Research Of High Strength IF Steel Car Plate Containing Rare Earth

With increasing demands of auto industry to the properties of steels, the strength oforiginal ordinary IF steel can no more meet it. It is significant to produce high strength IF steelwith proper ways to keep its good plasticity and improve its steel strength meanwhile. Thisexperiment adds Si, P, Mn for solid solution strengthening on the base of ordinary IF steel,which can make the strength of IF to over440MPa. But only one kind of solid solutionstrengthening for improving the strength of steel can cause some problems as well, especiallywhen adding a lot of P element into the steel in this experiment. The P element may easily toform segregation and there will be excessive segregation on the grain boundary of ferrite, whichcan result in a break when the steel is processed through cold impact. Above mentionedproblem is the secondary working embrittlement problem. According to the problem, thisexperiment is based on the rare earth resource that our county has and utilizes the special effectbetween rare earth Ce and P: When P content is low, Ce competes with P; when P content ishigh, Ce will change the state of P. Then, it has found a new direction to solve secondaryworking embrittlement problem.Under the laboratory smelting conditions, through reasonable element choice, it takesvacuum induction furnace to produce test steels. After cooling with the furnace, through forging,hot rolling, cold rolling and annealing, standard sample is made through molybdenum cuttingmachine. Then the crystal phase structure is observed through the confocal laser canningmicroscope. Inclusions and the fracture appearance is analyzed through S-3400N scanningelectron microscopy and VUestL2X-ray spectrometer machine. Tensile test is carried outthrough universal tensile testing machine. The test is carried out under room temperature inaccordance with national standard GB/T228.1-2010. The hardness is tested through Rockwellhardness test. The secondary working embrittlement is tested through cupping test. Theorganizations and mechanical property are analyzed for high strength IF steel containing rareearth. The conclusions are as followed:The test steel that is processed through annealing treatment has uniform equiaxed ferritegrain and it has a few inclusions, which are mainly complex compounds that formed by rareearth Ce with oxygen and sulphur a small part of Al2O3cluster type inclusion, but its size it between1and2μm, it is a little small.The tensile test result of the test steel is its tensile strength is more than440MPa. Thebiggest elongation rate can reach33.11%. Its average Rockwell hardness is around50. All thedata above indicates that high strength IF steel containing rare earth element not only has a highstrength, but also has a good plasticity.Though the observation of tensile fracture morphology, many dimples can be found, andsome oval dimples are found in some test samples. It indicates that the main fracturemechanism of the steel is ductile fracture, which means the steel has a good plasticity.When the test steels are processed through cupping experiments at the condition of-20℃、-40℃、-60℃, all the steels have no phenomenon of fracture, which means the IFautomobile plate steel containing rare earth has a good resistance to the secondary workingembrittlement.