Processing, microstructure, strength, and ductility relationships in ultrahigh carbon steel assessed by high strain rate torsion testing

Abstract

The torsional ductility and strength of an unalloyed ultrahigh carbon steel containing 1·3%C (UHCS–1·3C) has been studied at high strain rates (0·2–26 s-1 ) and high temperatures (750–1200°C). The strength–strain rate relationships are in agreement with a diffusion controlled dislocation creep model, where power law creep is observed with a stress exponent n of ∼5. The results were compared with the high temperature ductility and strength of a medium carbon (0·3%C) high strength, low alloyed (HSLA) steel, 304 stainless steel, and an alloyed ultrahigh carbon steel (UHCS–1·8C–1·6Al–1·5Cr). It is shown that the UHCS–1·3C material is the most ductile of the four materials, and has the lowest stress for plastic flow. The results are explained by the high rate of iron lattice diffusion and by the high stacking fault energy in the UHCS–1·3C material. It is proposed that contemporary processing and manufacturing equipment can be used to make pearlitic structure ultrahigh carbon steels for high strength room temperature applications.