The elements in steel can improve the performance of steel and also affect its performance. So what are the effects of various elements on the performance of steel?
H (hydrogen): H is the most harmful element in general steel. Hydrogen dissolved in steel can cause defects such as hydrogen embrittlement and white spots in steel. Hydrogen overflows before cooling and accumulates in the structure to form high-pressure fine pores, which sharply reduces the plasticity, toughness and fatigue strength of the steel. In severe cases, it will cause cracks and brittle fracture.
On the other hand, H can increase the magnetic permeability of steel, but it will also increase the coercive force and iron loss (the coercive force can be increased by 0.5 to 2 times after adding H).
C (hydrogen): C is the main element second only to iron, and it directly affects the strength, plasticity, toughness and welding performance of steel.
When the carbon content in steel is below 0.8%, as the carbon content increases, the strength and hardness of the steel increase, while the plasticity and toughness decrease; but when the carbon content is above 1.0%, as the carbon content increases, the strength of steel will decrease instead.
With the increase of carbon content, the welding performance of steel becomes worse (steel with carbon content greater than 0.3% has a significant decrease in weldability), cold brittleness and aging sensitivity increase, and atmospheric corrosion resistance decreases.
N (nitrogen): The effect of N on the properties of steel is similar to that of carbon and phosphorus. As the nitrogen content increases, the strength of the steel can be significantly improved, and the plasticity, especially the toughness, is also significantly reduced, the weldability becomes worse, and the cold brittleness becomes worse. At the same time, it increases the aging tendency, cold and hot brittleness, and damages the welding performance and cold bending performance of the steel. Therefore, the nitrogen content in steel should be minimized and limited. It is generally stipulated that the nitrogen content should not be higher than 0.018%.
O (oxygen): O is a harmful element in steel. It naturally enters the steel during the steelmaking process. Although manganese, silicon, iron and aluminum must be added for deoxidation at the end of the steelmaking process, it is impossible to remove it completely. Oxygen mainly exists in steel in the form of inclusions such as FeO, MnO, SiO2, Al2O3, etc., which reduces the strength and plasticity of steel, especially has a serious impact on fatigue strength and impact toughness.
Ca (calcium)
Adding calcium to steel can refine grains, partially desulfurize, and change the composition, quantity and shape of non-metallic inclusions. The effect of adding rare earth to steel is basically similar.
The addition of calcium to the cast steel greatly improves the fluidity of molten steel, improves the surface finish of the casting, and eliminates the anisotropy of the structure in the casting; its casting performance, thermal crack resistance, mechanical performance and cutting performance have been increased to varying degrees.
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