30CrMoQC Steel for Gas Cylinders
30CrMoQC Steel for Gas Cylinders: Properties, Equivalents & Applications
Explore 30CrMoQC steel standard for high-pressure gas cylinders, with chemical composition, mechanical properties, and international equivalent grades.
Hot rolling, cold drawing, quenching and tempering
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30CrMoQC Steel for Gas Cylinders Introduction
30CrMoQC is a chromium-molybdenum alloy steel specifically designed for seamless steel tubes used in high-pressure gas cylinders, conforming to the Chinese national standard GB/T 18248. It is characterized by its high strength, excellent toughness, good hardenability, and reliable performance under cyclic loading conditions. The material is supplied in the quenched and tempered (Q+T) condition to achieve a microstructure of tempered martensite or bainite, ensuring an optimum balance of tensile strength, yield strength, and impact toughness at low temperatures down to -50°C. Its enhanced cleanliness and tight control of harmful elements make it suitable for storing compressed natural gas (CNG), industrial gases, and fire extinguishing agents. The grade is widely used in the manufacture of seamless gas cylinders and pressure vessels, offering superior safety margins and long-term service reliability.
30CrMoQC Steel for Gas Cylinders Chemical Composition
The chemical composition of 30CrMoQC is strictly controlled according to GB/T 18248 to ensure sufficient hardenability, cleanliness, and low-temperature toughness. The low phosphorus and sulfur contents minimize embrittlement, while chromium and molybdenum provide strength, oxidation resistance, and creep strength.
| Element | Content (%) | Remarks |
|---|---|---|
| Carbon (C) | 0.26 – 0.34 | Key hardenability element |
| Silicon (Si) | 0.17 – 0.37 | Deoxidation and strength |
| Manganese (Mn) | 0.40 – 0.70 | Hardenability, de-sulfurization |
| Phosphorus (P) | ≤0.020 | Maximum limit for toughness |
| Sulfur (S) | ≤0.010 | Maximum limit for cleanliness |
| Chromium (Cr) | 0.80 – 1.10 | Primary carbide former & corrosion resistance |
| Molybdenum (Mo) | 0.15 – 0.25 | Improves hardenability & temper resistance |
| Nickel (Ni) | ≤0.30 | Residual element; limited to avoid cost |
| Copper (Cu) | ≤0.20 | Residual element; limited to avoid hot shortness |
30CrMoQC Steel for Gas Cylinders Thermal and Electrical Physical Properties
The following physical properties are typical values for Cr-Mo alloy steels similar to 30CrMoQC in the quenched and tempered condition. Actual values may vary slightly depending on exact heat treatment and composition. These data are provided for engineering reference.
| Property | Value | Unit | Test Condition |
|---|---|---|---|
| Density (ρ) | 7.85 | g/cm³ | 20°C |
| Modulus of elasticity (E) | 206 | GPa | 20°C |
| Shear modulus (G) | 80 | GPa | 20°C |
| Poisson's ratio (ν) | 0.3 | – | 20°C |
| Thermal expansion coefficient (α) | 12.2×10⁻⁶ | K⁻¹ | 20-100°C |
| Thermal expansion coefficient (α) | 12.6×10⁻⁶ | K⁻¹ | 20-200°C |
| Thermal expansion coefficient (α) | 13.0×10⁻⁶ | K⁻¹ | 20-300°C |
| Thermal conductivity (λ) | 46 | W/(m·K) | 100°C |
| Specific heat capacity (c) | 460 | J/(kg·K) | 20°C |
| Electrical resistivity (ρ_e) | 0.22 | μΩ·m | 20°C |
30CrMoQC Steel for Gas Cylinders Mechanical Properties
Mechanical properties are determined after quenching and tempering treatment, as specified in GB/T 18248. The testing is performed on longitudinal specimens machined from the wall of the seamless tube. The low-temperature impact energy requirement ensures safe operation in cold environments.
| Property | Value | Unit | Test Condition |
|---|---|---|---|
| Yield Strength (ReH) | ≥785 | MPa | Room temperature, longitudinal |
| Tensile Strength (Rm) | 930 – 1130 | MPa | Room temperature, longitudinal |
| Elongation (A) | ≥12 | % | Gauge length 5.65√So |
| Impact Energy (KV₂) | ≥27 | J | -50°C, longitudinal V-notch |
30CrMoQC Steel for Gas Cylinders Fully Equivalent Material Standards and Replaceable Grades
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 18248 | 30CrMoQC | Original gas cylinder tube grade |
| Europe | EN 10297-1 | 34CrMo4 (1.7220) | Comparable composition and mechanical properties for gas cylinder tubes |
| USA | ASTM A519 | 4130 | Similar chemistry; may require supplementary impact testing for gas cylinder applications |
| Japan | JIS G3441 | SCM430TK | Alloy steel tube for gas cylinders; closely matching strength and toughness |
30CrMoQC Steel for Gas Cylinders Application Introduction
30CrMoQC steel tubes are primarily used in the fabrication of seamless high-pressure gas cylinders. The material's combination of high strength and excellent low-temperature toughness makes it ideal for storing and transporting compressed gases under extreme conditions. Typical applications include natural gas vehicles (CNG cylinders), industrial gas cylinders for oxygen, nitrogen, argon, hydrogen, and fire suppression system cylinders. The steel can be formed by hot or cold pilgering, and the finished cylinder bodies are produced by hot spinning and closing of the tube ends. All welded joints must be subjected to strict non-destructive testing to ensure integrity.
Product Applications: Seamless steel gas cylinders (Type I), Pressure vessels, Accumulator shells, Tube trailers for gas transport, High-pressure storage tanks
Processed into products: Cylinder body (with closed ends by hot spinning), Neck rings and valve bosses (forged from same material), Tube sections for bundled cylinders, Adapter rings for multi-element gas containers (MEGC)
Application industries: Energy (CNG storage and transportation), Industrial gas (O₂, N₂, Ar, H₂ cylinders), Fire-fighting equipment, Medical gas supply, Breathing apparatus (SCBA), Automotive (alternative fuel vehicles)
30CrMoQC Steel for Gas Cylinders Recommendation of Similar / Alternative Materials
| Country/Region | Standard | Grade | Remarks |
|---|---|---|---|
| China | GB/T 3077 | 30CrMoA | Similar general-purpose alloy structural steel; additional testing required for cylinder service |
| Europe | EN 10083-3 | 25CrMo4 (1.7218) | Lower carbon; may need higher tempering to achieve toughness for gas cylinders |
| USA | ASTM A372 | Grade C (4130) | Similar strength class for pressure vessel forgings; can substitute with proper qualification |
| International | ISO 9809-1 | 34CrMo4 | Global gas cylinder standard; nearly identical requirements to GB/T 18248 30CrMoQC |
Notes:
The suffix QC in the grade designation indicates Gas Cylinder (Qì Píng) quality, with enhanced requirements for non-metallic inclusions, internal defects, and impact toughness compared to general 30CrMo. Flattening tests, flaring tests, and hydraulic pressure tests are mandatory per GB/T 18248. Ultrasonic or eddy current non-destructive testing is required on each tube. The material may also be supplied with a certificate to ISO 9809-1 or DOT specifications upon agreement.
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