| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing a hot forged non-heat treated connecting rod which can secure sufficient hardness of >=18HRC and a sufficient elastic limit even when inexpensive stock steel having a reduced V content is used. SOLUTION: Steel having a composition containing 0.35 to 0.50% C, 0.10 to 0.75% Si, 0.10 to 1.40% Mn, <=1.00% Cr and <=0.50% Cu, and, if required, further containing one or more kinds selected from <=0.08% V, <=0.120% S, <=0.30% Pb, <=0.01% Ca and <=0.30% Bi is hot-forged, and is subjected to coining at >=700 deg.C. After that, the steel is subjected to controlled air cooling at a cooling rate of 1.5 to 8 deg.C/s in the range of 800 to 600 deg.C, so that the connecting rod having hardness of 18 to 30HRC, and provided with a ferrite + pearlite mixed structure satisfying a conditional equation calculated from Mn, Si and V, the average ferrite area ratio, the average ferrite grain size, the average pearlite lamellar intervals is obtained.
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