Classification of non-metallic inclusions in steel

Classification of Nonmetallic Inclusions in Steel

Steel is a metal alloy composed of iron and other elements, including carbon, which is the main strengthening and hardening element in steel. The presence of nonmetallic inclusion in steel is an important factor affecting the performance and properties of the steel. Nonmetallic inclusions mainly refer to nonmetallic oxides, sulfides and silicates formed in the course of smelting, which are usually embedded in the matrix of steel and are difficult to melt and separate.

Nonmetallic inclusions can be divided into two types according to their composition and shape, one is porosity type and the other is pure particle type. Porosity type nonmetallic inclusions are mainly metal oxide films or irregular particles, and there are many small holes and depressions, which can make steel relatively weak. While pure particle type nonmetallic inclusions such as silicates and sulfides are usually solid metal crystals, which are relatively strong and not easy to be densified.

There are many kinds of nonmetallic inclusions in steel, and their characteristics vary depending on the content of their components. For example, calcium oxide, which is mainly composed of calcium oxide and a small amount of aluminum oxide, has a high reactivity, easily absorbs moisture, and is easy to form. In the steel matrix, they become pores and octahedral shape particles. Magnesium oxide, the main component of which is magnesium oxide and a small amount of calcium oxide and silicon oxide, is relatively strong and usually forms octahedral and plate-like particles.

Besides, there are a variety of other nonmetallic inclusions, including silicon oxide, aluminum oxide, chromium oxide, boron oxide, and carbon oxide. These nonmetallic inclusions form intergranular cracks in the steel and reduce the strength and plasticity of the steel. In addition, sulfur, phosphorus and other nonmetallic inclusions will make steel more brittle, reduce its strength and reduce its plasticity.

In summary, nonmetallic inclusions in steel play an important role in the formation of steel performance characteristics. It is necessary to identify and accurately classify these nonmetallic inclusions in steel in order to control and optimize the properties of steel. Identifying and accurately classifying nonmetallic inclusions in steel requires the we use different analysis techniques, including optical microscopy, scanning electron microscopy, X-ray diffraction technique, etc. On the basis of understanding the physical and chemical characteristics of nonmetallic inclusions, these techniques can be used to identify and classify them to improve the performance of steel products.

Non-metallic inclusions in steel are a type of foreign material that must be kept to an acceptable level to ensure that steel products meet required specifications. These non-metallic materials may either be deliberately added to the steel or may accidentally contaminate it. Non-metallic inclusions are generally classified according to their chemical composition, morphology and origin.

Chemical composition: Non-metallic inclusions can be divided into three main categories based on their chemical composition: Sulphides and Oxides, Carbides and Nitrides, and Refractory compounds. The sulphides and oxides are usually composed of minerals such as quartz and graphite, the carbides and nitrides are composed of metal-rich compounds such as iron and titanium, and the refractory compounds are composed of ceramic-like materials such as alumina and silica.

Morphological: In terms of morphology, non-metallic inclusions can be divided into three main types: flakes, particles, and tubules. The flakes are usually made of semiconductor, ceramic, or metallic materials while the particles are usually composed of sulphides, oxides, and carbides. The tubules are made of carbon, sulphur, and other elements.

Origin: Finally, non-metallic inclusions can be divided into two categories based on their origin, which are endogenous and exogenous. The endogenous inclusions are those which may either become incorporated into the metal during its formation, or are generated by the re-melting of metal and oxidation of the iron. The exogenous inclusions are those which are introduced into the metal through environmental means such as water, gases, and chemicals.

In conclusion, non-metallic inclusions can be divided into three categories based on their chemical composition, three types based on their morphology, and two categories based on their origin. All three categories help to identify the type and amount of foreign substances present in the steel, which is important for ensuring that steel products meet the required specifications.