304奧氏體不銹鋼超低溫軋制變形誘發(fā)馬氏體轉(zhuǎn)變的定量分析及組織表征

304奧氏體不銹鋼超低溫軋制變形誘發(fā)馬氏體轉(zhuǎn)變的定量分析及組織表征QUANTITATIVE ANALYSIS OF THE MARTENSITE TRANSFORMATION AND MICROSTRUCTURE CHARACTERIZATION DURING CRYOGENIC ROLLING OF A 304 AUSTENITIC STAINLESS STEEL

研究了304亞穩(wěn)態(tài)奧氏體不銹鋼在超低溫和室溫軋制變形過程中的宏、微觀組織演變, 變形引起的馬氏體轉(zhuǎn)變及其對合金性能的影響. 結(jié)果表明, 超低溫軋制比室溫軋制能更有效地加速馬氏體轉(zhuǎn)變, 其中20%超低溫軋制變形便可實(shí)現(xiàn) 50%室溫軋制變形下的馬氏體轉(zhuǎn)變量, 且超低溫軋制變形最終可實(shí)現(xiàn)完全的馬氏體轉(zhuǎn)變. 同時(shí), 超低溫軋制引起的馬氏體轉(zhuǎn)變在板厚方向上較均勻, 顯著優(yōu)于室溫軋制板材的板厚方向均勻性, 有助于提高亞穩(wěn)態(tài)奧氏體不銹鋼板厚方向性能的均勻性. 分析認(rèn)為, 亞穩(wěn)態(tài)奧氏體不銹鋼在超低溫和室溫軋制過程中具有不同的變形機(jī)理, 前者主要以馬氏體轉(zhuǎn)變及其變形為主, 后者以奧氏體變形為主. 超低溫軋制所獲板材的硬度比室溫軋制板材增長迅速, 但隨變形量增大位錯(cuò)密度差距縮小, 最終導(dǎo)致兩者硬度趨于一致. TEM 表征結(jié)果表明, 超低溫和室溫軋制過程中引起的馬氏體與母相基體間的取向關(guān)系遵循 K-S (Kurduumov-Sachs)關(guān)系。Advanced material processing techniques have been successfully used to produce metals or alloys with submicro- or nano-sized grain structures with some possibly required harsh working environment that limits their industrial application. Cryogenic deformation might promote extensively severe deformation or distortion of metals or alloys (such as Al or aluminium alloys, Cu or copper alloys, Ti, Zr, etc.) so as to accumulate higher deformation energy (e.g., higher defect density) for the depression of the (dynamic) recovery, which will contribute to the microstructure refinement. Presently, the macro-/micro-structural evolution, the martensitic transformation as well as its effect on the mechanical property during the cryogenic and room temperature rolling of 304 metastable austenitic stainless steel were studied. It shows that the cryogenic rolling can effectively accelerate the martensitic transformation, e.g., after 20% cryogenic rolling the volume fraction of the transformed martensitic is equal to that after 50% room-temperature rolling, and finally the cryogenic rolling can promote the complete martensitic transformation. Also the through-thickness uniformity of the martensitic transformation after cryogenic rolling is significantly better than that of the room-temperature rolled one, which can help to improve the through-thickness performance uniformity. It is found that the deformation mechanisms are different for cryogenic and room-temperature rolling metastable austenitic stainless steel: the martensitic transformation and its deformation occur in the former while austenitic deformation in the latter. The cryogenic rolling can quickly induce higher hardness than that of the room-temperature rolled ones, and the hardness tends to be equal finally because of the minimized dislocation density difference between these two rolled steels. TEM results indicate that the orientation relationship between the transformed martensite and the old austenite in the cryogenic and room-temperature rolled sheets can still keep the K-S (Kurduumov-Sachs) relationship.

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