Effect of Aging Temperature and Methods of Solution Treatmet on the Quench-Age-Hardening of Mild Steel

On the phenomena of quench-age-hardening of mild steels have already studied by many investigators for varied composition. But, there were little basic studied on the solution heat treatment of mild steels. In this paper, the present investigators studied the effect or relationship of aging temperature and methods of solution treatment on the phenomena of quench-age-hardening of mild steels with carbon 0.07% preceded by normalizing at 900℃ through means of hardness test. The results obtained may be summarised as follows : (1) In order to produce the maximum quench-age-hardening effects it is necessary to quench after holding 1 hour about 700℃. (2) Quench-age-hardening reaches about the same maximum for aging temperature up to about 10℃. (3) When aging temperature is 20℃, quench-age-hardening have reached the maximum for about 310 hours, and it is unconcerned in temperature of solution treatment being between A_1 arrest point and 680℃. (4) When aging temperature is lower and temperature of solution treatment is between A_1 arrest point and 680℃, two steps hardening are observed in the quench-age-hardening of mild steels.