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用金相方法研究了含少量钼、钛18/8 Cr-Ni不锈钢中δ-铁素体在900°—550℃恒温分解的过程。观察到在分解产物中没有σ-相。δ-铁素体分解形态及其机构随分解温度而有所不同。当分解温度高于750℃时,先析出奥氏体γ′,继之在未转变的铁素体中,才沉淀出碳化物。分解温度低于650℃时,则先析出碳化物,随后才出现有奥氏体γ′。介乎750°—650℃之间,δ-铁素体通过共析转变方式分解为碳化物及γ′。共析分解未能进行到底,在残留的铁素体中,有奥氏体γ′析出,由于合金元素分配的关系,δ→γ′的转变不久亦停止。在试验过程中,观察到电解磨光后,在碳化物未全部溶解或δ-铁素体已发生分解的样品表面上,出现有马氏体。用同佯手续制备1300℃固溶处理(碳化物全部溶解)的样品,则没有出现马氏体。初步认为马氏体的出现是由于电解磨光过程中产生自由表面所引起的。但是这种表面马氏体的形成似亦与奥氏体的含碳量有关,其形成机构尚待进一步的研究。
The phase transformation of δ-ferrite in a small amount of molybdenum and titanium 18/8 Cr-Ni stainless steels at 900-550 ℃ was studied metallographically. No sigma-phase was observed in the breakdown products. δ-ferrite decomposition morphology and its mechanism with the decomposition temperature is different. When the decomposition temperature is higher than 750 ° C, austenite γ ’is precipitated first, and then carbide is precipitated in the untransformed ferrite. When the decomposition temperature is lower than 650 ° C, carbides are precipitated first and then austenite γ ’appears. Between 750 ° -650 ° C, δ-ferrite decomposes into carbides and γ ’by eutectoid transformation. The eutectoid decomposition did not proceed in the end, in the remaining ferrite, austenite γ ’precipitation, due to the alloying element distribution, δ → γ’ transition soon ceased. During the test, it was observed that after electrolytic polishing, martensite appeared on the surface of the sample where the carbides did not dissolve completely or the δ-ferrite was decomposed. With the same procedure for the preparation of 1300 ℃ solution treatment (carbides all dissolved) samples, there is no martensite. Initially that the emergence of martensite is due to electrolytic polishing process to produce free surface caused. However, the formation of this kind of surface martensite is also related to the carbon content of austenite, and its formation mechanism needs further study.