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Steel Billets

Steel Billets

Steel billets are a member of the semi-finished casting category, the final products that come out of casting or drawing a billet are bar stock and wire. Steel Billets are the feedstock for larger products that are with a smaller cross section. Steel Billets are hot rolled square bars produced by hot rolling continuous casting billets. The steel billets produced commonly have a cross section between 12-50 millimeter in diameter, steel billets are heated in a pusher or walking beam furnaces at 1,200 degree Celsius. There are many ways in which billets may be arranged in a bar rolling mill, after being taken out of the furnace they are cooled with water jets, placed in a semi-continuous or continuous roll stand. They are geometrically sound to have sharp square or round edges, with the intention of either being machined further or drawn. The main components of a steel billet are low carbon/mild steel, high quality steel and other alloy components. Guiding the strands properly from roll gap to roll gap is crucial part of the current rolling technology. The use of horizontal rolls, the guide then twists the bar 90 degrees between diamond and square passes. This arrangement is usually continuous through close coupled mills, in which then several roll pairs or sets are then installed within a short distance from one to another, through gears by multiple motors. The bars are then made to buckle in a controlled vertical loop to maintain the lowest possible tension between the stands. The finished stand of a bar mill gives the bar its final shape and often a specific surface pattern, such as the protrusions on the reinforcing bars. The rolling speed increase as the cross section at each additional stand decreases, and the exit speed can be as fast as 15 meters a second, the red-hot bar is then cut by a flying shear and shot into a cooling bed, it is then inspected and shipped. The principle of heat treating is fairly straight forward, heat treating takes place when steel is rolled at a certain temperature and then cooled after at a specific rate, the cooling rate is what makes up the particular microstructures within the metal. The most common and simplest of heat-treating methods is that of normalizing, this principle consists of holding the steel product at the temperature between 20 and 40 degrees Celsius and then cooling it afterward in completely still air. This then transform the as-rolled or as-cast steel to contain the austenite microstructures, which dissolves carbides. Thus, during cooling a very uniform grain is formed, consisting of either pearlite and ferrite or pearlite and cementite, depending on carbon content. In all heat treatment of metals, the temperatures, holding times, and heating and cooling rates depends vastly on the chemical composition, size, and shape of the steel. In alloy steels, which possess a lower heat conductivity than carbon steels, they are then heated more slowly to avoid internal stressing.