Abstract: Microstructure and properties of hot formed steel containing niobium austenitized at different temperatures were studied. The results show that the tensile strength of the hot formed steel increases first and then decreases with the increase of austenitizing temperature. When austenitized at 850 ℃ for 7.5 min, the tensile strength up to 1758 MPa, the yield strength is 1205 MPa, and the elongation is about 6%, and the martensite grain is the smallest, about 2.87 μm, and the martensitic lath is about 322 nm. With the increase of austenitizing temperature, the austenitizing degree of matrix structure gradually increases, and the precipitation of (Nb, Ti) composite carbon nitride particles also gradually redissolve, and the austenite grains are coarsened. When austenitized at 930 ℃ for 5.0 min, the martensite grain increases to 4.936 μm, and the martensitic lath increases to 929.6 nm.

Key words: austenitizing temperature, hot-formed steel, tensile strength, microstructure, precipitated particle