Effect of Chemical Composition on Properties of Steel

 The basic elements of steel are iron (Fe), w (Fe) = 99% in common carbon steel, the rest are carbon (C), silicon (Si), manganese (Mn), and the harmful elements are sulfur (S), phosphorus (P), oxygen (O), nitrogen (N). A certain amount of elements such as chromium, nickel, copper, vanadium, titanium and niobium should be added into the alloy steel to improve the mechanical properties of the steel.

 Carbon is an important component of steel strength. W(C) in steel used in steel structure is less than 0.2%.

 Manganese can increase the strength of steel and improve the tendency of cold brittleness of steel, but it can reduce the weldability, so the content of manganese should be controlled.

 Silicon is a strong deoxidizer, which can make steel particle size finer, improve strength and do not affect other properties. W(Si)=0.12%-0.3% in common carbon steel and 0.2%-0.6% in low alloy steel.

 Vanadium can improve the strength and corrosion resistance of steel without significantly reducing its plasticity.

 Sulphur is a harmful impurity and can produce iron sulfide which is easy to melt. When the temperature reaches 800-1000 C, the steel cracks, called hot brittleness, will also reduce the impact toughness of the steel and affect the fatigue and corrosion resistance of the steel. Therefore, the mass fraction of sulphur should be strictly controlled within 0.05%.

 Phosphorus is also a harmful impurity, which makes ordinary carbon steel brittle at low temperature, called cold brittle, and reduces the plasticity of steel at high temperature.The mass fraction should be limited to 0.045%.

 Oxygen and nitrogen are also harmful elements. Oxygen can make steel hot brittle and nitrogen can make steel cold brittle. Therefore, its content should be strictly controlled.