What Is Stainless Steel Grade 304H? High-Temperature Properties and Uses

What is SS304H Material?

Grade 304H stainless steel (UNS S30409, EN 1.4948 / X6CrNi18-10) is a high-carbon variant of the widely used 304 austenitic stainless steel family. Its carbon content is specifically controlled within the range of 0.04% to 0.10% (in contrast to standard 304, which has a maximum carbon limit of 0.08%). It is engineered to enhance the material's creep-rupture strength in high-temperature environments, where standard 304 would soften and 304L would lose its structural integrity.

 

Why is the "H" in 304H important for high-temperature applications?

The "H" stands for "High Carbon." Higher carbon content provides greater tenslle and yield strength at temperatures exceeding
525°C (975° F). Unlike 304L, which loses structural integrity at extreme heat, 304H maintains its mechanical properties and creep resistance.

 

Grade 304H stianless steel  Equivalents

STANDARD / REGION	DESIGNATION	NOTES
UNS	S30409	Universal identifier for 304H
EN	1.4948 / X6CrNi18-10	Per EN 10088-1 and EN 10028-7. Not 1.4307 (1.4307 = X2CrNi18-9 = 304L)
JIS	SUS304H	Per JIS G 4303 (bars), JIS G 4304 (plates), JIS G 3459 (pipes)
GB	0Cr18Ni9H	Legacy designation; still found in older procurement documents
GB	07Cr19Ni10	Per GB/T 20878-2007 and GB/T 1220-2007
GOST	08X18H10	Per GOST 5632-2014

 

304 vs. 304L Vs. 304H:Chemical Composition

ELEMENT	304H (UNS S30409)	304 (UNS S30400)	304L (UNS S30403)
Carbon (C)	0.04–0.10	≤ 0.08	≤ 0.03
Chromium (Cr)	18.0–20.0	18.0–20.0	18.0–20.0
Nickel (Ni)	8.0–10.5	8.0–10.5	8.0–12.0
Manganese (Mn)	≤ 2.00	≤ 2.00	≤ 2.00
Silicon (Si)	≤ 0.75 (a)	≤ 0.75	≤ 0.75
Phosphorus (P)	≤ 0.045	≤ 0.045	≤ 0.045
Sulfur (S)	≤ 0.030	≤ 0.030	≤ 0.030

304 vs. 304L Vs. 304H: Mechanical Properties at Room Temperature

PROPERTY	304H (S30409)	304 (S30400)	304L (S30403)	TEST METHOD
Tensile Strength (min.)	515 MPa	515 MPa	485 MPa	ASTM A370 / ISO 6892-1
Yield Strength 0.2% Offset (min.)	205 MPa	205 MPa	170 MPa	ASTM A370 / ISO 6892-1
Elongation in 50 mm (min.)	40%	40%	40%	ASTM A370
Hardness (max.)	201 HBW / 92 HRB	201 HBW / 92 HRB	201 HBW / 92 HRB	ASTM E18 / ISO 6506
Elastic Modulus (typical)	193 GPa	193 GPa	193 GPa	-

 

304 vs. 304H: Creep Strength Advantage

Compared to standard 304, the primary advantage of 304H lies in its creep-rupture strength within the temperature range of 540–870°C. Creep, defined as the plastic deformation that occurs over time under constant stress at high temperatures, is the primary failure mechanism for high-temperature pressure equipment. According to the allowable stress intensity values in Table 1A of Section II, Part D of the ASME BPVC, the allowable stress for 304H is approximately 15%–25% higher than that of 304 at a temperature of 600°C and a design life of 100,000 hours. This means that for a given design pressure, it can either reduce wall thickness (thereby saving material costs) or extend service life.

 

 

304H Stainless Steel: Oxidation Resistance

304H stainless steel sheets contain a chromium content of 18%–20%, which allows a continuous and well-adhered chromium oxide (Cr₂O₃) scale to form on the exposed surface. In oxidizing atmospheres at temperatures up to approximately 870°C, this oxide layer is thermodynamically stable and possesses self-healing capabilities. Under cyclic operating conditions (repeated heating and cooling), this oxide layer continues to provide protection, provided that the thermal expansion mismatch between the oxide layer and the base metal does not lead to scale spalling.

SERVICE TEMPERATURE	RECOMMENDED GRADE	RATIONALE
Below 540°C	304 or 304L	304H provides no creep advantage; 304L preferred if welded without PWHT
540–815°C	304H (optimal range)	Maximum creep strength advantage; oxidation resistance fully adequate
815–870°C	304H (acceptable with caveats)	Creep strength remains adequate; oxidation rate increases; monitor for sigma phase embrittlement after >1,000 h
870–980°C	309S (UNS S30908)	Higher Cr (22–24%) for improved oxidation resistance
980–1,150°C	310S (UNS S31008) or Incoloy 800H/HT	Maximum oxidation and carburization resistance; 304H inadequate

 

Welding Performance of 304H Stainless Steel Plate

Grade 304H stainless steel plate has fair-to-good fusion welding performance using standard processes (like TIG, MIG, and MMA), but its higher carbon content (0.04–0.10%) increases the risk of carbide precipitation and sensitization in the heat-affected zone compared to low-carbon variants like 304L.

Welding Procedure Recommendations

Processes: GTAW (TIG) preferred for root passes and thin sections (≤6 mm); GMAW (MIG) or SMAW (stick) for fill and cap passes on thicker sections.
Heat input: Maintain 1.0–2.5 kJ/mm. Excessive heat input promotes grain growth in the heat-affected zone (HAZ), reducing both ambient and elevated-temperature toughness.
Interpass temperature: Maximum 150°C to minimize carbide precipitation time in the sensitization range.
Preheat: Not required for sections ≤25 mm. For thicker sections, preheat to 50–100°C to reduce restraint stress.
Post-weld heat treatment (PWHT): Solution anneal at 1,040–1,120°C followed by water quench or rapid air cool. Recommended for sections >12 mm or when maximum creep properties are required. For thin sections in non-critical service, as-welded condition is acceptable provided ER308H filler was used and interpass temperature was controlled.
Shielding gas (GTAW/GMAW): Pure argon (99.995%) or argon + 2–5% hydrogen for improved weld pool fluidity. Nitrogen additions (≤3%) can increase weld metal strength.

 

Applications of 304H Stainless Steel

304H is widely used in industries requiring materials that offer high-temperature resistance, corrosion resistance, and high strength. Specific applications include:
Petrochemical industry: Piping systems and heat exchangers.
Power generation industry: Superheater and reheater tubes in boilers.
Chemical processing: Pressure vessels and condensers.
Industrial furnaces: Furnace components and exhaust systems.

 

 

Product Forms & Applicable Standards

304H is produced across all common stainless steel product forms. When writing procurement specifications, reference the correct ASTM/ASME standard for the product form:

PRODUCT FORM	ASTM STANDARD	ASME EQUIVALENT	TYPICAL THICKNESS/DIAMETER RANGE
Plate, Sheet, Strip	A240 / A240M	SA-240	0.3–200 mm
Seamless Pipe	A312 / A312M TP304H	SA-312	NPS 1/8 – 30 (DN 6–750)
Seamless Tube	A213 / A213M TP304H	SA-213	OD 6–127 mm
Welded Tube	A249 / A249M TP304H	SA-249	OD 6–127 mm
Bar, Rod, Shapes	A276 / A276M	SA-276	6–600 mm (bar)
Forgings	A182 / A182M F304H	SA-182	Per forging design

FAQ

 What is the maximum service temperature for 304H stainless steel?
Answer: 304H exhibits excellent oxidation resistance during intermittent service (up to 870°C/1600°F) and can withstand temperatures up to 925°C (1700°F) in continuous service.
However, its most effective operating temperature range for structural applications involving stress is between 500°C and 800°C.

 

Does 304H become brittle after prolonged exposure to heat?
Answer: Although 304H is designed for high-temperature environments, prolonged exposure within the 425°C to 815°C range can lead to carbide precipitation (sensitization), which may affect its corrosion resistance in aqueous media.

 

What is the recommended grain size for 304H?
Answer: To maximize high-temperature creep performance, ASTM A213 and A312 standards typically require a grain size of ASTM No. 7 or coarser (i.e., larger grain size) for 304H. Larger grain sizes reduce the number of grain boundaries where creep can occur.

 

Is 304H suitable for offshore or marine environments?
Answer: While 304H offers good corrosion resistance (comparable to 304), it is not the optimal choice for chloride-containing marine environments. In such environments, duplex steel 2205 or grades 316/316H are recommended due to their higher molybdenum content, which provides effective resistance to pitting corrosion.