Ausforming of medium carbon steel

Abstract

The prospect of enhancing the hardness of low alloy steel for the manufacture of fasteners is examined using ausforming, in which the austenite is deformed rapidly at a low temperature to increase its dislocation density before quenching in order to obtain the harder martensite. Surprisingly, small deformations accomplish large gains in hardness and the dislocation density of martensite, with diminishing returns at larger deformations. The main contribution to the hardness has been identified as the extra dislocations inherited by the martensite from the deformed austenite, rather than the refinement of microstructure by the ausforming process. Clear evidence is reported for the mechanical stabilisation of the austenite due to ausforming. Tempering heat treatments tend to diminish the advantages of ausforming.