347 / 347H
UNS S34700 / S34709
Overview
Niobium-stabilized austenitic stainless steel offering higher temperature strength than 321. Niobium (columbium) stabilization prevents intergranular corrosion and provides superior creep resistance at temperatures up to 925°C. 347H (high carbon) delivers enhanced high-temperature strength. The preferred grade for refinery hydroprocessing units, thermal oxidizers, and nuclear applications.
Chemical Composition (wt%)
| Element | Min | Max |
|---|---|---|
| C (Carbon) | — | 0.08 |
| Mn (Manganese) | — | 2 |
| Si (Silicon) | — | 0.75 |
| P (Phosphorus) | — | 0.045 |
| S (Sulfur) | — | 0.03 |
| Cr (Chromium) | 17 | 19 |
| Ni (Nickel) | 9 | 13 |
| Nb (Niobium) | 0.5 | 0.7 |
Mechanical Properties
| Property | Value | Condition |
|---|---|---|
| Tensile Strength | ≥ 515 MPa (75 ksi) | — |
| Yield Strength (0.2%) | ≥ 205 MPa (30 ksi) | — |
| Elongation | ≥ 40% | — |
| Hardness | ≤ 90 HRB | annealed |
| Density | 8.0 g/cm³ | — |
Physical Properties
| Property | Value |
|---|---|
| Melting Range | 1400 – 1425 °C |
| Max Service Temp | 925°C |
| Thermal Conductivity | 16.1 W/m·K (at 100°C) |
Corrosion Resistance
Comparable to 304 with superior high-temperature intergranular corrosion resistance. Niobium stabilization provides better protection than titanium (321) in certain environments including strong oxidizing conditions. Resistant to polythionic acid SCC. Excellent for repeated heating/cooling cycles in refinery service. Not intended for severe chloride pitting environments.
Typical Applications
Related Standards
Available Products in This Material
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