1. Chemical Composition
Table 1 – Chemical composition, mass fraction %
| No. | Unified digital code | Grade | Chemical composition (mass fraction)/% | |||||
|---|---|---|---|---|---|---|---|---|
| C | Si | Mn | P | S | Alₜ | |||
| 10 | U40208 | ML20Al | 0.18〜0.23 | ≤0.10 | 0.30〜0.60 | ≤0.035 | ≤0.035 | ≥0.020 |
| When determining acid-soluble aluminum Al, Al≥0.015%. | ||||||||
When determining acid-soluble aluminum Al, Al≥0.015%.
2. Mechanical Properties
Table 2 Tensile strength, reduction of area, and hardness of HD process steel wire
2.1 For cold heading wire produced by the HD process, tensile strength and reduction of area shall comply with the requirements specified in Table 2.
| Grade a) | Nominal wire diameter d / mm | Tensile strength Rm / (N/mm²) | Reduction of area Z / % | Rockwell hardness b) / HRB |
|---|---|---|---|---|
| ML18MnAl ML20Al ML20 ML22MnAl | ≤3.00 | ≥850 | ≥35 | — |
| >3.00〜4.00 | ≥690 | ≥40 | — | |
| >4.00〜5.00 | ≥570 | ≥45 | — | |
| >5.00〜25.00 | ≥480 | ≥45 | <97 | |
| Note: For nominal wire diameters greater than 20 mm, the reduction of area may be reduced by 5%. | ||||
| a) The chemical composition of the grades may refer to GB/T 6478. b) Hardness values are for reference only. | ||||
Note: For wire with a nominal diameter greater than 20 mm, the reduction of area may be reduced by 5%. a) The chemical composition of the grades may refer to GB/T 6478. b) Hardness values are for reference only.
Table 3 Tensile strength, reduction of area, and hardness of wire produced by the SALD process
2.2 For cold heading wire produced by the SALD process, the tensile strength and reduction of area shall comply with the requirements specified in Table 3.
| Grade a) | Tensile strength Rm/ (N/mm²) | Reduction of area Z / % | Rockwell hardness b) HRB |
|---|---|---|---|
| ML18Mn ML20Al ML20 ML22Mn | 450〜570 | >65 | <90 |
| Note: For nominal wire diameters greater than 20 mm, the reduction of area may be reduced by 5%. | |||
| a) The chemical composition of the grades may refer to GB/T 6478. b) Hardness values are for reference only. | |||
Note: For wire with a nominal diameter greater than 20 mm, the reduction of area may be reduced by 5%. a) The chemical composition of the grades may refer to GB/T 6478. b) Hardness values are for reference only.
2.3 The mechanical properties of wire with a nominal diameter greater than 25.00 mm shall be determined by agreement between the supplier and the purchaser.
2.4 The mechanical properties of wire grades not listed in the table shall be determined by agreement between the supplier and the purchaser.
2.5 Upsetting Cold heading wire produced by the HD process: Wire samples shall show no cracks or fissures after being cold upset to one-half of their original height. Cold heading wire produced by the SALD process: Wire samples shall show no cracks or fissures after being cold upset to one-third of their original height. No upsetting test is required for wire with a diameter ≤ 5.0 mm.
2.3 The mechanical properties of wire with a nominal diameter greater than 25.00 mm shall be determined by agreement between the supplier and the purchaser.
2.4 The mechanical properties of wire grades not listed in the table shall be determined by agreement between the supplier and the purchaser.
2.5 Upsetting Cold heading wire produced by the HD process: Wire samples shall show no cracks or fissures after being cold upset to one-half of their original height. Cold heading wire produced by the SALD process: Wire samples shall show no cracks or fissures after being cold upset to one-third of their original height. No upsetting test is required for wire with a diameter ≤ 5.0 mm.
3. Microstructure
Table 4 Permissible range for decarburized layer depth
| Table 4 Permissible range for decarburized layer depth | Unit: mm | |
|---|---|---|
| Nominal wire diameter/d | Depth of complete decarburization | Total decarburized layer depth |
| <10.00 | ≤0.02 | ≤0.01 d |
| ≥10.00—15.00 | ≤0.02 | ≤0.15 |
| ≥15.00〜25.00 | ≤0.03 | ≤0.20 |
| Note: When the nominal wire diameter exceeds 25.00 mm, the permissible range for decarburized layer depth shall be determined by agreement between the supplier and the purchaser. | ||
6.1 Microstructure For wire produced by the SALD process, the microstructure shall be spheroidized. The spheroidizing grade shall be agreed upon by the supplier and the purchaser and assessed in accordance with JB/T 5074. The test method for the decarburized layer shall be determined by agreement between the supplier and the purchaser.
6.2 Decarburized layer depth Wire produced by the SALD process shall undergo decarburization testing. The permissible ranges for the depth of complete decarburization on one side and the total decarburized layer depth (ferrite + transition layer) shall comply with the provisions of Table 4. The test method for the decarburized layer shall be determined by agreement between the supplier and the purchaser.
6.3 Carburization Wire produced by the SALD process shall not exhibit surface carburization. Testing may be omitted if guaranteed by the supplier.
4. Comparison table of non-heat-treated cold heading steel grades with domestic and international equivalents; see Table B.1 for grade comparisons.
Table B.1 Cross-reference of non-heat-treated cold heading steel grades with domestic and international equivalents
| Unified digital code | This standard | GB/T 6478 | ISO 4954 | EN 10263-2 | JIS G3507-1 | ASTM A29/A29M |
|---|---|---|---|---|---|---|
| U40208 | ML20Al | ML20Al | CC21A | C20C | SWRCH20A | 1020 |