回火处理对一种低碳贝氏体钢组织及低温韧性的影响

Effect of tempering treatment on microstructure and low temperature toughness of a low carbon bainite steel

对一种含硼的低碳贝氏体钢进行了不同工艺的回火处理,并通过室温拉伸、摆锤冲击实验和扫描电镜研究了回火处理对实验钢的晶粒尺寸、晶界比例、贝氏体板条块的演变及强韧性的影响。结果表明,回火处理可使实验钢屈服强度升高,低温韧性显著改善,高温回火后塑性提高。300T实验钢-20℃下断口为韧窝断裂和准解理组成的混合型断裂,而500T和650T实验钢断口为韧窝断裂,600℃出现回火脆性区间,韧性恶化,属混合型断裂。650T钢的低温韧性最优,较高的回火温度促进了小角度晶界的迁移、亚晶合并过程,亚板条块数量减少,大角度晶界的比例、数量提高,晶粒尺寸有效细化,同时单位面积内板条块数目显著增加,有效地钝化了裂纹,提高了低温韧性。

A boron-containing low-carbon bainite steel was tempered in different processes, and the effect of tempering on the grain size, grain boundary ratio, evolution of bainite block and the obdurability of the experimental steel were studied by room temperature stretching, pendulum impact test and scanning electron microscopy. The results show that the tempering treatment can increase the yield strength of the experimental steel, significantly improve the low temperature toughness, and improve the plasticity after high temperature tempering. Besides, the fracture of 300 T steel at-20 ℃ is quasi-dissociation fracture, while the fractures of 500 T and 650 T steel are dimple fracture, and the temper brittle zone occurs at 600 ℃. In addition, the low temperature toughness of 650 T steel is optimal. The higher tempering temperature promotes the migration of small-angle grain boundaries and the subgrain combination process. So, the number of sub-block decreases, the proportion and number of large-angle grain boundaries increase, and the grain size is fine. At the same time, the number of block per unit area is significantly increased, which effectively passivates the crack and improves the low temperature toughness.