How to represent alloy with letters?

The standard commonly used in the UK is the BS standard (BritishStandsrd). This set of standards does not have a complete and unified method for expressing grades. In the past, carbon steel, alloy steel, stainless steel, and heat-resistant steel often used the "EnXX" series to represent grades. This representation method is mainly divided according to the use. It cannot represent the main components of tapped steel, and there is no reasonable classification. New grades cannot be inserted. Taking into account the shortcomings of this grade representation method and the use of computers, the British Standards Institution has decided to use a fixed-digit number system as the basis of the new steel grade system, and selected a 6-digit number system to obtain sufficient adaptability. In 1967, 1968, and 1969, new standards for stainless steel (including heat-resistant steel), carbon steel (including free-cutting carbon steel), and alloy steel (including alloy structural steel, spring steel, etc.) were proposed in the form of PD6290, PD6423, and PD6431 documents. branding system. This grade system basically refers to the numerical system of the American Iron and Steel Institute (AISI). New standards such as BS970 have been adopted. The new grade system for carbon steel, alloy steel, and stainless steel has a 6-digit symbol (the 4th digit in the middle is a Latin letter, and the rest are numbers). The basic structure is as follows: 1. Carbon steel The first digit of carbon steel (from left to right) is 0, 1, 2, which means the following: 0 - represents ordinary carbon steel with manganese content (generally Mn content is 1.00% (below); 1—Indicates carbon steel with a higher manganese content (generally the Mn content is above 1.00%); 2—Indicates free-cutting carbon steel. The meanings of the second and three digits are as follows: For carbon steel with ordinary manganese content, it represents the value of a few ten thousandths of the average manganese content; for carbon steel with higher manganese content, add the first digit*** The same value indicates the average manganese content in ten thousandths; for free-cutting carbon steel, it indicates the minimum or average sulfur content in ten thousandths. The fourth digit is an English letter (A, M, H), indicating the supply conditions. The meaning of the letters is as follows: A - guaranteed chemical composition ("A" is the first letter of "Analyse"); M - guaranteed mechanical properties (" M" is the first letter of "Mechanical"); H - Guaranteed hardenability ("H" is the first letter of "Hardenability"). The fifth and sixth digits indicate the average carbon content in ten thousandths. 2. Alloy steel (including spring steel, alloy structural steel, bearing steel) The first digit is 5-9. The first, second and third digits are used to represent the alloy series group. The fourth digit is an English letter (A, M, H), indicating the supply conditions, and the meaning of the letters is the same as that of carbon steel. The fifth and sixth digits indicate the average carbon content in ten thousandths. Examples of alloy steel grade expression methods are shown in Table 3-1-12. 3. Stainless steel (including heat-resistant steel and valve steel) The first digits are 3 and 4, among which: 3—is austenitic stainless steel series; 4—is martensite and ferrite stainless steel series. The second and third digits represent the sequence numbers of different groups, and most commonly used grades are consistent with the American Iron and Steel Institute (AISI) number system. The fourth digit is the English letter "S", which represents the broad characteristics of this type of steel ("S" is the first letter of "Stainless"). The fifth and sixth digits represent the distinguishing codes of different grades in steel groups with the same basic composition. For example, it is generally stipulated that "01" is the basic composition number of this steel group, while 11-99 is a rigid rule, and there is no obvious rule.