调质工艺对汽车大梁钢700L组织性能的影响

摘 要: 通过金属摆锤冲击和显微硬度试验,采用OM、SEM、TEM等表征手段,研究了不同调质工艺对700L汽车大梁钢组织和力学性能的影响。结果表明,随着淬火温度的提高,粒状贝氏体(GB)组织有所减少,板条状贝氏体铁素体(BF)数量逐渐变多,板条宽度增加,铁素体基体及边界上的白色析出物数量增多;随着回火温度的提高,块状铁素体有所长大,马奥岛组织和残余奥氏体分解现象明显,且出现了数量较少的等轴状铁素体,回火析出物数量增多,回火温度超过600 ℃后粒子出现粗化长大现象。低温冲击功在不同淬火与回火条件下均表现为上下波动的状态,这主要与第二相粒子及基体组织规律性的变化有关;试验钢在经600 ℃回火后具有最佳低温冲击韧性,其主要原因是钢基体中存在数量较多的具有高密度位错的贝氏体铁素体(BF)与尺寸合适、分布均匀的第二相纳米粒子。

Effect of quenching and tempering process on microstructure and properties of automobile large beam steel 700L

The effects of different quenching and tempering processes on the microstructure and mechanical properties of 700L automobile beam steel were studied by means of metal pendulum impact test and microhardness test with the methods of OM, SEM, TEM. The results showed that with the increase of quenching temperature, the granular bainite (GB) structure decreased, the number of lath bainite ferrite (BF) increased gradually, the width of lath increased, and the number of white precipitates on the ferrite matrix and boundary increased. With the increase of tempering temperature, the massive ferrite grew up, the M/A structure and the decomposition of residual austenite were obvious, and a small number of equiaxed ferrite appeared. The number of tempering precipitates increased, and particle coarsening and growing phenomenon occurred when the tempering temperature exceeded 600 ℃. The low temperature impact energy fluctuated at different quenching and tempering conditions, which was mainly related to the change of microstructure regularity for the second phase particles and the matrix. The experimental steel had the best low temperature impact toughness after tempering at 600 ℃, which was mainly due to the presence of a large number of bainite ferrite (BF) with high density dislocation and the second phase nanoparticles with appropriate size and uniform distribution in the steel matrix.