The distinction between steel is based on the content and low alloy. We are now measuring five elements; the content of carbon, sulfur, manganese, silicon, and phosphorus. Sulfur and phosphorus are harmful things. There is a limit. National standards tell you that sulfur and phosphorus must be less than 0.045%. Qualified below 0.045%. The basic task of the tempering laboratory is to determine the five elements, detect impurities in steel, and most importantly measure carbon.
For example: how to identify some brands as a national standard in mechanics? There is a 20SiMn grade, the national unified standard. What does 20 refer to? 20 means the average carbon content does not exceed 0.20. What is the average number? The range is 0.17-0.25%. The average of the two numbers is about 0.20%. At first glance, the grade is 20. You know that it is about 0.2. From the delivery note, you can see that the amount of silicon and manganese alloy elements does not exceed 2%. The second type of steel is A3 called No. 3 steel. It is not accepted by chemical composition, but by mechanical properties. It is accepted by mechanical tests, tensile tests, and strength indicators. More or less in the composition is not a standard. It can only be For reference, this is the standard for steel.
Chemical composition classification
According to the chemical composition, steel can be divided into carbon steel and alloy steel. Carbon steel is an iron-carbon alloy, which contains a small amount of harmful impurities such as phosphorus and sulfur. Some Si and Mn added due to the need for deoxidation, according to the different carbon content, carbon steel is divided into three types: low carbon steel, medium carbon steel and high carbon steel. It is a low carbon steel, a steel higher than 0.60% is a high carbon steel, and a steel of 0.25% to 0.55% is a medium carbon steel.
Alloy steel is a type of steel that is intentionally added with a certain amount of other alloying elements in order to improve certain properties of the steel. For the purpose of alloying, steels whose content of Si and Mn exceeds the amount required for deoxidation are also included in the category of alloy steels. According to the types of main alloying elements contained in steel, alloy steel can be divided into Mn steel, Cr steel, SiMn steel, CrMo steel, CrMnMo steel, CrMnTi steel, CrMoV steel and many other types.
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