Effect of cryogenic treatment on the hardness and tensile behaviour of AISI 4140 steel

Abstract

This paper deals with the influence of cryogenic treatment on the hardness and tensile behaviour of AISI 4140 steel. The impetus for studying the tensile properties of steels is to ensure that steels used in shafts and gears have sufficient tensile strength to prevent failure when they are subjected to tensile or fatigue loads, and to provide basic design information on the strength of 4140 steel. A comparative study on the effects of deep cryogenic treatment (DCT, 77 K × 5 h) and conventional heat treatment (CHT) was made by means of hardness and tension testing. Fracture features of tensile specimens were also compared. It has been shown that the hardness of shallow and deep cryogenically treated specimens are higher whereas the tensile strength of the shallow and deep cryogenically treated specimens are lower when compared to that of conventionally treated steel. The transformation of retained austenite to martensite is responsible for present result.