长时效期BH钢的烘烤硬化性能及其机理研究

Bake hardening properties and mechanism of BH steel with long-term aging

采用万能材料试验机、TEM/EDS、3DAP,分别对时效3个月和6个月的超低碳烘烤硬化钢(钢号HC180B)进行力学性能测试和组织、析出相表征,并分析了烘烤硬化过程中的元素偏聚行为。结果表明,与时效3个月相比,钢板在时效6个月后仍具有优异的力学性能,展示出良好的抗时效性。TEM和3DAP分析显示,退火冷轧板中仅有C原子在晶界处轻微偏聚,B、Mn、Nb、Ti均匀分布在钢中;2%预拉伸变形后,这些元素在相同晶界处表现出不同程度的偏聚现象,TiN多呈矩形优先在晶界大量析出,NbC则少量析出;进一步烘烤后,C、B、Mn、Nb、Ti在晶界处的偏聚现象更为显著且连续,NbC呈椭球形大量析出。析出相与位错、晶界的交互作用显著提升了钢板的烘烤硬化性能。

By using a universal testing machine,TEM/EDS and 3DAP,the mechanical properties,microstructure,and precipitates of ultra-low carbon bake-hardening steel(HC180B)aged for 3 and 6 months were characterized,and the element segregation behavior during the bake-hardening process was analyzed.The results show that,compared with 3-month aging,the steel plate still exhibits excellent mechanical properties after 6 months of aging,demonstrating good aging resistance.TEM and 3DAP analyses indicate that in annealed cold-rolled plates,only C atoms exhibit slight segregation at grain boundaries,while B,Mn,Nb,and Ti are uniformly distributed within the steel.After 2%pre-stretching deformation,these elements show varying degrees of segregation at the same grain boundaries,with TiN preferentially precipitating in large amounts in the rectangular shape at the grain boundaries and NbC precipitating in smaller amounts.After further baking,the segregation of C,B,Mn,Nb,and Ti at the grain boundaries becomes more significant and continuous,with NbC precipitating in large amounts in the ellipsoidal shape.The interaction between precipitates,dislocations,and grain boundaries significantly enhances the bake-hardening properties of the steel plate.