Mill scale in welding has become an important factor for welders over the many years. It is the layer of rust that forms on the surface of steel when it is exposed to oxygen, and it can significantly affect the welding process.
It is estimated that mill scale can account for as much as 20% of the overall cost related to welding and metal work. Therefore, a thorough understanding of what mill scale is, how to handle it and how to prevent it, is essential to quality welding and metal working. In this article, we will explore what mill scale is and how to best handle it in order to maximize productivity and quality in welding.
What is Mill Scale in Welding?
Mill scale, referred to as ‘blue scale’, is a by-product formed while welding. It is a thick layer that develops on the surface of the metal due to the high temperatures involved in the welding process. Mill scale appears bluish-black in color and has a rough texture.
How Does Mill Scale Form?
Mill scale is formed when the metal is exposed to high heat, i.e. >700 degree Celsius. During the welding process, the metal is subjected to very high heat that promotes oxidation.
The oxidation results in the formation of a layer of mill scale that can be up to 5 mm thick.
Effect of Mill Scale on Weld Quality
Mill scale can have an adverse effect on the quality of welds.If the mill scale is not removed before welding, it can lead to the formation of cracks in the weld. The cracks are more likely to form when welding materials of different thicknesses.
Moreover, mill scale also causes distortion in the weld by reducing its ductility. This can also lead to cracking in the weld.