Products Description
Among the steels used in welded gas cylinders, HP325 stands out as an ideal choice for medium- and high-pressure cylinder manufacturing due to its significantly improved strength and excellent overall performance. Compared to HP295, HP325 achieves a substantial increase in strength while maintaining good weldability and machinability, meeting the safety requirements of cylinders with higher pressure ratings.
The "325" in HP325 indicates that its yield strength is not less than 325 MPa, which is about 10% higher than HP295 (≥295 MPa) and nearly 40% higher than the basic grade HP235 (≥235 MPa). This strength level makes it the main grade of steel for medium and high pressure gas cylinders.
HP325 welding cylinder steel
Comparison of strength grades of steel for welding cylinders
| Grade | Yield Strength (≥MPa) | Tensile Strength (MPa) | Elongation (t≥3mm, ≥%) | Application Scenario |
|---|---|---|---|---|
| HP235 | 235 | 380–500 | 29 | Ordinary pressure gas cylinders |
| HP265 | 265 | 410–520 | 27 | General pressure vessels |
| HP295 | 295 | 440–560 | 26 | LPG cylinders |
| HP325 | 325 | 490–600 | 22 | Medium and high pressure gas cylinders |
| HP345 | 345 | 510–620 | 21 | High pressure gas cylinders |
Chemical Composition
The chemical composition design of HP325 balances strength and processability. Its core feature is to achieve strengthening by increasing the manganese content, while strictly controlling impurity elements.
| Grade | C (≤%) | Si (≤%) | Mn (≤%) | P (≤%) | S (≤%) | Als (≥%) |
|---|---|---|---|---|---|---|
| HP325 | 0.20 | 0.35 | 1.50 | 0.025 | 0.015 | 0.015 |
| HP295 | 0.18 | 0.10 | 1.00 | 0.025 | 0.015 | 0.015 |
- Increased Manganese Content: HP325's manganese content limit reaches 1.50%, significantly higher than HP295's 1.00%. Manganese, as a solid solution strengthening element, effectively improves steel strength while minimizing damage to plasticity and toughness.
- Relaxed Silicon Content: The upper limit for silicon content has been increased to 0.35%, which helps deoxidize and strengthen the matrix.
- Purity Control: Strict limits on harmful impurities such as phosphorus and sulfur (P≤0.025%, S≤0.015%) ensure the purity of the steel and reduce the adverse effects of inclusions on weldability and low-temperature toughness.
Mechanical properties and processing properties
Strength Specifications
HP325 has a minimum tensile strength of 490 MPa and a maximum of 600 MPa. This strength level allows it to withstand higher test pressures (typically 3.2 MPa and above), meeting the design requirements of medium- and high-pressure gas cylinders.
Plasticity Specifications
Despite the increased strength, HP325 maintains considerable plasticity reserves:
Elongation: Elongation ≥22% for thickness ≥3mm, ≥18% for thickness <3mm
This elongation level is sufficient to meet the stamping requirements of gas cylinder heads.
Weldability
HP325 employs a low-carbon design (carbon content ≤0.20%), resulting in low sensitivity to weld cracks and allowing for reliable weld joints without complex preheating processes.
Cold Bending Performance
HP325 exhibits excellent cold bending forming capabilities, meeting the requirements of deep drawing processing for gas cylinder heads while ensuring uniform wall thickness reduction.
Applicable Scenarios and Standard Status
Main Application Areas
HP325 is mainly used in the manufacture of the following types of gas cylinders:
- Medium and high pressure liquefied petroleum gas cylinders
- Industrial high pressure gas cylinders (oxygen cylinders, nitrogen cylinders, etc.)
- Fire extinguisher cylinders
- Other welded gas cylinders with high test pressure
Currently, the national standard for steel plates and strips used in welded gas cylinders (GB/T 6653) is being revised and transformed into a mandatory national standard, with the grade system covering HP235, HP265, HP295, HP325, and HP345. This transformation reflects the country's emphasis on gas cylinder safety, and the application of HP325, as a core material for medium and high-pressure gas cylinders, will be more standardized.
Comparison with HP295
| Comparison Item | HP295 | HP325 | Selection Suggestion |
|---|---|---|---|
| Yield Strength | ≥295 MPa | ≥325 MPa | HP325 is recommended for higher pressure levels |
| Tensile Strength | 440–560 MPa | 490–600 MPa | HP325 has stronger load-bearing capacity |
| Elongation | ≥26% | ≥22% | HP295 has slightly better formability margin |
| Manganese Content | ≤1.00% | ≤1.50% | HP325 shows more significant strengthening mechanism |
| Typical Application | Ordinary LPG cylinders | Medium and high-pressure gas cylinders | Select according to design pressure requirements |
conclusion
HP325 welding cylinder steel, with its yield strength of 325 MPa, refined grain structure, and strict purity control, has established an irreplaceable position in the field of medium and high-pressure gas cylinder steel.
While maintaining the good weldability and cold formability of welded gas cylinder steel, it achieves a significant increase in strength, providing reliable material support for lightweight cylinder design and the development of products with higher pressure ratings. As gas cylinder safety standards continue to rise, HP325's position as the "high-strength choice for medium and high-pressure gas cylinders" will be further solidified.
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How is the weldability of HP325? Is it prone to cracking?
HP325 has good weldability and is not prone to cracking.
How is the stamping performance of HP325? Is it suitable for deep drawing?
HP325 has good cold stamping performance and can meet the deep drawing requirements of gas cylinder heads.
How good is the low-temperature toughness of HP325? Is it suitable for use in cold regions?
HP325 has good low-temperature toughness and can meet the requirements for use in cold regions.
What are the common specifications of HP325? What is the thickness range?
HP325 products are available in both hot-rolled and cold-rolled states. Common specifications are as follows:
- Hot-rolled steel sheet and strip: Thickness range 2.0mm to 14.0mm, with the thinnest specifications of 2.5mm - 5.0mm being the most widely used for stamping cylinder heads.
- Cold-rolled steel sheet and strip: Thickness range 1.5mm to 4.0mm, with higher surface quality and dimensional accuracy.
