Abstract: In order to reveal the precipitation behavior of B-containing carbides during tempering and its effect on the mechanical properties of heat-resistant steel, the morphology and distribution of B-containing carbides in a heat-resistant steel with boron content of 0.01% isothermally quenched at 950 ℃ and tempered at 700 ℃ for different time(10, 30, 60, 90, 120 and 150 min) were observed by means of optical microscope and scanning electron microscope. And the effect of precipitation behavior of B-containing carbides on Brinell hardness and tensile properties of the tested steel was studied by Brinell hardness test and room temperature tensile test. The results show that with the increase of tempering time, the matrix of the tested steel is lath tempered martensite, while the B-containing carbides grow in size gradually, with the shape changing from blocky to long blocky clustered. With the increase of tempering time, the hardness decreases first, then increases and finally decreases, while the tensile strength and yield strength increase first and then decrease. When the tempering time is ≥30 min, the tensile fracture of the tested steel is ductile fracture with dimples, and the strengths of the tested steel are the best when tempering at 700 ℃ for 60 min, with the tensile strength and yield strength of 931 MPa and 817 MPa, respectively.

Key words: heat-resistant steel, tempering time, B-containing carbides, mechanical properties