Effect Of Rare-earth Ce On The Microstructures And Properties Of IF Steel

"lightweight" will be the primary direction of future automotive development, in orderto guarantee the safety of the personnel, in the meantime, as much as possible to reduce theweight of the automobiles, which is bound to the rapid development of high-strengthautomotive steel.This paper takes the Interstitial-Free Steel as the research object, relying onabundant Rare Earth resources in Baiyanobo region, Baotou, Inner Mongolia, by addingmicro-alloying elements Rare Earth Cerium to improve the microstructures and the materialcomprehensive properties.Different content of Cerium in IF steel was smelted under laboratory conditions.Thestructures and inclusions of the investigated steel had been analyzed by using Axiovert25Zeiss microscope, S-3400N scanning electron microscopy, VUESTL2X-ray spectrometerand other testing equipment.The true stress-strain curves were drawn for the investigated steel on a Gleeble-1500Dthermo-mechanical simulator.Then the austenite hot deformation activation energy, theindex of dynamic recrystallization kinetics equation and static recrystallization volumefraction had been calculated.The influences of Ce on the microstructures and mechanicalproperties of IF steel had been studied.Ce has the strong ability to purify liquid steel, the deoxidation rate was44.4%anddesulfurization rate was40.0%when the Ce content was0.0042%. And Ce could distinctlyimprove the microstructures of the steel，refine the grains and distribute well with theincreasing of Ce content，meanwhile the inclusions are changed from polygonal aluminumoxide and titanium nitride complex inclusions into axiolitic or globular rare earth ones whichcontain aluminum and titanium.The mechanical properties of IF steel were improved significantly with the increasingof Ce content.The tensile strength was increased by44.4%, from114.78MPa to165.71MPa,yield strength was increased by37.1%, from96.41MPa to132.17MPa, elongation wasincreased by13.0%, from43.67%to49.35%, room temperature impact energy was increased by34.5%, from229.5J to308.6J, at the Ce content was0.0042%.Ce can improve the high temperature mechanical properties of IF steel, the reduction ofarea and tensile strength were increased by8.3%and22.7%in average respectively, whenthe Ce content was0.0042%with temperature between750℃to1150℃, strain rate of0.1s-1, and the strengthening mechanism is fine grain strengthening.The flow stresses were increased with the increasing of Ce content, the thermaldeformation of activation energy was increased and the index of Avrami equation wasdecreased., the Q value was increased from122.92KJ/mol to182.75KJ/mol and kdvalueswas decreased from3.796to3.377when Ce content was0.0042%. Ce significantly restrainsthe IF steel static and dynamic recrystallization behavior during the strain rate no more than5s-1.