基于混晶评价的大锻件热锻晶粒组织演变

Evolution of grain structure in hot forging of large forgingsbased on mixed grain evaluation

以大型锻件超超临界转子用12%Cr耐热钢为研究对象,采用拔长实验和数值模拟相结合的方式,探究了大锻件热锻过程晶粒组织演变情况。研究表明:热锻后坯料横截面晶粒不均匀性受锻造温度、锻比以及上模压下速度综合影响,小锻比和较低锻造温度与大锻比和较高锻造温度均可改善晶粒不均匀性。基于此,通过拟合得到了12%Cr耐热钢热锻过程坯料横截面晶粒不均匀性与锻造工艺参数之间的量化关系模型;针对大锻件“因大而生”的混晶问题,在现有混晶评价方法的基础上,提出了一种普适性更好的混晶评价方法,即采用统计学方法划分各小组,以每小组晶粒弦长和占总弦长的频率为基础,分别确定大、小晶粒分界组进行评价,对比拔长实验后的混晶组织演变规律验证了该方法的优越性。

Taking 12%Cr heat-resistant steel used for large forgings and ultra supercritical rotors as the research object,the grain structure evolution in the hot forging process of large forgings was explored using the combinated method of drawing tests and numerical simulations.The research shows that the non-uniformity of grain size in the cross-section of hot forged billets is influenced by forging temperature,forging ratio,upper die pressing speed.Both small forging ratio,lower forging temperature and large forging ratio,higher forging temperature can improve non-uniformity of grain.Based on this,a quantitative relationship model between the non-uniformity of grain size in the cross-section of 12%Cr heat-resistant steel in hot forging process and forging process parameters was obtained through fitting.A good generality mixed grain evaluation method was proposed based on the existing mixed grain evaluation methods for the problem of mixed grain in large forgings.Statistical methods were used to divide each group,and based on the chord length of grains of each group and the frequency of the total chord length,the boundary groups of large and small grains were determined for evaluation.The superiority of this method was verified by comparing the evolution law of mixed grain structure after drawing tests.