本文關(guān)鍵詞： 奧氏體不銹鋼 熱鍛 再結(jié)晶模型 有限元模擬 斷裂　出處：《北京科技大學(xué)》2016年博士論文　論文類型：學(xué)位論文

【摘要】：超低C控N的316LN奧氏體不銹鋼,具有良好的加工性能、優(yōu)良的綜合力學(xué)性能以及耐晶間應(yīng)力腐蝕性能,被選用作第三代AP1000壓水堆核電站的一回路主管道材料。不同于第二代壓水堆核電站的鑄造主管道,AP1000主管道采用管體和管嘴整體鍛造成形,制造難度很大。AP1000主管道鍛造工藝的關(guān)鍵是有效地解決鍛造過程中的混晶問題,使晶粒細(xì)勻化；在鋼錠鐓粗、拔長等壓實階段,有效地控制裂紋尤其是表面裂紋的產(chǎn)生。西屋公司對AP1000主管道的晶粒度提出了嚴(yán)格要求,要求其晶粒度整體大于ASME 2級,而316LN鋼是單相奧氏體不銹鋼,不能通過熱處理改善組織,故熱鍛完成后的組織對主管道的最終力學(xué)性能起著決定性作用。因此,掌握316LN鋼在多道次熱鍛過程中的微觀組織演變規(guī)律和斷裂行為對AP1000主管道的制造技術(shù)控制至關(guān)重要。本文針對AP1000核電站主管道的鍛造過程,通過大量的Gleeble實驗和熱處理實驗,研究了316LN鋼在多道次熱變形過程中的動態(tài)再結(jié)晶、靜態(tài)再結(jié)晶和亞動態(tài)再結(jié)晶組織演變規(guī)律、奧氏體晶粒長大規(guī)律和斷裂行為,建立了再結(jié)晶、晶粒長大和韌性斷裂模型。實驗結(jié)果將有助于主管道在鍛造過程中的組織控制及裂紋預(yù)防,并可為主管道加工工藝優(yōu)化設(shè)計提供參考數(shù)據(jù)和數(shù)值模擬模型。通過大量的Gleeble單道次和雙道次熱壓縮實驗,研究了主管道材料316LN鋼在熱變形過程中動態(tài)再結(jié)晶、靜態(tài)再結(jié)晶以及亞動態(tài)再結(jié)晶行為。研究發(fā)現(xiàn),在熱變形過程中,316LN鋼較難發(fā)生動態(tài)回復(fù),其主要的軟化機(jī)制是動態(tài)再結(jié)晶,動態(tài)再結(jié)晶臨界應(yīng)變與峰值應(yīng)變的比值僅為0.38;動態(tài)再結(jié)晶優(yōu)先在晶界、三叉晶界和孿晶界形核,也可在形變帶附近形核,再結(jié)晶主要形核機(jī)制為形變誘導(dǎo)晶界遷移機(jī)制。在多道次熱變形過程中,當(dāng)變形施加的真應(yīng)變小于動態(tài)再結(jié)晶臨界應(yīng)變時,隨后的間歇過程中的軟化行為表現(xiàn)為靜態(tài)回復(fù)和靜態(tài)再結(jié)晶；當(dāng)變形施加的真應(yīng)變超過亞動態(tài)再結(jié)晶臨界值時,道次間歇過程中發(fā)生亞動態(tài)再結(jié)晶。有效地解決了由于DEFORM-3D有限元模擬軟件在計算的過程中以等效應(yīng)變和等效應(yīng)變速率為變量,而引起的再結(jié)晶組織演變模擬結(jié)果與實驗值偏差較大的問題。根據(jù)熱模擬實驗數(shù)據(jù),建立了再結(jié)晶動力學(xué)、晶粒尺寸與真應(yīng)變、真應(yīng)變速率之間的經(jīng)典關(guān)系方程。將這些模型直接應(yīng)用于DEFORM-3D軟件中,模擬316LN鋼的變形過程組織演變行為時會產(chǎn)生較大偏差,因此必須對再結(jié)晶模型進(jìn)行修正,采用等效應(yīng)變和等效應(yīng)變速率替代真應(yīng)變和真應(yīng)變速率。借助DEFORM-3D軟件將真應(yīng)變和真應(yīng)變速率轉(zhuǎn)換為相應(yīng)的等效應(yīng)變和等效應(yīng)變速率,以等效應(yīng)變和等效應(yīng)變速率為參數(shù)重新構(gòu)建了再結(jié)晶模型,利用重建后的再結(jié)晶模型進(jìn)行DEFORM-3D有限元模擬時,模擬結(jié)果和實驗值之間符合地很好。通過大量的熱處理試驗研究了316LN鋼900～1200℃下保溫0.25～10h的奧氏體晶粒長大規(guī)律。當(dāng)溫度低于1000℃時,316LN鋼的奧氏體晶粒長大速度較慢;當(dāng)溫度高于1050℃時,奧氏體晶粒長大速度較快。當(dāng)保溫時間短于0.5 h時,316LN鋼的奧氏體晶粒長大速度較快；由于晶粒長大驅(qū)動力的不斷減小,保溫時間長于0.5 h時,奧氏體晶粒長大速度明顯放慢。316LN鋼長時間高溫下保溫后的晶粒尺寸基本不受初始晶粒尺寸的影響。根據(jù)熱處理實驗數(shù)據(jù),建立了316LN鋼奧氏體晶粒尺寸隨溫度、時間和初始晶粒尺寸變化的方程,奧氏體晶粒長大常數(shù)n為2.47。在900～1200℃、0.01～1s1-的熱拉伸變形參數(shù)范圍內(nèi),當(dāng)頸縮發(fā)生后,頸縮附近的變形比較劇烈,形變量較大。當(dāng)變形溫度為1200℃、應(yīng)變速率為1s-1時,斷口附近的再結(jié)晶形核率和再結(jié)晶晶粒長大速率都較高,在形核和長大兩個過程的共同作用下,斷口附近的再結(jié)晶組織最為均勻細(xì)�。捍俗冃螚l件下試樣的斷面收縮率也最高,塑性最好。在900～1100℃下,316LN鋼的斷面收縮率在應(yīng)變速率為0.1s-1時出現(xiàn)峰值。316LN鋼基于正則化的Cockcroft Latham準(zhǔn)則的臨界斷裂因子與其Zener-Hollomon參數(shù)的對數(shù)之間存在線性關(guān)系。
[Abstract]:316LN austenitic stainless steel with ultra low C N control, has a good processing performance, excellent comprehensive mechanical properties and resistance to intergranular stress corrosion, was used as a main material pipeline loop reactor nuclear power plant third generation AP1000 water pressure. The casting main pipeline is different from the second generation PWR nuclear power plant, the main AP1000 the pipeline pipe body and nozzle whole forging, the key.AP1000 main pipe forging manufacturing difficulty is effectively solve the problem of mixed crystal in the forging process, the grain refining and homogenizing; in the ingot upsetting, stretching compaction stage, effectively control the crack especially the surface crack. Westinghouse the grain size of AP1000 main pipe made stringent requirements, the grain size of the whole is greater than 2 ASME, and the 316LN steel is austenitic stainless steel, not through the heat treatment to improve the organization, so the hot forging after the completion of the organization in charge of the road The end plays a decisive role in the mechanical properties. Therefore, mastering the microstructure during multipass hot forging process of 316LN steel evolution and fracture behavior of AP1000 manufacturing technology of the main pipeline control is very important. In this paper, the forging process for AP1000 nuclear power plant main pipeline, through a lot of experiments and Gleeble experiments of heat treatment of 316LN steel was studied, and then the crystallization in deformation in the dynamic process of multi pass hot, static recrystallization and meta dynamic recrystallization microstructure evolution, austenite grain growth behavior and fracture behavior, established recrystallization, grain growth and ductile fracture model. The experimental results will be helpful to the main pipeline in the forging process of the organization control and crack prevention, and can the main pipeline processing technology optimization design provides reference data and numerical simulation model. Through a large number of Gleeble single and double pass hot compression experiment of primary pipe material 316LN Steel during hot deformation process of dynamic recrystallization, static recrystallization and meta dynamic recrystallization behavior. The study found that during hot deformation process, 316LN steel is difficult to occur in the dynamic response, the main softening mechanism is dynamic recrystallization and recrystallization critical strain and peak strain dynamic ratio value is only 0.38; dynamic crystallize preferentially at the grain boundaries, triple grain boundary and twin boundary nucleation, also can bring near nucleation during deformation, recrystallization nucleation mechanism is the main deformation induced grain boundary migration mechanism in multi pass hot deformation process, when the true strain deformation applied less than dynamic recrystallization critical strain softening behavior, the subsequent batch process the performance for the static recovery and static recrystallization; when the true strain deformation applied over metarecrystallization critical value, dynamic recrystallization occurred in sub pass batch process. Because DEFORM-3D can effectively solve the finite element simulation Software to strain in the process of calculation and the equivalent strain rate as the variable, caused by the recrystallization microstructure evolution simulation results and experimental results of large deviation. Based on the thermal simulation experiment data, establish the recrystallization kinetics, grain size and true strain, it should be classic rate between the equation. These models are applied directly to the DEFORM-3D software, simulation of deformation process of 316LN steel microstructure evolution behavior will produce larger deviations, it is necessary to revise the model of recrystallization, the equivalent strain and equivalent strain rate instead of the true strain and true strain rate. The true strain and true strain rate is converted to equivalent strain and the equivalent strain rate by means of DEFORM-3D software, with strain and strain rate parameters to construct the model of recrystallization, the reconstruction of the recrystallization model by DEFORM-3D finite element During the simulation, the simulation results and experimental values fit in well. Through the heat treatment experiments of 316LN steel were studied under 900~1200 DEG C for 0.25 ~ 10h insulation austenite grain growth behavior. When the temperature is below 1000 DEG C, grew slower austenite grain of 316LN steel; when the temperature is higher than 1050 DEG C, the austenite grain growth fast. When the holding time is shorter than 0.5 h, the austenite grain of 316LN steel grew faster; the driving force of grain growth continues to decrease, the holding time is longer than 0.5 h, the austenite grain growth slowed down significantly the grain size of.316LN steel after long time insulation under high temperature are not affected by the initial grain size according to. Heat treatment of the experimental data, the austenite grain size of 316LN steel with temperature is established, and the time of the initial grain size variation equation, the austenite grain growth constant n was 2.47. at 900~1200 C, 0 The tensile deformation parameters of 1 ~ 1s1- range when necking occurs after Necking Deformation near intense deformation is larger. When the deformation temperature is 1200 DEG C, the strain rate of 1s-1, near the fracture rate of recrystallization nucleation and recrystallization grain growth rate is higher, the interaction up to two in the process of nucleation and recrystallization, the fracture near the most uniform and fine for the organization: the deformation section shrinkage rate for the sample is the highest, the best plastic. At 900~1100 DEG C, the rate of contraction of 316LN steel at the strain rate of 0.1s-1 appeared the linear relationship between the logarithmic peak parameters of.316LN steel the critical fracture factor and Zener-Hollomon regularization Cockcroft based on the Latham criterion.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG142.71;TG316

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