1. Chemical Composition
Chemical composition, mass fraction %, refers to GB 28906
2. Mechanical Properties
Table 5 Mechanical Properties of Boron-Containing Steel Wire
| Grade a) | BALANCE | SA | ||||
|---|---|---|---|---|---|---|
| Tensile strength Rm/MPa | Reduction of area Z / % | Rockwell hardness/HRB | Tensile strength Rm/MPa | Reduction of area z % | Rockwell hardness/HRB | |
| ML20B | ≤600 | ≥55 | ≤89 | ≤550 | ≥65 | ≤85 |
| Note: The reduction of area for steel wire with a diameter less than 3.00 mm is for reference only. | ||||||
| a) The chemical composition of grades may refer to GB/T 6478. | ||||||
2.1 For wire delivered in the HD condition, mechanical properties shall be determined by agreement between the supplier and the purchaser.
2.2 The mechanical properties of boron-containing steel wire in the delivery condition, with a nominal diameter not greater than 25.0 mm, shall comply with the requirements specified in Table 5.
2.3 When wire is delivered in straight lengths or in a polished condition, a 10% variation in mechanical properties is permitted.
2.4 For wire with a nominal diameter greater than 25.00 mm, the mechanical properties shall be determined by agreement between the supplier and the purchaser.
2.5 The mechanical properties for grades not listed in the table shall be determined by agreement between the supplier and the purchaser.
2.6 Upsetting: Wire samples shall be cold upset to one-half of their original height without surface cracks or fissures. By mutual agreement, upsetting may also be performed to one-third or one-quarter of the original sample height.
3. Microstructure
Table 6 Permissible range for decarburized layer depth
For spheroidizing annealed wire, the spheroidized microstructure may be inspected upon the purchaser's request and as specified in the contract; the acceptance criteria and test methods shall be agreed upon by the supplier and the purchaser.
| Nominal diameter of wire | Depth of complete decarburization | Total decarburized layer depth |
|---|---|---|
| ≤8.00 | ≤0.02 | ≤0.10 |
| >8.00-15.0 | ≤0.02 | ≤0.15 |
| >15.0-25.0 | ≤0.03 | ≤0.20 |
| >25.0-45.0 | By agreement | By agreement |
3.1 Decarburized layer: Upon the purchaser's request and as specified in the contract, the decarburized layer on the wire surface may be inspected. The permissible depth of the total decarburized layer (ferrite + transition zone) and the complete decarburized layer on one side shall comply with Table 6. Special requirements for the decarburized layer shall be determined by agreement between the supplier and the purchaser. For wire grades with a carbon content not greater than 0.30%, the test method shall be agreed upon by the supplier and the purchaser.
3.2 Carburization: The wire surface shall be free from carburization. Inspection may be omitted if the supplier can provide assurance.
4. Surface quality
4.1 The wire surface shall be smooth and free from cracks, scabs, folds, laminations, drawing marks, and rust. However, individual pits, raised surfaces, indentations, and scratches with a depth not exceeding half the diameter tolerance are permitted. Wire delivered in the annealed condition may exhibit oxidation colors on the surface.
4.2 Requirements for wire surface coatings shall be determined by mutual agreement between the supplier and the purchaser.