Abstract
By this time, the authors constructed and reported many continuous cooling transformation diagrams in case of maximum heating temperature 1350°C for numerous kinds of mild steel and Mn-Si type high tensile steel showing various tensile strengths in the range of 35-57kg/mm2. In this report, chemical analyses of numerous kinds of mild and Mn-Si type high tensile steels, continuous cooling transformation diagrams for these steels, critical cooling times Cz', Cf', Cp', Ce' and 50% martensite cooling time obtained from the above mentioned diagrams are summarized. In particular, relations between the Cz'-, Cf'- cooling time or the 50% martensite cooling time and C-, Si- or Mn-content of steels were discussed, and the following experimental formulas were determined:
{log(50%MCT)=8.79Ceq-1.52
log Cf'=8.59Ceq-1.69
log Cz'=7.84Ceq-1.81
where Ceq=(C+1/12Mn+1/24 Si)%.
These formulas were obtained for killed, semi-killed and rimmed steels containing 0.10-0.18% C, 0.01-0.53% Si, 0.41-1.40% Mn and P, S, Cu, Ni, Cr, etc. as impurities.
When those results obtained in this report and the method for predicting cooling times from welding conditions, mentioned in other reports by one of authors, are combined, the optimum welding conditions of optional steels used can be determined previously. On this occasion the Cf' critical cooling time of a steel is an important criterion for this determination.
