Abstract:The strain induced precipitation of medium-carbon Nb microalloyed steel was investigated by the stress relaxation method and DS precipitation kinetics model, the effects of Si and Mn on the precipitation kinetics of Nb carbonitride added to the DS equation. The results show that the caculated precipitation-time-temperature PTT diagrams are in good agreement with experimental results obtained from isothermal stress relaxation, and the shape of PTT is typical C curve; The fastest precipitation was about 900℃, strain rate accelerates the precipitation kinetics and shifts the PTT diagrams leftside.