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...

Historical aspects of the Continuous Casting and related Technologies for Steel Mar06

Historical aspects of the Continuous Casting and related Technologies for Steel...

Historical aspects of the Continuous Casting and related Technologies for Steel Continuous casting (CC) technology of steel, as a method of solidification processing of liquid steel has a relatively short history —not much longer than oxygen steelmaking. Different to other processes in steel production, continuous casting is the vital link between the liquid and the solid phase and has to live with metallurgical effects as well as mechanical challenges at the same time. Continuous casting transforms liquid steel into solid on a continuous basis and includes a variety of important commercial processes. These processes are the most efficient way to solidify large volumes of liquid steel into simple shapes for subsequent processing. The CC ratio for the world steel industry is now around 96 % of crude steel output which was a mere 4 % in 1970. Continuous casting is distinguished from other solidification processes by its steady state nature. The liquid steel solidifies against the mould walls while it is simultaneously withdrawn from the bottom of the mould at a rate which maintains the solid / liquid interface at a constant position with time. The process works best when all of its aspects operate in this steady-state manner. Relative to other casting processes, continuous casting generally has a higher capital cost, but lower operating cost. It is the most cost- and energy- efficient method to mass-produce semi-finished steel products with consistent quality in a variety of sizes and shapes. Cross-sections can be rectangular, for subsequent rolling into plate or sheet, square or circular for long products and seamless pipes, and even dog-bone shapes, for rolling into I or H beams. Today continuous casting machines consist of modularized technological/mechatronic packages to allow fast design and short project execution time as well as rapid production ramp-up...