Black Steel & Bright Drawn Steel
What is the difference between black steel & bright drawn steel? Black steel is produced by rolling the steel at a high temperature (typically over 1700° F), as it needs to be hotter than steel’s recrystallization temperature. When it is above the recrystallization temperature it can be formed and shaped more easily. It can also be made in much larger sizes. Black steel tends to be cheaper than bright drawn steel due to the fact that it can be manufactured without any delays in the process. However, when the steel cools down it shrinks slightly, which results in less control on the shape and size of the finished product compared to bright drawn steel. It can have a scaly, rough surface and is not precise in its dimensions, flatness or straightness. As this type of steel has some undesirable characteristics, bright drawn steel has been devised to make a product more acceptable to the engineering industry. Due to its enhanced appearance, cold finished steel is more commonly known as bright steel. Bright drawn steel is fundamentally black steel that has gone through additional processing. In a cold reduction mill it is cooled to room temperature followed by annealing and/or tempers rolling. This produces steel with closer dimensional tolerances and a broader range of surface finishes. The term bright drawn refers to the rolling of flat rolled sheet and coil products. It is a higher quality material, free of scale and has closer dimensional tolerances. It is cold worked (rolled or drawn) to size and is more suitable for repetition precision machining. Some of the properties of bright drawn steel include: • An improved surface finish and scale free condition • Improved accuracy of size and degree of straightness • Enhanced mechanical properties • Better machinability • Tighter tolerances Black steel products are used where precise shapes and tolerances are not required. For example, black steel bars are used in the construction and welding trades to produce railroad tracks and Ibeams. Bright drawn steel is used in any project where surface condition, tolerances, straightness and concentricity are important. These include machining tools, springs, gears, white goods and office equipment.