Carbon Steels and the Iron-Carbon Phase Diagram...

Carbon Steels and the Iron-Carbon Phase Diagram Steels are alloys having elements of iron (Fe) and carbon (C). C gets dissolved in Fe during the production of steels. Pure Fe melts at a temperature of 1540 deg C, and at this temperature, C readily dissolves into the liquid iron, generating a liquid solution. When this liquid solution solidifies, it generates a solid solution, in which the C atoms are dissolved into the solid iron. The individual C atoms lie in the holes between the Fe atoms of the crystalline grains of austenite (at high temperatures) or ferrite (at low temperatures). Austenite has a face centred cubic (fcc) structure while the ferrite has a body centred cubic (bcc) structure (Fig 1). If the amount of C dissolved in the liquid iron is kept below 2.1 %, the product is steel, but if it is above this value, then the product is cast iron. Although liquid iron can dissolve C at levels well above 2.1 % C, solid iron cannot. This leads to a different solid structure for cast irons (iron with total C greater 2.1 %). In addition to C, all the types of steels contain the element manganese (Mn) and low levels of the impurity atoms of phosphorus (P) and sulphur (S). Hence, steels can be considered as alloys of three or more elements. These elements are Fe, C, other element/elements additions, and impurities. It is normal to classify steel compositions into two categories namely (i) plain C steels, and (ii) alloy steels. In plain C steels, other elements consist only of Mn, P, and S, whereas in alloy steels, one or more additional alloying elements are added. Solid solutions are similar to the liquid solution; that is, after the solid substance is dissolved,...

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...