含銅低炭素鋳鋼の析出硬化性におよぼす焼準時の質量効果について

含銅低炭素鋼に関する研究-II

抄録

The effect of cooling rate in normalizing of copper-bearing low-carbon cast steels containing 0.1% C, 0.5% Si, 1.0% Mn and various amounts of copper up to 3.0%, on the precipitationhardening by subsequent tempering has been studied and discussed. The main results obtained are as follows:
(1) In steels containing 1.0-1.5% copper, the most significant precipitation-hardening on tempering is found to occur, the hardening being apparent even after a considerably slow cooling by normalizing. While, in steels containing copper more than 2.0%, the precipitation of copper occurs easily during cooling in normalizing, and the hardening due to the subsequent tempering is smaller as compared with that containing less copper.
(2) It is concluded that during the normalizing-cooling of steels containing copper more than 2.0%, copper-rich phase precipitates quickly at a temperature above 700°C together with ferrite as a binary eutectoid from austenite, facilitating the precipitation of copper from ferrite during cooling down to lower temperatures.
(3) Due to the cooling rate in normalizing, the copper content, and the tempering, the change of tensile strength of the steels is found to be proportional to the hardness change described above. While, elongation of the steels is decreased only when the cooling rate is increased, and it is not affected by copper content and by tempering treatment at 550°C.
(4) It is also certified that the addition of copper improves the fluidity of molten steels.