Achieving stable ultrafine grain structure through cold shearing and heat treatment of Cr4Mo4Ni4V martensitic steel

In this study, a full view of the shear location was presented and ultrafine grain structure with excellent thermal stability during 700–850 °C was obtained through cold shearing and heat treatment of martensitic Cr4Mo4Ni4V steel. The results reveal that initial martensite blocks were refined through local rotating the elongated blocks into small grains in the shear region with effective strain 2–2.5. Driven by the shear deformation and heat treatment, ferrite recrystallization (about 1 μm) bands formed in the shear region mainly through continuous recrystallization at 700–850 °C, and mixed-grain structure (6.2 μm in average) formed at 1000 °C. Interestingly, the size and distribution of carbides in the shear region and undeformed region exhibited a dramatic difference due to the ultrafine recrystallization. This study provided information regarding achieving stable ultrafine grain structure through cold shearing and heat treatment of Cr4Mo4Ni4V martensitic steel.