中锰马氏体NM500钢奥氏体晶粒长大行为

 中锰马氏体耐磨钢是一种新型的低成本高性能耐磨钢,揭示钢中奥氏体晶粒长大行为,并建立精确的预测模型,对其组织和性能的调控至关重要。利用Gleeble-3500型热模拟试验机、金相显微镜和透射电子显微镜等设备,系统研究了中锰马氏体NM500钢在不同加热温度和保温时间下的奥氏体晶粒长大行为,探讨了微合金第二相对奥氏体晶粒长大行为的影响。研究结果表明,加热温度对试验钢中奥氏体晶粒长大的影响明显大于保温时间,且试验钢中奥氏体晶粒长大行为受基体中V(C,N)粒子析出行为的影响,其可分为两个阶段。当加热温度小于950 ℃时,试验钢中存在大量未溶的纳米级球状和短棒状V(C,N)粒子,能够有效地钉扎奥氏体晶界,奥氏体晶粒长大缓慢;但当加热温度不低于950 ℃时,试验钢中V(C,N)粒子大量溶解和粗化。其中,加热温度为950 ℃、保温时间为60 min时,试验钢中V(C,N)粒子的体积分数仅为0.041%,平均粒径增大至45.78 nm。其对奥氏体晶粒的钉扎作用显著减低,且随着温度升高,原子扩散速度加快,奥氏体晶粒快速长大。基于Beck模型,建立了试验钢中奥氏体晶粒等温长大动力学模型,计算得到低温及高温阶段试验钢中奥氏体晶粒长大表观激活能分别为66.561 kg/mol和170.416 kJ/mol,且奥氏体晶粒的理论计算值与实测结果吻合较好。

Austenite grain growth behavior of medium manganese martensitic NM500 steel

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.