长期时效对低碳Ni-Cr-W-Mo耐热合金组织和力学性能的影响

Effect of Long-Term Thermal Aging on the Microstructure and Mechanical Properties of Low-Carbon Ni-Cr-W-Mo Heat-Resistant Alloy

研究了长期时效对低碳Ni-Cr-W-Mo耐热合金组织和力学性能的影响。结果表明,长期时效后低碳Ni-Cr-W-Mo耐热合金存在3种析出相:M6C型初生碳化物相、二次M23C6型碳化物相和μ相;其中M6C型初生碳化物相存在于供应态和时效态。因为合金含碳量低,所以合金在750℃时效超过200h和在900℃时效超过100h时,就析出μ相。合金在750℃时效至1 000h时,随着时效时间的延长,合金硬度值不断增加;而合金在900℃时效至1 000h时,随着时效时间的延长,合金硬度值首先增加至最大值,随后合金硬度值随着时效时间的延长而降低;这是因为二次M23C6型碳化物析出形态在时效过程中发生了变化。合金时效前后的室温拉伸性能数据证实微量μ相对合金室温拉伸影响很小。

Microstructural change after long term aging at 750 and 900℃ till 1 000 h and their effects on the mechanical properties were investigated in a low-earborx Ni-Cr-W-Mo heat-resistant alloy. Three types of precipitates were identified in this aged alloy, they are primary M6 C carbide, secondary M23 C6 carbide and μ phase. Primary M6C carbide is observed in the as-received materials and all aged samples. The μ phase is found in the specimens aged at 750 ℃ over 200h and aged at 900 ℃ over 100h. This is attributed to the low-carbon content of the Ni-Cr- W-Mo heat-resistant alloy. Longer thermal aging results in hardening of the alloy aged at the temperature of 750 ℃ up to 1 000h, but initial thermal aging results in hardening of the alloy aged at the temperature of 900 ℃ up to 1 000 h and when the hardness value reaches to the peak subsequent aging results in softening of the alloy. Both of the results are attributed to the change of the morphology of secondary M23 C6 carbides. The room-temperature tensile results of the as-received material and the aged material confirmed that the small content of μ phase precipitation have little influence on the ductility of this alloy.