Abstract
In this study, the effect of tempering conditions on microstructure, grain size, and carbide phase compositions of spray-formed high-speed steel after quenching at 1180 °C was studied. The influence of carbide phase, size of carbides, and retained austenite content on secondary hardening of the steel was analyzed by field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), electron backscattered diffraction (EBSD), and differential scanning calorimetry (DSC); the hardness, microhardness of carbide, and bending strength were tested. The results show that M3C, M6C, M7C3, and MC carbides may precipitate at different tempering temperatures and the transformation of the retained austenite can be controlled by tempering. The phase composition of carbides, microstructure, and retained austenite content strongly influences the performance characteristics of M42 high-speed steel after tempering. In contrast, the secondary carbides produced by tempering thrice at 540 °C are mainly M6C carbides rich in W and Mo elements, and the content of retained austenite is effectively reduced. At this stage, the Rockwell hardness reaches 67.2 HRC, bending strength reaches 3115 MPa, and the properties and microstructure are optimal.
Highlights
High-speed steel (HSS) is a type of Fe-C-X high alloy and high carbon content steel, where X represents Mo, W, Cr, and another alloy [1,2]
The microstructure of M42 HSS is shown in Figure 1 under different tempering conditions
The results show that the sample had a martensite matrix after tempering under 600 ◦ C, and the grain size of the martensite became smaller and the microstructure finer with the increase of tempering temperature (Figure 1a–e)
Summary
High-speed steel (HSS) is a type of Fe-C-X high alloy and high carbon content steel, where X represents Mo, W, Cr, and another alloy [1,2]. It has been used as a tool material for almost 100 years, and is still used to manufacture taps, dies, cutters, drills, and other cutting equipment [3,4,5]. Its excellent performance in the cutting process is mainly due to a combination of strengthening of the martensite matrix and secondary hardening of carbides [6]. In terms of chemical composition, HSS usually contains a high content of W, Mo, Cr, V and other strong carbide-forming elements. The dispersion of alloy carbides is the basis of HSS’ hot hardness, wear resistance, and bending strength. Cast HSS has problems in alloy element segregation and coarseness of carbides, among others
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