热处理对铸造4Cr9Si2耐热钢显微组织和性能的影响

Effect of Heat Treatment on Microstructure and Properties of Cast 4Cr9Si2 Heat Resistant Steel

研究了热处理对铸造4Cr9Si2耐热钢的显微组织和性能的影响。结果表明:铸造4Cr9Si2钢在铸态下组织为板条马氏体,经860℃×2 h退火处理后,在铁素体基体上析出粗大粒状和条状M_(23)C_6型碳化物,硬度降低,但冲击吸收功很低;经1020℃×2 h空冷正火+720℃×2 h回火热处理后,随后的冷却速率对显微组织和冲击吸收功影响很大。采用炉冷方式冷却的4Cr9Si2耐热钢存在高温回火脆性现象,组织中有细小弥散碳化物析出,造成二次硬化,硬度较720℃回火后水冷的试样高,冲击吸收功低。

Effect of heat treatment on the microstructure and mechanical properties of a cast 4Cr9Si2 heat resistant steel was studied. The results show that the as-cast 4Cr9Si2 steel possesses typical lath martensitic microstructure. After annealing treatment at 860 ℃ for 2 h, coarse M_(23)C_6 carbide with particular and stripy shapes precipitate in the ferrite matrix, and the hardness of the steel decreases obviously but its impact absorbed energy is very low. When the as-cast steel is normalized at 1 020 ℃ for 1 h followed by air cooling then tempered at 720 ℃ for 2 h, the cooling rate after the tempering treatment has much influence on the microstructure and impact absorbed energy of the steel. In contrast to the water cooling, the tempering treatment followed by furnace cooling causes high temperature tempering embrittlement, and a lower impact absorbed energy and a higher hardness because the fine dispersive carbide particles are densely distributed in the matrix and secondary hardening is obtained in the furnace-cooling condition.