D6A钢在轧制过程中的强韧化机理EI北大核心CSCD

通过轧制-热处理工艺能够使D6A钢的强度显著提高。为了探究其强韧化机理,本实验采用热轧及两相区温轧退火工艺,获得微米级D6A合金钢样品,微观组织为铁素体基体及粒状渗碳体。通过室温拉伸实验、SEM、X射线衍射、EBSD等手段对实验钢的显微组织和力学性能进行表征,结果表明:随着变形量的增加,晶粒尺寸由4.5μm细化为1.5μm,渗碳体的含量逐渐增加,小角度晶界的比例升高,屈服强度和抗拉强度不断增加,伸长率略有降低,说明轧制过程使亚晶粒的尺寸不断降低,晶界面积增加,位错滑移受到的阻力增大。同时,本研究对不同轧制变形量实验钢的位错密度进行计算,当轧制变形量为88%时,位错密度最高,此时加工硬化的程度最高。随着变形量的增加,第二相强化和晶粒细化引起的强度增量呈不断上升的趋势,位错强化引起的强度增量先升高后降低,D6A钢的主要强化方式为第二相强化、细晶强化及位错强化。

Toughening mechanism of D6A steel during rolling process

The rolling-heat treatment process can significantly improve the strength of D6A steel. In order to explore the toughening mechanisms of D6A alloy steel, the micrometer grade D6A alloy steel is obtained by hot rolling and intercritical warm rolling plus annealing process, which consists of ferrite matrix and granular cementite. The microstructure and mechanical properties of the experimental steel were characterized by tensile test at room temperature, SEM, X-ray diffraction and EBSD. The results show that the grain size is refined from 4.5 μm to 1.5 μm with the increase of rolling pass, the cementite content increases gradually, and the proportion of grain boundary with small angle increases. The yield strength and tensile strength increase continuously, while the elongation decreases slightly, indicating that the size of subgrain decreases continuously during the rolling process, grain boundary area, and the resistance to dislocation slip increase. At the same time, the dislocation density of the experimental steel with different rolling pass was calculated. When the thickness reduction is 88%, the dislocation density is the highest, and then the degree of working hardening is the highest. The analysis shows that with the increase of the deformation, the strength increment caused by the strengthening of the second phase and grain refinement shows an increasing trend, while the strength increment caused by dislocation enhancement first increases and then decreases. The main strengthening methods of D6A steel are second phase strengthening, fine grain strengthening and dislocation strengthening.