镀锌热冲压钢板成形过程中的裂纹产生及扩展

Cracks generation and propagation mechanism of galvanized hot stamping steel plate during hot deformation

采用Gleeble热模拟机,利用扫描电镜SEM(附带EDS)及电子探针EPMA研究了镀锌热冲压钢变形过程中裂纹的产生原因和扩展机理。结果表明:镀锌热冲压钢板高于782℃成形时,易产生液态金属致脆断(LMIE)的裂纹。镀层主要由固态的α-Fe(Zn)和液态Zn组成。裂纹产生于α-Fe(Zn)和液相界面处,液态锌沿奥氏体晶界渗透并与基板不断产生α-Fe(Zn),裂纹沿α-Fe(Zn)和液相界面处不断扩展,导致基体发生脆断。为避免或减轻LMIE裂纹的出现,可控制奥氏体化工艺使镀层仅含固态的α-Fe(Zn)相或者使液态相远离基体,并采用较低的热成形温度。

Cracks generation and propagation mechanism of galvanized hot stamping steel during hot deformation were studied by means of Gleeble simulator,scanning electron microscopy (SEM) with energy dispersive spectrometer system (EDS) and electron probe micro analyzer (EPMA). The results show that liquid metal induced embrittlement (LMIE) cracks are easy to generate when the hot forming temperature is above 782 ℃,coating mainly consists of solid α-Fe (Zn) phase and liquid zinc,cracks are generated at the interface betweenα-Fe (Zn) and liquid zinc,the liquid zinc is penetrated along the austenite grain boundaries and react with Fe to generate the α-Fe (Zn),cracks are continuously propagated along the α-Fe (Zn)/liquid zinc and finally cause the base metal breakage. To avoid or reduce LMIE cracks,one way is to control the coating phase with mainly solid α-Fe (Zn),or liquid phase far away the base,and employ low hot forming temperature.