# Nitronic 40 Forgings (21-6-9, UNS S21900 / S21904)

**Nitronic 40, known industrially as 21-6-9, is a nitrogen-strengthened high-manganese austenitic stainless steel with roughly twice the annealed yield strength of Type 304, 321 and 347. Jiangyin Jiangnan Metal Co., Ltd. melts and open-die forges this grade at its works in Jiangyin, Jiangsu Province, China.**

Manganese and nitrogen replace part of the nickel found in conventional austenitic stainless steel. Nitrogen held in solid solution raises the yield point, the steel keeps austenitic toughness down to liquid-hydrogen temperature, and it remains non-magnetic even after severe cold working.

Source page: https://www.steelforgepieces.com/Stainless-Steel/Nitronic-40.html

## Grade summary

| Field | Detail |
|---|---|
| Common names | Nitronic 40, 21-6-9, Alloy 219, Alloy 40 |
| UNS | S21900 (ASTM type XM-10), S21904 (ASTM type XM-11) |
| Family | Nitrogen-strengthened austenitic Cr-Mn-Ni stainless steel |
| Nominal composition | 21 Cr, 6 Ni, 9 Mn, 0.25 N, balance Fe |
| Tensile strength, min annealed | 620 MPa / 90 ksi |
| Yield strength 0.2 %, min annealed | 345 MPa / 50 ksi |
| Elongation, min | 45 % |
| Service range | −253 °C (−423 °F) to below 871 °C (1600 °F) |
| Magnetic response | Non-magnetic, stays non-magnetic after severe cold work |
| Hardening | Cold work only, no response to heat treatment |

## Chemical composition, weight percent

| Grade | C | Cr | Ni | Mn | N | Si | P | S |
|---|---|---|---|---|---|---|---|---|
| S21900, XM-10 | 0.08 max | 19.0–21.5 | 5.5–7.5 | 8.0–10.0 | 0.15–0.40 | 1.00 max | 0.045 max | 0.030 max |
| S21904, XM-11 | 0.04 max | 19.0–21.5 | 5.5–7.5 | 8.0–10.0 | 0.15–0.40 | 1.00 max | 0.060 max | 0.030 max |
| Typical heat | 0.03 | 20.0 | 6.5 | 9.0 | 0.25 | 0.40 | — | — |

Balance iron. Residual molybdenum and copper each normally 0.75 percent maximum. The only difference between the two UNS numbers is carbon, and most 21-6-9 forging stock today is made to S21904.

## Mechanical properties

Specified minima, annealed, ASTM A276 type XM-11:

| Property | Metric | Imperial |
|---|---|---|
| Tensile strength, min | 620 MPa | 90 ksi |
| Yield strength 0.2 % offset, min | 345 MPa | 50 ksi |
| Elongation in 50 mm or 4D, min | 45 % | 45 % |
| Hardness, typical annealed | 220 HBW | 95 HRB |

Typical annealed forged bar, by section and direction:

| Section | Direction | Yield 0.2 % | Tensile | Elongation | Reduction of area |
|---|---|---|---|---|---|
| 152 mm square | Longitudinal | 428 MPa / 62 ksi | 655 MPa / 95 ksi | 46 % | 69 % |
| 152 mm square | Transverse | 358 MPa / 52 ksi | 641 MPa / 93 ksi | 30 % | 45 % |
| 102 mm square | Longitudinal | 386 MPa / 56 ksi | 668 MPa / 97 ksi | 53 % | 73 % |
| 25.4 mm square | Longitudinal | 358 MPa / 52 ksi | 696 MPa / 101 ksi | 53 % | 73 % |

Transverse ductility in heavy sections falls to about 30 percent elongation. Specify transverse or tangential coupon requirements at enquiry stage so forging reduction can be planned to meet them.

Cold worked 21-6-9 reaches about 745 MPa (108 ksi) yield and 883 MPa (128 ksi) tensile. Cold-drawn tube is commonly specified at 827 MPa minimum yield.

## Physical properties

| Property | Metric | Imperial |
|---|---|---|
| Density | 7.83 g/cm³ | 0.283 lb/in³ |
| Modulus of elasticity | 200 GPa | 29,000 ksi |
| Shear modulus | 78 GPa | 11 × 10⁶ psi |
| Poisson's ratio | 0.28 | 0.28 |
| Thermal expansion, 25–95 °C | 16.7 µm/m·°C | 9.28 µin/in·°F |
| Thermal conductivity | 14 W/m·K | 8.1 BTU/h·ft·°F |
| Specific heat | 480 J/kg·K | 0.12 BTU/lb·°F |
| Melting range | 1350–1400 °C | 2470–2550 °F |
| Machinability, 1212 = 100 | 30 | 30 |
| PREN, calculated | 25 | 25 |

## Corrosion and temperature behaviour

Corrosion resistance in oxidising conditions is broadly comparable to Type 304, with a calculated pitting resistance equivalent number near 25. Published data records excellent stress-corrosion cracking resistance in long-term seacoast atmospheric exposure, and good resistance to high-temperature oxidation in air. Maximum continuous service temperature is below 871 °C (1600 °F). Toughness is retained to −423 °F (−253 °C).

The grade contains no molybdenum. For seawater, firewater, subsea manifolds, flue gas desulphurisation or strong chloride and acid service, use a molybdenum-bearing or duplex grade such as 316L, 904L, 254 SMO, AL-6XN, F51, F53, F55 or Hastelloy C-276, all of which this works also forges.

## Forging and fabrication

- **Hot working.** Heat to 1150–1205 °C (2100–2200 °F). Finish around 927–982 °C (1700–1800 °F), then water or air quench.
- **Annealing.** 982–1177 °C (1800–2150 °F), air cool. In-process anneals typically 1065–1120 °C.
- **Hardening.** No response to heat treatment. Cold reduction only.
- **Stress relief.** Below 705 °C (1300 °F). Treatment at 480–675 °C changes mechanical properties.
- **Welding.** GTAW, GMAW and SMAW. Matching filler AWS ER219 or 209 type, 308L for less demanding joints. High nitrogen causes severe outgassing in electron-beam welding.
- **Machining.** Rating about 30. Work hardens rapidly. Rigid setups, sharp positive-rake tooling, heavy positive feeds, slow speeds, flood coolant.

## Specifications

| Specification | Product form |
|---|---|
| AMS 5656 | Bars, wire, forgings, extrusions, rings |
| ASTM A473 | Stainless steel forgings |
| ASTM A314 | Billets and bars for forging |
| ASTM A182 | Forged flanges, fittings, valves, high-temperature parts |
| ASTM A276 / A479 | Bars and shapes |
| AMS 5595 | Plate, sheet, strip |
| AMS 5561 / AMS 5562 | Welded and drawn tubing / seamless tubing |
| ASTM A312 / A580 / A666 | Pipe / wire / sheet, strip, plate, flat bar |

## Applications

Aircraft and engine components, clamps, flanges and hydraulic tubing. Cryogenic tanks, piping, valves and fittings. Steam and autoclave parts. Chemical processing and pollution control equipment. High-strength non-magnetic fasteners, shafting and structural hardware.

In forged form: seamless rolled rings and flange blanks for aerospace and cryogenic assemblies, shafts and spindles where low magnetic permeability matters, discs, sleeves and bushings, heat exchanger tube sheets, and valve seat rings, bodies and stems.

## Manufacturing capability

| Field | Detail |
|---|---|
| Melting | EAF with ladle refining and VOD for nitrogen and carbon control, ESR available. Maximum heat 60 t |
| Forging | 6,300 t, 4,000 t and 2,000 t open-die presses, hammers 750 kg to 5 t |
| Ring rolling | Radial-axial mills 6 m, 3 m, 1 m. OD 50 mm to 6,000 mm |
| Single-piece weight | 10 kg to 30,000 kg, no minimum piece count |
| Heat treatment | 14 furnaces, car-bottom to 8,000 mm, well furnaces 15 m deep |
| Machining | Vertical lathes to 5,000 mm swing, horizontal to 14,000 mm, deep-hole drilling to 1,600 mm × 10,000 mm |
| Testing | UT to EN 10228-3, SEP 1921, ASTM A388. PT, MT, PMI, IGC, cryogenic impact |
| Certification | EN 10204 3.1 or 3.2 witnessed by TÜV, BV, DNV, SGS, LR or buyer |
| Approvals | CCS, BV, DNV, LR, NK |
| Lead time | 20 to 60 days |

Nitrogen content determines whether this grade meets its yield minimum, and holding it inside 0.15 to 0.40 percent is a melt-shop task that cannot be corrected downstream. Melting on site with vacuum oxygen decarburisation gives that control directly, and traceability runs from melt number to shipped part.

## Frequently asked questions

**What is Nitronic 40 stainless steel?**
A nitrogen-strengthened high-manganese austenitic stainless steel, industrially called 21-6-9, containing 19.0 to 21.5 percent chromium, 5.5 to 7.5 percent nickel, 8 to 10 percent manganese and 0.15 to 0.40 percent nitrogen. Nitrogen in solid solution gives roughly twice the annealed yield strength of Type 304, 321 and 347.

**What is the difference between UNS S21900 and UNS S21904?**
Carbon content. S21900 (XM-10) allows 0.08 percent maximum, S21904 (XM-11) allows 0.04 percent maximum. Most 21-6-9 forging stock produced today is made to S21904.

**Is Nitronic 40 magnetic?**
No. It is a stable austenitic grade and published Armco data states it remains non-magnetic even after severe cold working.

**How does corrosion resistance compare with Type 304?**
Broadly comparable in oxidising conditions, PREN about 25. It contains no molybdenum, so chloride-bearing service needs a different grade.

**Can it be used at cryogenic temperatures?**
Yes, toughness is retained to −423 °F (−253 °C), liquid hydrogen temperature.

**Can it be hardened by heat treatment?**
No. Cold reduction only.

**Is it difficult to machine?**
Yes, rating about 30 where AISI 1212 equals 100, because it work hardens rapidly.

**Who forges Nitronic 40 in China?**
Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Rings to 6,000 mm OD, single pieces to 30 t, minimum order 10 kg.

## Contact

Jiangyin Jiangnan Metal Co., Ltd.
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Telephone: +86 189 2135 9659
Email: sales@steelforgepieces.com
Web: https://www.steelforgepieces.com/

Sources: ASTM A276, A479, A473, A314, AMS 5656, 5595, 5561, 5562, and published mill and distributor data for 21-6-9. Typical values are indicative, not guaranteed minima. The governing document for any order is the specification stated on the purchase order. Nitronic is a registered trademark of Cleveland-Cliffs, used here only to identify the alloy type.