退火溫度對(duì)冷軋7Mn鋼拉伸行為的影響及模擬研究

退火溫度對(duì)冷軋7Mn鋼拉伸行為的影響及模擬研究Effects of intercritical annealing temperature on the tensile behavior of cold rolled 7Mn steel

研究了退火溫度對(duì)冷軋中錳鋼7%Mn-0.3%C-2%Al(質(zhì)量百分?jǐn)?shù))組織和力學(xué)性能的影響。試驗(yàn)結(jié)果表明，隨著退火溫度的上升逆轉(zhuǎn)變奧氏體的機(jī)械穩(wěn)定性逐漸降低，使得應(yīng)變誘導(dǎo)馬氏體的轉(zhuǎn)變動(dòng)力學(xué)快速上升。在700℃退火時(shí)，逆轉(zhuǎn)變奧氏體的穩(wěn)定性適中，此時(shí)材料的綜合力學(xué)性能最優(yōu)，強(qiáng)塑積高達(dá)65GPa?%。為闡明不同溫度退火后冷軋中錳鋼力學(xué)行為差異的內(nèi)在機(jī)制，本文利用具有物理冶金意義的本構(gòu)模型研究了冷軋中錳鋼退火后的拉伸和加工硬化行為。模擬結(jié)果表明，奧氏體穩(wěn)定性對(duì)材料的拉伸行為有決定性的影響。退火溫度偏低則奧氏體穩(wěn)定性過(guò)高，材料的加工硬化率和均勻延伸率都較低；若退火溫度適中則奧氏體穩(wěn)定性也適中，變形時(shí)能持續(xù)的產(chǎn)生TRIP效應(yīng)硬化基體，使材料的加工硬化率和均勻延伸率均較高；退火溫度偏高會(huì)導(dǎo)致奧氏體穩(wěn)定性過(guò)低，應(yīng)變誘導(dǎo)馬氏體會(huì)在短期內(nèi)大量形成，致使材料的抗拉強(qiáng)度較高但均勻延伸率降低。

Effects of intercritical annealing (IA) temperature on the microstructures and tensile properties of a newly designed medium Mn steel, Fe-7 wt.% Mn-0.3 wt.% C-2 wt.% Al, have been studied in this paper. Experimental results showed that with the increase of IA temperature the mechanic stability of reverted austenite decreased gradually and the kinetics of strain induced martensite rose rapidly. The stability of the reverted austenite was moderate when intercritically annealed at 700℃, this leaded to the best plasticity and the optimal mechanical properties, namely the product of strength and plasticity was up to 65GPa?%. A constitutive model based on dislocation density for the tensile and work hardening behavior of the cold-rolled medium Mn steel was developed, simulated results exhibited that the mechanic stability of austenite has a decisive influence on the deformation behavior of the material. The austenite stability will be too high if the IA temperature is lower, this will lead to the lower work hardening rate and uniform elongation; when the IA temperature is moderate the stability of austenite will be optimum, consequently strain-induced martensite would be progressively produced during straining and result in the higher work hardening rate and prolonged uniform elongation; the stability of austenite will be too lower if the IA temperature is higher, thus larger number of strain-induced martensite would be formed in a short period, this would result in the higher tensile strength but the inferior uniform elongation.

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