旋转电磁搅拌时机对GCr15轴承钢凝固组织的影响

通过石墨型铸造研究了旋转电磁搅拌时机对GCr15轴承钢凝固组织的影响.结果表明:在钢液凝固过程的不同时间段施加电磁搅拌，对轴承钢的凝固组织具有显著影响，越早施加电磁搅拌，磁泰勒数(表征磁场作用下强制流动的无量纲数)越大，钢液所受的电磁力越大，越有利于柱状晶向等轴晶转变；在0~05min时间段施加电磁搅拌，铸锭等轴晶率提高了52%.此外，电磁搅拌引起的钢液对流推动了凝固前沿枝晶的折断、熔断和游离，枝晶碎片在强烈对流作用下增殖并被带到熔体心部成为异质核心，凝固前沿的温度梯度减小，成分过冷增大，促进了柱状晶向等轴晶转变.

Effects of Time of Applying Rotating Electromagnetic Stirring on the Solidification Microstructure of GCr15 Bearing Steels

The effects of the time of applying rotating electromagnetic stirring on the solidification microstructure of GCr15 bearing steels were investigated via graphite mold casting. The results showed that imposing rotating electromagnetic stirring at different periods during the solidification process of the molten steel significantly influences the solidification microstructure of the bearing steel ingots. The sooner rotating electromagnetic stirring is imposed， the larger magnetic Taylor number (the characteristic non dimensional parameter to describe the forced convection by the magnetic field) is. Accordingly， the electromagnetic force generates remarkably in the molten steel， which indicates that the fluid flow is strong enough for the columnar equiaxed transition (CET). The equiaxed crystal ratio of the ingot increased to 52% when the rotating electromagnetic stirring is imposed during the period of 0~05min after the accomplishment of pouring. Furthermore， the fluid flow generated by rotating electromagnetic stirring promotes the breaking， melting and drifting away of the dendrites in the solidification front. The fragments of the dendrites proliferated and were brought to the centre of the molten pool which became the heterogeneous nucleus under the strong fluid convection. The constitutional supercooling degree increases with the decrease of temperature gradient which consequently in favor of the promotion of CET.