Superplastic behaviour of powder metallurgy 1.3%C-1.6%Cr-0.8%B steel

Abstract

The high temperature deformation behaviour of an ultrahigh carbon boron tool steel containing 1.3wt-%C-1.6wt-%Cr-0.8wt-%B was investigated. The steel was processed by powder metallurgy methods, involving argon atomisation and consolidation by hot isostatic pressing at 180 MPa for 2 h at 700°C. The microstructure of the consolidated material retains the dendritic solidification structure of the rapidly solidified powders. Aferritic grain size of 1 μm was measured. This steel presents a superplastic behaviour in the temperature range 660 to 1050°C with stress exponents of ∼2 at low strain rates and tensile elongations as high as 520% at 1000°C. A change in the activation energy at the α-γ transformation temperature (738°C) was clearly observed. The creep data are in agreement with grain boundary sliding and slip creep models.