During steel making Calcium Cored Wire is used as addition agent. It is encapsulated in U shape steel sheath and through wire injection system, it is injected deep into the liquid steel ladle.
Ca treatment significantly changes the composition, size and shape of oxide and sulfide inclusions, thereby improving fluidity and cleanliness. It also improves machinability and ductility of the finished product.
Generally speaking, a cored wire is a type of covered electrode that contains both a steel sheath and a ferrite/manganese based core of fluxing and alloying compounds. They perform the same functions as a coated electrode except they also have the added advantage of having higher conductivity due to their metallurgical design.
This unique chemistry allows cored wires to have a much higher recovery rate than traditional bismuth shots in steel metallurgy. This leads to improved fluidity and cleanliness in the steel melt.
The silicon calcium cored wire (or pure solid calcium wire) is an important treatment in the off-furnace refining process of stainless steel. By feeding core wires into molten steel using a metal feeder, deoxidation, desulfurization, non-metallic inclusion denaturation and microalloying can be accomplished. In addition to these key functions, calcium treatment has the effect of purifying molten steel and changing the inclusion form in molten steel which improves cast ability. However, proper measures must be taken to ensure protection of the molten steel after calcium treatment. This includes the use of protective slag blankets, inert gas or refractory shrouded nozzles.
Calcium has a strong affinity for oxygen and sulfur. In addition it forms oxysulfides, oxides and sulfides when exposed to air. This makes it an ideal deoxidizer and desulfurizer.
When Ca is added to molten steel, the violent agitation that accompanies it can reduce the gas content of the steel melt and significantly reduce the amount of side lath ferrite that develops in the weld metal. This results in more acicular ferrite, which is the most desirable microstructure for weldability.
The Bismuth Manganese cored wire is made by encapsulating high grade of BiSb and Mn powder in U shaped steel sheath and then stuffing it through professional cored wire machine. The resulting cored wire is then inserted into the steel melt through special nozzles to achieve high concentration of bismuth in liquid steel. This process also reduces the formation of oxidation inclusions that can negatively impact corrosion resistance. It is a highly efficient method of introducing Ca into the steel melt.
The core of metal-cored wire is filled with a mix of alloys, powders and arc stabilizing agents that create distinct welding characteristics. Welding with metal-cored wire can lower oxidation and improve the microstructure of the weld, resulting in increased tensile strength and impact toughness.
Metal-cored wire can also help reduce weld defects such as undercutting and lack of fusion by minimizing the formation of side lath ferrite. This allows weld operators to achieve greater travel speeds and deposition rates, maximizing the productivity of the welding operation.
A thorough assessment of the pre- and post-weld activities in a particular process is essential when assessing whether calcium cored wire can increase productivity. This includes evaluating all activities and associated labor costs in these areas, as well as determining the volume of rework and parts rejection that could be eliminated with the use of metal-cored wire. It’s important to be able to demonstrate that these potential savings would justify the additional cost of using metal-cored wire.
Calcium (Ca) additions to molten steel significantly improve the fluidity and cleanliness of cast irons and welded or sensitization-prone austenitic stainless steels. Ca agitates the liquid steel reducing gas content and modifies the shape of inclusions to reduce their impact on mechanical properties in the final product.
The high density and reactivity of Ca make it difficult to introduce and retain in the steel melt. Cored wire enables Ca to be injected into the steel melt using a continuous caster nozzle, with greater recovery than calcium lumps.
Proper treatment of steel with Ca results in the conversion of solid oxide inclusions like alumina to soluble inclusions of calcium aluminates that are liquid at steelmaking temperatures. As a result, nozzle clogging is minimized. In addition, the globular nature of these inclusions reduces the susceptibility to intergranular corrosion. Similarly, the shape of SiO2 and Al2O3 stringers that form in a weld and cause directional anisotropy can be modified during Ca treatment to improve through-thickness ductility.
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