Study On Hot Deformation Process Of 300M Steel

300M steel is a typical ultra high strength steel,mainly used for the landing gear and other aircraft key components of the manufacturing,the current landing gear using the whole forging process,forming a difficult,high quality requirements.This paper is devoted to the study of the hot deformation process parameters of 300 M steel,to provide guidance for forging process,not only to ensure the forging process,but also with a small,uniform grain.In this paper,the influence of deformation temperature?900¹250??and strain rate(0.01⁵0s^-1)on stress-strain relationship and dynamic recrystallization of 300 M steel was studied by means of thermal simulation experiment.The constitutive model of 300 M steel,the dynamic recrystallization model and the hot working diagram are established,providing reference for the parameter selection of grain size control and forging process range.In order to investigate the influence of the original grain size on the processing performance,two kinds of thermal simulation test schemes were developed.All samples in the scheme A were first heated to 1250? before hot compression,and heat insulation,and then reduced to deformation temperature for thermal compression,ensuring that the samples had the same grain size before deformation.The scheme of B was directly heated to the temperature of hot compression deformation.This paper obtained the following results:?1?The true stress of 300 M steel is affected by temperature and strain rate,the flow stress decreases with the increase of temperature and the decrease of strain rate.The activation energy,hot deformation parameters and the constitutive equations of 300 M steel is established by linear regression analysis.?2?The establishment of the dynamic recrystallization of 300 M steel constitutive equation can be used to predict the dynamic recrystallization fraction.The establishment of the average grain size model provides a theoretical reference of grain for the forging process.?3?The establishment of 300 M steel hot processing map,hot processing map shows that the power dissipation of 300 M steel value increase with the increase of the strain,regional instability regions firstly decrease and then increase with the increase of the strain.Thermal processing area temperature favorable 1100¹170?,the strain rate of 0.1¹.99s^-1and temperature of 1100¹250?,the strain rate range of 10⁵0s^-1.The results also show that the original grain size has a certain influence on dynamic recrystallization of 300 M steel,mainly affecting the critical temperature of recrystallization,when the original grain is larger,recrystallization temperature of 300 M steel is higher.When the original grain size rangs from 114.56?m to132.49?m,the critical temperature of recrystallization is 1100?.When temperature is above 1100?,recrystallization complete at various strain rate 0.01⁵0s^-1.When temperaturebelow 1100?,recrystallization cannot fully complete,still retaining the elongated grain structure.When the original grain size rangs from 10.29?m to 121.13?m,the critical recrystallization temperature is 900 ?,the strain rate(0.01⁵0s^-1),completing recrystallization.In addition,when the temperature is below 1100?,the average grain size small,but the grain boundary bending,is not a steady state;when the temperature is above 1100?,average grain greater,but grain boundaries straight,the grain boundaries pentagonal and hexagonal shape,is a steady state.