2008 Volume 48 Issue 10 Pages 1419-1428
Austenitic grain growth behavior after dynamic recrystallization in HSLA steels and the austenitic stainless steel of Type 316L was investigated focusing on grain growth during a very short holding time period immediately after hot deformation. Hot compressed specimens were isothermally held at temperatures of 1373 K, 1423 K and 1473 K for various time periods from 0.1 s to 1.8 ks. The grain size in all steels was coarsened by 1.5 to 2.5 times in a short holding time period of 20 s. Addition of 0.078%Zr or 0.018%Ti in HSLA steel could not prevent this rapid grain growth, which retarded grain growth in a longer holding time period over 60 s. The grain growth exponent of the n value was evaluated using a formulated grain growth kinetic equation, and two n values largely differing in the fine and coarse grain size regions were obtained in a respective temperature and alloy. The n value in the latter region ranged from 2.3 to 3.2, being almost consistent with values of various materials reported in the past studies. The very high n value over 7.7 was obtained in the fine grain size region for dynamic recrystallization in all steels, where n values for static recrystallization was relatively lower than those for dynamic recrystallization. The similar result of n values was obtained from grain growth data after dynamic recrystallization in pure nickel. The cause for very high n value and the difference of n values obtained from grain growth data after dynamic and static recrystallizations were discussed based on features of the microstructure and the grain boundary evolved by dynamic or static recrystallization and annealing.
