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Showing papers on "Maraging steel published in 2019"


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the solution phenomenon, aging behavior and room-temperature mechanical properties of maraging steel manufactured by selective laser melting (SLM), and different heat treatment experiments, including solution treatment (ST), direct aging treatment (DAT) and solution+aging treatment (SAT), were designed.
Abstract: This work investigates the solution phenomenon, aging behavior and room-temperature mechanical properties of maraging steel manufactured by selective laser melting (SLM). Different heat treatment experiments, including solution treatment (ST), direct aging treatment (DAT) and solution + aging treatment (SAT) are designed. Microstructure analysis indicates that ST and SAT will eliminate the cellular and lath structures, but DAT has little effect on these. The content of austenite increases with the addition of DAT temperature and holding time. While austenite is almost undetectable in ST and SAT samples. Meanwhile, both the elongation and toughness of the samples with DAT gain a slight improvement with the temperature increasing. Importantly, DAT yields similar microhardness, tensile strength and impact toughness to SAT, although the resultant microstructures are completely different. The results demonstrate that DAT can achieve the similar mechanical properties to SAT samples. Samples with high mechanical properties (microhardness of 653.93 HV and ultimate strength of 2126.30 MPa) have been obtained by DAT at 520 °C for 6 h as well as solution treatment at 900 °C for 1 h and aging treatment at 520 °C for 6 h. This investigation reveals the evolution regularity of microstructure, microhardness, tensile performance and impact toughness of maraging steel manufactured by SLM after different heat treatments.

96 citations


Journal ArticleDOI
TL;DR: In this paper, an interesting co-precipitation mechanism of Ni3Ti and Mo-rich nanoparticles in a 2.5 GPa grade maraging steel was revealed, and four modified theoretical prediction models were introduced to describe the yield strength as a function of microstructure and precipitates characteristics.

90 citations


Journal ArticleDOI
TL;DR: In this paper, an analysis of the defects influence on fatigue behavior is performed on the basis of the initial stress intensity factor of the killer defects examined by SEM observations of the fracture surfaces.

84 citations


Journal ArticleDOI
TL;DR: In this article, the combined effect of three primary additive manufacturing (AM) build orientations (0°, 45°, and 90°) and an extensive array of heat treatment plans on the plastic anisotropy of maraging steel 300 (MS1) fabricated on the EOSINT M280 Direct Metal Laser Sintering (DMLS) system was investigated.
Abstract: This experimental study investigates the combined effect of the three primary Additive Manufacturing (AM) build orientations (0°, 45°, and 90°) and an extensive array of heat treatment plans on the plastic anisotropy of maraging steel 300 (MS1) fabricated on the EOSINT M280 Direct Metal Laser Sintering (DMLS) system. The alloy's microstructure, hardness, tensile properties and plastic strain behaviour have been examined for various strengthening heat-treatment plans to assess the influence of the time and temperature combinations on plastic anisotropy and mechanical properties (e.g. strength, ductility). A comprehensive visual representation of the material's overall mechanical properties, for all three AM build orientations, against the various heat treatment plans is offered through time – temperature contour maps. Considerable plastic anisotropy has been confirmed in the as-built condition, which can be reduced by aging heat-treatment, as verified in this study. However, it has identified that a degree of transverse strain anisotropy is likely to remain due to the AM alloy's fabrication history, a finding that has not been previously reported in the literature. Moreover, the heat treatment plan (6h at 490 °C) recommended by the DMLS system manufacturer has been found not to be the optimal in terms of achieving high strength, hardness, ductility and low anisotropy for the MS1 material. With the use of the comprehensive experimental data collected and analysed in this study, and presented in the constructed contour maps, the alloy's heat treatment parameters (time, temperature) can be tailored to meet the desired strength/ductility/anisotropy design requirements, either for research or part production purposes.

84 citations


Journal ArticleDOI
TL;DR: In this paper, a very narrow interface was formed between the additively manufactured maraging steel and the conventional H13 without forming cracks or discontinuities, indicating a robust interface.
Abstract: In this paper, maraging steel powder was deposited on top of an H13 tool steel using laser powder bed fusion (LPBF) technique. The mechanical properties, microstructure, and interfacial characteristics of the additively manufactured MS1-H13 bimetals were investigated using different mechanical and microstructural techniques. Several uniaxial tensile tests and micro-hardness indentations were performed to identify the mechanical properties of the additively manufactured bimetal. Advanced electron microscopy techniques including electron backscatter diffraction and transmission electron microscopy were used to identify the mechanism of interface formation. In addition, the microstructure of the additively manufactured maraging steel along with the conventionally fabricated substrate-H13 were studied. It was concluded that, a very narrow interface was formed between the additively manufactured maraging steel and the conventional H13 without forming cracks or discontinuities. The first deposited layers possessed the highest hardness due to grain size refinement, solid solution strengthening, and cellular solidification structure. Finally, under uniaxial tensile loading, the additively manufactured bimetal steel failed from the underlying tool steel, indicating a robust interface.

82 citations


Journal ArticleDOI
TL;DR: In this paper, the precipitates found in the 300 grade maraging steel built by Selective Laser Melting (SLM), which is globally one of the fastest-growing additive manufacturing (AM) technology, were investigated.

79 citations


Journal ArticleDOI
TL;DR: In this paper, the 18 Ni maraging steel powder was processed by selective laser melting and different heat treatments were applied to the built parts, aiming for homogenization, microstructural refinement and martensite-to-austenite reversion.
Abstract: Additive manufacturing techniques allow the creation of complex parts in a layer by layer fashion, bringing new opportunities in terms of applications and properties when compared to conventional manufacturing processes. Among other ultra-high-strength steels, the 18 Ni maraging 300 steel offers a good toughness/strength ratio. However, when fabricated by additive manufacturing, this steel presents lower ductility and strain-hardening than its forging counterparts. One way to enhance ductility and toughness is to promote martensite-to-austenite reversion. Therefore, in the present study, 18 Ni maraging steel powder was processed by selective laser melting and different heat treatments were applied to the built parts, aiming for homogenization, microstructural refinement and martensite-to-austenite reversion. Thermodynamic simulations were used to assess a range of temperatures for the reversion heat treatments. Microstructural characterization was performed by scanning electron microscopy, electron backscattered diffraction and x-ray diffraction.

74 citations


Journal ArticleDOI
TL;DR: In this paper, an 18Ni maraging steel sample was built by selective laser melting, homogenized at 820°C and then subjected to different isothermal tempering cycles aiming for martensite-to-austenite reversion.
Abstract: Reverted austenite is a metastable phase that can be used in maraging steels to increase ductility via transformation-induced plasticity or TRIP effect. In the present study, 18Ni maraging steel samples were built by selective laser melting, homogenized at 820 °C and then subjected to different isothermal tempering cycles aiming for martensite-to-austenite reversion. Thermodynamic simulations were used to estimate the inter-critical austenite + ferrite field and to interpret the results obtained after tempering. In-situ synchrotron X-ray diffraction was performed during the heating, soaking and cooling of the samples to characterize the martensite-to-austenite reversion kinetics and the reverted austenite stability upon cooling to room temperature. The reverted austenite size and distribution were measured by Electron Backscattered Diffraction. Results showed that the selected soaking temperatures of 610 °C and 650 °C promoted significant and gradual martensite-to-austenite reversion with high thermal stability. Tempering at 690 °C caused massive and complete austenitization, resulting in low austenite stability upon cooling due to compositional homogenization.

69 citations


Journal ArticleDOI
TL;DR: In this article, the effect of heat treatment on microstructure and mechanical behaviour of SLM-built 18Ni-300 maraging steels was investigated, and the experimental results showed that the densest parts with the smallest number of defects were fabricated at optimum laser energy density of 70 J/mm3 and laser power of 275 W.
Abstract: Selective laser melting (SLM) of 18Ni-300 maraging steel is an important research area in view of its numerous applications in the automotive domain. Heat treatment plays a significant role in the microstructure and mechanical behaviour of maraging steels and is a major area of interest. This paper investigated the effect of heat treatment on microstructure and mechanical behaviour of SLM-built 18Ni-300 maraging steel. The experimental results showed that the densest parts with the smallest number of defects were fabricated at optimum laser energy density of 70 J/mm3 and laser power of 275 W. When the laser power was fixed at 275 W, lower laser energy density resulted in the formation of balling and irregular pores, while higher laser energy density induced spherical pores and microcracks. The as-built samples consisted of cellular and columnar microstructures due to the fast cooling and solidification rates during SLM. However, solution treatment led to changes in the typical microstructure and massive lath martensite phase. The tensile strength and microhardness decreased slightly due to grain growth and residual stress relief upon solution treatment; an opposite effect was observed when the samples were subjected to solution treatment followed by aging at 490 °C for 2 h. With regard to the tensile anisotropy, yield strength and ultimate tensile strength of the horizontally-built samples slightly exceeded those vertically-built. These findings are significant as they allow an informed prediction about the effect of various heat treatments on the microstructure and mechanical behaviour of components manufactured from 18Ni-300 maraging steel using the SLM process.

69 citations


Journal ArticleDOI
TL;DR: In this paper, solution annealing and hardening treatments were applied to the printed samples to induce changes in their microstructures and mechanical properties, and compared to those of a bar of conventional steel with the same chemical composition.
Abstract: Additive manufacturing (AM) is an advanced technology used for the manufacture of products that have intricate shapes and complex inner geometries. Various metal powders can be used for AM; however, the resulting microstructures will differ profoundly from those obtained via the casting, heat treatment, or thermomechanical processing of metals with the same chemical composition. This is because of the rapid heating and cooling rates used during three-dimensional (3D) printing. Further complications arise from the repeated heating and cooling of some regions, which is owed to the step-by-step formation of the solidified layers. A powder consisting of 1.2709 (X3NiCoMoTi 18-9-5) low-carbon maraging steel was used in an AM experiment. Given the high residual stresses that exist within printed metals, a post-processing heat treatment is desirable to limit the risk of cracking. In this study, solution annealing and hardening treatments were applied to the printed samples to induce changes in their microstructures and mechanical properties. The mechanical properties and microstructures of the builds were characterised and compared to those of a bar of conventional steel with the same chemical composition. During tensile loading, the fracture that was initiated at the sites of metallurgical defects was observed in situ.

59 citations


Journal ArticleDOI
TL;DR: In this article, cold spraying additive manufacturing (CSAM) and selective laser melting (SLM) were used to manufacture steel 300 (MS300) composite reinforced by WC particles, and the results showed that the SLM composite possesses a relatively higher densification rate and a lower porosity than that of the CSAM composite.
Abstract: Till now, additive manufacturing (AM) technologies based on different principles have been widely applied to produce metal matrix composites (MMCs). In this study, AM technologies of cold spraying additive manufacturing (CSAM) and selective laser melting (SLM) were used to manufacture maraging steel 300 (MS300) composite reinforced by WC particles. The results show that the SLM composite possesses a relatively higher densification rate and a lower porosity than that of the CSAM composite. Dry sliding wear test and microhardness measurements were performed to characterize the mechanical properties. The CSAM composite possesses a slightly higher microhardness value than that of the SLM composite. However, the SLM composite shows a significantly lower wear rate than that of the CSAM composite, presenting a stable evolution of the friction coefficient and a worn morphology without obvious scratches. However, these differences in the mechanical properties can be contributed to the distinct evolution features of the WC reinforcement particle during these two AM processes. Through understanding the composite formation mechanisms and the WC evolution, it is possible to provide a guidance for application of the different AM technologies for preparation of MMCs.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the mechanical properties of samples of MS1 Maraging Steel (untreated and heat treated), which were produced by additive technology in various orientations in the working area of the building machine.
Abstract: The objective of this paper is to investigate the mechanical properties of samples of MS1 Maraging Steel (untreated and heat treated), which were produced by additive technology in various orientations in the working area of the building machine. MS1 steel (European 1.2709 and German X3NiCoMoTi 18-9-5) is well known for its high strength, high fracture toughness, good weldability, and dimensional stability during aging. The literature review, related to the mechanical properties and fracture of MS1 steel, found that there are no available studies of the effects of both building direction and heat treatment on the mechanical properties of MS1 steel. The authors decided to address this omission and present this entirely new research in this article. The uniaxial tensile tests to fracture were completed at two of the authors’ workplaces. The results were statistically assessed using Grubbs’ test for outliers, and then the data were processed using box plots to be easily comparable from the point of view of print direction, heat treatment, and the values declared by the metal powder producer or in the tables (for conventionally produced steel). Scanning electron microscopy was used to analyze the fracture surfaces obtained after tensile testing cylindrical samples. The results showed that there was an impact on the mechanical properties depending on the sample orientation within the same heat treatment type; there was also significant influence of heat treatment, while the possibility of the natural aging effect on mechanical properties was also noted.

Journal ArticleDOI
TL;DR: In this article, a complete metallurgical and mechanical assessment of additively-manufactured maraging tool steels has been undertaken, beginning with the initial powder and ending at hybrid builds.
Abstract: A complete metallurgical and mechanical assessment of additively-manufactured maraging tool steels has been undertaken, beginning with the initial powder and ending at hybrid builds. The effect of powder recycling on powder characteristics is investigated using flowability, size distribution, and density measurements. Virgin and re-used powder have similar characteristics in terms of size distribution and chemical and phase homogeneity, but no flowability. A microstructural characterization of the as-built and heat-treated samples is undertaken, showing the phase evolution, and the formation of porosity between build layers. The age-hardening response of the alloy at 490 °C and 650 °C is demonstrated to be similar to the material in the wrought condition. Finally, hybrid build scenarios are examined – maraging steel powder deposited onto C300 maraging steel, as well as H13 tool steel substrates – using digital image correlation. In both cases, the interface remains coherent without any sign of de-bonding during tensile deformation. In the case of the maraging steel powder / C300 substrate, the deformation is homogeneous throughout until failure localizes away from the interface. In the case of the maraging steel powder / H13 substrate, the deformation is predominantly within the substrate until failure localizes at the interface. A heat treatment strategy for the maraging steel powder / H13 tool steel substrate is proposed.

Journal ArticleDOI
TL;DR: In this article, the use of cold metal transfer-based additive manufacturing (WAAM) process for the production of maraging steel bulk material is reported, and the effect of building strategies including oscillation, parallel and weaving on bead shape is investigated.
Abstract: Wire + arc additive manufacture (WAAM) is a new process for fabricating large-scale metallic components. In this paper, the use of cold metal transfer-based WAAM process for the production of maraging steel bulk material is reported. Process parameters were studied, and the effect of building strategies including oscillation, parallel and weaving on bead shape was investigated. The structural integrity of the WAAM bulk material regarding the surface finish, lack-of-fusion issue and microstructure was characterized. Results proved the feasibility of applying WAAM to producing maraging steel bulk material, and weaving was identified to be most recommended building strategy.

Journal ArticleDOI
TL;DR: In this paper, the tensile mechanical properties and anisotropy levels of identical test-coupons, fabricated from maraging steel 300 (MS300) using two alternative EOS EOSINT M280 additive manufacturing (AM) systems, have been examined.
Abstract: The tensile mechanical properties and anisotropy levels of identical test-coupons, fabricated from maraging steel 300 (MS300) using two alternative EOS EOSINT M280 Additive Manufacturing (AM) systems, have been examined. The mechanical performance variations resulting from process differences between the two suppliers and the part's build volume orientation (0°, 45°, and 90°) are investigated. Significant microstructural discrepancies, affecting mechanical performance, plasticity and anisotropy levels, have been observed in the as-built samples obtained from the two suppliers. A difference in the angle of the laser scan strategy, in conjunction with unfavourable powder feedstock characteristics, are understood to have had a profound influence on the plasticity and anisotropy divergences observed in the AM MS300 alloy. Plastic anisotropy levels can be largely reduced through application of aging heat-treatments, however, a degree of transverse strain anisotropy is likely to remain due to the AM alloy's fabrication history. Moreover, in this work both the anisotropic and elasticity tensors for this material are derived. These tensors can be used by researchers working on modelling and simulation of the MS300 mechanical properties.

Journal ArticleDOI
TL;DR: In this article, the effect of adjusting the process parameters on the microstructure and properties of maraging steel 300 parts built by selective laser melting technology has been studied, and a simple analysis of the manufacturing time as a function of the SLM parameters was also performed.
Abstract: Although selective laser melting technology (SLM) provides significant advantages over conventional manufacturing processes, it is still a relatively expensive and slow manufacturing method for high-volume production. Increasing the manufacturing speed by optimizing process parameters may increase the porosity of manufactured parts, thus degrading their mechanical properties. Here, in experimental Phase 1 of the paper, the effect of adjusting the process parameters on the microstructure and properties of maraging steel 300 parts built by SLM has been studied. The porosity, hardness, and roughness were highly dependent on the processing parameters, whereas the microstructure was not significantly affected. The SLM parameters optimized in Phase 1 were subsequently used in experimental Phase 2 for elucidating the relationships between the part position on the machine table and the final mechanical properties. The part porosity had the greatest effect on the mechanical properties. A simple analysis of the manufacturing time as a function of the SLM parameters was also performed.

Journal ArticleDOI
25 Sep 2019
TL;DR: Mugwagwa et al. as mentioned in this paper investigated the effect of process parameters on residual stresses, distortions, and porosity in selective laser melting of steel 300, and found that process parameters had little impact on the porosity.
Abstract: CITATION: Mugwagwa, L., Yadroitsev, I. & Matope, S. 2019. Effect of process parameters on residual stresses, distortions, and porosity in selective laser melting of maraging steel 300. Metals, 9(10):1042, doi:10.3390/met9101042.

Journal ArticleDOI
Asuka Suzuki1, Ryoya Nishida1, Naoki Takata1, Makoto Kobashi1, Masaki Kato2 
TL;DR: In this article, the effects of laser power and scan speed on the relative density, melt pool depth, and Vickers hardness of selectively laser melted (SLM) maraging steel were systematically investigated.
Abstract: In this study, the effects of laser power and scan speed on the relative density, melt pool depth, and Vickers hardness of selectively laser melted (SLM) maraging steel were systematically investigated. The change in these structural parameters and hardness could not always be clarified by the volumetric energy density, which is widely used in the SLM processes. The deposited energy density, wherein the thermal diffusion length is used as a heat-distributed depth, can express the change in these structural parameters and the hardness with one curve. To clarify the effect of the laser parameters, the deposited energy should be used instead of the volumetric energy density. Thus, this study provides a new insight on the selection of the laser condition for SLM-fabricated materials.

Journal ArticleDOI
TL;DR: In this article, a detailed analysis of selective laser melting (SLM) fracture surfaces was carried out on the X3NiCoMoTi18-9-5 (or 18Ni300) maraging steel and the results revealed a highly anisotropic fatigue performance dependent on the build direction.

Journal ArticleDOI
TL;DR: In this paper, a WC particle was reinforced by selective laser melting (SLM) to enhance the tribological performance of maraging steel 300 (MS300) composites to improve the wear-resistance.
Abstract: Owing to the limited wear resistance, Maraging steels has limited applications in the harsh environments, leading to a shortened service-life or even failure. In this study, WC particles reinforced maraging steel 300 (MS300) composites were produced by selective laser melting (SLM) to enhance the tribological performance. The microstructure and phase analysis of SLM-produced composites were investigated by SEM-EDS. Dry sliding wear test and microhardness were used to investigate the mechanical properties of WC/MS300 composites. As laser energy density increases, the microhardness drops rapidly and the maximum value of 562.2 HV2 was measured at the linear energy density of 110 J/m. Dry sliding tests show that the wear rate was decreased by >1500 times through the WC reinforcement compared with pure MS300 sample, which emphasizes the superior wear-resistance properties of MS300/WC composite. Besides, the best wear-resistance performance at the improved linear energy density of 125 J/m. The study on wear mechanism shows that formation of carbide layer between WC and MS300 matrix significantly prevent the plowing effect. The present work provides an effectively method to improve the tribological performance MS300 through the reinforcement of WC particle by selective laser melting.

Journal ArticleDOI
TL;DR: In this paper, the impact of aging temperature on microstructural evolution and strengthening behavior on low lattice misfit cobalt-free maraging steel was elucidated, and the best combination of high strength (1850 MPa) and high-toughness (125.4 MJm−3) was obtained at the optimal aging temperature of 520°C, without sacrificing ductility.
Abstract: We elucidate here the impact of aging temperature on microstructural evolution and strengthening behavior on low lattice misfit cobalt-free maraging steel. The best combination of high-strength (1850 MPa) and high-toughness (125.4 MJ m−3) was obtained at the optimal aging temperature of 520 °C, without sacrificing ductility. Electron back scattered diffraction studies suggested that preferred orientations of {101}, fraction of high-angle grain boundary (HAGB) and total length of grain boundary per unit area (μm/μm2) were increased with increase of aging temperature, which was beneficial to both strengthening and toughening of maraging steel. The strengthening contribution from the precipitates was transformed from shearing mechanism to bypass mechanism when the aging temperature is greater than 520 °C. The aging tempered steel of 520 °C provided maximum strengthening increment of 1463 MPa through shearing mechanism, while granular reverted austenite at this temperature contributed to high toughness.

Journal ArticleDOI
TL;DR: In this article, a plastic deformation was introduced through interpass cold rolling during the layer-by-layer deposition process, which promoted the atoms diffusion to enable a more uniform solutionizing process and improved subsequent aging response by 105-110%.
Abstract: Maraging steel gains ultrahigh strength through aging; however, wire plus arc additively manufactured maraging steel features a columnar-dendritic structure with associated segregation and shows a much less pronounced aging response. In this paper, plastic deformation was introduced through interpass cold rolling during the layer-by-layer deposition process. After aging, the ultimate tensile strength (UTS) was improved substantially from 1410 MPa (unrolled) to 1750 MPa (50 kN rolled). Rolling induced partial recrystallization to break the dendritic structure and form high-angle grain boundaries, which promoted the atoms diffusion to enable a more uniform solutionizing process and improved the subsequent aging response by 105–110%. The main contribution of overall strengthening of the rolled alloy was attributed to the effective aging process, accounting for more than 95% of the entire strength increase.

Journal ArticleDOI
TL;DR: In this paper, a maraging steel 300 (MS300) was fabricated by cold spray additive manufacturing followed by solution-aging treatment and phase analysis through X-ray computed tomography (XCT) and optical microscope (OM) showed a densified microstructure with a minimum porosity of 0.168%.
Abstract: For the moment, the additive manufacturing (AM) of maraging steel has attracted increasing attention due to its outstanding mechanical properties. As a recently-emerged AM method, the solid-state cold spray has been widely used to fabricate the metallic components. In this work, the maraging steel 300 (MS300) was fabricated by cold spray additive manufacturing followed by solution-aging treatment. Analyses based on X-ray computed tomography (XCT) and optical microscope (OM) show a densified microstructure with a minimum porosity of 0.168%. Phase analysis through XRD and EBSD exhibits that as-fabricated samples possess well-retained phase composition compared with feedstock material, and the solution-aging can lead to a highly martensitized microstructure in the prepared samples. EBSD analysis shows the ultrafine grain structure of as-fabricated samples indicating the formation of dynamic recrystallization during the CS deposition. Tensile tests show that through the cohesive diffusion and precipitation-strengthening, the solution-aging treatment can lead to a significantly improved tensile properties (ultimate tensile strength and elongation) with the fracture morphology featured by extensive dimples. The wear resistance of CS MS300 was also significantly improved through the precipitation-hardening. As a summary, this study demonstrates cold spray as a promising AM method can fabricate high-performance grade 300 maraging steel parts.

Journal ArticleDOI
Dong Pan1, Yuguang Zhao1, Xiaofeng Xu1, Yitong Wang1, Wenqiang Jiang1, Xueying Chong1 
TL;DR: In this article, a high-energy and instantaneous electropulsing is devised to improve the ductility of T250 steel, and the substructure evolution and aging behavior of T 250 steel was systematically investigated by Transmission Electron Microscope (TEM) characterization, APT, Finite Element Modelling (FEM) simulation and Electron Back-Scattered Diffraction (EBSD) technology.

Journal ArticleDOI
TL;DR: In this article, the effects of the prior austenite grain sizes in hydrogen embrittlement of Co-containing 18Ni 300 maraging steel were studied employing Slow Strain Rate Testing (SSRT) in 0.6m NaCl electrolyte under simultaneuos cathodic polarization.

Journal ArticleDOI
TL;DR: In this paper, the effect of grain orientations, boundary characteristics, and crystal effects on the crack formation of a 350 high strength Maraging steel elbows exposed to hydrofluoric acid was investigated.

Journal ArticleDOI
29 Mar 2019
TL;DR: In this article, the effects of aging treatments, in terms of microstructure and micro-hardness, on 18 Ni 300 Maraging steel samples processed by Selective Laser Melting (SLM) and to compare them with those of the same material made by casting were evaluated.
Abstract: The aim of this work was to evaluate the effects of aging treatments, in terms of microstructure and micro-hardness, on 18 Ni 300 Maraging steel samples processed by Selective Laser Melting (SLM) and to compare them with those of the same material made by casting. Optimized process parameters were used to build SLM parts in order to obtain almost full density (above 99%). For aging treatments, following the principles of the Design of Experiments, a full factorial plan with 4 levels of temperature and 6 levels of time was used. Before aging, the microstructure consisted of many overlapping fused/resolidified zones with a dendritic solidification morphology and epitaxial growth of the grains. After aging, the fused/resolidified zones disappeared and the hardening of the material was mainly governed by the mechanism of precipitation. The maximum value of hardness, on selective laser melted samples, was obtained, for a treatment temperature of 480 °C for 10 h: whereas, at the same temperature and after 10 h, on casting sample, it stabilized at 640 HV. Compared to samples produced by casting, SLM samples showed a lower increment in micro hardness at the aging temperature of 440 °C, while for 510 °C and 560 °C, trends were similar.


Journal ArticleDOI
W. X. Yu1, Baoxi Liu1, Jining He1, C.X. Chen1, Wei Fang1, Fuxing Yin1 
TL;DR: In this paper, a multilayer TWIP/Maraging steel with high strength, high toughness and interfacial shear strength of 564 MPa is obtained by vacuum hot rolling, subsequent cold rolling and aging treatment.
Abstract: The multilayer structure design of steels can accomplish the purpose of strengthening and toughening. Multilayer TWIP/Maraging steel with high strength, high toughness and interfacial shear strength of 564 MPa is obtained by vacuum hot rolling, subsequent cold rolling and aging treatment. It is found that hot rolling can achieve effective interface bonding ability. Grain refinement, twinning proliferation and dislocation strengthening are generated in TWIP layers with the increase of cold rolling reduction, which can improve the strength and toughness of multilayer steel. However, when the reduction reaches more than 90%, the nanocrystalline and nano twins are appeared in TWIP layers, and plasticity is seriously reduced. The proper adjustment of the cold rolling and ageing process, interface alloying elements diffusion, twinning proliferation, nano-precipitation strengthening, and work hardening can obviously improve the interface bonding ability, strength and toughness, this research provides theoretical basis and experimental support for the lamination design and strengthening-toughening mechanism of a series of metal materials.

Journal ArticleDOI
TL;DR: In this paper, high-performance WC reinforced MS300 composites were fabricated by high-pressure cold spray, which enables the additive manufacturing of bulk material well below its melting point, and the distribution and morphology of the WC particles in the composite samples were characterized by X-ray computed tomography (XCT).