2000 年 40 巻 11 号 p. 1164-1169
The effects of alloying elements on thermal properties of the HSLA (High Strength Low Alloy) cast steels have been investigated by thermal fatigue, thermal shock, and tensile tests. The thermal fatigue resistances of the HSLA cast steels were superior to those of SC42 cast steels. Excellent thermal resistances of the HSLA cast steels were mainly caused by high thermal conductivity, elastic modulus and tensile strength. In case of the HSLA cast steels, the steels with both Nb and V had more excellent thermal fatigue life than those with Nb or V individually. Increment of C contents gave a harmful effect on thermal fatigue resistance. In case of Mn contents, HSLA cast steels with 1.2 % Mn content had the highest thermal fatigue life among them and that with 1.5 % Mn had lower thermal fatigue life than that with 1.2 % Mn content. This result was attributed to rapidly increased bainitic acicular structure obtained by high Mn contents. Therefore, the optimum composition of HSLA cast steels to obtain the highest thermal fatigue resistance was 0.1%C–1.2%Mn–0.05%Nb–0.05%V, resulting in polygonal ferrite plus small amounts of bainitic microstructure. Thermal shock resistance of HSLA cast steels was also superior to that of SC42 cast steels. However, the difference between the HSLA cast steels with both Nb and V, and those with Nb or V individually has not been found.
