PH Stainless Steel Research Articles

On the possibilities of merging additive manufacturing and powder injection molding in the production of metal parts

PurposeThis study aims to enhance merging of additive manufacturing (AM) techniques with powder injection molding (PIM). In this way, the prototypes could be 3D-printed and mass production implemented using PIM. Thus, the surface properties and mechanical performance of parts produced using powder/polymer binder feedstocks [material extrusion (MEX) and PIM] were investigated and compared with powder manufacturing based on direct metal laser sintering (DMLS).Design/methodology/approachPIM parts were manufactured from 17-4PH stainless steel PIM-quality powder and powder intended for powder bed fusion compounded with a recently developed environmentally benign binder. Rheological data obtained at the relevant temperatures were used to set up the process parameters of injection molding. The tensile and yield strengths as well as the strain at break were determined for PIM sintered parts and compared to those produced using MEX and DMLS. Surface properties were evaluated through a 3D scanner and analyzed with advanced statistical tools.FindingsAdvanced statistical analyses of the surface properties showed the proximity between the surfaces created via PIM and MEX. The tensile and yield strengths, as well as the strain at break, suggested that DMLS provides sintered samples with the highest strength and ductility; however, PIM parts made from environmentally benign feedstock may successfully compete with this manufacturing route.Originality/valueThis study addresses the issues connected to the merging of two environmentally efficient processing routes. The literature survey included has shown that there is so far no study comparing AM and PIM techniques systematically on the fixed part shape and dimensions using advanced statistical tools to derive the proximity of the investigated processing routes.

Taguchi DoE analysis and characterization of 17-4 PH stainless steel parts produced by material extrusion (MEX) process

Material extrusion (MEX) of metallic components is an indirect additive manufacturing (AM) process that is recently gaining a lot of attention in the industry. This multi-step process with debinding and sintering, provides an inexpensive safe alternative, that is effective, flexible and office-friendly for several corporations compared to other metal AM techniques. However, optimizing the manufacturing parameters of the MEX process is still challenging due to the lack of research on their impact on the mechanical and surface properties of the fabricated materials.For this purpose, this paper investigates how various processing parameters impact the mechanical properties and surface roughness of 17-4 PH stainless steel parts produced by MEX. The parameters analyzed include layer thickness, build orientation, number of contours, and aging thermal treatment for 1 h at 482°C (H900). A Taguchi design of experiments (DoE) was employed to conduct the parametric analysis and the results were post-evaluated via the analysis of variance (ANOVA). The experimental results show that H900 treatment increases the micro-hardness by ∼50 HV0.3 and contributes in augmenting the ultimate tensile strength (UTS) by ∼200 MPa. The build orientation and its interaction with the layer thickness have the highest impact on the surface roughness. Moreover, the amount of enclosed porosity is higher in the samples with lower layer thickness. The absorbed impact energy (Wabs) is relatively low due to the enclosed porosity content and is not linked to the analyzed processing parameters. The best mechanical properties were obtained for parts built with solid infills, 0° build orientation, 0.125 mm layer thickness, two contours, and H900 as a post-treatment.

Effect of surface modification of metal powders (by aluminum stearate) on the properties of metal injection molding feedstock

Metal injection molding (MIM) is a net-forming technology for manufacturing miniature metal parts, which can improve the manufacturing accuracy of complex-shaped parts. In this study, aluminum stearate was used to modify the 17-4PH stainless steel powder, the binder was composed of (PMMA) and (PEG) with the volume ratio of 7:3. The effects of aluminum stearate surfactant amount on the feedstock viscosity, water debinding rate and thermal debinding shape were studied. The results showed that the coating of aluminum stearate breaks the agglomeration between the powders and decreases the viscosity of the feedstock. When the addition of aluminum stearate was 0.6wt% of the powder mass, the melt index, density and flexural modulus of the feedstock were 81.5 g/10 min, 5.44 g/cm3, and 1643Mpa, respectively, and the thermal debinding shape retention was the best of all debinded parts. However, too much aluminum stearate makes the feedstocks thicker and the green part weaker.

Tensile properties and microstructural evolution of 17–4 PH stainless steel fabricated by laser hybrid additive manufacturing technology

Wire-based laser directed energy deposition (LDED) technology is an attractive and efficient additive manufacturing technology, which shows great potential in the process of manufacturing high-value engineering components. However, the thermal effect will lead to a large amount of residual tensile stress in the components, and the large crystal structures after solidification seriously affects the tensile performance. The pursuit of high mechanical properties in additive manufacturing components have prompted researchers to seek new strengthening process to produce high-strength components. Therefore, in this paper, laser shock peening (LSP) composite wire-based LDED were used for the additive manufacturing of 17–4 PH stainless steel under the specified experimental conditions, and the effects of LSP on microstructure evolution, microhardness, and tensile properties of wire-based LDED components were systematically studied. Results showed that uniform grains with an average size of 2.31 μm were generated on the top surface of specimen due to the ultra-high plastic strain induced by LSP shock wave. The size of hierarchical martensitic units shows varying degrees of reduction after LSP treatment, which is shown by the width decrease of packet, block and lath. Dynamic recrystallization caused by rearrangement and annihilation of high-density dislocations promoted the grain refinement. Meanwhile, the residual stress was completely converted from tensile state into compressive state with a maximum value of 425 MPa, and the microhardness was also enhanced to a peak value of 432 HV. In addition, we observed that the high-density dislocation environment created by LSP treatment promoted the further precipitation, and the aggregation phenomenon of precipitates was observed in the dense dislocation area. Furthermore, the tensile strength and elongation of LSP treated specimen were improved significantly, which was attributed to the combined effects of grain refinement, introduction of dislocation structures, precipitation strengthening and gradient residual compressive stress. In summary, laser hybrid additive manufacturing technology provides a new idea and method for the production of high-performance precipitation hardening stainless steel components.

The influence of hatch spacing on the metallurgical characteristics of 17–4 PH stainless steel processed by DED

AbstractThe quality and performance of additively manufactured part is linked to the process parameters such as laser power, scanning speed, powder feed rate, and layer thickness. However, hatch spacing is one of the process parameters that affect the quality and performance of the part, but its effect has not been fully investigated. Therefore, this study seeks to investigate the effect of hatch spacing on the metallurgical characteristics, including microstructural evolution, microhardness, and corrosion behavior of 17–4 PH stainless produced through direct energy deposition. A LENS system was used to manufacture 17–4 PH SS cubes and the hatch overlap was varied from 20 to 80%. Subsequently, the printed cubes were subjected to heat treatment (H900) followed by material characterization which includes microstructural analysis, microhardness, and corrosion behavior. This study deduced that varying the percent overlap had an impact on the proportion of delta ferrite and the grain size. Furthermore, increasing the percent overlap from 20 to 80% was found to cause a reduction in hardness (340–331 HV). Meanwhile, it was found that traditionally manufactured 17–4 PH SS is more susceptible to corrosion than additively manufactured 17–4 PH SS.

Enhancing wear performance: A comparative study of traditional vs. additive manufacturing techniques for 17–4pH SS

This study investigates the microstructural, mechanical, and tribological characteristics of 17–4 PH stainless steel specimens produced through Additive Manufacturing (AM) techniques, namely Selective Laser Melting (SLM) and Fused Filament Fabrication (FFF), in comparison to conventionally wrought steel (W). The wear test carried out on the samples were pin-on-disk, ball-on-plate and lubricated pin-on-disk. The counter part was an alumina ball with a diameter of 3 mm. The wear scar was less pronounced on lubrication test than in dry conditions for all samples. The coefficients of friction (COFs) were higher in dry conditions (in the order of 10−1) than in lubrication conditions (in the order of 10−2). Moreover, the wear rate had a significant reduction under lubrication conditions (in dry tests are in the order of 10−7, while lubrication conditions led to results in the order of 10−9). Additionally, FFF and SLM exhibited remarkably low wear rates in comparison to the wrought sample showing a superior dry and lubricated wear behaviour. AM allows for comparable or improved properties, despite slightly lower hardness due to retained austenite/delta ferrite and reduced precipitates. That significant improvement enhances the appeal of AM for high-performance components, particularly for small production runs and complex geometries being a promising and efficient technology for diverse industries.

The effect of surface finish and post-processing on mechanical properties of 17-4 PH stainless steel produced by the atomic diffusion additive manufacturing process (ADAM)

This study investigates the influence of surface finish and post-processing conditions on the mechanical properties of 17-4 PH stainless steel (SS) produced using the atomic diffusion additive manufacturing process (ADAM). Diverse sample orientations, including horizontal (0°), 30°, 60°, and vertical (90°), were examined, with selected samples undergoing post-processing through machining, polishing, and heat treatment. Tensile strength testing, surface roughness measurement, and hardness measurement were conducted to assess the effect of surface finish conditions and post-processing on mechanical properties. The results reveal significant variations in the tensile strength of the samples based on the build orientation (183.5 to 1034.5 MPa), and subsequent machining. Notably, post-built machining is found to enhance both the absolute ultimate tensile strength (UTS) and the isotropy of the material. Further improvements are attainable through heat treatment. A microstructure analysis, in conjunction with tensile testing outcomes, demonstrates the potential for refining the properties of ADAM-printed samples through suitable machining, heat treatment, and geometry modifications. This study identifies avenues for ongoing process development and outlines possibilities for enhancing mechanical properties of additive manufactured parts, particularly through ADAM process.

Rapid repair of thermal aging embrittlement in 17-4PH martensitic stainless steel using pulsed electric current

The 17-4PH stainless steel serves as the main steam isolation valve in a light water reactor due to excellent comprehensive mechanical properties and corrosion resistance. Nonetheless, the thermal aging resulting from prolonged service poses a threat to the safe operation of nuclear power plants. The mechanism of thermal-aging embrittlement of 17-4PH stainless steel and its repairing behavior under the action of the pulsed electric current were studied using transmission electron microscopy and 3D atom probe tomography. The ductile to brittle transition occurred following the spinodal decomposition and G phase formation during the thermal aging of 5000 h at 673 K, resulting in a 100 HV increase in hardness of the 17-4PH stainless steel, of which 94.4 HV was attributed to the spinodal decomposition. Under the action of a pulsed electric current at 733 K, the hardness and impact energy can be restored to its original state, whereas heat treatment at the same temperature is unable to restore these properties. This is because the pulsed electric current treatment decreased the thermodynamic barrier to dissolution for the spinodal decomposition and G phases. The Kolmogorov-Johnson-Mehl-Avrami model was used to calculate the kinetics of spinodal decomposition dissolution. The results suggest that the pulsed electric current could increase the diffusion pre-exponential factor of Cr element and accelerate the elimination of spinodal decomposition. This process ultimately facilitates the quick regeneration of the 17-4PH stainless steel's performance.

Low strain hardening enables improved water droplet erosion performance through deep rolling

The present work investigates the role of deep rolling surface treatment on the water droplet erosion behavior of 17–4 PH stainless steel. Standard heat treatments were first applied to samples of 17–4 PH stainless steel to achieve three states, solution treated and two different aging conditions. The mechanical properties of these conditions were determined using hardness and tensile tests. Then, deep rolling surface treatments were applied to the various conditions of the 17–4 PH. Water droplet erosion tests were subsequently performed at impact velocities of 250 m/s and 300 m/s, and the erosion performance in terms of incubation period and maximum erosion rate before and after the deep rolling treatment is compared. It was found that deep rolled samples exhibited considerably longer incubation periods compared to only heat-treated samples. The improvement in erosion resistance of the 17–4 PH stainless steel is attributed to its lower strain hardening exponent values, which reduces embrittlement that is usually associated with the work hardening due to deep rolling. Hence, it is concluded that low strain hardening exponent is essential to the effectiveness and success of mechanical surface treatments to combat water droplet erosion.

Structural integrity of 15-5PH stainless steel flow formed pressure vessel for launch vehicle applications

15-5 PH stainless steel is a martensitic precipitation-hardenable stainless steel (0.07C-15Cr-5Ni-3.5Cu-Fe). Presently, high strength low alloy steel, AFNOR 15CDV6 is used for the fabrication of Thrust Vector Control system of satellite launch vehicle. These pressure vessels are used for storing strontium perchlorate, intended for attitude (pitch and yaw) control of the launch vehicle during first stage. The tanks are fabricated through welding of rolled plates, machined rings, and end domes from forgings. AFNOR 15CDV6 steel is prone for corrosion and requires alumina barrier coating to protect from strontium perchlorate. Therefore, as a superior alternative, 15-5PH steel with improved corrosion resistance, simple heat treatment avoiding distortion was selected for the fabrication of pressure vessel. In order to improve the structural integrity of the pressure vessel, flow forming technology was adopted for realization of cylindrical portion of the tank, which eliminated the long seam weld joint and reduced the number of circumferential weld joints. As a part of the developmental program, the tank was designed, shells were flow formed and welded with end domes and were directly aged. The fabricated tank was subjected to a series of pressure tests followed by final burst test for estimating structural margins and ensuring quality requirements.This paper describes the design of the pressure vessel, process followed for manufacture, qualification program adopted and detailed metallurgical analysis carried out on the burst tested hardware. The 15-5PH pressure vessel has successfully withstood the proof pressures and test results are better than the predicted analysis results, indicating structural integrity of the pressure vessel for flight.

Fatigue Life and Crack Growth Rate Prediction of Additively Manufactured 17-4 PH Stainless Steel using Machine Learning

The present work is focused on machine learning-assisted predictions of the low cycle fatigue behaviour and fatigue crack growth rate (FCGR) of 17- 4 PH SS processed through L-PBF and post-processing. Various machine learning techniques reported in the literature provided a flexible approach for explaining the complex mathematical interrelationship among processing-structure-property of the materials. In the present work, four machine learning (ML) algorithms, such as K- Nearest Neighbor (KNN), Decision Trees (DT), Random Forests (RF), and Extreme Gradient Boosting (XGB) algorithms, are implemented to analyze the Fatigue Crack growth rate (FCGR) of 17-4 PH SS alloy. After optimizing the hyper parameters for these algorithms, the trained models were found to estimate the unseen data as equally well as the trained data. The four tested ML models are compared among each other over the training as well as the testing phase based on their mean squared error and R2 scores. Extreme Gradient Boosting model has performed better for the FCGR predictions providing the least mean squared errors and higher R2 scores compared to other models.

Fatigue crack-growth behavior of wrought and additively manufactured 17 - 4 PH stainless steel specimens

Additive Manufacturing (AM) technologies potentially offer numerous advantages, first and foremost the reduction of the lead-time of new products and the possibility of producing any kind of complex shape. Selective laser melting (SLM) processes are the most popular processes for AM of metals; currently, several types of stainless steel have been widely processed via SLM as steel provides a broad range of desirable properties like good ductility, high strength, low cost, and recyclability. Therefore, it is largely used in both industrial and domestic products. However, many factors, such as crack orientation, porosities, residual stresses, heat treatments, corrosion, etc., can degrade the performances of SLM materials significantly, if compared to those of the wrought ones. Therefore, in this work the fatigue crack propagation behaviors of wrought and AM 17-4 PH stainless steel were measured experimentally by considering different crack orientations. Tests were carried out using standard compact-tension C(T) specimens tested at R = 0.1 at a frequency of 5 Hz. The main objective was to study the effect of the crack orientation on crack-length vs. number of cycles curves.

Production and characterization of lattice samples with solid shell in 17-4 PH stainless steel by Laser Powder Bed Fusion technology

In this work, 17-4 PH stainless steel square-based lattice structures with solid shell were manufactured by Laser Powder Bed Fusion. Face Centered Cubic unit cell was chosen as lattice cell geometry. The main aim of this work was to study the role of the shell in the mechanical behavior under compression load and to identify any critical issue due to the connection of the shell with lattice part. This is a relevant topic since often lattice structure are integrated with solid walls and the study of the relative behavior can support the understating of the performance of complex components. The manufactured samples were tested in as-built and heat-treated condition. In detail, solution and aging treatment was performed as a conventional route for 17-4PH steel. In particular, microhardness and compressive tests were performed, and the mechanical behavior and the fracture mechanisms of the samples were investigated. Furthermore, the defects, the geometry of the struts and the connection with the solid part were analyzed.The detachment of the shell from the lattice did not occur. In fact, the solid part followed the deformation of the structure. The microstructural evolution after heat treatment was found to be responsible for an increase in hardness, strength and deformation for the investigated structures.

Shrinkage evaluation and geometric accuracy assessment on 17–4 PH samples made by material extrusion additive manufacturing

Material Extrusion Additive Manufacturing (MEX) is one of the most common Additive Manufacturing (AM) technology. The possibility to realize metal parts using this technology has several advantages and generates great costs reduction with respect to other metal Additive Manufacturing technologies. However, there are some disadvantages related to the design and production of these extrusion-based metal parts, especially when considering the fabrication of complex geometries. One of the main problems is related to the oversizing of the parts due to the shrinkage phenomenon occurring after the debinding and sintering steps.In this work, a comprehensive study about the shrinkage phenomenon was conducted on 17–4 PH stainless steel parts realized via MEX, analyzing the influence of printing and sintering orientation, infill strategy and aspect ratio. With this aim, by using the Design of Experiment approach, samples were analyzed in both as-printed and as-sintered conditions. Shrinkage percentage values, geometric accuracy and density were the main investigated outputs. A commercial 3D structured-light scanner was used to collect the dimensional and geometric data.Results showed a strong shrinkage anisotropy, more relevant for samples with different orientation during the printing and the sintering phase. Geometric accuracy, in terms of flatness, was also assessed comparing green and sintered parts.

Electrochemical analysis of friction welded 17-4 PH stainless steel components manufactured by selective laser melting

Electrochemical analysis of friction welded 17-4 PH stainless steel components manufactured by selective laser melting

Tribological Properties of Additively Manufactured Al-Si Alloys and Steels

Metals are prone to wear through the separation of wear debris particles as well as the plastic displacement of surface and near-surface material. Particle sizes range from millimetres to nanometres. Erosion is the gradual, layer-by-layer destruction of a metallic object's surface brought on by mechanical pressure or electrical discharges. Metals erode as a result of surface friction, wear, cavitation, and the influence of powerful gas or liquid currents on a surface. Jet engines, nuclear reactors, steam turbines, and boilers might all suffer damage from erosion. By enhancing process technology or unit design, using better materials, and applying heat treatment, it is possible to strengthen the resistance of components against erosion. AlSi10Mg is a hypoeutectic alloy that may be additively manufactured due to its limited solidification range, which reduces hot cracking susceptibility during cooling. Complex bulk and open-cell structures with outstanding strength ratio (strength-to-weight ratio) and good formability may be created using additive manufacturing of aluminium alloys, particularly AlSi10Mg. Carbon, manganese, sulphur, silicon, phosphorus, chromium, nickel, copper, and niobium are all present in the pH grade of 17-4. This combination of high strength and corrosion resistance benefits a 17-4 PH stainless steel grade. It may be utilised effectively in a variety of applications due to its high tensile strength and exceptional corrosion resistance.Powder bed fusion is one of the most mature metal additive methods, and as such, it benefits from decades of industrial expertise. PBF can satisfy demands of creating a new component and need to iterate on ideas quickly or are searching for a more efficient procedure to produce sophisticated components. Material waste is reduced because building the part layer by layer reduces the majority of the waste associated with subtractive manufacturing processes. Any surplus powder is collected and recycled when the item is finished. This review researches about the wear and erosion behaviour of Al-Si Alloy and steels printed using additive manufacturing methods. Finally, the findings of this review are summarised, and recommendations are made for future research aimed at resolving current issues and advancing technology.

Microstructure and wear behaviors of 17-4 PH stainless steel fabricated by laser cladding with post laser shock peening treatment

Laser cladding (LC) technology provides an attractive and cost-effective way to prepare wear-resistant coating on high-value engineering components. However, the thermal effect of coating will lead to a large amount of residual tensile stress in the coating, which seriously affects the wear performance. This paper investigated the influence of laser shock peening (LSP) on the microstructure and wear behaviors of wire-based LC 17-4 PH coating. Results showed that there was no laser remelting phenomenon during LSP process, and all residual austenite in cladding layer transformed into martensite after LSP treatment, accompanied by a more compact and uniform microstructure. LSP can introduce severe plastic deformation to form dislocation structures on the top surface of the coating, which lead to grain refinement through dynamic recrystallization (DRX), and the average grain size decreased from 4.15 μm to 1.81 μm when the laser energy is 9J. Meanwhile, the high strain rate plastic deformation induced by LSP generated high residual compressive stress on the material surface, with a maximum value of 500 MPa. The surface microhardness of the cladding layer increased by 100HV after LSP treatment, reaching to a peak of 458HV at a laser power of 9J, and gradually decreased along the depth direction, presenting a gradient distribution. After LSP treatment, GCr15 steel counter ball was used to simulate the sliding friction of solid particles under real working conditions. Results showed that the friction coefficient (COF) and wear rate of 17-4 PH coating were significantly reduced. Furthermore, the wear type changed from dominative adhesive to slight abrasive wear. The improvement of microhardness and wear properties were attributed to the combined effects of Hall-Petch and Taylor hardening strengthening.

Optimization of Aging Temperature and Heat-Treatment Pathways in Additively Manufactured 17-4PH Stainless Steel.

This study investigates the tensile behaviors of additively manufactured (AM) 17-4PH stainless steels heat-treated within various temperature ranges from 400 °C to 700 °C in order to identify the effective aging temperature. Despite an aging treatment of 400-460 °C increasing the retained austenite content, an enhancement of the tensile properties was achieved without a strength-ductility trade-off owing to precipitation hardening by the Cu particles. Due to the intricate evolution of the microstructure, aging treatments above 490 °C led to a loss in yield strength and ductility. A considerable rise in strength and a decrease in ductility were brought about by the increase in the fraction of precipitation-hardened martensitic matrix in aging treatments over 640 °C. The impact of heat-treatment pathways on aging effectiveness and tensile anisotropy was then examined. Direct aging at 482 °C for an hour had hardly any effect on wrought 17-4PH, but it increased the yield strength of AM counterparts from 436-457 to 588-604 MPa. A solid-solution treatment at 1038 °C for one hour resulted in a significant drop in the austenite fraction, which led to an increase in the yield (from 436-457 to 841-919 MPa) and tensile strengths (from 1106-1127 to 1254-1256 MPa) with a sacrifice in ductility. Improved strength and ductility were realized by a solid-solution followed by an aging treatment, achieving 1371-1399 MPa. The tensile behaviors of AM 17-4PH were isotropic both parallel and perpendicular to the building direction.

Simulation-driven-design of metal lattice structures for a target stress–strain curve

Additive manufacturing (AM) allows for the creation of novel complex structures previously impossible using traditional subtractive methods; however, there is a need for new design approaches to fully exploit this potential. Metal lattice structures have attracted attention for their broad customisable range of configurations and potential properties, and to take advantage of these possibilities there is a need for intelligent design tools to optimise the lattice according to the desired application and properties. This study presents and demonstrates a method to automatically design lattice structures which achieve a desired compressive stress–strain curve and satisfy user-defined manufacturing limits. A genetic algorithm iterates selected design variables (unit cell aspect ratio, strut taper, and thickness gradient) and minimises the error between the target stress–strain curve and predicted curve which is determined via automated finite element (FE) modelling of each lattice design. The optimised design is validated through manufacture and compression testing of 17-4PH stainless steel lattice structures, and micro-CT imaging to assess build quality. The tool's versatility is demonstrated by successfully designing lattices to fit a range of target curves. This work demonstrates the potential of this smart inverse design tool to exploit AM and optimise lattice design based on desired performance. The custom written design tool presented in this study is available open source at https://github.com/I-Form/LiDOT.

Selective Laser Melting Parametric Optimization for Microhardness of 17-4 PH Stainless Steel

The 17-4 PH stainless steel is a structural material possessing inherent properties suitable for employment in industrial applications. Selective Laser Melting (SLM) technology has overcome many shortcomings of conventional processing routes to fabricate structural parts possessing higher hardness and strength. Hardness is the most dominant factor that affects the quality of structural parts. Laser power, scan speed, and hatch distance affect the microhardness of 17-4 PH stainless steel parts. Taguchi method is applied to conduct experiments and perform statistical analysis and optimization for higher microhardness of SLM parts. Laser power showed the highest contribution equal to 87.76%, followed by a scan speed of 12.05% and hatch distance of 0.18% towards microhardness. The Taguchi method determined the optimal conditions (laser power: 300 W, scan speed: 1000 mm/s and hatch distance: 0.08 mm) resulting in a higher microhardness value equal to 351.2 HV.