Effect of Austenitizing Temperature on the Microstructure and Mechanical Properties of Modified T23 Ferritic Heat-resistant Steel

Heat treatment tests at different austenitization temperatures were conducted on the modified T23 ferritic heat-resistant steel. The microstructure of modified T23 ferritic heat-resistant steel after austenitizing, quenching and tempering at different temperatures was characterized by metallographic microscope, scanning electron microscope and transmission electron microscope, and its mechanical properties at room temperature were analyzed . Combined with the equilibrium phase diagram of the experimental steel calculated by Thermo–Calc thermodynamic software, the distribution relationship of C, N, V and other elements between the matrix and the second phase was explored, and the effect of austenitizing temperature on the microstructure and mechanical properties of the modified T23 ferritic heat-resistant steel was revealed. The results show that in the austenitizing temperature range of 1 080–1 140 ℃, with the increase of temperature, the grain size of the experimental steel gradually increases, the bainite lath coarsens, and the carbide size gradually decreases. When the austenitizing temperature is 1 080 ℃, the refined bainite laths provide conditions for the aggregation and growth of carbides, and the carbides in the steel show a tendency of cluster aggregation. When the austenitizing temperature is increased to 1 120 ℃, the bainite laths within the grain coarsen obviously, the solid solubility of alloy elements in the matrix increases, the nucleation sites of carbides reduce, and the dispersion degree of carbides greatly improves. At the same time, with the increase of austenitizing temperature, the yield strength and tensile strength of the modified T23 ferritic heat-resistant steel exhibit a trend of first decreasing and then increasing, while the elongation shows a trend of first increasing and then decreasing. This is primarily due to the coupled effect of grain size, carbide size and distribution, and solid solution strengthening of the alloy ,which vary with the austenitizing temperature.