The short answer: an alloy steel grade is a chemistry designation defined by a specific standard. In 35CrMo to GB/T 3077-2015, “35” indicates a nominal average carbon content of about 0.35%; Cr and Mo identify chromium and molybdenum. The permitted composition is not calculated from the name—it must be read from the standard. That is why a complete material callout includes both the grade and the standard.[1] [2]
A material family is not a material grade
“Alloy steel” describes a broad family. “Chromium-molybdenum steel” narrows the family, but still covers many compositions. 35CrMo identifies one grade within that family, and 35CrMo to GB/T 3077-2015 ties the name to the document that defines its chemistry and technical requirements.
| Wording | What it identifies |
|---|---|
| Alloy steel | A broad material family |
| Chromium-molybdenum steel | A family grouped by important alloying elements |
| 35CrMo | A grade designation, but without the governing standard |
| 35CrMo to GB/T 3077-2015 | A traceable material grade and standard |
A complete purchasing specification identifies both the grade and its governing standard. Different systems use different designation rules, and the same-looking number does not carry a universal meaning.
Read a Chinese alloy structural steel grade from left to right
GB/T 221-2008 defines the notation used for Chinese steel grades. For alloy structural steel, the opening number, alloy-element symbols and any following numbers each have a specific job.[1]
| Part of the designation | Meaning under GB/T 221 | Example |
|---|---|---|
| First two digits | Nominal average carbon content in hundredths of a percent | “35” means about 0.35% C |
| Chemical symbols | Main alloying elements intentionally named in the grade | Cr = chromium; Mo = molybdenum |
| No number after an alloy symbol | Nominal average content of that element is below 1.50% | Cr and Mo in 35CrMo |
| Number after an alloy symbol | A rounded alloy-content band; “2” means 1.50–2.49%, not exactly 2% | Cr2 in 25Cr2MoV |
| Suffix A or E | A quality level defined by the material standard | A = high-grade quality; E = special-grade quality |
This makes 35CrMo easy to parse:
- 35 → nominal average carbon content of about 0.35%
- Cr → chromium is a named alloying element
- Mo → molybdenum is a named alloying element
- No numeral after Cr or Mo → each nominal average content is below 1.50%
Under Table 2 of GB/T 3077, ordinary quality steel has maximum phosphorus and sulfur contents of 0.030% each. The A suffix identifies high-grade quality steel, with maximum phosphorus and sulfur contents of 0.020% each. The E suffix identifies special-grade quality steel, with maximum phosphorus of 0.020% and sulfur of 0.010%. Add the suffix only when that quality level is ordered.[2]
The code gives a compact description, not the complete acceptance limits. Those limits come from the grade table in GB/T 3077.
The first number separates closely related Cr-Mo grades
GB/T 3077-2015 contains several chromium-molybdenum grades. Their names look similar because they use the same designation grammar. The table below shows three adjacent examples from the standard's ladle-analysis table.[2]
| Grade | C | Si | Mn | Cr | Mo |
|---|---|---|---|---|---|
| 35CrMo | 0.32–0.40% | 0.17–0.37% | 0.40–0.70% | 0.80–1.10% | 0.15–0.25% |
| 42CrMo | 0.38–0.45% | 0.17–0.37% | 0.50–0.80% | 0.90–1.20% | 0.15–0.25% |
| 50CrMo | 0.46–0.54% | 0.17–0.37% | 0.50–0.80% | 0.90–1.20% | 0.15–0.30% |
The opening number tracks the nominal carbon level: roughly 0.35%, 0.42% and 0.50%. It is not a strength ranking. A finished part's hardness and mechanical properties also depend on its delivery condition, heat treatment, size and applicable product requirements.
The element symbols identify the alloy system, but they do not show every controlled element or every permitted range. Silicon and manganese, for example, appear in the standard's composition table even though neither symbol appears in 35CrMo.
35CrMo, 4135, SCM435 and 34CrMo4 belong to different naming systems
Appendix A of GB/T 3077 places 35CrMo beside the following similar grades:[2]
| Standard named in GB/T 3077 Appendix A | Similar grade listed for 35CrMo |
|---|---|
| GB/T 3077-2015 | 35CrMo |
| EN 10083-3:2006 | 34CrMo4 |
| ASTM A29/A29M-2012 | 4135 |
| JIS G 4053:2008 | SCM435 |
These are not four spellings of one universal grade. Each designation belongs to its own standard, with its own composition limits, product scope and technical conditions. The appendix presents them as similar grades, not automatic substitutes.
For comparison or substitution, place the actual chemistry limits from both standards side by side. Then check product form, metallurgical-quality requirements, delivery condition and certificate requirements. A drawing that says only “35CrMo or equivalent” leaves the word “equivalent” undefined.
What the material grade does—and does not—tell you
A material grade identifies the specified steel chemistry and governing material standard. The mill certificate can then report the heat number and actual analysis against that grade.
It does not, by itself, identify the finished bolt's property class. 35CrMo and 10.9, for example, are different types of designation: the first names a steel grade; the second names mechanical requirements for a finished metric fastener. Keep them on separate lines of the specification rather than treating one as proof of the other. See Bolt Grades 8.8, 10.9 and 12.9 for the property-class side of that distinction.
How to write an unambiguous material callout
For a drawing or inquiry, state the material in this order:
- Exact grade: 35CrMo
- Governing material standard and edition: GB/T 3077-2015
- Required quality level or suffix, when applicable
- Required delivery or heat-treatment condition, when the material specification does not already settle it
- Material certificate, heat number and actual chemical analysis requirements
- Approved alternative grades and standards, if substitution is allowed
A concise material line could read: 35CrMo to GB/T 3077-2015; heat number and ladle analysis reported on the material certificate; substitutions require drawing approval.
That line identifies the material without pretending that the grade name also defines the finished fastener. Dimensions, mechanical class and other product requirements belong elsewhere on the drawing or inquiry.
References
- Standardization Administration of China. GB/T 221-2008 — Notations for Designation of Iron and Steel. Rules for carbon figures, alloy-element symbols and metallurgical-quality suffixes.
- Standardization Administration of China. GB/T 3077-2015 — Alloy Structure Steels. Composition limits for alloy structural steel grades and the informative comparison of similar foreign grades.
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