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17/5/6 Cr-Ni-Mo不锈钢经1100℃水淬后含40%的δ-铁素体。高温保留下来的铁素体极为不稳定,加热至550°—1000℃在δ—铁素体内发生了一系列的变化。δ-铁素体分解产物的性质视加热温度而定,在700°—1000℃主要为X-相,在550°—700℃主要为Fe_3No_3C及(Cr,Fe,Mo)_(23)C_6。X-相形成的形态及其机构亦随加热温度而有所不同。在900°—1000℃δ-铁素体通过共析转变方式分解为X-相及奥氏体γ′δ-共析组织先在γ/δ,δ/δ相界成核然后逐渐向铁素体内部推进。在1000℃粒状的δ-共析组织居多,温度稍低则出现较多的层状组织。在700°—900℃X-相成核后,奥氏体γ′未能及时成核,因而当X-相的沉淀进行到一定阶段后,δ→γ′的转变才开始。在600℃保温观察到在奥氏体基体有马氏体的形成,这个现象可能与碳化物在低温的沉淀有关。
17/5/6 Cr-Ni-Mo stainless steels contain 40% δ-ferrite after water quenching at 1100 ° C. Ferrite retained at high temperature is extremely unstable, and a series of changes occur in δ-ferrite when heated to 550 ° -1000 ° C. The nature of the δ-ferrite decomposition products depends on the heating temperature and is mainly X-phase at 700 ° -1000 ° C and mainly Fe 3 N 3_C and (Cr, Fe, Mo) _ (23) C_ 6 at 550 ° -700 ° C. The form of X-phase and its mechanism also vary with the heating temperature. The δ-ferrite decomposes into X-phase and austenite γ’-δ-eutectoid structures by eutectoid transformation at 900 ° -1000 ° C, nucleating first at γ / δ, δ / δ phases and then gradually to ferrite Body to promote. At 1000 ℃ granular δ-eutectoid tissue mostly, the temperature is slightly lower there are more layered structure. The austenite γ ’fails to nucleate in time after the X-phase nucleation at 700-900 ° C, so the transformation of δ → γ’ does not begin until the precipitation of the X-phase reaches a certain stage. The formation of martensite at the austenite matrix was observed at 600 ℃, which may be related to the precipitation of carbides at low temperature.