When it comes to steel bars, quality matters. And when talking specifically about carbon bars, that quality comes in two distinct forms: MBQ (merchant bar quality) and SBQ (special bar quality).
So, what’s the difference? It starts with the way in which each is made. Both go through the standard process of producing metal—molten steel poured as it is solidified into a billet -- it’s at that point in which the process (or lack thereof) dictates the end quality of the bar.
Let’s focus first on MBQ bars. This is the bar used in beams, channels and angles, among others. Once going through the standard production process, the billets are pretty much left as is. In other words, the chemical ranges stay within the standard limits for carbon, manganese, phosphorus and sulfur.
This is due primarily to the fact the product, for the most part, is used in applications that don’t require much, if any, additional machining. Think of a sign post or the arm of a metal stand.
Now let’s talk SBQ bars. These are a bit more specialized, as the name indicates. When the end use, method of fabrication or subsequent processing requires unique characteristics, SBQ is the quality of bar you should use.
The billets are modified based on their conditions. For example, certain defects that occur during production may go through a bit of processing to ensure the smoothest surface with as few imperfections as possible.
These are the bars that will go into an engineered application and most likely have multiple processes done to the metal before you get to the finished part. For example, engineered applications like a crank shaft in a car or a motor shaft in a power tool.
In the end, MBQ vs. SBQ is not an apples-to-apples comparison. It essentially comes down to the application and the quality that needs to come through in the end product.