研究开发了Incoloy800H耐腐蚀合金立式电磁连铸制备方法,成功制备出截面为100 mm×100 mm的Incoloy800H连铸坯,并研究了其内部凝固组织、内部裂纹和TiN分布等物理现象。结果表明,常规立式连铸Incoloy800H铸坯的内部组织粗大、存在严重的内部裂纹和大量TiN夹杂物;采用立式电磁连铸后,制备的Incoloy800H合金连铸坯的中心等轴晶率从2.45%增加至41.45%,且中心等轴晶的平均晶粒尺寸由10.83 mm 减小至1.28 mm,并有效地消除了内部裂纹。TiN数量与分布的研究结果表明,立式电磁连铸条件下,铸坯中心的大尺寸TiN (大于2 μm)数量由3.71×10-4 μm-2降至1.59×10-4 μm-2,使易于诱发内裂纹的TiN数量显著减少,并抑制了TiN团簇的形成,有助于枝晶间的液态合金的补缩;另一方面,电磁连铸促使Incoloy800H合金连铸坯形成细小的等轴晶,减轻了合金元素偏析并减少了大尺寸TiN的数量,从而减少了萌发裂纹的机率,有效地抑制了内部裂纹的形成。
Incoloy800H is a kind of corrosion-resistant Ni-Cr-Fe base alloy with wide application in industrial fields. Vertical continuous casting process was developed to replace conventional mould casting process to increase product rate and decrease energy consumption. However, seriously internal quality issues of the continuously cast Incoloy800H alloy have been revealed. In this work, the square billet of Incoloy800H alloy, whose cross-sectional size were 100 mm×100 mm, were successfully fabricated in vertical continuous casting process with and without electromagnetic field (EMF), and the solidification structure, TiN inclusion distribution and internal crack were investigated. The result showed, without EMF, the Incoloy800H alloy billet had some seriously internal quality issues like coarse column grains, internal cracks and large TiN inclusion. With EMF, The equiaxed grain ratio of Incoloy800H alloy billet increased from 2.45% to 41.45%, the equiaxed grain size decreased from 10.83 mm to 1.28 mm and internal cracks were eliminated. TiN is a kind of detrimental inclusion in Incoloy800H alloy billet, which can act as stress concentration sites to form cracking. Most of TiN inclusions were located at interdendritic area and formed into TiN cluster to block interdendritic feeding channel. The application of EMF reduced the number of TiN inclusion from 3.71×10-4 μm-2 to 1.59×10-4 μm-2 in the center of billet. Further analysis illustrated that the EMF can refine the equiaxed grain size, reduce the degree of element segregation and the number of large TiN inclusion, which can reduce the probability of the crack initiation and inhibit the formation of TiN cluster to enhance the interdendritic feeding, thereby remarkably reduce the internal crack in Incoloy800H alloy billet.
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