SUS316H High-carbon Knowledge

SUS316H is a high-carbon variant of SUS316, with carbon content ranging from 0.04% to 0.10% to enhance high-temperature strength and creep resistance. It retains SUS316's excellent chloride corrosion resistance, while being optimized for long-term service in high-temperature and corrosive environments, making it ideal for petrochemical and power generation equipment.

Chemical Composition (Key, % JIS G4305): C0.04–0.10; Cr16.0–18.0; Ni10.0–14.0; Mo2.0–3.0; Mn≤2.0

Mechanical Properties (Annealed): Tensile Strength≥515MPa; Yield Strength≥205MPa; Elongation≥40%; Hardness≤217HB

Performance Advantages: Superior high-temperature creep resistance vs. SUS316; excellent chloride corrosion resistance; suitable for continuous service at 800–900°C; good thermal stability.

Applications: Petrochemical reactor tubes, boiler superheater tubes, high-temperature heat exchangers, offshore oil platform pipelines.

Equivalent Grades: ASTM 316H, EN 1.4406, DIN X6CrNiMo17-12-2

Comparison with SUS316: SUS316H has higher carbon content and better high-temperature strength, but is prone to intergranular corrosion after welding; SUS316 is more suitable for low-temperature non-welded applications.

FAQs

How does high carbon content improve SUS316H's high-temperature performance?

The high carbon content (0.04–0.10%) of SUS316H enhances its high-temperature strength and creep resistance by promoting the formation of fine chromium carbides at grain boundaries. At high temperatures (above 600°C), these carbides act as barriers to restrict the movement of grain boundaries, reducing the creep deformation of the steel under long-term stress. For standard SUS316, the lower carbon content results in fewer carbides, so its grain boundaries slide more easily at high temperatures, leading to faster creep failure. SUS316H's higher carbon content ensures the formation of a sufficient number of uniformly distributed carbides, which significantly improve its structural stability at 800–900°C. This advantage makes it the preferred material for petrochemical reactor tubes and boiler superheater tubes that operate under high temperature, high pressure and corrosive conditions for a long time. In addition, the combination of molybdenum and carbides also enhances its high-temperature corrosion resistance in chloride-containing environments.

 

What makes SUS316H suitable for petrochemical reactor applications?

SUS316H is widely used in petrochemical reactors due to its excellent combination of high-temperature strength, creep resistance and corrosion resistance, which can meet the harsh operating conditions of petrochemical processes. Petrochemical reactors usually operate at high temperatures (600–800°C) and high pressures, and the medium often contains corrosive substances such as hydrocarbons, acids and chlorides. SUS316H's high carbon content provides excellent creep resistance, ensuring that the reactor tubes do not deform under long-term stress. Its 2–3% molybdenum content enhances its resistance to chloride-induced pitting corrosion, preventing the reactor from leaking due to localized corrosion. In addition, SUS316H has good thermal cycling stability, which can withstand the repeated heating and cooling during reactor start-up and shutdown. Compared with other high-temperature materials such as nickel alloys, SUS316H also has a significant cost advantage, reducing the investment cost of petrochemical equipment.

 

Is SUS316H suitable for welded applications, and what precautions should be taken?

SUS316H is not ideal for welded applications, because its high carbon content makes it prone to intergranular corrosion in the heat-affected zone after welding. When SUS316H is welded, the heat-affected zone is heated to the 425–815°C sensitization range, which promotes the precipitation of chromium carbides at grain boundaries, depleting chromium in the surrounding areas and creating corrosion-vulnerable zones. To restore the corrosion resistance of the weld joint, post-weld heat treatment (annealing at 1010–1120°C and water quenching) is required to dissolve the carbides and restore the uniform chromium distribution. However, for large welded components such as reactor tubes, post-weld heat treatment is often impractical due to size limitations. Therefore, for welded high-temperature and corrosive applications, stabilized grades such as SUS316Ti or low-carbon SUS316L are more suitable choices. If SUS316H must be welded, it is recommended to use SUS316L filler wire to reduce the carbon content of the weld and minimize the risk of carbide precipitation.

How does SUS316H compare to SUS304H in terms of performance and applications?

SUS316H and SUS304H are both high-carbon stainless steel grades optimized for high-temperature applications, but they differ significantly in corrosion resistance and application scope due to the presence of molybdenum in SUS316H. SUS316H contains 2–3% molybdenum, which gives it excellent chloride corrosion resistance, making it suitable for high-temperature and corrosive environments such as petrochemical reactors and offshore oil platforms. SUS304H does not contain molybdenum, so its corrosion resistance is limited to general atmospheric and mild chemical environments, and it is mainly used in power plant boiler tubes and industrial furnace parts. In terms of high-temperature performance, both grades have excellent creep resistance, but SUS316H has better high-temperature corrosion resistance in sulfur-containing and chloride-containing environments. In addition, SUS316H has a higher nickel content than SUS304H, which improves its cryogenic toughness and high-temperature stability. However, SUS316H is more expensive than SUS304H, so it is only used when corrosion resistance requirements are high.

 

What heat treatment is required for SUS316H to optimize its performance?

The recommended heat treatment for SUS316H is solution annealing, which is designed to optimize its microstructure and maximize high-temperature strength and creep resistance. The specific process is to heat the steel to 1010–1120°C, hold it for 30–60 minutes per 25mm of thickness, and then cool it rapidly with water. This process dissolves the existing chromium carbides into the austenitic matrix, and the rapid cooling prevents the carbides from re-precipitating during cooling, ensuring a uniform and fine-grained microstructure. After annealing, SUS316H has a uniform carbide distribution and excellent high-temperature performance, which can extend the service life of high-temperature components. It should be noted that SUS316H should not be tempered at low temperatures, because tempering will promote the precipitation of carbides at grain boundaries, reducing its toughness and corrosion resistance. For welded SUS316H components, post-weld annealing is also required to eliminate intergranular corrosion, but this process is only feasible for small components due to size constraints.