High Temperature Tensile Properties of Cryogenically treated AISI 4340 Steel

Abstract

Deep cryogenic treatment is now extensively adopted as a supplementary process for many engineering applications such as for improving wear resistance, for improving stability of precision measurement equipment, in press tools, etc. In this study, the tensile properties of quenched, tempered and cryotreated AISI 4340 Ni-Cr-Mo low alloy steel are investigated under different process parameters including time and temperature. This steel finds application in press dies, landing gears of aircraft, crankshafts, connecting rod, heavy duty axles, etc. The results have demonstrated that the hardness of test samples is been increased by 6.366% for HCT (Hardened-cryotreated-tempered) samples and by 19.36% for HTC (Hardened-tempered-cryotreated) samples with reference to 377 Hv of HT (hardened-tempered) samples. Improved tensile properties are observed at elevated temperatures (200 and 4000C) for cryotreated samples. This is because the internal stresses developed due to martensite transformation of hardened samples are relieved to a large extent. The improved tensile strength and reduced %elongation can be attributed to coarsening and homogenization of carbide in microstructure.