Ti-Nb-Mo微合金钢回火过程中纳米碳化物的析出行为及组织演变

Performance of nanosized carbides precipitation and microstructure evolution in tempering process of Ti-Nb-Mo microalloyed steel

通过SEM和TEM等方法对Ti-Nb-Mo微合金钢在两种不同冷却工艺下回火处理后的析出相分布、形貌和粒度进行了观察和分析,结合拉伸实验结果和硬度测试结果研究了回火过程中纳米析出颗粒的变化对试验钢强度变化的影响。结果表明,热轧淬火后试验钢基体组织为板条贝氏体,经650℃回火处理后并未形成纳米析出相,因此导致试验钢强度明显下降;而热轧空冷后试验钢基体组织主要为铁素体,部分铁素体中形成了大量的相间析出颗粒并具有良好的热稳定性,经650℃回火0.5 h后屈服强度提升明显,回火过程中铁素体基体和位错上形成了大量的纳米碳化物颗粒,这类碳化物的析出量大,尺度分布均匀,颗粒尺寸细小,是试验钢获得高强度最主要的原因。

Distribution, morphology and size of precipitates in a hot-rolled Ti-Nb-Mo microalloyed steel by different processes and then tempering were investigated by means of scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The effect of nanosized carbides precipitation on strength of the steel during tempering was studied by tension and hardness tests. The results show that the microstructure is bainite in the hot-rolled steels by water quenching（ process A1 ） , in which no nanosized precipitates are observed after tempering at 650 ℃ , and its strength is lower. However, the microstructure of the hot-rolled steel by air cooling （process A2） consists of ferrite and interphase precipitates with good thermal stability. Additionally, the yield strength of the steel by process A2 increased obviously after tempering at 650 ℃ for 0.5 h, and a large number of nanosized carbides are observed in ferrite matrix and on dislocations. The improvement of strength of the experimental steel is attributed to the precipitation strengthening of the nanosized carbides.