12%Cr超超临界转子钢微观组织演变规律及数值模拟的研究

发布时间：2019-01-20 18:09

【摘要】：大锻件制造是综合大型钢锭冶炼、锻造与热处理一体化复杂工艺过程,锻造和热处理是大锻件制造过程中非常重要的两个环节。晶粒度不均匀和变形不均匀在很大程度上影响大锻件产品的质量,严重时直接导致产品报废。大锻件成形过程钢锭内部发生复杂的微观组织演变,产品最终的晶粒度和均匀性受变形温度、压下量和变形均匀性等多种因素控制,如果处理不恰当,都将会给后续热处理带来非常大的麻烦。因此,研究成形过程组织均匀性、锻件内部组织演变和晶粒大小分布对于获得优质大锻件具有非常重要的意义。本文以核电大型转子材料12%Cr超超临界转子用钢为对象,主要研究了奥氏体晶粒长大规律和拔长过程微观组织演变。首先,通过箱式电阻炉研究了此钢在不同保温时间和不同加热温度内奥氏体晶粒长大规律。再利用非线性回归分析方法和Arrhenius晶粒长大模型,得到了此钢奥氏体晶粒长大动力学方程。接着,运用DEFORM-3D数值模拟技术和缩比试验相结合的方法,研究了不同锻比上平砧下V型砧拔长工艺对12%Cr超超临界转子钢微观组织演变的影响,分析了锻件不同锻比不同截面特征点晶粒大小分布和变形均匀性等,对比分析了试验结果和数值模拟结果。由此得出:当锻比从1.1逐渐增大到1.3过程中,锻件的变形不均匀性随之增加,但平均晶粒尺寸有减小的趋势,锻件组织不均匀性也能得到一定改善。最后,再次运用DEFORM-3D数值模拟软件分析了12%Cr超超临界转子用钢在上下平砧(FM拔长法)、上平砧下梯型砧和上下梯型砧三种不同砧型下各自的成形过程和变形特点,与上平砧下V型砧拔长的效果进行对比。并从等效应变、等效应力、温度场和动态再结晶百分数分布等方面,详细对比分析了四种砧型拔长工艺的优劣。最终结果表明:上平砧下V型砧拔长与上平砧下梯型砧拔长效果较好。
[Abstract]:The manufacturing of large forgings is a complex process of integrated smelting, forging and heat treatment of large ingots. Forging and heat treatment are two very important links in the manufacturing process of large forgings. Grain size inhomogeneity and deformation inhomogeneity affect the quality of large forgings to a great extent and lead to product scrapping directly when serious. During the forming process of large forgings, complex microstructure evolves inside the ingot, and the final grain size and uniformity of the product are controlled by many factors, such as deformation temperature, reduction amount and deformation uniformity, etc., if the treatment is not appropriate, Will bring great trouble to the follow-up heat treatment. Therefore, it is very important to study the microstructure homogeneity, microstructure evolution and grain size distribution in forging for obtaining high quality forgings. In this paper, the austenitic grain growth law and microstructure evolution during pull-out process of 12%Cr ultra-supercritical rotor steel for nuclear power large rotor material are studied. First, the austenite grain growth law of this steel at different holding time and different heating temperature was studied by box resistance furnace. The dynamic equation of austenite grain growth in this steel is obtained by using nonlinear regression analysis and Arrhenius grain growth model. Then, the effect of V-shaped anvil drawing process under different forging ratios on the microstructure evolution of 12%Cr ultra-supercritical rotor steel was studied by using DEFORM-3D numerical simulation technique and shrinkage test. The grain size distribution and deformation uniformity at different forging ratios and cross section characteristic points of forgings are analyzed, and the experimental results and numerical simulation results are compared and analyzed. It is concluded that when the forging ratio increases from 1.1 to 1.3, the deformation inhomogeneity increases, but the average grain size decreases, and the microstructure inhomogeneity of the forging can be improved to some extent. Finally, DEFORM-3D numerical simulation software is used to analyze the forming process and deformation characteristics of 12%Cr ultra-supercritical rotors under three different anvil types: upper and lower trapezoidal anvil (FM), upper and lower trapezoidal anvil and upper and lower trapezoidal anvil. The results were compared with that of V type anvil under upper flat anvil. From the aspects of equivalent strain, equivalent stress, temperature field and dynamic recrystallization percentage distribution, the advantages and disadvantages of four anvil drawing processes are compared and analyzed in detail. The final results showed that the drawing length of V type anvil under upper flat anvil and trapezoidal anvil under upper flat anvil was better than that of trapezoidal anvil under upper flat anvil.
【学位授予单位】：太原科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1;TG316.12

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