1000MPa热镀锌双相钢组织和断裂机理

Microstructure and fracture mechanism of 1000 MPa hot dip galvanized dual phase steel

模拟热镀锌工艺,在实验室生产了1000MPa级热镀锌双相钢.利用原位拉伸实验,对其断裂行为进行了观察,进一步探讨了其断裂机理.结果表明:实验用钢经820℃退火后,可以获得抗拉强度为1022MPa、延伸率为9.5%的F+M双相钢;动态拉伸过程中,裂纹尖端的塑性区会萌生新的微裂纹,塑性区内的铁素体晶粒内部会产生"波状"滑移带;当裂纹扩展到马氏体岛时会改变方向绕过马氏体,扩展到铁素体晶粒时,以微孔相连的塑性方式使铁素体开裂;最终断裂以塑性断裂的形式发生,断口形貌为韧窝状.

1 000 MPa grade hot dip galvanized dual phase steel was produced by simulating the process of hot dip galvanizing.The fracture behavior of the dual phase steel was observed by in-situ tension experiment,and its fracture mechanism was further analyzed by SEM and TEM.The results show that dual phase steel（F＋M）with a tensile strength of 1 022 MPa and an elongation of 9.5% can be obtained when the annealing temperature is 820 ℃.During the process of dynamic tension,new micro-cracks initiate in the plastic zone of crack tips and wave-like slip bands generate in ferrite grains in the plastic zone.When the crack meets martensite,it changes its propagation direction and get around the martensite island;but when the crack meets ferrite,the ferrite grain is plastically broken up through the way of joining micro-pores.The final fracture pattern is plastic fracture and the fracture morphology of the sample is a dimple pattern.