Properties Of 316L Stainless Steel Research Articles

Effect of Processing Atmosphere and Secondary Operations on the Mechanical Properties of Additive Manufactured AISI 316L Stainless Steel by Plasma Metal Deposition

Plasma metal deposition (PMD) is an interesting additive technique whereby diverse materials can be employed to produce end parts with complex geometries. This study investigates not only the effects of the manufacturing conditions on the final properties of 316L stainless steel specimens by PMD, but it also affords an opportunity to study how secondary treatments could modify these properties. The tested processing condition was the atmosphere, either air or argon, with the other parameters having previously been optimized. Furthermore, two standard thermal treatments were conducted with the intention of broadening knowledge regarding how these secondary operations could cause changes in the microstructure and properties of 316L parts. To better appreciate and understand the variation of conditions affecting the behavior properties, a thorough characterization of the specimens was carried out. The results indicate that the presence of vermicular ferrite (δ) varied slightly as a consequence of the processing conditions, since it was less prone to appear in specimens manufactured in argon than in air. In this respect, their mechanical properties suffered variations; the higher the ferrite (δ) content, the higher the mechanical properties measured. The degree of influence of the thermal treatment was similar regardless of the processing conditions, which affected the properties based on the heating temperature.

Deformation mechanisms and enhanced mechanical properties of 304L stainless steel at liquid nitrogen temperature

The deformation mechanisms and enhanced mechanical properties of a fine-grained 304 L stainless steel were revealed at liquid nitrogen temperature. A remarkable Lüders-type deformation and subsequent dislocation slipping/accumulation deformation synergistically contribute to its good ductility. The enhanced strength was resulted from low-temperature strengthening and high density of dislocation storage hardening.

Effects of build direction on tensile and creep properties of 316L stainless steel produced by selective laser melting

AbstractThe influence of build direction on the mechanical properties of SS316L produced by selective laser melting was investigated. The tensile tests were performed at room temperature for vertical and horizontal specimens. Large crater‐like voids were found, which are believed to be responsible for the reduced strength and premature failure of the vertical specimens, whereas the nano‐sized dimples were detected on the fracture surface of the horizontal specimens. Creep tests were also conducted at 650°C in the applied stress range of 149 to 226 MPa in vertical and horizontal directions. The vertical direction specimen showed better creep resistance. The micro‐cracks were delayed compared with the horizontal case. Optical micrographs of the tip of the creep rupture specimens along the cross‐sectional area were observed. The micro‐cracks located at grain boundaries. The grain shapes orientated in the applied stress direction for the vertical specimens, and perpendicular to the applied stress direction for the horizontal specimens.

Study on microstructure and tensile properties of 316L stainless steel fabricated by CMT wire and arc additive manufacturing

An austenitic stainless steel 316L part was fabricated by cold metal transfer wire and arc additive manufacturing (CMT-WAAM), and its microstructure, microhardness and tensile properties were investigated. Results showed that the as-built 316L part exhibited a multilayered structure along the building direction. In the transverse direction (perpendicular to scanning direction) of each layer, there was also a multilayered structure of alternating overlapping zone (OA) and re-melting zone (RA). Compared with the OA, the RA had higher ferrite content, smaller austenite dendrite size, more dispersed orientation and lower residual stress. The overall multilayered structure and the intra-layer non-equilibrium microstructure exhibit a great influence on the mechanical properties of as-built 316L part. Along the building and transverse direction, the microhardness distribution in the OA was uniform, while the RA showed a trend of lower hardness in the middle and higher hardness on both sides of the RA layer. The effect of multilayered structure on tensile properties was stronger in the transverse direction than that in the building direction. The deformation feature was obviously inconsistent between the OA and RA. Local necking and fracture always occurred in the OA. Microvoids trended to initiate at silicate impurity particles, grow into large cracks, and finally lead to material failure during tension.

Effect of scanning strategies on the microstructure and mechanical behavior of 316L stainless steel fabricated by selective laser melting

Five scanning strategies were applied for relating the microstructural and crystallographic morphology to the mechanical properties of 316L stainless steel fabricated by selective laser melting (SLM). The results indicate that scanning strategies have a significant effect on the microstructure, grain growth, grain size and therefore mechanical properties of SLM-built 316L stainless steel. Applying the scanning strategy with the rotation angle between successive layers breaks the columnar growth of grains and fine equiaxial grains are formed, leading to an improvement of tensile strength and good ductility of SLM-built samples. Moreover, the microhardness is improved by applying the scanning strategy with a rectangular pattern. This work demonstrates the scanning strategy during SLM process acts as an essential factor affecting energy input, and therefore tailors the meso-/micro-scale structure and mechanical behavior of metals.

Impact of industrially applied surface finishing processes on tribocorrosion performance of 316L stainless steel

This investigation addresses the effect provided by industrial surface finishes on the tribocorrosion properties of 316L stainless steel exposed to NaCl solution. Three distinct surface treatments were evaluated: passivation (SSO), electropolishing-passivation (SSEP) and micro-undulation (SSM mechano-chemical + electropolishing + passivation). For the tribocorrosion tests, a potentiostatic approach was considered in order to highlight the alloy behavior under two opposite situations, where repassivation of the surface would be thermodynamically possible or not (anodic or cathodic polarization, respectively). The outcomes demonstrated that the surface treatments were either harmful (SSEP) or beneficial (SSM) in terms of resulting tribocorrosion resistance. The specific topography of the micro-undulated sample decreased the real contact area and improved the surface lubrication in aqueous medium. SSEP presented the highest chemical wear and several factors seemed to have contributed for it, including the chemical, mechanical and structural properties of the passive film. Regardless the surface treatment, the tribocorrosion response was modified by the applied potential and more severe damage was determined under anodic polarization. At this potential, calculations of the total surface degradation suggested that volume loss was mainly dominated by chemical wear.

Electroplating titanium film on 316L stainless steel in LiCl–KCl–Tix+ (2 < x<3) molten salts

To improve the anti-corrosion properties of 316L stainless steel, titanium (Ti) metal films were electroplated on it using LiCl–KCl molten salts as the electrolyte, and low-valence Tix+ (2 < x<3) as the solute. The solute was produced by the reaction of Ti4+ and Ti0 via mixing K2TiF6, and Ti metal (sponge Ti) in the melts. Anti-corrosion test has shown significant enhancement in the stability of the Ti-coated 316L due to the presence of Ti film. However, the anti-corrosion properties did not enhance with an increase in the thickness of the Ti layers owing to a possible defect in the thicker Ti layers.

Experimental characterization and micromechanical-statistical modeling of 316L stainless steel processed by selective laser melting

Additive manufacturing (AM) is regarded as one of the breakthrough innovations since the 19th century, whose impact on the manufacturing world is recognized as the same with the impact of airplane on the transportation industry [1]. Selective laser melting (SLM), one of the most popular AM techniques for processing metallic materials, has demonstrated its great potentials in medical, aerospace and automotive applications. The SLM technique itself is a complex metallurgical process, involving multi-physics phenomenon in laser scanning, powder melting and bonding procedure. Such a process may introduce a variety of defects and flaws such as pores and cracks, significantly reducing the mechanical performance of the final products. In this paper, we present experimental studies and micromechanical modeling to investigate the effects of the internal pores on the mechanical properties of 316L stainless steel (SS316L) processed by the SLM technique. Specifically, the internal pore characteristics such as size, morphology, spatial distribution and porosity (defined as the total volume of the pores divided by the total volume of the material) of the SLM processed SS316L is experimentally characterized and correlated with the mechanical properties. More importantly, a micromechanical model taking into account the statistical pore characteristics from the XCT analysis is developed to predict the elastic properties of the SS316L product. The numerical prediction results show good agreement with two analytical models and the experimental characterization of the mechanical properties. The present study provides future designers a methodology in predicting the mechanical properties using the XCT analysis results, which is a promising possibility of saving the expensive cost on destructive testing.

Microstructural evolution and mechanical properties of 316L stainless steel using multiaxial forging

ABSTRACT In order to investigate the effect of multi-axial forging on microstructural evolution and mechanical properties, warm multi-axial forging (MAF) on stainless steel 316L is performed. MAF 316L stainless steel exhibits higher specific strength that is used in a wide number of applications such as in body implants. In the present study, stainless steel 316L was warm multi-axially forged at 600ºC for cumulative strains of 1.4, 2.8 and 4.2 and studied their microstructural evolution and mechanical properties. Microstructural evolution was seen using light optical microscopy and observed continuous reduction in grain size with pass. The average grain size of the material is reduced from 37 µm to 8 µm after nine pass. The hardness of the material increased due to combination of strain hardening and Hall-Petch strengthening. Fracture type is clearly visible with the help of SEM. The size of the dimples is continuously reducing with increasing pass, and peaks and valleys are formed due to the introduction of some brittleness in the material.

Effect of Build Direction on Fatigue Performance of L-PBF 316L Stainless Steel

The microstructure and fatigue and tensile properties of 316L stainless steel fabricated via laser powder bed fusion (L-PBF) were investigated. Two 316L stainless steel specimens with different loading directions which are either perpendicular to or parallel to building direction were prepared by L-PBF process. The results of X-ray diffraction tomography showed that there was no significant difference in morphology and size/distribution of the defects in the HB and VB samples. Since long axis of columnar grains is generally parallel to the build direction, the fatigue crack encounters more grain boundaries in VB samples under cyclic loading, which led to enhanced fatigue resistance of VB samples compared with HB sample. In contrast to HB sample, the VB sample has a higher fatigue strength due to a higher resistance to localized plastic deformation under cyclic loading. The differences in fatigue properties of L-PBF 316L SS with different build directions were predominantly controlled by solidification microstructures.

Effects of inter layer time and build height on resulting properties of 316L stainless steel processed by laser powder bed fusion

Laser powder bed fusion (L-PBF) is the most prominent additive manufacturing (AM) technology for metal part production. Among the high number of factors influencing part quality and mechanical properties, the inter layer time (ILT) between iterative melting of volume elements in subsequent layers is almost completely unappreciated in the relevant literature on L-PBF. This study investigates the effect of ILT with respect to build height and under distinct levels of volumetric energy density (VED) using the example of 316L stainless steel. In-situ thermography is used to gather information on cooling conditions during the process, which is followed by an extensive metallographic analysis. Significant effects of ILT and build height on heat accumulation, sub-grain sizes, melt pool geometries and hardness are presented. Furthermore, the rise of defect densities can be attributed to a mutual interplay of build height and ILT. Hence, ILT has been identified as a crucial factor for L-PBF of real part components especially for those with small cross sections.

选区激光熔化中316L不锈钢的组织与力学性能

选区激光熔化中316L不锈钢的组织与力学性能

选区激光熔化成型316L不锈钢多孔结构的力学性能

选区激光熔化成型316L不锈钢多孔结构的力学性能

Optimization of tensile properties of 316L stainless steel and Monel 400 weld joints using genetic algorithm

Main aim of this paper is to carry out an analysis of dissimilar weld joints of Monel 400 to stainless steel 316L by GTAW process. Welding was carried out using different process parameters such as filler wire, welding current, gas flow rate and welding speed. The welded specimens were examined using X ray radiography before specimen preparation for tensile testing. Tensile tests were conducted to study the effect of process parameters on Ultimate tensile strength (UTS) and %Elongation. The results were used in regression analysis for development of mathematical models for the process characteristics. Non-dominated Sorting Genetic Algorithm (NSGA II) has been used for parameter optimization for different filler wires.

Build Orientation Effects on Mechanical Properties of 316SS Components Produced by Directed Energy Deposition

Laser Directed Energy Deposition (DED) is an additive manufacturing process whereby a laser fuses metal feed stock to the surface of a part. The process can be complete once to form a cladded layer or can be carried out numerous times to build complex three-dimensional structures. One major obstacle to the widescale acceptance of DED technology is the tightly coupled relationship between mechanical performance and process parameters.This study investigated the effects of layer orientation on the mechanical properties of 316L stainless steel (SS) parts fabricated via DED process. Quasi-static tensile tests were conducted on DED 316L SS specimens fabricated in orientation increments of 15 degrees with respect to the loading direction. Specimens were tested in their as-built condition without post process heat treatments. Yield, ultimate tensile strength (UTS), and maximum elongation measurement were taken, contributing to the ultimate finding that: Young’s Modulus is largely unaffected, yield stress may vary by 73 MPa corresponding to a 30 degree change in layer orientation, ultimate tensile strength does not show a strong statistical outcome based on layer orientation, and ductility shows a strong positive correlation to increases in layer angle with respect to axis of tensile stress.

Comparison of Linear and Nonlinear Ultrasonic Parameters in Characterizing Grain Size and Mechanical Properties of 304L Stainless Steel

Ultrasonic nondestructive techniques can be used to characterize grain size and to evaluate mechanical properties of metals more practically than conventional destructive optical metallography and tensile tests. Typical ultrasonic parameters that can be correlated with material properties include ultrasonic velocity, ultrasonic attenuation coefficient, and nonlinear ultrasonic parameters. In this work, the abilities of these ultrasonic parameters to characterize the grain size and the mechanical properties of 304L stainless steel were evaluated and compared. Heat-treated specimens with different grain sizes were prepared and tested, where grain size ranged from approximately 40 to 300 μm. The measurements of ultrasonic velocity and ultrasonic attenuation coefficient were based on a pulse-echo mode, and the nonlinear ultrasonic parameter was measured based on a through-transmission mode. Grain size, elastic modulus, yield strength, and hardness were measured using conventional destructive methods, and their results were correlated with the results of ultrasonic measurements. The experimental results showed that all the measured ultrasonic parameters correlated well with the average grain size and the mechanical properties of the specimens. The nonlinear ultrasonic parameter provided better sensitivity than the ultrasonic velocity and the ultrasonic attenuation coefficient, which suggests that the nonlinear ultrasonic measurement would be more effective in characterizing grain size and mechanical properties than linear ultrasonic measurements.

Effect of energy density and scanning strategy on densification, microstructure and mechanical properties of 316L stainless steel processed via selective laser melting

Laser-based additive manufacturing opens up a new horizon in terms of processing novel alloys that are difficult to process using conventional techniques. Selective laser melting (SLM) is a powder bed fusion type additive manufacturing (AM) process, for fabricating metallic parts where powder particles are fused using a high energy laser beam as a thermal source. Although SLM is widely used for manufacturing end-use metal tools and components, it requires careful tailoring of a range of parameters (e.g. layer thickness, laser spot size, laser power, hatch spacing, scanning strategy, etc.) to achieve the required densification, microstructures, and mechanical properties. Therefore, there is a critical need to systematically investigate the effect of these processing parameters on densification, microstructures and mechanical properties of materials. In this research work, 16 samples fabricated by SLM process with varying processing parameters have been investigated. We have studied the effect of scanning speed, scanning strategy, and energy density on microstructure and mechanical properties of these samples by performing microhardness tests, tensile tests, and a scanning electron microscopy (SEM) analysis. We have concluded that samples fabricated with alternate hatches and single pass of a laser beam exhibited highest densification and most refined microstructure. Furthermore, samples processed at higher scanning speeds had better densification, as well as excellent mechanical properties. We have also observed an increase in the width of dendrites as a result of decreasing the scanning speed primarily due to decrease in cooling rate.

Microstructure and Mechanical Properties of 316L Stainless Steel Fabricated Using Selective Laser Melting

ABSTRACTThe microstructure homogeneity and variability in mechanical properties of 316L stainless steel components fabricated using selective laser melting (SLM) have been investigated. The crack free, 99.9% dense samples were made starting from SS316L alloy powder, and the melt pool morphology was analysed using optical and scanning electron microscopy. Extremely fast cooling rates after laser melting/solidification process, accompanied by slow diffusion of alloying elements, produced characteristic microstructures with colonies of cellular substructure inside grains, grown along the direction of the principal thermal gradient during laser scanning. In some areas of the microstructure, a significant number of precipitates were observed inside grains and at grain boundaries. Micro hardness measurements along the build direction revealed slight but gradual increase in hardness along the sample height. Uniaxial tensile tests of as manufactured samples showed the effect of un-melted areas causing scatter in room-temperature mechanical properties of samples extracted from the same SLM build. The ultimate tensile strength (UTS) varied from 458MPa to 509MPa along with a variation in uniform elongation from 3.3% to 14.4%. The UTS of a sample exposed to the Cl- rich corrosion environment at 46oC temperature revealed a similar strength as of the original sample, indicating good corrosion resistance of SLM samples under those corrosion conditions.

Tribological Property of Selective Laser Melting–Processed 316L Stainless Steel against Filled PEEK under Water Lubrication

As a 3D printing technology, selective laser melting has remarkable advantages such as high processing flexibility, high material utilization, and short production cycle. The applications of selective laser melting technology in industry have become quite extensive. There are many tribological studies on selective laser melting materials, but few based on water lubrication (Zhu, et al., Journal of Zhejiang University-Science A, 19(2), pp 95–110). In this article, the tribological properties of 316L stainless steel processed by selective laser melting and traditional methods have been studied under water lubrication. Polyether ether ketone (PEEK) filled with carbon fiber (CF)/polytetrafluoroethylene (PTFE)/graphite was selected as the counterpart. 316L stainless steel and PEEK are a tribopair commonly used in water hydraulics. This study is of great significance to the application of selective laser melting material of tribopairs in water hydraulics. Friction and wear tests were carried out on a pin-on-disc contact test apparatus under different operating conditions. The friction coefficient, specific wear coefficient, scanning electron microscopy (SEM) of the worn surface, and energy-dispersive spectroscopy (EDS) of the surface adhesions of the three tribopairs were measured and compared. The results revealed that the friction coefficient of the selective laser melting (SLM) 316L stainless steel was significantly higher than that of traditionally processed (TP) 316L stainless steel, which might be caused by the pores on the surface of SLM 316L stainless steel. Adhesion and cutting on the surface of SLM 316L stainless steel were also more serious, resulting in a higher specific wear coefficient of its counterpart PEEK composite compared to PEEK composite against TP 316L stainless steel.

Investigation of Micro-Hardness, Wear Resistance, and Defects of 316L Stainless Steel and TiC Composite Coating Fabricated by Laser Engineered Net Shaping

The influence of processing parameters in laser engineered net shaping (LENS) on the properties of 316L stainless steel and titanium carbide (TiC) composite coating was studied. The key processing parameters were laser power, scanning speed, TiC powder ratio, and powder feed rate. Mathematical models were developed to investigate the micro-hardness, wear volume, and defect area of the coating. The accuracy of the models was examined by analysis of variance and experimental validation. Results showed that micro-hardness was positively correlated with TiC powder ratio. Increasing TiC powder ratio could reduce the wear volume. In addition, the wear volume displayed an increase then decrease with increasing laser power and decreasing scanning speed. Both scanning speed and TiC powder ratio showed a recognizable impact on the defect area. Reducing the scanning speed and TiC powder ratio can effectively reduce the defect area. The targets for the processing parameters optimization were set to maximize micro-hardness, minimize wear volume, and defect area. The difference between the model prediction value and experimental validation result for micro-hardness, wear volume, and defect area were 0.46%, 4.54%, and 8.82%, respectively. These results provide guidance for the LENS processing parameters optimization in controlling and predicting of 316L/TiC composite coating properties.