Ordering 35CrMo bar stock without pinning down one variable usually costs more than the material itself. Two prints can call out 34CrMo4 and 35CrMo for the same shaft, but one may arrive annealed at roughly 207 HB and the other quenched and tempered to 31 HRC. The turning speeds, tooling, and final inspection points must change accordingly. This grade is used where medium-carbon chromium-molybdenum steel needs higher hardenability than plain carbon steel, but the condition you machine in often matters more than the composition.
Grade Overlap and Specification Boundaries
35CrMo is the Chinese GB/T 3077 designation, while 34CrMo4 is the EN 10083-3 equivalent with material number 1.7220. The two are not identical in allowed chemistry. 35CrMo permits slightly higher carbon and manganese ranges in some cases, while 34CrMo4 has a tighter sulfur and phosphorus ceiling under EN standards. For a shaft or flange drawing that lists 35CrMo, a European mill certificate often reads 34CrMo4, and the substitution is generally accepted when the required mechanical properties after heat treatment are met.
Before quoting machined parts, confirm whether the print asks for the raw bar condition or the final heat-treated condition. This matters because the yield strength can move from below 550 MPa in a normalized bar to over 650 MPa after a proper oil quench and temper, and machinability changes with it. Compare other alloy steel grades when the drawing leaves the grade open.
Ladle Chemistry for 34CrMo4
The table below gives the chemical composition per EN 10083-3:2018 for 34CrMo4. Treat these as ladle analysis limits, not guaranteed values in every product form. For GB/T 3077 35CrMo, carbon may range 0.32–0.40%, manganese 0.40–0.70%, chromium 0.80–1.10%, and molybdenum 0.15–0.25%, depending on the specific steelmaking route.
| Element | Content % |
|---|---|
| Carbon (C) | 0.30–0.37 |
| Silicon (Si) | ≤0.40 |
| Manganese (Mn) | 0.60–0.90 |
| Phosphorus (P) | ≤0.025 |
| Sulfur (S) | ≤0.035 |
| Chromium (Cr) | 0.90–1.20 |
| Molybdenum (Mo) | 0.15–0.30 |
The chromium and molybdenum combination promotes through-hardening in sections where a plain 35 carbon steel would show a soft core. Molybdenum also reduces temper embrittlement, which is why this grade shows up in bolts and shafts that must hold impact energy after tempering.
Quenched and Tempered Mechanical Properties
Do not design around maximum tensile strength alone. For 34CrMo4, the minimum yield strength drops as the ruling section increases. The values below apply to quenched and tempered condition, oil quenched from approximately 830–860°C and tempered to the desired strength, for a ruling section of 16–40 mm. These are minimum or range values per EN 10083-3; actual mill test results are typically higher.
| Property | Value | Unit |
|---|---|---|
| Tensile strength Rm | 900–1100 | MPa |
| Yield strength ReH (0.2% offset) | ≥650 | MPa |
| Elongation A | ≥12 | % |
| Reduction of area Z | ≥55 | % |
| Impact energy KV at 20°C | ≥40 | J |
| Typical hardness after tempering | 28–34 | HRC |
For sections from 40 mm to 100 mm, the minimum yield strength falls to 550 MPa and tensile range to 800–950 MPa in the same +QT condition. If the drawing only states hardness, request the tensile and impact requirements too. Hardness alone will not catch low ductility or poor impact values caused by an improper temper.
Where 35CrMo Actually Goes
This grade is common in parts that need a balance of strength, toughness, and hardenability without the higher alloy cost of 42CrMo4. Specific examples include:
- Hydraulic cylinder piston rods for mobile equipment: Q&T to 650 MPa yield, then hard chrome plated or HVOF coated. The core toughness helps handle side loads and bending stress.
- Wind turbine anchor bolts and high-strength fastener bars: often specified as 10.9 class after quenching and tempering. Impact testing at -20°C is a frequent additional requirement.
- Downhole tool bodies and crossover subs in oil and gas drilling: 35CrMo resists shock loading while remaining machinable in the normalized condition before hardening.
- Off-highway transmission shafts and steering knuckles: induction hardening of bearing journals can use the base grade while the core remains tough.
- Medium-duty gear blanks and coupling hubs: when 42CrMo4 would be overkill but 40Cr lacks the specified impact energy.
The common thread is not just tensile strength. Parts made from 35CrMo typically see cyclic loading, stress concentration at threads or keyways, and a requirement to avoid brittle fracture after heat treatment.
CNC Machining 35CrMo: Baseline Cut Data
The table below assumes annealed or normalized stock at 190–220 HB, using coated carbide inserts and a rigid setup. If you are machining quenched and tempered material at 30–34 HRC, reduce speed by 30–40% and drop the depth of cut by about one-third. Always adjust based on tool overhang, fixture stiffness, and actual hardness readings.
| Operation | Speed | Feed | DOC |
|---|---|---|---|
| Rough turning (coated carbide) | 180–240 m/min | 0.20–0.35 mm/rev | 2.0–4.0 mm |
| Finish turning (coated carbide) | 220–280 m/min | 0.08–0.15 mm/rev | 0.3–0.8 mm |
| Face milling (indexable carbide) | 150–200 m/min | 0.10–0.20 mm/tooth | 1.0–3.0 mm |
| Drilling (HSS-Co, 10 mm drill) | 20–30 m/min | 0.12–0.20 mm/rev | Peck 3–5 mm |
For long shafts, use a follower rest or center support. The material does not work-harden aggressively like austenitic stainless steel, but chatter on a slender 35CrMo shaft can generate surface tears that become stress raisers after heat treatment.
Processing Pitfalls Before the Chip
One recurring issue is hard spots in hot-rolled 35CrMo bars. A normalized blank will usually machine more uniformly than an as-rolled bar with uneven cooling. If the bar has been flame cut, the heat-affected zone can reach 45 HRC locally. Remove the HAZ with roughing before finish turning; do not force a finish insert through it.
Another pitfall is chip control. This grade has low sulfur in most EN heats, so it does not produce the short chips of a free-cutting steel. Use a chipbreaker geometry designed for steel, and avoid letting long stringers wrap around the tool turret on rough OD turning. On CNC lathes, peck drilling or through-tool coolant is better than flooding for holes deeper than 3xD.
When parts need tight tolerances after heat treatment, machine to a roughing allowance of 0.2–0.5 mm per side, then quench and temper, then finish machine or grind. Do not assume a 34CrMo4 part will hold a 0.02 mm tolerance through heat treatment. Distortion is not just scale growth; asymmetry from keyways, bores, or uneven quenching will move features in ways that cannot be corrected by polishing alone. Review our heat treatment process notes before locking the machining sequence.
For finish milling, using an air blast instead of heavy coolant can reduce thermal cracking of carbide inserts in interrupted cuts. If the part is pre-hardened to 32 HRC, choose a C6 or C7 carbide grade with a tougher edge preparation. A sharp edge with positive rake will cut with less spindle load than a heavily honed edge, especially on small boring bars.
Specifying the Job So It Can Be Quoted Correctly
A vague print leads to broad quotes. For 35CrMo or 34CrMo4 parts, the critical information includes the starting bar condition, the required final hardness and tensile/yield values, the impact test temperature if any, and which surfaces are functional after heat treatment. If a shaft needs nitriding or induction hardening on a bearing journal, say so before the toolpath is planned. For more general machining practice on this type of material, our CNC machining steel page covers baseline process selection.
Send your drawings, material specification or grade callout, quantity, required tolerances, and surface finish requirements. A clear material condition on the RFQ prevents quoting the wrong cutting strategy and prevents surprises when the first article inspection checks hardness and impact energy. Request a quote at https://www.cncmachiningfactory.com/custom-quote/.
Turn this machining question into a manufacturable part
Need this material or process for your next CNC project?
Send your STEP, STP, IGES, DXF, PDF, material, quantity, surface finish, and tolerance requirements. We will review manufacturability and reply with practical quotation guidance.
