Stainless Steel Powder Research Articles

Experimental study on high-cycle fatigue performance of laser cladding additively manufactured 316L stainless steel

Laser cladding (LC) technology has garnered significant attention for its application in the repair of corrosion damage in steel structures. However, research on the high-cycle fatigue performance of LC materials remains limited. This study employed 316L stainless steel powder to produce LC specimens and conducted uniaxial tensiletensile high-cycle fatigue tests to explore various laser deposition directions and surface roughnesses. The resulting SN curves provide insights into the high-cycle fatigue behaviour of LC materials. Additionally, SEM images were utilized to analyse the fatigue failure fracture characteristics. The experimental results reveal that cladding materials deposited parallel to the loading direction exhibit superior high-cycle fatigue performance. Fatigue fractures in the specimens generally originate from laser fusion defects, which not only reduce the lifespan of the specimen but also influence the failure location. Fatigue failure assessments of the laser-cladded materials were conducted via equivalent life diagrams, which revealed a high degree of correlation with the actual failure conditions. Existing fatigue design curves for base materials can be applied to the high-cycle fatigue performance design of laser-cladded 316L stainless steel, demonstrating a performance that surpasses the average level of steel butt welds.

Fabrication of Mo-encapsulated stainless steel by powder metallurgy and assessment of localized corrosion resistance

As a source of corrosion inhibitors, 2.5% Mo powder was mixed with Type 304L stainless steel powder and spark-plasma sintered to a fabricate Mo-encapsulated Type 304L stainless steel. The Mo particles formed a core/shell structure. The localized corrosion resistance of the fabricated Mo-encapsulated Type 304L stainless steel was compared with those of spark-plasma-sintered Type 304L and Type 316L stainless steels. Potentiodynamic polarization in 0.1 M NaCl suggested that the Mo cores could release molybdate, which acts as an inhibitor. However, the shells did not dissolve, preventing the Mo-enriched particles from acting as pit initiation sites. Similarly, the surface of the Mo core dissolved during dip-and-dry cycles using 0.1 M NaCl, but the shell was less prone to dissolution. Although the fabricated Mo-encapsulated stainless steel did not contain Mo as a solid solution, its rust resistance was equivalent to that of spark-plasma-sintered Type 316L stainless steel. In potentiodynamic polarization, the initiation potential for localized corrosion of the Mo-encapsulated Type 304L stainless steel was remarkably higher than those of the sintered Type 304L and Type 316L stainless steels. The corrosion inhibition mechanism of the Mo-encapsulated Type 304L stainless steel was discussed from three viewpoints: (1) passive film modification on the steel matrix, (2) cathodic protection of the steel matrix by the Mo core dissolution, and (3) corrosion inhibition by molybdate dissolved from the Mo-enriched particles, and the last one appeared to be the most likely.

Numerical Studies of Influencing Factors on the Homogeneity of the Powder Mixture during the Powder Spreading Process of Powder Bed Fusion–Laser Beam/Metal

Recent studies have focused on the alloying of nitrogen (N) in high‐alloy stainless steels by powder bed fusion–laser beam/metal (PBF‐LB/M). However, N‐induced pore formation remains a challenge. To overcome this, a combined PBF‐LB/M and hot isostatic pressing (HIP) process is developed. AISI 304L stainless steel powder was mixed with silicon nitride (Si3N4) powder and processed by PBF‐LB/M, allowing partial retention of Si3N4. This helps to maintain sufficient N content while reducing pore formation. The microstructure is then homogenised by HIP. A major challenge of this process is to maintain the homogeneity of the deposited powder mixture on the powder bed to ensure a consistent N content in the final products. This study combines experimental and numerical methods to address this issue: scanning electron microscopy is used to characterize the microstructure and map the local N content, while various numerical studies based on the discrete element method are carried out to investigate the effects of layer thickness, substrate surface roughness, and powder properties on the intermediate product. The numerical approach effectively predicts the N content distribution and homogeneity on the powder bed. The models are validated with experimental data and optimal process conditions for PBF‐LB/M are identified.

Applying design complexity metrics for post-processing cost modeling in metal additive manufacturing

The recent Additive manufacturing (AM) literature has primarily concentrated on exploring new avenues for improving the current technology and its applicability. It has also delved into research investments aimed at addressing the last remaining prediction challenges associated with current AM processes, particularly focusing to surface quality, accuracy, and internal composition. These limitations can often be mitigated though the application of post-processing techniques. Such techniques are often very costly both in time and monetary terms.When it comes to the impact that shape complexity has on post-fabrication costs for AM parts, a gap in the literature is apparent. In recent years, more attention has been devoted to researching a general shape complexity metric. It has been suggested in the literature to combine multiple of complexity metrics techniques, to reach more comprehensive model. This aspect has not received enough attention in previous works. In addition, the relationship between shape complexity and post-processing costs has not been assessed. And there are no predictive models for post-processing costs based on complexity.In this study, AM shapes for prototyping application are analysed. In this regard, previously established complexity metrics are used, together with expert’s assessments of post-processing costs, to create a model capable of predicting post-processing costs. This is achieved through a regression analysis using costs and complexity metrics values. The result of this research are two regression models, named 7 V and Vol/Sur Models, capable of predicting post-processing costs for AM parts produced through DMLS techniques with SS316L stainless steel powder. The accuracy of the two models is discussed.

The effect of the method for producing chromium-nickel stainless steel powders on the strain state and properties of the outer cage of a spherical hinge joint

The paper substantiates the relevance of studying powder metallurgy methods and efficiency of applying them to the production of spherical bearings of highly loaded spherical hinge joints. It proves that the force and work of deformation, as well as the kinetics of forming of the outer cage of a spherical hinge joint made of sintered corrosion-resistant chromium-nickel steels, are influenced by the chemical composition of powders and lubricants, the protective environment and the method of sintering, the microstructure and mechanical properties of the workpiece material. It is shown that the plastic properties of ring specimens under testing depend on the perfection of interparticle contacts, the presence and distribution of chromium oxides, forming schemes and workpiece porosity. The influence of the method for the production of stainless chromium-nickel powders on the density and mechanical properties of the sintered blanks is studied. A method is proposed for evaluating the strain state during radial deformation of ring specimens made of these steel powders and estimating the maximum allowable values of strain intensity below which no cracks are formed during cold forming of porous blanks. It is revealed that, to calculate the stress state and, accordingly, strain resistance in the cold forming of the outer cages of spherical hinge joints, made of sintered corrosion-resistant steels, it is possible to use the known constitutive equations if strain intensity does not exceed the experimentally obtained limit values. The feasibility of implementing the proposed method and selecting the process parameters of cold forming of spherical hinge parts made of chromium-nickel austenitic steels is substantiated.

Study on microstructure and properties evolution of duplex stainless steel powders by high-energy ball milling

Powder metallurgy duplex stainless steels have garnered significant attention due to its exceptional mechanical properties. The preparation of raw material powders plays a crucial role in the sintering process of duplex stainless steels. The effects of high-energy ball milling on microstructure and properties of duplex stainless steel powders have been studied. Results show that the particles size are effectively reduced by increasing the rotation speed. After milling at 800 r/min for 15 h, the particles size of duplex stainless steel were reduced from 86.17 μm to 69.46 μm and the α and γ phases were uniformly distributed. Additionally, the microstructure of sintered duplex stainless steel milled at 800 r/min is refined and the microhardness is increased from 267 HV0.3 to 313 HV0.3, with improvement of 17.23%, which is attributed to the grain refinement through high-energy ball milling.

High nitrogen steels produced by laser powder bed fusion – Processability of an additivated austenitic steel powder

The additivation of conventional metal powders allows the expansion of the range of materials and alloys suitable for powder bed fusion additive manufacturing of metals. The combination of material properties, the improvement of currently used powder properties, and their processability are the focus of this technique. This work investigates the influence of the additivation of Si3N4 particles to X2CrNi18–9 austenitic stainless-steel powder on the resulting powder properties and processability by PBF-LB/M. The aim is to process a composite material consisting of a steel matrix in which retained Si3N4 particles are embedded. A subsequent heat treatment by hot isostatic pressing should allow dissociation of Si3N4 and the associated nitrogen diffusion into the austenitic matrix to produce a high nitrogen steel (HNS). Despite some degradation in powder properties, as indicated by a decrease in the Hausner ratio from 1.24 to 1.15, PBF-LB/M successfully produced samples in a process window of 30–36 J/mm3.

Creating heterostructures via laser powder bed fusion using titanium and stainless steel mixtures

This study addresses the challenge of breaking the trade-off dilemma between strength and ductility in additively manufactured Titanium (Ti) products. By leveraging concentration non-uniformity and controlled diffusion during in-situ alloying of unalloyed titanium (CP-Ti) and 316L stainless steel (SS316) powders via laser powder bed fusion (LPBF), we formulated a novel Fe-containing alloy with improved printability and enhanced mechanical performance. The microstructure of the as-built Ti alloy comprises a heterostructure of nano-scaled martensitic α′ within the micro-scaled equiaxed prior-β grains, resulting from rapid solidification inherent in LPBF. Since the modified laser-powder bed fusion in this work lacks a pre-heating function, a stress-relief annealing process was conducted to enhance the mechanical properties of the as-built parts. The annealed in-situ alloyed Ti-Fe achieves a superb balance between strength and ductility, with an ultimate tensile strength (UTS) of approximately 1118.0 MPa and an elongation of ∼9.0 %. This study provides insights for designing high-performance Ti alloys with heterostructures using a mixture of elemental powder and alloyed powders via LPBF. The significance of concentration non-uniformity and diffusion during solidification is highlighted, demonstrating how these factors contribute to the formation of superior heterostructures through additive manufacturing.

Assessment of High-Temperature Oxidation Properties of 316L Stainless Steel Powder and Sintered Porous Supports for Potential Solid Oxide Cells Applications

Assessment of High-Temperature Oxidation Properties of 316L Stainless Steel Powder and Sintered Porous Supports for Potential Solid Oxide Cells Applications

Spreading anomaly semantic segmentation and 3D reconstruction of binder jet additive manufacturing powder bed images

Variability in the inherently dynamic nature of additive manufacturing introduces imperfections that hinder the commercialization of new materials. Binder jetting produces ceramic and metallic parts, but low green densities and spreading anomalies reduce the predictability and processability of resulting geometries. In situ feedback presents a method for robust evaluation of spreading anomalies, reducing the number of required builds to refine processing parameters in a multivariate space. In this study, we report layer-wise powder bed semantic segmentation for the first time with a visually light ceramic powder, alumina, or Al2O3, leveraging an image analysis software to rapidly segment optical images acquired during the additive manufacturing process. Using preexisting image analysis tools allowed for rapid analysis of 316 stainless steel and alumina powders with small data sets by providing an accessible framework for implementing neural networks. Models trained on five build layers for each material to classify base powder, parts, streaking, short spreading, and bumps from recoater friction with testing categorical accuracies greater than 90%. Lower model performance accompanied the more subtle spreading features present in the white alumina compared to the darker steel. Applications of models to new builds demonstrated repeatability with the resulting models, and trends in classified pixels reflected corrections made to processing parameters. Through the development of robust analysis techniques and feedback for new materials, parameters can be corrected as builds progress.

Investigation into microstructure, mechanical properties, and compressive failure of functionally graded porous cylinders fabricated by SLM

As the utilization of additively manufactured (AM) functionally graded porosity (FGP) structures continues to rise in various industries, there is a growing need for a comprehensive understanding of their design, microstructure, mechanical behavior, and failure mechanisms. This study involves the design and fabrication of FGP specimens with an 85 % volume fraction using selective laser melting (SLM) and 316L stainless steel powder, focusing on characterizing porosities, printing quality, and microstructure. Experimental tests, including tensile, quasi-static compression, and Split Hopkinson Pressure Bar tests, are conducted to assess the material behavior. Additionally, finite element analysis (FEA) and experimental compression tests are employed to investigate the compressive mechanical behavior and failure modes of FGP structures. The findings indicate that porosity distribution has minimal impact on the compressive behavior, specific energy absorption (SEA), and toughness of FGP structures. Furthermore, reducing the volume fraction from 85 % to 75 % in the S1FG samples increases the SEA by 7.2 % and changes the toughness by 5.9 %. Notably, porosity distribution influences fracture position and failure mechanisms during compression tests.

On the use of slurry as an alternative to dry powder for laser powder bed fusion of 316L stainless steel

Laser powder bed fusion (LPBF) is a well-established additive manufacturing process for producing high-quality metal components with unparallelled design freedom. However, LPBF also has its limitations, including a limited materials palette, low productivity and high costs, mainly due to the expensive feedstock powders. These powders must meet highly stringent requirements regarding particle size (15–45μm), particle size distribution (mono-modal) and morphology (spherical), which is achievable only through expensive gas- and plasma-atomised powders. This paper investigates slurry-LPBF as an alternative to conventional dry powder LPBF. The use of slurry removes some of the stringent powder requirements by allowing deposition of smaller particles with a variety of particle morphologies. Slurry-LPBF can therefore increase the useful yield of the atomisation process and expand the materials palette for LPBF, by enabling the use of powders for which atomised variants are not commercially available. This study used 316L stainless steel powder with an average particle size <18μm. An existing slurry-LPBF machine was re-designed and re-built, allowing successful slurry processing. Two optimal parameter sets were obtained, resulting in component density of 99.4%. Tensile testing revealed an ultimate tensile strength (UTS) of 622 ± 2 MPa and an elongation at break of 66 ± 2%. These results are consistent, and fall within the range of reported values in literature for dry-powder LPBF, with the UTS being on the lower side of the range, whilst elongation at break being on the higher side.

The Evaluation of the Cytotoxicity and Corrosion Processes of Porous Structures Manufactured Using Binder Jetting Technology from Stainless Steel 316L with Diamond-like Carbon Coating

With the growing interest in additive manufacturing technology, assessing the biocompatibility of manufactured elements for medical and veterinary applications has become crucial. This study aimed to investigate the corrosion properties and cytotoxicity of porous structures designed to enhance the osseointegration potential of implant surfaces. The structures were fabricated using BJ technology from 316L stainless steel powder, and their surfaces were modified with a DLC coating. The studies carried out on porous metal samples with and without DLC coatings demonstrated low cytotoxicity. However, no significant differences were found between the uncoated and DLC-coated samples, likely due to variations in the thickness of the coating on the porous samples and the occurrence of mechanical damage.

Fabrication and characterization of self-lubricating anti-wear 316L stainless steel/h-BN composite coatings on Q235 substrate via laser cladding

This paper presents the fabrication and characterization of self-lubricating, anti-wear 316L stainless steel composite coatings on a Q235 substrate using 316L stainless steel powders and nanoscale hexagonal boron nitride (h-BN) ceramic particles via coaxial powder feeding laser cladding. The influence of process parameters on cladding quality and geometry, and the impact of h-BN contents (2 wt% and 5 wt%) on the microstructure and mechanical properties of the coatings were studied. Optimal process parameters for 316L/5wt%BN coatings were identified: a powder feeding rate of 3–4 rpm, a laser power of 2200–2400 W, a scanning speed of 4–5 mm/s, and an overlapping rate of 40 %. Microstructural analysis showed a smooth surface without cracks or pores. X-ray diffraction revealed intermetallic compounds such as CrB, Cr2N, Fe3N, BN, and γ-(Fe, Ni). The inclusion of h-BN nanoparticles enhanced grain refinement, significantly increasing microhardness. Coatings with 5 wt% h-BN achieved an average microhardness of 438.8 HV10, 2.5 times higher than the substrate and the 316L stainless steel. Additionally, h-BN reduced friction coefficients, leading to substantial wear reduction. The 316L/5 wt% h-BN sample experienced only 4.2 mg of wear, 45.16 % of the substrate’s wear. These findings highlight the beneficial effects of h-BN nanoparticles on 316L stainless steel coatings, enhancing wear resistance, hardness, and overall performance.

Mechanical Properties and Cooperation Mechanism of Corroded Steel Plates Retrofitted by Laser Cladding Additive Manufacturing under Tension.

As a metal additive manufacturing process, laser cladding (LC) is employed as a novel and beneficial repair technology for damaged steel structures. This study employed LC technology with 316 L stainless steel powder to repair locally corroded steel plates. The influences of interface slope and scanning pattern on the mechanical properties of repaired specimens were investigated through tensile tests and finite element analysis. By comparing the tensile properties of the repaired specimens with those of the intact and corroded specimens, the effectiveness of LC repair technology was assessed. An analysis of strain variations in the LC sheet and substrate during the load was carried out to obtain the cooperation mechanism between the LC sheet and substrate. The experimental results showed that the decrease in interface slope slightly improved the mechanical properties of repaired specimens. The repaired specimens have similar yield strength and ultimate strength to the intact specimens and better ductility as compared to the corroded specimen. The stress-strain curve of repaired specimens can be divided into four stages: elastic stage, substrate yield-LC sheet elastic stage, substrate hardening-LC sheet elastic stage, and plastic stage. These findings suggest that the LC technology with 316 L stainless steel powder is effective in repairing damaged steel plates in civil engineering structures and that an interface slope of 1:2.5 with the transverse scanning pattern is suitable for the repair process.

Minimizing Porosity in 17-4 PH Stainless Steel Compacts in a Modified Powder Metallurgical Process

Nowadays, powder-based manufacturing processes are recognized as cost-efficient methods frequently employed for producing parts with intricate shapes and tight tolerances in large quantities. However, like any manufacturing method, powder-based technologies also have several disadvantages. One of the most significant issues lies in the degree of porosity. By modifying the morphology of the gas-atomized spherical 17-4PH stainless steel powder via prior ball milling and then raising both the pressure of cold compaction (1.6 GPa) and sintering temperature (1275 °C), the porosity could be reduced considerably. In our novel powder metallurgical (PM) experimental process, an exceptionally high green density of 92% could be reached by employing die wall lubrication instead of internal lubrication and utilizing induction heating for rapid sintering. After sintering (at temperatures of 1200, 1250, and 1275 °C), the samples aged in the H900 condition were then mechanically tested (Charpy impact, HV hardness, and tensile tests) as a function of porosity. Sintering at 1275 °C for one hour enabled porosity reduction to below 4%, resulting in 1200 MPa yield strength and 1350 MPa ultimate tensile strength with significant (16%) fracture strain. These values are comparable to those of the same alloy products fabricated via ingot metallurgy (IM) or additive manufacturing (AM).

Quantification of δ-ferrite and austenite retention in laser-deposited martensitic stainless steel

Type 420 martensitic stainless-steel powder was clad onto a CF3M austenitic stainless steel substrate using laser direct-energy-deposition (L-DED). Through comprehensive characterization and numerical simulation, the evolution of microstructures, particularly the retention of δ-ferrite and austenite, was investigated. In the clad fusion zone, the primary phase to solidify was δ-ferrite, followed by austenite resulting from the peritectic reaction. The segregation patterns developed during rapid solidification from the L-DED process exerted a significant effect on the stability of the austenite in the room temperature microstructures. Due to the fast cooling rate in the solid state, the time available for transformation of the δ-ferrite to austenite regarding the segregation patterns was limited, and the transformation was incomplete. The room temperature microstructure was therefore comprised of δ-ferrite distributed in the dendrite core regions, surrounded by martensite, which was further surrounded by a small fraction of retained austenite in the interdendritic regions. The retained austenite region was enriched with segregated alloying elements, which pushed the martensite start temperature Ms below room temperature. The retention of both δ-ferrite and interdendritic austenite was proved to have caused a softened fusion zone with a lowered martensite fraction.

Fabrication of a Plate-Type Porous Stainless Steel 316L Powder Filter with Different Pore Structures without Use of a Binder

Generally, when fabricating porous filters using metal powder, about 1 to 2 wt% of a binder is added to increase the formability of the metal powder. If the binder is not completely removed through a debinding and sintering process, however it can cause defects such as discoloration and the generation of fine particles. In this study, a study was conducted to fabricate a plate-type porous stainless steel powder filter with a different pore structure without the use of a biner. First, the metal powder is charged into a ceramic mold to form a plate-shaped powder filter, and then covered with a ceramic top plate. In order to observe the pore properties according to the pressure, the unpressurized specimen and the specimen pressurized with a pressure of 30 MPa were then sintered at 1050℃ for one hour in a high vacuum atmosphere furnace. The microstructure of the sintered plate-shaped powder filter was observed through an optical microscope and in order to analyze its pore properties as a filter, gas permeability and porosity were measured using a capillary flow porometer and Archimedes’ law.

Compaction behaviours of 17-4 PH, 316L, and 1.4551 stainless-steel powders during cold pressing

Despite numerous recent technological developments, conventional powder metallurgy (CPM) remains the most commonly applied technique for fabricating stainless-steel products. However, the compressibility of stainless-steel powders is still a critical issue. Martensitic stainless-steel powders (i.e., 17-4 PH) are significantly harder than austenitic stainless-steel powders (i.e., 316L and 1.4551). Herein, three different stainless-steel (DSS) powders (i.e., 17-4 PH, 316L, and 1.4551) were investigated using a high cold pressing pressure (i.e., 1.6 GPa) and a relatively low sintering temperature of 1200 °C during CPM. Dimensional and Archimedes density measurements, volume and radial shrinkage calculations, optical and scanning electron microscopy analyses, and compressive strength measurements were conducted to investigate the physical and mechanical properties. Using 1.6 GPa resulted in a 10 % and 6 % increase in the relative green density of the 17-4 PH and 316L samples, compared with the reported literature. For the first time, relative sintering densities of approximately 97 % and 99 % were obtained for 316L and 1.4551 at a sintering temperature of 1200 °C, respectively. Despite the insufficient sintering process, the relative density of the 17-4 PH sample increased by 2 % compared with the literature values reported for higher sintering temperatures. The shrinkage ratios were much lower than those reported in the literature. Furthermore, the present 316L samples achieved 90 % of the compressive yield strength observed in cast 316L, a 25 % increase compared with that previously reported in the literature. This study extends the CPM procedure for enhancing green densities, employing low sintering temperatures, and reducing the shrinkage values of stainless-steel powders with differing hardness.

Comprehensive analysis of ultrasonically atomized 316L stainless steel powder using adjusted additive manufacturing suitability factor

This study focuses on the 316L stainless steel powder produced by using an innovative ultrasonic atomization (UA) method. The production process was optimized at electrical currents with 120 A and vibration amplitude with 80% proving the most effective for maximizing productivity. The study extensively evaluated particle size and shape, bulk and tapped densities, Hausner's ratio, and Carr index, finding the UA steel powder to possess high sphericity, minimal satellite particles, and excellent flowability, qualities crucial for additive manufacturing (AM). A new approach for calculating the additive manufacturing suitability factor was developed, incorporating custom weighting factors for rheological parameters to reduce the influence of parameters with high uncertainty or statistical insignificance, thus improving accuracy. When compared using this method, the UA powder demonstrated superiority over its commercial counterparts by approximately 1% and 10%, underscoring its promise for AM applications.