Influence of initial grain distribution on upsetting grain structure of large-sized GH4738 alloy bar
Employing the finite element method,the influence of the initial grain distribution on the grain structure after upsetting of large-size GH4738 superalloy bar was investigated. Based on the experimentally measured grain characteristics of the bar,four different initial grain distribution curves were designed,and the effects of deformation temperature,deformation strain and heating/soaking time on the grain structures were analyzed. The results show that,for a uniform grain distribution,the grain size after deformation is mainly determined by the strain level,exhibiting a gradient distribution with finer grains in the center and coarser grains at the edge. For non-uniform grain distributions,the grain size after deformation is determined by both the initial distribution and the strain field,and the coordination between the two can achieve a uniformly fine deformed grain structure. The optimum deformation temperature is 1040 ℃,which can make the deformed bar form a relatively large strain gradient and dynamic recrystallization degree,resulting in a relatively uniform and fine grain structure. Increasing the deformation strain from 35％ to 50％ is beneficial for further grain refinement,but has a limited effect on extremely fine initial grains. Preheating before upsetting leads to grain coarsening and a tendency towards uniformity,but the non-uniformity of the grain distribution after deformation increases,and the influence of the initial grain distribution is still significant.
万方数据
维普
