304H vs 304L Carbon Content and Weldability Differences

304H vs 304L: Carbon Content and Weldability Differences

At Gangsteel, a leading manufacturer and exporter of stainless steel products, we supply premium SA 240 GR 304H and SA 240 GR 304L plates compliant with ASME SA 240 and ASTM A240 standards.

304H stainless steel(UNS S30409, AISI 304H, EN 1.4948) is a high-carbon austenitic stainless steel optimized for high-temperature strength and creep resistance up to 1500°F (815°C), while 304L stainless steel (UNS S30403, AISI 304L, EN 1.4306/1.4307) is a low-carbon variant designed for superior weldability and corrosion resistance in mild environments.

This guide focuses on the carbon content and weldability differences between 304H vs 304L, alongside other properties, for applications like plat stainless 304 and SA 240 GR 304 pipe. For inquiries, contact us at admin@gangsteel.com or explore our ASME SA240 Stainless sheet offerings.

Carbon Content Differences: 304H vs 304L

The primary difference between 304H and 304L stainless steel lies in their carbon content, which significantly impacts their performance and weldability:

• 304L Carbon Content: Ultra-low carbon (≤0.03%) reduces the formation of chromium carbides during welding, preventing sensitization (carbide precipitation in the 797°F-1580°F/425°C-860°C range) that depletes chromium and reduces corrosion resistance in weld zones.
• 304H Carbon Content: Higher carbon (0.04-0.10%) enhances creep resistance and strength at high temperatures, making it ideal for applications like boilers and heat exchangers. However, it increases sensitization risk, requiring careful welding practices or post-weld annealing.
• Impact: 304L prioritizes weldability and corrosion resistance in mild environments, while 304H is designed for high-temperature structural integrity, sacrificing some weldability. For detailed specs, refer to our SS 304 data sheet.

Weldability Differences: 304H vs 304L

Weldability is a critical factor differentiating 304H vs 304L stainless steel, driven by their carbon content:

• 304L Weldability:
  • Excellent: Low carbon (≤0.03%) minimizes sensitization, reducing chromium carbide precipitation during welding. This preserves corrosion resistance in weld zones, often eliminating the need for post-weld annealing.
  • Filler Material: Typically uses ER308L fillers, which match the low-carbon composition to maintain corrosion resistance.
  • Applications: Ideal for welded structures like SA 240 GR 304 pipe, chemical tanks, and food processing equipment where corrosion resistance is critical post-welding.
  • Advantages: Minimal heat input required (typically <2.0 kJ/mm), and welds retain excellent corrosion resistance in mild acids and atmospheric conditions.
• 304H Weldability:
  • Fair: Higher carbon (0.04-0.10%) increases sensitization risk, as chromium carbides can form in the 797°F-1580°F (425°C-860°C) range during welding, depleting chromium and reducing corrosion resistance in weld zones.
  • Filler Material: Uses ER308H or ER308 fillers to match the high-carbon composition, ensuring strength at elevated temperatures.
  • Requirements: Requires controlled heat input (<2.0 kJ/mm) and often post-weld annealing (1870-2050°F/1020-1120°C) to dissolve carbides and restore corrosion resistance.
  • Applications: Suitable for high-temperature welded components like boilers and heat exchangers, but less forgiving than 304L. For high-temperature welds, consider sa240 gr 321 for titanium stabilization.

For applications requiring both weldability and chloride resistance, see sa240 gr 316l.

Mechanical Properties Comparison

The carbon content influences mechanical properties for annealed plates (8-75 mm thick):

• Tensile Strength: 304H’s higher carbon boosts strength (515 MPa vs. 485 MPa), particularly at high temperatures, per ASME BPVC Section II, Part D.
• Yield Strength: 304H’s 205 MPa outperforms 304L’s 170 MPa, supporting high-temperature load-bearing applications like boilers.
• Elongation/Hardness: Identical values ensure both grades are formable and machinable, suitable for applications like plate 2 mm SUS 304.

For comparison with other grades, see sa240 gr 304.

Physical Properties Comparison

Both grades share identical physical properties due to similar compositions:

• 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).
• Electrical Resistivity: 0.72 × 10⁻⁶ Ω·m.
• Service Temperature:
  • 304L: Continuous up to ~800°F (427°C), suitable for mild environments.
  • 304H: Continuous up to 1500°F (815°C); intermittent up to 1600°F (871°C), with scaling onset at ~1200°F (649°C).

For cost-effective alternatives, see sa240 gr 201.

Corrosion Resistance Comparison

Both 304H and 304L stainless steel offer excellent corrosion resistance in:

• Atmospheric conditions, freshwater, and mild acids (food-grade).
• General environments, outperforming SS204 vs SS 304 due to higher nickel (8-12% for 304L, 8-10.5% for 304H).

Key Differences:

• 304L: Superior in welded applications, as low carbon (≤0.03%) prevents sensitization, maintaining corrosion resistance in weld zones without annealing.
• 304H: Higher carbon (0.04-0.10%) increases sensitization risk in weld zones (797°F-1580°F), potentially reducing corrosion resistance unless annealed post-weld (1870-2050°F).

Both are less resistant to chloride-induced pitting compared to molybdenum-enhanced grades like sa240 gr 317l.

Applications Leveraging Carbon Content and Weldability

• 304L: Ideal for welded applications in mild environments, including:
  • Food processing (tanks, conveyors, plat stainless 304).
  • Chemical equipment (vessels, SA 240 GR 304 pipe).
  • Architecture (plate 2 mm SUS 304, decorative panels).
  • Medical devices (non-magnetic components).
    See sa240 gr 304l.
• 304H: Suited for high-temperature welded applications, including:
  • Boilers and pressure vessels (steam drums, headers).
  • Heat exchangers (tubes, shells).
  • Power generation (superheaters, reheaters).
  • High-temperature piping and fittings.
    See sa240 gr 304h.

Cost Comparison

As of October 19, 2025:

Gangsteel offers competitive pricing: $1.50/kg FOB for 304L and $1.60/kg FOB for 304H (MOQ 1 ton). Contact admin@gangsteel.com or visit astm a 240 stainless plate.

Which is Better for Welded Applications?

• Choose 304L: For welded applications in mild environments (e.g., chemical tanks, food processing) where low carbon ensures corrosion resistance without annealing.
• Choose 304H: For welded high-temperature applications (e.g., boilers, heat exchangers) where creep strength is critical, provided annealing or controlled welding is feasible.

Summary

304L stainless steelexcels in weldability due to its low carbon content (≤0.03%), preventing sensitization and maintaining corrosion resistance in weld zones, ideal for food-grade and chemical applications. 304H stainless steel, with higher carbon (0.04-0.10%), offers superior creep strength up to 1500°F but requires careful welding or annealing to mitigate sensitization risks, making it suitable for high-temperature applications like boilers. Gangsteel offers both grades at competitive prices ($1.50/kg for 304L, $1.60/kg for 304H FOB). Contact admin@gangsteel.com for quotes.