Effect Of Hot Working Process On Microstructure And Properties Of GH4738 Superalloy

GH4738 alloy is a precipitation hardening superalloy,which has good tensile strength and high working temperature.Still,its hot deformation is complex,the hot processing window is narrow,and it is easy to appear mixed crystal.The selection of suitable hot working technology significantly influences the microstructure uniformity and property stability of alloy forgings.To meet the higher requirements of the current use of the alloy,it is necessary to conduct more in-depth research on the microstructure evolution of the alloy during the hot working process,the precipitation rule of the precipitate phase,and the anti-high-temperature erosion ability.Given the above problems,the related research on the alloy was carried out in this paper.Using the bar-shaped billet of GH4738 alloy as the initial material,the deformation behavior of the billet under different hot working processes was studied,the grain refining mechanism of the billet,the precipitation rule of the second phase,and carbide during the hot deformation process of the alloy were analyzed,and the recrystallization form of the alloy during the hot deformation process was determined.The analysis results show that the grains of the forgings with large deformation are refined to different degrees under different hot deformation processes when the alloy is deformed in ? single-phase region.With the increase of deformation temperature,the grain refinement effect of forgings is weakened,and the grain refinement effect of forgings at higher deformation temperature(>1150 ?)is insufficient.Still,at lower deformation temperature(<1150 ?),the grain refinement effect of forgings is better.The grain size decreases with the increase of deformation,and the grain refining effect is better with the growth of deformation.The characteristics of the second phase in different forgings are similar,and the second phase is not entirely precipitated out.A small amount of granular carbide precipitates at the grain boundary of the forgings,but no carbide precipitates inside the grains.The recrystallization forms of ? single-phase hot deformation forgings are all discontinuous dynamic recrystallization.The heat treatment experiments of different schemes were carried out to study the grain growth behavior and the dissolution and precipitation laws of precipitated phases during the heat treatment process of the alloy.The influence of the heat treatment scheme on the microstructure and mechanical properties of the alloy was explored,and the difference in the high-temperature erosion resistance of the heat-treated parts with different deformations was also investigated.The analysis results show that the grain size of the forgings after the subsolid solution heat treatment(1020?/4h/AC+845?/4h/AC+760?/16h/AC)grows up to a large extent.Although the second phase has been wholly precipitated,the grain size of the forgings has exceeded the optimal strengthening size,which leads to the hardness of the forgings decreased to a certain extent after the subsolid solution heat treatment.After the "improved" heat treatment(960?/7min/WC+845?/15min/AC+760?/30min/AC),the grain size of the alloy forgings has little change,the second phase is wholly precipitated,and the distribution is more uniform,but the grain size of the second phase has grown to a certain extent.There is less carbide precipitation in the grain boundary and more lamellar carbide precipitation in the grain.After heat treatment,the hardness of the forgings has been dramatically improved.The high-temperature erosion rate of forgings with different deformations under stepped heating decreases gradually with the increase of deformations after the "improved" heat treatment scheme.Still,the difference between each other is minimal.