2004 年 44 巻 7 号 p. 1167-1172
The cast hot working die steel is treated by mechanical vibration (MV) with a frequency of 50 Hz during the solidification process. The experimental results indicate that the MV may break off the dendrites growing from mould wall towards center in the steel during solidification. Therefore, the growth of the dendrites is restrained and the microstructure in the steel is refined; furthermore, MV can decrease the amount of defects such as shrinkage cavity and inclusion and enhance the compactness of the steel. The impact toughness of the steel treated with MV is as 1.5 times larger as that of the untreated steel. During thermal fatigue (TF) test, it is found that TF crack is longer and wider and the chap are more severe in the untreated steel than in the steel treated with MV. Simultaneously, the average velocity of crack propagation is 1.7 times faster in the untreated steel than in the steel treated with MV.
