Modification of metastable microstructure of CPM15V steel by heat exposure after treatment in semi-solid state

Processing in the semi-solid state allows the benefits of the process of forming and casting to be combined. In addition to obtaining complicated shapes, unusual forms of structures with exceptional properties can also be formed. A special processing procedure in the semi-solid state for very small parts has been developed, which is called mini-thixoforming, is able to handle CPM15V steel powder. From the original ferrite matrix with primary chromium-vanadium carbides - a mixed structure was obtained by processing consisting of metastable austenite, rod-shaped chromium-vanadium carbides and the original chromium-vanadium carbides. Compared to the initial state (micro hardness approx. HV10 330), this structure achieved, as a result of the relatively high rate of cooling in the form, a hardness of approx. 730 HV10. Due to the fact that this is a metastable structure, experimental heating to temperatures 400, 500, 600, 700, 800 °C for 1 h was performed. With exposure at temperatures 400 and 500 °C there was a slight decrease in hardness of approx. 20 points, heat treatment at 600 °C achieved hardness of 960 HV10. This state corresponds to an equivalent value of compressive strength of approx. 2880 MPa, Further increase in temperature leads to a continuous decrease in hardness due to decomposition of the metastable matrix. Thermal exposure at 700 °C, resulted in hardness of 585 HV10. After exposure to 800 °C there was a significant decrease of hardness to 425 HV10.