Additive manufacturing is a good alternative to conventional methods for the production of near net shape geometries with high geometric complexity shorter lead times, being a good option for the ...manufacturing of dies for die casting process. In this research, a novel hot-work tool steel for aluminum die casting applications manufactured by laser powder bed fusion was investigated. As-built and stress-relieved (AS-B + SR) state was established and used as the reference condition, and subsequent post-treatments were added and compared to the reference condition. Test parts were evaluated using tensile, impact, hardness and thermal fatigue testing. Compared to the reference condition, heat treatment (HT), significantly increased the hardness, yield and ultimate tensile strengths of the material, due to the obtained tempered martensite microstructure. Hot isostatic pressing (HIP) prior to HT significantly increased the impact toughness and ductility, and slightly increased the yield and ultimate tensile strength values compared to the HT condition. The addition of nitriding treatment after HT, without intermedium HIP step, resulted in the highest surface hardness and lowest impact toughness. Thermal fatigue was mostly affected by the hardness and the softening of the material during the thermal fatigue testing. Results showed that a high surface hardness resulted in a higher thermal fatigue crack nucleation, meanwhile conditions with a high softening during thermal fatigue performance resulted in a higher crack propagation.
Additive manufacturing (AM) is increasingly used for the manufacturing of tools and dies; in this respect, apart from the optimization of processing parameters, it is important to establish the most ...proper heat treatment conditions for the fabricated parts. In this paper, the microstructure, and some properties of H13 hot work tool steel fabricated by selective laser melting (SLM) have been evaluated after direct tempering and in quenched and tempered condition. The as-built microstructure consists of a partially tempered martensite and a much higher amount (up to 19%vol) of retained austenite (RA) compared to the quenched steel (RA<2%vol), leading to a much stronger secondary hardening during tempering. Quenching further produces a partial recovery of the solidification structure, removing the cellular/dendritic SLM structure as well as the uneven local hardness. Dilatometry highlights a much different tempering behaviour for as-built and quenched steel. Very promising fracture toughness values were measured particularly when the samples were tested with a notch plane perpendicular to the build plane (XY plane). In spite of higher hardness, the fracture toughness of tempered samples was comparable to that of quenched and tempered ones.
The X40CrMoV5-1 (H13) hot work tool steel was densified by selective laser melting (SLM) using different laser parameters and preheating temperatures. The porosity and crack densities of the ...processed specimen were determined, the resulting microstructure characterized, tempering hardness diagrams recorded and the reusability of the powder assessed.
The X40CrMoV5-1 steel showed a good densification behaviour. Relative densities of above 99.5% were obtained. After SLM densification, the specimen showed a fine-grained microstructure, with a cellular arrangement consisting of ferrite and austenite. Although the microstructure did not change with preheating temperature, a decrease in crack density could be observed for higher preheating temperatures. By combining microstructural observations with some simulations, a new model describing the microstructural evolution of SLM-densified X40CrMoV5-1 is suggested. The peak in secondary hardness after tempering SLM-densified X40CrMoV5-1 was observed at higher temperatures compared to the cast reference steel in the same heat treatment condition.
Coarse TiC particles (more than 50 μm) reinforced H13 steel composites produced by laser cladding with various ceramic volume fraction were investigated. The effects of the ceramic volume fraction on ...the microstructure and hardness of the produced TiC/H13 composite were obtained. The results indicated that preheating conbined with slowing laser beam scanning speed were relatively useful for crack suppression and formation of composites with high TiC volume fraction. The microstructure of the TiC/H13 composite consisted of various TiC particles, including coarse TiC, initial fine TiC, primary TiC, lamellar-type eutectic TiC, austenite and martensite. By increasing the concentration of TiC in the composite, the volume fraction of residual austensute and the carbon content of martensite as well as the composite hardness had a significant increase. Nanoindentation hardness results showed that the hardness of the initial TiC particle was the highest, followed by the primary TiC, among the various shaped TiC within the deposit. The highest average hardness of the TiC/H13 composite was 1365 HV, which was more than twice as much as the H13 substrate hardness.
•High content of coarse TiC/H13 composites were successfully produced by laser cladding.•The TiC/H13 composite is well improved in hardness compared to the matrix metal.•The carbon content of the matrix increases with increasing ceramic content.
This study presents investigations on the additive manufacturing of hot work steel with the energy-reduced gas metal arc welding (GMAW) process, which is a cold metal transfer (CMT) process. The ...paper analyses the influence of arc energy and the thermal field on the resulting mechanical properties and microstructure of the material. The investigations were carried out with hot work tool steel X37CrMoV 5-1, which is used for the manufacturing of plastic moulds, hot extrusion dies, and forging dies. The results show that this steel can be used to generate 3D metal components or structures with high reproducibility, near-net-shaped geometry, absence of cracks, and a deposition rate of up to 3.6 kg/h. The variation of the wire feed speed and the welding speed enables the production of weld beads of width up to 9.4 mm. The mechanical properties of the generated structures can be adapted by the dominant thermal field, which in turn is influenced by the bypass temperature and the electric arc energy. A determining factor to describe the main variables of the welding process is represented by energy per unit length EL. If the bypass temperature is above the martensite start temperature (Ms), there is a homogeneous hardness level along the height of the additively manufactured structure height as long as the energy produced by the welding arc is enough to keep the temperature of all layers above Ms.
In this research, samples of the H13 steel, a commonly used hot work tool steel in the die/mould manufacturing industry, were additively manufactured using selective laser melting (SLM). Their ...as-built microstructures were characterised in detail using transmission electron microscopy (TEM) and compared with that of the conventionally manufactured H13 (as-supplied). SLM resulted in the formation of martensite and also its partial decomposition into fine α-Fe and Fe
3
C precipitates along with retained austenite. TEM analyses further revealed that the lattice of the resulting α-Fe phase is slightly distorted due to enhanced Cr, Mo and V contents. Substantially high residual stresses in the range of 940–1420 MPa were detected in the as-built H13 samples compared with its yield strength of ~1650 MPa. In addition, it was identified that the high residual stress existed from just about two additive layers (100 µm) above the substrate along the build direction. The high residual stresses were mainly attributed to the martensitic transformation that occurred during SLM. The research findings of this study suggest that the substantially high residual stresses can be easily problematic in the AM of intricate H13 dies or moulds by SLM.
The study is aimed to analyse the comparative behaviour of the high-temperature abrasive wear of H13 steel surfaces modified by laser melting and cladding with Stellite 6 and Stellite 6 + 30 wt% WC. ...3-body abrasive tests were conducted at room temperature, 450 °C, 550 °C, and 650 °C. The microstructural evolution, microhardness, wear surface morphology and mechanisms, and various phases formed during laser surface modifications were also studied. The laser remelting of H13 steel surface increased its room temperature microhardness to 750 ± 35 HV0.01, whereas laser cladding of Stellite 6 powder yielded hardness of around 600 ± 20 HV0.01 in the clad layer; and Stellite 6/WC composite clad layer had marginally higher hardness than the Stellite 6 clad layer in the matrix and much higher hardness of ~3000 HV0.01 at the sporadically distributed WC particle sites. Though the room temperature microhardness of laser remelted H13 surface is the highest, the volumetric wear loss in it was comparable to that of the Stellite 6 cladding. However, Stellite 6/WC composite layer recorded a relatively less volumetric loss as WC particles resisted the abrasive wear. With increasing temperature, the wear loss in laser remelt surfaces increased at a fast rate, while that in Stellite 6 and composite clad layers varied marginally with no definite trend. Overall, Stellite 6/WC composite cladding performed better than others in the current temperature range.
Additive manufacturing (AM) has a strong potential for the formation of a new class of multifunctional nanocomposites. In this study, nanocomposite feedstock powders were prepared by a mechanical ...alloying method based on high-energy ball milling. The evolution of constitutional phases and microstructural features of the milled powders was investigated as a function of milling time. The results showed that the milled powder particles experienced significant cold-welding during the entire milling time, with a wide size distribution. Selective laser melting (SLM), a promising AM fabrication technique, was applied to produce nanoscale 15% (by volume) TiC-reinforced H13 steel matrix nanocomposites. After SLM, uniformly dispersed nanoscale TiC particles with a mean particle size of 50nm were obtained and a fine heterogeneous structure was observed. Relative to the unreinforced H13 steel part, the TiC/H13 steel nanocomposite parts exhibited higher hardness and elastic modulus, along with lower friction and a lower wear rate; these improvements are attributed to the combined effects of grain refinement and grain boundary strengthening.
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•TiC/H13 steel nanocomposites were fabricated by selective laser melting.•Fabricated nanocomposites have high hardness and elastic modulus.•TiC/H13 steel parts have low friction and wear rate.•These properties arise from grain refinement and grain boundary strengthening.•TiC/H13 nanocomposite is a potential candidate for future tooling applications.
This study refers to an analysis of the dies used in the first operation of producing a valve forging from chromium-nickel steel NC3015. The analyzed process of manufacturing forgings of exhaust ...valves is realized in the co-extrusion technology, followed by forging in closed dies. This type of technology is difficult to master, mainly due to the increased adhesion of the charge material to the tool substrate as well as the complex conditions of the tools' operations, which are caused by the cyclic thermo-mechanical loads and also the hard tribological conditions. The average durability of tools made from tool steel WLV (1.2365), subjected to thermal treatment and nitriding, equals about 1000 forgings. In order to perform an in-depth analysis, a complex analysis of the presently realized technology was conducted in combination with multi-variant numerical simulations. The obtained results showed numerous cracks on the tools, especially in the cross-section reduction area, as well as sticking of the forging material, which, with insufficient control of the tribological conditions, can cause premature wear of the dies. In order to increase the durability of forging dies, alternative materials made of hot work tool steels were used: QRO90 Supreme, W360, and Unimax. The preliminary tests showed that the best results were obtained for QRO90, as the average durability for the tools made of this steel equaled about 1200 forgings (with an increase in both the minimal and maximal values), with reference to the 1000 forgings for the material applied so far.
Selective laser melting (SLM) is a powder-based additive manufacturing capable to produce parts layer-by-layer from a 3D CAD model. Currently there is a growing interest in industry for applying this ...technology for generating objects with high geometrical complexity. To introduce SLM process into industry for manufacturing real components, high mechanical properties of final product must be achieved. Properties of manufactured parts depend strongly on each single laser-melted track and each single layer. In this study, effects of the processing parameters such as scanning speed and laser power on single tracks formation are explored. Experiments are carried out at laser power densities (0.3–1.3)
×
10
6
W/cm
2 by cw Yb-fiber laser. Optimal ratio between laser power and scanning speed (technological processing map) for 50
μm layer thickness is determined for stainless steels (SS) grade 316L (−25
μm) and 904L (−16
μm), tool steel H13 (−25
μm), copper alloy CuNi10 (−25
μm) and superalloy Inconel 625 (−16
μm) powders. A considerable negative correlation is found between the thermal conductivity of bulk material and the range of optimal scanning speed for the continuous single track sintering.
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