Relation between ingot segregation part of large forged product and quenching crack

Abstract

Some of the causes of quenching cracks are considered to be related to ununiform cooling and variation of the material composition. Segregation is always generated in the inner parts of large steel ingots during production process. Especially in the forging process of large products, it is considered that the variation of the material composition affects the quenching crack generation. It is important to clarify the effect of extent of the segregation in the large forged products on quenching crack generation. Quenching test using cylindrical test specimens, which were cut out from the segregated part and the less-segregated part in large forged materials of a 40 ton ingot, was conducted. As a result, it is found that test materials from the segregated parts showed low resistance against quenching crack that means high possibility of quenching crack generation than those of the less-segregated parts. In addition, quenching test using large forged products which have no-segregation and segregation in the surface were conducted. In case of no-segregation in the surface, quenching cracks did not initiate in the surface where high quenching stress was estimated to occur by the quenching analysis. In case of segregation in the surface, however, quenching crack initiated in the surface. Those results reveal that segregation affects the initiation of quenching crack. It should be noted that the existence of segregation in the material surface has the substantial influence on quenching crack generation.