The Research Of Thermoplasticity And The Establishment Of Rheological Stress Model About Q345B Casting Blank On High Temperature

The crack defects of casting blank are main influence factors for the quality of castingblank. In continuous casting process,600℃-900℃temperature range is austenitic areaand diphasic area, this temperature range should be relatively with the process ofstraightening and deformation. In the process of straightening, casting blank which isbended and deformed will engender crack initiation of surface and grain boundary,especially transverse fracture. Because rare earth have the function of purification,deterioration and micro alloying, rare earth can improve casting quality in the industry. It isimportant factor that affecting the crack of casting steel is high temperature mechanicalproperties, therefore, researching on high temperature mechanical properties andrheological stress prediction model of rare earth Q345B casting steel could provideexperimental basis for casting blank production.Therefore, using Gleeble–1500D thermal simulation tensile testing machine, castingbillet containing RE and no RE were researched in brittle zone III600℃~900℃range.throughing the reduction of area of each temperature could determine the temperature ofthe lowest plasticity and thermoplasticity. Then using phase electronic microscope andscanning electron microscopy (SEM) analyzed the causes and the effect of rare earths;Simulation of the casting billet straightening process could analyze high temperaturethermoplastic of160ppm RE continuous casting billet under the action of low tensile stress.At the same time, using environmental scanning electron microscope energy spectrum, themechanism of grain boundary RE segreation and its effect on the cast steel thermoplasticwere analysed; By single-channel compression test of160ppm RE and40ppm REcontinuous casting billet, activation energy were calculated and high temperaturerheological stress prediction model was set up. All of these can provide scientificexperimental basis for the casting blank straightening and the subsequent production.The calculation results show that: in brittle zone III600℃~900℃range, the samples’ reduction of area present decreased firstly and then increased with the increasing ofstretching temperature, and the temperature of lowest plasticity is800℃. In thistemperature, reduction of area of160ppm RE casting billet is50.8%, reduction of areawithout RE casting billet is36.6%. It is thus clear that adding160ppm RE can improvehigh temperature thermoplasticity about15%. For high temperature and low tensile stresstests, rare earths in the grain boundary being the time of critical segregation; By calculatingdynamic recrystallization activation energy of casting billet containing rare earth, we findthat dynamic recrystallization occur to40ppm RE casting billet could more easier than to160ppm RE casting billet, At the same time, establishing high temperature rheologicalstress prediction model has high reliability. Therefore, the research results to guide theQ345B rare earth casting blank through continuous casting and hot rolling processoptimization.