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应用金相法研究了18/8/3/1 Cr-Ni-Mo-Ti不锈钢经1300℃固溶处理后在950℃,850℃及750℃恒温分解初期金相组织的变化,并用电解分离及X射线衍射方法鉴定在不同恒温分解阶段δ-铁素体分解的产物。观察到由于提高了固溶处理温度,高温固定下来的铁素体极为不稳定,在分解为奥氏体的同时有TiC的沉淀出现。当δ→γ的转变,由于Cr,Mo等合金元素的偏聚不能继续进行时,才发现残留的δ-铁素体转变为σ-相。过去一般认为18/8型不锈钢在550—1000℃保温后,室温冲击靭性的降低是由于σ-相的沉淀所引起的,试验结果指出在σ-相出现之前,钢的冲击靭性已显著下降,这种现象可能与δ-铁素体分解初期TiC的沉淀有关。
The microstructure of 18/8/3/1 Cr-Ni-Mo-Ti stainless steel after initial solution treatment at 1300 ℃ for 950 ℃, 850 ℃ and 750 ℃ was investigated by metallographic method. The microstructure of the 18/8/3/1 Cr- The diffraction method identifies the product of δ-ferrite decomposition at different pyrolysis stages. It was observed that due to the increase of the solution treatment temperature, the ferrite fixed at a high temperature was extremely unstable, and precipitation of TiC occurred while being decomposed into austenite. When the δ → γ transformation, due to the segregation of Cr, Mo and other alloying elements can not continue, we found that the residual δ-ferrite transformed into σ-phase. It is generally believed that the reduction of room temperature impact toughness due to the precipitation of the σ-phase after the 18/8 stainless steel was heat-insulated at 550-1000 ° C indicates that the impact toughness of the steel has decreased significantly before the σ-phase occurs, This phenomenon may be related to the precipitation of TiC in the initial stage of δ-ferrite decomposition.