【作者】 杨磊；

【导师】 何宜柱；

【作者基本信息】 安徽工业大学 ， 材料科学与工程， 2010， 硕士

【摘要】 随着轧制技术的发展,对轧制产品的要求也越来越高。不仅要求轧制产品的外观尺寸达到要求,同时要求得到良好的组织性能。而产品的组织性能和轧制工艺、产品的成分相关,但生产过程中合金成分往往在一定范围内波动,这可能导致相对稳定的生产工艺生产得到的产品却有差异。通过微观组织演变模型来预测轧制过程中再结晶类型和奥氏体晶粒尺寸,通过流变应力模型可以预测轧制道次流变应力值的变化规律。目前对于板带材轧制模拟研究较多,棒材属于孔型轧制,其变形过程比较复杂,所以预测其轧制过程中微观组织演变比较困难。本文针对低合金钢棒材轧制过程,建立了热轧变形过程中微观组织演变预测模型和每道次流变应力值预测模型。由于Nb(C, N)析出会阻止热轧过程中奥氏体晶粒长大,所以本文对含Nb低合金钢和不含Nb低合金钢分别进行讨论。棒材每一道次变形都是在孔型中完成,所以其变形过程较板材复杂,为了准确计算变形时的应变,本文采用最大宽度法计算各个道次变形后的等效应变值。再结晶模型中需要道次平均温度,本文通过温度场模型模拟计算轧制过程道次平均温度。对于微观组织演变模型,通过临界应变参数判断再结晶类型,然后根据静态再结晶模型或动态再结晶模型模拟计算奥氏体晶粒尺寸演化过程。当发生不完全再结晶时,残余应变将累积到下一道次,下一道次的应变值会相应的增加。考虑到再结晶软化过程,结合微观组织演化,通过流变应力模型,模拟计算轧制变形时流变应力值。运用微观组织演变模型和流变应力模型对低合金棒材热轧过程进行了模拟,并用实际值对预测值进行验证,结果发现预测值比较好的吻合实际值。对于不含Nb低金钢,动态再结晶是奥氏体晶粒细化的主要方式,轧制过程单道次发生动态再结晶就可以细化奥氏体晶粒。而对于含Nb低合金钢,由于轧制过程会发生Nb(C, N)析出,阻碍再结晶软化的发生,所以当Nb(C, N)析出时,可以得到细小的奥氏体晶粒尺寸。在轧制起始阶段发生动态再结晶主要是因为高应变、低应变速率和轧制温度高,而终轧阶段发生动态再结晶主要是由于残余应变累积的结果。更多还原

【Abstract】 With the development of the rolling technology, the product quality is required higher than ever. The products need not only the qualified dimension, but also the good microstructure and properties. The microstructure and properties of the products are related with the chemical composition and the rolling technologies, which are different in a reasonable range. The changes of the rolling technologies can make the different of the properties of the products. Through predicting the evolution of the austenite size and the flow stress, the models can be useful tools to predict the products properties. Now there are many researches on model of hot strip rolling technologies. Because the rod rolling is a groove rolling, the deformation process of the hot rod rolling is more complicate than that of hot strip rolling. And the prediction of the rod rolling process is more difficult than the prediction of the hot strip rolling process.This paper proposes a model for predicting the microstructure evolution and the flow stress during the rod rolling. Due to the precipitation of Nb(C, N) can stop the growth of austenite, the prediction should discussed in different way. The deformation of the hot rod rolling is more complicate than hot strip rolling, the Max Width method is used to calculate the strain. The temperature model is used to compute the average temperature in each pass. The dynamic recrystallization will occur when the strain exceed the critical strain. When incomplete recrystallization happens, the residual strain will accumulate to the next pass. Combined with the microstructure evolution model, the flow stress can be calculated in different pass.The simulation of the hot rod rolling is proposed by a microstructure model. The prediction is compared of the mill data, and the results are good fit to the actual value. The main method refining the austenite size is the dynamic recrystallization. But when the steel is content of a little Nb, the precipitation of Nb(C, N) will prevent the recrystallization occurring and the austenite size changing. The small austenite size can be got when the dynamic recrystallization and precipitation happen together. The dynamic recrystallization occurs during the initial passes due to the high strains, low strain rates and high temperatures, or in the final passes as a consequence of strain accumulation.更多还原