Anisotropic size change during continuous quenching and deep freezing of tool steel *

Abstract

Abstract The size change of a low carbon maraging steel and of a ledeburitic cold work tool steel produced by ingot (IN) or powder metallurgy (PM) was measured by dilatometry using specimens taken in longitudinal or transverse direction of hot working. The anisotropy of the size change during martensitic transformation ΔεM was negative for the maraging and the PM steel, but positive for the IN steel and the more so, if the cooling rate was raised by injecting liquid nitrogen during quenching to −150 °C. The microstructure and texture was investigated by high resolution SEM equipped with microprobe analysis and respective imaging as well as by EBSD. The results show that Δεis not related to a texture M of the martensitic matrix but to a microstructural banding caused by microsegregation and hot working. The alignment of the eutectic M7 C3 carbides in the direction of hot working coincides with their texture.