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用热膨胀仪测定了3种不同钒、氮含量试验钢的CCT曲线,观察了在不同冷速下的组织,分析了钒的析出行为,计算了各形核基底与铁素体的晶格平面点阵错配度,研究了增氮对钒微合金化钢连续冷却相变行为的影响。结果表明,增氮促进了铁素体的形成,提高了试验钢的相变开始温度,也提高了形成全贝氏体组织的临界冷却速率;在冷速0.8-1.6℃/s范围内,低氮钢的显微组织为粒状贝氏体+板条贝氏体,而在增氮钢内则有大量的针状铁素体;在低氮钢中钒主要在相变前后析出,析出物以VC为主,增加钒含量只能提高其析出量,不能改变析出温度和析出物的成分;而增氮后钒在奥氏体内析出,以VN为主;在900℃,奥氏体、VC和VN与铁素体的平面点阵错配度分别为6.72%、3.89%和1.55%,VN与铁素体存在近似共格的低能界面,能作为铁素体优先形核位置,有效促进铁素体形成。
The CCT curves of three kinds of test steels with different vanadium and nitrogen contents were measured with a dilatometer. The microstructure of the test steels was observed under different cooling rates. The precipitation behavior of vanadium was analyzed. The lattice plane points The effect of increasing nitrogen on the continuous cooling transformation of vanadium microalloying steel was studied. The results show that nitrogen increased the formation of ferrite, increased the initial transformation temperature of the test steel and also increased the critical cooling rate of the formation of the whole bainite. In the range of 0.8-1.6 ℃ / s, The microstructure of nitrogen steel is granular bainite + lath bainite, while there is a large amount of acicular ferrite in the nitrogen-increasing steel; vanadium mainly precipitates before and after transformation in low-nitrogen steel, VC, the increase of vanadium content can only increase the amount of precipitation, can not change the precipitation temperature and the composition of precipitates; while increasing nitrogen precipitation in the austenite, VN-based; at 900 ℃, austenite, VC And the planar lattice mismatch between VN and ferrite are 6.72%, 3.89% and 1.55%, respectively. VN and ferrite have a nearly coherent low-energy interface, which can serve as the ferrite preferential nucleation sites and effectively promote the iron Body formation.