Effect of Different Rolling Passes on Microstructure and Mechanical Properties of M390 Powder Metallurgy High-Speed Steel

The microstructure and mechanical properties of M 390 powder metallurgy (PM) high-speed steel after rolling processes are systematically investigated and compared by scanning electron microscope microstructure observation, x-ray diffractometer phase analysis and room-temperature tensile experiments. The results found that the microstructure of M390 PM high-speed steel with different rolling passes is composed of ferrite matrix, trace martensite and MC carbides, M₇C₃ carbides and M₂₃C₆ carbides. On the one hand, the rolling deformation refines the microstructure; on the other hand, the high temperature during hot rolling processes causes the carbides to grow and coarsen, so the rolling pass has no regular effect on the carbides of the powder metallurgy high-speed steel. With the increase in the number of the rolling passes, the hardness and strength of the M390PM high‐speed steel plate increase firstly and then do not significantly change. Because the smaller the carbide size is, the higher the roundness is, the more the dispersed carbide is, and the higher the hardness and strength is. The increase in the rolling passes induces the number of carbides distributed on the matrix, which decreases the dispersed strengthening effect.