347 vs 347H stainless steel

Q1: What is the key difference in chemical composition between 347 and 347H stainless steel?

A: The main distinction is carbon content.

347 has a standard carbon range of 0.04–0.08%, stabilized with niobium (Nb = 10×C – 1.00%) and tantalum.

347H is a high-carbon variant with a carbon range of 0.04–0.10%, also niobium-tantalum stabilized to avoid sensitization.

Q2: How do their high-temperature mechanical properties compare?

A: 347H exhibits superior high-temperature performance.

347H's higher carbon content boosts creep and rupture strength at temperatures above 550°C, enabling long-term service under sustained heat and load.

347 has good oxidation resistance but lower structural stability than 347H when exposed to high temperatures for extended periods.

Q3: Do 347 and 347H have the same intergranular corrosion resistance?

A: Yes, both grades share excellent intergranular corrosion resistance via the same mechanism.

Niobium and tantalum in both grades react with carbon to form stable carbides, preventing chromium carbide precipitation at grain boundaries during welding or high-temperature exposure.

Neither grade requires post-weld heat treatment to maintain corrosion resistance.

Q4: Which grade is more suitable for high-temperature pressure vessel applications?

A: 347H is the ideal choice for such applications.

Its enhanced high-temperature strength complies with standards like ASME for pressure vessels operating at elevated temperatures.

347 is better suited for general corrosion-resistant uses at moderate temperatures (below 550°C).

Q5: How to choose between 347 and 347H for industrial applications?

A: Select based on operating temperature and service load:

Choose 347 for chemical processing tanks, exhaust manifolds, and cryogenic equipment (prioritizing corrosion resistance at moderate temperatures).

Choose 347H for steam boiler superheaters, gas turbine components, and high-temperature heat exchangers (prioritizing long-term creep strength).