2007 年 2007 巻 52 号 p. 35-43
The newly designed springs tend to demand a steel capable of greater strength resulting in the increased possibility of delayed fracture. The study of delayed fracture, mainly on bolt steel, has been reported a good deal. However, the delayed fracture characteristics are evaluated in a variety of ways, and its evaluation method has not been established yet. In general, a spring is subject not only to static load but also to dynamic load. This makes it difficult to apply the method for bolt steel to spring steel in the practice of delayed fracture evaluation. Because of this situation, this committee, which is aimed to standardize the delayed fracture evaluation method for spring steel in future, started to implement followings: (1)Research of current delayed fracture evaluation method, (2)Survey of delayed fracture phenomena in springs, (3)Examination of charging and chemical analysis method of hydrogen. As a result of these activities, (1)understanding of delayed fracture of springs has been enhanced by the research of current delayed fracture evaluation method of bolt steel, (2)the effect of hydrogen on delayed fracture has been identified as a key study subject by the analysis of delayed fracture phenomena in springs. And (3)fundamental findings for standardizing the chemical analysis of hydrogen have been obtained through the study with a standard spring steel(JIS-SUP7).