表面脱碳对Al-Si镀层热冲压钢弯曲韧性的影响  

Effect of surface decarburization on bending toughness of Al-Si coated hot stamping steel

作　　者：曾林林 王程 杨达朋 易红亮[1,2] ZENG Linlin;WANG Cheng;YANG Dapeng;YI Hongliang(The State Key Laboratory of Rolling and Automation,Northeastern University,Shenyang 110819,Liaoning,China;Easyforming Materials Technology Co.,Ltd.,Suzhou 215123,Jiangsu,China)

机构地区：[1]东北大学轧制技术及连轧自动化国家重点实验室,辽宁沈阳110819 [2]育材堂(苏州)材料科技有限公司,江苏苏州215123

出　　处：《钢铁》2023年第9期209-217,共9页Iron and Steel

基　　金：国家自然科学基金资助项目(52101128);中国博士后科学基金资助项目(2022M710021)。

摘　　要：Al-Si镀层热冲压钢因为其超高的强度而被广泛应用于车身,研究发现镀层会严重恶化热冲压钢的弯曲韧性。基于“界面富碳致脆”理论,以国内某钢厂生产的22MnB5热冲压钢为研究对象,研究了表面脱碳对表面镀层组织和力学性能的影响,为提高Al-Si镀层热冲压钢的弯曲韧性提供参考。结果表明,在920℃保温6 min后,试验钢的镀层组织由FeAl相和铁素体层构成,基体组织均为马氏体。表面脱碳对Al-Si镀层热冲压钢的拉伸性能影响较小,但对弯曲性能影响较大。钢材表面脱碳后,降低了热冲压后镀层/基体界面碳富集程度,提高了界面马氏体的韧性,进而提高了热冲压钢的弯曲韧性。随着表面脱碳厚度的增加,试验钢的弯曲性能逐渐提高,完全脱碳层为30.3μm时,最大载荷弯曲角为82.4°±2.9°。在弯曲过程中,裂纹扩展分成2类,一类是裂纹穿过铁素体层后,在镀层/基体界面钝化,随后基体发生变形及断裂;另一类是裂纹穿过铁素体层后,进入到马氏体基体,在马氏体基体中钝化,随后基体发生变形和断裂。裂纹扩展路径取决于界面马氏体的强度,马氏体强度高时,发生第一种扩展;马氏体强度低时,发生第二种扩展。Al-Si coated hot stamping steel is widely used in car bodies due to its ultra-high strength.Research has found that the coating seriously deteriorates the bending toughness of hot stamping steel.The effect of surface decarburization on the surface coating microstructure and mechanical properties of 22MnB5 hot stamping steel is investigated to provide a guide for improving the bending toughness of Al-Si plated hot stamping steel,based on the theory of"interfacial carbon enrichment causing brittleness".The results show that after holding at 920℃for 6 min,the coating microstructure of the experimental steels is composed of a FeAl phase and a ferrite layer,and the substrate is martensite.Surface decarburization has a small effect on the tensile properties of Al-Si coated hot stamping steel,but has a large effect on the bending properties.The surface decarburization of the steel reduced the carbon enrichment at the coating/structure interface after hot stamping,increasing the toughness of the interfacial martensite and the bending toughness of the hot stamped steel.As the thickness of the surface decarburization increases,the bending properties of the experimental steel gradually improve.When the fully decarburized layer is 30.3μm,the bending angle at peak load is 82.4°±2.9°.In the bending process,crack propagation is divided into two categories.One is where the crack passes through the ferrite layer and passivates at the coating/substrate interface,followed by deformation and fracture of the substrate;the other is where the crack passes through the ferrite layer and enters the martensitic substrate,where it passivates in the martensitic substrate,followed by deformation and fracture of the substrate.The path of crack propagation depends on the strength of the interfacial martensite,with the first propagation occurring when the martensite strength is high and the second propagation occurring when the martensite strength is low.

关 键 词：Al-Si镀层 热冲压钢 弯曲韧性 表面脱碳 组织性能 

分 类 号：TG142.1[一般工业技术—材料科学与工程]