Kinetic Analysis of the Austenite Grain Growth in GCr15 Steel

Abstract

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.

The influence of niobium content on austenite grain growth in microalloyed steels

“…The quantitative analysis of the optical measurements of austenite grain growth, is shown in Figure 6, which confirms the substantial influence of an increased Nb content on austenite grain growth inhibition in these steels. Quantitative evaluations of the average grain size as a function of austenitizing time and temperature in the 0.03 wt% Nb microalloyed steel are shown in Figures 7 and 8 respectively.A comparative analysis of Figures 7 and 8 indicates the expected greater effect of temperature compared with time on grain growth, as recorded by numerous studies (Seok et al, 2014;Yue et al, 2010;Nanba et al, 1992;Akamatsu, Senuma and Hasebe, 1992;Sha and Sun, 2009;Zhao et al, 2011) The influence of niobium content on austenite grain growth in microalloyed steels …”

“…It is generally accepted that the grain boundary migration velocity (v) is proportional to the driving force (Seok et al, 2014;Maalekian et al, 2012;Yue et al, 2010;Olasolo et al, 2011;Alogab et al, 2007;Hodgson and Gibbs, 1992;Nanba et al, 1992), an approximation justified at the relatively small driving forces involved in grain growth. This velocity is given by the expression (Stumpf, 2010) [1]…”

“…It is also known that the austenite grain size directly influences the microstructure, and thus the mechanical properties, of the steel (Maalekian et al, 2012;Yue et al, 2010). Effective grain growth control is reported to be achieved through addition of precipitate-forming elements, such as Nb that, slow down the grain boundary migration through pinning and solute drag mechanisms (Yu et al, 2010;Olasolo et al, 2011;Alogab et al, 2007).…”

Predictive Model for Austenite Grain Growth during Reheating of Alloy Steels

“…Experimental data on AGS over wide ranges of chemical composition and reheating conditions were collected from literature; 1,2,4,[8][9][10][13][14][15][16][17][18][19][20][21][22][23][24]27,28,30,31) the 457 data collected are summarized in Table 1 …”

“…The austenite grain growth rate gradually decreased with holding time; this is because the driving force for austenite grain growth decreased with time, as the austenite grain growth continued and the total surface energy diminished at the grain boundary area. 28) The *** considered separately in the pre-exponential term. Fig.…”