Austenitic Stainless Steel Grade Research Articles

SEM with EDAX analysis on plasma arc welded butt joints of AISI 304 and AISI 316 steels

Abstract Austenitic stainless steels possessing excellent mechanical properties, Exceptional corrosion resistant, non-magnetic, non-hardenable by heat treatment, are very robust, and are easily formed and fabricated. The AISI 304 and AISI 316 grades are two of the most widely used austenitic stainless steel grades. This investigation was carried out to characterize the microstructures of the welded joints of plasma arc butt obtained on identical and dissimilar combinations of AISI 304 and AISI 316. The weldments were characterized by a combination of Image Analyzer and Scanning Electron Microscope (SEM) techniques. Finally Energy Dispersive X-Ray Analysis (EDAX) used to identify the elemental composition of materials after welding.

Solidification cracking sensibility of narrow gap laser welding on ITER-grade austenitic stainless steel

This study aimed to investigate the solidification cracking in narrow gap laser welding (NGLW) of ITER grade austenitic stainless steel 316LN. The results show that NGLW of ITER grade 316LN presents high solidification cracking sensitivity. The cracking always occurred in the centerline of build-up weld with a certain depth, not in root and cosmetic layers. The crack mostly propagates on the surface of the weld and it could be be healed by the following layer welding. The healing efficiency depends on the overlapping zone between the two layers. Other various laser welding processes such as autogenous laser welding (ALW), double-sided NGLW, and narrow gap pulsed laser welding (NGPLW) were studied. These welding processes present better cracking resistance than that of NGLW because of the stress distribution, microstructural characteristic and constraint condition of welded joints.

Closed-loop control of microstructure and mechanical properties in additive manufacturing by directed energy deposition

A closed-loop directed energy deposition (CDED) system is developed to control the microstructure and mechanical properties of laser additive manufactured material in real-time. An austenitic stainless-steel grade of S316-L, which avoids eutectoid phase transformation, is examined to evaluate this unique control technique's performance. A set of walls are constructed in an open-loop manner by the laser additive manufacturing process to study the thermal dynamics and microstructure variations of a multi-layer structure under fixed processing conditions. The microstructure and subsequent mechanical properties of different thicknesses are affected mainly by the cooling rate change, resulting in a graded microstructure profile and mechanical properties in the deposition cross-section. The CDED system is implemented to eliminate cooling rate variations and locally control the deposition cooling rate to the desired setpoint value in similar five-layer depositions. This control is achieved by adaptively adjusting the traveling speed in real-time rather than keeping it constant. The closed-loop control of the cooling rate results in a uniform microstructure and hardness throughout the deposition cross-section and different layers. Although improved uniformity is observed in closed-loop samples, some microstructural and hardness deviations are still present, caused by post-solidification heating cycles of subsequent layers.

An Eulerian thermomechanical elastic\u2013viscoplastic model with isotropic and directional hardening applied to computational welding mechanics

An Eulerian thermomechanical elastic–viscoplastic model with isotropic and directional hardening is used to analyse the residual mechanical state resulting from the arc welding of a multi-pass weld. Details of the weld test plate, weld filler material, and numerical implementation of the model are provided, including integration algorithms and consistent tangent modulus. For the computational welding mechanics analyses, the austenitic ASME stainless steel grade 316L was considered so that no phase transformations of solid states needed to be considered. The maximum residual stresses were found to be about 500–600 MPa, which is of the order of the yield stress of the base material. Variations in the heat input and the resulting weld cooling time had a significant influence both on the residual stress state and on the resulting geometry of the weld. The predicted stress levels were compared to the experimental results. Overall, the proposed Eulerian framework seems to be a promising tool for analysing melting/solidification processes and residual mechanical states.

Stress corrosion cracking failure of friction stir welded nuclear grade austenitic stainless steel

Stress Corrosion Cracking behavior of Austenitic Stainless Steels (SS) in a chloride environment has been investigated by several methods. In this investigation failure of emerging structural material for nuclear reactor (316LN grade austenitic stainless steel) and its Friction Stir Welded (FSW) joint due to stress corrosion cracking were analyzed in a chloride environment. FSW joint was fabricated between 316LN plates with optimized process parameters. Initially, hardness and tensile properties were analyzed across the weld zone to evaluate the mechanical properties of the welded joint. Microstructural characterization of base metal (BM) and weld zone were done by Optical Microscope (OM), and Scanning Electron Microscope (SEM). Grain boundary analysis was done by Transmission Electron Microscope (TEM). Microstructural evolution revealed that the FSW process is capable to refine and reduce grain size nearby 12 times that of the base metal by Continuous Dynamic Recrystallization mechanism (CDRX). Improved strength and hardness are also recorded at the weld zone compared to the base metal. Boiling 45 wt% MgCl2 solution at constant load condition as per ASTM standard G36 was used to assess SCC failure on base metal and FSW joint. Failure due to Chloride Stress Corrosion Cracking (CSCC) on weld samples were investigated and compared with its base metal samples at different tensile stress conditions (20%, 40%, 60%, 80%, 100% of base metal yield stress values). From the experimental result steady-state elongation rate (ISS), Transition time (tss) and time to failure (tf) were evaluated and generalized equations to predict time to failure of base metal and FSW weldment was generated. The impact of microstructural morphology on SCC failure of the FSW joint was investigated. The fracture location of the weld joint, nature of crack advancement of both base metal and FSW joint was analyzed by the SEM study. A study of fracture surface displayed brittle nature transgranular failure for base metal as well as FSW samples.

Evaluation of Microstructure and Impact Toughness of Shielded Metal Arc Dissimilar Weldments of High Strength Low Alloy Steel and Austenitic Stainless Steel

There is a growing interest for novel materials of dissimilar metals due to higher requirements needed for some critical engineering applications. In this research, different dissimilar weld joints of high strength low alloy (HSLA) and 316 austenitic stainless steel grades were successfully produced using shielded metal arc welding (SMAW) process with 316L-16 and E7018 electrodes. Five variations of welding currents were employed within the specified range of each electrode. Other welding parameters such as heat inputs, welding speeds, weld sizes, arc voltages and time of welding were also varied. Specimens for different weld joint samples were subjected to microstructural studies using optical and scanning electron microscopes. The impact toughness test was also conducted on the samples using Izod impact testing machine. The analysis of the weld microstructures indicated the presence of type A and AF solidification patterns of austenitic stainless steels. The results further showed that the weld joints consolidated with E7018 electrode presented comparatively superior impact energy to the weldments fabricated by 316L-16 electrode. The optimum impact energy of E7018-weld joints (51J) was attained at higher welding heat inputs while that of 316L-16-weld joints (35J) was achieved at lower welding heat inputs, which are necessary requirements for the two electrodes used in the experiment. Hence, the dissimilar weld joints investigated could meet requirement for engineering application in offshore and other critical environments.Keywords—Dissimilar metal weld, heat input, impact toughness, microstructures

Effect of Cryorolling–Annealing and Bake-Hardening on the Microstructure and Mechanical Properties of AISI 301LN Grade Austenitic Stainless Steel

Steel is a valuable material for automotive and structural applications. Due to global warming, vehicle manufacturers are trying to lower the weight of the automobiles without hampering the safety. Austenitic stainless steel has recently gained attention for its superior strength and ductility along with lower maintenance costs. AISI 301LN grade austenitic stainless steel produces a high percentage of strain-induced martensite on cold rolling than other grades of austenitic stainless steel, like AISI 304, AISI 316, and AISI 301, etc. After annealing at elevated temperatures, cold-rolled austenitic stainless steel produces ultra-fine grain structures (~ 0.2–0.5 µm) which improve the yield strength due to the Hall–Petch effect. In the present work, cold rolling was performed at liquid nitrogen (~ 196 °C) temperature, followed by annealing at 700 °C for 20 min ,and finally bake-hardened at 170 °C for 2 h, exhibiting nearly 1000 MPa yield strength, ~ 1200 MPa ultimate tensile strength, and ~ 26% ductility. These demonstrate better mechanical properties (~ 20% improvement in tensile strength) than previously obtained results. The micro-structures and texture of the newly developed advanced steel were examined by TEM, EBSD, and XRD characterization techniques.

Investigation of the Microstructure and Wear Properties of AISI 304 Steel Friction Weldments

            In this study, a rotary friction welding technique was used to join austenitic stainless-steel grade AISI 304.  The effect of different forging pressure (192.4, 240.5, 288.6 and 384.8 MPa) on wear resistance of AISI 304 were examined using a modified pin on disc tester. The microstructure of the AISI 304 was examined as well using an optical microscope. The wear resistance results of the welded specimens were reported better than as received. The variation of increasing wear loss was uniformly changed with sliding distance. Further, it was noted from the experiments that the wear rate increased with increasing forging pressure in which the minimum wear rate was 3 mm3 at 192.4 MPa while a maximum wear rate (25.823 mm3) occurs at a forging pressure of 384.8 MPa.  This is due to the microstructure changes which is decreasing grain size and formation of twin grains and also precipitating carbides.&nbsp

Optimization of TIG welding parameter in dissimilar joints of low nickel stainless steel AISI 205 and AISI 216

Abstract Low nickel 200 series grade austenitic stainless steels are popular due to their low price and the welding of these materials is of interest to engineers and fabricators. Therefore, the dissimilar joining of AISI 205 and AISI 216 stainless steels are examined in this paper. The study used a TIG welding process with an ER307 filler metal and stepped up welding speeds with varying mixtures of H2 in the argon shielding gas. The weldments on the weld bead (shape and size), solidification mode (predicted on WRC-1992) and the delta-ferrite content (compared between the predicted and calculated lath ferrite with vermicular ferrite) were examined. The microstructure (volume and formation of delta-ferrite in the austenite matrix), mechanical properties (hardness and tensile strength tests) and pitting corrosion resistance (pitting potential and pitted initial) are also studied. The results indicate that the welding speed can be stepped up from a minimum of 1 to a maximum of 3.5 mm/sec. This parameter affected to an increase weld bead size, delta-ferrite, hardness, tensile strength and pitting corrosion resistance of the weld metals. The role of H2 can help heat collection in the weld pool during welding allowing the welding speed to increase up to a maximum 5.2 mm/sec. This was achieved with a 6 vol.% of H2 in the argon shielding gas. These results can help increase productivity and thus be considered a successful outcome for this work.

Microstructure, mechanical properties and pitting corrosion of TIG weld joints alternative low-cost austenitic stainless steel grade 216

This present work aims to study 200 series austenitic stainless steel as a replacement for 300 series austenitic stainless steel. This is due to 200 series austenitic stainless steel being inexpensive and also due to its popularity in Southeast Asia. This study investigated the behavior and properties of the weld metal produced from 216 grade austenitic stainless steel. The microstructure, mechanical properties and pitting corrosion resistance that were produced by the tungsten inert gas welding process (TIG) with filler metal ER316 are studied in this paper. The variable parameters of the welding process were heat inputs at high (0.78 kJ/mm), medium (0.52 kJ/mm) and low (0.39 kJ/mm) ranges. It was found that the weld metal with a high heat input level increased the width of the face weld, root weld, PMZ and HAZ. However, the opposite result was achieved when the heat input was reduced. The microstructure of all the weld metals formed delta-ferrite content in the austenite matrix. This was shown to be greater in the weld metal with a low heat input, under the solidification mode FA. The results were shown to agree with the predictions outlined in the Schaeffler diagram. In addition, it was discovered that a high heat input level produced a more discontinuous form of delta-ferrite content than for the low heat input model. This corresponded to the dendrite length and inter-dendrite spacing in the weld zone. The hardness, ultimate strength and elongation tended to decrease when the heat input increased. The fractures for all the weld metals were found to occur in the location of the weld zone. The pitting corrosion resistance increased when the heat input was reduced, which related to the volume of delta-ferrite content in the weld metal zone. This corresponds to the pitting corrosion resistance in the weld metals being higher than for the base metal material. Furthermore, it was found that pitting occurred initially at the interface between the delta-ferrite and austenite phase and the corrosion then spread into the austenite phase.

A Descriptive Model on the Grain Size Dependence of Deformation and Martensitic Transformation in Austenitic Stainless Steel

A descriptive model is presented on the austenite grain size dependence of deformation and martensitic transformation upon tensile loading of a metastable 301L grade austenitic stainless steel. Cold rolling and subsequent short-duration annealing of the as-received coarse-grained material at 973 K to 1023 K (700 °C to 750 °C) resulted in a mixed microstructure consisting of fine and ultra-fine grains (UFG) that showed a more pronounced γ → e-martensite and γ → twin formation (precursors of α′-martensitic transformation) and finally more α′-martensite in the tensile-tested specimen. Whereas their coarse-grained (CG) counterpart facilitates only the former reaction, which eventually leads to less severe martensitic transformation in CG than that in UFG. The evolution of texture under tensile deformation is simulated using visco-plastic self-consistent (VPSC) model and compared with the experimental data obtained from interrupted tensile tests. Besides a thermodynamic approach, microstructural characterization using optical and electron microscopy (scanning and transmission), electron backscattered diffraction, nanoindentation, and transmission Kikuchi diffraction studies were realized to establish a mechanistic explanation on the grain size dependence of austenite stability against deformation-induced martensitic transformation.

Investigations on mechanical properties and microstructural examination of activated TIG-welded nuclear grade stainless steel

Nuclear grade austenitic stainless steel 321 contains titanium for severe corrosive conditions and is used for process equipment, aircraft exhaust manifolds and boiler shells. Taguchi-based grey relational analysis technique has been considered to optimize the input parameters for welding SS321 material using activated tungsten inert gas welding process. The optimized input parameters were identified from the multiple output responses, i.e. arc length of 3 mm, welding current of 220 Amps and welding speed of 120 mm/min (A1B3C1). The analysis of the variance table was performed to calculate the importance of the input parameters in the weldment quality. Also, the influence of the heat input on the depth of penetration and bead width at different arc lengths has been studied. The mechanical integrity is evaluated in terms of tensile strength for base metal (BM) (621 MPa) and weld metal (WM) (624 MPa) specimens by conducting the uniaxial tensile test. The 180° bend test with WM sample revealed the ductility level and was free from fissures and cracks. Charpy impact test results depicted the toughness values of BM (123.17 J) and WM (113.46 J) samples. Microstructural investigations at the SS321 WM highlighted the existence of columnar and equiaxed dendrites in the fusion zone. Moreover, the formation of titanium carbide reduces the chances of weld decay. Ferrite number measurement shows that the amount of delta ferrite is higher in WM (5.9) than in BM (1.2). The existence of dimples and voids in the fractographic analysis of the failed specimens (tensile and impact) confirms the ductile type of failure.

The effect of laser surface melting of stainless steel grade AISI 316L welded joint on its corrosion performance in molten Solar Salt

Whereas there are numerous studies dedicated to the corrosion performance of different grades of austenitic stainless steel (ASS) exposed to the conditions of thermal storage of solar energy, there is no data concerning the resistance of the welding joints, which are unavoidable when fabricating large structures. Because the microstructure of a weld bead can significantly differ from that of the base metal and the heat-affected zone (HAZ), increased susceptibility to localized corrosion can be expected. This work explores corrosion resistance of a welding joint of ASS grade 316 L when exposed to molten Solar Salt (60% NaNO3 – 40% KNO3) at 565 °C. Further, the application of laser surface melting (LSM) is proposed as a method to modify the microstructure of the weld bead and HAZ to enhance the corrosion resistance of the joint. Isothermal exposure to molten Solar Salt was implemented in static immersion, in the presence of atmospheric air, for the duration of up to 1008 h (6 weeks). The gravimetric analysis revealed a corrosion rate of 54 μm/y at the weld joint, which is at least twice as high as that expected for the same non-welded alloy in similar conditions. Although LSM reduces the rate of uniform corrosion in the first 2 weeks, there is no long term benefit in this regard. However, the onset of localized corrosion of the intergranular type is effectively prevented, presenting a potential approach for diminishing the risk of catastrophic failure of HAZ by fracture.

The Effect of Heat Treatment on Hardness for Various Submerged Arc Welded Parts

In industrial applications, the welding of different materials is widely used for taking advantage of the superior properties and reducing the overall costs. While a wide variety of welding methods are used in joining these different materials, the most widely used welding method in the automotive industry, especially in the use of thin sheet designs, is submerged welding. In this study, the application of submerged welding in joining different metals was discussed in detail. The advantages and limitations of the method compared to other welding methods used in joining different metals are given. Various welding procedures that may be an alternative to the method for joining different materials are also included. As an application, 304 grade austenitic stainless steel and St 37 sheet materials were welded under 3 different currents and 3 different designs by submerged welding, and their effects on the hardness values of the weldments were analyzed.

Microstructure and mechanical properties of the 316 stainless steel nuclear grade experimental component made by wire and arc additive manufacturing

An experimental component of nuclear grade austenitic stainless steel 316 (SS316) shielding plate was manufactured by wire and arc additive manufacturing (WAAM) method. Its microstructure, tensile properties at room and high temperatures, Vickers hardness, and impact properties were analyzed. The results show that the microstructure of WAAM SS316 product is mainly composed of austenite (γ) and delta-ferrite (δ) phases. The δ exhibits a fine vermicular morphology in the austenite matrix and is distributed at the boundaries of and inside the grains. The tensile properties of WAAM SS316 product are comparable to those of wrought SS316 and exceed the corresponding requirements of the nuclear industry. WAAM SS316 product has good uniform impact toughness in all directions, and the impact energy can fully meet the technical requirements of the nuclear industry with excellent performance. The results of nondestructive testing show that the quality of the WAAM SS316 shield plate product meets the evaluation requirements of the nuclear industry.

Spark plasma assisted diffusion bonding of titanium and stainless steel: Role of pulse current in diffusion kinetics and microstructural evolution

The work details the role of pulse current during the spark plasma assisted diffusion bonding of titanium (Ti) and austenitic stainless steel grade AISI 304L (SS 304L) at different temperatures (i.e. 550 °C, 650 °C and 750 °C) under 44 MPa pressure. The microstructural evolution and phase analyses of bonded Ti-SS 304L dissimilar alloys were studied using microscopy, X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) analyses. The alloy (Ti-SS 304L) bonded at 650 °C exhibits the superior bonding of 7 μm interface thickness and exhibits the superior shear strength (429 ± 18 MPa) and Vickers micro-hardness (290 ± 7 HV0.2). The Ti-SS 304L bonded at 550 °C show the voids at interface regions and whereas, at 750 °C exhibits the significant microstructure variation with Widmanstatten structure adjacent to the bonding track lowering the compressive strength to 392 ± 15 MPa.

Wear and corrosion behaviour of Ti-based coating on biomedical implants

ABSTRACT Biomedical implants are immensely manoeuvered devices that fix various deformities and injuries on medical grounds. With an emergent exploration in this field by researchers, countless combinations of materials have been discovered that perks global mankind. The ultimate goal of this experimentation is to appraise the characteristics of wear and corrosion resistance of Ti–Co–Cr-coated 316L grade austenitic stainless steel (SS) in contrast with TiN-coated and uncoated 316L SS. A micro-abrasion test was conducted on every single sample at 3N, 5N and 7N loads and were characterized in accordance with weight loss, coefficient of friction, surface roughness, Scanning Electron Microscope (SEM) analysis, X-ray Diffraction pattern (XRD), Energy Dispersive X-Ray Analysis (EDAX), Fourier-transform infrared spectroscopy (FTIR) and corrosion resistance. The findings showed that Ti–Co–Cr-coated substrate at 3N load have good mechanical tolerance and offers admirable performance. The corrosion resistance of the specimens divulges the biocompatibility of Ti–Co–Cr as being more distinct because of the existence of titanium metal.

Evaluation and characterisation of ASS316L at sub-zero temperature

ABSTRACT Austenitic Stainless-Steel grade 316L is one among the significant ASS grades which is most used in various industry sectors. It has excellent corrosion resistance in ordinary atmospheric and in more arduous environments such as saltwater. Whilst performing well when exposed to relatively high temperatures, this grade of ASS also maintains its strength and toughness at sub-zero temperatures, making this an excellent choice for various applications in industrial sectors such as Marine, general construction and water treatment. Therefore, present study focused on evaluating the mechanical properties, ultimate tensile strength (UTS), yield strength (YS) and strain hardening exponent (n) are evaluated based on the experimental data obtained from the uniaxial isothermal tensile tests performed at an interval of −25°C from 0°C to −50°C and at three orientations 0, 45, 90 degrees to the rolling direction and cross-head velocity 3, 5, 7 mm/min were chosen. Total of 27 experiments have been planned based on design-of-experiments. A mathematical model for the prediction of UTS, YS and n was developed using process parameters such as temperature, orientation and cross-head velocities. Results have shown that mechanical properties can be predicted with a reasonable accuracy within the range of process parameters considered in this study.

Correlation between Tensile Deformation Behavior and Microstructural Morphology of Nuclear Grade Austenitic Stainless Steel Weld Joints using Infrared Thermography Technique

Tensile deformation behavior of nuclear grade Austenitic Stainless Steel (SS) and its weld joints fabricated by Gas Tungsten Arc Welding (GTAW) and Activated flux Gas Tungsten Arc Welding (AGTAW) processes were studied and correlated with relevant microstructural morphologies using Infrared Thermography (IRT) technique. The microstructure of base metal showed a complete austenite phase. GTAW Fusion Zone (FZ) exhibited both primary ferrite and primary austenite mode of solidification. Meantime, AGTAW FZ exhibited only primary austenite mode of solidification A strain rate of 4.4x10-4 s-1 was used during the tensile test of the base metal and weld samples. The failure locations of the base metal, GTAW and AGTAW samples were noticed at the center of the gauge portion, the base metal side away from Fusion Line (FL) and Heat Affected Zone (HAZ) respectively. Temperature variations of the base metal and weld zones were recorded in the form of thermograms using the IR camera at the different stages of the tensile deformation. During deformation study, peak temperatures of 39.2 oC, 38.8 oC and 34 oC were observed at the base metal, GTAW and AGTAW samples respectively. The lesser peak temperature of the AGTAW sample compared to the base metal and GTAW samples indicated that the AGTAW sample undergone lesser deformation. Moreover, tensile deformation behaviors of the base metal and weld samples were correlated with their microstructural morphologies using corresponding temperature curves.

The effect of sensitization treatment on chloride induced stress corrosion cracking of 304L stainless steel using U-bend test

Chloride induced stress corrosion cracking (CI-SCC) commonly occurs for 300 series of austenitic stainless steels that are widely used in the petrochemical industry. The occurrence of CI-SCC requires certain circumstances such as corrosive environment, tensile stress, and susceptible material. Heat treatment temperature between 550 °C–650 °C followed by cooling process causes the sensitization of austenitic type stainless steel in which a chromium-depleted band is formed adjacent to the grain boundary. In this study, the impact of sensitization on CI-SCC was examined using austenitic stainless steel grade 304L (SS 304L). The specimens were shaped into U-bend as per ASTM G30 and exposed for long-term immersion test. U-bend samples were heat sensitized at 600 °C for 2 h followed by air cooling. Samples were immersed in 0.1 wt%, 1.0 wt% and 3.5 wt% NaCl into the water bath at temperature of ambient (baseline), 70 °C and 90 °C for 42 days. They were monitored weekly for visual examined for crack. Stereo and optical microscopy were used to identify the CI-SCC and morphology of U-bend specimens. In the beginning, pit corrosion was observed and followed by cracks growth initiated from the localized pit. The results indicated that Cl-SCC was observed for all sensitized SS 304L specimens at elevated temperature conditions which was more susceptible than the as-received type specimens. The trend indicated that the higher the temperature or chloride concentration, the shorter the time for crack initiation. There was no CI-SCC for both types of specimens at ambient condition. Two CI-SCC likelihood graphs with respect to chloride concentration versus temperature are plotted based on the test data.