PH Steel Research Articles

Technical Note: Hardness, Corrosion Behavior, and Microstructural Characteristics of a Selective Laser Melted 17-4 PH Steel

In this work, we report the hardness and corrosion behavior of a selective laser melted 17-4 PH steel. Microstructure analysis using a scanning electron microscope (SEM) revealed a fine-grained material with a grain size of 1 μm. Phase analysis using SEM-EBSD (electron backscatter diffraction) revealed a ferritic-austenitic microstructure with 96% ferrite and 4% austenite. The material was also found to bear a combination of <001> and <111> fiber texture. The grain boundary character distribution revealed 68% low-angle grain boundaries, 10% CSL boundaries with predominantly Σ3 boundaries, and 21% high-angle grain boundaries. The Vickers hardness of this material was found to be quite high at 3.66±0.17 GPa which is probably due to the fine-grained structure of the material. Potentiodynamic polarization tests in 3.5 wt% NaCl solution yielded a corrosion current density, icorr of 1.4 × 10−6 A/cm2 and corrosion potential, Ecorr of −55 mVAg/AgCl electrode. Immersion tests in salt water for a period of 96 h showed hardly any pit formation although an AISI 304 stainless steel bearing grain size of 29 μm showed significant pit formation during the same time period.

Bonding integrity of hybrid 18Ni300-17-4 PH steel using the laser powder bed fusion process for the fabrication of plastic injection mould inserts

Laser powder bed fusion (LPBF) is a metal additive manufacturing (AM) process for fabricating high-performance functional parts and tools in various metallic alloys, such as titanium, aluminium and tool steels. One specific AM application is fabricating conformal cooling channels (CCC) in plastic injection moulding tool inserts to improve cooling efficiency. This article reports the development of a novel hybrid powder-wrought alloy steel combination intended for injection mould inserts use. In this investigation, cylindrical parts made of 18Ni300 steel powder and wrought 17-4 PH steel were additively fabricated using a hybrid-build LPBF AM technique, followed by various post-build heat treatments. Standard mechanical and microstructural techniques were employed to examine the bonded powder-substrate interface. Microstructure analysis revealed defect-free, fully dense, homogenous powder-substrate fusion across a 280-µm-thick region. Tensile tests confirmed strong powder-substrate bonding due to solid solution strengthening within the region. All tensile fractures were ductile under all heat treatment conditions and occurred about 8 mm from the interface, at the side where the materials were of lower strength. The hybrid-built parts exhibited an ultimate tensile strength of 1009–1329 MPa, with 16.1–17.4% elongation at fracture. Hardness values on the AM-deposited and substrate sides were 31–55 HRC and 32–43 HRC, respectively. A direct post-build 490 °C/1 h age-hardening treatment achieved the best combination of hardness, tensile strength and ductility. The overall result demonstrates that hybrid-built powder 18Ni300-wrought 17-4 PH steel can be a material choice for manufacturing durable and high-performance injection mould inserts for high-volume production.

Lattice structures in stainless steel 17-4PH manufactured via selective laser melting (SLM) process: dimensional accuracy, satellites formation, compressive response and printing parameters optimization

By the term, lattice structures are intended topologically ordered open-celled structures consisting of one or more repeating unit cells. Technological development and especially the growth of the additive manufacturing (AM) industry allows innovative structural design, including complex lattice structure. Selective laser melting (SLM) is an AM process that enables the manufacture of space filling structures. This work investigated the influence of the most important process parameter settings on lattices printability, focusing on the geometrical accuracy, the quantity of powders adhered to the main frame (satellites) and their compression behaviour. The process parameters such as the laser power, scan speed and layer height affect vigorously the design, quality and mechanical properties of the part. The aim of the paper is to evaluate how different parameter combinations affect the cellular structures’ printing. Twenty-four lattice structures with cubic and rhombic dodecahedron unit cells made of stainless steel 17-4PH (AISI-630) were printed using different combinations of SLM process parameters. Each structure was analysed considering its geometrical, topological and mechanical properties. Finally, the best parameter combination was evaluated comparing results achieved. Although this work investigated the 17-4PH stainless steel, physical principles related to the printing process described are generally true for the SLM process. Therefore, the adopted approach could still be suitable also for all the other materials commonly used with this AM technology.

Near Net Forming Process Optimization of 17-4PH Steel Based on High Temperature Deformation Behaviour and Microstructure Control

In this paper, the high temperature deformation behaviour of 17-4PH steel was studied. A new forming optimization method was proposed. The study will help guide the obtainment of high-precision and high-mechanical properties forging products in the aerospace industry. A hot compression test was carried out on a Gleeble1500D test machine (DUFFERS SCIENTFIC, Beijing, China). The stress–strain behaviour at a temperature of 1000 °C~1150 °C and strain rate of 0.1~10 s−1 was analysed. Through the analysis of multiple heating tests, we come to the conclusion that the heating times should be controlled within 1 or 2 times in order to obtain a grain size above grade 6. Optimization analysis of the forming process was carried out to shorten the process and ensure the precision of the product. The preform shape was obtained quickly by fourth-order curve fitting. According to the method of finite element numerical simulation, the near net forming process within two heating procedures was determined. A 17-4PH forging product with precise shape and qualified structure was obtained through actual forming test.

On the Short-Term Creep Response at 482 °C (900 °F) of the 17-4PH Steel Produced by Bound Metal Deposition

The creep response of the 17-4PH precipitation hardening steel produced by a new additive manufacturing technology (Bound Metal Deposition) was investigated at 482 °C (900 °F), under stresses ranging from 350 to 600 MPa. Two different sets of samples produced with different deposition parameters were considered. Prior heat treatment consisted of ageing either at 482 °C (state H900) or at 621 °C (H1150). The minimum creep rate and time to rupture dependencies on applied stress were obtained. The creep response in terms of time to rupture under a given stress, in particular, was compared with the only other available literature dataset on a similar steel processed by traditional technologies. The analysis of the experiments demonstrated that the presence of dispersed defects causes, in the Bound Metal Deposited steel, a substantial reduction (35–40%) of the creep strength.

Effect of Solution Temperature on the Microstructure and Properties of 17-4PH High-Strength Steel Samples Formed by Selective Laser Melting

Samples of 17-4PH high-strength steel were processed by selective laser melting (SLM) and solution-processed. The effects of the solution temperature on the microstructure and mechanical properties of the samples were studied. The 17-4PH high-strength steel is primarily composed of martensite, with a small number of austenite phases, and contains many dislocations. After the solution treatment, the grain size gradually increased, yielding typical martensite. The samples were subjected to an aging treatment after the solution treatment. Precipitates formed in the samples, conducive to improving their strength and hardness. The Vickers hardening and wear properties of the 17-4PH high-strength steel samples first increased and then decreased with increasing solution temperature. After the solution treatment at 1040 °C for 2 h and aging at 480 °C for 4 h, the Vickers hardening of the 17-4PH high-strength steel increased to 392 HV0.5, and the friction coefficient was approximately 0.6. These values were, respectively, 7% and 5% higher than those for the untreated samples.

Fatigue life optimization for 17-4Ph steel produced by selective laser melting

PurposeThe mechanical characterization of selective laser melting (SLM) parts is an industrial challenge. This paper aims to propose a methodology to control the fatigue life of 17-4Ph stainless steel by selecting the most relevant manufacturing parameters: i.e. laser power, laser travel speed, hatch spacing and laser defocusing.Design/methodology/approachA rough and refined design of experiment (DOE) is carried out to target the best combination of process parameters. A response surface model is then constructed to predict the parameter combination that optimizes the fatigue performance.FindingsThis study results show that the fatigue limit of the specimens manufactured by SLM (471.7 MPa at 107 cycles) has reached near 90% of the value found in samples machined from a bar. This demonstrates the applicability of the method proposed to optimize the SLM process and control the fatigue life of 17-4Ph stainless steel. The study results are compared with other research works and provide an increase of 18% to the fatigue limit.Originality/valueThis study showcases a DOE methodology to optimize the SLM parameters to achieve fatigue performance as great as that of solid 17-4Ph stainless steel.

Failure in an AISI 17-4PH steel component caused by stress corrosion cracking: Case study

Failure in an AISI 17-4PH steel component caused by stress corrosion cracking: Case study

Effect of Aging Treatment on Toughness and Hardness Behavior in Custom 450 PH Steel

Effect of Aging Treatment on Toughness and Hardness Behavior in Custom 450 PH Steel

Transient Phase-Driven Cyclic Deformation in Additively Manufactured 15-5 PH Steel.

The present work extends the examination of selective laser melting (SLM)-fabricated 15-5 PH steel with the 8%-transient-austenite-phase towards fully-reversed strain-controlled low-cycle fatigue (LCF) test. The cyclic-deformation response and microstructural evolution were investigated via in-situ neutron-diffraction measurements. The transient-austenite-phase rapidly transformed into the martensite phase in the initial cyclic-hardening stage, followed by an almost complete martensitic transformation in the cyclic-softening and steady stage. The compressive stress was much greater than the tensile stress at the same strain amplitude. The enhanced martensitic transformation associated with lower dislocation densities under compression predominantly governed such a striking tension-compression asymmetry in the SLM-built 15-5 PH.

Nonlinear analysis of compressive behavior of 17-4PH steel structures with large spherical pores built by selective laser melting

Nonlinear analysis of compressive behavior of 17-4PH steel structures with large spherical pores built by selective laser melting

Experimental analysis of the impact of an artificially generated tool wear pattern on the residual stress induced by 15-5PH steel turning

Finish turning is one of the key operations governing the residual stress of functional surfaces. The residual stress state is determined by the cutting conditions and the selected cutting tool system (macro geometry, cutting edge preparation, tool substrate, multi-layer coating…). However, this initial configuration evolves over time due to tool wear. Therefore, it seems very instructive to reproduce the wear process of the tool in order to understand the evolution of thermo-mechanical loadings applied to the machined surface. Flank wear is a parameter which can be difficult to fully control, and it is complex to reproduce experimentally. In this work, a simple, controlled and repeatable method of producing a known flank wear state is introduced and the impact of the flank wear on the surface integrity is assessed. This involves two parts, first reproducing a given flank wear state and second, evaluating experimentally the residual stress induced by the flank wear state on the workpiece. Carbide tools are used to turn 15-5PH steel under dry conditions. It is shown that the method produces consistent results. The effect of flank wear on residual stress is most notable and can generate data to validate numerical modelling. Areas for improving the method are also discussed.

Microstructures and hydrogen embrittlement fracture mechanisms in 17-4PH martensitic stainless steel

Martensitic stainless steel 17-4PH is a precipitation hardening material with a combination of high strength and good ductility and has been widely used in various modern industries. However, it is also susceptible to hydrogen embrittlement in some environments. In this paper, susceptibility to hydrogen embrittlement in this material with different conditions has been studied using a slow strain rate tensile test with an in-situ electrochemical hydrogen charging. By fracture and microstructure analysis, the hydrogen embrittlement mechanisms have been evaluated. It was found that the 17-4PH steel in the solution annealed condition is susceptible to hydrogen embrittlement. Hydrogen-enhanced decohesion (HEDE) is the main hydrogen embrittlement mechanism. Tempering at 510°C reduces susceptibility to hydrogen embrittlement by precipitation of different nano precipitates, mainly nano Cu rich phase and nano austenitic phase. This also leads to a transition of hydrogen embrittlement mechanism from HEDE to HELP (hydrogen enhanced localized plasticity). A synergetic effect of HELP and HEDE has been observed. This work increases the knowledge to reduce and finally avoid susceptibility to hydrogen embrittlement in 17-4PH steel material.

Architectured Metamaterial Structural Lattices by Laser Powder-Bed Fusion of 17-4PH Steel

Architectured Metamaterial Structural Lattices by Laser Powder-Bed Fusion of 17-4PH Steel

Processing of 17-4 PH steel in turning operation with hybrid textured tools

ABSTRACT Surface modification on the cutting tools (textured tools) emerged as an efficient machining technique that engages high productivity and avoids the cost associated with coolants. However, textured tools performance is significantly influenced by the type of texture design and geometry of the texture. Moreover, more research is available only on the performance of single pattern textured pattern tools. In this context, the novel hybrid textured tools were fabricated in the present research and investigated its cutting mechanism in turning of 17–4 precipitated hardened stainless steel (PH SS) materials under dry and conventional method (flood) cooling conditions respectively. Results of the current study indicate that hybrid textured tools under conventional cooling significantly minimized the cutting zone temperature (T), tool wear and surface roughness (Ra) to a maximum of 43%, 42% and 45%, respectively, over the dry cutting conditions. Further, tool wear analysis revealed that adhesion wear mechanism was observed in hybrid textured tools under both dry and wet cooling conditions, respectively. Furthermore, favorable chips were observed in hybrid tools under conventional cooling conditions that resulted in low cutting temperatures. As a whole, microgrooves act as lubrication storage sites.

Additive manufacturing of 17–4 PH steel using metal injection molding feedstock: Analysis of 3D extrusion printing, debinding and sintering

The amalgamation of 3D extrusion printing (3DEP) and sintering results in a low-cost process compared to other laser-based additive manufacturing techniques. This work used metal injection molding (MIM) raw material of 17–4 PH steel for additive manufacturing. The 3D printing, debinding, and sintering steps were thoroughly evaluated to achieve the highest sintered density. First, the 3DEP of the MIM feedstock was carried out using a screw-based extrusion system at optimum parameters to acquire the high green density and fine surface roughness. The solvent debinding step was carried out on 3D printed samples to remove water-soluble polymer by immersion method. Thermogravimetric analysis was performed to evaluate the decomposition temperature of the backbone material. Further, thermal debinding and sintering steps were conducted in a single step. The thermal debinding temperature was 500 ℃ , and the sintering temperatures were chosen as 1100, 1200, 1300 and 1360 ℃ . The highest density of ~95.6% was attained at a high sintering temperature. The micro-tomography evaluation was carried out on the 3D printed green and high-density sintered samples to evaluate the internal porosity. The mechanical properties and the microstructure were also evaluated for sintered samples. The work opens a way to fabricate metal complex-shaped parts at low cost using market available MIM feedstock.

Ultra Low-Cycle Fatigue Behavior Comparison between Additively Manufactured and Rolled 17-4 PH (AISI 630) Stainless Steels

This study investigates the mechanical behavior of additively manufactured (AM) 17-4 PH (AISI 630) stainless steels and compares their behavior to traditionally produced wrought counterparts. The goal of this study is to understand the key parameters influencing AM 17-4 PH steel fatigue life under ULCF conditions and to develop simple predictive models for fatigue-life estimation in AM 17-4 steel components. In this study, both AM and traditionally produced (wrought) material samples are fatigue tested under fully reversed (R = −1) strain controlled (2–4% strain) loading and characterized using micro-hardness, x-ray diffraction, and fractography methods. Results indicate decreased fatigue life for AM specimens as compared to wrought 17-4 PH specimens due to fabrication porosity and un-melted particle defect regions which provide a mechanism for internal fracture initiation. Heat treatment processes performed in this work, to both the AM and wrought specimens, had no observable effect on ULCF behavior. Result comparisons with an existing fatigue prediction model (the Coffin–Manson universal slopes equation) demonstrated consistent over-prediction of fatigue life at applied strain amplitudes greater than 3%, likely due to inherent AM fabrication defects. An alternative empirical ULCF capacity equation is proposed herein to aid future fatigue estimations in AM 17-4 PH stainless steel components.

Role of Retained Austenite in Corrosion Resistance of Si-Mn Steel

Si-Mn steels are used for many industrial applications because of their high strength. One of the most important characteristics of the microstructure of Si-Mn steels is the retained austenite embedded in the matrix of martensite or bainite. The existence of the retained austenite promotes TRIP (Transformation-Induced Plasticity) effect, and therefore, provides Si-Mn steels with their excellent strength. While the retained austenite has the beneficial effect on the mechanical properties, corrosion mechanisms of the steels with the retained austenite have been unclear. In reality, the actual application of high-strength steels almost always involves outdoor corrosion environments which can be characterized as predominantly near-neutral pH environments with chloride ions. Even if the steels are successfully protected from corrosion by coating and/or painting, pitting corrosion readily occurs at the cut edges and in coating defect areas due to the presence of chloride ions. In this research, the objective is to clarify the effect of the retained austenite on the corrosion resistance of the Si-Mn steel in near-neutral pH environments.The specimens were Si-Mn steel (0.39%C, 1.51%S, 2.01%Mn, 0.010%P, 0.002%S, 0.04%Al, 0.004%N). The metallographic inspection was performed to ascertain the characteristics of the microstructure of the specimen by using EPMA (Electron Probe Micro Analyzer). It was confirmed that the microstructure consisted of the retained austenite and the matrix of martensite. To assess the corrosion behavior of the specimen, immersion tests were performed in the boric-borate buffer solutions with NaCl (pH 7.0). It was confirmed that the pits were initiated only in the matrix and not in the retained austenite.To clarify the reason for the high corrosion resistance of retained austenite, the corrosion behavior of two types of specimens were compared: Full martensitic specimen (0.44%C, 0.20%S, 0.85%Mn, 0.008%P, 0.002%S, 0.035%Al, 0.003%N) and full austenitic specimen (0.45%C, 0.32%S, 29.40%Mn, 0.014%P, 0.002%S, 0.025%Al, 0.005%N). In the case of the austenitic specimen, higher amount of Mn was added to form full austenitic structure even at room temperature. The austenitic and martensitic specimens simulated the retained austenite and matrix phases in the Si-Mn steel. The depassivation pH values of the austenitic and martensitic specimens were measured in boric-borate buffer solutions. The pH of the solution was decreased stepwise with 0.35 M H3BO3, and the open circuit potentials were measured. It was confirmed that the depassivation pH of the austenitic specimen was lower than that of the martensitic specimen. In other words, the depassivation occurred more readily on the martensite than the austenite. AES (Auger Electron Spectroscopy) depth analysis was performed to investigate the thickness of the surface oxide films on the austenitic and martensitic specimens. It was clarified that the oxide film on the austenite was about 1 nm thicker than that on the martensite, suggesting that the protective ability of the oxide film formed on the austenite is higher than that on the martensite. According to the above results, the high corrosion resistance of the retained austenite in Si-Mn steels appeared to be related with the nature of the oxide film formed on the austenite.

Wear of 17-4 PH Stainless Steel Patterned Surfaces Fabricated Using Selective Laser Melting

The recent developments in additive manufacturing (AM) are providing unprecedented opportunities in various fields, including the fabrication of advanced materials for tribological applications. The present work describes the results of an exploratory study focused on the analysis of 17-4 PH steel surfaces obtained using selective laser melting (SLM). In particular, the study includes the analysis of baseline (as-produced) and textured steel surfaces. Surface texturing comprises hexagonal prism structures (with or without dimples) arranged in a honeycomb pattern with 50 µm or 100 µm gap spacing. Starting from the minimum printing size enabled by the 3D printing platform, various textures are prepared by scaling up the characteristic dimensions of the prisms up to 500%. The obtained surface patterns are characterized (qualitatively and quantitatively) using a non-contact computerized numerical control (CNC) measuring system. The coefficient of friction (COF) was investigated using a Ball-on-Disk configuration using bearing steel balls as counterparts. For a fixed sliding speed, different contact loads and sliding radii were considered, while the tests were carried out in either dry or lubricant-impregnated conditions. The results of wear tests in both dry and lubricated conditions indicated that the baseline samples are provided with lower COF compared to the textured ones. For the latter, neither the gap spacing nor the presence of dimples led to significant variations in the COF. However, in lubricated conditions, the values of the COF for baseline and textured surfaces were closer and much smaller. In particular, the results provide clear indications regarding reducing the gap between prisms, which had a beneficial effect on the COF in lubricated conditions. Similarly, sensitivity to dimples was quite remarkable, with a reduction in the COF of about 30% when the larger gap spacing between the prisms was used.

Optimization of Parameters and Prediction of Response Values Using Regression and ANN Model in Resistance Spot Welding of 17-4 Precipitation Hardened Stainless Steel

17-4[Formula: see text]PH steel, also known as UNS 17400 steel or called SAE type 630 stainless steel, is a very important category of steel which has tremendous and extraordinary properties. The superior properties include high corrosion resistance, high hardness and high strength due to the conversion or phase change of the austenite to martensite by cooling the material to room temperature after heating to a temperature around 1030[Formula: see text]C. Normally, this procedure is called as precipitation hardening and hence the name. Due to its extensive properties, the 17-4[Formula: see text]PH steel finds its applications in a variety of industries including pump shafts, oil path, mechanical seals, and within the aerospace industry, parts of the aircrafts, chemical industries and petroleum industries. When a material is used in any kind of applications, fastening is the major process involved. Hence, there should be a standard welding procedure involved in generating a permanent fastening. In this work, resistant spot welding is considered as the welding process and the major parameters are considered which have a crucial effect on the whole process. The responses are considered to be the nugget diameter and tensile strength which denote the weld quality majorly. The process parameters with the help of literature are considered and they are electrode force, voltage and weld current. Taguchi method is used to design the experiments along with the NN tool to generate and predict the new response values. The results show that the major affecting factor is electrode force followed by current and then the voltage. Comparison is done to choose a better model for predicting the optimum responses with the given values of the input parameters. The results are pretty much accurate for both but still the regression model yields better results and almost similar values to the experimental values. Therefore, better results can also be obtained by ANN model by continuous training of the model.