RESEARCH OF 600C GRADE WELDING V-N MICRO-ALLOYED STEEL USED ON TRUCK AXLE HOUSING AFTER THERMAL FORMING

摘要

Automobile axle housing is the basic element to install the main reducing gear, differential mechanism, semi-axis, wheel hub and suspension. The main function of automobile axle housing is to support the automobile quality with driven axle, fix the driving wheel relative axial position and bear the driving wheel transmission force during the automobile running. Axle housing steel with the thickness of not less than 12mm is produced by the thermal forming method, which is to heat the plate to 830 degree and hold some time, then thermal forming, and cool to room temperature. The steel plate should maintain the original strength and good ductility and toughness requirements with thermal forming process.In China, automobile manufacturing plants commonly use Q345B to produce automobile axle housing steel. Now, for reducing vehicle weight, it is tried to reduce steel thickness by improving steel strength. But from the test results, it is shown that the ordinary 600C steel strength is decreased significantly after thennal forming process, which causes the car safety problems. So, there is an urgent to develop a kind of economic 600C type plate, wliich has a tensile strength of not less than 600MPa and zero impact power of not less than 54J.Three types of designed materials, which have component systems of Nb-V, Ti and V-N are studied. The mechanical properties and welding performances of three experimental steel plates can meet requirements. But with the process of thermal forming and slow cooling to room temperature, only V-N micro-alloyed steel properties reach the user requirements. The precipitations before and after thermal forming are analyzed. The main reason for the material strength could meet the requirements is that VN precipitation is not easy to be coarsened in the thennal forming processes.