Some Chemical Effects of Certain Elements on Carbon Steel

The performance of carbon steel depends mainly on the carbon content and microstructure of the steel. In the annealed or hot rolled state, the strength and hardness of the steel increase as the carbon content increases. However, its plasticity and impact toughness are lowered, and weldability and cold bendability are deteriorated. Therefore, the steel used in engineering structures often limits the carbon content.


Residual elements and impurity elements such as manganese, silicon, nickel, phosphorus, sulfur, oxygen, nitrogen, etc. in carbon steel also have an effect on the properties of carbon steel. These effects sometimes reinforce each other and sometimes offset each other. For example:


1 Sulfur, oxygen, nitrogen can increase the hot brittleness of steel, and the right amount of manganese can reduce or partially offset its hot brittleness.


2 Residual elements reduce the impact toughness of steel and increase the cold brittleness except manganese and nickel.


3 In addition to reducing the strength of sulfur and oxygen, other impurity elements increase the strength of the steel to varying degrees.


4 Almost all impurity elements can reduce the plasticity and weldability of steel.


Hydrogen can cause many serious defects in steel, such as white spots, point segregation, hydrogen embrittlement, surface bubbling and cracks in the weld heat affected zone. In order to ensure the quality of steel, it is necessary to reduce the hydrogen content in the steel as much as possible. Residual elements such as aluminum, which are deoxidized, can reduce the aging tendency of low carbon steel, and can also refine grains and improve the toughness of steel at low temperatures. But the rest should not be too much. The residual elements brought in by the charge, such as nickel, chromium, molybdenum, copper, etc., can increase the hardenability of the steel when it is high, but are disadvantageous for special steels requiring high plasticity.