Rolled Steel Defects
Rolling is an important process used in the manufacture of steel products. The process involves flattening steel ingots and billets into thin sheets or plates by passing them through heated rolls. Most steel used in the marketplace today is rolled. To ensure that the rolled steel meets the highest specifications and has the best structural integrity, production must be carefully monitored and defects are regularly checked. Detecting and correcting defects during production can help reduce rejects, improve safety of the products and keep scrap costs low. In order to do so, it is important to understand what some of the most common rolled steel defects are.
One of the most common rolled steel defects is lamination. Lamination is a thin layer of material which is stuck to another layer. This layer can often be seen as a slight indentation on the surface of the steel caused by a breakage or welding abnormality. Lamination defects can also be caused by improper rolling speeds, poor lubrication or poor roll contact.
Mill scale is another rolled steel defect caused by inadequate cleaning, improper rolling speed or the use of insufficiently hot working temperatures. Mill scale consists of a thin layer of extremely hard and brittle iron oxides and magnetite. It become adherent to the steel during the rolling process and can lead to corrosion problems down the line if not corrected.
Slivers are thin strips of steel that can occur when rolls become excessively worn or when the steel ingot is not fully rolled. Slivers are also a result of a misalignment of the rolls which can cause thin, cracked areas to form on the surface of the steel. Slivers can often lead to an uneven surface finish, shortened service life and flared edges.
Rolling defects can also arise when too much force is applied to roll the steel ingots. This often leads to splits and cracks. This is a common flaw in polished steel. Cracks and splits can cause the surface of the steel to be weaker and more prone to corrosion, which can cause the steel to fail prematurely.
Finally, dust spots are round patches which can occur when internal debris has been left on the steel surface. Dust spots can be caused by oscillations in the rolling speed or uncontrolled rolling direction changes. The dust spots can lead to a reduced surface finish, a thicker than desired thickness, and a less accurate surface.
In conclusion, rolled steel defects can occur during the production process. The most common of these defects is lamination, mill scale, slivers, splits and cracks, and dust spots. If these defects are detected and corrected early during the rolling process, the quality of the steel is greatly improved, resulting in better performance and a longer service life.
