SUS 347 Forgings: Nb-Stabilized Austenitic Stainless Steel (UNS S34700 / AISI 347 / 1.4550)

Forged rings, seamless rolled rings, flanges, round bars, discs, sleeves, bushings, tube sheets, shafts and forged tubes, produced to drawing by Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory in Jiangyin, Jiangsu, China.
Page last reviewed 4 October 2026

1. Chemical Composition of SUS 347

EN 1.4550 narrows nickel to 9.0 - 12.0 % and sulfur to 0.015 % max. Several pipe and forging specifications hold silicon to 0.75 %. The 347H variant raises carbon to 0.04 - 0.10 % for better creep strength. We melt to the limits of whichever specification appears on the purchase order.

2. Mechanical Properties, Solution-Annealed

Behaviour at temperature

For the equivalent grade 1.4550, published 0.2 % proof strength runs at roughly 175 MPa at 100 C, 155 MPa at 200 C, 136 MPa at 300 C, 125 MPa at 400 C and 119 MPa at 500 C, with the elastic modulus falling from 194 GPa to 165 GPa across the same span. Niobium stabilization is what holds these values after long exposure in the carbide precipitation range, and it is the main reason 347 outperforms titanium-stabilized 321 in creep and stress rupture. Continuous service is limited by scaling at 871 C (1600 F).

3. Physical Properties

4. SUS 347 Equivalent Grades

Product forms and governing standards

The same chemistry is supplied under the JIS designation SUS 347 where a Japanese specification is nominated. If your order is written to the ASTM forging standard, see our page on A182-F347 forgings.

5. Forging and Heat Treatment

Melting routes available at our works for this grade are EAF plus VOD, with ESR remelting where a cleaner and more homogeneous structure is needed for rotating or pressure-retaining parts.

Welding

All common shielded-fusion and resistance processes are suitable. Oxyacetylene welding is not recommended because of carbon pick-up. AWS E347 and ER347 consumables are the normal match. Keep heat input, base-metal dilution and joint restraint low to limit hot cracking. The alloy can be used as welded. Tests on the equivalent 1.4550 grade show resistance to intergranular attack both as heat treated and after a sensitizing treatment, so post-weld heat treatment is not normally mandatory, though a stabilizing treatment is worth considering for hot service.

6. Corrosion Resistance

Annealed SUS 347 resists atmospheric corrosion, foodstuffs, sterilizing solutions, many organic chemicals and dyestuffs, and a broad range of inorganic chemicals. Published ratings are good in nitric acid and salt spray and excellent in humid atmospheres. Performance is moderate in sulfuric and phosphoric acid, acetic acid, sodium hydroxide and sour oil and gas service, and restricted in sea water. Like every austenitic stainless steel it stays vulnerable to pitting and crevice attack at high chloride levels, so it is not a replacement for a duplex or 6Mo grade in seawater duty. For those services see A182-F53, A182-F55 or A182-F44. Surfaces should be free of scale, lubricant and embedded iron. Cleaning and passivation after machining is recommended.

7. Typical Applications for SUS 347 Forgings

The grade is specified wherever a welded or hot-running 18-8 component would otherwise sensitize. Forged rings, seamless rolled rings and shafts in SUS 347 go into aircraft collector rings and piston-engine exhaust manifolds, expansion joints and high-temperature chemical process equipment. Forged flanges, tube sheets, forged tubes and pipe components serve heat exchangers, separators, superheaters, boilers and chemical piping, together with pulp and paper digesters, liquor tanks and paper machines.

In refining, the stabilized structure is the reason 347 is chosen for polythionic acid service, where unstabilized austenitics are open to intergranular stress corrosion cracking during shutdowns. Forged valve bodies, stems, seat rings and blocks in SUS 347 are used in ball, gate, globe, check and plug valves. Forged bars, gears, spindles and sleeves go into turbines, gas compressors, gearboxes and power transmission. Forged discs, bushings and nozzles are used in food processing and storage equipment, pharmaceutical and biochemical plant, thermal oxidizers in waste treatment, shipbuilding and general heavy machinery.

8. Our SUS 347 Forging Capability

9. SUS 347 Questions and Answers

10. Related Stainless Steel Forging Grades

• A182-F347
• A182-F321
• A182-F44
• A182-F51
• A182-F53
• A182-F55
• A182-F61
• 904L
• Sanicro 28
• Alloy 24
• 17-4PH
• Nitronic 50

Technical data on this page is compiled from published alloy datasheets and material standards for the 347 / UNS S34700 / 1.4550 family and is given for guidance. Values are typical figures or specification minimums and are not a guarantee of the properties of any individual heat. The specification stated on the purchase order takes precedence.