347 Stainless Steel (UNS S34700)
Austenitic (Nb-stabilized) · ASTM A240/A240M · Density 8 g/cm³
Type 347 (UNS S34700) is a niobium-stabilized 18/8 austenitic stainless steel used where welding or elevated-temperature exposure makes stabilization part of the approved material strategy. Refinery piping, boiler components and exhaust fabrications are common contexts, but allowable stress, creep life and corrosion performance must come from the applicable product and design standards.
Quotation brief
Quote 347 When
Quote 347 when a niobium-stabilized 18/8 grade is explicitly required for welded or elevated-temperature equipment and the governing design code provides the needed basis. It is relevant to refinery piping, boiler parts, expansion joints and exhaust systems that can experience a sensitizing thermal cycle and later aqueous exposure. The grade label does not by itself establish creep life, allowable stress, weld-metal chemistry or suitability for chlorides.
Best fit
- Refinery and boiler fabrications whose approved material specification names UNS S34700 and requires niobium stabilization after welding.
- Expansion joints, exhaust parts and hot piping evaluated under a design code with defined temperature, load, duration and shutdown environment.
- Orders that need traceable stabilized chemistry, solution-treated delivery, qualified filler practice and documented inspection requirements.
Limits to check
- 347 is not 347H unless the ordered chemistry, product requirements and inspection document satisfy the higher-carbon designation.
- The alloy is not a molybdenum-bearing chloride grade, so stabilization should not be confused with improved pitting or crevice resistance.
- Elevated-temperature strength and creep behavior require code data for the product form and condition; room-temperature A240 values are insufficient for design.
Quoted product forms
Quoted product forms for 347 Stainless Steel (UNS S34700)
We quote 347 Stainless Steel as sheet / plate, pipe / tube, bar against the named product standard.
- Traceability: heat or lot identity plus the inspection document named in the RFQ (EN 10204 3.1 when that route supports it).
- Processing: decoiling, cutting, polishing, shearing and beveling as ordered.
- Next step: send product form, size and quantity; we quote the supply route.
Chemical Composition (wt%)
| C | Mn | Si | Cr | Ni | Nb | P | S |
|---|---|---|---|---|---|---|---|
| ≤0.08 | ≤2.00 | ≤0.75 | 17.0–19.0 | 9.0–13.0 | 10×C–1.00 | ≤0.045 | ≤0.030 |
Single values are maximums unless a range is shown. Balance: Fe. Per ASTM A240/A240M.
Mechanical Properties
| Tensile strength | ≥515 MPa (75 ksi) |
|---|---|
| Yield strength (0.2%) | ≥205 MPa (30 ksi) |
| Elongation (50 mm) | ≥40% |
| Hardness | ≤201 HBW |
Room-temperature minimum values are summarized for annealed flat product under ASTM A240/A240M unless a condition is named in the property label; product form and thickness can change the requirement.
Physical Properties & Structure
| Density | 8 g/cm³ |
|---|---|
| Magnetic response | Essentially non-magnetic after solution annealing; cold work can introduce a measurable magnetic response. |
| Microstructure | Austenitic (Nb-stabilized) |
Corrosion Resistance & Limits
- 347 has an 18/8 chromium-nickel base without an intentional molybdenum range, so wet-corrosion behavior is closer to stabilized 304-family material than to 316. Chlorides, crevices, deposits and shutdown condensate still require separate assessment.
- Niobium stabilization reduces sensitization risk only within a compliant chemistry and heat-treatment condition. Weld heat tint, filler selection, surface contamination and long thermal exposure can still affect local corrosion and must be included in the inspection plan.
Fabrication & Heat Treatment
| Welding | The welding specification must define filler, purge, heat input and any code-required treatment for the joint. Stabilized base metal does not automatically qualify weld metal or eliminate the need to remove heat tint in corrosive shutdown service. |
|---|---|
| Forming | 347 can be formed in the annealed condition, with work hardening and springback increasing as reduction rises. Heavy forming, weld-joint placement and any intermediate anneal need review because the final thermal history matters to stabilization. |
| Machining | Use rigid tooling and positive feed to cut beneath the work-hardened surface, with coolant and chip control suited to niobium-stabilized austenitic material. Avoid dwell that raises tool wear and distorts thin-wall parts. |
| Heat treatment | Solution treatment and any stabilization treatment must follow the governing product and fabrication procedure. 347 is not hardened by conventional quench-and-temper practice, and an unqualified thermal cycle can alter grain size and dimensional stability. |
Equivalent Grades
The closest international equivalents of 347 Stainless Steel are 1.4550 (X6CrNiNb18-10) in the EN system, SUS347 in the JIS system, 06Cr18Ni11Nb in the GB system.
These are common corresponding designations, not unconditional substitutes. Verify chemistry, mechanical properties, product standard, delivery condition, dimensions and project approval before changing designation.
| System | Designation |
|---|---|
| UNS | S34700 |
| EN | 1.4550 (X6CrNiNb18-10) |
| JIS | SUS347 |
| GB | 06Cr18Ni11Nb |
Ordering Checks for 347
- State UNS S34700 or the exact approved designation, governing product standard, form, dimensions, condition and surface finish.
- Identify whether the design requires 347 or 347H, then specify the code, temperature, duration, load case and any stabilization treatment.
- Provide welding code, filler classification, purge, heat input, post-weld cleaning and examination requirements for the finished joint.
- Request the required inspection certificate and verify heat chemistry, niobium stabilization, tensile properties, heat treatment and traceability.
Reference Product Forms & Dimensional Ranges
Common reference product forms for 347 stainless steel: Sheet / Plate, Pipe / Tube, Bar.
| Finishes | No.1, 2B |
|---|---|
| Sheet / coil thickness | 0.5–6.0 mm |
| Plate thickness | 6–50 mm |
Common surface and delivery options
- No.1, 2B, BA or mechanically polished finish when supported by the product route
- Annealed and pickled, descaled or polished tube finish as specified
- Hot rolled, peeled, bright drawn, ground or polished bar condition according to tolerance
These published ranges are engineering references, not a live-stock or production-capability promise. Send the required product form, dimensions, condition and finish; we quote the matching supply route.
Browse related product hubs:Sheet & plate,Coil & strip,Pipe & tube,Bar & rod.
Typical Applications
- Refinery and petrochemical piping
- Boiler and superheater tubes
- Aircraft and gas-turbine exhaust
- Expansion joints and bellows
- High-temperature process equipment
347 Compared With Other Grades
Frequently Asked Questions
What is the difference between 347 and 321 stainless steel?
Both are stabilized 18/8 grades: 321 uses titanium and 347 uses niobium. That difference affects ordered chemistry, filler practice and elevated-temperature design data. Neither is an unconditional substitute for the other; confirm the product standard, weld procedure, code allowables and current quotation.
When is 347 required instead of 304L?
347 may be specified when a welded component sees a sensitizing thermal cycle and must retain intergranular-corrosion resistance for later aqueous exposure, or when the design code specifically uses stabilized-grade data. 304L and 347 have different chemistry and code allowables, so the duty and approved specification decide.
What is 347H?
347H is a separately controlled higher-carbon variant used where the governing code and product specification require its elevated-temperature properties. A certificate marked only 347 does not establish compliance with 347H; verify carbon range, stabilization, product form, heat treatment and all ordered requirements.
Published by Tsingshan (Shandong) Iron & Steel Co., Ltd..Sources, update policy and technical limitations.
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