Abstract: Composition design of low cost V-N microalloying steel was studied without adding Mo， Cr， Ni. The thermo-mechanical control process (TMCP) test was conducted. The phase transition mechanism and precipitation behavior were discussed. The microstructure and comprehensive mechanical properties of the hot-rolled Bainitic steel were systematically studied by optical microscopy， scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that the microstructure is consisted of acicular ferrite， quasi-polygonal ferrite and granular bainite and small triangular M/A island. The fine precipitates present disks and distribute dispersedly in the ferrite matrix. The yield strength， tensile strength and elongation of the steel are 618MPa， 701MPa and 19%， respectively. The property of cold bending is qualified， the hold-expansion ratio reaches 94%， and strentch-flangeability and the low temperature impact performance is good. The above results can meet the demand of the automotive wheel disc. The fine grain strengthening， solid solution strengthening， precipitation strengthening and phase transformation strengthening are the main strengthening mechanisms.

Key words: low carbon vanadium steel, TMCP(thermo-mechanical control process), strengthening mechanism, bainite, mechanical properties