稀土Ce对薄带连铸无取向6.5%Si钢组织、高温拉伸性能和断裂模式的影响

Effect of Ce on the Microstructure, High-Temperature Tensile Properties, and Fracture Mode of Strip Casting Non-Oriented 6.5%Si Electrical Steel

研究了Ce元素对薄带连铸无取向6.5%Si钢凝固组织、有序相、高温拉伸性能和断裂模式的影响。结果表明,添加Ce可以在薄带连铸过程中形成高熔点Ce_(2)O_(2.5)S和Ce_(2)O_(2.5)S_(3),促进钢液异质形核,细化铸带凝固组织。Ce对有序相变无明显影响,铸带有序度由高至低所对应的拉伸温度分别为650、400和800℃。随拉伸温度提高,铸带的屈服强度与抗拉强度降低,断后延伸率提高。当拉伸温度高于500℃,Ce元素的钢液净化和凝固组织细化作用有助于提高晶界强度,避免沿晶断裂。铸带在拉伸过程中发生动态回复和再结晶,最终发生韧性断裂,断后延伸率得到显著提高。研究结果证实,稀土处理可以作为薄带连铸无取向6.5%Si钢增塑的一种有效途径。

Non-oriented 6.5%Si electrical steel exhibits excellent high-frequency magnetic properties, such as low iron loss and near-zero magnetostriction. Moreover, the high Si content causes poor deformability due to the solution strengthening effect of Si and the resulting ordering transformations, delaying the commercial application. Strip casting is a near-net forming technology that directly produces thin strips from the melt and reduces the required rolling deformation for the fabrication of thin sheets. This technology could be a viable option for industrializing the production of non-oriented 6.5%Si electrical steel. Despite this, even in the strip casting process, this brittle material is prone to edge cracks. Thus, improving the intrinsic plasticity of strip casting non-oriented 6.5%Si electrical steel is necessary through chemical modification to eliminate the deforming defects. The effect of Ce on the ordered phase of the solidification microstructure, high-temperature tensile properties, and fracture mode of strip casting nonoriented 6.5%Si electrical steel was investigated in this work. The results showed that the addition of Ce introduced high-melting Ce_(2)O_(2.5)S and Ce_(2)O_(2.5)S_(3)during strip casting, which promoted heterogeneous nucleation and refined the solidification microstructure of the as-cast strip. The presence of Ce did not affect the ordering condition of the as-cast strip. In decreasing order, the tensile temperatures corresponding to the ordered degree of the as-cast strip were 650, 400, and 800℃. With the tensile temperature increasing, the yield and tensile strengths of the as-cast strip decreased, whereas the elongation gradually increased. When the tensile temperature exceeded 500℃, the purification and microstructure refining effects of Ce improved grain-boundary cohesion and prevented intergranular cracking. Moreover, the occurrences of dynamic recovery and recrystallization eventually made the as-cast strip doped with Ce fractured by dimples, leading to a considerably enhanced tensile ductility. According to the findings, the rareearth treatment should be considered as an effective method for increasing the ductility of strip casting non-oriented 6.5%Si electrical steel.