Properties Of Duplex Stainless Steel Research Articles

Surface layer investigation of duplex stainless steel S32205 after stress peening utilizing X-ray diffraction

Residual stresses and micro-hardness of duplex stainless steel S32205 after stress peening are measured and domain sizes and microstrain are calculated. The results show that stress peening can significantly improve the compressive residual stresses and micro-hardness in both austenite and ferrite, and the former is affected by both the prestress and the measurement directions. Microstructure investigation reveals that material deformation is enhanced after stress peening, and smaller domain sizes and higher microstrain are introduced. The compressive residual stress enhancement by stress peening in ferrite is more than that in austenite under the same stress peening, which is due to the more elastic deformation recover in ferrite. Therefore, the difference of residual stresses between ferrite and austenite can be narrowed down by conducting appropriate stress peening. Based on these investigations, it is concluded that stress peening is superior to conventional shot peening treatment to improve the surface properties of duplex stainless steel.

Influence of long-term low-temperature aging on the microhardness and corrosion properties of duplex stainless steel

An investigation was made of the influence of long-term aging (up to 7000h) at low temperatures (300 and 400°C) on the corrosion and mechanical properties of a 2205 duplex stainless steel. The selective corrosion behavior of austenite and ferrite phases was found to reverse in response to aging treatment at 400°C. The degree of Cr depletion (Ir/Ia) increased considerably with the increase in aging time at 400°C and no self-healing process was observed even after aging for 7000h. A good correlation was observed between the electrochemical results and the microhardness of ferrite phase.

듀플렉스 스테인레스 소재의 고온 변형 안정성 및 어닐링 온도에 따른 특성 분석

The aim of this study was to analyze high temperature deformation stability and properties of duplex stainless steels(DSS) according to annealing temperature. In order to analyze high temperature deformation stability, a number of compression tests were carried out with a stain rate of 10 s~10 s up to a compression ratio of 50% in a temperature range of 950°C-1300°C. The analysis of high temperature deformation stability of DSS was performed based on the Ziegler model. In order to analyze the high temperature properties of DSS, annealing treatments were conducted by isothermal holding for 1 hr at 950°C to 1300°C with 50°C intervals followed by water cooling. The hardness and tensile tests were performed on specimens with different volume fractions of constituent phases, such as austenite, ferrite and sigma. The hardness and tensile strength of 2507 according to the annealing temperature are better than those of 2205. The strain rate sensitivity and Ziegler parameter are higher in 2205 than in 2507 as a whole, which implies that 2205 is better than 2507 in terms of forgeability at high temperature. (Received January 25, 2012)

Use of Superficial Magnetic Techniques to Evaluate the Mechanical Properties of Duplex Stainless Steels

Aim of this study is the correlation among magnetic properties, tensile deformation and microstructure of the duplex stainless steel 2205. This correlation is achieved by the magnetic ferrite phase of the two phase microstructure. The amount of Barkhausen noise for a given material is linked with the amount of impurities, crystal dislocations, etc. and can be a good indication of mechanical properties of the material. Specimens of the alloy DSS2205 were tested under tensile deformation in different percentages and the magnetic measurements were taken online, during the tensile deformation. The measurements of the parameters of BHN combined with the percentages of the deformations and their graphic plot showed an exponential relationship. Microstructure studied with SEM technique. Macro hardness also measured and its measurements compared with those of BHN. The resultant plots showed a linear proportion among them.

Ageing effects on the lattice strain behaviour of duplex stainless steel

The mechanical properties of duplex stainless steel (DSS) are known to display embrittlement due to ageing effects. Knowledge of the micro behaviour of aged DSS is important for understanding the mechanisms of deformation and failure, but it has proved difficult to obtain due to the complex effects created by the duplex structure. Lattice strain measurements of DSS aged under various conditions of temperature and time have been performed in order to determine the strain behaviour of individual ( hkl) planes in the α- and γ-phases using white synchrotron radiation X-rays at SPring-8. It was found that the lattice strain of α-Fe(200) depends strongly on the ageing conditions and that the lattice strain behaviour in the γ-phase is more stable than that in the α-phase. These results suggest that the changes in macro mechanical properties, including yield strength and ultimate strength, which are revealed by standard tensile tests, are solely due to ageing effects in the α-phase. The results further suggest that the lattice strain of α-Fe(200) can be used as an index to evaluate 475 °C ageing effects in DSS.

Microstructure and mechanical properties of duplex stainless steels sintered in different atmospheres

Present investigation is aimed at developing duplex stainless steels through powder metallurgy route and study the effect of sintering atmospheres on density, mechanical properties and microstructures. Duplex stainless steel composition was prepared from the mixture of 316L and 430L alloyed powders. The powders were mixed in a pot mill for 12 h and compacted at a pressure of 560 MPa. The green compacts were sintered at 1350°C in four different atmospheres such as nitrogen, argon, hydrogen and partial vacuum. Sintered duplex stainless steels were subjected to density measurement, metallography examinations and tensile testing. Duplex stainless steel sintered in partial vacuum showed highest densification of 96% theoretical, tensile strength and ferrite content, when compared with stainless steels sintered in other three atmospheres. Microstructure of stainless steels sintered in argon, hydrogen and partial vacuum showed the bi-phase structure. SEM fractographs of the stainless steels sintered in partial vacuum and hydrogen revealed completely ductile mode of failure.

Mechanical Property of Duplex Stainless Steel with Nanostructured Layer by Surface Mechanical Attrition Treatment

A grain size gradient layer material was produced by means of surface mechanical attrition treatment on a UNS S32304 duplex stainless steel. In this study, the mechanical property was characterized by tensile test, while microstructure was investigated by transmission electron microscopy, scanning electron microscopy and electron backscatter diffraction. The deformed layer enhanced both the yield strength and maximum strength with large ductility retained, as revealed by tensile test that the yield stress of 30 minutes processed sample was 702 MPa as compared with 454 MPa of as-annealed sample. The elongation to failure, however, decreased from 0.41 to 0.27.

Effect of Laser Beam Welding Parameters on Microstructure and Properties of Duplex Stainless Steel

The present study is concerned with laser beam welding and its effect on size and microstructure of fusion zone then, on mechanical and corrosion properties of duplex stainless steel welded joints. In this regard, influence of different laser welding parameters was clarified. Both bead-on-plate and autogenously butt welded joints were made using carbon dioxide laser with a maximum output of 9 kW in the continuous wave mode. Welded joints were subjected to visual, dye penetrant and radiography tests before sectioning it for different destructive tests. Accelerated corrosion test was carried out based on tafel plot technique. The results achieved in this investigation disclosed that welding parameters play an important role in obtaining satisfactory properties of welded joint. High laser power and/or high welding speed together with adjusting laser focused spot at specimen surface have produced welded joints with a remarkable decrease in fusion zone size and an acceptable weld profile with higher weld depth/width ratio. Besides, acceptable mechanical and corrosion properties were obtained. Using nitrogen as a shielding gas has resulted in improving mechanical and corrosion properties of welded joints in comparison with argon shielding. This is related to maintaining proper ferrite/austenite balance in both weld metal and HAZ in case of nitrogen shielding. As a conclusion, laser power, welding speed, defocusing distance and type of shielding gas combination have to be optimized for obtaining welded joints with acceptable profile as well as mechanical and corrosion properties.

Texture and mechanical properties of duplex stainless steel through symmetric hot rolling

Experimental rolling trials were performed at different temperatures on EN 1.4462 duplex steel imposing also different reduction ratios and a possible solution quenching. A clear and significant relation between the applied thermo-mechanical process and the microstructural evolution was shown, and it is useful for designing the steel microstructure. The mechanical properties, the micro-structural features and the texture characteristics were defined for each condition in order to point out the operative parameters (i.e. thermal level, imposed strains and application of solution quenching) that permit to maximize the formability of the final hot-rolled products.

Investigation of secondary phase effect on 2205 DSS fracture toughness

The fracture toughness properties of duplex stainless steels (DSS) are strongly reduced by intermetallic phases, precipitating at 600–1000°C. In this investigation, the embrittlement effect induced by a low content of these phases has been studied in a 2205 DSS, by means of instrumented Charpy V impact testing. Different contents of intermetallic phases have been produced by isothermal treatments at 800–950°C. The microstructure has been analysed by scanning electron microscope/backscattered electron images. The impact test results, the examination of the fracture surfaces and of the cross-sections close to the notch root allows us to elucidate the role of secondary phases contents in reducing impact fracture toughness. When the quantity of secondary phases is <0·5%, these precipitates are rare and insignificant, reducing the absorbed energy by facilitating a ductile fracture. When the content is >1%, the fracture is completely brittle. The plastic deformation at the notch root and in the resisting section provokes a secondary phase breakage with a high density microcrack formation, inducing an easy nucleation and propagation of the final fracture crack. When the content of secondary phases is between 0·5 and 1%, fracture is mixed. Both the sigma σ and chi χ phases have been found to be responsible for the embrittling of the 2205 DSS, and fracture toughness mainly depends on their density and dimension.

Overview of the applications and problems associated with the use of austeno-ferritic steels and aluminium alloys in welded structures

This paper describes the typical mechanical and metallurgical characteristics of the austeno-ferritic steels for structural applications, with particular reference to their weldability. Some examples of the uses of these materials for the construction of certain welded structures are also given. The paper also discusses the various types of aluminium alloys and their advantages and disadvantages in the construction of welded structures. General remarks regarding the welding processes commonly used are thus provided along with an overview of the welded structures built using aluminium alloys. In this paper, the mechanical and metallurgical properties of duplex stainless steel for structural purposes are presented, with particular attention to their weldability. Some typical uses of these materials for welded structures are shown in detail. This paper also deals with the use of aluminium alloys in welded structures pointing out the advantages and disadvantages. Information about suitable welding processes are also reported.

Fatigue behaviour of duplex stainless steel reinforcing bars subjected to shot peening

ABSTRACTThe influence of shot peening on the fatigue properties of duplex stainless steel reinforcing bars manufactured using both hot‐ and cold‐rolled processes was studied. The S‐N curves of the bars before and after the shot‐peening process were determined, showing that shot peening improves the fatigue behaviour of the rebars. This improvement is essentially due to the introduction of a compressive residual stress field in the surface of the reinforcing bars, but also to the smoothing of the surface flaws and cold working generated during the manufacturing process. This improvement is much greater in the case of the hot‐rolled bars, mainly as a result of their much higher ability for plastic deformation, whereas cold‐rolled bars had a much higher hardness. A more severe peening action capable of promoting greater plastic deformation on the bar surface is judged necessary to improve the fatigue resistance of cold‐rolled rebars.

Effect of prior hot rolling on the microstructures and mechanical properties of duplex stainless steel containing tempered martensite and ferrite

A duplex structure of δ-ferrite and lath martensite with interlath retained austenite film is developed in this study by modifying the alloy addition. The presence of δ-ferrite can further strengthen the grain refinement of austenite during hot rolling. As a result, the amount of retained austenite is enhanced. Tempered martensite embrittlement occurs due to the decomposition of retained austenite, and grain refinement can in fact ameliorate the tempered martensite embrittlement by delaying the onset of the embrittlement to a higher temperature. The combined effect of uniform and small grains as well as a large amount of retained austenite provides a further increase in the mechanical properties. After identical tempering treatments, all mechanical properties measured in the as-rolled condition were found to be higher than those of direct quenching without rolling. After hot rolling, the increase in the hardness and tensile strength was not accompanied by a drop in the ductility and toughness.

In vitro biocompatibility of duplex stainless steel with and without 0.2% niobium.

Stainless steel is frequently used as a biomaterial. Chemical composition alterations can be undertaken to improve its mechanical and biological properties. This investigation aimed to compare the biocompatibility of duplex stainless steel, with and without 0.2% niobium, with austenitic stainless steel and titanium-6-aluminium-4-vanadium (Ti6Al4V) using rat bone marrow (RBM) cell culture. Cell attachment was evaluated at 24 hr. Cell proliferation, cell viability, total protein content, and alkaline phosphatase (ALP) activity were evaluated at 7, 14 and 21 days. Bone-like nodule formation was evaluated at 21 days. Cell attachment, proliferation and viability were unaffected by the chemical composition of the stainless steels and the Ti6Al4V. Total protein content, ALP activity, and bone-like nodule formation were unaffected by the chemical composition of the stainless steels, but these parameters were greater on the Ti6Al4V than on the stainless steels. Our results demonstrated that initial cell events were unaffected by the chemical composition of the tested alloys, while events indicating osteoblast differentiation including increased ALP activity and bone-like nodule formation were favored by the Ti6Al4V. Moreover, the evaluated parameters were unaffected by the presence of niobium in the stainless steel composition. As niobium affects microstructure and, consequently, improves the mechanical properties of duplex stainless steel, it is suggested that the addition of niobium to metallic alloys could be useful in developing alloys with acceptable biocompatibility and improved mechanical features. (Journal of Applied Biomaterials & Biomechanics 2004; 2: 162-8).

σ-phase morphologies and their effect on mechanical properties of duplex stainless steels

Abstract The aim of the presented study is to investigate the influence of the different σ-phase morphologies on the mechanical, wear and corrosive behaviour of the duplex stainless steel 1.4462 (X2CrNiMoN 22 5 3). Different amounts of σ-phase were precipitated in tensile, impact strength, wear and corrosion samples by annealing at 750 °C, 850 °C and 938 °C. σ-phase shows a detrimental influence on the impact strength and the corrosion behaviour. To a very limited extent it can be used to slightly raise the strength under quasi-static load and to improve the wear resistance. Finally, it can be concluded that σ-phase has more unfavourable influences on the material' behaviour than advantageous ones. Therefore, it should be avoided in duplex stainless steels.

The Fatigue Properties of Duplex Stainless Steels: Role of Microstructure

The paper analyzes the role of microstructure on the low cycle fatigue behaviour of duplex stainless steels. The alloys are investigated in their as received condition and after ageing at 475°C. The fatigue resistance and the cyclic accommodation of these DSS are strongly controlled by the volume fraction of α and γ "phases which is related to the chemical composition in particular nitrogen. It is shown that DSS with a high fraction of austenite present a good combination of fatigue resistance and cyclic softening especially in the aged condition. The mutual interaction between ferrite and austenite referred to load transfer is beneficial for increasing the fatigue resistance. Alloying with nitrogen appears to be a promising way to master an optimised microstructure leading to high mechanical resistant DSS.

Effect of heat treatment on microstructure and mechanical properties of duplex stainless steel

Present study concerns the effect of deformation and heat treatment on the microstructure and mechanical properties of a duplex stainless steel. While hot rolling causes the coarse distribution of the constituent phases (ferrite and austenite), 50% cold rolling results into the elongated and splintered two — phase structure. Supersaturated ferrite structure established by water quenching from 1300°C results into the strengthening due to the formation of fine dispersed austenite precipitates within ferrite grain after isothermal heat treatment (1000°C, 0.5 hour). Duplex structure consisting of ferrite and austenite in a fine-grained form is obtained after isothermal heat treatment of cold rolled sample. Cold deformed and heat treated steel exhibits best combination of strength and ductility among all the investigated steel samples.

Effect of brazing conditions on the microstructure and mechanical properties of duplex stainless steels to Cr−Cu alloy with Cu−base insert metal

The brazing of a copper-chromium alloy and DSS (Duplex stainless steel) was conducted under various conditions to investigate the bonding phenomena, microstructures and mechanical properties. The reactions of liquid insert metal with dissimilar base metals, a Cu−Cr alloy and DSS produced various phases in the bond zone. The chemical composition and the volume fraction of the phases varied as a function of the brazing conditions. The Cu phase for the DSS and piece of stainless steel separated from the DSS was produced from the reaction of the insert metal and the SSS. In addition, the Cr−Mn phase, Mn−Fe phase and Fe−Cr phase were formed by the reaction between the insert metal and each base metal. As the brazing temperature and time increased; the amounts of the Cu phase and the number of stainless steel pieces increased. In addition, the Mn−Fe phase varied compared to the Fe−Cr phase after brazing at 1273 K at 0 min. The Cr−Mn phase initially increased but eventually decreased after holding times of 15 min at 1273 K and 7 min at 1303 K.

Influence of chemical composition and residual stresses on mechanical properties of duplex stainless steel studied by X-ray and neutron diffraction

The parameters characterizing the elastoplastic mechanical behaviour of each phase in textured austeno-ferritic duplex stainless steels were determined using X-ray and neutron diffraction during uniaxial tensile test. A self consistent model was used to predict the evolution of the internal stresses during loading, and to identify critical resolved shear stresses \and strain hardening parameters of the material. Calculations based on this model were compared with the results of mechanical tests and diffraction data. The effect of residual stresses and the chemical composition on the elastoplastic phase behaviour was determined.

Estudo comparativo entre os aços inoxidáveis dúplex e os inoxidáveis AISI 304L/316L

Os aços inoxidáveis dúplex ferríticos-austeníticos fazem parte de uma classe de materiais com microestrutura bifásica, composta por uma matriz ferrítica e ilhas de austenita, com frações volumétricas aproximadamente iguais dessas fases. Essa classe de materiais é caracterizada por apresentar interessante combinação de elevadas propriedades mecânicas e de resistência à corrosão e, por isso, é considerada bastante versátil. Os aços inoxidáveis dúplex são, freqüentemente, utilizados nas indústrias química e petroquímica, de papel e celulose, siderúrgicas, alimentícias e de geração de energia. O presente trabalho estabelece um comparativo entre as propriedades físicas, mecânicas e de resistência à corrosão dos aços inoxidáveis duplex e os tradicionais aços inoxidáveis austeníticos AISI 304L e 316L, largamente utilizados na indústria brasileira. Resultados de ensaios laboratoriais e dados relevantes de experiências práticas desses materiais também são apresentados.