升温速率对热冲压超高强钢奥氏体化的影响

Effect of Heating Rate on Austenization of Hot Stamped Ultrahigh Strength Steel

利用Gleeble 3500热模拟实验机研究热冲胍成形超高强钢B1500HS快速加热过程中的奥氏体化。研究结果表明随着升温速率的增加，相变温度Ac1，Ac3和奥氏体均匀化温度逐渐升高，这与用JMatPro热力学计算的TFA图结果基本吻合。当奥氏体化温度低于940℃时，在保温10min以内，不同升温速率下奥氏体晶粒尺寸均可保持在5-15μm范围内。当奥氏体化温度更高时，奥氏体晶粒快速长大，升温速率越大，长大的潜能也越大。碳化物的固溶受升温速率，奥氏体化温度和保温时间的影响。在940℃下保温5min碳化物能够全部固溶。研究结果还证明，在足够快速冷却且未变形的情况下，碳化物的固溶程度对淬火马氏体硬度几乎不产生任何影响。

Austenization of hot stamped ultrahigh steel B1055HS during heating at high rate is analyzed with Gleeble 3500 simulation testing machine. The result reveals the phase transition temperature Ac1 and Ac3 and homogenizing temperature of austenite components rise gradually with the increase of heating rate. This matches the TTA diagram that is calculated with JMatPro thermodynamics software, When austenization temperature is below 940 ℃ and is hold for 10 minutes or less, the austenite gain obtained at different heating rates are sized in the range of 5-15 μm. When anstenization temperature increases higher than 940 ℃, the austenite grain grows rapidly, and higher the heating rate is, higher the growth potentiality becomes. The solid solution of carbides depends on heating rate, austenization temperature and soaking time. Solid solution of all carbides can be achieved when the temperature is hold at 940 ℃ for 5 minutes. The carbides solution degree has little effect on the quenching hardness of martenite at high cooling rate without deformation.