马氏体板条控制单元对20CrNi2Mo钢韧性的影响

Effect of the Martensite Lath on Toughness of 20CrNi2Mo Steel

测试了不同淬火温度下20CrNi2Mo低碳钢的冲击韧性和断裂韧性,并使用OM、SEM、EBSD、TEM定量分析了试验钢的多层次组织。结果表明,在1200℃淬火处理的试样具有较好的韧性,断裂韧性和冲击韧性的最大增幅分别为43.58%和27.78%。同时,随着淬火温度的提高试验钢原奥氏体晶粒(dr)、马氏体束(dp)、马氏体块(db)增大,而马氏体板条(dl)略微减小。根据裂纹扩展路径和韧窝尺寸分析并结合Hall-Petch关系,证明了马氏体板条是韧性的有效控制单元。同时,根据EBSD应力分析揭示了裂纹扩展的塑性变形能,并计算了断裂韧性和冲击韧性在裂纹扩展过程中的能量关系。

The impact toughness and fracture toughness were studied for 20CrNi2Mo steel quench- ing at different temperatures and the hierarchical microstructures obtained were investigated by OM, SEM, EBSD and TEM. Results showed that materials quenching at 1200℃ had best toughness in which the fracture toughness and impact absorption energy increased 43.58% and 27.78%, respectively. The size of prior austenite grain （dr）, packet （dp） and block （db） was increased with the increase of quenching temperature, while the martensite lath （d1） was decreased slightly with the coarsen of prior austenite grain. It was proved that the effective control unit of toughness for the tested steel was martensite lathes by crack propagation path analyzing and the statistic of dimple size combined with the HalI-Petch formula. Inaddition, the difference of plastic deformation was declared by EBSD and the relationship between fracture toughness and impact toughness during crack propagation process was calculated.