The effect of various alloying elements such as Si, Ni, Mn, Cr, Mo in copper-bearing low carbon steels on the age hardening phenomena was investigated and discussed. The results obtained were as follows:
(1) Only a hardening due to the C precipitation from ferrite was found to take place with the steels solution-quenched from 680°C. after the usual annealing, and the hardening due to the Cu precipitation was not observed to occur except with the steel containing Mo.
(2) With the steels furnace-cooled from 930°C. to 680°C. by 13·3°C. /mn. and subsequently quenched from the latter temperature, both of these precipitation hardenings were found to occur, the quenched state being supersaturated with copper as well as with carbon. The hardening caused by the C precipitation was found at the range from room temperature to 100°C., and the hardening by the Cu precipitation was found at above 350°C. In the stage of the C precipitation, the carbide-forming elements such as Mn, Cr, Mo retarded the hardening and reduced the maximum hardness. While, in the stage of the Cu precipitation, only Mo retarded the hardening and increased the hardness.
(3) With the steels water-quenched directly from 930°C., as a whole, the hardening due to the Cu precipitation was not clearly found, because of the increased resistance to softening on tempering by addition of the alloying elements. With the steels oil-quenched directly from 930°C., nearly the same precipitation hardening behavior was observed as that described in (2), except with one containing Mo, in which especially high hardness due to the Cu precipitation was attained.
(4) With the cold worked steels super-saturated with Cu, the recrystallization softening was found to be superposed with the precipitation hardening, and the softening temperature was raised by the Cu precipitation and the existence of carbide-forming elements, particularly of Mo.
(5) It was also certified that the addition of Ni reduced the red-shortness of the steel containing Cu.