| Automobile frame steel is a kind of steel for automobile structures,and it is mainly used in structural parts such as longeron and crossbeam.In order to respond to the call of the national energy-saving and emission reduction,lightweight car body has become a development trend of automotive structural steel.the automobile frame steel 510L'scomposition design and performance indicators already cannot satisfies the design and use of frame steel' s requirements.Now the manufactures not only require a higher strength,but also good ductility and excellent cold bending performance,therefore,The development of low-cost automotive 610L frame steel is imminent.Conventional automobile manufacturers used the idea of controlled rolling and controlled cooling that low-temperature rolling combined with low-temperature coiling in the production process,and its requirements for the capacity of rolling mill and coiler were higher.Based on this background,the automobile frame steel designed in this paper mainly uses the idea of composition design that Ti micro-alloyed,adding the appropriate amount of Nb and Mn meanwhile,the cost of alloy is significantly reduced.At the same time,The effects and mechanism of high temperature deformation behavior and cooling process on the microstructure and mechanical properties of the experimental steel are systematically studied,which provides a theoretical basis for the actual production and upgrading of automobile frame steel.The main results of this paper are as follows:(1)Through the thermal simulation experiment we studied the behavior of grain growth and micro-alloy's dissolution and precipitation of experimental steel during the austenitizing process.The results showed that when the heating temperature increased,the austenite grain size increased gradually,and the solid solution amount of the micro-alloying elements increased.The optimal heating temperature of the experimental steel is 1220?.(2)In the single-pass compression experiment,there are two types of stress-strain curves:dynamic recovery and dynamic recrystallization,and the higher the deformation temperature was,the lower the peak strain ?p was.(3)We used phase-change meter(Formastor-F)and thermal simulation machine to measure the static and dynamic CCT curves,they gave the micro structure of experimental steel at different cooling rates.The deformation made starting temperature of phase transition rise,and promoted the occurrence of phase transition.(4)Through the simulation of different controlled rolling and controlled cooling processes in the hot rolling and deformation process,it was found that the hardness of the experimental steel increased slightly with the increasing of the cooling rate after deformation and the decreasing of deformation,coiling temperature.(5)The experimental results of hot rolling in laboratory showed that the yield strength decreased gradually with the increasing of the cooling rate and the coiling temperature after rolling deformation,and obvious interphase precipitation was found in the microstructure of the experimental steel,which had a great effect on the yield strength of the experimental steel.The frame steel 610L was industrialized in a domestic steel plant,and mechanical property tests showed that the properties of the 610L were stable,which could meet the requirements of various technical indexes. |
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