Development of Unidirectionally Solidified Large Scale Ingots for Heavy Gauge Plates

Abstract

The unidirectionally solidified large scale (USL) ingots, which have low height and large expanse, were developed based on the results of the simulation experiments with the ammonium chloride solution. The USL ingots were found to be free from V segregates, the loose structure and the accumulation of non-metallic inclusions. The intensity of top segregation of USL ingot closely related to that of the negative segregation in the region which solidified from the mold wall. Both segregations, however, can be minimized by optimizing the mold wall design and they can be completely removed by conditioning to obtain the highly homogeneous and sound ingot. It was found that the wider the ingot, the milder the top segregation. It was realized that the USL ingot was suitable for production of high grade heavy gauge plates of the large unit weight. The manufacturing process of high grade heavy gauge plates was completed by the combination of USL ingots and the low-speed heavy-reduction plate rolling technique. The qualities of the plates produced by the process were found to show superior mechanical properties, homogeneity, cleanliness and workabilities for manufacturing pressure vessels. The maximum thickness and the size of the plate were both substantially expanded.The formation mechanisms of the sedimental crystal zone and the top segregation in the ingot were also suggested in the course of development of the USL ingots.