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Precipitation hardening (PH) stainless steels, such as 15-5PH, have a high strength combined with excellent corrosion resistance. These properties make them valuable in critical industries such as defence, construction, aerospace, energy and maritime. Recent advancements in additive manufacturing (AM) technology enable the rapid and cost-effective production of components. In the case of 15-5PH components manufactured using wire arc additive manufacturing (WAAM), the as-deposited mechanical properties are not suitable at present for industrial applications. This paper explores the mechanical properties of this process and alloy combination without post weld heat treatment with the aim of eventual adoption in this condition by industry. The impact of weld heat input on the microstructure and mechanical properties of stainless steel 15-5PH produced using WAAM was investigated. The microstructure was examined using hardness testing in addition to optical and electron microscopy. Furthermore, mechanical properties were measured with tensile and impact testing. Investigations were conducted on material produced using weld heat inputs of 0.223 kJ/mm and 0.565 kJ/mm. These results indicate that reducing the weld heat input leads to a minor decrease in strength but an 80% increase in impact toughness. This reduction in weld heat input is correlated with a 50% reduction in volume fraction of δ-ferrite while also noting a 55% increase in carbide precipitates. In addition, the fracture surfaces were predominantly cleavage or quasi-cleavage in morphology. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement (HE) of 1.4614 and 1.4543 maraging stainless steels is characterized with fine structural TEM-ASTAR, hydrogen electrochemical permeation, thermodesorption and tensile testing (with slow strain rate during H cathodic charging) experiments. Both solutions annealed and 550 °C aged states are studied. When aged, 1.4614 grade contains nanometric hexagonal Ni3Ti precipitates whereas 1.4543 grade contains three families of nanometric precipitates, namely, hexagonal Ni3Ti, non fcc-rich Cu and G-phase rich in Si, Ti and Ni with cube-cube relations with martensite. From the permeation and thermodesorption results, it appears that austenite and nanometric precipitates seem to constitute deep traps for hydrogen in both grades. From tensile tests with in situ H charging, 1.4614 and 1.4543 maraging grades show a high susceptibility to HE with relative reduction of area (RRA) strictly superior to 80% for both metallurgical states. The presence of retained austenite does not seem to bring any HE resistance because of its transformation into martensite during deformation. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement (HE) of 1.4614 and 1.4543 maraging stainless steels is characterized with fine structural TEM-ASTAR, hydrogen electrochemical permeation, thermodesorption and tensile testing (with slow strain rate during H cathodic charging) experiments. Both solutions annealed and 550 °C aged states are studied. When aged, 1.4614 grade contains nanometric hexagonal Ni3Ti precipitates whereas 1.4543 grade contains three families of nanometric precipitates, namely, hexagonal Ni3Ti, non fcc-rich Cu and G-phase rich in Si, Ti and Ni with cube-cube relations with martensite. From the permeation and thermodesorption results, it appears that austenite and nanometric precipitates seem to constitute deep traps for hydrogen in both grades. From tensile tests with in situ H charging, 1.4614 and 1.4543 maraging grades show a high susceptibility to HE with relative reduction of area (RRA) strictly superior to 80% for both metallurgical states. The presence of retained austenite does not seem to bring any HE resistance because of its transformation into martensite during deformation.

Precipitation hardening stainless steels have attracted extensive interest due to their distinguished mechanical properties. However, it is necessary to further uncover the internal quantitative relationship from the traditional standpoint based on the statistical perspective. In this review, we summarize the latest research progress on the relationships among the composition, microstructure, and properties of precipitation hardened stainless steels. First, the influence of general chemical composition and its fluctuation on the microstructure and properties of PHSS are elaborated. Then, the microstructure and properties under a typical heat treatment regime are discussed, including the precipitation of B2-NiAl particles, Cu-rich clusters, Ni3Ti precipitates, and other co-existing precipitates in PHSS and the hierarchical microstructural features are presented. Next, the microstructure and properties after the selective laser melting fabricating process which act as an emerging technology compared to conventional manufacturing techniques are also enlightened. Thereafter, the development of multi-scale simulation and machine learning (ML) in material design is illustrated with typical examples and the great concerns in PHSS research are presented, with a focus on the precipitation techniques, effect of composition, and microstructure. Finally, promising directions for future precipitation hardening stainless steel development combined with multi-scale simulation and ML methods are prospected, offering extensive insight into the innovation of novel precipitation hardening stainless steels. [ABSTRACT FROM AUTHOR]

3D-printed components have potential applications in the fabrication of complex parts because of their advantages such as low wastage and cost-effectiveness. However, the durability of additively manufactured metallic components is not comparable to that of conventionally fabricated components, owing to the defects introduced during fabrication. The effect of inclusions on the fatigue strength of additively manufactured metallic components has been extensively investigated using the Murakami model. However, the interaction between the defects and the typical microstructure fabricated by additive manufacturing is yet to be revealed, although the unusual heating history during the fabrication process considerably affects the microstructure. This study aims to reveal the synergistic effect of defects and microstructure on the fatigue strength of additively manufactured precipitation-hardened 17-4PH stainless steel. Fatigue tests were conducted on additively manufactured precipitation-hardened 17-4PH stainless steel. The fatigue limit estimated using Murakami's model revealed that the summed area of the defects with the surrounding aggregation region could provide a better prediction. The carbide aggregates, produced via heating/cooling during Powder Bed Fusion (PBF), promoted microcrack propagation. • The localized microstructure surrounding defects has carbide aggregation. • Heat treatment exaggerated carbide aggregation and reduce enhance element in matrix. • Brittle microcracks propagated from the defect promoted fatigue crack initiation. [ABSTRACT FROM AUTHOR]

Conventional and two-step heating transient liquid phase bonding (TLP) experiments of martensitic precipitation hardening stainless steel 17-4-PH were studied employing AMS 4777 braze filler at temperature of 1050 °C for different times (15 to 90 min) to accomplish the ideal brazing condition. The effect of TLP methods and bonding conditions on the microstructure and shear bond strength was investigated. The critical bonding time for isothermal solidification in conventional and two-step heating TLP was 60 min and 45 min, respectively. The microstructure of isothermal solidification zone consisted of Ni-rich solid solution phase. Eutectic constituents Cr-rich boride and Ni3Si were formed in the joint centerline in the athermally solidified zone. In the conventional method planar interface was formed, however in TLP bonding under temperature gradient non-planar interface was formed, high angel grain boundaries merged at the end of isothermal solidification and homogenous bond was produced. Due to the decrease of athermally solidified zone the shear strength increased by increasing the holding time and when using the two-step heating process because of better metal to metal contact, the shear strength was higher. The optimum condition was a temperature gradient TLP in 60 min bonding time, which led to shear strength of 435 MPa. [ABSTRACT FROM AUTHOR]

Precipitation hardening stainless steels have attracted extensive interest due to their distinguished mechanical properties. However, it is necessary to further uncover the internal quantitative relationship from the traditional standpoint based on the statistical perspective. In this review, we summarize the latest research progress on the relationships among the composition, microstructure, and properties of precipitation hardened stainless steels. First, the influence of general chemical composition and its fluctuation on the microstructure and properties of PHSS are elaborated. Then, the microstructure and properties under a typical heat treatment regime are discussed, including the precipitation of B2-NiAl particles, Cu-rich clusters, Ni3Ti precipitates, and other co-existing precipitates in PHSS and the hierarchical microstructural features are presented. Next, the microstructure and properties after the selective laser melting fabricating process which act as an emerging technology compared to conventional manufacturing techniques are also enlightened. Thereafter, the development of multi-scale simulation and machine learning (ML) in material design is illustrated with typical examples and the great concerns in PHSS research are presented, with a focus on the precipitation techniques, effect of composition, and microstructure. Finally, promising directions for future precipitation hardening stainless steel development combined with multi-scale simulation and ML methods are prospected, offering extensive insight into the innovation of novel precipitation hardening stainless steels.

The selective laser melting (SLM) process has gained considerable attention from industry and academia over the recent years. Furthermore, the hot isostatic pressing (HIP) technique has been widely applied as a post-treatment to increase the relative density of the fabricated parts. The main aim of this study is to investigate the effects of porosity elimination and mechanical properties on precipitation hardening stainless steel using SLM, HIP, solid-solution and aging treatments. This study also applied various laser scanning pitches (170, 210 and 250 μm), so that a significant phase transformation occurred between the SLM, HIP, solid-solution and aging treatments. The results showed that the laser scanning pitch was 170 μm, and after HIP, solid-solution and aging treatments the materials possessed optimal mechanical properties. The highest hardness (48.8 ± 0.5 HRC) and TRS (2247.0 ± 157.8 MPa) could be acquired. [ABSTRACT FROM AUTHOR]

The effects of Co element on the microstructure of precipitation hardening stainless steel was investigated by metallographic microscope (OM), transmission electron microscopy (TEM) and X-ray diffractometry (XRD), and the mechanical properties were measured by tensile, hardness and impact tests. The results show that with increasing Co content, the volume fraction of reversion austenite is increased. The precipitation of ε-Cu phase is remarkably decreased, leading to the improvement of ductility, while the strength and hardness are decreased. Co element improves the strength and toughness of stainless steel through fine-grain strengthening, solution strengthening and austenitic toughening. [ABSTRACT FROM AUTHOR]

Nanoscale Cu-rich precipitates (CRPs) are important to achieve high strength for the extensively applicated 17-4 precipitation hardening (PH) stainless steel (SS). Traditionally, the precipitation of CRPs requires high-temperature and long-time heat treatments. In this work, ultrasonic vibration (UV) was introduced into the laser direct energy deposition (L-DED) process to fabricate 17-4 PH deposits, a large density of nanoscale CRPs was directly and uniformly precipitated during depositing, the microstructure was also improved. Consequently, the mechanical properties of the deposit, both at the vertical and horizontal directions, were enhanced remarkably compared with those of the deposit manufactured by normal DED. Especially, the elongation was improved significantly, reached to around 20%. Moreover, the isotropy of mechanical property was improved, all the counterpart mechanical properties of the UV-DED sample were nearly close. This investigation supplied a potential method to mitigate the post heat treatments during fabricating 17-4 PH with L-DED. Graphical abstract [Display omitted] [ABSTRACT FROM AUTHOR]

High strength materials are of interest for hydrogen powered mobility where structural components can be exposed to high pressure (350–700 bars) of dihydrogen. However, high strength stainless steels such as 17-4 PH grade with a martensitic matrix are known to be more prone to hydrogen embrittlement (HE). The mechanisms affecting this type of grade have not been completely elucidated yet. In particular, in this work, the role of copper rich precipitates (Cu-pp) and reverted austenite (γ rev) on mechanical behavior in presence of hydrogen was investigated. At first, advanced structural characterizations (Synchrotron-XRD, ACOM/TEM) were performed on different metallurgical conditions. Then, hydrogen trapping ability of Cu-pp and γ rev was investigated using thermal desorption spectroscopy (TDS). Hydrogen embrittlement susceptibility was qualified through slow strain rate tensile testing. The results showed that the formation of tiny Cu-pp (< 10 nm) during ageing was deleterious for the HE resistance of the steel, since it increased the ultimate tensile strength. In addition to their role in the steel hardening, tiny Cu-pp actively trapped hydrogen at the Cu-pp/matrix interfaces. The nature of Cu-pp/matrix interfaces, which affects their surface energy and therefore the binding energy of hydrogen, impacted clearly the HE resistance. In particular, TDS experiments showed that tiny 'slightly coherent' Cu-pp acted as a low energy hydrogen trap contrary to tiny 'incoherent' fcc Cu-pp which strongly trapped hydrogen. The former was found to have a deleterious effect while the latter had a rather beneficial effect. Besides, a high fraction of reverted austenite was beneficial for the HE resistance since it softened the material, and trapped rather strongly hydrogen at the γ rev /matrix. The fcc (Cu-pp or γ rev)/martensitic matrix interfaces seemed to play a major role in hydrogen trapping in 17-4-PH stainless steel. When hydrogen is tightly bound to these interfaces, it happens to reduce the hydrogen embrittlement susceptibility of the material, 17-4 PH that is generally 'H fragile' because of its martensitic matrix. • 'Incoherent' Cu precipitates/α' and γ rev /α' interfaces trapped rather strongly H. • 'Coherent' Cu precipitates might increase HE susceptibility. • 'Incoherent' precipitates and reverted austenite might decrease HE susceptibility. [ABSTRACT FROM AUTHOR]

In the present study, effects of blade and shroud thickness profiles on the stress distribution and fatigue life of centrifugal compressor impellers are investigated. Impeller geometry is generated based on an available data of a single-stage centrifugal compressor and is simulated in actual operating conditions. Pressure distribution on the impeller blades is obtained using Computational Fluid Dynamics (CFD) simulation which is then incorporated into Finite Element (FE) structural analysis. Equivalent stress and total deformation contours on the impeller are employed to pinpoint critical areas and maximum stress values. Simulations are performed for multiple cases with various shroud and blade thickness values to capture the role of these important parameters in aeromechanical behavior of the structure. Furthermore, fatigue stress amplitude limit and fatigue-life are evaluated based on the results of the FE analyses. It will be demonstrated that semi-open configuration is the most desirable design from mechanical stress and fatigue-life viewpoints. For shrouded impellers, it is shown that the mechanical stress increases and fatigue life decreases with increasing the blade thickness while for the shroud thickness, there exist an optimal point with minimum stress level and maximum fatigue life. The methodology and results of this paper can be employed for other impellers with different geometries and operating conditions to find the optimal design points from the structural mechanics perspective. • A centrifugal compressor impeller is simulated in actual operating conditions using combination of CFD and FE analyzes • Stress and deformation distribution are obtained for various blade and shroud thickness cases. • Effects of shroud and blade thickness profiles is investigated on maximum equivalent stress and maximum total deformation. • Stress amplitude limit and fatigue-life are calculated for the impeller under different geometrical conditions. • An optimal shroud thickness is found which leads to the smallest maximum stress and highest fatigue-life. [ABSTRACT FROM AUTHOR]

In order to investigate the recrystallization behavior of peened surface deformation layer of precipitation hardening stainless steel, a classic x-ray diffraction line profile analysis, Voigt method, was carried out on peened 17-4PH with different isothermal annealing temperatures. The activation energy of domain boundary migration (Qa) and the activation energy of microstrain relaxation (Qb) were calculated by regression analysis in different annealing temperature conditions. The results show that the value of Qa decreases with annealing temperature increasing, which is due to the influence of precipitation (ε-Cu) size on the movements of grain and subgrain boundaries. The maximum growth rate of ε-Cu particles occurs during 400 to 500 °C interval. Compared with growth behavior of domain size, microstrain relaxation behavior is less sensitive to precipitation particle size. The effects of annealing temperature and time on dislocation density are both significant when annealing temperature is lower than 500 °C. However, the effect of annealing temperature on dislocation density becomes insignificant when annealing temperature is higher than 500 °C. 300 °C annealing temperature only leads to the microstrain relaxation but nearly cannot lead to the domain size growth even if prolonging annealing time. Microstructure enhancement effect still exists in plastic deformation layer when 300 °C annealing temperature lasts for 60 min but nearly disappears when 600 °C annealing temperature lasts for 20 min. [ABSTRACT FROM AUTHOR]

• The PHSS aged for 1 h has the best fatigue strength in VHCF regime. • Both inclusion and non-inclusion induced crack initiation mechanism were observed. • NIICI mechanism is due to the nucleation of the microvoids in δ-ferrite. • Interaction between Cu precipitates and dislocations affects fatigue properties. Very high cycle fatigue behavior of precipitation hardening stainless steel (PHSS) with various aging times was investigated. The PHSS aged at 480°C for 1 h exhibits the highest fatigue strength, followed by aged for 4 h and 0.5 h. Both subsurface or internal inclusion induced crack initiation (IICI) and non-inclusion induced crack initiation (NIICI) were observed. NIICI phenomenon is due to the nucleation and connection of microvoids within δ-ferrite. Aging treatment has an important influence on the dominant crack initiation mechanism by changing the interaction of dislocations and copper precipitates, which ultimately affects fatigue performance. [ABSTRACT FROM AUTHOR]

The Additive Manufacturing (AM) of high strength Stainless Steel (SS) metallic parts by Laser Powder Bed Fusion (L-PBF) process has been able to reduce cost and time significantly, leading to a successful adaption in various high technology industries. In this study, the static and dynamic mechanical properties of L-PBF 15–5 Precipitation Hardening (PH) SS in two different loading directions have been studied, and Laser Shock Peening (LSP) has been used as a post-processing tool to improve the part properties. Optimized parameters were chosen for the mechanical property evaluation based on the residual stress profile of the specimens subjected to LSP. Improvement in microhardness, uniaxial tensile properties and high cycle fatigue life due to LSP are reported. With LSP applied on vertically loaded L-PBF 15–5 PH SS specimens (loading axis parallel to building direction), the fatigue life has increased by more than four times, making it comparable to horizontally loaded L-PBF 15–5 PH SS base specimens. Thus, the viability of the LSP process as a post-processing technique to mitigate the fatigue life anisotropy due to loading direction has been established. The associated microstructure and phase analysis revealed an increased depth of plastic deformation with successive LSP shots without causing any phase changes. The central strengthening mechanisms for the enhancement of mechanical properties of L-PBF 15–5 PH SS due to LSP are reported. [Display omitted] • Low angle grain boundaries increased with the LSP shots indicating lath-impeded dislocations in the grain structure. • In 2 mm thick specimens subjected to LSP, nearly 40% of the thickness transformed to compressive residual stress state. • Fatigue life of the vertically loaded L-PBF 15–5 PH SS specimens increased by more than 4 times with the LSP. • Significant improvement in static mechanical properties with multiple shots LSP process. • LSP could be a potential post-processing tool for mitigating the anisotropy in the fatigue life of AM parts. [ABSTRACT FROM AUTHOR]

Precipitation hardening maraging steels possess of great importance with attractive properties in various industrial applications. However, a major confusion about the fine precipitate evolutions and the relationships between the strengthened particles and mechanical properties of PH13–8Mo steels under various heat treatment conditions remains to be further investigated. To shed light on the direct relationships between the fine nano-phase and mechanical properties, a combination of thermodynamics predictions and experimental measurements were carried out to model the issues. The investigation results reveal that the coherent NiAl nano-precipitates distributed on the lath-like martensite matrix firstly presented a steady growth and then a significant coarsening of approximately 9 nm at 593 °C for 5 h. The acicular or block-like diffusion-controlled reverted austenite enriched in Ni element with a tendency of growth was clarified, which maintains the K–S orientation relationship with martensite matrix after diverse aging treatments. The current studied PH13–8Mo steel displays comparable mechanical properties despite over-aging conditions, and the sharp drops in hardness and the steady increment in impact energy were systematically examined. The excellent work hardening behaviors of the present steel were modeled, which indicates that the modified Ludwik model displays significantly improved agreement with the experimental data than the widely accepted Hollomon model. The five strengthening mechanism models are discussed and the C–O-M model exhibits high consistency with the experimental data with a value of 652 MPa. The growth of nano-precipitates maybe prohibits the dislocations from cutting the particles, which promotes the hardening behaviors. This work offers a valuable reference for further quantitively experimental illustrates. • The present investigated PH13–8Mo steel displays promising balanced mechanical properties despite over-aging conditions. • The modified Ludwik model is more suitable to predict the work hardening behavior. • The fine NiAl precipitate evolutions under various heat treatment are systematically investigated. • The current estimation results of the C–O-M model exhibit strong applicability to the tensile yield strength after the five strengthening mechanisms' discussion. [ABSTRACT FROM AUTHOR]

The recent interest for dihydrogen concerning its ability to decarbonize numerous sectors of our society highlighted the necessity to develop alloys combining high mechanical properties and good resistance to hydrogen embrittlement. With this in mind, the 17–4 PH precipitation hardened stainless steel was studied in order to understand the interactions between hydrogen and the different microstructural elements. Advanced physicochemical characterizations (XRD, SEM, ACOM/TEM) were coupled with electrochemical permeation tests on different metallurgical states of 17–4 PH alloy. The apparent hydrogen diffusivity was around 10−13 m2.s−1 at 23 °C and was found highly dependent on the microstructure. More specifically, when copper precipitates were fine, the copper precipitates/matrix interfaces were found to be the major trapping site. In addition, nature of these interfaces, which can be varied depending on thermal treatments, seemed to influence reversibility of the trapping. • Five heat treatments had been applied to 17–4 PH to obtain various microstructures. • Advanced characterizations coupled with electrochemical permeation were conducted. • Cu precipitates and martensitic matrix orientation relationships are highlighted. • Cu/matrix interfaces act as major H trapping sites for tiny precipitates (~10 nm). [ABSTRACT FROM AUTHOR]

Hydrogen diffusivity in Custom 465 ® martensitic precipitation hardened stainless steel is determined using electrochemical permeation tests. Hydrogen diffusivity in the solution annealed (SA) condition is approximately 10 times higher than in the aged H900 (480 °C, 4 h) condition because of hydrogen traps such as Ni 3 Ti nano-precipitates and reverted austenite. The microstructure of the alloy is characterized by TEM, XRD and ESEM/EBSD, both in the aged H900 and in the SA conditions. In the aged condition, η-Ni 3 Ti nano-precipitates with hexagonal structure and a rod-like shape are observed. In addition, reverted austenite is found at grain boundaries and inter-lath interfaces. In the SA condition, these microstructural features are not evident, which may explain the higher diffusivity measured. The diffusivity is almost unaffected by prior microplastic deformation of H900. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of a duplex plasma nitriding followed by an oxidizing stage process (which is also referred as oxy-nitriding) on the corrosion behavior of a 17-4PH precipitation hardening stainless steel. The formation of both, expanded martensite (b.c.t. α′-phase) and chromium oxide (type CrO) in the subsurface of oxy-nitrided samples at specific controlled conditions, leads in a noticeable increasing in the time-to-rupture during the sulfide stress cracking test, in comparison with an untreated reference sample. Oxy-nitriding improves the corrosion performance of the alloy when it is immersed in solutions saturated by sour gas, which extends the application potential of this type of steel in the oil and gas extraction and processing industry. The presence of the oxy-nitrided layer inhibits the corrosion process that occurs in the near-surface region, where hydrogen is liberated after the formation of iron sulfides, which finally produces a fragile fracture by micro-crack propagation; the obtained results suggest that oxy-nitriding slows this process, thus delaying the rupture of the specimen. Moreover, oxy-nitriding produces a hard, sour gas-resistant surface, but do not significantly affect the original chloride ion solution resistance of the material. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the tribological behavior and adhesion of SiNx films deposited by PACVD on nitrided and non-nitrided Corraẍ PH stainless steel were evaluated. The films were characterized by FTIR and EDS, hardness was assessed with a nanoindenter and the microstructure was analyzed by Optical Microscopy, SEM and FIB. To evaluate the tribological behavior, fretting and linear sliding tests were performed using WC and alumina balls as counterparts, and the adhesion of the SiNx films was characterized using the Scratch Test and Rockwell C indentation methods. Erosion tests were conducted in sea water and sand flux. Corrosion behavior was evaluated by the Salt Spray Fog Test. The film reached a hardness of 2300 HV and a thickness of about 1.4 microns. The duplex coated sample had a better tribological behavior than the simple coated sample, the nitrided layer allowed a graded interlayer which improved the wear resistance. Regarding the film adhesion, the duplex coating had an acceptable adhesion; the nitrided layer reduced the interface stress and enhanced the adhesion. Additionally, the films evidenced good corrosion resistance in a saline environment. [Copyright &y& Elsevier]

A novel type of martensitic precipitation hardening stainless steel, Fe-12Cr-9Ni-2Al steel (CX steel), was successfully fabricated via selective laser melting (SLM) technology. The influence of the heat treatment regime on the surface microstructure, high-temperature oxidation resistance and tribological properties of the SLM Fe-12Cr-9Ni-2Al steel was studied. A series of vacuum heat treatment methods including austenitizing treatment and tempering treatment were determined by means of a differential scanning calorimetry (DSC) method. Reverted austenite (γ-Fe phase) would be induced by tempering treatment to generate along the martensite (α′-Fe phase) grain boundaries. During a 400 °C high-temperature oxidation experiment, a loose oxide layer consisted of Al 2 O 3 , Cr 2 O 3 and Fe 3 O 4 was formed on its surface. A high-temperature oxidation process model was put forward to illustrate this phenomenon. After austenitizing-tempering treatment, massive nano-NiAl precipitates enhanced the hardness of the SLM CX steel from 356 ± 14.3 HV 0.2 in the as-built state to 527 ± 5.2 HV 0.2 in the austenitizing-tempering treated state. Correspondingly, the coefficient of friction (COF) and wear rate of the SLM Fe-12Cr-9Ni-2Al steel samples decreased from 0.58 and 16.1 ± 3.1 × 10−5 mm3/(N·m) in the as-built state to 0.49 and 8.1 ± 3.3 × 10−5 mm3/(N·m) in the austenitizing-tempering treated state, respectively. [Display omitted] • The heat treatment regime of the SLM CX steel is determined by the DSC method for the first time. • The high-temperature oxidation behavior of SLM CX steel is systematically studied. • The tribological behavior and wear mechanisms of the SLM CX steel are clarified. [ABSTRACT FROM AUTHOR]

Abstract: Results of the investigation of nitrided layers on 17-4 PH type precipitation hardening stainless steel are presented in this paper. The layers have been produced in the process of gas nitriding in a partly dissociated ammonia at temperatures between 410 and 570 °C. Hydrogen chloride admixture to active atmosphere was used as a surface activator. Structure of the nitrided layers were examined using scanning and transmission electron microscopy, X-ray microanalysis (EDX and WDX), and X-ray diffraction. The influence of the initial steel heat treatment on the nitriding kinetics has been considered. 17-4 PH stainless steel was nitrided at various heat treatment conditions, i.e. after solution treatment or ageing at different temperatures. The influence of precipitation processes taking place during the heat treatment before nitriding on the diffusive process kinetics was proven. It was found that, that increasing of steel ageing temperature up to 600 °C before nitriding effects on an increasing of the nitriding kinetics. [Copyright &y& Elsevier]

Abstract: Systematic microstructure characterisation of plasma nitrided (350–500 °C for 10 to 30 h) 17-4PH alloy was carried out using SEM, XRD and TEM. Experimental results have shown that the microstructure and phase constituents of the plasma surface alloyed cases are highly treatment temperature dependent. When treated at low-temperatures (≤420 °C), the microstructure is dominated by nitrogen supersaturated martensite (α''N-expanded martensite); Nitrogen S-phase grains can be formed from the pre-existent retained austenite by converting the retained austenite grains in 17-4PH but no continuous S-phase layer was found. When treated at high-temperatures (above 420 °C), a surface γ′–Fe4N compound layer was formed, CrN precipitated and S-phase was decomposed. [Copyright &y& Elsevier]

Abstract: This article addresses simultaneous bulk precipitation hardening and low temperature surface engineering of two commercial precipitation hardening stainless steels: Sandvik Nanoflex® and Uddeholm Corrax®. Surface engineering comprised gaseous nitriding or gaseous carburising. Microstructural characterisation of the cases developed included X-ray diffraction analysis, reflected light microscopy and micro-hardness testing. It was found that the incorporation of nitrogen or carbon resulted in a hardened case consisting of a combination of (tetragonal) martensite and expanded (cubic) austenite. The duration and temperature of the nitriding/carburising surface hardening treatment can be chosen in agreement with the thermal treatment for obtaining optimal bulk hardness in the precipitation hardening stainless steel. [Copyright &y& Elsevier]