Macro-Segregation in Steel Ingots...

Macro-Segregation in Steel Ingots With the large scale reduction of the crude steel production through the ingot casting route, there is now-a-days a tendency of producing extremely heavy weight steel ingots weighing over 600 t and continuous cast strands with thickness over 450 mm and rounds with diameter over 800 mm. These large size crude steel products are mainly applied for retaining components like reaction vessels for nuclear power plant and rotating components such as drive shafts of gas turbines and generator rotors. These high value products require high quality of the as-cast crude steel products, and hence, the production of the heavy crude steel products with adequate control of the quality is a big concern for steelmakers worldwide. The macro-scale segregation of alloying elements during the casting of steel ingots continues to afflict the manufacturers of steel ingots, despite many decades of research into its prediction and elimination. Defects such as A-segregates are still common, and components are regularly scrapped due to their presence, leading to increased economic and environmental costs. With the growth of the nuclear power industry, and the increased demands placed on new pressure vessels, it is now more important than ever that today’s steel ingots are as chemically homogeneous as feasible. During the solidification of alloys (liquid steel), solute is partitioned between the solid and liquid to either enrich or deplete the inter-dendritic regions. This obviously leads to variations in the composition on the scale of micro-metres (micro-segregation). Macro-segregation is a composition inhomogeneity in the scale from several millimeters to centimeters or even meters. The effects of macro-segregation are critically important in the present day applications of steel ingots and hence the ability to predict segregation severity and location is very important and highly sought after these days. Almost...