Abstract: By studying a V-N micro-alloyed non quenched and tempered steel using thermal simulation testing machine, the strain induced precipitation behavior was analyzed and the Precipitation-Temperature-Time (PTT) curve was drawn. A thermomechanical treatment was designed, the microstructure was characterized by means of OM, SEM and TEM. The mechanical properties was tested by universal tensile testing machine. The results show that the precipitation temperature of V(C,N) at the nose tip is around 800 ℃ during the stress relaxation process, and it begins to precipitate after 12 and ends after 90. During the deformation process at 800 ℃, the yield strength and tensile strength gradually increase by 30 MPa and 45 MPa respectively, while the deformation amount increases from 15% to 30%. Elongation varies within the range of 11%-12%. The impact absorbed energy increases from 19.5 J to 25 J. With the increase of isothermal deformation, the dislocation density inside the matrix grains significantly increases, the number of precipitates increases, and the distribution becomes more dispersed. Precipitated phases with lengths ranging from 50 nm to 150 nm and widths ranging from 20 nm to 50 nm are found both within the grain and at the grain boundaries.

Key words: non-quenched and tempered steel, strain induced precipitation, V(C,N) phase, dislocation, precipitation