| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To secure the hardness necessary in a high hardness need portion by effectively utilizing the remained heat after hot-forging, and to surely suppress the raising of hardness in a low hardness need portion adjacent to the high hardness need portion. <P>SOLUTION: After hot-forging to a connecting rod as a steel part (P1 time point), this forged material is air-cooled as it is, and it is waited until the whole body temperature is lowered to just below A1 transformation point (Ar transformation point) (P2 time point). Successively, only column part in the connecting rod is heated to A1 transformation point (Ac transformation point) or higher, with a high frequency induction coil (P3 time point). Thereafter, the whole body is rapidly cooled and only the column part is hardened to secure a desired strength and a large end part and a small end part at both end sides of the column part are made to low hardness, and good machinability is secured. <P>COPYRIGHT: (C)2007,JPO&INPIT</p> |
