Key Feature

The Columbium-Stabilized High-Temperature Austenitic Stainless Steel Bar Stock. Niobium addition prevents sensitization in welded structures and provides improved high-temperature strength compared to 304/304L.

The preferred choice for welded and high-temperature bar applications exposed to corrosive environments in the 425-900°C range.

Common Designations

UNS S34700
AISI 347
ASTM A276 (Stainless Steel Bars)
ASTM A479 (Bars for Pressure Vessels)
EN 1.4550, X6CrNiNb18-10
JIS SUS347
BS 347S17

Columbium (Cb) is also known as niobium (Nb); both designations refer to the same element.

Chemical Composition (Typical wt.%)

C: ≤ 0.08
Cr: 17.0 - 19.0
Ni: 9.0 - 12.0
Cb (Nb): ≥ 10×C (min 0.80%)Mn: ≤ 2.00
Si: ≤ 1.00
P: ≤ 0.045
S: ≤ 0.030

Columbium content is critical: minimum 10 times carbon content, typically 0.8-1.1%.

Mechanical Properties

Tensile Strength: ≥ 515 MPa
Yield Strength: ≥ 205 MPa
Elongation: ≥ 40%
Hardness: ≤ 201 HB
Machinability: 45% of B1112 steel

Similar to 304 in annealed condition, but with better high-temperature properties.

Elevated Temperature Properties

Continuous Service: Up to 900°C
Intermittent Service: Up to 870°C
Creep Strength: Better than 304
Stabilized up to: 900°C

Superior to 304/304L for long-term exposure in the 425-900°C range.

Physical Properties

Density: 7.90 g/cm³
Melting Range: 1399 - 1454 °C
Thermal Expansion: 17.3 × 10⁻⁶/K (20-100°C)
Thermal Conductivity: 16.3 W/m·K (100°C)
Non-magnetic when annealed

Essentially identical to 304 in physical properties.

Available Forms

Rounds: 6mm - 250mm diameter
Squares: 6mm - 125mm
Hexagons: 6mm - 100mm
Flats: Various sizes
Billets: For forging applications
Forgings: Custom forged parts

Full range of bar stock forms and sizes available.

Surface Conditions

Hot Rolled: Black bar
Cold Drawn: Bright finish
Centerless Ground: Precision ground
Polished: For specific applications
Peeled: Improved surface for machining

Various surface finishes available for different requirements.

Corrosion Resistance

Excellent general corrosion resistance similar to 304. Superior resistance to intergranular corrosion after exposure to sensitizing temperatures (425-900°C).

Specifically designed to prevent weld decay in corrosive high-temperature environments.

Machining Characteristics

• Similar to 304 in machinability
• Columbium carbides can be abrasive
• Good surface finish achievable
• Proper tool selection important
• Standard machining practices apply

Columbium carbides may slightly increase tool wear compared to 304.

Welding Characteristics

Excellent weldability
Columbium stabilization prevents sensitization
No post-weld annealing required for most applications
Matching filler metals recommended

Superior weld performance compared to non-stabilized grades like 304.

High-Temperature Strength

At 600°C: ~60% of room temp strength
At 700°C: ~45% of room temp strength
At 800°C: ~30% of room temp strength

Good high-temperature strength retention for bar applications.

Key Standards

ASTM A276 347: Stainless Steel Bars
ASTM A479 347: Bars for Pressure Vessels
ASTM A484: General Requirements
EN 10088-3: Stainless Steel Bars
JIS G4303: Stainless Steel Bars
ASME SA479: Code Construction
AMS 5512 (Aerospace)

Widely specified in pressure vessel and high-temperature codes.

Common Applications

• High-Temperature Components: Valve bodies, turbine parts, heat exchanger components
• Welded Fabrications: Chemical reactor parts, pressure vessel components, heat exchangers
• Aerospace: Jet engine components, afterburner parts, exhaust system components
• Power Generation: Superheater supports, boiler components, high-temperature fasteners
• Chemical Processing: Reactor agitator shafts, pump shafts, valve stems
• Food Processing: High-temperature processing equipment, sterilization system parts
• Industrial Heating: Furnace parts, radiant tubes, heat treatment fixtures

Specifically selected where welding and high-temperature exposure combine with corrosive conditions.