Abstract: Low carbon high copper HSLA steel was solution treated and aged at different temperatures. The effect of aging temperature on the microstructure and mechanical properties of the low carbon high copper HSLA steel was studied by means of scanning electron microscopy, transmission electron microscopy, tensile test, hardness test and low temperature impact test. The results show that after solution treatment at 880 ℃ for 1 h, with the increase of aging temperature, the tensile strength and hardness of the HSLA steel increase first and then decrease, the elongation increases gradually, and the impact absorbed energy at low temperature decreases first and then increases. The tensile strength and hardness of the HSLA steel aged at 440 ℃ reach the peak value, and the impact absorbed energy at low temperature is the lowest. A large number of 5-10 nm Cu particles precipitate from the HSLA steel matrix when aged at 440 ℃, which has a good strengthening effect on the HSLA steel. When the aging temperature reaches 600 ℃, the size of precipitated Cu particles reaches 20-30 nm, and the coarsening effect is weakened. The mechanical properties of the HSLA steel aged at different temperatures are jointly affected by two factors which are Cu particle phase precipitation strengthening and matrix softening. When the aging temperature is below 440 ℃, the strengthening effect of Cu particle phase precipitation is dominant. When the aging temperature exceeds 440 ℃, matrix softening plays a dominant role.

Key words: low carbon high copper HSLA steel, heat treatment, microstructure, mechanical properties