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。
The decompsition of δ-ferrite in the temperature range 550°—1000℃ inquenched 17/5/6 Cr-Ni-Mo Stainless steel specimens has been studied by meansof microscopic and X-ray diffraction method. It is shown that the nature of thedecomposition product of δ-ferrite varies with the reheating temperature, Chi andaustenite appeared in the temperature range 700—1000℃, Whereas below 700℃Fe_3Mo_3C and (Cr, Fe, Mo)_23C_6 were formed from δ-ferrite instead of Chi. The morphology and mechanism of Chi formation are also dependent on thereheating temperature. Above 900℃, δ-ferrite was found to decompose into Chiand austenite as eutectoid, the leading phase being probably Chi. Between 700℃and 900℃, it is likely that the nucleation of austenite couldnot keep pace withthat of Chi, thus Chi was found to precipitate first and the remaining δ-ferritethen transformed to austenite. Below 700℃ the precipitation of carbides in δ-ferrite was accompanied bymartensite formation in the austenitic matrix. This may be caused by the diffu-sion of carbon from the austenitic matrix to δ-ferrite to supply the carbon re-quired for the carbide precipitation.
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