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Carbon steel defect

Carbon steel defect is caused by the equipment, processes and operations in carbon steel smelting and rolling (forging) process, including scarring, cracks, residual shrinkage, layered, white point, segregation, non-metallic inclusions, such as osteoporosis and banded.

Scarring
No scarring and the base steel surface weld metal or metalloid scar blocks. Some parts of the body is connected with the base, was tongue; others not connected with the matrix, scaly. The latter is sometimes off during processing, forming pits. Steel (cast) scarring caused by scar generally have lower non-metallic inclusions visible to the naked eye. Scarring defects directly affect the quality and appearance of the mechanical properties of the steel. Scarring are not allowed in the presence of finished steel. Scarring can be grinding parts for repair after repair of steel grinding size should meet the standard requirements.

Crack
Cracks formed by the shape and name a variety of reasons, such as crack, transverse crack, crack, crack, hairline, burst (loud crack), rattle (Jiao crack), rolling and shear crack bifida. From steel making, rolling into steel processing almost every procedure has factors causing cracks.

Residual shrinkage
The molten steel during solidification, due to the volume shrinkage in the ingot or billet has not been sufficiently filled central portion formed by a tubular or dispersion holes. Before thermal processing, because cutting head is too small or craters deeper, causing endless resection, the residual part is called residual shrinkage. The residue was distributed in the shrinkage at the upper center of the ingot, and the ingot through the top is called a cratering.

Stratified
Binding and do not appear on the two-layer structure of the steel substrate. Stratification generally parallel to the surface pressure processing, in longitudinal section transverse black lines are low magnification specimen. Layered severe cracks occurred in fractures tend to have iron, non-metallic inclusions and severe segregation substances. Killed steel ingot ingot boiling craters and holes by the end of the balloon and rolling (forging) can not be welded together to produce stratification. Large inclusions in steel and can produce severe segregation layering. Layering is not allowed in the steel defects seriously affect the use of steel.

White Point
On steel vertical, cross-sectional acid leaching test piece, there's no rule of different lengths hairline. It is the low times in the transverse specimen radial, concentric or irregularly distributed, multi-center, or from the steel surface has a certain distance. Steel fracture in the transverse or longitudinal, circular or oval white highlights. Average diameter of 3 ~ 10mm. Steel plate in the longitudinal, transverse fracture characteristic white spots is not obvious, but the fracture presented to strip or oval-shaped white spots in z. When using fracture checks white spots, it is best to first quenched specimens and quenched.

Segregation
Uneven steel components. This phenomenon is not only common element (such as carbon, manganese, silicon, sulfur, phosphorus) uneven distribution, but also non-metallic inclusions and gas distribution uniformity. The reason is that the segregation arising during solidification of molten steel, the resulting crystals separators. Often associated with the degree of segregation ingot, steel, smelting and casting operation conditions. Alloying elements, segregation of impurities and gases, with the casting temperature and the casting speed, the more serious the degree of segregation. Even steel using electromagnetic stirring can reduce the degree of segregation. In addition, the increase in steel cleanliness is an important measure to reduce segregation.

Non-metallic inclusions
The steel contains a metal component and the substrate different nonmetallic materials. It destroys the continuity and isotropic properties of the metal matrix. According to the source of non-metallic inclusions can be divided into endogenous inclusions, foreign inclusions and their mixtures. Endogenous inclusions are deoxidation and various physical and chemical reaction performed by the formation of crystals, mainly steel oxygen, sulfur, nitrogen, among other components with the reaction product.

Loose
Not dense thermal etching phenomenon steel sectional tissue specimen. Thermal etching on the steel cross-section specimen, there are many pores and black specks promoter, rendering the phenomenon is not dense tissue, called loose when one of these pores and black specks distributed throughout the sub-test piece, concentrated in the center of the center is called osteoporosis . Thermal etching in the longitudinal specimens showed loose stripes of different lengths, but careful observation or observation with 8 to 10 times magnifying glass, striped no depth. Porosity was observed by scanning electron microscopy or streaks can be found distal dendrites are free of surface features metal crystals.

Banded
After thermal processing of low-carbon steel, the microstructure of ferrite and pearlite parallel along the rolling direction, zonal distribution, formed steel banded structure. Banded structure is essentially a steel tissue uneven performance, the impact properties of the steel, producing equipment to the opposite sex. Banded lower steel ductility, toughness and reduction, especially greater impact on the transverse mechanical properties.





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