1984 年 55 巻 2 号 p. 110-120
Effects of chemical composition and hot working condition on the toughness of microalloyed steels for machine structural use were investigated. The results obtained were as follows.
(1) Decrease of C content, increase of Mn and Cr content, refining of prior austenite grain size and increase of cooling rate improve the toughness of microalloyed steel.
(2) Improved toughness by grain refining is mainly due to decrease of cleavage facet size. It is assumed that decrease of it lowered the brittle ductile transition temperature.
(3) Improved toughness by increase of Mn and Cr content is mainly due to decrease of cementite lath thickness. It is assumed that decrease of it is owing to “pearlite dilution”.