Maraging Steel Powder Research Articles

Microstructure of Built Part Obtained by Powder Bed Fusion Process with Metal

The influence of various process parameters on the building of maraging steel powder by the selective laser melting (SLM) processes is investigated. The microstructure in the built part was observed and the influence of the heat treatment was evaluated. As results, the depth of solidified layer was higher than that of deposited metal powder, and its value was influenced with the process parameters. The microstructure in the boundary between the built part and the substrate was quite different from the built part even if the suitable heat treatment was performed.

Structure and magnetic properties of milled maraging steel powders

We demonstrate that high-energy ball milling of gas-atomized maraging steel powder followed by suitable thermal-treatment produces nanocrystalline maraging steel powders having improved magnetic properties, compared to the gas-atomized powders. Milling for five to eighthours formed powders comprised of, primarily, nanocrystalline martensite. The saturation magnetization (MS) of the milled powders ranged between ~164 Am2/kg and ~169 Am2/kg, while the intrinsic coercivity (HCI) ranged between ~4.9kA/m and ~6.7kA/m. At sub-ambient temperatures, from 60K to 390K, both MS and HCI decremented with the increment in temperature. The thermomagnetic behavior of the milled powders was somewhat reversible. At supra-ambient temperatures (500K–900K), both MS and HCI monotonically decreased with the increase in temperature. The thermally treated powders constituted nanocrystalline martensite and exhibited increment (by ~6%) in MS and decrement (~nearly halved) in HCI compared to the milled powder, i.e., the powders exhibited improvement in soft-magnetic properties.

Evaluation of structure and magnetic properties of maraging steel powder feedstock for additive manufacturing of magnetic components

We investigated the structure as well as the magnetic properties of a commercial maraging steel powder feedstock—EOS MS1—and elucidated the stability of supersaturated martensite phase upon thermal-treatment. The investigation unfolds the potential reusability/recyclability of the powder feedstock, which is essential from an economic as well as an environmental perspective in the manufacturing of magnetic components. The as-supplied powder feedstock predominantly constituted martensite (lattice parameter ∼0.2881 nm). The coercivity (HCI), remanence (MR), and magnetic saturation (MS) of the powder feedstock were estimated as 3.03 ± 0.12 kA/m, 1.4 ± 0.1 A m2/kg, and 176.0 ± 2.0 Am2/kg, respectively. The supersaturated martensite phase was stable during thermal treatment. The MS, MR, and HCI of the thermally-treated powders, on an average, were ∼1% more, ∼0.8 times less, and ∼0.9 times less, respectively, than the as-supplied powder feedstock: thermal-treatment marginally enhanced the soft-magnetic behavior. The similarities in the structure and the magnetic properties between the as-supplied and thermally-treated powders suggest that the powder feedstock is reusable/recyclable in the manufacturing of magnetic components.

Additive manufacturing of maraging steel-H13 bimetals using laser powder bed fusion technique

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.

Effect of Powder Type and Particles Size on Microstructure of Selective Laser Sintered Parts

The goal of this work was to investigate microstructure of the selective laser sintering (SLS) produced parts evaluating effect of powder type and fraction size. Studies have shown that printed samples of 316L and GP1 metal powders had a higher defect content compared to printed components from MP1 powder material. From scanning electron microscopy (SEM), it was found that iron-based printed parts melted worse than Co-Cr alloy components. Iron-based 316L and GP1 metal powders did not get enough energy from laser to perform a better microwelding between particles. Surface roughness Ra numerical values for samples 316L, GP1, MP1 respectively are Ra = 13.7 μm; 11.4 μm; 3.0 μm. Stainless steel powder material contains particles which size varies between 20 – 120 μm. The Co-Cr alloy and the maraging steel powder materials are made of 10 – 80 μm particles. The chemical and elemental composition of powder materials were examined using SEM-EDS technology.

Effect of thermal cycling and aging stages on the microstructure and bending strength of a selective laser melted 300-grade maraging steel

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.

Metallurgical and mechanical assessment of hybrid additively-manufactured maraging tool steels via selective laser melting

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.

Effect of locally increased melted layer thickness on the mechanical properties of laser sintered tool steel parts

Additive technologies have several advantages over conventional manufacturing, such as the freedom of geometry of the products and internal structures. There are also some limitations and problems, deriving from stopping the process during the production. By restarting the process, the building often continues with a thicker starting layer due to the deposition of two or more layers. The effect of skipped melting of layers is investigated in this paper. Maraging steel powder (MS1) was used in direct metal laser sintering (DMLS) process to produce samples with increased thickness of melted layers. The layer thickness was increased in 20 μm steps up to 160 μm with 0.5 mm offset between the increased thickness layers. Porosity caused by the uneven melting was measured by optical microscope, mechanical tests were carried out to quantify the effect of skipped layers and fractured surfaces were observed under SEM. We have found that the yield strength and tensile strength are not affected if the layer thickness is slightly increased locally in the laser sintered part, while even a small increase in porosity greatly reduces the total elongation of the specimen. The decrease of impact energy due to the porosities shows similar correlation with the decrease of percentage elongation at break. However, the Charpy impact test is much more sensitive to layer skipping, the lack of melted layers lowers the impact strength significantly.

Characterization of Internal Stresses in Hybrid Steel Structures Produced by Direct Metal Laser Sintering

In this study hybrid structure were produced by direct metal laser sintering of maraging steel (MS1) powder onto the surface of commercial mold steels. The over-sintering method should be analyzed to find the optimum pre-and post-heat treatment to minimize the internal stresses. The internal stress is directly proportional to the deformation if the solid thick part is reduced to thin plate like parts. Based on this recognition the deformation of the plates over-sintered with MS1 could be analyzed in order to explore the internal stresses and the effect of different pre-and post-heat treatments were examined.

Design, development and evaluation of 3D mold inserts using a rapid prototyping technique and powder-sintering process

In this research work, attempts have been made to design, develop and evaluate the performance of mould inserts for injection moulding by using a powder-sintering process. Maraging steel powder, sintering aid and binder are materials used in this proposed development process. Attempts have been made to perform in-depth studies and to apply the powder-sintering process, to eventually produce the final sintered components. In addition, an analysis of the dimensional accuracy of the respective stereolithography master models and an analysis of the sintered specimens during various stages of powder-sintering process have been carried out. The intelligent manufacturing systems (IMS) test part with minor modifications has been used in the evaluation of dimensional accuracy, tolerances, distortion and volumetric variations. The main reason for using this unique geometry is the suitability of its design for injection-moulding processes and tooling.

Sintering of maraging steel with phosphorous additions

The aim of this study was to develop a steel powder system for rapid tooling applications. The properties required are rapid densification, dimensional precision, high mechanical strength and corrosion resistance. To this end, the densification and microstructural development of a loose packed 200 grade maraging steel powder sintered with ferrophosphorous additions was examined. Liquid initially formed from a reaction of the Fe3P and carbon, which was a residue of the polymeric binder used to shape the powder compact. This liquid caused a burst of sintering which ceased as the liquid dissipated. On further heating, a phosphorous rich supersolidus liquid appeared at triple points and grain boundaries leading to rapid densification and a sintered density of 98%.

Effect of hot isostatic pressing temperature on the properties of inert gas atomized maraging steel

Pre-alloyed 250-grade maraging steel powder formed by inert gas atomization was hot isostatically pressed (HIP) at five different temperatures ranging from 1285 to 1535 K. Both conventional and non-conventional aging treatments were applied to the resulting compacts. At HIP temperatures below approximately 1400 K incomplete densification resulted in poor mechanical properties, notably poor ductility. At a HIP temperature of 1480 K optimal properties were obtained, with a slight additional benefit being derived from an altered aging cycle involving an 800 K pre-age. The strength, ductility and toughness approached those of wrought material. At lower HIP temperatures, where the ductility was low, both titanium segregation and low density were observed. This segregation at prior particle surfaces was reduced and the density was improved at higher HIP temperatures.

Ductility in hot isostatically pressed 250-Grade maraging steel

Prealloyed 250-grade maraging steel powder produced by the rotating electrode process was fully consolidated by hot isostatic pressing (HIP) at 1100 and 1200°C. The strength following aging (3 h at 480°C) equalled that of wrought material; however, ductility was negligible. This lack of ductility in the powder metallurgy product was traced to titanium segregation which occurred at the powder surface during powder production. The formation of a titanium intermetallic at the prior particle boundaries during aging caused failure at low plastic strains. Altered aging treatments successfully broke up the embrittling film and resulted in a significant ductility recovery for the HIP material. Analysis of the fracture process indicates that further ductility gains are possible by reducing the titanium content, refining the particle size, and optimizing the thermal cycles.

Study on Dispersion Strengthening of Precipitation-Hardened Type 12% Cr Steel

The authors made on effort to develop the material having superior elevated temperature properties by applying dispersion strengthening and liquid-phase sintering techniques in tile sintering of 12%Cr maraging steel powder, and the results obtained were as follows:(1) Addition of a small amount of ferro-titanium alloy powder, which yields liquid phase at the sintering temperature, is effective for the improvement of the sintering characteristics of 12%Cr maraging steel powder.(2) Sintered 12% Cr maraging steel with dispersed γ-Al2O3 exhibiting high creep rupture strength at the temperature of 550°C could be obtained. This sintered material has a superior creep rupture strength compared with similar sintered 13 CrMoTi steel examined separately.