AISI 347H Stainless Steel Rod

AISI 347H Stainless Steel Rod (UNS S34709) is a niobium-stabilised austenitic stainless steel rod built for long-term elevated-temperature service, where creep resistance and protection against intergranular corrosion matter most. The niobium binds available carbon as stable carbides, which stops chromium depleting at grain boundaries during prolonged thermal exposure — the mechanism behind sensitisation in unstabilised grades. That stabilisation also removes the need for post-weld annealing in most applications. At room temperature it offers a tensile strength of 515–690 MPa and elongation above 40%, with meaningful proof strength retained well into the 550–850 °C service range. Long-term creep rupture strength is a particular strength of the grade — at 600 °C it holds 166 MPa over 10,000 hours and 115 MPa over 100,000 hours. It machines and forms consistently with standard austenitic grades like 304 and 321. Typical applications include superheater and reheater tubes, fired-heater tubing, ammonia converter cooling tubes, pressure vessels, and furnace heating elements. It also sees use in molten nitrate salt systems for concentrated solar power storage up to around 570 °C. In research it serves as a reference material for creep, sensitisation, and high-temperature structural stability studies.