Analysis of 28 Steel Defects and Common Terms
Analysis of Steel Defects and Common Terms
Roundness: For circular cross-sections of rolled materials, such as round steel and round steel pipes, the diameters in all directions are not equal.
2. Incorrect shape: The cross-sectional geometry of the rolled material is skewed and uneven. Such as the six sides of hexagonal steel being unequal, the top Angle of Angle steel being large, and the section steel being twisted, etc.
3. Uneven thickness: The thickness of different parts of the steel plate (or steel strip) varies. Some are thicker on both sides and thinner in the middle, some are thinner at the edges and thicker in the middle, and some have a difference at the head and tail exceeding the specified limit.
4. Bending degree: The rolled piece is not straight in the length or width direction, presenting a curved shape.
5. Sickle bend: The length direction of a steel plate (or steel strip) bends to one side on a horizontal plane.
6. Ladle curvature: When a steel plate (or steel strip) shows undulating waves in both the length and width directions, it becomes "ladyshaped" or "boat-shaped".
7. Twisting: Twist the strip-shaped rolled piece along the longitudinal axis into a spiral shape;
8. Square and rectangular cross-section: Materials with square or rectangular cross-sections have unequal opposite sides or unequal diagonals of the cross-section.
9. Scratch marks (scratches) : They are in the shape of straight grooves, and the bottom of the grooves can be seen with the naked eye, distributed locally or throughout the entire length of the steel.
10. Crack: Generally in a straight line, sometimes in a Y shape, mostly consistent with the drawing direction, but there are also other directions. Generally, the opening is an acute Angle.
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11. Double skin (scabs) : A thin, raised sheet with a tongue-like or fish-like surface. One type is connected to the steel body and folded onto the surface, making it difficult to fall off. Another type is not connected to the main body of the steel, but is bonded to the surface and is prone to fall off.
12. Folding: There is local overlap on the surface of the steel, with obvious folding patterns.
13. Rust: Rust formed on the surface, with a color ranging from apricot yellow to blackish red. After rust removal, severe cases may have pitting.
14. Hairline: The surface hairline is a very shallow and extremely wide fine hairline, usually extending along the rolling direction to form fine lines.
15. Delamination: There are obvious local metal structure separations on the steel section. In severe cases, it is divided into 2-3 layers, and there are visible inclusions between the layers to the naked eye.
16. Bubbles: These are irregularly distributed circular protrusions of various sizes on the surface. Their outer circles are relatively smooth, and most of them are bulging. Some are not bulging but have a shiny surface after acid washing and flattening. The shear section shows delamination.
17. Pitting (rough surface) : The surface presents as local or continuous patches of rough surface, with four pits of different shapes and sizes distributed. In severe cases, there may be pitting spots similar to orange peels, larger and deeper than the pitting.
18. Oxidation color: After annealing, the steel plate (or steel strip) shows light yellow, dark brown, light blue, dark blue or bright gray, etc. on its surface.
19. Roller marks: The surface has periodic roller marks in the form of strips or sheets. The imprinted area is relatively bright and there is no obvious convex or concave feeling.
20. Porosity: A manifestation of the non-compactness of steel. After being eroded by acid solution, the slices expand into many caves, which can be classified into general porosity and central porosity according to their distribution.
21. Segregation: The phenomenon where the chemical composition and non-metallic inclusions in various parts of steel are unevenly distributed. According to their manifestations, they can be classified as: dendritic, box-shaped, point-like segregation and reverse segregation, etc.
22. Residual shrinkage cavities: Irregular voids or cracks appear in the center of the transverse acid-soaked test piece. Foreign impurities are often residual in cavities or cracks.
23. Non-metallic inclusions: Some non-metallic luster is observed on the transverse acidic test piece, presenting colors such as grayish white, beige, and dark gray. These are residual oxides, sulfides, silicates, etc. in the steel.
24. Metal inclusions: Some metal salts with metallic luster and obviously different from the base metal were observed on the transverse low-magnification test piece.
25. Overburning: When observing the microstructure after erosion, decarburization can often be seen on the base metal around the networked oxides. For other metals such as copper and its alloys, copper oxide extends along the grain boundaries in a networked or point-like manner into the sample.
26. White spot: It is a type of internal fracture in steel. On the longitudinal fracture surface of the steel part: there are round or oval silvery-white spots. On the transverse sections after grinding and acid etching, it presents as slender fissured, sometimes radially distributed, and sometimes parallel to the deformation direction or randomly distributed.
27. Coarse grains: There is a strong metallic luster on the acid-soaked fragments.
28. Decarburization: The phenomenon where the carbon content in the surface layer of steel is lower than that in the inner layer is called decarburization. The full decarburization layer refers to the part of the steel surface that is entirely ferrite structure due to decarburization. Partial decarburization refers to the area where the carbon content of the steel has not decreased after the full decarburization layer.
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