本文阐述了常温下钢质板材平面应力断裂韧性Kc的测试及用图解法计算裂纹扩展力Gc然后转换为Kc的原理,得到计算平面应力断裂韧性的一般公式,并根据此公式对18Mn2CrMoB钢模冷空淬后不同温度回火后Kc值进行了计算,讨论此钢常温下平面应力断裂韧性Kc值与回火温度的关系,并进行了理论分析,指出了此钢二个回火脆性区及产生回火脆性的原因,本文具有一定的理论意义和实用价值。 This paper expounds the test of plane stress fracture toughness Kc of steel plate at room temperature and the principle of calculating crack propagation force Gc and then Kc by graphic method. The general formula for calculating plane stress fracture toughness is obtained. Based on this formula, the die cooling of 18Mn2CrMoB steel After quenching at different temperatures, the Kc value was calculated. The relationship between Kc value and tempering temperature at normal temperature was discussed and the theoretical analysis was conducted. The two temper brittleness zones The reason of temper brittleness, this article has a certain theoretical significance and practical value.