Evolution of grain structure in hot forging of large forgings based on mixed grain evaluation
Taking 12％Cr heat-resistant steel used for large forgings and ultra supercritical rotors as the research object,the grain struc-ture evolution in the hot forging process of large forgings was explored using the combinated method of drawing tests and numerical simula-tions.The research shows that the non-uniformity of grain size in the cross-section of hot forged billets is influenced by forging tempera-ture,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.
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