Additive Manufactured Stainless Steel Research Articles

Irradiation-Induced Microstrain and Dislocation Density in Additively Manufactured 316H Stainless Steel

This study investigated the response of additively manufactured (AM) 316H stainless steel (SS) compared to its conventionally manufactured counterpart under simulated irradiation conditions. We irradiated both types of steels with 0.5 MeV H+ ions at room temperature and analyzed their microstructural and mechanical properties. X-ray diffraction revealed higher initial dislocation densities in AM SS due to its fabrication process. Interestingly, at lower irradiation doses (0.6 dpa), the AM SS showed a decrease in microstrain, while the conventional SS showed an increase. This suggests differing defect annihilation mechanisms. At 6.0 dpa, AM SS exhibited a rise in mi- crostrain and dislocation density, potentially due to saturation effects. Conversely, conventional SS showed a decrease, possibly indicating disordering from the irradiation. Microhardness measure- ments supported these findings, with AM SS displaying a more gradual response compared to the pronounced hardening and softening observed in conventional SS. Tensile testing revealed lower hardening and strength in irradiated AM SS compared to its pristine state. Scanning electron mi- croscopy showed contrasting fracture behavior between the two steel types, with AM SS exhibiting less embrittlement despite its higher initial hardness. Overall, AM SS demonstrated superior mi- crohardness and microstructural integrity after irradiation, suggesting its potential for applications in harsh irradiated environments.

Comparative study on hydrogen embrittlement resistance in additive manufactured and forged austenitic stainless steel

In this work, the hydrogen embrittlement resistance of additively manufactured (AM) and conventionally manufactured (CM) Cr21Ni6Mn9N (21−6−9) stainless steels were comparatively investigated. The mechanical properties and microstructure evolution of both AM and CM conditions were studied using slow strain rate tensile tests and microanalytical techniques such as scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and electron channeling contrast imaging (ECCI). The results indicated that compared to the CM condition, the AM stainless steel demonstrated enhanced resistance to hydrogen embrittlement, coupled with a reduction in plasticity loss. The primary factor contributing to this resistance was identified as an increased occurrence of deformation twinning in both steels after hydrogen charging. The superior resistance observed in the AM stainless steel was attributed to the occurrence of higher-density deformation twinning and microbands.

Effect of Layer Addition on Residual Stresses of Wire Arc Additive Manufactured Stainless Steel Specimens

Abstract Residual stresses have been characterized in four Wire Arc Additive Manufacturing specimens with neutron diffraction technique. First, two methods are investigated for obtaining the reference diffracted angle θ0 that is required for the computation of microstrains and, thus, the stresses; θ0 was obtained with two approaches. The first one required a strain-free specimen in order to get directly the reference diffracted angles θ0 in the three principal directions. The second one is based on the plane stress assumption to get θ0 indirectly by imposing that the normal stress was equal to zero. Both methods led to similar residual stress profiles for the one-layer specimen which validated this approach for all specimens without a strain-free specimen available. The second part of this work focused on the modification of the residual stresses in the specimen following the addition of a new deposit. The neutron diffraction measurements showed that the longitudinal stress was tensile in the heat-affected and fusion zones with a maximum value located at the parent material–layers interface where the thermal loadings were applied. A decrease of this maximum value from 257 MPa to 199 MPa appeared after deposition of a new layer which is due to some stress relaxation effect. Inside the parent material, a large zone presents compressive longitudinal stress up to −170 MPa. The bottom part of the parent material is under tensile stress likely due to its upward bending following the thermal contraction of the deposited layers during cooling to ambient temperature.

Achieving impressive strength and mitigated anisotropy in high-power laser-arc hybrid additive manufacturing of stainless steel through tailored microstructures composition

High-power laser-arc hybrid additive manufacturing (HP-LHAM) is beneficial to improving tensile properties and reducing anisotropy, but the mechanisms remain unclear. This work focused on the effects of parameters on microstructures, tensile properties, and anisotropy in HP-LHAM of stainless steel quantitatively. The HP-LHAMed sample exhibited a heterogeneous microstructure featuring fine grains in remelting zone (FGRZ) and coarse grains in melting zone (CGMZ). By observing the microstructure characteristic, it was determined that the δ-ferrite shape in CGMZ can be transformed under the impact of large pulsed current triggered solution heat treatment effect or high-frequency laser beam oscillation, while kept as strip shape in FGRZ. Furthermore, investigations demonstrated that the utilization of a high-power laser with beam oscillation not only led to a synchronous increase in strength and elongation, but also brought about a pronounced reduction in anisotropy. This results in an optimized horizontal yield strength (YS) of 363 MPa, which was superior to that of the as-deposited sample without laser beam (∼318 MPa). The corresponding YS anisotropy had decreased from 7.5% to below 2.0%. YS modeling analysis proved that the improved properties were primarily ascribable to fine-grain strengthening rather than solution or precipitation strengthening, because their contributions for the YS improvement were 166.6, 27.7, and 3.3 MPa, respectively. While for the anisotropy of tensile properties, the value of Taylor factor and range of FGRZ were the main factors, and the influence of the latter was more remarkable than the former. Two methods for improving tensile properties and reducing anisotropy were then proposed accordingly. These new findings will deepen the understanding and expand the application of HP-LHAM process in the preparation of large size components.

Deep Learning-Based Automatic Defect Detection of Additive Manufactured Stainless Steel

Accumulating interest from academia and industry, the part of quality assurance in metal additive manufacturing (AM) is achieving incremental recognition owing to its distinct advantages over conventional manufacturing methods. In this paper, we introduced a convolutional neural network, YOLOv8 approach toward robust metallographic image quality inspection. Metallographic images accommodate key information relating to metal properties, such as structural strength, ductility, toughness, and defects, which are employed to select suitable materials for multiple engineering execution. Therefore, by comprehending the microstructures, one can understand insights into the behavior of a metal component and make predictive assessments of failure under specific conditions. Deep learning-based image segmentation is a robust technique for the detection of microstructural defects like cracks, inclusion, and gas porosity. Therefore, we improvise the YOLOv8 with dilated convolution mechanisms to acquire automatic micro-structure defect characterization. More specifically, for the first time, the YOLOv8 algorithm was proposed in the metallography dataset from additive manufacturing of steels (Metal DAM) to identify defects like cracks and porosity as a novel approach. A total of 414 images from ArcelorMittal engineers were used as an open-access database. The experimental results demonstrated that the YOLOv8 model successfully detected and identified cracks and porosity in the metal AM dataset, achieving an improved defect detection accuracy of up to 96% within just 0.5 h compared to previous automatic defect recognition processes.

Control of texture and microstructure in additive manufacturing of stainless steel 316 L

This investigation deals with exploring the effect of rotation scan strategy on microstructural evolution and hence mechanical behaviour of 316 L stainless steel prepared by additive manufacturing using selective laser melting technique. Higher anisotropy has been observed for samples where no hatch rotation was employed compared to the samples where a hatch rotation was involved during printing. The morphology of grains gets perturbed for samples prepared by hatch rotation 60˚ and hatch rot 74˚ when compared to the samples prepared using no hatch rotation or a hatch rotation of 90˚. The crystallographic texture component of the sample consists of a combination of < 100 > and < 110 > orientation (// building direction) except for the hatch rot 60˚ sample where the texture comprises of only < 110 > . It has been noticed that texture control is possible through giving a rotation such as 60˚ or 90˚. The samples prepared without any hatch rotation exhibited higher strain hardening due to combined action of slip and twin activity when compared to hatch rot 60˚ sample where < 110 > texture reduces the deformation mechanism to slip only. This study paves a new pathway to control the mechanical properties by tuning the appropriate texture along the BD.

Correction to: Post-processing of Wire Arc Additive Manufactured Stainless Steel 308L to Enhance Compression and Corrosion Behavior using Laser Shock Peening Process

Correction to: Post-processing of Wire Arc Additive Manufactured Stainless Steel 308L to Enhance Compression and Corrosion Behavior using Laser Shock Peening Process

Post-processing of Wire Arc Additive Manufactured Stainless Steel 308L to Enhance Compression and Corrosion Behavior using Laser Shock Peening Process

Post-processing of Wire Arc Additive Manufactured Stainless Steel 308L to Enhance Compression and Corrosion Behavior using Laser Shock Peening Process

An inferential analysis of stainless steel in additive manufacturing using bibliometric indicators

In this work, we analyse previous research in the subject, spanning an extensive range of publications, to give an exhaustive bibliometric analysis of the literature concerned with the influence of stainless steel on additive manufacturing (AM). A bibliometric study hasn't been done by many academics, despite the fact that AM is one of the most significant industrial revolutions. Through the investigation of the metadata of all publications included in the bibliographical database Web of Science, this article seeks to examine the scientific output on AM of stainless steel based on 376 publications from 2010 to 2023. This study's five-stage process, which includes research study design, data collection, data analysis, data visualization, and data inference, identifies the most relevant sources, authors, and nations active and influential via the use of bibliometric indicators. To highlight research streams, co-citation of authors and co-occurrence analysis on all keywords were carried out. The associated rising research areas were discovered by keyword analysis. Using VOSviewer software, bibliographic data was graphically analysed. According to this analysis, the journals “International Journal of Advanced Manufacturing Technology“, “Additive Manufacturing”, “Materials“, “Materials Science and Engineering A-Structural Materials Properties”, “Rapid Prototyping Journal,“ and “Materials & Design” are the most effective and significant in AM of stainless-steel research. Also, linear regression analysis was used to estimate the number of publications in the upcoming years. The findings and recommendations of this study may be used as forecasts for future research in the field of AM in stainless steel.

Weldability of Additive Manufactured Stainless Steel in Resistance Spot Welding

The manufacture of complicated automobile components that are joined by resistance spot welding requires considerable cost and time. The use of additive manufacturing technology to manufacture automobile components helps reduce the overall time consumption and yields high accuracy. In this study, the weldability of conventional (C) 316L stainless steel and additive manufactured (AM) 316L stainless steel was evaluated and analyzed. After deriving the lobe diagram for both the materials, the monitoring data, nugget diameter, tensile shear strength, and hardness were analyzed. The findings of the study have opened up a massive potential for use in resistance spot welding technology for additive manufactured materials’ industries in the forthcoming years. When AM 316L stainless steel was welded in the constant current control mode, a nugget diameter of up to 4.7 mm, which is below the international standard, could be secured. Through the constant power control mode, however, the nugget diameter could be improved to a sufficient level of 5.8 mm.

Intergranular Corrosion of Feedstock Modified—Additively Manufactured Stainless Steel After Sensitization

Laser powder bed fusion (LPBF), a metal additive manufacturing technique, was conducted on feedstock-modified 316L stainless steel (316L) powder produced by ball-milling of commercial 316L and 1 wt% additive (cerium oxide—CeO2, lanthanum (III) nitrate hexahydrate—La(NO3)3·6H2O, and chromium nitride—CrN). The feedstock-modified LPBF-316L specimens were sensitized at 675°C for 24 h, and the influence of additives on intergranular corrosion (IGC) was investigated following ASTM G108-94 and A262-14 standards. The LPBF-316L with La(NO3)3·6H2O showed higher IGC resistance. The microstructure of the LPBF specimen was investigated and correlated to understand the improved IGC resistance of LPBF-316L with La(NO3)3·6H2O additive.

3D thermal simulation of powder bed fusion additive manufacturing of stainless steel

3D thermal simulation of powder bed fusion additive manufacturing of stainless steel

Correlation between Cellular Structure Morphology and Anisotropic Yield in Additively Manufactured Stainless Steel 316L

Additively manufactured austenitic stainless steel 316L is composed of a cellular structure, which has a directionality, and is observed with a different morphology depending on the observation direction. The cellular structure morphology that appears with a high probability in grains with a specific grain orientation is determined. Taylor factor, which is calculated by considering grain orientation, is related to cellular structure morphology due to the directional cellular structure in additively manufactured austenitic stainless steel 316L. The Taylor factor affects the mechanical properties. The yield strength of additively manufactured SUS316L can be explained by the correlation between cellular structure morphology, grain orientation, and Taylor factor.

Corrosion Performance of Wire Arc Additive Manufacturing of Stainless Steel: A Brief Critical Assessment.

To enhance the products fabricated from wire arc additive manufacturing (WAAM) processes, it is very important to implement a critical assessment of the corrosion performance of additively manufactured stainless steel (SS) for the application of additive manufacturing parts widely used in industries. The common defects in metal additive manufacturing, which include porosity, poor surface finish, oxidation, environmental factor, residual stress, and microstructural defects, are known to significantly influence the corrosion behavior of WAAM-processed SS components prepared to be used under different corrosive and marine environments. This article reviews the recently published works on WAAM-processed SS and provides a critical overview method to improve the corrosion performance of SS components built with the WAAM processes. It also documents some significant factors that determine the corrosion resistance of WAAM-processed SS and identifies key areas for future work.

Elastic properties of additively manufactured steel produced with different scan strategies

The current study reports the application of a novel integrated process-structure-property approach in laser powder bed fusion (LPBF) additive manufacturing of stainless steel, focused on the analysis of local stress fields and effective orientation-dependant elastic properties. Specifically, the finite difference method is applied for thermal simulations of the LPBF process at the melt pool scale. The calculated temperature data serve as an input for grain structure modelling with cellular automata. Microstructural information, including the grain geometry and crystallographic orientations, is taken explicitly into account in micromechanical finite element simulations. The study discusses the relationship between the process-induced microstructure and the anisotropic elastic response of LPBF 316L steel samples fabricated using uni- and bidirectional scanning. In addition, the contribution analyses the scan strategy impact on the incipience of plastic deformation in additively manufactured steel. Commonly for both types of samples, the elastic moduli have the least values when tension is applied along the scan direction. Local stress fields form a laminated-like pattern of alternating through-the-thickness layers of lower and higher stresses following the process-induced mesoscopic material structure. The results indicate that the crystallographic texture has a more substantial effect on the anisotropy of elastic properties than the laminated-like pattern of LPBF 316L steel. Comparing microstructure-based finite element simulations and analytical calculations based on the Voigt-Reuss-Hill scheme, this paper presents new evidence for the ability of the fast and simple analytical texture-based approach to give an accurate prediction of anisotropic elastic properties of additively manufactured materials.

Study on sintering mechanism for extrusion-based additive manufacturing of stainless steel through molecular dynamics simulation

Unlike conventional metal powder based additive manufacturing (AM) technology, a Printing-Debinding-Sintering (PDS) process that adopts polymer-based filaments with highly filled metal particles can be employed as an economical approach to create metal parts at high fabrication rate and a low manufacturing cost. To achieve dense metal parts, the underlying sintering mechanism should be well understood, which has not yet been documented. In this study, molecular dynamics (MD) simulation was conducted to comprehensively unveil the sintering mechanisms during PDS of stainless steel 316L using a novel Fe-Ni-Cr three-element, three-particle sintering configuration. The mechanism of Cr element aggregation at the grain boundaries was revealed by analyzing the evolution of particle structure, diffusion activation energy, and interactions among solute elements during the unique heating process of PDS. In addition, the microstructure of the PDS-built 316L samples was characterized to verify such an aggregation phenomenon. It was found that the self-diffusion coefficient of Cr element increased substantially at the 1600 K holding stage. Meanwhile, Cr element was diffused to grain boundary and formed severe grain boundary aggregation due to its lower diffusion activation energy and stronger interactions between atoms. Moreover, the extra energy released due to this aggregation phenomenon promoted a further coalescence of particles. This study provides an atomic-scale understanding of sintering behavior of PDS-built Fe-based alloys, which paves a way for the multiscale modeling of the sintering process in PDS of other alloy systems.

Modeling of microscale internal stresses in additively manufactured stainless steel

Additively manufactured (AM) metallic materials often comprise as-printed dislocation cells inside grains. These dislocation cells can give rise to substantial microscale internal stresses in both initial undeformed and plastically deformed samples, thereby affecting the mechanical properties of AM metallic materials. Here we develop models of microscale internal stresses in AM stainless steel by focusing on their back stress components. Three sources of microscale back stresses are considered, including the printing and deformation-induced back stresses associated with as-printed dislocation cells as well as the deformation-induced back stresses associated with grain boundaries. We use a three-dimensional discrete dislocation dynamics model to demonstrate the manifestation of printing-induced back stresses. We adopt a dislocation pile-up model to evaluate the deformation-induced back stresses associated with as-printed dislocation cells. The extracted back stress relation from the pile-up model is incorporated into a crystal plasticity (CP) model that accounts for the other two sources of back stresses as well. The CP finite element simulation results agree with the experimentally measured tension–compression asymmetry and macroscopic back stress, the latter of which represents the effective resultant of microscale back stresses of different origins. Our results provide an in-depth understanding of the origins and evolution of microscale internal stresses in AM metallic materials.

Processing Techniques, Microstructural and Mechanical Properties of Wire Arc Additive Manufactured Stainless Steel: A Review

Processing Techniques, Microstructural and Mechanical Properties of Wire Arc Additive Manufactured Stainless Steel: A Review

Initial stages of oxide growth on AM stainless steel exposed to a supercritical CO2 environment

Wrought and additively manufactured (AM) 316 L stainless steel samples were exposed to a simulated Brayton cycle supercritical CO2 (sCO2) environment, at temperature of 450 °C and pressure of 76 bar in 99.999% CO2 for 2 weeks. The ground surfaces of wrought and AM 316 L specimens had average oxide thickness of 95 and 51 µm, respectively, composed primarily of Fe and Cr oxides. An as-printed AM 316 L sample was also exposed to the sCO2 environment and exhibited negligible oxidation during the 2-week exposure because of a thick Cr rich Mn silicate native oxide covering most of surface.

High cycle fatigue behavior of 316L steel fabricated by laser powder bed fusion: Effects of surface defect and loading mode

The mechanical performances of additive manufactured (AM) material are highly dependent on the fabrication process which inevitably results in surface imperfection as well as porosity. In the present study, the high cycle fatigue (HCF) behavior of an AM stainless steel 316L is experimentally investigated to characterize and evaluate the effect of the inherent surface defects. Profilometry and Computed Tomography are used. A series of fatigue experiments is carried out under different loading modes including tension, bending, and torsion fatigue tests. For each loading condition, different surface preparations are used to investigate the effect of surface state. Fatigue tests reveal that surface treatment can improve fatigue performances, the improvements observed being higher under tension/bending loading than under torsion loading. The fractographic analysis is performed for all the available tested specimens to reveal the mechanism of fatigue crack initiation. Lack-of-fusion (LoF) defects play the predominant role in the fatigue performance of SS 316L fabricated by laser powder bed fusion (LPBF). The presence of multiple LoF defects at the surface or subsurface is detrimental to the endurance under cyclic loading. By using Murakami approach modeling the relationship between fatigue strength and defect size, it is found that the multiple clustering defects act synergistically as one large virtual crack to initiate the fatigue crack.