1959 Volume 28 Issue 12 Pages 864-870
For the steel DT containing low carbon, Ni, Mo, V and B, of which ultimate tensile strength is about 90 kg/mm2 in the state quenched from 930°C and water cooled after tempering for 1hr at 630°C, as well as USS "T-1" steel, the continuous cooling transformation diagram in case of maximum heating temperature 1350°C was constructed. Then this continuous cooling transformation diagram was compared with that obtained in case of maximum heating temperature 1093°C by Nippes, Savage and Allio.
The following results were obtained :
1. The A3-transformation point of steel DT is extremely low. In the continuous cooling transformation diagram, the time at the Ac3 temperature 833°C was adopted as 0 sec of a datum point.
2. Critical cooling times of steel DT are determined as follows ; Cz'=6 sec, Cf'=18 sec, Cp'=56 sec, Ce'>2000 sec. The cooling time corresponding to 50% martensite is 18.5 sec, namely, near the value of Cf'.
3. The positions of the beginning curves and the ending curves of each consitituents of microstructures in the authors' continuous cooling transformation diagram in case of maximum heating temperature 1350°C, remove to the longer cooling time and lower temperature side, compared with those in the continuous cooling transformation diagram in case of maximum heating temperature 1093°C constructed by Nippes, Savage and Allio.
4. In the author's continuous cooling transformation diagram, critical cooling time Cz', Cf', Cp', 50% martensite cooling time and others are determined, but in that diagram by Nippes, Savage and Allio, Cz' critical cooling time was only determined and 4.6 sec of the value is smaller than 6 sec of the author's value.