Abstract: The precipitation of copper-enriched clusters was induced into pressure vessel model steel（with higher Cu content） of nuclear reactors by water quenching and thermal aging.The mechanical property tests showed that the presence of copper-enriched clusters led to a large shift of the ductile-to-brittle transition temperature,a tiny increase in the yield strength and tensile strength,and a tiny decrease of plasticity.In addi-tion,this paper also studied the effect of the presence of Nickel element on the ductile-to-brittle transition temperature.Three-dimensional atom probe test revealed that the number density of enriched clusters was about 10²³ m^-3,and the size of copper-enriched clusters was in the range of 1nm to 3nm in diameter.