| 摘要 |
A surface treatment method for a steel material includes a carbonitriding step, a quenching step, and a tempering step, in this order. The steel materials 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 S, 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 A 3 point of the steel 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 mixed gas atmosphere consists of not less than 50 vol % of NH 3 and the balance of inert gas and inevitable impurities. 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. |
