# AISI 347H Stainless Steel Forgings

**UNS S34709 · ASTM A182 F347H · DIN 1.4961 (X8CrNiNb16-13) · SAE 30347H**

| | |
|---|---|
| Manufacturer | Jiangyin Jiangnan Metal Co., Ltd. — open-die forging factory |
| Address | No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China |
| Telephone | +86 189-2135-9659 (also WhatsApp and WeChat) |
| Email | sales@steelforgepieces.com |
| Page | http://www.steelforgepieces.com/Stainless-Steel/AISI-347H.html |
| Last checked | 1 October 2026 |

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## Contents

1. [Grade description](#1-grade-description)
2. [347 against 347H](#2-347-against-347h)
3. [Standards and equivalents](#3-standards-and-equivalents)
4. [Chemical composition](#4-chemical-composition)
5. [Mechanical properties](#5-mechanical-properties)
6. [Physical properties](#6-physical-properties)
7. [Service temperature](#7-service-temperature)
8. [Corrosion behaviour](#8-corrosion-behaviour)
9. [Heat treatment](#9-heat-treatment)
10. [Forging and hot working](#10-forging-and-hot-working)
11. [Machining and welding](#11-machining-and-welding)
12. [Products supplied](#12-products-supplied)
13. [Common questions](#13-common-questions)
14. [Enquiries](#14-enquiries)

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## Grade at a glance

| Item | Value |
|---|---|
| UNS number | S34709 |
| Structure | Austenitic, niobium stabilised |
| Carbon | 0.04–0.10 % |
| Chromium | 17.0–20.0 % |
| Nickel | 9.0–13.0 % |
| Tensile strength, min | 515 MPa / 75 ksi |
| Yield strength, min | 205 MPa / 30 ksi |
| Oxidation and creep strength to | 816 °C / 1500 °F |
| Hardenable by heat treatment | No, cold work only |
| Magnetic | No, in the annealed condition |
| Forms supplied | Forged bars, rings, rolled rings, discs, blocks, hollow sections, valve and fitting blanks, studs and bolting |

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## 1. Grade description

AISI 347H, unified number S34709, is a chromium-nickel austenitic stainless steel stabilised with niobium and tantalum. Niobium ties up carbon as niobium carbide instead of allowing chromium carbide to form at the grain boundaries, so chromium stays in solution and the steel keeps its corrosion resistance after exposure to 800–1500 °F (427–816 °C).

The H suffix means carbon is held to a range of 0.04 to 0.10 % rather than a 0.08 % ceiling. That carbon addition was made to improve creep resistance and to raise strength at temperatures above 1000 °F (537 °C). In most heats the carbon level allows dual certification to both 347 and 347H.

The structure is face centred cubic. The steel is non-magnetic in the annealed condition and cannot be hardened by heat treatment — strength is raised only by cold work. It is ductile enough to be stamped, blanked, spun and drawn.

## 2. 347 against 347H

| Item | Type 347 | Type 347H |
|---|---|---|
| UNS number | S34700 | S34709 |
| Carbon, % | 0.08 max | 0.04–0.10 |
| Nb + Ta stabilisation | 10 × (C + N) min, 1.00 max | 8 × (C + N) min, 1.00 max |
| Creep strength above 537 °C | Lower | Higher, the reason the grade exists |
| Toughness and durability | Good | Tougher and generally more durable |
| Dual certification | Usually possible, since the carbon ranges overlap | |

The 10 × and 8 × ratios are the ASTM A240 plate limits. Name the governing specification on the order, because the stabilisation ratio and the silicon ceiling are written differently in the plate, forging and tube standards.

## 3. Standards and equivalents

| Standard or system | Designation |
|---|---|
| UNS | S34709 |
| AISI / ASTM type | 347H |
| Forgings | ASTM A182 / A182M Grade F347H · ASTM A336 · ASTM A403 |
| Bar | ASTM A479 |
| Plate, sheet, strip | ASTM A240 · ASME SA 240 · ASTM A480 |
| Tube and pipe | ASTM A213 · A249 · A271 · A312 · A376 · A430 · A813 · A814 |
| DIN / EN | 1.4961 · X8CrNiNb16-13 |
| SAE | SAE 30347H |

**Note on 1.4550.** DIN 1.4550 / X6CrNiNb18-10 is the European equivalent of Type *347*, not of 347H. The 347H counterpart is 1.4961 / X8CrNiNb16-13, classified as a creep resisting steel under EN 10302. The composition bands of 1.4961 and S34709 are not identical, so a drawing calling for one should not be filled with the other without written agreement.

## 4. Chemical composition

Composition limits in weight %.

| Element | ASTM A182 F347H, forgings | ASTM A240 347H, plate |
|---|---|---|
| Carbon, C | 0.04–0.10 | 0.04–0.10 |
| Chromium, Cr | 17.00–20.00 | 17.00–19.00 |
| Nickel, Ni | 9.00–13.00 | 9.00–13.00 |
| Niobium + tantalum, Nb + Ta | Stabilising addition | 8 × (C + N) min, 1.00 max |
| Manganese, Mn | 2.00 max | 2.00 max |
| Silicon, Si | 1.00 max | 0.75 max |
| Phosphorus, P | 0.045 max | 0.045 max |
| Sulfur, S | 0.030 max | 0.030 max |
| Iron, Fe | Balance, roughly 63 to 74 % | Balance |

**On the niobium figure.** The stabilisation requirement is a ratio, not a fixed band, so the minimum niobium moves with the carbon and nitrogen of the heat. Datasheets that quote a flat 0.32 to 1.00 % niobium are reporting the range the ratio produces at typical carbon levels. We work to the ratio in the governing standard and report the measured niobium on the certificate.

## 5. Mechanical properties

### ASTM A182 F347H minimum requirements, room temperature

| Property | Metric | Imperial |
|---|---|---|
| Tensile strength, min | 515 MPa | 75 ksi |
| Yield strength, 0.2 % offset, min | 205 MPa | 30 ksi |
| Elongation in 50 mm or 4D, min | 30 % | 30 % |
| Reduction of area, min | 50 % | 50 % |
| Brinell hardness | Not specified in A182 for this grade | |

### Typical values, annealed condition

| Property | Metric | Imperial |
|---|---|---|
| Tensile strength | 515 MPa | 75,000 psi |
| Yield strength, 0.2 % offset | 205 MPa | 30,000 psi |
| Elongation in 50 mm | 40 % | 40 % |
| Hardness, Brinell | 201 max | 201 max |
| Hardness, Rockwell B | 95 | 95 |
| Modulus of elasticity | 193 GPa | 28.0 × 10⁶ psi |
| Poisson's ratio | 0.27–0.30 | 0.27–0.30 |
| Rupture strength, 750 °C, 100,000 h | 38–39 MPa | 5,510–5,660 psi |

**Conflicting published figures.** Some grade datasheets list 480 MPa tensile and 29 % elongation as typical for 347H. Those numbers fall below the 515 MPa and 30 % minima of ASTM A182 F347H and should not be used for design or acceptance. Where a published value sits below the governing specification, the specification governs. What a heavy forged section actually achieves depends on section size, reduction and test coupon position, all agreed before production starts.

## 6. Physical properties

| Property | Value | Condition |
|---|---|---|
| Density | 7.96 g/cm³ (0.288 lb/in³) | 20 °C. One source gives a wider band of 7.7–8.03 g/cm³ |
| Modulus of elasticity | 193 GPa (28.0 × 10⁶ psi) | Room temperature |
| Thermal conductivity | 16.3 W/m·K | 100 °C, equal to 13.3 BTU/hr/ft²/ft/°F at 200 °F |
| Specific heat | 500 J/kg·K | 0–100 °C, equal to 0.12 BTU/lb·°F over 32–212 °F |
| Melting range | 1398–1446 °C | 2550–2635 °F |
| Electrical resistivity | 72 microhm·cm | As published, at 20 ° |
| Thermal expansion | 16.0 × 10⁻⁶ /°C | 20–100 °C · 9.2 × 10⁻⁶ in/in·°F over 68–212 °F |
| Thermal expansion | 18.9 × 10⁻⁶ /°C | 20–600 °C · 10.5 × 10⁻⁶ in/in·°F |
| Thermal expansion | 20.5 × 10⁻⁶ /°C | 20–1000 °C · 11.4 × 10⁻⁶ in/in·°F |
| Magnetic response | Non-magnetic | Annealed. May turn slightly magnetic after cold work |

The expansion coefficient is high compared with ferritic and martensitic grades and rises further with temperature. Allow for it when 347H forgings are bolted or welded to lower-expansion materials in hot service.

## 7. Service temperature

Three temperatures matter when specifying 347H and they are often confused.

- **427–816 °C (800–1500 °F)** — the chromium carbide precipitation range. Unstabilised grades such as 304 sensitise here. 347H is stabilised specifically to survive it, and in this range its overall corrosion resistance is superior to Type 321.
- **Above 537 °C (1000 °F)** — where the added carbon of 347H gives higher strength and creep resistance than plain 347.
- **816 °C (1500 °F)** — the published figure for good oxidation resistance and creep strength, and for performance in strongly oxidising conditions.

The safe limit for a particular part is not a single number. It depends on the atmosphere, the stress, the design life and the operating cycle, and must be taken from the design code governing the equipment rather than from a grade datasheet. The 100,000 hour rupture strength of 38 to 39 MPa at 750 °C shows how little load the grade carries indefinitely at the top of its range.

The steel also retains good low temperature toughness, which is why it appears in equipment that cycles between cryogenic and hot service.

## 8. Corrosion behaviour

General corrosion resistance is comparable to Type 304. The advantage of the stabilised grade shows after exposure to elevated temperature, where it resists the intergranular attack that would damage an unstabilised steel.

**Suited to:** nitric solutions; most dilute organic acids at moderate temperature; pure phosphoric acid at lower temperature and dilute solutions to about 10 % at elevated temperature; chloride-free and fluoride-free caustic solutions at moderate temperature; polythionic acid stress corrosion cracking service in hydrocarbons.

**Not suited to:** chloride solutions, including low concentrations; sulfuric acid. For chloride-bearing or marine duty, select a duplex or high-molybdenum austenitic grade instead.

## 9. Heat treatment

347H is unresponsive to hardening heat treatment. There is no quench and temper route. The only thermal treatment in normal use is solution annealing, which dissolves precipitates, restores the austenitic structure and relieves forging stresses.

| Stage | Practice |
|---|---|
| Temperature | 1010–1193 °C (1850–2000 °F) |
| Soak | By section thickness, long enough to bring the whole section to temperature |
| Cooling | Water quench |
| Hardening | Not applicable. Strength is raised only by cold work |

**Upper end of the range.** ASTM A182 carries a caution that a solution annealing temperature above 1950 °F may impair properties in the stabilised grades F347, F347H, F348 and F348H. Where the certificate has to satisfy A182, agree the annealing temperature in writing before the charge goes in, rather than working to the top of the wider 2000 °F figure quoted in general datasheets.

## 10. Forging and hot working

| Stage | Temperature or action |
|---|---|
| Hot working range | 1149–1232 °C (2100–2250 °F) |
| After forging | Solution anneal and water quench |
| Cold forming | Readily stamped, blanked, spun and drawn. Work hardens, so interstage annealing may be needed |

Forging, upsetting and other hot work is carried out at 1149 to 1232 °C. The grade does not air harden, so there is no risk of untempered martensite on cooling, but the work must finish hot enough to avoid tearing and then be solution annealed to restore the structure.

### In-house capability

- **Open-die forging** — bars, blocks, solid and hollow shafts and stepped shafts, made to customer drawings.
- **Ring rolling** — seamless rolled rings, sleeves, flange blanks and casings with circumferential grain flow.
- **Heat treatment** — solution annealing with recorded furnace charts and quench records.
- **Testing** — chemical analysis, tensile, impact and hardness testing, ultrasonic and liquid penetrant inspection.

## 11. Machining and welding

### Machining

347H is slightly tougher to machine than Type 304, and the cold work hardening rate makes it less machinable than Type 410. Hold the speed down, keep the feed constant and positive, and do not let the tool dwell, because the surface work hardens under a rubbing edge.

Turning guidelines for the 347 group:

| Tool | Lubrication | Depth of cut | Feed | Speed |
|---|---|---|---|---|
| High speed steel | Cutting oil | 6 mm | 0.5 mm/t | 12–16 m/min |
| High speed steel | Cutting oil | 3 mm | 0.4 mm/t | 18–23 m/min |
| High speed steel | Cutting oil | 1 mm | 0.2 mm/t | 23–28 m/min |
| Carbide | Dry or cutting oil | 6 mm | 0.5 mm/t | 67–76 m/min |
| Carbide | Dry or cutting oil | 3 mm | 0.4 mm/t | 81–90 m/min |
| Carbide | Dry or cutting oil | 1 mm | 0.2 mm/t | 99–108 m/min |

### Welding

The grade welds readily by most standard fusion and resistance processes and post-weld heat treatment is not required. Oxyacetylene welding is not preferred. Use a matching filler and clean the weld area afterwards for best corrosion resistance. Because the stabilising element is in the parent metal, a filler that is not itself stabilised gives a weld deposit with less resistance to intergranular attack than the material either side of it.

## 12. Products supplied

| Form | Items |
|---|---|
| Bars | Forged round bars, square bars, flat and rectangular bars, stepped bars |
| Hollow sections | Hollow bars, sleeves, bushings, barrels, casings, shells, cylinders, hubs, housings |
| Rings | Forged rings, seamless rolled rings, flange blanks |
| Discs and blocks | Forged discs, blocks, plates, tubesheet blanks |
| Pressure parts | Forged valve bodies and body blanks, fitting blanks, header and nozzle forgings |
| Fasteners | Double-ended studs, bolts, nuts, high-temperature bolting stock |

Every shipment carries a mill test certificate to EN 10204 3.1. Third party inspection by SGS, BV, TUV or the customer's own inspector is welcome at our works.

### Where the grade is used

- **Power generation** — superheater and reheater components, boiler tubes and casing, radiant superheaters, high pressure steam piping and the forged parts that connect them.
- **Refining and chemical** — equipment for severe corrosive duty in chemical processing and petroleum refining, heat exchangers and tube, waste heat recovery, pharmaceutical plant.
- **Aerospace and process** — aircraft exhaust stacks and collector rings, cabin heaters, heavy wall welded equipment, food processing equipment and storage vessels.

## 13. Common questions

**What is the difference between 347 and 347H?**
Carbon. Type 347 is capped at 0.08 % carbon while 347H is held to 0.04 to 0.10 %. The higher carbon was specified to improve creep resistance and give higher strength above 1000 °F (537 °C), and it makes the steel tougher and generally more durable. The niobium stabilisation ratio also differs: 10 × (C + N) minimum for 347 against 8 × (C + N) minimum for 347H in ASTM A240. Because the carbon ranges overlap, many heats can be dual certified.

**Can 347H be hardened by heat treatment?**
No. It is austenitic and unresponsive to hardening heat treatment. Hardness and strength increase only by cold working. The solution anneal at 1010 to 1193 °C followed by a water quench dissolves precipitates and relieves stress; it does not harden the steel.

**What is the maximum service temperature?**
Published data gives good oxidation resistance and creep strength to 1500 °F (816 °C), and the grade is intended for the 800 to 1500 °F (427 to 816 °C) carbide precipitation range where unstabilised grades sensitise. The usable limit for a given part is set by the design code, the atmosphere, the stress and the required life. For reference, the 100,000 hour rupture strength at 750 °C is only 38 to 39 MPa.

**Is 347H the same as DIN 1.4961?**
1.4961, X8CrNiNb16-13, is the European creep resisting steel normally cross-referenced to 347H under EN 10302. It is not the same as 1.4550, X6CrNiNb18-10, which corresponds to plain Type 347. The composition bands of 1.4961 and S34709 are not identical, so the order must name which standard governs.

**Does 347H need post-weld heat treatment?**
Not as a rule. It can be readily welded by most standard processes and a post-weld heat treatment is not necessary, which is one reason it is chosen over unstabilised grades for hot service. Oxyacetylene welding is not preferred. Where the fabrication code or client specification calls for a solution anneal after welding, we carry it out and record it.

**Is 347H magnetic?**
It is non-magnetic in the annealed condition because the structure is austenitic. Cold working can make it slightly magnetic. A weak magnetic response in a machined or cold worked surface is normal and is not on its own evidence of a wrong grade.

**Will 347H work in seawater or chlorides?**
No. It does not perform well in chloride solutions even at small concentrations and is unsuitable for sulfuric acid. Its strengths are nitric solutions, dilute organic acids, phosphoric acid within limits, chloride-free caustics and polythionic acid service in hydrocarbons.

**Can you supply one-off or small quantity 347H forgings?**
Yes. Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory, so single pieces, prototypes and production batches are all made to drawing. Send the drawing or dimensions, quantity, governing standard and test requirements to sales@steelforgepieces.com.

**What do you need for a quotation?**
Grade, dimensions or drawing, quantity, governing standard, delivery condition and any inspection requirement. A quotation normally follows within one working day.

## 14. Enquiries

**Jiangyin Jiangnan Metal Co., Ltd.** — open-die forging factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Tel, WhatsApp and WeChat: +86 189-2135-9659
Email: sales@steelforgepieces.com
Website: http://www.steelforgepieces.com/

Include in your enquiry: grade and governing standard, dimensions rough or finished with machining allowance, quantity and required date, delivery condition (as forged or solution annealed), and testing and inspection requirements.

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## Related pages

- All stainless steel grades — http://www.steelforgepieces.com/Stainless-Steel/
- UNS S34709 — http://www.steelforgepieces.com/Stainless-Steel/UNS-S34709.html
- UNS S34700 — http://www.steelforgepieces.com/Stainless-Steel/UNS-S34700.html
- SUS 347 — http://www.steelforgepieces.com/Stainless-Steel/SUS-347.html
- X7CrNiNb18-10 — http://www.steelforgepieces.com/Stainless-Steel/X7CrNiNb18-10.html
- 1.4550 — http://www.steelforgepieces.com/Stainless-Steel/1.4550.html
- 347S51 — http://www.steelforgepieces.com/Stainless-Steel/347S51.html
- AISI 348 — http://www.steelforgepieces.com/Stainless-Steel/AISI-348.html
- Nickel alloys — http://www.steelforgepieces.com/Nickel-Alloy/
- Contact us — http://www.steelforgepieces.com/Contact-Us/