Stainless Steel Grade 304H: High-Carbon for High-Temperature Strength

Stainless steel 304H is a high-carbon variant of 304, designed to enhance creep strength and structural stability at elevated temperatures. With a carbon content of 0.04–0.10%, it outperforms standard 304 in high-heat industrial applications like boilers, furnaces, and heat exchangers.

Chemical Composition (ASTM A240)

18–20% chromium, 8–10.5% nickel, 0.04–0.10% carbon, ≤2% manganese, ≤0.75% silicon, trace phosphorus/sulfur.

Mechanical Properties (Annealed)

Yield strength: ≥205 MPa

Tensile strength: 515–655 MPa

Elongation: ≥35%

Hardness: Max 217 HB

Performance Advantages

304H retains 304's general corrosion resistance but offers superior creep strength (resistance to deformation under long-term heat/stress) at 540–870°C. It is weldable with matching fillers and maintains structural integrity in cyclic high-temperature environments.

Applications

Boiler tubes, industrial furnace components, heat exchanger tubes, and high-temperature piping in power plants.

Equivalent Grades

EU: EN 1.4307; Japan: JIS SUS304H; China: GB 0Cr18Ni9H

304H vs. 304/304L: Heat Resistance

304H (0.04–0.10% C) has best creep strength; 304 (≤0.08% C) is intermediate; 304L (≤0.03% C) is poorest for high heat. 304H is for sustained high temps; 304L for welded/cryogenic use.

FAQs

What is creep strength, and why is it critical for 304H?Creep strength is a material's ability to resist permanent deformation under constant heat and stress-vital for components like boiler tubes that operate at 600°C for years. 304H's higher carbon content (0.04–0.10%) forms stronger grain boundaries, slowing creep compared to 304 (≤0.08% C) or 304L (≤0.03% C). For example, a 304H boiler tube will maintain its shape and pressure resistance for decades, while 304 may stretch or fail prematurely under the same conditions. This makes 304H essential for power plants and refineries where high-temperature reliability is non-negotiable.

Can 304H be used in continuous high-temperature service?Yes-304H is designed for continuous operation at 540–870°C, making it suitable for furnace liners, heat exchanger tubes, and steam pipelines. Its chromium content (18–20%) forms a stable oxide layer that resists oxidation and scaling at high heat, preventing material degradation. Unlike 304, which may soften above 650°C, 304H retains tensile strength and structural stability. It should avoid continuous exposure above 870°C (use 309S instead), but for most industrial high-temperature applications, it offers optimal performance and cost-effectiveness.

How does welding affect 304H's high-temperature performance?304H is weldable with TIG/MIG methods, but proper filler selection (e.g., ER308H, which matches its carbon content) is critical to retain creep strength. Using low-carbon fillers like ER308L would reduce the weld joint's high-temperature performance, leading to premature creep. Controlling heat input during welding prevents grain growth and carbide precipitation, which can weaken the joint. Post-weld annealing is not required for most applications, but thick sections may benefit from stress relief to avoid cracking. Welded 304H joints maintain the base metal's creep resistance, making it suitable for welded boiler and furnace components.

Why not use 304H for low-temperature or welded non-heat applications?304H's higher carbon content is a disadvantage in non-high-temperature scenarios. It is more prone to intergranular corrosion in welded structures than 304L, so it should not be used for chemical pipelines or pharmaceutical equipment where post-weld corrosion resistance is key. At low temperatures, it offers no advantage over 304 and is slightly less ductile, making 304L a better choice for cryogenic use. Additionally, 304H is more expensive than 304 due to tighter carbon control, so using it for non-high-heat applications wastes cost without added benefit.

How does 304H compare to 316H in high-temperature applications?304H and 316H are both high-carbon, high-temperature grades, but 316H contains 2–3% molybdenum, enhancing chloride corrosion resistance. 316H is better for high-temperature, corrosive environments (e.g., chemical plant heat exchangers handling saltwater), while 304H is ideal for clean, non-corrosive high-heat settings (e.g., power plant steam tubes). 316H is more expensive due to molybdenum, so 304H is preferred for cost-sensitive, non-corrosive high-temperature applications. Both offer excellent creep strength, but their alloy differences make them suited for distinct industrial needs.