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900~1100℃淬火后,研究了250~600℃回火对高钒高速钢残留奥氏体转变及碳化钒析出的影响。结果表明:高钒高速钢的回火温度存在临界值(约450℃)。当回火温度低于临界值时,残留奥氏体含量变化不明显。当回火超过临界值后,随回火温度提高,残留奥氏体含量迅速降低。回火过程中碳化钒自残留奥氏体中析出是残留奥氏体转变的前提条件。碳化钒的析出取决于非平衡热力学条件,而其析出量在回火温度超过450℃后可根据平衡热力学估算。碳化钒的析出使得残留奥氏体向马氏体转变的相变驱动力大于临界相变驱动力,为残留奥氏体转变提供可能,但残留奥氏体的转变量主要取决于动力学因素。回火温度提高引起马氏体形核率呈指数提高,导致残留奥氏体含量迅速降低。
After quenching at 900-1100 ℃, the effect of tempering at 250-600 ℃ on the retained austenite transformation and vanadium carbide precipitation in high vanadium high speed steel was studied. The results show that there is a critical value (about 450 ℃) for the tempering temperature of high vanadium high speed steel. When the tempering temperature is below the critical value, the retained austenite content does not change significantly. When the tempering exceeds the critical value, with the tempering temperature increases, the residual austenite content decreased rapidly. Tempering vanadium carbide precipitation from residual austenite is the prerequisite for the transformation of retained austenite. Vanadium carbide precipitation depends on the non-equilibrium thermodynamic conditions, and its precipitation after the tempering temperature exceeds 450 ℃ can be estimated based on equilibrium thermodynamics. The precipitation of vanadium carbide makes the phase transformation of residual austenite to martensite larger than the critical phase change driving force, which provides the possibility for the transformation of retained austenite. However, the amount of retained austenite transformation mainly depends on the kinetic factors. Tempering temperature increase caused by martensite nucleation rate increased exponentially, resulting in rapid reduction of retained austenite content.