Stainless Steel 304H
Stainless Steel 304H (UNS S30409, EN 1.4948) is the high-carbon version of the standard grade 304. The “H” designation refers to a controlled carbon range of 0.04 – 0.10%, which is higher than the ≤0.08% allowed in standard 304. It has much better creep resistance and long-term strength retention due to the higher carbon content. It is specified by ASTM A213 for boiler and superheater tubing and is extensively used in power generation and petrochemical processing.
1. Chemical Composition
The chemical composition of Stainless Steel 304H, along with its proportion, is given in the table below.
| Grade | Carbon, max | Manganese, max | Phosphorus, max | Sulfur, max | Silicon, max | Chromium | Nickel | Molybdenum | Iron |
| TP304H | 0.04 – 0.10 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 | ≤ 0.75 | 18.0 – 20.0 | 8.0 – 10.5 | -- | Balance |
The defining feature of 304H is the carbon range of 0.04–0.10%. This carbon level stabilises the austenitic matrix under prolonged thermal exposure, which directly improves creep-rupture strength at temperatures above 550°C.
2. Mechanical Properties
The mechanical properties of Stainless Steel 304H is listed in the table given below.
| Property | Tensile Strength (Min) | Yield Strength 0.2% Proof (Min) | Elongation (Min) | Hardness (Max) | Service Temperature Range | Condition |
| Value | 515 MPa (75 ksi) | 205 MPa (30 ksi) | 35% | 192 HBW | 550°C – 800°C (continuous) | Solution annealed |
3. Equivalent Grade
The international designations equivalent to Stainless Steel 304H is listed in the table given below.
| Grade | UNS | GB/T | JIS | DIN / EN (W.Nr.) | GOST |
| 304H | S30409 | 06Cr19Ni10 | SUS304H | X6CrNi18-10 / 1.4948 | 08Kh18N10 |
3. Key Technical Advantages
Below are the key advantages of Stainless Steel 304H.
- Higher Carbon for Creep Resistance: In 304H stainless steel, 0.04–0.10% carbon greatly improves resistance to creep and rupture above 550°C, giving 2–3 times longer life than 304L at 650°C by stabilising grain boundaries.
- Suitable for Long-Term High-Temperature Service: 304H stainless steel is approved by ASME for boiler and pressure vessel applications up to 816°C, unlike standard 304, making it essential for boiler superheater tubes operating under continuous high-temperature duty cycles.
- Good Oxidation Resistance: The 18–20% chromium content provides oxidation resistance up to approximately 870°C in intermittent service. This helps maintain surface integrity in superheater and reheater environments where tubes experience repeated heating and cooling cycles.
- Weldability with Appropriate Filler Selection: 304H stainless steel can be welded easily using standard fabrication methods and generally does not require post-weld heat treatment. For demanding high-temperature applications, ERNiCrMo-3 filler wire improves weld strength and enhances resistance to heat-affected zone sensitisation.
- Established Material Traceability: 304H stainless steel follows clear global standards like ASTM A213 and A312 with defined allowable stresses, making it easy for engineers and inspectors to confirm suitability using consistent documentation and certifications worldwide.
4. Common Manufacturing Standards
The common manufacturing standards of Stainless Steel 304H are listed in the table given below.
- ASTM A213: Covers seamless ferritic and austenitic alloy steel boiler, superheater, and heat exchanger tubes.
- ASME SA-213: ASME equivalent of ASTM A213 for boiler and pressure vessel applications.
- ASTM A312: Covers seamless, welded, and heavily cold-worked austenitic stainless steel pipes.
- EN 10216-5: European standard for seamless stainless steel tubes used in pressure applications.
- JIS G3463: Japanese standard for stainless steel boiler and heat exchanger tubes.
- GB/T 13296: Chinese standard covering seamless stainless steel tubes for boilers and heat exchangers.
- ASTM A262: Defines practices for detecting susceptibility to intergranular attack in austenitic stainless steels.
5. Primary Applications
The Stainless Steel 304H are used in the following high-performing industries.
- Power Generation: Used in high-pressure steam circuits operating above 550°C, where standard 304 does not meet allowable stress requirements under ASME codes.
- Petrochemical Processing: Handles sustained high-temperature hydrocarbon service where both oxidation resistance and creep strength are needed simultaneously.
- Oil Refinery Heat Exchangers: Specified for tube bundles in crude distillation and vacuum tower service where operating temperatures exceed the limits for standard austenitic grades.
- Industrial Furnaces: Recommended for furnace tube service in chemical plants and refineries requiring continuous service at elevated temperatures.