时效热处理对HR3C钢组织结构及力学性能的影响

Effect of ageing treatment on microstructure and mechanical properties of HR3C steel

根据Larson-Miller参数法制订HR3C钢热处理工艺,文章研究时效热处理对HR3C钢组织结构和性能的影响。结果表明,供货态HR3C钢奥氏体晶粒较大,组织孪晶特征明显,晶界、晶内弥散分布着细小的M23C6及MX第二相颗粒;经800℃、110.4 h时效处理,M23C6在晶界析出,呈半连续的链状分布,同时,晶内也析出微细第二相颗粒,弥散强化效应增强度,导致HR3C钢的强度、硬度升高,但韧性降低;经900℃、17.7h时效处理,M23C6在晶界连续分布,厚约2μm;奥氏体晶内第二相颗粒粗大,导致HR3C钢综合力学性能显著降低;时效处理态HR3C钢的拉伸和冲击断口呈沿晶断裂特征,不同于供货态的微孔聚集型断裂特征。

Microstructure and properties of HR3C steel after ageing treatment are studied based on the Larson-Miller parameter. The results show that the supplied HR3C steel is composed of big austenitic grains with twins, in which the second-phase particles of M2a C6 type carbides and MX-type compounds are dispersed. After being annealed at 800℃ for 110.4 h, the semi-continuous M23C6 carbides are deposited along the austenitic grain boundaries, while the second-phase particles disperse inside the austenitic grains. Owing to the strengthening of dispersion effect, the strength and hardness of the heat-treated HR3C steel increase, however the toughness of it decreases. After being annealed at 900℃ for 17.7 h, the M23C6 carbides continuously distribute along the austenitic grain boundaries with a thickness of about 2μm, while the coarse second-phase particles randomly distribute inside the austenitic grains. All of these result in the deterioration of mechanical properties of the heat-treated HR3C steel. The fractural mechanism of the heat-treated HR3C steel is of the intergranular fracture, different from the dimple-congregation-type fracture of the supplied HR3C steel.