以Q235低碳钢为研究对象,研究其在不同温度和应变速率热变形过程中的膨胀曲线改变,揭示低碳钢在动态再结晶过程的临界条件和晶粒尺寸。结果表明,当变形温度大于850℃,应变速率在0.1~60.0 s-1之间,应力应变曲线上对应峰值为动态再结晶过程。奥氏体动态再结晶发生的前提条件是εc=3.628×10-4DA0.21Z0.17,且可以通过控制钢的冷却速度获得较小尺寸的铁素体晶粒。 Taking Q235 mild steel as the research object, the change of its expansion curve during hot deformation under different temperature and strain rate was studied, and the critical condition and grain size of low carbon steel during dynamic recrystallization were revealed. The results show that when the deformation temperature is higher than 850 ℃ and the strain rate is between 0.1 ~ 60.0 s-1, the corresponding peak value on the stress-strain curve is the dynamic recrystallization process. The precondition for the dynamic recrystallization of austenite is εc = 3.628 × 10-4DA0.21Z0.17, and the smaller size ferrite grains can be obtained by controlling the cooling rate of the steel.