Effect of Tempering Air Cooling Temperature on Surface Residial Stress of 40Cr Steel Quenched and Tempered Heavy Forging

In order to investigate the surface residual stress of 40Cr steel quenched and tempered heavy forging after high temperature tempering,relationship between surface residual stress and tempering cooling temperature of mm and mm 40Cr steel specimens was studied by using X-ray stress measurement.The maximal instantaneous thermal stress in the mm quenched and tempered heavy forging cooling below 400 ℃ was caculated.The results show that effect on the residual stress was serious as the quenched and tempered heavy forging cooling in air and its center temperature was above 400 ℃, and the effect was slight as the temperature was lower than 400 ℃.The maximal instantaneous thermal stress of the quenched and tempered heavy forging which size was smaller than mm could not cause the cracking.