Cu和Ni对微合金高强钢组织性能及第二相析出行为的协同作用

Synergistic effect of Cu and Ni on microstructure properties and second phase precipitation behavior of micro-alloyed high-strength steel

研究了在相同Cu/Ni比的情况下,Cu、Ni含量的变化对含铜时效强化钢组织性能及第二相析出行为的影响。利用扫描电镜(SEM)、透射电镜(TEM)、电子背散射衍射(EBSD)、X射线衍射(XRD)等分析表征手段研究不同Cu、Ni含量低碳微合金高强钢在调质处理下的显微组织和力学性能。研究结果表明,随着Cu、Ni含量增加,试验钢的强韧性得到提升(抗拉强度提升3.3%,冲击韧性提升10%)。显微组织中部分粒状贝氏体转变为回火索氏体,回火索氏体占比提升了10%。组织中的大角度晶界含量增加,亚结构和位错密度显著升高。通过Thermo-Calc热力学计算发现,Ni含量的增加,降低了奥氏体相变温度。Ni元素的加入细化了回火索氏体板条(由332 nm细化至264 nm),增加了组织中的板条束数量。板条界出现大量的位错缠结,为第二相析出提供更多的形核位点,降低Cu析出的形核能,促进并细化了Cu析出,进而提高微合金高强钢的强韧性。

The effects of the relative contents of Cu and Ni on the microstructure and second phase precipitation behavior of copper-bearing aged steel with the same Cu/Ni ratio were investigated. SEM, TEM, EBSD, XRD and other analytical characterization methods were used to analyze the microstructure and mechanical properties of low carbon micro-alloyed high strength steel with different Cu and Ni contents under quenching and tempering treatment. The results show that the strength and toughness of the test steel are improved with the increase of Cu and Ni content(tensile strength increased by 3.3%, impact toughness increased by 10%). In the microstructure, some granular bainite is transformed into tempered sorbite(the proportion of tempered sorbite increased by 10%), the content of large-angle grain boundaries increases, and the substructure and dislocation density improve significantly. It is found that the austenite phase transition temperature decreases with the increase of Ni content by Thermo-Calc thermodynamic calculation. The addition of Ni element refines the tempered sorbite lath(from 332 nm to 264 nm) and increases the lath bundles in the structure. A large number of dislocation entanglement in the slat boundary provides more nucleation sites for the second phase precipitation, reduces the form energy of Cu precipitation, promotes and refines Cu precipitation, and then improves the strength and toughness of micro-alloyed high strength steels.