Engineering Guide · 3 min read
Low-Carbon Steel for Cold Heading: ML08Al, ML10 and ML20 (GB/T 28906)
What are ML08Al, ML10, ML15 and ML20? Explore GB/T 28906 chemistry, aluminum requirements and the incoming rod properties that matter for cold heading.
The short answer: ML08Al, ML10, ML15 and ML20 are low-carbon cold-heading steels supplied for forming fastener heads, with different carbon, silicon and aluminum requirements. [1] [2]
Cold heading compresses wire in dies to form the head. The stock must flow into the cavity without cracking, so cold-heading specifications address surface quality and deformation behavior as well as chemistry. [1] [2]
This article is part of the Chinese GB/T steel grades series.
The low-carbon ML family
The ML prefix identifies steel for cold heading and cold extrusion. The numbers indicate nominal carbon content. The Al-designated sequence includes ML04Al, ML06Al, ML08Al, ML10Al, ML12Al, ML15Al and ML20Al. Other low-carbon names include ML10, ML12, ML15 and ML20.
The parameters in this article use GB/T 28906-2025, the hot-rolled wire-rod specification. GB/T 6478-2015 remains the separate cold-heading and cold-extrusion steel specification. The specified product form and document establish the supply requirements.
ML08Al, ML10, ML15 and ML20 composition
| Grade | C (%) | Si (%) | Mn (%) |
|---|---|---|---|
| ML04Al | ≤0.06 | ≤0.10 | ≤0.60 |
| ML06Al | ≤0.08 | ≤0.10 | ≤0.60 |
| ML08Al | 0.05–0.10 | ≤0.10 | 0.30–0.60 |
| ML10Al | 0.08–0.13 | ≤0.10 | 0.30–0.60 |
| ML10 | 0.08–0.13 | 0.10–0.30 | 0.30–0.60 |
| ML15Al | 0.13–0.18 | ≤0.10 | 0.30–0.60 |
| ML15 | 0.13–0.18 | 0.10–0.30 | 0.30–0.60 |
| ML20 | 0.18–0.23 | 0.10–0.30 | 0.30–0.60 |
Composition values are mass percentages. Selected heat-analysis limits, Table 1. Al-designated grades have total Al 0.020–0.060%; acid-soluble Al is 0.015–0.055% when measured instead. [2]
ML08Al contains C 0.05–0.10%, with low silicon and a specified aluminum range. Aluminum acts as a deoxidizer in steelmaking. [3]
ML10Al and ML10 share a carbon range but have different silicon and aluminum provisions. ML15 and ML20 increase the carbon interval.
The carbon progression within low-carbon ML steel
The table spans C 0.05–0.10% in ML08Al to 0.18–0.23% in ML20. The rod structure and delivery condition also influence how readily the stock deforms during heading.
Parameters of the incoming hot-rolled rod
The following limits describe hot-rolled rod before it is drawn or headed. They set the permitted incoming strength and required tensile-test ductility.
| Grade | Maximum tensile strength Rm (MPa) | Minimum reduction of area Z (%), diameter ≤12 mm |
|---|---|---|
| ML08Al | 410 | 65 |
| ML10 | 430 | 60 |
| ML15 | 460 | 55 |
| ML20 | 530 | 50 |
Selected requirements for hot-rolled, non-heat-treated-type wire rod, Table 6. The Z values shown apply only at rod diameter ≤12 mm; larger rod has different limits. Rm is an upper limit for the incoming rod. [2]
Reduction of area, Z, is the percentage decrease from the specimen’s original cross-sectional area to its minimum area at fracture. Across these four rod grades, the maximum permitted tensile strength rises from 410 to 530 MPa while minimum Z falls from 65% to 50%. These are distinct requirements for the strength and ductility of the incoming rod, rather than allowable deformation percentages for a finished head.
What this adds to ordinary carbon stock
Compared with the 35# and 35Mn numerical carbon-steel family, cold-heading stock adds requirements directed at forming the head, including surface quality and deformation behavior.
During upsetting, wire flows outward to fill the head cavity. Surface defects and inadequate ductility can lead to cracking, which is why the rod specification matters alongside the carbon grade.
Surface hardening and the next carbon range
GB/T 28906 lists these low-carbon grades in its non-heat-treated use category. It also permits ML15Al, ML15, ML20Al and ML20 in the surface-hardening category. For that route, specify the required surface-hardened layer and core properties of the part. [2]
When the selected production route instead calls for a medium-carbon cold-headed part followed by quenching and tempering, continue with ML35, ML40 and ML45 steel. That family increases the carbon range while retaining the cold-heading-stock purpose.
Browse the HexFastener homepage or submit a drawing with the required material callout.
References
- GB/T 6478-2015 — Steels for cold heading and cold extruding. Material specification and current status.
- GB/T 28906-2025 — Hot-rolled steel wire rod for cold heading. Official online text; Clause 4 and Tables 1–6.
- Nippon Steel — Special Steel Strip. Printed pages 29–30; general effects of alloying and heat treatment.