316L Austenitic Stainless Steel Research Articles

Effect of Copper Addition on the Formability of 304L Austenitic Stainless Steel.

To improve the antibacterial properties of 304L austenitic stainless steel, copper is often added as an antibacterial agent, but the forming performance of the resulting material is poor, impacting its actual production and use. Therefore, this study investigated the influence of copper addition on the formability of 304L austenitic stainless steel with drawing, cupping and conical cup forming tests. Mechanical properties were determined with tensile and hardness tests. The microstructure and phase transformation were further characterized by metallographic microscopy, scanning electron microscopy and x-ray diffraction analysis. It was found that the addition of copper impaired the mechanical properties of 304L austenitic stainless steel, increased the stacking fault energy of the material and inhibited the occurrence of strain-induced martensite transformation, leading to a decrease in the formability of 304L austenitic stainless steel.

Hydrogen embrittlement behavior in interstitial Mn–N austenitic stainless steel

The susceptibility to hydrogen embrittlement behavior was investigated in an interstitial Mn–N austenitic steel HR183 and stainless steel 316L. Hydrogen was introduced by cathodic hydrogen charging at 363 K. HR183 has stronger austenite stability than 316L despite its lower nickel content, the addition of manganese and nitrogen inhibited martensitic transformation during the slow strain rate tensile deformation. Due to the diffusion of hydrogen being delayed by the interstitial solution of nitrogen atoms and the uniform dislocation slips, hydrogen permeates more slowly in HR183 than 316L, contributing to an 84.79 μm thinner brittle fracture layer in HR183 steel. Hydrogen charging caused elongation losses in both 316L and HR183 steels associated with the hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) mechanism. However, the hydrogen embrittlement susceptibility of HR183 is 3.4 times lower than that of 316L according to the difference in elongation loss between the two steel after hydrogen charging. Deformation twins trapped a lot amount of hydrogen leading to brittle intergranular fracture in 316L. The multiple directions of slip in HR183 steel suppressed the strain localization inside grains and delayed the adverse effects conducted by HELP and HEDE mechanism, eventually inhibiting server hydrogen embrittlement in the HR183 steel. This study is assisting in the development of low-cost stainless steel with excellent hydrogen embrittlement resistance that can be used in harsh hydrogen-containing environments.

Residual stress analysis, microstructural characterization, and mechanical properties of tungsten inert gas-welded P92/AISI 304L dissimilar steel joints

In the present work, the creep strength-enhanced ferritic martensitic P92 steel was welded with 304L austenitic stainless steel. The dissimilar joining of these two different grades of material was performed by using tungsten inert gas welding process. The nickel-based ERNiCr-3 welding consumable was used. The influence of post-weld heat treatment (760 °C, 2h), called as tempering, was also investigated. The secondary electron and optical image confirmed that ERNiCr-3 weld metal is accompanied by an equiaxed austenitic microstructure with Ni weight percentage of 68.29%. The energy-dispersive X-ray spectroscopy and electron probe microanalyzer results of the weld fusion zone revealed the Nb, Cr, and Ti segregation in the inter-dendritic region. The elemental mapping of the carbon-depleted zone, and the interface was performed using an electron probe microanalyzer, which revealed the diffusion of Ni, Cr, and Fe across the interface of P92 steel and ERNiCr-3 filler weld. The tensile test result indicated that part of the dissimilar weld joints (DWJs) with relatively weak ultimate tensile strength was ERNiCr-3 weld metal. The ultimate tensile strength value of the DWJs was observed as 610 MPa and 580 MPa in the as-weld and post-weld heat treatment situations, respectively. The Charpy V-notch impact energy of the ERNiCr-3 weld fusion zone was achieved as 135 ± 2 J and 140 ± 2 J in as-weld and post-weld heat treatment situations, respectively. The low impact toughness of the ERNiCr-3 weld metal was attributed to the presence of niobium carbide (NbC) and titanium carbide (TiC) particles. The peak longitudinal residual stress of 490 MPa and transverse residual stress of 442 MPa were noted in the ERNiCr-3 weld fusion zone at a depth of 3 mm from the top surface. The tempering heat treatment exhibited a significant drop in the residual stresses value for the weld fusion zone and heat affected zone (HAZ).

Mechanical and Microstructural Behaviors of Gas Tungsten Arc Dissimilar Metal Welds of High-Mn Steel and Stainless Steel 316L Using Various Fillers for Cryogenic Fuel Tanks

The gas tungsten arc (GTA) weldability of high-Mn (HMn) steel and austenitic stainless steel (STS) 316L using dissimilar metal welds (DMWs) was investigated, to fabricate a fuel tank for an LNG-fueled ship. Three types of welding fillers, HMn steel, STS 309LMo and Inconel 625, were applied to the DMWs. The weldability of the DMWs was examined by investigating mechanical properties at 25 and -196 o C, followed by microstructural evolution and weld deformation. The GTA welding process was performed with a heat input range of 0.72–1.89 kJ/mm. All of the fillers employed in the study produced reasonable mechanical properties and low levels of precipitation, such as M<sub>7</sub>C<sub>3</sub> and Fe<sub>3</sub>C. However, the DN specimen using the Inconel 625 filler exhibited reduced ductility in the bending test. This was attributed to Nb-carbide precipitations at dendrite boundaries at the root weld. The DM specimen using HMn filler experienced severe thermal deformation because it had a relatively higher coefficient of thermal expansion than the other fillers during heating by arc and solidification. Therefore, STS 309LMo and HMn wires were determined to be the appropriate fillers for the DMW of HMn steel and STS 316L for cryogenic applications, and the HMn wire requires attention to weld deformation.

Microstructure and corrosion behavior of friction-surfaced 304L austenitic stainless steels

Friction surfacing is a solid-state deposition process that provides microstructural and mechanical property benefits over fusion-based deposition methods as a result of the lower heat input and hot working. The study examines microstructure and corrosion properties for friction-surfaced 304L stainless steel consumable rods on 304L stainless steel substrates. Microstructural characterization revealed fine-grained microstructure with distributed strain-induced martensite and high residual compressive stresses. Corrosion studies of friction-surfaced specimens were carried out by exposure to FeCl3 and MgCl2 solutions per ASTM G48 and ASTM G36 standards, respectively. The corrosion tests showed friction surfacing led to shallower and smaller pits than the uncoated substrate, however, the pit number density was higher in the friction-surfaced specimens. The microstructural transformations during friction surfacing are beneficial to mitigating pitting corrosion and potentially chloride-induced stress corrosion cracking (CISCC).

A micropillar compression investigation into the plastic flow properties of additively manufactured alloys

Solidification cells and a high density of dislocations are two common features of additively manufactured (AM) alloys that are processed using techniques such as laser powder bed fusion (L-PBF) and directed energy deposition (DED). A critical assessment of their role in determining the plastic properties (yield strength, σy, and work hardening behavior) was performed via the micropillar compression tests on the austenitic 316L stainless steel (316L) and the Inconel 718 (IN718) alloys manufactured using the L-PBF and DED techniques, and comparing the results obtained with those of the compression and tensile tests on bulk samples. While both the L-PBF alloys contain submicron-scale cells whose boundaries are decorated with the dislocation networks, the DED 316L consists of micron-scale cells (whose boundaries are enriched with elemental segregation) with a uniform distribution of dislocations within them. The variations in σywith the pillar size are similar to those reported on pillars fabricated from pre-strained Ni but are opposite to those reported on pillars of micro/nano-crystalline alloys. The mechanical responses of the DED 316L pillars with and without cell boundaries (CBs) are similar. These observations suggest that the high density of dislocations (arranged in the network fashion or distributed uniformly) —and not the CBs—determine σy of the AM alloys. The stress-strain responses of pillars and transmission electron micrographs obtained on the deformed bulk samples suggest that the dislocation networks significantly enhance dislocation storage, leading to bulk-like deformation behaviors and superior work hardening capability in the L-PBF pillars with larger diameters.

Torsion of a rectangular bar: Complex phase distribution in 304L steel revealed by neutron tomography

Metastable austenitic stainless steel (304L) samples with a rectangular cross-section were plastically deformed in torsion during which they experienced multiaxial stresses that led to a complex martensitic phase distribution owing to the transformation induced plasticity effect. A three-dimensional characterization of the phase distributions in these cm-sized samples was carried out by wavelength-selective neutron tomography. It was found that quantitatively correct results are obtained as long as the samples do not exhibit any considerable preferential grain orientation. Optical microscopy, electron backscatter diffraction, and finite element modeling were used to verify and explain the results obtained by neutron tomography. Altogether, neutron tomography was shown to extend the range of microstructure characterization methods towards the meso- and macroscale.

Regression Modeling and Process Analysis of Resistance Spot Welding on Dissimilar Steel Sheets

The resistance spot welding process is used to weld dissimilar materials. Dissimilar joining is formed by two 2mm thick sheet metals of 304L austenitic stainless steel and galvanized steel. This study investigates the effects of welding parameters such as welding current, welding time, and welding force. The welding time and the welding force were, respectively, in the range of 10-13 cycles and 7-8bar, while the welding current was in the range of 10–16kA. Tensile tests were applied to determine the resistance parameters of dissimilar joining. The experimental results showed that increasing the welding current increased the tensile shear stress of the weld coupon. Regression analysis was carried out to determine the significance of the process parameters by using the coupled of the full factorial experimental design with statistical and graphical analysis of the results. Furthermore, analysis of variance was used to determine the optimal parameters and combinations to achieve the highest strength level.

Effect of Cooling Rate on Pitting Corrosion Behavior of 904L Austenitic Stainless Steel in a Simulated Flue Gas Desulfurization Solution

Effect of Cooling Rate on Pitting Corrosion Behavior of 904L Austenitic Stainless Steel in a Simulated Flue Gas Desulfurization Solution

Tipping effect of tetra-alkylammonium on the potency of N-(6-(1H-benzo[d]imidazol-1-yl)hexyl)-N, N-dimethyldodecan-1-aminium bromide (BIDAB) as corrosion inhibitor of austenitic 304L stainless steel in oil and gas acidization: Experimental and DFT approach

• BIDAB consists of benzimidazole and tertiary ammonium moieties separated by a C-12 alkyl chain has been synthesized. • The corrosion inhibition efficiency of BIDAB on 304L SS in 15% HCl was demonstrated experimentally and by DFT studies. • The corrosion inhibition of 404.37 μM BIDAB on a susceptible 304L SS in 15% HCl was found to be greater than 98% at 298.15 K. • The electrochemical studies show that BIDAB exhibits a mixed-type corrosion inhibition mechanism. • Adsorption of BIDAB obeyed Langmuir adsorption and exhibited a typical physisorption adsorption mechanism. A new class of quaternary ammonium bromide; N-(6-(1H-benzo[d]imidazol-1-yl)hexyl)- N, N -dimethyldodecan-1-aminium bromide (BIDAB) was successfully synthesized and characterized with FTIR, elemental analyzer, 1 H, and 13 C NMR spectroscopy instruments revealing embedded benzimidazole and other functional groups in the compound. The efficacy of 404.37 μM BIDAB as an effective corrosion inhibitor of 304L SS in 15% HCl exhibited over 97% inhibition efficiency at 298.15 K by electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS), polarizations, and weight loss measurements. The adsorption of BIDAB on the 304L stainless steel surface was studied by FESEM-EDX and X-ray photoelectron spectroscopy (XPS). The adsorption of BIDAB was found to obey the Langmuir isotherm model and demonstrate a typical physisorption behavior at elevated temperatures. The withdrawer of electrons from the benzimidazole ring owing to the tipping effect phenomenon of the tetra-alkyl ammonium functional group was suspected to be responsible for the typical physisorption behavior of BIDAB inhibitor as disclosed by the density functional theory (DFT) calculation’s chemical descriptors and the frontier orbitals (HOMO-LUMO) structures of the protonated BIDAB.

AISI 316L stainless steel modification by surface alloy and a-C:H:SiOx coating synthesis

AISI 316L austenite stainless steel is often used in orthopedics, although metal particles and metal ions are the major weakness of metallic prostheses associated with the tissue inflammation and proliferation. This paper presents the surface modification of the AISI 316L steel substrate to reduce its wear and corrosion rate using a combination of two methods. For that, the titanium alloy is synthesized on the substrate surface using the magnetron sputtering and electron-beam treatment. The elemental and phase compositions of the surface are investigated by energy dispersive X-ray spectrometry and X-ray diffraction. The a-C:H:SiOx coating is deposited onto substrates with the surface alloy by plasma assisted chemical vapor deposition to significantly improve the mechanical, anti-corrosion and wear-resistant properties of AISI 316L austenite stainless steel. The mechanical properties and the surface of the obtained coating are examined by nanoindentation and optical microscopy, respectively. It is shown that substrates with the surface alloy and a-C:H:SiOx coating manifest stability to autoclave sterilization proven by the results of optical microscopy.

Corrosion, Heat Treatment, and Microstructural Studies of GTA Welded 316 Austenitic Stainless-Steel Joint

The formation of a protective chromium carbide passive film makes austenitic stainless steel (ASS) alloys suitable for corrosive and high-temperature environments. This paper examined the transformation of the microstructure, corrosion, and mechanical properties of gas tungsten arc welded 316 austenitic stainless steel. The scientific principles governing metallurgical transformation and corrosion dynamics were discussed. The review shows that passive film on 316L ASS gradually erodes as the concentration of chloride ion rises. Metallurgical properties of FZ are completely changed, and solid-state transformation occurs at HAZ during the GTA welding process. These transformations affect the microstructure, corrosion, and mechanical properties of GTA welded ASS alloys.

Optimization of Selective Laser Melting (SLM) Additive Manufacturing Process Parameters of 316L Austenitic Stainless Steel

Optimization of Selective Laser Melting (SLM) Additive Manufacturing Process Parameters of 316L Austenitic Stainless Steel

Effect of initial dislocation density on the plastic deformation response of 316L stainless steel manufactured by directed energy deposition

The relationship between the microstructural features (such as the solidification cells and initial dislocation densities) and the tensile properties of alloys additively manufactured (AM) using techniques such as laser powder bed fusion (L-PBF) and directed energy deposition (DED) is yet to be firmly established. In this work, a detailed investigation into the structure-property relations in DED 316L austenitic stainless steel (316L SS) was conducted. The microstructural parameters were varied systematically by changing the laser energy employed. Results show that while the sizes of grains and cells and the volume fraction of the oxide particles increase with increasing laser energy, the dislocation density decreases. Importantly, a uniform distribution of dislocations, instead of dislocation networks that are reported in many AM alloys, was observed. The connection between these microstructural features and the yield strength and work hardening capability of the DED 316L SS, which vary systematically with the laser energy, are explored. The correlation shows that a Hall-Petch type relation cannot capture the measured yield strength variation. Instead, the initial dislocation density dominates both the yield strength and the work hardening behavior. These results suggest a strategy for manipulating the mechanical performance in AM alloys through the control of dislocation densities and their distribution.

Microstructure and mechanical properties of dissimilar inertia friction welded 316L stainless steel to A516 ferritic steel for potential applications in nuclear reactors

Defect-free welds between A-516 ferritic and 316L austenitic stainless steel were achieved using inertia friction welding (IFW) under varying friction and forge pressures. The microstructural evolution and the associated mechanical properties were characterised across different weld regimes. The welds were free from microcracks and demonstrated higher strength and hardness than the parent metal (PM), indicating enhanced properties. Carbide precipitates were not observed at the weld interface, implying no occurrence of sensitisation in the stainless steel. The presence of refined grains coupled with low grain orientation spread (GOS) values was the indication of continuous dynamic recrystallisation (CDRX) occurring during IFW.

Application of Taguchi Method Design to Investigate Tribological Performance of Laser-Surface-Textured 316L Austenitic Stainless Steel

Application of Taguchi Method Design to Investigate Tribological Performance of Laser-Surface-Textured 316L Austenitic Stainless Steel

Effects of filler material selection on the microstructural, mechanical and corrosion properties of TIG welded AISI/SAE 304L stainless steel sheets and rings

Abstract Austenitic stainless steels are mainly preferred especially for resistance to aggressive oxidizing medias and high temperature applications such as equipments and mechanical parts which are used in defense and conventional industries. In this study; 3 mm thick 304L austenitic stainless steel sheets and rings are joined to each other by using Tungsten Inert Gas welding method under pure argon shielding gas with ER316L and ER2209 filler metals. Weld metals and heat-affected zones of welded joints were examined by metallurgical and scanning electron microscopes. Microhardness, tensile and Charpy impact tests of weld regions are investigated. It has been determined that the filler metals have dominantly changed the microstructure of weld metals. The microhardness values of the welded samples joined with ER2209 filler metal was lower than the sample joined with ER316L filler metal in weld metal regions. Besides, corrosion tests indicated that the corrosion rates of welded samples joined with ER2209 filler metal is lower than the samples joined with ER316L filler metal.

Exploration on the fatigue behavior of low-temperature carburized 316L austenitic stainless steel at elevated temperature

The fatigue behavior of low-temperature carburized 316L austenitic stainless steel at elevated temperature was investigated. Uniaxial tensile tests and rotating bending fatigue tests were performed on untreated and carburized 316L austenitic stainless steel at 300 °C, 400 °C, 500 °C and ambient temperature. Results show that carburized case can improve the fatigue strength at both ambient and elevated temperatures significantly. The improvements of tensile strength and endurance limit by carburized case at elevated temperature are even higher than those at ambient temperature. Moreover, the higher improvement of fatigue performance at elevated temperature is mainly due to the better strengthening effect of carburized case on the strength, the brittleness reduction and the redistributions of carbon content of carburized case. Based on the observation of fracture morphologies, fatigue fracture mechanisms of untreated and carburized specimens at different temperatures were analyzed. For untreated specimens, fatigue cracks always initiate from the surface at both ambient and elevated temperatures. For carburized specimens, fatigue cracks initiate at subsurface near the boundary between carburized case and substrate at ambient temperature. At elevated temperature, fatigue cracks initiate near the boundary under the high applied stress while under low applied stress, fatigue cracks initiate from the inclusions.

Effects of Grain Boundary Engineering on the Microstructure and Corrosion Fatigue Properties of 316L Austenitic Stainless Steel

Grain boundary engineering (GBE) treatment was performed through thermomechanical processing (TMP) to optimize the grain boundary character distribution (GBCD) of 316L austenitic stainless steel. The effects of TMP on the GBCD and corrosion fatigue properties in high-temperature and high-pressure water were investigated. The results indicated that a high fraction (about 74%) of special boundaries as well as the interrupted network of random high-angle grain boundaries were obtained through 5% strain followed by annealing at 1,273 K for 90 min. The Σ9 and Σ27 boundaries were generated by the reaction of special boundaries. The highest corrosion fatigue life for 3,187 cycles was obtained when the TMP parameters of the 316L ASS were of 5% strain, annealing temperature of 1,273 K, and annealing time of 45 min. The low-energy special boundaries had strong intergranular corrosion resistance, but the strength of these boundaries was not enough to resist the propagation of transgranular fatigue cracks.

Microstructure anomaly during welding and its influence on the mechanical properties of dissimilar weldments of P92 martensitic steel and AISI 304L austenitic stainless steel

In this investigation, microstructural characteristics, mechanical properties, and residual stress magnitude of dissimilar weld joints (DWJs) between creep strength enhanced ferritic-martensitic (CSEF) P92 steel and austenitic stainless steel (ASS) 304L has been investigated. The Thermanit MTS 616 (P92 filler) filler metal was employed to prepare P92/304L SS DWJs. The groove geometry also plays a crucial role in DWJs, so the conventional V-groove and narrow shape groove geometry was adopted for P92/304L SS DWJs. The microstructure characterization was performed using optical microscope (OM), scanning electron microscope (SEM), and filed emission SEM (FESEM). The microstructural examination showed the formation of the δ-ferrite grains and unmixed zone (UZ) at the weld interface. The martensitic microstructure produced after welding is brittle due to quenched martensite and the dissolution of precipitates. Thus, the post-weld heat treatment (PWHT) known as tempering was carried out at 760 °C for the period of 2 h to get tempered martensitic microstructure. The ultimate tensile strength (UTS) of the as-weld (AW) and PWHT tensile specimen of the P92/304L SS DWJs was 660 MPa and 643 MPa, respectively for V-groove geometry specimens and 640 MPa and 609 MPa, respectively for narrow groove geometry specimens. The tensile fracture was experienced at 304L base metal, and the UTS value of DWJs was very close to the UTS of the 304L SS. The average microhardness value of the martensitic weld metal (352HV0.5) and coarse-grain heat-affected zone (CGHAZ, 366HV0.5), fine grain HAZ (FGHAZ, 320HV0.5) in the AW state was beyond the maximum permissible hardness value of 265HV0.5, as per the A335/A335M − 15a standard. The hardness value beyond 265HV0.5 indicates the undesirable brittle martensitic microstructure. After PWHT, the micro-hardness value of the CGHAZ (235HV0.5), FGHAZ (215HV0.5), and inter-critical HAZ (ICHAZ, 201HV0.5) was below the maximum allowable value of 265HV0.5 for P92 material because of the tempering of the quenched martensite. However, the Charpy test result concluded that the problem associated with the martensitic P92 filler is to obtain an acceptable value of the impact toughness of weld metal in AW state. The Charpy impact toughness of weld metal for P92/304L SS DWJs in AW condition was 10 J (V-groove geometry) and 37 J (narrow groove geometry), while for PWHT condition, it was 188 J (V-groove geometry) and 150 J (narrow groove geometry). The impact toughness of the P92 filler weld was below the minimum requirement of 47 J (EN ISO 3580:2017) in AW state. However, the impact toughness of the welds made by using P92 filler metal met the minimum requirement of 47 J (EN ISO 3580:2017) after PWHT due to the tempering of the martensite. The residual stress analysis using deep hole drilling (DHD) technique revealed the existence of the compressive residual stresses in the weld metal and P92 HAZ in as-weld and PWHT condition. The compressive stress was dominant because of the martensitic phase transformation.