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).
What is a steel bar?
Carbon steel formed into long shapes from billets are made into bar products. They can be rounds, squares, hexagons, or flats, either hot or cold finished. These products can be used in a variety of applications from stamped forging to machine gears.
Other carbon bars are considered to be structural products. These products include I-beams, H-beams, wide-flange beams, and sheet piling. These products are used in multi-story buildings, bridges, and vertical highway supports, among other products.
So, how do you choose the right steel bar product for your project? Let's take a look at two types: MBQ (merchant bar quality) and SBQ (standard bar quality). Both MBQ and SBQ 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.
Specifications of MBQ Steel Bars
MBQ bars are used in rounds, flat, squares, 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.
SBQ Steel Bars
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.