V对H13型压铸模具钢相变特性的影响

Effect of V on Phase Transformation Characteristic of H13 Die-casting Die Steel

本研究采用热膨胀仪测定了不同钒(V)含量的H13型压铸模具钢的连续冷却转变(Continuous cooling transformation,CCT)曲线及等温转变(Time temperature transformation,TTT)曲线,并结合扫描电镜、显微硬度仪、X射线衍射仪分别探究了V元素含量对H13型压铸模具钢相变点(加热过程中珠光体转变为奥氏体的温度A c1,加热过程中渗碳体和碳化物完全溶入奥氏体的温度A ccm和奥氏体化后冷却过程中奥氏体向马氏体转变开始温度M s)、连续冷却转变规律、等温转变规律以及硬度的影响。结果表明:随着V元素含量的增加,试样的M s点升高,CCT和TTT曲线中的珠光体及贝氏体相区出现左移,CCT曲线中珠光体和贝氏体相区的临界冷却速度加快,试样的淬火态硬度降低。这主要是因为随着V含量的升高,试样中形成了更多稳定的V系碳化物,从而降低了奥氏体化过程中溶入基体的碳含量,进而降低了过冷奥氏体的稳定性,最终促进珠光体及贝氏体相变的发生,即CCT和TTT曲线中珠光体及贝氏体相区左移。

The continuous cooling transformation(CCT)curves and time temperature transformation(TTT)curves of H13 die-casting die steels with different mass fractions of V were measured by dilatometry.The effects of V on the phase transformation points(A c1,A ccm and M s)CCT curves,TTT curves and hardness of H13 die-casting die steels with different mass fractions of V were studied by scanning electron microscopy(SEM),Vickers hardness test and X-ray diffractometer(XRD).The results show that the M s of H13 significantly increase,pearlite and bainite phase regions in CCT curves and TTT curves shift to the left,critical cooling rate of pearlite and bainite phase regions in the CCT curves increase,and the quenched hardness decreases with the increase in mass fraction of V.Subsequently,our work also explored the mechanism about the effect of different mass fractions of V on the phase transformation characteristic.It can been seen that more stable V-based carbides are formed with the increase in mass fraction of V,which reduce the carbon content dissolved in the matrix during the complete austenitizing process,and then reduce the stability of the undercooled austenite.Eventually,the pearlite and bainite transformations are promoted,which means the pearlite and bainite phase regions in the CCT curves and TTT curves are shifted to the left.