【摘要】：304L奧氏體不銹鋼是核電大鍛件的主要材料之一。核電不銹鋼大鍛件不僅體積大,而且要求材料純凈、鍛件組織性能均勻。由自由鍛引起的溫度、材料流線和變形不均勻性導(dǎo)致鍛造過程中大鍛件實際生產(chǎn)中存在著熱鍛開裂、晶粒粗大且不均勻技術(shù)問題。解決以上問題的關(guān)鍵在于鍛件內(nèi)部晶粒細(xì)化和均勻,其技術(shù)的核心就是鍛造過程中大鍛件內(nèi)部晶粒度的有效控制。然而目前國內(nèi)對于該鋼的基礎(chǔ)研究還遠不能滿足實際生產(chǎn)要求,進而影響大鍛件熱變形工藝的進一步優(yōu)化。 本文采用GLEEBLEl500D熱模擬實驗機對鍛態(tài)304L不銹鋼進行了單道次熱壓縮實驗,在不同應(yīng)變速率、變形溫度下得到了304L不銹鋼的應(yīng)力-應(yīng)變曲線,研究了304L不銹鋼熱變形過程初始晶粒尺寸、變形溫度、變形量、應(yīng)變速率等變形參數(shù)對奧氏體動態(tài)再結(jié)晶和流變應(yīng)力的影響規(guī)律。建立了304L不銹鋼動態(tài)再結(jié)晶的動力學(xué)模型、運動學(xué)模型、流變應(yīng)力模型、再結(jié)晶晶粒尺寸模型以及位錯密度模型。通過金相試驗、透射電鏡(TEM)實驗得到動態(tài)再結(jié)晶后304L不銹鋼的再結(jié)晶晶粒尺寸、位錯組態(tài)以及密度分布。 采用ANSYS有限元軟件模擬了熱模擬試驗的變形過程,分析了304L不銹鋼試樣的不同變形區(qū)域在熱變形過程中的等效應(yīng)變、應(yīng)力以及溫度場的分布情況。并參照金相圖,分析了非均勻應(yīng)變對奧氏體動態(tài)再結(jié)晶及晶粒尺寸的影響。結(jié)果表明,在試樣的不同區(qū)域,等效應(yīng)變和應(yīng)力分布相差很大;溫度分布也有差異,剪應(yīng)變對動態(tài)再結(jié)晶程度的影響比等效應(yīng)變大。在試驗所設(shè)定的最大變形量下,等效應(yīng)變對晶粒細(xì)化的影響存在一個臨界值,而隨著剪應(yīng)變的增加,奧氏體晶粒不斷細(xì)化,可見剪應(yīng)變對奧氏體晶粒尺寸的影響更大。仿真結(jié)果與實驗結(jié)果較為一致,這表明該模型能用來準(zhǔn)確描述304L不銹鋼熱變形過程。 通過的熱模擬試驗和數(shù)值模擬,探究熱變形下晶粒尺寸、分布情況,引起的原因和微觀機理,建立與變形量、變形溫度、保溫時間、應(yīng)力狀態(tài)等宏觀變形參數(shù)之間的關(guān)系。研究成果可為核電奧氏體不銹鋼大鍛件生產(chǎn)中的塑性加工質(zhì)量預(yù)報和控制技術(shù)提供可靠的科學(xué)依據(jù)。
[Abstract]:304L austenitic stainless steel is one of the main materials for nuclear power forgings. Nuclear stainless steel forgings are not only large in volume, but also pure in material, uniform in structure and properties. The temperature, material streamline and deformation inhomogeneity caused by free forging lead to hot forging cracking, coarse grain size and inhomogeneous technical problems in the actual production of large forgings. The key to solve the above problems lies in the grain refinement and uniformity in the forging. The core of the technology is the effective control of the internal grain size in the forging process. However, at present, the basic research on the steel in China is far from meeting the actual production requirements, which will affect the further optimization of the hot deformation process of large forgings. In this paper, the single pass thermal compression test of forged 304L stainless steel was carried out with GLEEBLEl500D thermal simulation machine. The stress-strain curves of 304L stainless steel were obtained at different strain rates and deformation temperatures. The effect of deformation parameters such as initial grain size, deformation temperature, deformation amount and strain rate on dynamic recrystallization and rheological stress of austenite during hot deformation of 304L stainless steel were studied. The dynamic model, kinematics model, rheological stress model, recrystallization grain size model and dislocation density model of 304L stainless steel were established. The recrystallization grain size, dislocation configuration and density distribution of 304L stainless steel after dynamic recrystallization were obtained by metallographic test and transmission electron microscope (TEM) test. The deformation process of thermal simulation test was simulated by ANSYS finite element software, and the distribution of equivalent strain, stress and temperature field in different deformation regions of 304L stainless steel specimen was analyzed. The effect of inhomogeneous strain on the dynamic recrystallization and grain size of austenite was analyzed by referring to the metallographic diagram. The results show that the distribution of equivalent strain and stress varies greatly in different regions of the specimen, and the temperature distribution is different, and the effect of shear strain on dynamic recrystallization degree is greater than that of equivalent strain. There is a critical value of the effect of equivalent strain on grain refinement under the maximum deformation set in the experiment. However, with the increase of shear strain, austenite grain is refined continuously, and the effect of shear strain on austenite grain size is greater. The simulation results are in good agreement with the experimental results, which indicates that the model can accurately describe the hot deformation process of 304L stainless steel. Through the thermal simulation test and numerical simulation, this paper explores the grain size, distribution, causes and microscopic mechanism of hot deformation, and establishes the relationship between deformation amount, deformation temperature, holding time, stress state and other macroscopic deformation parameters. The research results can provide a reliable scientific basis for the prediction and control of plastic working quality in the production of austenitic stainless steel forgings.
【學(xué)位授予單位】：太原科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2011
【分類號】：TG142.15

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本文編號：2362815