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"Steel Classification" (GB/T 13304) is divided into 2 parts:
- Part 1: Classification of according to Chemical Composition;
- Part 2: Classification of according to Main Quality Classes and Main Property or Application Characteristics
This part is Part 1 of "Steel Classification" (GB/T 13304).
This part is modified in relation to "Steel - Classification - Part 1: Classification of Steels into Unalloyed and Alloy Steels Based on Chemical Composition" (ISO 4948-1:1982).
Compared with ISO 4948-1: 1982, the main changes in this part are as follows:
- Basic principles for low alloy steel and its classification were added according to the actual situations in China;
- Editorial changes were conducted for Chapter 3 and requirements for significant digits were added;
- The limit for content of element (like B, Cu, Mn, Mo, Nb, V and La) specified for unalloyed steel was modified;
- The limit for content of element (like B, Cu, Mn, Mo, Ni, Si, Ti, V and Zr) specified for alloy steel was modified.
- Table 1 was changed to Table A.1 in Appendix.
Those technical differences have already been marked with perpendicular single line on the margin of relevant clauses for the convenience of comparison.
This part replaces Part 1 of "Steel Classification" (GB/T 13304-1991).
Compared with Part 1 of GB/T 13304-1991, the main changes in this standard are as follows:
- Editorial changes were conducted for Chapter 3 (see Chapter 3);
- Example description was added to the original Article 3.1.2.1 (Article 3.1.2.1 in 1991 edition and Article 3.2.2 in this edition);
- “Unless otherwise negotiated for the contract or order, the limits specified in the table for the elements of Bi, Pb, Se, Te and La series and other specified elements (except S, P, C and N) shall not be considered for custom tariff purposes for demarcating unalloyed and alloy steels” was added to Table 1 (see Table 1);
- "Limit for Element Content of Unalloyed Steel and Alloy Steel Specified in ISO 4948-1" was added (see Appendix A).
Appendix A of this Part is informative.
This part was proposed by China Iron and Steel Association.
This part is under the jurisdiction of the National Technical Committee on Iron and Steel of Standardization Administration of China.
Drafting organizations of this part: Metallurgical Information and Standardization Institute and Shougang Group.
Chief drafting staff of this part: Luan Yan, Dai Qiang, Wang Liping and Liu Baoshi.
This part was firstly issued in December, 1991.
Steels Classification - Part 1: Classification of according to Chemical Composition
鋼分類 第1部分：按化學成分分類
1 Scope
This part specifies a basic classification rule of steels into unalloyed, low alloy and alloy steels based on chemical composition as well as the basic limit for the element content in above steels.
This part is applicable to the classification of steels according to chemical composition.
2 Term and Definition
For the purpose of this part, the following term and definition apply.
2.1 Steel
A material with iron as the predominant element, having a carbon content generally less than 2% and containing other elements.
Note: a limited number of chromium steel may have more than 2% carbon, but 2% is the usual dividing line between steel and cast iron.
3 Classification
The classification of steels according to chemical composition is as follow:
a) unalloyed steels;
b) low alloy steel;
c) alloy steels.
3.1 Basic principles
3.1.1 Where a minimum value or range is specified for the ladle analysis of the chemical compositions given in the standard, specification or the order, the minimum value shall be taken for classification.
3.1.2 Where a maximum value is specified for the ladle analysis of the chemical compositions given in the standard, specification or the order, the 0.7 time of this maximum value shall be taken for classification.
3.1.3 Where there is no standard, specification or ordered composition, the ladle analysis reported by the manufacturer shall be taken for classification. Under special circumstances, where only analyzed value of steel product is available, the analysis analyzed value of product may be taken for classification. In case of critical condition between the above two situations, the effect of permissible deviation of chemical composition shall be considered and the originally preset classification of steel shall be accurately certified.
3.1.4 The element content specified in standard, specification or order or the residual content of element existing in the steel not purposely added as alloying element shall not be taken for classification.
3.1.5 All specified, calculated or actual ladle analysis values (expressed in mass fraction) of each alloying element shall be accurate to the same digit with the limits shown in Table 1.
3.2 Classification method
3.2.1 Where the content (expressed in mass fraction) for each element (listed in Table 1) is within the range of corresponding element specified for unalloyed steel, low alloy steel or alloy steel according to that specified in Section 3.1, such steel shall be respectively regarded as unalloyed steel, low alloy steel or alloy steel.
3.2.2 Where two or more elements of Cr, Cu, Mo and Ni are simultaneously specified in steels, the specified content of each element shall be simultaneously considered for the low alloy steel; the sum of specified content of such elements shall not be larger than the 70% the sum of their upper limits specified in Table 1, otherwise they shall be classified into alloy steel even though the specified content of each element is lower than the specified upper limit.
Examples:
The chemical compositions (mass fraction) for ladle analysis of certain designation specified in certain product standard respectively are: Cr: 0.40%~0.49%, Ni: 0.40%~0.49%, Mo: 0.05%~0.08%, Cu: 0.35%~0.45%; the remaining is residual element.
First, the specified content (mass fraction) for Cr, Ni, Mo and Cu of such designation are: Cr 0.40%, Ni 0.40%, Mo 0.05%, Cu 0.35%; all of them are with the range of “low alloy steel” specified in Table 1, therefor they shall be classified into low alloy steel.
Second, the “sum of specified content” of Cr, Ni, Mo and Cu is compared with “70% the sum of upper limit of each element” (expressed in mass fraction).
the “sum of specified content” of Cr, Ni, Mo and Cu of such designation is:
0.40%+0.40%+0.05%+0.35%=1.20%
“70% the sum of upper limit of each element” of Cr, N, Mo and Cu for low alloy steel as specified in Table 1 is:
(0.50%+0.50%+0.10%+0.50%)×70%=1.12%
Obviously, the “sum of specified content” (1.20%) of Cr, Ni, Mo and Cu is greater than“70% the sum of upper limit of each element” (1.12%) of such elements, so such designation shall be classified into “alloy steel”.
3.2.3 The principle specified in Article 3.2.2 is also applicable to Nb, Ti, V and Zr.
Table 1 Limit for Element Content Specified for Unalloyed Steel, Low Alloy Steel and Alloy Steel
Alloying element Specified content limit for alloying element (mass fraction)/%
Unalloyed steel Low alloy steel Alloy steel
Al <0.10 — ≥0.10
B <0.0005 — ≥0.0005
Bi <0.10 — ≥0.10
Cr <0.30 0.30~<0.50 ≥0.50
Co <0.10 — ≥0.10
Cu <0.10 0.10~<0.50 ≥0.50
Mn <1.00 1.00~<1.40 ≥1.40
Mo <0.05 0.05~<0.10 ≥0.10
Ni <0.30 0.30~<0.50 ≥0.50
Nb <0.02 0.02~<0.06 ≥0.06
Pb <0.40 — ≥0.40
Se <0.10 — ≥0.10
Si <0.50 0.50~<0.90 ≥0.90
Te <0.10 — ≥0.10
Ti <0.05 0.05~<0.13 ≥0.13
W <0.10 — ≥0.10
V <0.04 0.04~<0.12 ≥0.12
Zr <0.05 0.05~<0.12 ≥0.12
La series (each element) <0.02 0.02~<0.05 ≥0.05
Other specified elements (except S, P, C and N) <0.05 — ≥0.05
Unless otherwise negotiated for the contract or order, the limits specified in the table for the elements of Bi, Pb, Se, Te and La series and other specified elements (except S, P, C and N) shall not be considered for custom tariff purposes for demarcating unalloyed and alloy steels.
Notes
1 Element content for La series may also be regarded as the total content of misch metal.
2 "-" in this Table means that such value is not specified and not taken for classification.
Foreword I
1 Scope
2 Term and Definition
3 Classification
Appendix A (Informative) Limit for Element Content of Unalloyed Steel and Alloy Steel Specified in ISO 4948
