Controlling of reheated quenching temperature of 1000MPa grade steel plate for hydropower station

The strength and toughness of 1000MPa grade steel plate for hydropower station treated by different reheated quenching temperatures were investigated. With the increasing of reheated quenching temperature, the yield strength and tensile strength increase sharply, whereas the value of impact toughness decreases slowly. The lath martensite with high density dislocations enhances dislocation strengthening. On the contrary, the acicular or block ferrite (soft phase) produced by intercritical quenching reduces the phase transformation strengthening. Moreover, the ferrite has a low solubility of interstitial carbon due to the body-centered-cubic lattice structure. The bar-shaped precipitates occur during the isothermal holding at the intercritical temperature and it will reduce the precipitation strengthening. The ferrite phase and high misorientation boundaries are the main factors that contribute to the toughening of the experimental steel. The lower the reheated quenching temperature is, the higher proportion of ferrite and high misorientation boundaries becomes. Considering the requirements for mechanical properties of 1000MPa grade steel plate for hydropower station, the optimal temperature of reheated quenching is approximate to 920 degrees C.