M2钢连铸过程中碳化物析出行为

Precipitation behaviors of carbides in M2 steel continuous casting process

在实验室条件下采用立式连铸的方法连铸φ100 mm M2钢,在扫描电镜下观察分析其碳化物的分布、形貌、尺寸和类型,研究了析出碳化物的演变规律,并对其在液相区、固-液两相区和固相区的析出规律进行了热力学计算。结果表明:φ100 mm M2钢连铸坯碳化物呈网状分布,网状碳化物的厚度从铸坯边部的1.5μm增大到中心的30μm,增大约20倍。碳化物形貌包括:块状、片层状和棒状,其中块状碳化物为VC,而片层状和棒状碳化物为M_2C。在液相和固-液两相区δ铁素体析出过程中,各种碳化物均不具备析出的热力学条件;在固-液两相区中γ奥氏体转变过程中,W_2C在1504 K具有析出的热力学条件;当温度降到固相线以下时,碳化物的析出顺序为VC>Mo_2C>W_2C,其析出温度分别为1475 K、549 K和333 K。

The M2 steel with cross section size of φ100 mm had been casted using vertical continuous caster under laboratory condition. The distribution, morphology, size and type of the carbides were observed and analyzed by means of scanning electron microscopy. The precipitation behavior of the carbides in the liquid phase region, the liquid-solid phase region and the solid phase region was calculated by thermodynamically calculation. The results show that the carbides in the cast M2 steel are network distribution. The thickness of the carbides nets increases from 1.5 μm at the billetg surface to 30 μm at the center. The shapes of the carbides include block, laminar and fibrous structure. The block carbide is VC, and the laminar and fibrous carbides are M2C. The precipitations of the carbides have no thermodynamic condition in the liquid phase region and the 8 liquid-solid phase region. The precipitation temperature of W2C is 1504 K in the 7 liquid-solid phase region. The precipitation order of the carbides is VC, Mo2C and W2C under solidus temperature, and the precipitation temperatures of VC, Mo2C and W2C are 1475 K, 549 K and 333 K, respectively.