Calcium treatment is a process that modifies the composition and morphology of oxide inclusions. It is especially useful for avoiding nozzle clogging in continuous casting.
It also helps improve machinability in low sulfur free-machining steels by transforming hard alumina inclusions into soft calcium aluminates. This enables the avoidance of excessive tool wear.
Traditional calcium treatment consists of adding Ca to liquid steel containing O and S for the purpose of deoxidizing and desulphurizing the steel. It also changes the composition, size and structure of oxide, sulfide and silicate inclusions in the steel. It is used to eliminate nozzle clogging in continuous casting and to control the morphology of the nonmetallic inclusions in the cast metal, especially their globular shape which helps to mitigate directional anisotropy in hot rolling, thus improving through-thickness ductility.
The method consists of the following steps: a. plumbous fusion; b. directly add the calloy (or other alloying elements) to molten steel and stir it for 20
Continuous casting allows the production of a large variety of steel shapes with high dimensional accuracy and excellent mechanical properties. The most critical factor in a successful cast is the precise matching of the flow rate of molten steel into the mold and the withdrawal speed of the cast shape out of the mold.
Liquid metal is ladled into a tundish, a small refractory-lined distributor that provides a constant head for the steel to pour into a copper mold at a regulated rate. The liquid metal flows down into the mold through a water-cooled submerged entry nozzle (SEN). A dummy bar of steel seals the bottom of the mold.
Drive rolls lower in the CC machine continuously withdraw the dummy bar of steel and the resulting solidified cast shape until it has reached a predetermined position within the withdrawal system. When this point is reached, the dummy bar and solidified cast shape are mechanically disconnected and removed from the withdrawal system.
Hot rolling is the process that converts cast steel to a flat, thin sheet suitable for use in railroads and construction steel beams. It also is used in furniture, cabinetry and beverage cans.
When Ca is added to molten steel, it reacts with oxygen and sulfur to form inclusion compounds, such as Ca-aluminates (CaO) and Ca-sulfides (CaS). This reaction shifts the equilibrium for the inclusions toward their surroundings in the liquid metal so that they are less likely to interact with the oxide phase and more likely to form sulfide or arsenic containing phases.
The presence of these inclusions can be beneficial, as they prevent the formation of elongated stringers in the hot rolled strip. They can, however, negatively impact through-thickness ductility and toughness by their ability to promote work hardening in the austenite matrix. Consequently, they must be stabilized by calcium treatment during the hot rolling process.
Forging is a metal forming process that combines compressive force with heat to shape metal parts into the desired design. It is typically used for metals that are difficult to form through other processes like casting or machining, and it produces parts with superior mechanical properties.
A major advantage of hot forging is that it can achieve close tolerances, and it can produce a finished product with minimal scrap. However, forging can create parts with rough surfaces that require additional machining or finishing to ensure the proper aesthetics and durability of the final product.
Controlling the calcium treatment is a challenge because Ca is very reactive to O and S, which makes it hard to measure the amount of inclusions in steel during the steelmaking process. This reactivity leads to variation in the concentration of bound oxygen measured by SEM/EDS in ladle and tundish samples. The reactivity of calcium is also problematic for the calculation of non-metallic inclusion composition in steel using SEM/EDS due to matrix effects.
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