Special steel, that is, special steel, is the most important type of steel used in most industries of the national economy, such as machinery, automobiles, military industry, chemical industry, household appliances, ships, transportation, railways and emerging industries. According to the purpose, special steel can be divided into high-quality carbon structural steel, alloy structural steel, carbon tool steel, alloy tool (die) steel, high-speed tool steel, bearing steel, spring steel (carbon spring steel and alloy spring steel) ), stainless steel (heat-resistant, acid-resistant) eight categories. Except for high-quality carbon structural steel, carbon tool steel and carbon spring steel, the rest are alloy steel, and alloy steel accounts for about 70% of special steel. According to the technical content and product grade, it is roughly divided into three levels: high, medium and low: one is low-end special steel products based on high-quality carbon structural steel (carbon steel); th…