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M38合金经定向后与普通精铸M38合金比较,由于基本消除了垂直于主应力轴的横向晶界,因而其高温持久塑性得到显著提高。但由于该合金的结晶温度间隔宽,凝固速度慢,枝晶粗大,偏折严重,γ,γ+γ′共晶和MC相粗大,不均,导致其高温持久寿命降低。而采用通用的1120℃/2h空冷+850℃/24h空冷的热处理制度,不能有效地提高定向M38合金高温持久寿命。本文采用新的热处理制度即1190℃/2h空冷+1090℃/2h空冷+850℃/2h空冷,由于均匀了显微组织,减小了偏析,细化了γ′相,γ+γ′共晶及初生MC充分分解和溶解,并且由粒状的M_(22)C_6组成了链状晶界。因而在基本保持较高的持久塑性前提下,较大幅度地提高定向M38合金的持久寿命。
M38 alloy after orientation compared with the ordinary cast M38 alloy, due to the basic vertical axis perpendicular to the grain boundary to eliminate the horizontal, so its high temperature plasticity was significantly improved. However, due to the wide crystallization temperature interval, slow solidification rate, coarse dendrites and serious deflection, the γ, γ + γ ’eutectic and MC phases are coarse and uneven, leading to the decrease of their long-life at high temperature. However, the common heat treatment system of 1120 ℃ / 2h air cooling + 850 ℃ / 24h air cooling can not effectively improve the high temperature long-term life of the M38 alloy. In this paper, the new heat treatment system is 1190 ℃ / 2h air cooling + 1090 ℃ / 2h air cooling + 850 ℃ / 2h air cooling, due to uniform microstructure, reduced segregation, refined γ ’phase, γ + γ’ eutectic And primary MC fully decomposed and dissolved, and the granular M_ (22) C_6 formed a chain-like grain boundary. Therefore, under the premise of maintaining a relatively high permanent plasticity, the durable life of the oriented M38 alloy is greatly improved.