Steel has been used in many industrial fields in recent years, including automobile manufacturing, construction, and shipbuilding. According to the characteristics and application requirements of the industry, the alloy element content in the steel must be strictly limited, so as to ensure the quality and performance of the steel used. This paper firstly briefly introduces the difference between non-alloy steel, low alloy steel and alloy steels, and then puts forward the boundary value of the alloy elements stipulated in Chinas national standard.
Non-alloy steel, also known as carbon steel, is a type of steel with an total alloy element content lower than certain limit, usually 0.3%-1.7%. It is generally with a carbon content of 0.15%~0.3%. Non-alloy steel is widely used in the manufacture of common engineering parts and components due to its relatively low cost, low alloy content and strong mechanical properties.
Low alloy steel is a kind of alloy steel in which the total alloy element content is at the lower end of the alloy steel, usually 2.11%-4.99%, and the carbon content is generally 0.21%~0.35%. The advantage of low alloy steel is that it has slightly better mechanical properties than non-alloy steel due to its low alloy element content. Low alloy steels are widely used in structures, tools and machinery parts.
Alloy steel is a kind of steel with more than 5% alloy elements. Due to the higher alloy content, alloy steels generally have better physical and mechanical properties compared with general structural steels and high strength structural steels. Alloy steels are also widely used in the manufacture of various parts and components due to their better properties.
China presented the limits of alloy elements in steel in the national standard of Steel Classification and Coding System(GB/T225-1988), specifying the contents of some commonly used alloy elements and the Steel-Making methods. The maximum content of Alloy elements in steel is as follows:
1) Manganese (Mn): Mainly for the improvement of strength and toughness, the content of Mn should not exceed 2.50%.
2) Silicon (Si): Mainly used to improve the strength, plasticity and the weldability of the steel, the content of Si should not exceed 0.60%.
3) Nickel (Ni): Mainly used to improve the strength, plasticity and weldability of the steel, the content of Ni should not exceed 0.60%.
4) Chromium (Cr): Mainly used to improve the strength, plasticity and creep resistance of the steel, the content of Cr should not exceed 1.50%.
5) Vanadium (V): Mainly used to improve the strength, toughness, hardenability, and corrosion resistance of the steel, the content of V should not exceed 0.20%.
6) Molybdenum (Mo): Mainly used to improve the strength, plasticity, and corrosion resistance of the steel, the content of Mo should not exceed 0.30%.
7) Titanium (Ti): Mainly used to improve the strength, plasticity and weldability of the steel, the content of Ti should not exceed 0.20%.
8) Copper (Cu): Mainly used to improve the strength and corrosion resistance of the steel, the content of Cu should not exceed 0.20%.
9) Cobalt (Co): Mainly used to improve the strength and corrosion resistance of the steel, the content of Co should not exceed 0.20%.
According to the national steel standard, the maximum content of these alloy elements in steel should not exceed the above-mentioned value. In the standard, there is also a clear stipulation that for steel with a total alloy element content of 2.11%-4.99%, no single alloy element should exceed the above-mentioned value by more than 0.05%. For steel with a total alloy element content of 0.3%-1.7%, no single alloy element should exceed the above-mentioned value by more than 0.03%.
In conclusion, the total content of alloy elements in steel should be strictly limited in accordance with the above-mentioned national standard, so as to ensure the quality and performance of the steel used.
