintenance costs and production loss, eventually lowering evaporator availability. Bare carbon steel can’t withstand aerated seawater or the high salinity of flashing brine. Operating experience proved that bare carbon steel wasn’t the correct material for an evaporator shell and internal components. The selected material must exhibit high corrosion resistance to aerated seawater, hot brine recycle, and concentrated brine. Water boxes were protected by 3 mm 90/10 copper–nickel (Cu–Ni). The evaporator floor was lined with 3 mm 317L (3 percent molybdenum), which exhibits excellent resistance to pitting corrosion. The evaporator’s side walls, from stage floor to ceiling, were lined with 316L. The ceiling was protected by 304L, and the distillate trough, division walls, flashing brine gates, and deflectors were replaced by solid 316L. After using austenitic stainless steel to control corrosion of an evaporator’s internal components, it was extremely important to reduce dissolved oxygen in the evaporator, reduce dissolved oxygen in the feedwater to less than 20 ppb, and inject sodium sulfite in the brine recycle to scavenge the remaining dissolved oxygen to nil ppm. This important step controls corrosion of the evaporator’s internal components and condenser tubes. By selecting the proper materials, it was possible to reduce evaporator operating costs, increase availability to 93 percent, and achieve sustainable production. Because the price of nickel increased dramatically, reverting to lean duplex stainless steel made evaporator capital costs more competitive. A new generation of MSF and MED evaporators replaced austenitic stainless steel 304L, 316L, and 317L with lean duplex stainless steel UNS 32202, UNS 32304, and UNS 32205, respectively. Lean duplex stainless steel is characterized by low-nickel, highchromium content, which improves stress corrosion properties and provides greater pitting resistance than austenitic stainless steel. To better understand the importance of proper material selection, consider an MSF evaporator’s primary components.

Precipitation of Secondary Phases in Lean Duplex Stainless Steel 2101 during Isothermal Ageing

In the present paper, the precipitation behavior of secondary phases in Lean Duplex Stainless Steel (LDX) 2101 had been studied. The alloy has a typical ferritic-austenitic duplex structure after solution treatment. Isothermal ageing treatments were carried out over the temperature range from 700 to 850°C for the period between 2 min and 1440 min. Cr2N-type nitrides were formed as the main product of precipitates, together with small amount of Cr23C6-type carbides. Increase of N content and decrease of Cr and Mo contents in the steel had led to the absence of σ-phase. Due to the solid solution strengthening by interstitial atoms, the hardness value of austenite was measured to be higher than that of ferrite. With increasing the isothermal ageing time, precipitates were observed to be preferentially nucleated at the δ/γ interface and grown toward the δ phase. The δ/γ interfce migrated from the precipitate particles into δ phase, leaving the precipitates behind along the original interfaces, which could increase the size of the secondary austenite (γ′) phase and decrease the hardness of both austenite and ferrite. Inside γ′ phase, the hardness was measured to increase from about 3.20 GPa at the original interface to about 3.75 GPa at the newly formed interface of δ/γ′. The isothermal kinetics for the precipitation of secondary phases was measured to obey the JMAK-type law. The TTT (time-temperature-transformation) curve was constructed based on the measurements, which seems to have resulted from the overlap of two different precipitated products. The average impact energy at room temperature for the sample after solid solution treatment was measured to be 105 J. When 2% secondary phases were precipitated during ageing, the impact energy decreased to about 43 J, reduced by about 59% as compared with the as-annealed sample, indicating that formation of secondary phases can result in dramatic decrease of steel toughness.

Application of the modified electrochemical potentiodynamic reactivation method to detect susceptibility to intergranular corrosion of a newly developed lean duplex stainless steel LDX2101

The present work aimed at defining optimal conditions using double loop electrochemical potentiokinetic reactivation (DL-EPR) method for evaluating intergranular corrosion (IGC) susceptibility of lean duplex stainless steel (LDX2101) aged at 700 °C between 3 min and 300 h. The results demonstrated that the modified DL-EPR measurement (solution of 33% H 2SO 4 + 0.1% HCl at 20 °C and scan rate of 2.5 mV/s) could successfully characterize the interactions between precipitation, chromium depletion and IGC of LDX2101 with high sensitivity and reproducibility. In addition, there was no indication of healing because the effect of formation of chromium-enriched precipitates was more dominative than that of redistribution of chromium in depleted zones.

Effect of aging on the corrosion resistance of 2101 lean duplex stainless steel

The microstructure and localized corrosion behavior of a 2101 lean duplex stainless steel aged at 700 °C were investigated. The results showed that changes in the microstructure of the duplex stainless steel, due to the formation of precipitates, affected its pitting corrosion resistance. The values of the pitting potential and the critical pitting temperature dropped drastically before aging time up to 30 min. The potentiostatic pitting corrosion measurement indicated more sensitive to the small amount of precipitates compared to the potentiodynamic test. Pitting nucleated mainly in the ferrite phase for the solution-annealed specimen, while the initiation of pitting corrosion for the aged specimen took place at Cr-depletion area around the precipitates, i.e. in the newly formed secondary austenite phase.

Testing and numerical modelling of lean duplex stainless steel hollow section columns

Stainless steels are employed in a wide range of structural applications. The austenitic grades, particularly EN 1.4301 and EN 1.4401, and their low-carbon variants EN 1.4307 and EN 1.4404, are the most commonly used within construction, and these typically contain around 8%–11% nickel. The nickel represents a large portion of the total material cost and thus high nickel prices and price volatility have a strong bearing on both the cost and price stability of stainless steel. While austenitic stainless steel remains the most favourable material choice in many applications, greater emphasis is now being placed on the development of alternative grades with lower nickel content. In this study, the material behaviour and compressive structural response of a lean duplex stainless steel (EN 1.4162), which contains approximately 1.5% nickel, are examined. A total of eight stub column tests and twelve long column tests on lean duplex stainless steel square (SHS) and rectangular hollow sections (RHS) are reported. Precise measurements of material and geometric properties of the test specimens were also made, including the assessment of local and global geometric imperfections. The experimental studies were supplemented by finite element analysis, and parametric studies were performed to generate results over a wider range of cross-sectional and member slenderness. Both the experimental and numerical results were used to assess the applicability of the Eurocode 3: Part 1-4 provisions regarding the Class 3 slenderness limit and effective width formula for internal elements in compression and the column buckling curve for hollow sections to lean duplex structural components. Comparisons between the structural performance of lean duplex stainless steel and that of other more commonly used stainless steel grades are also presented, showing lean duplex stainless steel to be an attractive choice for structural applications.

Effect of Aging on the Fracture Behavior of Lean Duplex Stainless Steels

The influence of aging in the range of 550 °C to 850 °C for 5 to 120 minutes on the impact fracture behavior of 2101 and 2304 lean duplex stainless steels (DSS) was investigated in the present study. The 2304 steel displayed ductile behavior irrespective of aging conditions. In contrast, the 2101 steel displayed a ductile behavior only in the case of aging for 5 minutes at 550 °C and 650 °C, whereas in all other cases, it fractured in a brittle manner. The brittle fracture behavior of the 2101 steel has been attributed to the precipitation of small black particles at the α/α and α/γ grain boundaries (nitrides), which form paths for easy crack propagation. In the 2304 steel, such particles precipitated at 750 °C and 850 °C, but they were located inside the austenitic grains because of the formation of secondary austenite. They therefore did not embrittle the steel. The larger Ni content of the 2304 steel favored the formation of the secondary austenite that is absent in the 2101 steel.

Lean duplex UR2202: how to keep in the welds the excellent mechanical properties of the base metal?

The new Mo free duplex stainless steel UR2202 was developed by Industeel in close cooperation with Ugitech - Schmolz + Bickenbach. It can be used in many construction or transport applications, as a substitute for 304 and 304L. With at least the same corrosion properties, the new UR2202 has higher mechanical properties. This provides the potential for significant weight savings for fabricated tanks, pressure vessels etc., when compared to the austenitic grade. Different welding products are considered to achieve homogeneous or heterogeneous welds with the lean duplex base metal and can be selected according to the required corrosion resistance, toughness and tensile properties.

Investigation of selective corrosion resistance of aged lean duplex stainless steel 2101 by non-destructive electrochemical techniques

Lean duplex stainless steel 2101 (LDX2101) shows wide application potential due to its better corrosion performance and lower cost than traditional 304 austenite steel. This paper investigates the effects of thermal aging treatments at 700 °C for various aging times up to 100 h on the selective corrosion resistance of LDX2101 by two non-destructive electrochemical measurements: double-loop electrochemical potentiokinetic reactivation (DL-EPR) and electrochemical impedance spectroscopy (EIS). The evolution of microstructure was examined by optical microscopy, SEM microscopy and X-ray diffraction techniques (XRD). The results showed that the two applied electrochemical measurements agreed very well. Both methods were able to reveal the relationship between microstructure and selective corrosion resistance, which was related to the formation of chromium- and molybdenum-depleted zones around the precipitates, especially the σ phase, during aging. Nevertheless, more information could be obtained using EIS methods, including the interfacial charge transfer reaction and the corrosion product adsorption process. The results suggest that the susceptibility of the aged alloy to selective corrosion is presumably codetermined by the formation of chromium- and molybdenum-depleted areas, as well as by the replenishment of them, in these areas from the bulk during aging.

Lean Duplex UR2202: an alternative to 304L with increased corrosion resistance and mechanical properties

The paper presents the new Mo free duplex stainless steel UR2202 (EN 1.4062) developed to provide a cost effective alternative to 304L (EN 1.4307), concrete, organic materials or galvanized carbon steel in potable water systems, pulp & paper industry and construction applications. The reduction of Ni is balanced by a nitrogen addition in order to obtain a microstructure containing approximately 50% ferrite and 50% austenite. Several industrial heats were produced with 22Cr%, 2Ni% and 0.2N% as the typical composition. The new lean duplex grade UR2202 has better localized and uniform corrosion resistance and twice the yield strength than 304L.

Influence of annealing treatment on the corrosion resistance of lean duplex stainless steel 2101

The effect of annealing temperatures in the range 1000–1200 °C on the microstructure and corrosion behavior of 2101 lean duplex stainless steel was investigated. The results demonstrated that the volume fraction of austenite phase decreased with increasing annealing temperature. However, lower values for the pitting potential ( E pit) and the critical pitting temperature (CPT) were obtained after annealing at higher temperatures. Pitting was initiated preferentially in the ferrite/austenite boundaries or inside the ferrite domains, indicating that the ferrite phase had inferior pitting corrosion resistance as compared to the austenite phase in as-received steel. Moreover, the PRE values of the ferrite phase fell with the annealing temperature, while the values for the austenite phase rose. No equal PRE values in the ferrite and austenite phase were found for this steel in the range of annealing temperatures. This was determined by evaluating the PRE values of both phases from EDS results and the Thermo-Calc database.

UR 2202

Abstract UR 2202 is a lean duplex stainless steel designed to match the corrosion resistance of Type 304SS. This datasheet provides information on composition, physical properties, elasticity, tensile properties, and shear strength as well as fracture toughness. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: SS-1033. Producer or source: Industeel USA, LLC.

Fracture Toughness of Welded Commercial Lean Duplex Stainless Steels

Duplex stainless steels are successfully used in pressure vessel applications due to high mechanical strength combined with superior corrosion resistance. There has been a debate concerning the tou ...

New Lean Duplex Stainless Steels for Structural Applications

The continuous improvement of the applications of duplex stainless steels (DSS) is justified mainly by their excellent corrosion resistance in very aggressive environments and by their mechanical strength, often twice than that of conventional austenitic grades. Therefore more extensive applications have been suggested, like constructions, structural components, automotive applications, etc. However for such not advanced but quantitatively important applications the base cost of the alloy is one of the more constraining features. A way to obtain leaner alloys is to reduce the Ni content and to compensate with manganese and nitrogen additions. In the present paper the structural and mechanical properties of two low Ni duplex grades are analyzed in order to investigate the structural stability of the austenite against its possible transformation to martensite and the secondary phase’s precipitation. The detailed characterization has been performed with SEM-EDS on as received and heat treated (600-850 °C) alloys. A limited precipitation of chromium carbides and nitrides at the grain boundaries has been detected in both grades. The martensite formation has been revealed only in the 2101 grade. With regard to the impact toughness the behaviour of 2101 grade is quite similar to that of the common DSS, while in the 2304 the drastic drop of toughness is avoided. The corrosion behaviour of both grades in aggressive chloride environments is quite similar to that of austenitic AISI 304 grade.

Weld oxide formation on lean duplex stainless steel

Weld oxides have a strong influence on corrosion resistance, but have hitherto only been studied to a limited extent for duplex stainless steels. X-ray photoelectron spectroscopy (XPS) has here been used to study heat tint formed on gas tungsten arc (GTA) welds on the commercial duplex grades LDX 2101 (EN 1.4162/UNS S32101) and 2304 (EN 1.4362/UNS S32304) welded with and without nitrogen additions to the shielding gas. The process of heat tint formation is discussed in terms of transport phenomena to explain the effect of atmosphere, temperature and composition. The oxides formed were found to be enriched in manganese and corrosion testing shows that nitrogen has a strong influence on the weld oxide. A mechanism is proposed including evaporation from the weld pool and subsequent redeposition.

Development of a Lean Duplex Stainless Steel

The classic series of duplex stainless steels shows very high corrosion resistance and can be used for very demanding applications. A new lean duplex steel, LDX 2101® (EN 1.4162, UNS S32101), has been developed with corrosion resistance on a par with standard austenitic grades. Application areas include: structural components, chemical industry, tanks and containers. The steel was designed to have equal amounts of ferrite and austenite in annealed condition and with an austenite that is stable against strain‐induced martensite. Thanks to its high nitrogen content, the steel has a fast austenite reformation when subjected to thermal cycling, e.g. welding. Unlike conventional duplex grades, the formation of intermetallic phase is very sluggish, although precipitation of nitrides and carbides has a certain impact on material properties after exposure in the temperature range 600 to 800°C. The precipitation behaviour after different isothermal treatments is described and its influence on different product properties is shown. A good agreement was found between impact toughness and corrosion resistance for a wide range of thermal treatments.

Duplex Stainless Steels ‐ a Review after DSS ‘07 held in Grado

Duplex stainless have always been an exiting area of interest for researchers, stainless steel producers, fabricators and end users. They present very diversified technical challenges and simultaneously attractive in‐service properties at excellent cost/properties ratios, particularly in critical markets including oil and gas, chemical industry, pulp and paper industry, water systems, desalination plants, pollution control equipments, chemical tankers, etc. This explains why although they still remain a marginal production in the stainless steel business (less than 1%) dedicated international conferences have been organised since about 25 years. The purpose of this paper is to present a review of the 100 scientific contributions presented during the latest international duplex stainless steel conference witch took place in Grado, Italy, on 18‐20 June 2007. The main topics concerned microstructure and mechanical properties, weldability, corrosion resistance and in‐service properties. The “standard” duplex stainless steels, i.e. the 2304, 2205, and the family of 2507 (Cu,W, ...) grades were confirmed as very valuable grades with outstanding performances proven in more than 20 years successful in‐service applications. New grades including the so‐called lean duplex dedicated to volume oriented markets (possible replacement of 304/316 grades) and some “niche” grades dedicated to very specific markets were presented. It was pointed out that the duplex grades start to be well established products particularly suitable for corrosion resistance applications. They show a two‐digit yearly growth thanks to the production of new grades and production ranges (coils and bars) targeting the replacement of the more costly 300 series including 304 but also rusty carbon steel in e.g. structural application.

Role of Microstructure on the Corrosion Susceptibility of UNS S32101 Duplex Stainless Steel

Abstract Effect of heat treatments and resulting changes in microstructure on general and localized corrosion susceptibility of lean duplex stainless steel UNS S32101 in caustic and chloride solutions was investigated. Results show that changes in the microstructure (ferrite phase/austenite phase ratio and inter-metallic precipitation) of the duplex stainless steel (DSS), due to different annealing and aging treatments, affect its general and pitting corrosion resistance. The role of DSS microstructure in localized corrosion susceptibility was found to be significantly different in the chloride environments as compared to caustic environments.