Banding in steel can limit the quality and stability of steel products. Here is a closer look at how banding occurs and why you want to minimize or sometimes avoid it in steel.
What is Banding?
Banding occurs with hot rolled steel products when alloying elements segregate during solidification. A variety of factors can cause banding, such as the composition of the material, temperature, impurities etc which are all related to the steel casting practice. Subsequent hot-working operations result in segregation aligned in the direction of hot working, which results in the banded appearance delineated in the microstructure. The diffusion rates of the alloying elements in steel control the homogenization of the casting. For example, chromium and molybdenum homogenize readily, while nickel homogenizes very slowly. The alternating bands of varying alloy chemistry result in different microstructures, orientated parallel to the rolling direction of the material.
Why is Banding Harmful?
Banding can heavily influence hardness and microstructure of alloy steel. The microstructure in the darker band tends to be more martensite and bainite and the lighter band tends to be more ferrite and perlite (these are the names of the microstructure) or vice versa. In case-hardened steels, it can pose a challenge in achieving uniformity in hardness in case banding is more. It can also pose several risks to the finished product, including:
- Difficulty coating or painting the surface
- Variations in hardness and strength
- Reduced structural integrity
The uneven appearance of light and dark bands can also make it more difficult to apply paint or other coatings to the surface. Dark bands can absorb materials differently compared to light bands, resulting in uneven application and less effective protective coatings.
Banding can create variations in the overall hardness, strength, and ductility of rolled steel products. Load-bearing elements and structural components that require consistency from each part may suffer from reduced structural integrity. It is important to note that tensile, yield and fatigue strength tend to be relatively unaffected by banding but ductility and toughness properties are negatively impacted in case banding is high.
Working with a trusted manufacturer, such as KISCO Steel, helps mitigate these risks. You can rely on experienced manufacturers for the highest level of quality assurance and the most effective steel making techniques for minimizing and/or eliminating banding in steel.