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GB/T 20878-2024: PDF in English (GBT 20878-2024)

GB/T 20878-2024 GB NATIONAL STANDARD OF THE PEOPLE’S REPUBLIC OF CHINA ICS 77.140.20 CCS H 40 Replacing GB/T 20878-2007 Stainless steels - Designation and chemical composition ISSUED ON: JULY 24, 2024 IMPLEMENTED ON: FEBRUARY 01, 2025 Issued by: State Administration for Market Regulation; Standardization Administration of the People's Republic of China. Table of Contents Foreword ... 3 1 Scope ... 5 2 Normative references ... 5 3 Terms and definitions ... 5 4 General guidelines for determining chemical composition limits ... 6 5 Methods for indicating designations and unified digital codes ... 8 6 Stainless steel designations and unified digital codes, their chemical composition and applications... 8 Annex A (normative) Methods for indicating stainless steel designations and unified digital codes ... 32 Annex B (informative) Physical performance parameters of some stainless steel designations in this document ... 38 Annex C (informative) Comparison table of stainless steel designations in this document and foreign standard stainless steel designations (or similar designations) 50 Bibliography ... 70 Stainless steels - Designation and chemical composition 1 Scope This document specifies the designations and unified digital codes of stainless steel and their chemical composition. It also provides the physical properties of some designations, and a comparison table of designations and unified digital codes with foreign standard designations (or similar designations). The stainless steel designations, unified numerical codes and chemical compositions specified in this document are applicable to guiding the formulation and revision of stainless steel (including ingots and semi-finished products) product standards. NOTE: In this document, the content of each element representing the chemical composition of stainless steel is expressed in mass fraction. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. GB/T 8170, Rules of rounding off for numerical values & expression and judgement of limiting values 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 stainless steel Steel containing at least 10.5% chromium (mass fraction) and not more than 1.2% carbon (mass fraction). NOTE: Stainless steel is divided into corrosion-resistant steel, heat-resistant steel and creep- resistant steel according to its main characteristics. 3.2 austenitic stainless steel Stainless steel that the matrix is mainly composed of austenite with a face-centered cubic crystal structure, which is mainly strengthened by cold working or nitrogen alloying. 3.3 austenitic-ferritic (duplex) stainless steel Stainless steel with a matrix consisting of both austenite and ferrite phases (the content of the lesser phase is at least 25%) that can be strengthened by cold working. 3.4 ferritic stainless steel Stainless steel that the matrix is mainly composed of ferrite with a body-centered cubic crystal structure, which generally cannot be hardened by heat treatment, but can be slightly strengthened by cold working. 3.5 martensitic stainless steel Stainless steel that the matrix is mainly composed of martensite with a distorted centroidal cubic crystal structure, and its mechanical properties can be adjusted by heat treatment. 3.6 precipitation hardening stainless steel Stainless steel with a matrix mainly composed of martensite or austenite structure, which can be hardened (strengthened) by precipitation hardening (also known as aging hardening). 4 General guidelines for determining chemical composition limits 4.1 Carbon When the carbon content is greater than or equal to 0.04%, it is recommended to take two decimal places. When the carbon content is equal to or less than 0.030%, it is recommended to take three decimal places. 4.2 Silicon Unless used as an alloying element, the silicon content of pipes and related products shall not exceed 0.75%, and the silicon content of long strips and forgings shall not exceed 1.00%. For designations that produce both long strips and flat products, the silicon content shall not exceed 1.00%. The choice of the lower or higher limit value is determined by the specific product technical requirements. 4.3 Manganese The manganese content of austenitic stainless steel (except Cr-Mn-Ni or Cr-Mn-Ni-N steel) shall not exceed 2.00%. The manganese content of other types of stainless steel shall not exceed 1.00%. But it does not include free-cutting steel containing high sulfur or selenium or steel that needs to increase nitrogen solid solubility. 4.4 Phosphorus 5 Methods for indicating designations and unified digital codes 5.1 The methods for indicating stainless steel designations shall comply with the provisions of A.1 in Annex A. 5.2 The unified numerical code for stainless steel designations shall comply with the provisions of A.2. 5.3 Each unified digital code is only applicable to one standard designation. Conversely, each standard designation only corresponds to one unified digital code. When a standard designation is cancelled, generally speaking, the original corresponding unified digital code will no longer be assigned to another standard designation. NOTE: The unified digital code system for standard stainless steel designations is uniformly compiled and managed by the committee to which this document is affiliated (SAC/TC183/SC2). 6 Stainless steel designations and unified digital codes, their chemical composition and applications 6.1 Stainless steel is divided into five categories according to metallurgical characteristics: austenitic steel, austenitic-ferritic (duplex) steel, ferritic stainless steel, martensitic steel and precipitation hardening stainless steel. The designations and unified digital codes of various types of stainless steel and their chemical compositions are listed in Tables 1 to 5. a) Table 1 shows the designations, unified digital codes and chemical compositions for austenitic stainless steel. b) Table 2 shows the designations and unified digital codes as well as their chemical compositions for austenitic-ferritic (duplex) stainless steel. c) Table 3 shows the designations, unified digital codes and chemical compositions for ferritic stainless steel. d) Table 4 shows the designations, unified digital codes and chemical compositions for martensitic stainless steel. e) Table 5 shows the designations and unified digital codes and their chemical compositions for precipitation hardening stainless steel. 6.2 The chemical composition of the stainless steel designations in this document is determined based on the general criteria for the chemical composition limits of each element determined in Chapter 4. Due to special technical reasons, the chemical composition of the same stainless steel designation may vary slightly in the composition Annex A (normative) Methods for indicating stainless steel designations and unified digital codes A.1 Methods for indicating stainless steel designations A.1.1 General A.1.1.1 Stainless steel designations are indicated by combining chemical element symbols and Arabic numerals (A.1.1.2). The carbon content shall comply with the provisions of A.1.2. The content of other elements shall comply with the provisions of A.1.3. A.1.1.2 The Arabic numerals representing the content (mass fraction) of each element in the chemical composition of stainless steel shall be rounded to the specified number of digits in accordance with GB/T 8170. A.1.2 Carbon content Generally, two Arabic numerals are used to indicate the carbon content (in parts per ten thousand). For ultra-low carbon stainless steel with a carbon content not exceeding 0.030%, three Arabic numerals are used to indicate the carbon content (in parts per hundred thousand) and the following provisions shall be met. a) If only the upper limit is specified, if the carbon content upper limit is not greater than 0.10%, then 3/4 of the upper limit is taken to represent the carbon content (see Example 1). If the carbon content upper limit is greater than 0.10%, then 4/5 of the upper limit is taken to represent the carbon content (see Example 2). b) If upper and lower limits are specified, the average of the upper and lower limits is taken to express the carbon content (see Example 3). Example 1: When the upper limit of carbon content is 0.08%, the content is expressed as 06. When the upper limit of carbon content is 0.030%, the content is expressed as 022. When the upper limit of carbon content is 0.020%, the content is expressed as 015. Example 2: When the upper limit of carbon content is 0.20%, the content is expressed as 16. When the upper limit of carbon content is 0.15%, the content is expressed as 12. Example 3: When the carbon content is 0.16%~0.25%, 20 is used to represent the content. A.1.3 Main element content A.1.3.1 Use one or two Arabic numerals to indicate the average content of the main elements (except carbon) (in percent). If the average content of the main elements is less than 1.50%, only the elements shall be indicated in the designation, without indicating the content (see Examples 1 and 2). A.1.3.2 The main elements (except carbon) shall be arranged in descending order according to the element content. If the average content of two or more elements is equal, they shall be arranged in alphabetical order (see Example 3). If the same group of designations represent the same, "-1, -2, ..." can be added to the end of the designation to distinguish them (see Example 4). Example 1: For stainless steel with a carbon content of no more than 0.08%, a chromium content of 18.00%~20.00%, and a nickel content of 8.00%~11.00%, the carbon content is represented by 06, the average chromium content is 19%, and the average nickel content is 9.5% rounded to 10%, then its designation is represented by 06Cr19Ni10. Example 2: For stainless steel with a carbon content not exceeding 0.030%, a chromium content of 20.00%~22.00%, a nickel content of 23.50%~25.50%, a molybdenum content of 6.00%~7.00%, and a nitrogen content of 0.18%~0.25%, the carbon content is represented by 022; the average chromium content is 21%, the average nickel content is 24.5% revised to 24%, the average molybdenum content is 6.5% revised to 6%, and the average nitrogen content is 0.22% (the content is not indicated), then its designation is 022Ni24Cr21Mo6N, not 022Cr21Ni25Mo7N. Example 3: If the copper content and molybdenum content in 05Cr21Ni10Mn3Cu2Mo2N are the same, the copper element comes before the molybdenum element in alphabetical order. Example 4: 022Cr18NbTi-1 and 022Cr18NbTi. A.2 Methods for indicating unified digital code for stainless steel designations A.2.1 The unified digital code ISC (Iron and Steel Code) for stainless steel designations uses the English letter "S" as the prefix (the first letter of "Stainless"), followed by five Arabic numerals. The numbering rules are shown in Figure A.1. borrowed from the four digits in the American AISI or UNS system (see Examples 1 and 2); otherwise, the second and third digits indicate the average chromium content (in percentage), the fourth digit indicates the presence of special elements in the steel [but the average manganese content (in percentage) is used for manganese-added steel, see Example 3], and the fifth digit indicates the steel type or the serial number of the designation in the same steel group (see Example 4). Example 1: For 022Cr23Ni4MoCuN, the unified digital code is S23043, where the first four digits 2304 are borrowed from the four digits of the American AISI system 2304, and the fifth digit 3 indicates ultra-low carbon steel (carbon content not more than 0.030%). Example 2: For 022Cr25Ni7Mo4CuN, the unified digital code is S25203, where the first four digits 2520 are borrowed from the last four digits of the US UNS system S32520, and the fifth digit 3 indicates ultra-low carbon steel (carbon content not more than 0.030%). Example 3: For 022Cr21Mn3Ni3Mo2N, the unified digital code ISC is S22133, where the first digit 2 represents austenitic-ferritic (duplex) stainless steel, the second and third digits 21 represent the average chromium content, the fourth digit 3 represents the average manganese content, and the fifth digit 3 represents ultra-low carbon steel (carbon content not more than 0.030%). Example 4: For 12Cr21Ni5Ti, the unified digital code ISC is S22160, where the first digit 2 represents austenitic-ferritic (duplex) stainless steel, the second and third digits 21 represent the average chromium content, the fourth digit 6 represents the addition of titanium, and the fifth digit 0 represents the sequence number. A.2.4 For austenitic stainless steel S3××××, the first, second and third digits are used as the steel group, borrowing the three-digit number of the American AISI or UNS system; the fourth digit indicates that the steel contains special elements, and the fifth digit indicates the steel type or the serial number of the designation in the same steel group, see Example 1; but the last four digits of some designations are borrowed from the last four digits of the American AISI or UNS system (see Example 2). For Cr-Mn- Ni or Cr-MnNi-N stainless steel, 35× is used as the steel group (see Example 3), and the third digit × represents the following meanings: 0 -- blank or sequence number; 1 - - low chromium series (the upper limit of chromium content is generally not more than 16.5%); 2 -- low nickel series (corresponding to the 204 series in the AISI or UNS system of the United States); 3 -- manganese content is about 5%~8% (corresponding to the 201 series in the AISI or UNS system of the United States); 4 -- manganese content is about 7%~10% series (corresponding to the 202 series in the AISI or UNS system of the United States); 5 -- manganese content is about 10%~13% (manganese content is higher than the 202 series in the AISI or UNS system of the United States); 6 -- nickel content is lower than the 202 series in the AISI or UNS system of the United States; 7 -- high chromium and high nickel series; 8 -- molybdenum-added steel series, 9 -- blank or sequence number. Example 1: For 06Cr19Ni10, the unified digital code ISC is S30408, where the first digit 3 represents austenitic stainless steel, the first, second and third digits 304 represent the steel group (corresponding to AISI's 304), the fourth digit 0 represents the sequence number, and the fifth digit 8 represents low carbon steel (carbon content not more than 0.08%). Example 2: For 022Ni25Cr21Mo7N, the unified digital code ISC is S38367, where the first digit 3 represents austenitic stainless steel, and the last four digits 8367 borrow the last four digits of UNS N08367. Example 3: For 12Cr17Mn6Ni5N, the unified digital code ISC is S35350, where 353 represents the Cr-Mn-Ni- N steel group, the third digit 3 indicates that the manganese content is about 5%~8% (corresponding to AISI201), the fourth digit 5 indicates the addition of nitrogen, and the fifth digit 0 is the sequence number. A.2.5 For martensitic stainless steel S4××××, the first, second and third digits are used as the steel group, and are arranged using the three-digit number system of the American AISI and UNS systems; the fourth digit indicates that the steel contains special elements, and the fifth digit indicates the steel type or the serial number of the designation within the same steel group, see Examples 1 and 2. Example 1: For Y12Cr13, the unified digital code ISC is S41617, where the first digit 4 represents martensitic stainless steel, the first, second and third digits 416 represent the steel group (corresponding to AISI's 416), the fourth digit 1 represents the sequence number, and the fifth digit 7 represents free-cutting steel. Example 2: For 13Cr13Mo, the unified digital code ISC is S41092, where the first digit 4 represents martensitic stainless steel, the first, second and third digits 410 represent the steel group (borrowed from AISI's 410), the fourth digit 9 represents the addition of molybdenum, and the fifth digit 2 represents the sequence number. A.2.6 For precipitation hardening stainless steel S5××××, the second, third, fourth and fifth digits are numbered according to the two elements Cr-Ni and their contents, where the second and third digits represent the average chromium content (in percent), and the fourth and fifth digits represent the average nickel content (in percent), see Example ......
 
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.