抄録
The influence of manganese and sulfur contents of steel on its hot ductility just below solidus temperature which has close relation to the internal crack was investigated using a hot tensile testing machine.The shape and composition of sulfide were also examined in relation to the hot ductility of steel. In order to evaluate the hot ductility of steels below solidus temperature, two parameters were introduced, the first being Z.D.T. (Zero Ductility Temperature) and the second recovery ratio of reduction area. These two parameters have close relation to Mn3/S, where Mn and S are manganese and sulfer contents (wt%) in steel, respectively. In the steel whose Mn3/S is less than 1.5, the recovery state of ductility below solidus temperature changes for the worse abruptly, and hence internal crack was considered to occur easily.
