304H Grain Size Specifications and Importance

304H Grain Size: Specifications and Importance

At Gangsteel, a leading manufacturer and exporter of stainless steel products, we supply premium 304H stainless steel plates compliant with ASME SA 240 and ASTM A240 standards. 304H stainless steel, also known as AISI 304H, UNS S30409, or EN 1.4948, is a high-carbon austenitic stainless steel optimized for high-temperature strength and creep resistance up to 1500°F (815°C). This guide focuses on the grain size specifications of 304H stainless steel, its importance in high-temperature applications, and related properties for uses like boilers, heat exchangers, and SA 240 GR 304 pipe. For inquiries, contact us at admin@gangsteel.com or explore our ASME SA240 Stainless sheet offerings.

Grain Size Specifications for 304H Stainless Steel

The grain size of 304H stainless steel is typically specified under ASTM A240 and ASME SA 240, with additional guidance from ASTM E112 for grain size measurement. For 304H stainless steel plates, the grain size is generally:

• ASTM Grain Size Number: 5 to 8 (average grain diameter ~32-90 µm), as per ASTM E112, for annealed plates (8-75 mm thick). Smaller grain sizes (higher numbers, e.g., 7-8) are preferred for high-temperature applications to enhance creep resistance.
• Heat Treatment: Solution annealing at 1870-2100°F (1020-1149°C) followed by rapid cooling refines grain structure, ensuring compliance with grain size requirements.
• Standard Requirements: ASME SA 240 mandates a fine, uniform grain structure for 304H to ensure creep strength and corrosion resistance. Specific grain size may vary by manufacturer or application, but ASTM 5-8 is common for high-temperature service.

Grain size is not explicitly detailed in ASME SA 240 for 304H but is controlled during production to meet mechanical property standards. Gangsteel ensures 304H stainless steel plates meet ASTM E112 grain size standards for optimal performance. For related grades, see our sa240 gr 304h page.

Importance of Grain Size in 304H Stainless Steel

Grain size significantly impacts the performance of 304H stainless steel in high-temperature applications:

• Creep Resistance: Smaller grains (ASTM 7-8) increase grain boundary area, improving resistance to creep deformation at elevated temperatures (e.g., 1000°F/538°C). This is critical for applications like boilers and heat exchangers, where 304H stainless steel outperforms 304L due to its higher carbon content (0.04-0.10%).
• High-Temperature Strength: Fine grains enhance yield strength (205 MPa min) and creep strength (allowable stress 25.5 ksi at 1000°F), supporting structural integrity in pressure vessels.
• Corrosion Resistance: Uniform, fine grains reduce sensitization risks during welding in the 797°F-1580°F (425°C-860°C) range, though higher carbon in 304H requires annealing. Compared to sa240 gr 304l, 304H has higher sensitization risk but better high-temperature performance.
• Formability: Moderate grain size (ASTM 5-8) balances strength and ductility (40% elongation), enabling forming for applications like plat SS 304 3mm or plate 2 mm SUS 304.
• Weldability: Fine grains help maintain corrosion resistance in weld zones, though controlled heat input (<2.0 kJ/mm) or annealing is needed to mitigate sensitization.

For chloride-heavy environments requiring better corrosion resistance, explore sa240 gr 316l.

Chemical Composition Supporting Grain Size

The chemical composition of 304H stainless steel influences its grain structure:

Higher carbon content (0.04-0.10%) compared to 304 (≤0.08%) and 304L (≤0.03%) promotes finer grains during annealing, enhancing creep strength. For comparison with other grades, see sa240 gr 304.

Mechanical Properties Supporting Grain Size

The grain size (ASTM 5-8) supports robust mechanical properties for annealed plates:

Fine grains (ASTM 7-8) enhance yield strength and creep resistance, critical for high-temperature applications. For lower-temperature applications, see sa240 gr 304l.

Physical Properties

• Density: 8.00 g/cm³, ideal for lightweight designs.
• Melting Point: 1400-1450°C, suitable for high-temperature processing.
• Thermal Conductivity: 16.2 W/m·K at 100°C.
• Coefficient of Thermal Expansion: 17.2 × 10⁻⁶/K (20-100°C).
• Service Temperature: Continuous up to 1500°F (815°C); intermittent up to 1600°F (871°C).

These properties complement grain size for high-heat stability, unlike ferritic grades like sa240 gr 430.

Corrosion Resistance

304H stainless steeloffers excellent corrosion resistance in:

• Atmospheric conditions, freshwater, and mild acids (food-grade).
• General environments, outperforming SS204 vs SS 304 due to higher nickel (8-10.5%).

Fine grain size reduces sensitization risk, but higher carbon requires annealing in weld zones (797°F-1580°F). For chloride-heavy environments, see sa240 gr 317l.

Weldability

Weldability is fair using ER308H fillers. Fine grains help maintain weld zone integrity, but higher carbon risks sensitization, requiring low heat input (<2.0 kJ/mm) or annealing (1870-2100°F). For better weldability, see sa240 gr 321.

Applications Leveraging Grain Size

The fine grain size (ASTM 5-8) of 304H stainless steel supports:

• Boilers and pressure vessels (creep resistance).
• Heat exchangers (structural integrity).
• Power generation (superheaters, reheaters).
• Chemical processing (vessels, SA 240 GR 304 pipe).
• High-temperature piping and fittings.

For cost-effective alternatives, see sa240 gr 201.

Pricing and Availability

As of October 19, 2025, 304H stainless steel plate prices (2B finish, 3-6mm) range from $1.60-$3.50/kg. Gangsteel offers $1.60/kg FOB (MOQ 1 ton) for sa240 gr 304h. Contact admin@gangsteel.com or visit astm a 240 stainless plate.

FAQ on 304H Grain Size

What is the grain size specification for 304H stainless steel?

ASTM 5-8 (32-90 µm) per ASTM E112, ensuring creep resistance and strength in high-temperature applications like boilers.

Why is grain size important for 304H stainless steel?

Smaller grains (ASTM 7-8) increase creep resistance and strength at high temperatures, critical for structural integrity in heat exchangers.

How does 304H grain size compare to 304L?

Both have similar ASTM 5-8 grain size, but 304H’s higher carbon (0.04-0.10%) enhances creep resistance, while 304L prioritizes weldability.

How does grain size affect 304H weldability?

Fine grains reduce sensitization risk, but higher carbon requires low heat input or annealing to maintain corrosion resistance in welds.

What applications benefit from 304H’s grain size?

Boilers, heat exchangers, and SA 240 GR 304 pipe leverage fine grain size for creep resistance and durability at 1500°F.