Additive manufacturing (AM) is an attractive manufacturing technology in tooling applications. It provides unique opportunities to manufacture tools with complex shapes, containing inner channels for ...conformal cooling. In this investigation, H13, a widely used tool steel, was manufactured using a laser powder bed fusion method. Microstructure, tensile mechanical properties, hardness, and porosity of the AM H13 after stress relieve (SR), standard hardening and tempering (SR + HT), and hot isostatic pressing (SR + HIP + HT) were investigated. It was found that the microstructure of directly solidified colonies of prior austenite, which is typical for AM, disappeared after austenitizing at the hardening heat treatment. In specimens SR + HT and SR + HIP + HT, a microstructure similar to the conventional but finer was observed. Electron microscopy showed that SR and SR + HT specimens contained lack of fusion, and spherical gas porosity, which resulted in remarkable scatter in the observed elongation to break values. Application of HIP resulted in the highest strength values, higher than those observed for conventional H13 heat treated in the same way. The conclusion is that HIP promotes reduction of porosity and lack of fusion defects and can be efficiently used to improve the mechanical properties of AM H13 tool steel.
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.
In the present study, a modified H13 hot-work tool steel (M-H13) was fabricated by laser beam powder bed fusion (LB-PBF). The effect of two types of post processing, direct tempering from as-built ...condition (DT) and conventional quenching followed by tempering (QT), on the microstructure and mechanical properties was evaluated. The typical microstructure in QT condition was tempered martensite with carbides along lath boundaries. In DT condition, melt pool boundaries and cellular structure from as-built condition were still observed. While comparable tensile properties and hardness were obtained, DT samples exhibited significantly lower impact toughness compared to QT samples. This was attributed to the difference in work hardening ability and strain rate sensitivity originating from different microstructures obtained under these two heat treatment conditions. The study was also focused on the softening behavior and the correlation with the microstructure of the two post treatments at the elevated temperatures. It was found that the DT samples showed lower thermal softening compared to QT samples. The evolution of carbides was discussed based on the microanalysis results and the JMatPro simulation.
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
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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.
This study investigated laser powder bed fusion (LPBF) additive manufacturing of H13 tool steel to identify how laser power (P) and scan speed (V) influenced melt pool geometry, microstructure, and ...susceptibility to cracking. Sequential studies from tracks, pads to 3D cubes were performed. Tracks and pads were made by laser scan on H13 build plates with and without powder addition. P-V windows were identified where keyholing, balling and under-melt occurred. The only change in melt pool geometry between the powder and no-power experiments was a slight shift of P-V window for the onset of balling. An inhomogeneous microstructure was observed for some tracks and pads, with a cellular-network microstructure and isolated-whisker microstructure at different regions in the same melt pool. Cracks were found in the regions with the isolated-whisker microstructure. Based on these observations, P-V windows of higher and lower cracking tendency were predicted. 3D-cubes built by P-V sets in different windows showed crack densities in line with the predictions. The results of this study provide guidance for LPBF process control to obtain uniform microstructure and minimize cracking of H13 steel parts.
Among various processes for manufacturing complex-shaped metal parts, additive manufacturing is highlighted as a process capable of reducing the wastage of materials without requiring a post-process, ...such as machining and finishing. In particular, it is a suitable new manufacturing technology for producing AISI H13 tool steel for hot-worked molds with complex cooling channels. In this study, we manufactured AISI H13 tool steel using the laser power bed fusion (LPBF) process and investigated the effects of tempering temperature and holding time on its microstructure and mechanical properties. The mechanical properties of the sub-grain cell microstructure of the AISI H13 tool steel manufactured using the LPBF process were superior to that of the H13 tool steel manufactured using the conventional method. These sub-grain cells decomposed and disappeared during the austenitizing process; however, the mechanical properties could be restored at a tempering temperature of 500 °C or higher owing to the secondary hardening and distribution of carbides. Furthermore, the mechanical properties deteriorated because of the decomposition of the martensite phase and the accumulation and coarsening of carbides when over-tempering occurred at 500 °C for 5 h and 550 °C for 3 h.
This study focuses on post-deposition heat treatment for possible hardfacing of cold press dies using M4 high-speed tool steel. For the experimental investigations, using the direct energy deposition ...(DED) process, powdered AISI M4 (a high-speed tool steel) is deposited on a substrate of AISI D2 (a general-use die steel). Since the post-deposition heat treatment may change the metallurgical characteristics of the deposits, the effect of post-deposition heat treatment on the mechanical behavior was investigated by observing the microstructure evolution, hardness, wear behavior, and Charpy impact tests of the specimens with different post-deposition heat treatments. The experimental results showed that post-deposition quenching and tempering led to a reduction in hardness, which was attributed to the relieved residual stress, tempered martensite, and removal of carbon from the martensite during tempering. The M4-deposited specimen without post-deposition heat treatment and the tempered M4-deposited specimen had the better wear resistance, compared to the quenched–tempered M4-deposited specimen with fine carbides. Nevertheless, the toughness increased significantly in the quenched and tempered specimen. The results presented in this paper provide guidelines for practical hardfacing applications that use high-alloy tool steel powders to achieve highly improved die and mold performances in terms of wear resistance and toughness.
•This study examined heat treatment of M4 tool steel coated by laser melting.•The types and sizes of carbide particles have a great influence on wear resistance and impact toughness.•The tempered specimen presented higher wear resistance than the quenched–tempered specimen.•The total absorption energy of the quenched–tempered specimen was highest.
The impact of the addition of tungsten carbide (1 to 7 wt%) on the microstructure and wear characteristics of the nickel–tungsten carbide composite layer fabricated by the plasma transferred arc ...(PTA) process was studied. With the addition of nanoparticles, the degree of segregation becomes lower while heterogeneous nucleation increases and refining of the microstructure enhances. Wear rate and coefficient of friction for all samples with increasing the load from 1 to 5 N decrease and wear mechanism changes from abrasive to adhesive. The higher wear resistance for samples with 3%wt is due to a decrease in the porosity of the composite coatings, strong interfacial bonding, and promotion in the deposition efficiency at the same time.
Cold tool steels contain relatively larger amount of C and Cr to utilize carbide for increase of hardness and wear-resistance. However, in the large-scale ingots, coarsening of carbides caused by ...microsegregation would degrade steel properties. Also, micro-porosity generated during ingot casting affects the risk of cracking and the occurrence of unclosed defects in the subsequent forging process. Therefore, it is important to predict and control its occurrence. In order to investigate the effect of solidification conditions on the formation of carbides and micro-porosity of 8Cr type tool steel (Fe-1C-8Cr-2mass%Mo), unidirectional solidification experiment with different solidification conditions were conducted. As a result, primary carbides in the interdendritic zone were formed and estimated to be M7C3 and M6C. The distribution coefficients were analyzed using random sampling method. The solid fraction, at which dendrite growth terminated and carbides began to crystallize, changed to higher solid phase fraction as the pull-down speed decreased. G/√R was calculated using the temperature gradient G and cooling rate R, and the relationship between the micro-porosity area fraction was investigated. The results showed that porosity occurrence was minimal in the range of 1.6 to 7.0 (K-s)1/2/mm. In the larger range of G/√R, the porosity formation is considered to be caused by insufficient supply of liquid phase due to higher solid phase ratio and lower permeability to the final solidification zone when the eutectic phases start to crystallize.
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