水冷铜模与砂模铸造M2钢显微组织对比

采用实验室25 kg高频真空感应炉熔炼M2钢,并用水冷铜模和砂模均浇铸为横截面100 mm×50 mm的M2钢铸锭,研究冷却速度对M2钢二次枝晶间距、渗透率、碳化物和晶粒尺寸及分布的影响.研究结果表明：M2钢凝固过程中,快的冷却速度能有效减小二次枝晶间距、渗透率、晶粒和网状碳化物的尺寸,同时可以改善晶粒和网状碳化物的分布和均匀性；砂模和水冷铜模M2钢铸锭的平均二次枝晶间距分别为42.5μm和21.6μm,平均冷却速度为1.06 K·s-1和12.50 K·s-1,平均渗透率分别为0.13μm2和0.035μm2.快的冷却速度能有效减轻中心碳偏析程度,砂模和水冷铜模模铸的M2钢铸锭中心碳化物面积分数分别为0.46和0.30,且其较各自的平均值分别增大38.7%和2.2%；水冷铜模铸锭平均晶粒尺寸(43.1μm)较砂模铸锭的平均晶粒尺寸(72.6μm)减小约40.7%,铸锭中心晶粒尺寸减小43.2%,且水冷铜模铸锭的晶粒尺寸较砂模铸锭均匀.文中获得了M2钢凝固过程中晶粒尺寸与冷却速度的关系式.

Comparison between the microstructures of M2 steel cast by the water-cooled copper mould and the sand mould

M2 steel was melted by a 25 kg high-frequency vacuum induction furnace and was cast to ingots with a cross section of 100 mmí50 mm by the water-cooled copper mould and the sand mould. The effects of cooling rate on the ingot’ s secondary dendrite arm spacing (λ2 ) , permeability, and size and distribution of grains and carbides were studied. The results show that fast cooling rate can effectively decrease the λ2 , permeability and size of grains and network carbides, and improve the distribution and uniformity of network carbides and grains during solidification. Theλ2 values of ingots cast with the sand mould and the water-cooled copper mould are 42. 5μm and 21. 6μm, the cooling rate is 1. 06 K·s-1 and 12. 5 K·s-1 , and the permeability is 1. 3í10 -1 μm2 and 3. 5í10 -2μm2 , respectively. Fast cooling rate can effectively reduce the center carbon segregation degree. The area fraction of carbides is 0. 46 and 0. 30 respectively at the center of ingots cast with the sand mould and the water-cooled copper mould, and increases by 38. 7%and 2. 2% respectively compared with their average values. The average grain size of ingots cast with the water-cooled copper mould and the sand mould is 41. 3μm and 72. 6μm, respectively. Comparing with the sand mould ingot, the grain size at the center of the water-cooled copper mould ingot reduces by 43. 2%, and the grain size of the water-cooled copper ingot is more uniform. The relation-ship between grain size and cooling rate was presented in this paper.