熱間圧延せる硬質条鋼の側面中心部の裂疵および研磨割れならびに焼割れの生因について

抄録

When hard materials as high carbon chromium steel are rolled to bar at high temperature, it occurs fraquently that cracks appear at the centers of both the free sides of the bar which don’t come in contact with the roll surfaces. Grinding cracks are generated in the same sites when both the sides are grinded, and sites quenching cracks appear in the same way when quenched. The author concidered that some relations exist between the three cases and carried out some experiments whose results are as follows:
(1) From a microscopic study it is recognized that fiber structure is equally divided in two on the center line adjacent to the free sides and concentrated toward both corners, so severe tension operates on the free side when rolled, which suggests the cause of cracks. (2) It is clarified that severe tensile stress remains in region adjacent to the surface contacting with the rolls, while compression operates in the inner region and remains adjacent to the free sides. (3) When any region with different residual stress is partially and suddenly cut off by grinding, so the balance of stress is broken on the center line on which the stresses are symmetrical and then grinding cracks follows. (4) Since transformation stress due to quenching has the same tendency as residual stress due to rolling, so the latter is superposed by the former at quenching and the crack may be generated.