Circular Degree

Description: For round-section rolled products such as round bars and circular steel tubes, the diameters vary in different directions across the cross-section.

Incorrect shape (profile)
Description: The geometric profile of the cross-section is distorted or uneven. Examples include unequal sides on hexagonal bars, excessive corner angles on angle bars, or twisting in structural sections.

Uneven thickness
Description: Different parts of a steel plate (or strip) have varying thicknesses—some are thicker at the edges and thinner in the center, others thinner at the edges and thicker in the center, or the difference between head and tail exceeds specified limits.

Bending
Description: The rolled product is not straight along its length or width, forming a curved shape.

Scythe bend
Description: A steel plate (or strip) bends to one side horizontally along its length.

Dishing
Description: A wavy, undulating pattern appears simultaneously along both the length and width of the steel plate (or strip), giving it a "bowl-like" or "ship-like" appearance.

Twisting
Description: Bar-shaped rolled products are twisted into a spiral form along their longitudinal axis.

Out-of-square or out-of-rectangle
Description: In square or rectangular cross-section materials, opposite sides are unequal in length, or the diagonals of the cross-section differ in length.

Scratches (grooves)
Description: Linear grooves visible to the naked eye extend along part or the entire length of the steel, with clearly defined bottom surfaces.

Cracks
Description: Generally straight, sometimes Y-shaped, often aligned with the drawing direction but occasionally in other directions; typically with sharp corners at the opening.

Scale (scabs)
Description: Thin, raised flakes resembling tongues or fish scales appear on the surface. One type is firmly attached to the base metal and folded onto the surface, making it difficult to remove; the other type is loosely adhered and easily detached.

Folding
Description: Local overlapping of the steel surface, showing distinct folding marks.

Rust
Description: Naturally occurring iron oxide on the surface, ranging in color from light yellow to dark red. After rust removal, severe cases may show pitting corrosion.

Hairline cracks
Description: Very fine, hair-like lines extremely shallow in depth and narrow in width, generally extending along the rolling direction, forming fine, threadlike patterns.

Delamination
Description: Localized, obvious separation of metallic structure within the cross-section of the steel; in severe cases, it splits into 2–3 layers, with visible inclusions between the layers.

Blowholes
Description: Irregularly distributed, round protrusions of various sizes on the surface, with smooth outer edges. Most are bulging, while some are flat and become bright after pickling and leveling; the cut surface shows delamination.

Pitting (pitted surface)
Description: Localized or continuous rough areas on the surface, covered with pits of irregular shapes and varying sizes. Severe cases resemble orange peel, with larger and deeper pitted spots.

Oxidation color
Description: After annealing, the surface of the steel plate (or strip) displays colors such as pale yellow, dark brown, light blue, deep blue, or bright gray.

Roll mark
Description: Periodic banding or patchy impressions left by rolls on the surface, with the imprinted areas appearing brighter and without noticeable raised or depressed texture.

Porosity
Description: Indicates lack of density in steel. When a section is corroded in acid, numerous cavities develop. Based on distribution, it can be classified as general porosity or central porosity.

Segregation
Description: Uneven distribution of chemical composition and non-metallic inclusions throughout the steel. Depending on appearance, types include dendritic, box-shaped, dot-shaped segregation, and inverse segregation.

Shrinkage cavity residue
Description: Irregular cavities or cracks appear at the center of transverse acid etched specimens. These cavities or cracks often contain foreign impurities.

Non-metallic inclusions
Description: On transverse acid-etched specimens, non-metallic particles appear as dull, grayish-white, beige, or dark gray spots, representing residual oxides, sulfides, silicates, etc., in the steel.

Metallic inclusions
Description: On low-magnification transverse specimens, metallic salts appear with metallic luster, clearly distinguishable from the base metal.

Overheating
Description: Upon examination of the microstructure after corrosion, decarburized zones are often observed around network-like oxides. In other metals such as copper and its alloys, copper oxide forms network-like or dot-like structures extending inward along grain boundaries. White spots: A type of internal fracture in steel. On the longitudinal fracture surface of a steel component, they appear as round or oval silver-white spots; on polished and etched transverse sections, they manifest as fine, elongated cracks, sometimes arranged radially, sometimes parallel to the deformation direction, or distributed irregularly.

Coarse grain structure: Strong metallic luster appears on the fracture surface of acid-etched specimens.

Decarburization: The phenomenon where the carbon content at the surface of steel is lower than that in the interior is known as decarburization. The fully decarburized layer refers to the region at the steel surface where the microstructure consists entirely of ferrite due to decarburization; partial decarburization refers to the zone between the fully decarburized layer and the area where the carbon content has not decreased.