Research The Effect Of Solidification Terminal Heavy Reduction On The Cast Microstructure Of Wide-Thick Slabs

Solidification terminal heavy reduction technique applied to wide-thick slabs,not only can eliminate centerline segregation,but also can effectively improve center porosity.Moreover,heavy reduction supply large shell deformation for the casting slabs,inducing varied degree of dynamic recrystallization on the surface,where refine ferrite grains obviously,and center slabs,where polygons ferrite grain evolve to strips ones,eventually to acicular ferrite.The grain boundary area will be large with the decrease of the surface ferrite grain size,which could provide the resistance for crack extended and improve thermoplasticity.The acicular ferrite of central slabs possess favourable toughness and pinning effect for austenite grain boundary,which will prevent extension of the central crack and growing up of austenitic grain.So,the change of slabs microstructure are beneficial because of the heavy reduction.It has profound significance to research the effect of solidification terminal heavy reduction on microstructure evolution of wide-thick slabs,and this is the key to study the refined grain subsequent heating and rolling process.The paper used Q345C steel as the research object,and the experiments was required to analyze the macrostructure and microstructure of varied reduction slabs,and measured the austenitic grain size at the same time.The three-dimensional coupled thermo-mechanical finite element mode was established based on the heavy reduction process,which was to study strain rate on diverse position of slabs in shell changed process.The dynamic recrystallization on varied position of slabs under reduction condition was studied based on Gleeble tests.The conclusions were as follows:(1)The application of solidification terminal heavy reduction technique changed the normal growth of dendrite in slabs.The grain size decreased with the reduction increased on diverse position of slabs.No matter what kind of reduction model,the austenitic grain size increased gradually from the surface to center of slab.(2)The three-dimensional coupled thermo-mechanical finite element model was established to study the strain rate of different positions of slabs cross-section.The strain rate was increased from the corner to center of slab,and the range was between 10-3?10-1s-1.(3)The Gleeble tests was used based on strain rate of different positions of slabs cross-section by established model,obtaining that all the positions apart from the corner surface of slabs had varied degree of dynamic recrystallization combined with the productive conditions.(4)This paper established critical strain model and grain size model about dynamic recrystallization based on the true stress-strain and microstructure of tested sample by the Gleeble tests.