34CrMo4 (1.7220) is a high-quality alloyed quenched and tempered steel often used for high-pressure seamless gas cylinders, such as CNG or industrial gas tanks. It offers high tensile strength (≥980 MPa), high yield strength (≥835 MPa), and excellent toughness. Known for good hardenability and resistance to fatigue, it is ideal for high-pressure storage.
34. Average carbon content is 0.34%
Cr (Chromium)
Mo (Molybdenum)
4. Specific combination designation for alloying element content
1.7220 European standard numerical designation (W-Nr.)
What Is 34CrMo4 (1.7220) Steel?
34CrMo4 (European standard steel grade 1.7220) is a Cr-Mo alloy structural steel, manufactured according to EN 10083-3 standard, and is a typical quenched and tempered steel. Due to its excellent strength, toughness, and fatigue resistance, this material is the preferred material for manufacturing high-pressure seamless gas cylinders.
Chemical Composition (Typical)
| Element | Content (%) |
|---|---|
| C (Carbon) | 0.30 – 0.37 |
| Si (Silicon) | 0.10 – 0.40 |
| Mn (Manganese) | 0.60 – 0.90 |
| Cr (Chromium) | 0.90 – 1.20 |
| Mo (Molybdenum) | 0.15 – 0.30 |
| P / S | ≤ 0.025 |
Chromium (Cr): Improves strength and wear resistance
Molybdenum (Mo): Enhances hardenability and high-temperature strength
Controlled carbon: Balances strength and toughness
Mechanical Properties (Typical, Q&T Condition)
| Property | Value |
|---|---|
| Yield Strength | ≥ 850 MPa |
| Tensile Strength | 950 – 1100 MPa |
| Elongation | ≥ 12–14% |
| Impact Toughness | Excellent (depends on condition) |
Key Advantages for 34CrMo4 High-Pressure Cylinders
High Strength and Lightweight
The yield strength of 34CrMo4 exceeds 800 MPa, more than three times that of ordinary carbon steel. This means:
- Significantly reduced wall thickness: Compared to P355NB, the wall thickness can be reduced by approximately 60% under the same pressure conditions.
- Significantly reduced weight: The cylinder's weight is reduced, facilitating transportation and handling.
- Optimized material costs: Although the price per unit weight is higher, the material savings from the thinner design offset some of the cost.
Excellent Fatigue Resistance
High-pressure gas cylinders are subjected to cyclic pressure loads during filling and discharging, making fatigue performance crucial. 34CrMo4 possesses:
High fatigue limit
Good crack propagation resistance, especially excellent performance in high-pressure hydrogen environments.
34CrMo4 1.7220 steel
Superior Resistance to Hydrogen Embrittlement
This is a key advantage that distinguishes 34CrMo4 from ordinary alloy steels. Studies have confirmed that the improved form of 34CrMo4 (34CrMo44) exhibits the following characteristics in high-pressure hydrogen environments:
- Good hydrogen embrittlement resistance
- Excellent fatigue crack propagation characteristics
- This makes it an ideal liner material for hydrogen energy storage, suitable for:
- Stationary hydrogen storage containers at hydrogen refueling stations
- On-board hydrogen storage tanks for fuel cell vehicles (metal liners for Type 2/Type 4 gas cylinders)
Good hardenability
The hardenability of 34CrMo4 is superior to that of 40Cr steel, which means:
- A uniform tempered microstructure can be obtained even with thicker sections
- Suitable for manufacturing high-pressure gas cylinders with large diameters and thick walls
- Good performance uniformity with no risk of central performance degradation
Application areas for 34CrMo4 steel
34CrMo4 is the dominant material for manufacturing high-pressure seamless gas cylinders. Main product types and applications are as follows:
| Cylinder Type | Working Pressure | Typical Applications |
|---|---|---|
| Industrial Gas Cylinders | 150–200 bar | Storage of O₂, N₂, Ar, CO₂ and other industrial gases |
| CNG Cylinders | 200–250 bar | Compressed natural gas cylinders for vehicles |
| Breathing Air Cylinders | 200–300 bar | Air cylinders for fire fighting, diving and respirators |
| Hydrogen Storage Tanks | 350–700 bar | Hydrogen refueling stations and fuel cell vehicles |
Other Applications
Due to its excellent overall performance, 34CrMo4 is also widely used in:
- Oil Drilling: Drill pipe joints for wells below 2000m, fishing tools
- Heavy Machinery: Locomotive traction gears, turbocharger drive gears
- Power Generation Equipment: Steam turbine generator rotors, main shafts
- Automotive Industry: High-load connecting rods, spring clips
Manufacturing Process for Seamless Cylinders
34CrMo4 is mainly used in seamless cylinder production, involving:
- Billet heating
- Hot piercing (seamless tube formation)
- Hot rolling / elongation
- Heat treatment (Q&T)
- Machining and finishing
- Hydrostatic testing
Delivery Conditions
34CrMo4 can be delivered in the following conditions, which must be specified in the contract:
- Quenched and Tempered (QT): Quenched and tempered, ready to use.
- Annealed (A): Softened state, easy to process, requires quenching and tempering before use.
- Hot Rolled/Forged: Untreated, requires subsequent heat treatment.
Comparison with P265NB / P355NB
| Feature | P265NB | P355NB | 34CrMo4 |
|---|---|---|---|
| Type | Non-alloy | Non-alloy | Alloy steel |
| Yield Strength | 265 MPa | 355 MPa | ≥ 850 MPa |
| Manufacturing | Welded | Welded | Seamless |
| Pressure Level | Medium | Medium-high | Very high |
| Cost | Low | Medium | High |
P265NB / P355NB → welded, lower pressure
34CrMo4 → seamless, ultra-high pressure
At GNEE, we assist our clients in selecting the optimal grade based on their specific vessel design and safety requirements. Our technical team has decades of experience in the steel industry, ensuring you receive the most reliable advice.
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Why is 34CrMo4 used for seamless cylinders instead of welded steel?
Because it offers:
Much higher strength
No weld seam (eliminates weak points)
Better fatigue resistance
What pressure levels can 34CrMo4 handle?
Typically used for:
200–300 bar and above, depending on design
Is heat treatment mandatory?
Yes. 34CrMo4 must be quenched and tempered to achieve required properties.
Can 34CrMo4 be welded?
It can be welded, but:
Requires strict control
Preheating and post-weld heat treatment may be needed
How does it compare to aluminum cylinders?
Stronger and more fatigue-resistant
Heavier than aluminum
Better for high-pressure industrial use
Is it suitable for hydrogen storage?
A: Yes, but:
Must meet additional hydrogen embrittlement requirements
Requires strict quality control
What are the main cost factors?
Alloy content (Cr, Mo)
Heat treatment
Seamless manufacturing process
What certifications should I request?
EN 10204 3.1 certificate
Mechanical test reports
Hydrostatic and NDT results
