EFFECT OF HEAT TREATMENT ON DELAYED FRACTURE RESISTANCE OF HIGH STRENGTH STEEL 30CrMnSi2NiNb

摘要

The steel with nominal composition of 0.3C-1.0Cr-1.0Mn-2.0Si-1.0Ni-0.04Nb was quenched and tempered and isothermally quenched at several different temperatures, respectively. It was found that the K_(ISCC) value of the quenched and. tempered steel 30CrMnSi2NiNb, with a tensile strength of 1500～1600MPa, was below 15.0MPa·m~(1/2), whereas it was about 20.0MPa·m~(1/2) when the steel 30CrMnSi2NiNb was isothermally quenched, with a tensile strength of 1350～1750MPa. With the increase of isothermal temperature, the tensile strength decreases but the K_(ISCC) value does not pronouncedly change. It's also found that the strength of isothermally quenched 30CrMnSi2NiNb was related to the austenite fraction in the microstructure, and that the delayed fracture resistance was dependent on the austenite fraction as well as carbon content of austenite.