Aluminum, chromium, manganese, molybdenum. What is the role of the alloying elements on the properties of steels? When and why are they used?
Aluminum and Chromium. Why are they used?
ALUMINUM
During the preparation of the steel, aluminum (Al) is used both as
- deoxider (or flux)
- refining agent
of the metal grain, for all those fine-grained steels.
CHROMIUM
Chromium (Cr), on the other hand, has a very important role in the processing of steel. It increases:
- hardenability
- resistance and hardness (after the heat-treat)
- stability of tempering
- wear resistance
In addition, this alloying element is able to
- improve the combination of thoughness and resistance
- reduce the overheating sensitivity
What determines the chrome?
- resistance to corrosion and hot oxidation
- high temperature mechanical resistance (i.e. creep resistant)
Have a look at copper
After talking about aluminum and chromium, we want to focus on copper (Cu). This passes by a primary condition (extracted minerals) to a refined one. This is produced by refining both the raw and the one obtained from the recycling of scrap. Together with steel, it encourages the formation of cracks. The copper, during hot working, localizes to the surface and is particularly harmful. Why copper is added to steel? In CORTEN steels (low-alloy material), for example, copper improves resistance to atmospheric oxidation.
Manganese for construction steel
The last alloying element that we will discuss today is the Manganese (Mn) which is always present in iron ores. Such as aluminum, it can act as a flux (or deoxidizing). In addition, it also acts as desulfurizer. An high percentage of this element can increase the rate of strain hardening (such as manganese steels). High strength of steels depends on their chemical composition, as well as the addition of alloying elements such as manganese. This item, for example, can improve the combination strength-toughness on structural construction steels (building material used in the field of civil engineering). Manganese behaves similarly to nickel (Ni) and, in the absence of the latter, it is used in place as gammagen element in certain types of steels.
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