304H Heat Treatment Process and Temperature Range

What is 304H Heat Treatment: Process and Temperature Range

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 details the heat treatment process and temperature range for 304H stainless steel, highlighting their importance for applications 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.

Heat Treatment Process for 304H Stainless Steel

The heat treatment process for 304H stainless steel is primarily solution annealing, which optimizes its microstructure for high-temperature performance, corrosion resistance, and mechanical properties. The process is specified under ASME SA 240 and ASTM A240, with the following steps:

• Solution Annealing:
  • Temperature Range: 1870°F to 2100°F (1020°C to 1149°C).
  • Process: The material is heated to this range to dissolve carbides and stabilize the austenitic structure, followed by rapid cooling (water or air quenching) to prevent carbide precipitation and maintain corrosion resistance.
  • Purpose: Refines grain structure (ASTM 5-8), enhances creep resistance, and minimizes sensitization (chromium carbide formation) in the 797°F-1580°F (425°C-860°C) range, which can reduce corrosion resistance in weld zones.
• Post-Weld Annealing(optional):
  • Temperature Range: 1870°F to 2050°F (1020°C to 1120°C).
  • Process: Applied after welding to restore corrosion resistance in weld-affected zones, especially due to 304H’s higher carbon content (0.04-0.10%), which increases sensitization risk.
  • Cooling: Rapid cooling to avoid re-precipitation of carbides.
• Stress Relief(rarely used):
  • Temperature Range: 800°F to 1100°F (427°C to 593°C), but avoided unless necessary, as it risks sensitization.
  • Purpose: Reduces residual stresses from fabrication, though not standard for 304H due to corrosion concerns.

The solution annealing process ensures 304H stainless steel maintains its non-magnetic properties (SA 240 304 non magnetic) and achieves optimal performance for high-temperature applications. For comparison with low-carbon grades, see sa240 gr 304l.

Temperature Range for Heat Treatment

The temperature range for 304H stainless steel heat treatment is critical to achieving desired properties:

• Solution Annealing: 1870°F to 2100°F (1020°C to 1149°C).
  • Ensures dissolution of carbides and grain refinement for creep resistance.
  • Rapid cooling prevents sensitization, critical for 304H’s higher carbon content compared to 304 (≤0.08% C) or 304L (≤0.03% C).
• Post-Weld Annealing: 1870°F to 2050°F (1020°C to 1120°C).
  • Restores corrosion resistance in weld zones, mitigating sensitization risks.
• Service Temperature Limits(for context):
  • Continuous: Up to 1500°F (815°C), with excellent creep resistance (allowable stress 25.5 ksi at 1000°F).
  • Intermittent: Up to 1600°F (871°C).
  • Sensitization Range: Avoid prolonged exposure to 797°F-1580°F (425°C-860°C) during service or welding to prevent carbide precipitation.

For grades with better chloride resistance, see sa240 gr 316l.

Importance of Heat Treatment for 304H Stainless Steel

Heat treatment is essential for 304H stainless steel due to its high carbon content and high-temperature applications:

• Creep Resistance: Solution annealing refines grain size (ASTM 5-8), enhancing creep strength at temperatures above 800°F (427°C), critical for boilers and heat exchangers.
• Corrosion Resistance: Rapid cooling after annealing prevents sensitization, maintaining corrosion resistance in mild acids and atmospheric conditions, outperforming SS204 vs SS 304. For chloride-heavy environments, see sa240 gr 317l.
• Mechanical Properties: Heat treatment optimizes tensile strength (515 MPa) and yield strength (205 MPa), ensuring structural integrity in high-temperature applications like SA 240 GR 304 pipe.
• Weldability: Post-weld annealing mitigates sensitization risks, critical for 304H due to its higher carbon content compared to sa240 gr 304.

For stabilized grades with lower sensitization risk, see sa240 gr 321.

Chemical Composition Supporting Heat Treatment

The chemical composition of 304H stainless steel influences its heat treatment response:

Higher carbon (0.04-0.10%) necessitates precise annealing to avoid sensitization, unlike low-carbon sa240 gr 304l.

Mechanical Properties Post-Heat Treatment

Heat treatment optimizes the mechanical properties of 304H stainless steel for annealed plates (8-75 mm thick):

Annealing ensures fine grain size (ASTM 5-8), enhancing creep resistance (25.5 ksi at 1000°F) for applications like plat SS 304 3mm.

Physical Properties

• Density: 8.00 g/cm³, ideal for lightweight designs (e.g., a 1m x 1m x 3mm plate weighs ~24 kg).
• Melting Point: 1400-1450°C, suitable for 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 support heat treatment stability, unlike ferritic grades like sa240 gr 430.

Applications Leveraging Heat Treatment

Heat-treated 304H stainless steel is used in:

• 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 Stainless Steel Heat Treatment

What is the heat treatment process for 304H stainless steel?

Solution annealing at 1870-2100°F (1020-1149°C) with rapid cooling to dissolve carbides and enhance creep resistance.

What is the temperature range for 304H heat treatment?

Annealing at 1870-2100°F (1020-1149°C); post-weld annealing at 1870-2050°F to prevent sensitization.

Why is heat treatment important for 304H stainless steel?

It refines grain size, enhances creep strength, and prevents sensitization, ensuring corrosion resistance and high-temperature performance.

How does 304H heat treatment compare to 304L?

304H requires annealing to mitigate higher carbon (0.04-0.10%) sensitization risk, while 304L’s low carbon (≤0.03%) reduces this need.

What applications benefit from 304H heat treatment?

Boilers, heat exchangers, and SA 240 GR 304 pipe leverage heat-treated 304H for creep resistance and durability at 1500°F.