【摘要】：大型鍛件一般是重型裝備上的核心零部件,由于工作環(huán)境特殊,要求其具有優(yōu)良的綜合力學性能。而金屬的宏觀力學性能由其最終微觀組織結(jié)構(gòu)決定,在熱加工的過程中,金屬的宏觀塑性變形引起了內(nèi)部微觀組織的復雜變化。在工業(yè)生產(chǎn)中,利用動態(tài)再結(jié)晶機制來改善材料在熱變形中的微觀組織,是提高產(chǎn)品質(zhì)量的重要途徑。因此,了解和掌握金屬在熱變形時的微觀組織演變規(guī)律,對提高其綜合性能及控制產(chǎn)品質(zhì)量具有非常重要的意義。本文以大型軋輥用鋼Cr5為研究對象,將宏觀工藝參數(shù)與元胞自動機結(jié)合,以位錯密度為內(nèi)變量,建立能夠從本質(zhì)上反應Cr5鋼熱塑性變形過程的微觀組織演化模型,研究了Cr5鋼動態(tài)再結(jié)晶行為的演化規(guī)律與其變形參數(shù)之間的關系,從而可以達到預測組織性能和優(yōu)化工藝參數(shù)的目的。具體開展的研究工作如下:通過熱壓縮物理模擬實驗、初始位錯密度測量實驗以及母相初始晶粒尺寸測量實驗,分析了不同變形條件下Cr5鋼的流變應力行為和組織演化規(guī)律,建立了Cr5鋼高溫流變峰值應力模型,并獲取了元胞自動機(CA)模擬所需的材料參數(shù)。基于材料熱變形過程中的位錯密度變化、再結(jié)晶形核及晶粒長大等材料學物理冶金理論,通過追蹤唯一內(nèi)變量—位錯密度的變化,建立了用于模擬Cr5鋼動態(tài)再結(jié)晶行為的CA模型。利用所建立的動態(tài)再結(jié)晶CA模型,模擬了Cr5鋼在各個變形條件下的高溫流變應力曲線和動態(tài)再結(jié)晶動力學行為,并與實驗結(jié)果進行對比,驗證了模型的準確性。通過改變應變速率、變形溫度以及應變量三大熱變形參數(shù),研究了各熱力參數(shù)對Cr5鋼動態(tài)再結(jié)晶行為的影響規(guī)律。結(jié)果表明,基于材料學物理冶金原理所建立的CA模型,可以準確模擬和預測Cr5鋼動態(tài)再結(jié)晶微觀組織和流變應力的演變特征,從而為預測組織演變和控制產(chǎn)品質(zhì)量提供合理依據(jù)。
[Abstract]:Large forgings are generally the core parts of heavy equipment. Because of the special working environment, they are required to have excellent comprehensive mechanical properties. The macroscopic mechanical properties of metals are determined by their final microstructure. During the process of hot working, the macroscopic plastic deformation of metals causes complex changes of internal microstructure. In industrial production, it is an important way to improve the product quality by using dynamic recrystallization mechanism to improve the microstructure of materials in hot deformation. Therefore, it is of great significance to understand and master the law of microstructure evolution of metals during hot deformation in order to improve their comprehensive properties and control the quality of products. In this paper, taking Cr5 steel for large roll as the research object, combining macroscopic process parameters with cellular automata, taking dislocation density as internal variable, a microstructure evolution model which can essentially reflect the thermoplastic deformation process of Cr5 steel is established. The relationship between the evolution of dynamic recrystallization behavior of Cr5 steel and its deformation parameters is studied, which can be used to predict the microstructure and properties and optimize the process parameters. The research works are as follows: the rheological stress behavior and microstructure evolution of Cr5 steel under different deformation conditions are analyzed by means of thermal compression physical simulation experiment, initial dislocation density measurement experiment and parent phase initial grain size measurement experiment. The peak rheological stress model of Cr5 steel at high temperature was established and the material parameters needed for (CA) simulation of cellular automata were obtained. Based on the dislocation density change during hot deformation of materials, recrystallization nucleation and grain growth and other physical metallurgical theories of materials, the change of dislocation density, which is the only internal variable, is traced. A CA model was established to simulate the dynamic recrystallization behavior of Cr5 steel. The dynamic recrystallization CA model is used to simulate the high temperature rheological stress curve and dynamic recrystallization kinetic behavior of Cr5 steel under various deformation conditions. The experimental results are compared to verify the accuracy of the model. The effect of thermal parameters on the dynamic recrystallization behavior of Cr5 steel was studied by changing the strain rate, deformation temperature and strain. The results show that the CA model based on the principle of material physics metallurgy can accurately simulate and predict the evolution characteristics of dynamic recrystallization microstructure and rheological stress of Cr5 steel. Therefore, it provides reasonable basis for predicting organizational evolution and controlling product quality.
【學位授予單位】：河南科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG142.1

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