9Cr18合金半固態(tài)觸變壓縮變形行為及組織演變

9Cr18合金半固態(tài)觸變壓縮變形行為及組織演變Deformation Behavior and Microstructure Evolution of 9Cr18 Alloy During Semi-Solid Compression

以9Cr18合金為研究對象，分別對9Cr18熱軋態(tài)材料及半固態(tài)坯料進行觸變壓縮實驗。通過OM和SEM研究了其在加熱、半固態(tài)及變形冷卻后的顯微組織演變規(guī)律，分析了其壓縮過程的固液流動特性和應力-應變關系。研究表明，半固態(tài)坯料制備是保證材料發(fā)揮半固態(tài)變形特性的必備流程，坯料加熱至半固態(tài)溫度能夠保證固液三維均勻分布，充分發(fā)揮液相流動特性。僅通過對軋態(tài)材料加熱至半固態(tài)溫度區(qū)間會導致液相沿原帶狀組織區(qū)域熔化析出，固液分布不均勻。熱軋態(tài)材料帶狀熔化致使液相不能形成三維連通，液相流動只能在不同部位的若干區(qū)域進行，變形主要通過固相顆粒塑性變形完成，進入最后階段變形抗力上升。半固態(tài)坯料變形過程中固液相分布均勻，當變形進行至觸變階段，液相由于受到向外側壓力梯度作用，在固相間隙中流動，固相顆粒予以協(xié)調(diào)，發(fā)生宏觀固液分離，從而使變形抗力隨之下降。9Cr18合金在半固態(tài)溫度區(qū)間成形過程中表現(xiàn)出不同于傳統(tǒng)熱處理的組織演變規(guī)律。半固態(tài)溫度范圍內(nèi)奧氏體溶解合金元素的能力較傳統(tǒng)奧氏體化 (1050 ℃)極大提高，從而提高了奧氏體在快速冷卻過程中的穩(wěn)定性，在冷卻后得到過飽和的亞穩(wěn)奧氏體組織。半固態(tài)獨特的組織演變過程為材料組織性能控制提供一種新的可能，可以據(jù)此設計滿足特殊要求的熱處理工藝。

The compression behavior during semi-solid state is a fundamental basis for the following rheoforming or thixoforming. Coexist of solid/liquid phase leads to the unique deformation behavior. The chemical composition at each phase is different from conventional forming process. Deformation behavior and microstructure evolution is determined by various effects such as initial state, heating, cooling, etc. The semi-solid compression test of 9Cr18 as hot-rolled material and semi-solid billet were conducted, respectively. Microstructure evolution during heating, semi-solid state, deformation and cooling was investigated by OM and SEM. Solid/liquid flow behavior and the relationship of stress-strain were analyzed. The results showed preparation of semi-solid billet is essential for the uniformity of solid particle and liquid phase, which would help to demonstrate the flow behavior. Only heating the as hot-rolled material to semi-solid led to the banded precipitation of liquid phase. The banded melting of as hot-rolled material made it hard for liquid phase to connect with each other. Liquid flow only happened in partial area and plastic deformation of solid particles was the main deformation behavior. The stress increased at the final stage. As for semi-solid billet, solid particles and liquid film coexisted uniformly. Macro separation of solid/liquid occurred as deformation came into thixotropic stage. Liquid flew towards outside and solid particles rotated, thus leading to the decrease of stress. Microstructure evolution at semi-solid state was different from conventional heat treatment. Solid austenite particles at semi-solid state could dissolve more alloying elements than normal austenization (1050 ℃). This phenomenon would help to improve the stability of austenite and over-saturated meta-austenite was obtained after cooling. The special microstructure evolution during semi-solid state might provide a possible way to design a new heat treatment procedure.

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