In principle, alloy steel is divided into low alloy steel, medium alloy steel and high alloy steel. As the name implies, it is distinguished by the total amount of alloying elements. The total amount is less than 3%, which is called low alloy steel, and 5 to 10% is Medium alloy steel, more than 10% high alloy steel. In the domestic custom, special quality carbon steel and alloy steel are called special steel, and 31 special steel enterprises in the country specialize in producing such steel, such as high-quality carbon structural steel, alloy structural steel, carbon tool steel, alloy tools. Steel, high speed tool steel, carbon spring steel, alloy spring steel, bearing steel, stainless steel, heat resistant steel, electrical steel, but also high temperature alloys, corrosion resistant alloys and precision alloys. In the classification of steel, although efforts have been made to move toward international standards in recent years, there are still many differences.
1 With the development of special steel to “special”, “fine” and “high”, extending to deep processing, the field of special steel is becoming narrower. The US Special Steel Association has positioned special steel in tool steel, stainless steel, electrical steel, superalloys and nickel alloys. Japan categorizes structural steel and high-strength steel in the special steel category. With the technological transformation and technological progress of China's general steel enterprises, the product field of special steel enterprises is also shrinking. In 1999, the general steel products factory has produced 34% of the total special steel products.
2 Foreign low-alloy steel is actually a low-alloy high-strength steel that we are familiar with. It belongs to the special steel category. It is called high-strength low-alloy steel (HSLA-Steel) in the United States, and low-alloy construction steel in Russia and Eastern European countries. Japan is named high tensile steel. In China, the first is to put low-alloy steel into the scope of the general steel, the conceptual difference leads to differences in product quality. It has also changed in name, such as low-alloy construction steel, ordinary low-alloy steel, low-alloy structural steel, and was called low-alloy high-strength structural steel (GB/T1591-94) in 1994. So far, from the published literature, the name of low-alloy steel still varies with countries, companies and authors.
3 The concept clearly drawn between low-alloy steel and carbon steel, low-alloy steel and alloy steel does not exist. In foreign countries, low-alloy steel was defined in the 1950s. The general meaning is that all alloying elements are below 3%, yield strength is above 275Mpa, and it has good processability and corrosion resistance. Steel, plate, tube and other steel shapes, a substitute for mild steel directly used in hot rolling. Of course, in the process of technological development, low-alloy steels have changed a lot in terms of alloy content, performance levels and delivery status.