Steel is a popular metal and it is used for a number of construction materials as well as in other creations. It has many benefits, including being strong and sturdy as well as being easy to work with and to shape as may be necessary.
All metals are susceptible to increases and decreases in temperature and it is important to take note of this and see whether any Surface Treatments, like the ones from Poeton may be necessary to help increase the durability of the steel item. The surface treatment will give added protection to the outermost layer of the item and will help to prevent corrosion and damage from occurring that could compromise the integrity of the structure.
The reason why steel becomes brittle when heated is because the metal is not capable of sustaining a specific temperature for long enough to form the alloy. Heat can cause the metal to expand or contract and the wrong amount of heat can cause molecular motion which is impossible with a brittle metal.
This is one of the reasons why it is important to make sure that you are using the right metal for the structure that you need to make and that you take any measures necessary to help strengthen this with surface treatments, or to look for a more suitable metal for your needs.