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Carbon Steel Defects

During the smelting and rolling (forging) processing of carbon steel, the lack of steel is caused by equipment, process and operation. Mainly include scars, cracks, residual shrinkage, delamination, white spots, segregation, non-metallic inclusions, loose and banded tissues.
During the smelting and rolling (forging) processing of carbon steel, the lack of steel is caused by equipment, process and operation. Mainly include scars, cracks, residual shrinkage, delamination, white spots, segregation, non-metallic inclusions, loose and banded tissues.

1. Scarring

Metal or non-metallic scars on the surface of the steel that are not welded to the substrate. Some parts are connected to the base and are tongue-shaped; some are not connected to the base and are scaly. The latter sometimes fall off during processing, forming pits. Scars caused by steel-making (casting) usually have non-metallic inclusions visible to the naked eye. Scars caused by steel rolling are generally called “rolling scars”, and generally only oxide scales under the scars.

The main causes of scarring in steelmaking (casting) are:

(1) The upper casting ingot did not take anti-splash measures or the lower casting ingot was cast too sharply, causing splash scars.

(2) The slag performance of the lower ingot is not good or the mold is not clean and not dry, causing inclusions, bubbles and heavy skin on the surface or under the skin of the steel ingot (continuous casting slab).

(3) Severe defects in the mold wall or excessive casting temperature cause convex scars and sticky molds, which become scars after rolling or forging.

The causes of scars in steel rolling are:

(1) Defects or improper operation of a certain roll (roller) or guide guard device before the finished product cause convex parts, ears, and scars of the rolled parts, and then form scars after re-rolling.

(2) The flame clearing of the billet is too steep or the residue is not removed, and the foreign objects fall on the billet and are rolled into scars.

Scar defects directly affect the appearance quality and mechanical properties of steel. No scars are allowed on the finished steel. The scarred part can be repaired, and the steel size should be in accordance with the standard after the repair. In order to reduce and eliminate scars, the first is to improve the relevant processes and operations in steelmaking and rolling, and the second is to focus on the surface defects of the billet or clean it completely.

2. Cracks

There are various names according to the shape of the crack and the reason for its formation, such as tensile cracking, transverse cracking, cracking, cracking, hairline, bursting (sound cracking), brittle cracking (correction cracking), rolling cracking and shear cracking. Almost every process from steelmaking, steel rolling to deep processing of steel has cracking factors.

(1) Steelmaking

The content of sulfur and phosphorus in steel is high, and the strength and plasticity of steel are low; the temperature of ingot casting (die casting, continuous casting) is too high, the casting speed is too fast, and the casting flow is not correct; the design of the steel ingot mold and crystallizer is unreasonable; the cooling strength is insufficient Or the cooling is uneven, resulting in a thin chilled layer or excessive local stress; the steel ingot mold has serious defects or the insulation cap is installed poorly, causing the steel ingot to hang during the solidification process; the performance of the protective slag is poor, the mold tide and various casting operations can cause the steel ingot Poor surface quality and cracks formed on the steel.

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