High Strength Austenitic Stainless Steel Research Articles

Experimental investigation of cold-formed stainless steel built-up closed section stub columns

This paper presents an experimental investigation on the performance of cold-formed stainless steel built-up closed section stub columns. The built-up sections were composed by assembling two channel components at the flanges, which were brake-pressed from high-strength austenitic and duplex stainless steel thin sheets. Three types of built-up sectional profiles were formed by connecting two unstiffened channels (i.e., unlipped channels), two edge-stiffened channels (i.e., lipped channels) as well as one unstiffened channel and one edge-stiffened channel, respectively, using self-plugging rivets. Four sectional series were devised to cover nominal overall web height-to-plate thickness ratio values of 50, 60, 67 and 80. In order to obtain the actual material properties considering the cold-work effect, tensile coupon tests were carried out on both flat and corner longitudinal coupon specimens. In addition, a total of 29 fixed-ended stub columns including 19 specimens without holes and 10 specimens with circular web holes were tested under axial compression. The experimental results involving failure modes, ultimate capacities and responses of load versus axial shortening were obtained and fully documented. The effects of sectional profile types, overall web height-to-plate thickness ratio and hole diameter-to-overall web height ratio on the performance of cold-formed stainless steel built-up closed section stub columns were examined. Moreover, the appropriateness of design rules as prescribed in the recently updated American Specification ASCE/SEI 8–22 was evaluated. It was revealed that the codified design provisions generally provided unconservative strength predictions for the high-strength austenitic and duplex stainless steel built-up closed section stub columns both without and with circular web holes. Reliability analyses were performed in this study, and the compressive strength predictions of the built-up closed sections according to the existing design rules were found to be unreliable for the high-strength austenitic stainless steel stub columns without holes as well as the duplex stainless steel stub columns without and with circular web holes.

Evaluation of Reheat Cracking Susceptibility in High Strength Austenitic Stainless Steels

Evaluation of Reheat Cracking Susceptibility in High Strength Austenitic Stainless Steels

Friction stir welding of AISI 316LN high strength austenitic stainless steel for cryogenic application

Friction stir welding (FSW) is a solid state joining process that uses the heat generated by the friction of a rotating tool and the base material to join materials together. Due to the fact that the material is never melted, and that extensive plastic deformation is introduced in the weld seam, a unique set of properties is achieved. The technique has been extensively used to join aluminium and aluminium alloys, but very few developments are reported on high strength austenitic stainless steel, which is the material of choice for many high energy physics and fusion magnets. This paper contains a comprehensive microstructural and mechanical characterization, including at cryogenic temperature, of an 8 mm thick high strength austenitic stainless steel plates. The steel grade is the high alloy version of AISI 316LN (identified as 1.4429 or -X2CrNiMoN17-13-3 according to European standards). Special attention was given to cryogenic elastic – plastic J – integral testing of the weld seam. To the authors’ knowledge, this is the first time fracture toughness at cryogenic temperature on friction stir welded 1.4429 has been measured.

Direct energy deposition of high strength austenitic stainless steel matrix nanocomposite with superior ductility: Microstructure, tensile properties, and deformation behavior

Direct energy deposition (DED) was used to additively manufacture 22–13-5 austenitic stainless steel (SS), of which the mechanical properties and corrosion resistance are superior to those of SS316L and SS304L. Additionally, in-situ formed oxide-driven strengthening was utilized in this study. The DED-processed austenitic SS matrix nanocomposite (SSMNC) exhibited unique microstructural features of heterogeneous grains and dislocation networks. The nano-sized precipitates existed at the sub-structure boundaries and decorated the dislocation network. The results of the transmission electron microscopy (TEM)-energy loss spectroscopy (EELS) analyses revealed nano-sized precipitates with an average size of 21.1 nm that were identified as (Mn,Cr)-rich oxides. This means that, during the DED process, the oxygen in the powder feedstock transformed into nano-sized oxide particles by rapid solidification. The DED-processed SSMNC revealed a yield strength of 705.4±5.3 MPa, which is higher than those of reported AM-processed stainless steels. In addition, the elongation-to-failure was measured as 41.8±3.5%. This suggests that the DED-processed SSMNC has an excellent combination of strength and ductility at room temperature. The high ductility of the alloy developed in this work was found to be achieved by a twinning-induced plasticity (TWIP) mechanism that operated during the deformation. Based on the above findings, the relationships between the microstructure, mechanical properties, and deformation mechanism are also discussed.

Microstructure and properties of high-strength C + N austenitic stainless steel processed by laser powder bed fusion

In the developing field of laser powder bed fusion (L-PBF), austenitic stainless steels, such as AISI 316L, have gained great importance owing to their excellent processability. However, the moderate strength of these steels limits their applicability. This can be counteracted by the use of nitrogen as an alloying element to improve both strength and corrosion resistance.In this work, nitrogen-alloyed high-strength austenitic stainless steel X40MnCrMoN19-18-1 was processed by L-PBF, and the resulting microstructural and mechanical properties were investigated. The same material was also processed by hot isostatic pressing (HIP), which was used as a reference state. In the L-PBF process, argon and nitrogen were used as process gases to investigate the influence of process atmosphere on the microstructure and on changes in the chemical composition during processing. The results show a minor decrease in the nitrogen content of the steel after L-PBF, independently of the process gas, whereby argon resulted in a slightly higher specimen density. The microstructure after L-PBF processing contained small precipitates that could be removed by a short solution-annealing treatment. The tensile properties of the L-PBF-built steel are comparable to those of the steel produced by hot isostatic pressing in terms of ultimate tensile strength, but had lower elongation to fracture values. The ductility of the material was enhanced by solution annealing without significant impairment of the ultimate tensile strength. This work demonstrates that nitrogen-alloyed stainless steels can be processed by means of L-PBF and can extend the variety of appropriate steels towards applications with high requirements for the material strength and chemical resistance.

Evaluation of Reheat Cracking Susceptibility in High Strength Austenitic Stainless Steels

Evaluation of Reheat Cracking Susceptibility in High Strength Austenitic Stainless Steels

Corrosion and Cavitation Resistance of High-Strength Austenitic Nitrogen Stainless Steels in Seawater

Abstract—The corrosion and cavitation resistance of high-strength economically alloyed nitrogen-bearing chromium–nickel–manganese austenitic C10Cr19Mn10Ni6Mo2N and C09Cr19Mn10Ni6Mo2Cu2N stainless steels in seawater is compared experimentally with the properties of chromium–nickel C04Cr18Ni9 and C04Cr18Ni9N steels. The resistance to pitting corrosion is tested by a chemical method in a 100-g/L FeCl3 · 6H2O solution. The overall corrosion resistance is assessed by tests in synthetic seawater (3% NaCl). The cavitation resistance in seawater is tested by means of a high-intensity cavitation system based on a Hielscher Ultrasonic UIP 1000hd ultrasound unit in 3% aqueous NaCl solution (vibration frequency 20 kHz, power 1000 W, amplitude 25 μm) for 8–36 h. After cavitation treatment, the damage and change in microhardness at the sample surface is estimated, as well as the change in phase composition and mass of the samples in the tests. According to the tests, C10Cr19Mn10Ni6Mo2N and C09Cr19Mn10Ni6Mo2Cu2N steels are free of pits after exposure to seawater and iron-chloride solution. The overall corrosion rate is lower than for chromonickel Cr18Ni9 steel. Ultrasonic cavitation may lead not only to surface damage by erosion and intensification of local corrosion but also to change in the physical and mechanical properties on account of cold working and phase transformations. The resistance to ultrasonic cavitation in seawater is greater for C10Cr19Mn10Ni6Mo2N and C09Cr19Mn10Ni6Mo2Cu2N steels, containing thermally and mechanically stable austenite, than for chromonickel steels, especially C04Cr18Ni9, which is weaker and less stable. For example, after 36-h cavitational treatment in seawater, significant changes in state are seen in C04Cr18Ni9 and C04Cr18Ni9N steels: considerable damage (etching) and hardening of the surface and also the formation of a small quantity of martensite in C04Cr18Ni9 steel. For C10Cr19Mn10Ni6Mo2N and C09Cr19Mn10Ni6Mo2Cu2N steels, the tests indicate only slight change in state of the surface and hardening.

Investigation of Materials and Welds for the Precompression Structure of the ITER Central Solenoid

The central solenoid (CS) is the backbone of the ITER magnet system. It consists of six independent coils held together by a vertical precompression structure that must react to tensile loads and provide sufficient preload to maintain coil-to-coil contact during all stages of plasma operation. Material selection and specifications applicable to the structural components of the precompression structure are particularly demanding. These include large forgings manufactured from a high-strength austenitic stainless steel (FXM-19) with a stringent specification in terms of microstructure and maximum allowed magnetic permeability. Stringent requirements are also imposed on all welded joints. In particular, the attachment welds of the cooling pipes to the structure are subject to challenging restrictions in terms of weld imperfections and geometry. They must induce limited distortion of the components and are submitted to inspections carried out in accordance with the most severe acceptance levels of applicable national and international standards. The results of a campaign of tests covering nondestructive and destructive evaluation of samples from different components and welds are summarized in this paper, particularly focusing on the quality achieved at the microstructural and macrostructural level. The influence of the microstructure on the final properties and on the inspectability of the material by nondestructive examinations is also discussed.

Static strength of stainless steel K- and N-joints at elevated temperatures

This paper aims to investigate the static strength of stainless steel gap and overlapped K- and N-joints at elevated temperatures. A numerical parametric study was conducted on circular hollow section (CHS) K- and N-joints under axial loads in the braces at different temperatures ranging from 22 to 760°C. A wide range of geometric parameters and chord preload ratios of CHS K- and N-joints using duplex, high strength austenitic and normal strength (AISI 304) stainless steel was investigated. The joint strength reduction was compared with reduction factors of yield stress and elastic modulus of stainless steel materials at elevated temperatures. A unified strength equation for CHS K- and N-joints at elevated temperatures was proposed by adopting the reduction factor of yield stress. The statistical analysis shows that the proposed strength equation is accurate for stainless steel K- and N-joints at elevated temperatures.

Comprehensive Understanding of Ductility Loss Mechanisms in Various Steels with External and Internal Hydrogen

Hydrogen-induced ductility loss and related fracture morphologies are comprehensively discussed in consideration of the hydrogen distribution in a specimen with external and internal hydrogen by using 300-series austenitic stainless steels (Types 304, 316, 316L), high-strength austenitic stainless steels (HP160, XM-19), precipitation-hardened iron-based super alloy (A286), low-alloy Cr-Mo steel (JIS-SCM435), and low-carbon steel (JIS-SM490B). External hydrogen is realized by a non-charged specimen tested in high-pressure gaseous hydrogen, and internal hydrogen is realized by a hydrogen-charged specimen tested in air or inert gas. Fracture morphologies obtained by slow-strain-rate tensile tests (SSRT) of the materials with external or internal hydrogen could be comprehensively categorized into five types: hydrogen-induced successive crack growth, ordinary void formation, small-sized void formation related to the void sheet, large-sized void formation, and facet formation. The mechanisms of hydrogen embrittlement are broadly classified into hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP). In the HEDE model, hydrogen weakens interatomic bonds, whereas in the HELP model, hydrogen enhances localized slip deformations. Although various fracture morphologies are produced by external or internal hydrogen, these morphologies can be explained by the HELP model rather than by the HEDE model.

SUMITOMO SM2535-125

Abstract Sumitomo SM2535 is a very high strength austenitic stainless steel for use in oil country tubular goods as a material suitable for severe sour service. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming and heat treating. Filing Code: SS-1268. Producer or source: Nippon Steel and Sumitomo Metal Corporation.

고강도 오스테나이트계 스테인리스강(STS201) 일면전단 볼트접합부의 최대내력평가

고강도 오스테나이트계 스테인리스강(STS201) 일면전단 볼트접합부의 최대내력평가

SUMITOMO SM2242-110

Abstract Sumitomo SM2242 is a high strength austenitic stainless steel for use in oil country tubular goods as a material suitable for severe sour service. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming and heat treating. Filing Code: SS-1259. Producer or source: Nippon Steel and Sumitomo Metal Corporation.

SUMITOMO SM2535-110

Abstract Sumitomo SM2535 is a high strength austenitic stainless steel for use in oil country tubular goods as a material suitable for severe sour service. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming and heat treating. Filing Code: SS-1256. Producer or source: Nippon Steel and Sumitomo Metal Corporation.

Structural design of cold-formed stainless steel tubular X- and T-joints at elevated temperatures

This paper presents a numerical parametric study on ultimate strength of cold-formed stainless steel tubular X- and T-joints at elevated temperatures. Extensive numerical simulations were carried out on SHS, RHS and CHS tubular X- and T-joints subjected to brace axial compression at different elevated temperatures ranging from 22 to 760°C. A wide range of geometric parameters and chord preload ratios was considered. The material properties of duplex, high strength austenitic and normal strength stainless steel (AISI 304) were carefully incorporated in the finite element models. The joint strength reduction was compared with the reduction factors of yield stress and elastic modulus of stainless steel materials at elevated temperatures. A unified equation for predicting ultimate strength of X- and T-joints at elevated temperatures was proposed by introducing a temperature factor. The statistical analysis shows that the proposed strength equation is reliable and accurate.

Physical Properties of a High-Strength Austenitic Stainless Steel for the Precompression Structure of the ITER Central Solenoid

The ITER central solenoid (CS) consists of six independent coils kept together by a precompression support structure that must react vertical tensile loads and provide sufficient preload to maintain coil-to-coil contact when the solenoid is energized. The CS precompression system includes tie plates, lower and upper key blocks, load distribution and isolation plates and other attachment, support and insulating hardware. The tie plates operating at 4 K are manufactured starting from forgings in a high-strength austenitic stainless steel (FXM-19) with a stringent specification. Moreover, forged components for the lower and upper key blocks have to be provided in the same FXM-19 grade with comparably strict requirements. FXM-19 is a high-nitrogen austenitic stainless steel, featuring high strength and toughness, ready weldability, and forgeability. It features as well higher integral thermal contraction down to 4 K compared with the very high Mn steel grade selected for the CS coil jackets, hence providing an additional precompression of the CS modules during cooling down. The results of an extensive characterization of the physical properties of FXM-19, extended down to 4 K or lower, are reported here. The provided results allow requirements for the file for new materials described in French code RCC-MRx to be fulfilled, as well as to complete the material properties in the ITER database, where measurements were reported for room temperature and above only.

Mechanical Properties of Resistance Spot Welded Components of High Strength Austenitic Stainless Steel

Resistance multi-spot welding (MSW) in column, triangle and tetragonal symmetry arrangements was prepared using cold-rolled 301L high-strength sheets, and their static and fatigue properties were investigated. The effects of spot welds on the fracture strengths and fatigue limits were discussed. The results show that the static strengths can be estimated using an inherent linear relationship formula of the load versus the welding area. It was based on the 28%–33% volume fraction of α′ martensite induced at the interfacial spot weld fracture because of the failure deformation. The fatigue limits of the MSW nonlinearly increase with the number of spot welds. The arrangement of spot welds in the MSW significantly affects the average fatigue limit of each spot weld; its 26% maximum reduction occurred in the triangle, and the interaction stress between spot welds led to its 18% reduction in the tetragonal symmetry. The calculated fatigue stress of all MSW loadings with their mean fatigue limits was 230–270 MPa.

Mechanical Property and Corrosion Resistance of the E309L Buffer Layer in Weld Overlay

The weld overlay technology of high strength low alloy steel (HSLA) and austenitic stainless steel is widely applied in such fields as petroleum, chemical industry and energy, and its service environment is of high temperature and corrosion. As the matching performance is often poor for both austenitic stainless steel and high strength low alloy steel, cavities and crackles occur easily at the joints, which cause brittle fractures with dangerousness to some extent. So in the present study, the metal-inert gas welding (MIG) is used to clad the austenitic stainless steel to HSLA. In the experimental group, 4mm buffer layer (E309L) and 8mm cladding layer (E347L) were successively cladded on the substrate (Q345B), while 12mm cladding layer was directly deposited on the substrate in the control group. The hot corrosion tests were done, and through the scanning electron microscope (SEM), we observed the cross-sectional morphology. By the X-ray diffraction (XRD), we analyzed ingredients of the corrosion products. The corrosion products in the experimental group mainly consist of iron and nickel oxides, while the products are mainly iron complex compound and salt in the control group. The SEM results show the area near the welding seam of the specimens without buffer layer had been corroded severely. However, only a slight corrosion occurs adjacent to the welding seam. This demonstrates that the buffer layer can protect the specimens from being corroded.

2169 steel waveform measurements for equation of state and strength determination

In support of efforts to develop multiscale models of a variety of materials, we have performed a set of eleven gas gun impact experiments on 2169 steel, a high-strength austenitic stainless steel. These experiments provided carefully controlled shock, reshock, and release velocimetry data, with initial shock stresses ranging from 10 to 50 GPa. Both windowed and free-surface measurements on samples ranging in thickness from 1 to 5 mm were made to increase the utility of the data set. Target physical phenomena included the elastic/plastic transition (Hugoniot elastic limit), the Hugoniot, any phase transition phenomena, and the release/reshock paths (windowed and free-surface), with associated strength information. The Hugoniot is nearly linear in US–up space. Reshock tests with explosively welded impactors produced clean results, by contrast with earlier reshock tests with glued impactors which showed gap signatures. The free-surface samples, which were steps on a single piece of steel, showed lower wavespeeds for thin (1 mm) samples than for thicker (2 or 4 mm) samples. A preliminary strength analysis suggests the flow strength increases with stress from ∼1 GPa to ∼2.5 GPa over this range, consistent with other recent work but about 25% above the Steinberg model.

Web crippling behaviour of cold-formed duplex stainless steel tubular sections at elevated temperatures

This paper reports a numerical investigation of cold-formed high strength stainless steel square and rectangular hollow sections subjected to web crippling at elevated temperatures. Finite element analysis was conducted on cold-formed high strength austenitic and duplex stainless steel material. Four loading conditions specified in the American Specification and Australian/New Zealand Standard for cold-formed stainless steel structures were investigated in the numerical study. A non-linear finite element model which includes geometric and material non-linearities was developed and verified against experimental results. It was shown that the finite element model closely predicted the web crippling strengths and failure modes of the tested specimens under the four loading conditions. Hence, parametric study was carried out to investigate the web crippling behaviour of cold-formed high strength stainless steel square and rectangular hollow sections at elevated temperatures. The web crippling strengths predicted from the finite element analysis were compared with the design strengths obtained using the American, Australian/New Zealand and European specifications for stainless steel structures by substituting the reduced material properties in the current web crippling design equations. A unified web crippling equation for cold-formed high strength stainless steel square and rectangular hollow sections at elevated temperatures is proposed. It is demonstrated that the web crippling strength obtained using the proposed equation is safe and reliable using reliability analysis.