1, carbon (C): increased carbon content in steel, the yield point and the tensile strength increased, but the ductility and shock resistance, when the carbon content exceeds 0.23%, weldability deteriorates, so for soldering low alloy steel, the carbon content of not more than 0.20%. But it also reduces the amount of high carbon steel atmospheric corrosion resistance, high carbon steel in the open-air yard would easily corroded; In addition, the carbon can increase sensitivity to cold brittleness and aging steel.
2, silicon (Si): Si added as a reducing agent in the steel making process and deoxidizer, it killed steel containing 0.15-0.30% silicon. If the steel is more than 0.50-0.60% silicon, silicon even if alloying elements. Silicon can significantly improve the elastic limit of the steel, the yield point and tensile strength, it is widely used as a spring steel. 1.0 -1.2% silicon in quenched and tempered steel, the strength can be increased by 15-20%. Silicon and molybdenum, tungsten, chromium, combined with improve corrosion resistance and antioxidant effects, can produce heat-resistant steel. Silicon 1-4% of low-carbon steel, with a high permeability, do silicon steel for electrical industry. Increase the amount of silicon will reduce weldability.