Abstract: In order to study the effect of spheroidizing annealing on austenite grain size of 16MnCr5 steel hot rolled wire rods during the process of modification, hot-rolled wire rod specimen and specimens isothermally spheroidizing annealed at 700, 720, 740, 760 and 780 ℃, respectively, for 5 h were subjected to water quenching at 940 ± 5 ℃ for 1 h. The austenite grain size of the specimens was measured and compared. The results show that the “double high” processes (heating temperature of 1200-1250 ℃, finishing rolling temperature of 950-980 ℃) and rapid cooling between 800-600 ℃ (air cooling, cooling rate ≥ 10 ℃/s) are used in the rolling process to ensure that aluminum and nitrogen atoms are in a solid solution state. During the heat treatment process before austenite grain detection, AlN is uniformly and finely precipitated, resulting in fine and uniform austenite grains in the 16MnCr5 steel. When spheroidizing annealed at 700 and 720 ℃, AlN particles are uniformly and finely precipitated. Although Ostwald aging and growth occur, the AlN particles are still smaller than the critical radius, and the austenite grains are still fine and uniform. With the further increase of spheroidizing annealing temperature, the second phase particles undergo Ostwald aging and growth. The second phase particles in local areas exceed the critical radius, and local austenite grains grow abnormally, resulting in mixed grains. In practical production, in order to obtain uniform and fine austenite grains, as well as good spheroidized microstructure and mechanical properties, 16MnCr5 steel is spheroidizing annealed at 720 ℃. Through the above controlled rolling process and spheroidizing annealing process, the austenitic grain size of 16MnCr5 steel can reach 7.5 grade to 7 grade, meeting the requirements of austenitic grain size ≥ 5 grade and without mixed grains.

Key words: 16MnCr5 steel, spheroidizing annealing, grain size, mixed grain