Calcium is a metal like copper, aluminum, and gold but unlike those it does not have magnetic properties. To become magnetic a material needs unpaired electrons which it does not have.
During steelmaking Ca is fed deep into liquid steel and reacts with inclusions, oxygen, and sulfur to create non-detrimental trap sites. This is called Ca treatment.
In the steel industry, adding metal calcium and a calcium oxide-alumina alkaline solution to the molten steel is an effective way to denature the oxygen ingots to improve the microstructure, manufacturability, and electromagnetic properties of low-carbon and high-sulfur steels. However, this method has a number of disadvantages including high production costs and complicated processing.
In addition, the effect of sulfur on inclusions is very complex and cannot be determined simply from the morphologies. Inclusions can be classified as sulfide-rich (Type-3), sulfide-poor (Type-2), or sulfide-free (Type-1); they also have varying concentrations of other elements, especially nitrogen. These characteristics influence their chemical compositions and their evolution in the molten state.
As a result, it is important to study the relationship between the composition of inclusions and the effects of Ca on their magnetic properties. This can help determine the ideal condition for the production of low-sulfur, sulfide-free iron.
The composition of the inclusions was determined by Inductively Coupled Plasma-Atomic Emission Spectrometry. The proportion of typical three kinds of inclusions in each experiment is shown in Figure 3. The experiments with low sulfur were rich in Type-1 inclusions and those with high sulfur were rich in multi-phased inclusions. Moreover, the inclusions with multi-phased morphology are more prone to segregate than those with single-phased morphology.
Calcium is not a magnetic metal like iron or nickel, copper and aluminum. The reason is that for magnetism to occur a metal needs unpaired electrons and calcium does not have those. However, calcium can exhibit diamagnetism under certain laboratory conditions.
Technical calcium carbide, also known as silicocalcium, has a high affinity for oxygen and is used in place of aluminum when deoxidizing medium- and high-carbon steel grades. It is also used in the production of continuous casting to eliminate nozzle clogging and improve casting properties.
Research has shown that the addition of suitable calcium significantly decreases the size distribution of oxide-sulfide duplex inclusions in rolled steel. [24] Wu et al. showed that in rolled steel with calcium treatment, the number and size of the oxide-sulfide duplex inclusions decreased significantly, while their morphology was modified from strip shaped to spindle shaped, promoting the formation of smaller magnetic clusters.
It was found that the aluminate (Al2O3) precipitates in liquid steel in the presence of Ca, which can be further transformed into CaS in the presence of sulfur. CaS can then react with oxygen and sulfide to form calcium aluminates in the presence of g-Fe, thereby reducing the size of sulfide-oxide duplex inclusions. The reduction in the size of these inclusions results in improved mechanical properties, weldability and electromagnetic properties in ERW/HFI welded steel.
Adding calcium to steel can refine its grain, partially desulfurize it, and change the composition, quantity, and form of non-metallic inclusions. It can also improve the corrosion resistance, wear resistance, high-temperature and low-temperature performance, hardness, impact toughness, plasticity, and welding properties of steel.
Metal atoms in austenitic stainless steels are arranged in a face-centered cubic (fcc) crystal lattice, with one atom at each corner of the cube and one at the center of each of its six faces. An external magnetic field can orient these atomic domains, making the piece of steel magnetic.
In contrast, the atoms in non-ferromagnetic steel have widely spaced orbitals. Widely-spaced atoms do not interact well enough to align their magnetic moments. This is why a steel sample can be unmagnetized when it is removed from an external magnetic field.
Sulfur can form several soluble salts that cause corrosion. When sulfur is present in high concentrations, it can reduce the corrosion resistance of stainless steel, especially in the presence of acids. Sulfur can also increase the risk of localized corrosion such as pitting and crevice corrosion in stainless steels. In addition, it can promote the formation of oxides such as MnS and FeS. These compounds can be soluble in water or organic solvents, but they are insoluble in hydrochloric acid.
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