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含有0.04wt-％P的汽轮机转子用CrMoV钢,时效前在较高温度(600和570℃)进行预时效处理,然后在480℃时效,元素磷偏析到晶界的速度比没有经过预时效处理的钢快得多。这与预时效过程中碳化物析出,基体成分改变有关。Mo可抑制磷的偏析,但因时效过程中富Mo碳化物的生成和长大,使基体中Mo的含量降低,因此,磷从Mo的“束缚”下“解放”出来并偏析到晶界,使脆性转变温度升高,此外,碳化物的粗化也可能导致脆性转变温度升高。
CrMoV steels for turbine rotors containing 0.04 wt-% P were pre-aged at higher temperatures (600 and 570 ° C) prior to aging and then aged at 480 ° C for segregation of elemental phosphorus to grain boundaries without pre-aging The steel is much faster. This pre-aging process carbide precipitation, changes in matrix composition. Mo can inhibit the segregation of phosphorus, but due to the formation and growth of Mo rich carbides in the aging process, the content of Mo in the matrix is reduced. Therefore, the phosphorus is “liberated” from the “binding” of Mo and segregated to the grain boundaries Brittle transition temperature increases, in addition, the coarsening of the carbide may also lead to brittle transition temperature.