Surface Quality and Condition of High Strength Low Alloy Steel Hot Rolled Sheet and Strip and Cold Rolled Sheet
The steel products such as hot rolled sheets and strips and cold rolled sheets are extensively used in a variety of applications in the manufacturing industry. High strength low alloy (HSLA) steels are a special class of steel alloys that are produced with a composition different than that of regular steels, in order to provide enhanced mechanical and corrosion properties. This type of steel is especially suitable for use in structural applications for automotive, aerospace industry and also for construction purposes.
The performance of the steel sheets depend on their surface quality and condition. This is because the surface of the steel sheets affects the formability and dimensional accuracy of the finished product. Therefore, in order to produce the desired quality of products, it is essential to ensure that the surface of the steel sheets is in good condition. This includes checking the surface smoothness of the steel sheets, the amount of oxide layers present on the surface and the surface hardness.
The most significant factor affecting the surface quality of the steel sheets is the cooling process after they have been rolled. When the steel sheet is cooled, the cooling rate must be carefully controlled in order to prevent any temperature-related deformations or variations in mechanical properties. After the cooling process, the steel sheets need to be checked for their surface condition. This involves performing a visual inspection to check for any obvious surface defects such as pits and scale, followed by a surface finish inspection to check the smoothness and appearance of the surface.
In order to ensure a good surface quality of HSLA steel hot rolled sheet and strip, there should be no more than a 0.7 µm peak-to-valley height of the surface due to rolling and no more than a 1.5 µm peak-to-valley height due to rust. A high level of surface cleanliness should also be maintained. To prevent rust on the steel sheets, it is important to apply the appropriate anti-corrosion agents to the surface.
For cold rolled steel sheets, the surface condition is a very important factor in determining the final properties of the product. The surface must be clean and uniform so that any oxide or scale that has formed during the cold rolling process is removed. The surface should also be checked for its roughness, to ensure that it is in accordance with the customer’s requirements.
In order to improve the surface condition of both hot rolled and cold rolled HSLA steel sheets, they must be subjected to a post-rolling process such as annealing or pickling. Annealing involves heating the steel sheets to a certain temperature and then cooling them in order to reduce any hardening or brittleness that might have occurred during the rolling process. Pickling is another post-rolling process where the steel sheets are submerged in a bath of hydrochloric acid in order to remove any surface oxides. This process is also beneficial for improving the formability of the steel sheets.
It is essential to ensure that the surface quality and condition of HSLA steel hot rolled sheet and strip and cold rolled sheets is in optimal condition in order to achieve the desired product quality. The surface must be inspected and the post-rolling processes must be applied if necessary to improve the surface condition.
