Metallographic diagram of 15 steel (annealed state)

Fig 1.0 is a metallographic cross-sectional optical microscopy image of a 15 steel sample in an annealed condition. The sample was extracted from an industrial size bar using a standard cutting technique and mounted for examination using a standard light microscopy methodology with oil-immersion. Over the surface of the transverse cross-section the highly reflective surface of the steel sample revealed a pocket of evenly distributed inclusions. Along the field of view, several black spots are observed to link together a few smaller pockets of inclusions located near the center and the left side of the image.

The black spots in the image represent graphite inclusions which are formed as a result of congruent inclusions present in the steel, as a result of its non-homogenous composition. The inclusions likely originated from the steel’s manufacturing process, and due to the annealing process, the graphite inclusions are held in place reducing the potential for future structural or mechanical failure of the steel. Furthermore, the presence of these clusters of inclusions demonstrate that the steel has the appropriate thermal and acoustic properties needed for the desired mechanical and metallurgical properties.

These types of steel samples are widely used for the production of industrial components and require a high degree of rigidity and wear resistance for their intended functions. Therefore, it is necessary that the steel is analyzed to ensure its quality and longevity. As can be seen from the optical metallography, the 15 steel sample displays a uniform distribution of graphite inclusions throughout its cross-sectional area which is indicative of a homogenous structural composition. Furthermore, the absence of localized regions of increased or decreased surface features (such as waviness, cracks or other defects) further display the steel’s suitability for its intended uses.

In conclusion, the 15 steel sample displays a uniform surface and a homogenous structural composition. Through this image, one can infer that the steel is on target to fulfill its intended functions and should therefore be accepted for use in the intended industrial applications.

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Q235 Steel is a commonly used low-carbon structural steel material. Its full name is “carbon structural steel”. Its yield point is 235mpa and its tensile strength is 370-500mpa. It has an elongation of 22%.

Q235B has good plasticity, toughness and welding performance, so it is widely used in construction, bridges, ships, automobiles, etc. It is usually used as a steel structure for manufacturing in the United States with a thickness of 16mm.

The metallographic structure of Q235B is mainly ferrite and pearlite and its texture is second-grade texture. Ferrites are in different sizes, from even to irregular, and most of them are equiaxed crystals. Large grains of ferrite are distributed mainly in the eutectoid and in non-metallic zones. Below 1.1%, the carbides are dispersed uniformly in the ferrite, and there are small particles. There are few carbide networks in the pearlite region, but the carbides are evenly distributed, mainly depending on the size of the spheroidite, or on the amount of carbon and the number of spheroidal particles. There are dark secondary cementite layers along the grain boundaries, which can not be seen too clearly but only as dark lines.

Q235B steel is a low-carbon steel with a carbon content of 0.1-18%. It is a ferrite plus pearlite structure and is suitable for welding and rolling into various shapes. It is mainly used to manufacture bridge structures, ships, vehicles, boilers, pressure vessels, oil tanks, etc.