The microstructure and wear behavior of S390 high-speed steel (HSS) reinforced with different volume fractions of MC-type carbides produced via spark plasma sintering were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in this study. SEM and TEM results show that V-W-rich carbides are formed around the added MC-type carbides, and these carbides have a similar composition to the M(C, N) carbides precipitated at high temperatures according to thermodynamic calculations. Both macrohardness and three-point bending results show that the carbide type is the dominant factor increasing the hardness, and the volume fraction of the carbide is the dominant factor leading to a decrease in the three-point bending strength. The wear mechanism of HSS metal matrix composites (MMCs) is confirmed as abrasive wear and oxidative wear via wear tracks and oxidation films. Compared with the sample without reinforcement (85 HRA, wear coefficient of 1.50 × 10⁻¹⁵ m²/N), the best MT-3 sample exhibits a hardness increase of 1.8 HRA and a three-fold increase in wear resistance.

Repairing hot work molds can extend their lifespans and reduce the production costs. This study presents a proposed method for enhancing the red hardness and strength of repaired molds. The method involves utilizing PM23 high-speed steel powder to repair H13 steel molds with two distinct surface states through the process of hot isostatic pressing (HIP). The internal microstructure changes, bonding state, fracture morphology, and crack extension behaviors of the repaired molds are characterized using scanning electron microscopy and electron backscatter diffraction technology. Additionally, the mechanical properties, including red hardness and tensile strength, are quantitatively analyzed. The findings indicate that the repaired area in the sandblasted sample exhibits a rough and uneven structure, demonstrating exceptional toughness. The tensile strength of the repaired region is approximately 1195.42 MPa, while the hardness measures around 672.8 HV. These properties effectively enhance the performance of the molds. The experimental findings indicate that HIP can effectively restore molds, resulting in enhanced red hardness and improved toughness, particularly when combined with sandblasting as a pretreatment method.

High resistance to tempering and extended service life are pivotal research directions for cutting tools utilized in the machining of industrial machine tool. The design of alloys and their manufacturing processes have become methods for the development of cutting tool materials. Carbon-free Fe-Co-Mo steel (FCM) has garnered attention due to its excellent magnetic properties and high-temperature performance, as well as its superior thermal conductivity, making it an ideal choice for applications in high-temperature and high-pressure environments. The µ-phase within this alloy exhibits exceptional high-temperature stability and resistance to aggregation. Its characteristics suggest that it has the potential to replace carbide reinforcement phases, which are prone to coarsening, in high-temperature applications of powder high-speed steel. This application of the µ-phase could lead to an enhancement in the resistance to tempering and the service life of powder metallurgy high-speed steel cutting tools. However, there is a relative scarcity of published research regarding the preparation of carbon-free high-speed steel via hot isostatic pressing (HIP) technology and the subsequent heat treatment processes. In this study, Fe-Co-Mo alloys reinforced with the intermetallic compound µ-phase were prepared at hot isostatic pressing sintering temperatures of 1200 °C, 1250 °C, and 1350 °C. Furthermore, to investigate the influence of the solid-solution treatment temperature on the microstructure and macroscopic properties of the alloy, the as-prepared materials were subjected to solution annealing treatment at different temperatures (1120 °C, 1150 °C, 1180 °C, and 1210 °C). The results demonstrate that by moderately reducing the sintering temperature, the segregation phenomenon of the reinforcing µ-phase was significantly reduced, leading to an optimization of the microstructural uniformity of the prepared sample, with the micro-scale µ-phase being uniformly dispersed within the α-Fe matrix. As the temperature of the solid-solution annealing increased, the microstructural uniformity was further enhanced, accompanied by a reduction in the quantity of the reinforcing phase and refinement of the grain size. Notably, after solid-solution annealing at 1180 °C, the hardness of the samples reached a peak value of 500.4 HV, attributed to the decrease in the reinforcing phase and grain refinement during the annealing process. Aging treatment at 600 °C for 3 h facilitated the uniform precipitation of the nano-scale µ-phase, resulting in a significant increase in sample hardness to approximately 900 HV. The prepared material exhibited excellent resistance to tempering, indicating its potential for application in high-temperature service environments.