Kinetic Analysis of the Austenite Grain Growth in GCr15Steel.pdfVIP

Kinetic Analysis of the Austenite Grain Growth in GCr15 Steel Chongxiang Yue, Liwen Zhang, Shulun Liao, and Huiju Gao (Submitted June 9, 2008; in revised form February 6, 2009) The growth behavior of austenite grains in GCr15 steel was investigated through the isothermal annealing tests of the steel under different heating temperatures and holding times. The tests were performed on a Gleeble-3800 thermo-mechanical simulation machine. Austenitizing temperatures 1223, 1323, 1373, and 1423 K were chosen, and holding time varied from 0 to 480 s. Experimental results suggest that austenite grains grow gradually with the increase of heating temperature, and holding time has an important effect on the growth of austenite grains. The time exponent for the growth is bigger at higher temperature, and the growth rate decreases with increasing time. On the basis of previous models and experimental results, a mathematical model that can describe the growth behavior of austenite grains in the tested steel under different heating temperatures and holding times was obtained using regression analysis. The predicted grain sizes by the model are in good agreement with measured ones. Keywords annealing, austenite grain, GCr15 steel, growth kinetics 1. Introduction Austenite grain growth is an important factor to determine the microstructure because grain size influences the kinetics of phase transformation during the cooling cycle (Ref 1, 2). It is well known that the microstructure has a large effect on the mechanical properties of product, so it is important to control grain growth in metals and alloys. Some investigations on the grain growth kinetics for low carbon steel and microalloyed steel have already been reported (Ref 2-4), but few efforts have been expended to understand the grain growth behavior in bearing steel. The objective of this paper is to study the effect of heating temperature and holding time on the growth behavior of austenite grains in GCr15 bearing steel, and o