Engineering Guide · 2 min read
Chromium and Molybdenum in GB/T 3077: Comparing 40Cr, 35CrMo and 42CrMo
How do 40Cr, 35CrMo and 42CrMo differ? Compare GB/T 3077 carbon, chromium and molybdenum ranges, tempering response and related ML cold-heading grades.
The short answer: 40Cr is a chromium steel; 35CrMo and 42CrMo are chromium–molybdenum steels with different carbon ranges for hardening and tempering. [1] [2]
These grades serve two heat-treatment needs: hardening through the section during quenching and retaining hardness during tempering. GB/T 3077-2015 defines the general structural grades, including their carbon, chromium and molybdenum ranges. [1] [2]
This article is part of the Chinese GB/T steel grades series.
The chromium and CrMo grade families
The chromium series includes 20Cr, 30Cr, 35Cr, 40Cr and 45Cr. The chromium–molybdenum series includes 15CrMo, 20CrMo, 25CrMo, 30CrMo, 35CrMo and 42CrMo. The carbon number identifies the approximate carbon level; Cr and Mo identify the principal alloy additions.
For fastener stock, cold-heading wire-rod names include ML20Cr, ML30Cr, ML35Cr, ML40Cr, ML35CrMo, ML40CrMo and ML42CrMo. GB/T 28906-2025 defines those ML grades in its own tables. The examples below state the supply document on each row.
40Cr, 35CrMo and 42CrMo chemical composition
| Grade | Supply standard | C (%) | Mn (%) | Cr (%) | Mo (%) |
|---|---|---|---|---|---|
| 40Cr | GB/T 3077-2015 | 0.37–0.44 | 0.50–0.80 | 0.80–1.10 | — |
| 35CrMo | GB/T 3077-2015 | 0.32–0.40 | 0.40–0.70 | 0.80–1.10 | 0.15–0.25 |
| 42CrMo | GB/T 3077-2015 | 0.38–0.45 | 0.50–0.80 | 0.90–1.20 | 0.15–0.25 |
| ML40Cr | GB/T 28906-2025 | 0.38–0.43 | 0.60–0.90 | 0.90–1.20 | — |
| ML35CrMo | GB/T 28906-2025 | 0.33–0.38 | 0.60–0.90 | 0.90–1.20 | 0.15–0.25 |
| ML40CrMo | GB/T 28906-2025 | 0.38–0.43 | 0.60–0.90 | 0.90–1.20 | 0.15–0.25 |
| ML42CrMo | GB/T 28906-2025 | 0.40–0.45 | 0.70–1.00 | 0.90–1.20 | 0.15–0.25 |
Composition values are mass percentages. Selected heat-analysis ranges from the stated standard, Table 1 or Table 3 respectively. A dash indicates no specified Mo alloy addition is listed in this selected-element table. [1] [3]
Chromium and molybdenum ranges
40Cr and 35CrMo share the listed Cr interval, while 35CrMo adds Mo 0.15–0.25%. 42CrMo has a slightly higher specified Cr range.
What the alloying system adds
Chromium increases hardenability and resistance to temper softening. Molybdenum also increases hardenability; its carbide-forming role helps retain hardness during tempering. [2]
Compared with 35# or 45# carbon steel, CrMo grades add alloying elements that affect both quenching and tempering. The ML20MnTiB boron-steel route chiefly uses trace boron to assist hardenability at relatively low carbon.
Section size and the tempering cycle determine how useful those additions are. Compare the required hardness through the section after tempering, together with the stock condition needed for forming.
Where 20Cr and ML20Cr belong
GB/T 28906-2025 lists ML15Cr and ML20Cr as surface-hardening grades. Selection includes the required hardened surface and core properties of the part, as well as the bulk chemistry. [3]
ML35CrMo, ML42CrMo and CrMoV extensions
ML35CrMo follows the approximate 0.35% carbon convention. ML40CrMo and ML42CrMo are separate GB/T 28906-2025 grades; ML42CrMo has higher specified carbon and manganese intervals than ML40CrMo.
The same standard includes ML20CrMoV, ML35CrMoV and ML42CrMoV. V identifies vanadium. [3]
The next article changes the manufacturing route
MFT8, MFT9 and MFT10 non-quenched-and-tempered steels offer a different production choice: develop the required properties through rod processing and cold working, omitting the conventional final quench-and-temper operation.
Browse the HexFastener homepage or submit a drawing with the required material callout.
References
- GB/T 3077-2015 — Alloy structure steels. Table 1; chromium and chromium–molybdenum grades.
- Nippon Steel — Special Steel Strip. Printed pages 29–30; general effects of alloying and heat treatment.
- GB/T 28906-2025 — Hot-rolled steel wire rod for cold heading. Official online text; Clause 4 and Tables 1–6.