304H Stainless Steel: 304 Grade with Optimized High-Temperature Strength

304H is a high-carbon version of 304 (carbon content 0.04%-0.10%). By increasing the carbon content, it enhances the creep strength and rupture strength at high temperatures, solving the problem of 304 being prone to deformation during long-term service at 500-800℃. It is a cost-effective choice for medium and high-temperature structural parts.

Core Parameters

Chemical Composition (wt%): C=0.04-0.10, Si≤1.00, Mn≤2.00, P≤0.045, S≤0.030, Cr=18.00-20.00, Ni=8.00-10.50, Fe=Balance

Mechanical Properties (Annealed): Tensile Strength ≥515MPa, Yield Strength ≥205MPa, Elongation ≥40%, Brinell Hardness ≤201HB

Service Temperature: 500℃ to 870℃ (continuous service), up to 925℃ for short-term service

Equivalent Grades: SUS304H (JIS), EN 1.4307 (EN), UNS S30409 (ASTM)

Performance Advantages: The creep rupture life at 500-800℃ is 2-3 times that of 304; high-temperature oxidation resistance is equivalent to 304, with an oxidation rate ≤0.1mm/year at 800℃; good weldability, and matching ER308H welding wire can ensure high-temperature performance of the weld.

Typical Applications: Boiler superheater tubes, internal supports of industrial furnaces, high-temperature fan blades, internal parts of chemical reactors (500-700℃), steam pipelines of thermal power plants.

Practical Q&A

Q1: Will the "high carbon" of 304H cause corrosion problems? A1: Corrosion resistance at room temperature is similar to 304, but attention should be paid to intergranular corrosion after welding. The risk of carbide precipitation can be eliminated by controlling welding heat input (≤150J/mm), selecting low-hydrogen welding wire, or performing annealing treatment at 1050℃ after welding.

Q2: What are the differences in high-temperature performance between 304H and 316H? A2: 316H contains molybdenum (2%-3%), with stronger high-temperature corrosion resistance (such as in sulfur-containing gases), but its cost is more than 40% higher than 304H. In terms of pure high-temperature strength (without corrosion), they are similar, so 304H is preferred for high-temperature working conditions without corrosion.

Q3: What is the maximum safe service temperature of 304H? A3: Continuous service should not exceed 870℃. Beyond this temperature, carbides will dissolve rapidly, and strength will drop sharply. It can withstand 925℃ for a short time (≤100 hours), but the risks of oxidation and deformation must be evaluated.

Q4: Is 304H suitable for low-temperature environments? A4: Not suitable. High carbon reduces low-temperature toughness, and brittle fracture is prone to occur below -40℃. For low-temperature working conditions (such as liquid nitrogen equipment), 304L or 316L should be selected, whose low-carbon design can ensure low-temperature safety.

Q5: What should be noted in the hot working of 304H? A5: Control the hot working temperature at 1100-1200℃, avoid prolonged stay in the 800-1000℃ range to prevent sigma phase precipitation and subsequent embrittlement; air cooling or water cooling is required after processing to ensure a stable austenitic structure.