中文摘要：

为研究影响FB780先进高强度钢扩孔性能的主要因素，按GB/T 15825.4-2008标准进行扩孔试验，采用光学显微镜、扫描电镜、显微硬度计等对扩孔前后试验钢的显微组织、冲孔表面光亮带与撕裂带形貌、近冲孔孔缘2 mm的微区硬度梯度以及扩孔件上贯穿裂纹处的形貌及其中的第二相进行了分析，得到了影响FB780钢扩孔性能的主要因素。结果表明：影响试验钢扩孔性能的主要因素为孔缘附近微区的硬度、显微组织及冲孔表面的质量；扩孔率随着孔缘附近微区的硬度显著增大而降低；扩孔过程中裂纹的形成与扩展是通过微孔聚集模式进行的；显微组织及冲孔表面质量的提高对扩孔性能有利。

英文摘要：

To study the main factors influencing the hole expansion property of FB780 advanced high strength steel, hole expanding tests were carried out according to Chinese standard GB/T 15825.4-2008. The microstructures of the tested steel before and after hole expansion, morphology of burnish zone and fracture zone on the punching surface, hardness profile of the micro-area within 2 mm distance near punch holes, morphology and second phase in the position of the through-wall cracks on the specimens were studied with the help of optical microscope, scanning electron microscope, and micro-hardness tester, etc. The key factors influencing hole expansion property were obtained. The results reveal that key factors influencing hole expansion property of FB780 steel included hardness and microstructure of micro-area near punch hole and quality of punch holes surface. It is found that the hole expansion ratio decreased with the significant increase of hardness of the micro-area near punch holes. Crack＇s formation and expansion were conducted by microporous gathered mode during hole expansion process. The improvement of microstructure and punching quality was good for hole expansion property.