Abstract:Medium manganese martensitic wear-resistant steel is a new type of wear-resistant steel with low cost and high performance. It is of great significance for controlling the microstructure and properties of steel to reveal the growth behavior of austenite grains in the steel and to establish an accurate prediction model. The austenite grain growth behavior of medium manganese martensitic NM500 steel under different heating temperatures and holding times was systematically investigated by means of Gleeble-3500 thermal simulation testing machine,metallographic microscope and transmission electron microscope. The effect of second phase on the austenite grain growth behavior was also explored. The results showed that the effect of heating temperature on the austenite grain growth behavior in the experimental steel was significantly greater than that of the holding time,and the austenite grain growth behavior in the experimental steel could be divided into two regions due to the precipitation behavior of V(C,N) particles in the matrix. When the heating temperature was below 950 ℃,there were a large number of undissolved nanoscale spherical and short rod-like V(C,N) particles which can effectively pin the austenite grain boundaries in the experimental steel,and the austenite grains grew slowly. However,when the heating temperature was higher than or equal to 950 ℃,the V(C,N) particles in the experimental steel were dissolved and coarsened in large quantities. For example,when the heating temperature was 950 ℃ and the holding time was 60 min,the volume percent of V(C,N) particles in the experimental steel was only 0.041%,and the average particle size increased to 45.78 nm. Its pinning effect on the austenite grains was significantly reduced,and with the increase of heating temperature,the atomic diffusion speed was accelerated,resulting in the rapid growth of austenite. Moreover,based on the Beck model,the isothermal austenite grain growth kinetic model of the experimental steel was established,and the apparent activation energies of austenite grain growth in the experimental steel at lower and higher temperature regions were calculated to be 66.561 kg/mol and 170.416 kJ/mol,respectively. The calculated values of austenite grains were in good agreement with the measured results.
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