Abstract
In the previous reports, the continuous cooling transformation diagrams were constructed for many mild steels and Mn-Si type high tensile steels. In this report, the continuous cooling transformation diagrams in case of maximum heating temperature 1350°C have been constructed for steels containing a small quantity of Ni, Cr, Mo, V and Ti in addition to Mn and Si and having ultimate tensile strength of about 60 kg/mm2.
The field of the intermediate structure (Zw) in the continuous cooling transformation diagrams of this type of steel is extending through an extremely long range of cooling time, differing from those of mild steels and Mn-Si type high tensile steels. This fact is considered to be relating to the high tensile strength and excellent weldability of this kind of steel.
The effect of carbon content on critical cooling times for these types of high tensile steel is remarkable, as well as the case of mild steels and Mn-Si type high tensile steels. The critical cooling times Cz', Cf', Cp' and 50% martensite cooling time of steel YF containing 0.18% C differ remarkably from those of steel YG containing 0.11% C. If the carbon content of this type of steel is as low as that of steel YG, critical cooling times Cz', Cf', Cp' and 50% martensite cooling time of that steel have a tendency to approach to those of mild steel.
