| 摘要 |
A surface treatment method for a steel material includes carbonitriding, quenching, and tempering. The steel material consists of, by weight %, 0.27 to 0.48% of C, 0.01 to 2.2% of Si, 0.30 to 1.0% of Mn, not more than 0.035% of P, not more than 0.035% of 8, and the balance of Fe and inevitable impurities. The carbonitriding step is performed by heating the steel at a temperature of not less than the A3 point and not more than 1100° C. and bringing the steel into contact with a mixed gas atmosphere so as to concentrate nitrogen and carbon at a surface layer of the steel. The quenching step is performed by cooling the steel to room temperature at a rate of not less than 20° C./second. The tempering step is performed by heating the steel at a temperature of 100 to 400° C.
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