回火对C-Si-Mn系双相钢组织与性能的影响

Influence of Tempering on Microstructure and Mechanical Property of Dual Phase Steel of C-Si-Mn Alloy System

在实验室研究了回火温度对C-Si-Mn双相钢力学性能与显微组织的影响。力学性能测定结果表明,250℃以下的低温回火,对改善双相钢的伸长率具有良好作用,但是其它力学性能的变化不明显。高于300℃的高温回火对改善双相钢的延性作用不大,但会引起双相钢的屈服强度升高,抗拉强度、加工硬化与烘烤硬化值降低,使双相钢性能恶化。扫描电镜与透射电镜的观察结果表明,低温回火双相钢的显微组织变化不明显,马氏体为板条状,马氏体前沿的铁素体基体中分布着大量的可动位错,高温回火双相钢的显微组织则有较大变化,马氏体分解,边界变得模糊,岛内出现碳化物颗粒,铁素体中的位错密度减小,位错线附近出现粗大的析出物。高温回火后,马氏体的分解软化以及铁素体中位错密度减小是导致双相钢性能恶化的主要原因。

The influence of tempering temperature on the microstructure and mechanical properties of a dual phase steel was studied. The results of mechanical test show that elongation is improved by tempering below 250℃, but the change of other mechanical properties is not obvious. After tempering above 300 ℃, elongation does not increase much, but the yield strength is increased with decrease of tensile strength, work-hardening and bake-hardening capacity deteriorating the mechanical properties of the steel. The results of SEM and TEM analysis indicate that the variation of microstructure is not changed obviously after tempering below 250℃, the morphology of martensite is lath-shaped and a large number of unobstructed dislocations is observed in ferrite and around martensite islands. By tempering above 300 ℃, martensite decomposes obviously, making the boundaries illegible, and precipitation of carbide particles in the islands. In ferrite the density of dislocation decreases, and there are many coarse precipitates on dislocation lines. The decomposition of martensite and decrease of dislocation density in ferrite are the main reasons of deteriorating the mechanical properties of dual phase steel.