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The phase transitions in selective laser-melted 18-NI (300-grade) maraging steel
摘要： Dilatometric studies in 18-Ni steel components fabricated by selective laser melting technique were carried out to determine the influence of heating rate on transitions occurring during the heating cycle. SLM components have been examined in controlled heating and cooling cycles. For analysis, heating of the analysed materials was carried out at heating rates of 10, 15, 20, 30 and 60 °C min?1. During the heating process, two solid-state reactions were identified—i.e. precipitation of intermetallic phases and the reversion of martensite to austenite. A simplified procedure based on the Kissinger equation was used to determine the activation energy of individual reactions. For precipitation of intermetallic phases, the activation energy was estimated 301 kJ mol?1, while the martensite to austenite reversion was determined at the activation energy 478 kJ mol?1.
关键词： Precipitation,Martensite reversion,Phase transitions,Maraging steels
更新于2025-09-23 15:21:01
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Enhancement of the surface properties of selective laser melted maraging steel by large pulsed electron-beam irradiation
摘要： The present work aimed to decrease the surface roughness of maraging steel (MS) by selective laser melting (SLM) using large pulsed electron-beam (LPEB) irradiation as a post-treatment. The MS samples were fabricated using different combinations of laser power, scanning speed, hatch distance, and build angle. The morphological features, surface roughness, phase content, and corrosion resistance of the MS samples in their as-fabricated (ASF) state were compared after LPEB irradiation. The ASF SLM-MS samples exhibit the presence of partially melted particles that spread over the entire surface and many cracks in both the longitudinal and transverse directions. A higher arithmetical mean height (Sa: 2-17 μm), large variations in Sa measured at various locations, and a strong dependence of Sa on build angle were also observed. Post-treatment by LPEB irradiation removed the partially melted particles, while reflow of the molten mass filled the cracks and voids and facilitated the formation of a uniform surface with a bright metallic finish. This has resulted in a significant decrease in Sa (0.50-4.50 μm) and a smaller variation in Sa measured at different locations. Body-centered cubic α-martensite was the predominant phase for the ASF SLM-MS samples, along with a small fraction face-centered cubic γ-austenite phase. After LPEB irradiation, the martensite was reverted to the austenite phase. The corrosion resistance of the LPEB-irradiated samples was moderately better than that of the ASF SLM-MS samples. The uniform surface morphology, removal of partially melted particles, absence of pores and cracks, decrease in Sa, and moderate improvement in corrosion resistance suggests that LPEB irradiation can be used as a post-treatment for SLM-MS samples.
关键词： corrosion resistance,large pulse electron beam irradiation,maraging steel,Selective laser melting,surface roughness
更新于2025-09-23 15:19:57
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Hardening Effects of In-Situ Aging for a Laser Welded Maraging Steel
摘要： Maraging steels are ultra-high strength alloys which have been successfully laser welded to obtain structural components. For most of the applications these steels are in an aged state to attain tensile strength up to 1.5 GPa, although welding induces local softening due to dissolution of precipitates. This paper aims to investigate the effect of in-situ aging of the maraging steel plates after laser welding to reduce the local softening. For a preheating at 40°C, just below the martensite finish line, the hardness of the Fusion Zone (FZ) attained between 440 and 490 HV and the Heat-Affected Zone (HAZ) attained a maximum of 570 HV compared to 300 HV of the Base Material (BM) for aging temperatures between 450°C and 520°C and periods between 10 and 30 min. The intercritical aging (570°C/1 h) also promoted an increase in local hardness of FZ 320 HV and HAZ 400 HV. Using an intercritical aging, the hardness situated between room temperature and quenched and aged coupons and was more homogeneous considering FZ, HAZ and BM. The microstructure of the intercritical aged welds is marked by duplex-ferrite and martensite micro-constituents.
关键词： Aging,Post-Welding Heat Treatment,Maraging Steels,Laser Beam Welding
更新于2025-09-19 17:13:59
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Comparison of laser-MIG hybrid and autogenous laser welding of M250 maraging steel thick sectionsa??understanding the role of filler wire addition
摘要： The present work is directed towards understanding the role of filler addition in laser-MIG hybrid welding (LHW) process as compared with that in autogenous laser welding (ALW) process during welding of 10-mm-thick maraging steel plates. Addition of filler wire is beneficial in improving the edge bridging between the parts to be welded and also in improving the fusion zone microstructure. Single-pass LHW of the 10-mm-thick maraging steel plates was performed using a combination of 3.5-kW CO2 laser and synergic pulse MIG welding power source at a welding speed of 1 m/min. MIG filler wire with reduced solutes such as Mo and Ti contents was used for the LHW process. Simultaneously, double-sided single-pass ALW of similar plates was performed. The role of filler wire addition on the microstructure and mechanical properties of the LHW fusion zone (FZ) was studied and compared with that of ALW FZ. The usage of filler wire resulted in less solutes in the LHW FZ after welding, and hence, the volume fraction of “reverted austenite (RA)” formed during aging was minimized when compared with ALW FZ. During transverse weld tensile testing, the ALW welds yielded higher tensile properties when compared with the LHW weld due to their fine grain structure and high number density of precipitates. Whereas the KIc fracture toughness of the ALW FZ was low with the KIc value of 49.5 MPa√m due to the presence of the high amount of RA as compared with LHW which exhibited the KIc value of 77.5 MPa√m. The study vividly brings out the advantages of LHW process in improving the microstructure of the fusion zone due to the addition of filler wire.
关键词： M250,Laser,Maraging,Filler,Welding,Hybrid,Fusion
更新于2025-09-19 17:13:59
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Direct Metal Laser Sintering of Maraging Steel: Effect of Building Orientation on Surface Roughness and Microhardness
摘要： Direct Metal Laser Sintering (DMLS) is a powder bed fusion based Additive Manufacturing (AM) process in which a part is fabricated using layer by layer deposition. In this work, 18% Ni Maraging steel 300 was fabricated using DMLS to examine the variations in surface finish and microhardness using three building orientations i.e. 0?, 45? and 90?. Surface roughness was found to decrease after 20 mm for 45? and 90?. Correspondingly, microhardness was found to decrease in the building direction. Understanding the effect of building orientation on the surface finish and hardness will allow the producer to fabricate superior quality AM parts with desired properties.
关键词： Direct Metal Laser Sintering,Microhardness,Additive Manufacturing,Surface finish,Maraging Steel
更新于2025-09-11 14:15:04
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Influence of heat treatment under hot isostatic pressing (HIP) on microstructure of intermetallic-reinforced tool steel manufactured by laser powder bed fusion
摘要： Microstructure and properties of as-built laser powder bed fusion (LPBF) steels differ from the conventional ones, and they may contain some porosity and lack of fusion. Therefore, post-treatments, including hot isostatic pressing (HIP), are used to densify the material, and tailor the properties of the final product. Usually, HIP is performed as an operation separate from heat treatment. In the present investigation a new approach was used, in which the whole cycle of the heat treatment was carried out in HIP under pressure, and the influence of HIP on microstructure of an advanced stainless maraging tool steel manufactured by LPBF was investigated. For a comparison, a conventional steel grade of the same chemical composition, after a heat treatment at the same temperature-time conditions, was also characterized. The microstructure of the steel was investigated by means of advanced microscopy and atom probe tomography. The influence of the manufacturing route, heat treatment and HIP on microstructure, austenitic phase fraction and size distribution of precipitates was investigated, and the role of high pressure in stabilization of austenite in the microstructure was discussed. It was concluded that since HIP influences phase transformations, a fundamental understanding of the influence of HIP on microstructure is necessary, and development of new post processing regimes guaranteeing the best performance of the material is required.
关键词： Hot isostatic pressing (HIP),Atom probe tomography,Transmission electron microscopy,Maraging steel,Precipitation hardening,Laser powder bed fusion
更新于2025-09-11 14:15:04