AISI 403 – UNS S40300
Turbine-quality 12% Cr martensitic stainless steel
Variant of 410 with Si limited to 0.50%, produced for steam turbine and compressor blades and components. Hardenable by quenching and tempering, it combines moderate to high mechanical strength with mild corrosion resistance (atmosphere, steam, fresh water). Magnetic in all conditions.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | S40300 |
| W.Nr./EN | ≈ 1.4006 (X12Cr13) |
| DIN | ≈ X10Cr13 |
| JIS | SUS403 |
| Trade names | Type 403 (turbine quality) |
| Others | GB 12Cr12 (formerly 1Cr12); AMS 5611 (bar/forging) |
Standards by product form
| Form | Standard |
|---|---|
| Bar | ASTM A276 / A479 (403); AMS 5611 |
| Forging | ASTM A473 (403); AMS 5611 |
| Plate | ASTM A240 (403, on request) |
| Wire | ASTM A580 |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7222.30.00 | 7222.30 | 7222.30.0024 | 7222 30 51 |
| Hot-rolled bar | 7222.11.00 | 7222.11 | 7222.11.0059 | 7222 11 11 |
| Plate (> 10 mm, width ≥ 600 mm) | 7219.21.00 | 7219.21 | 7219.21.0020 | 7219 21 10 |
| Flange and fitting | 7307.21.00 | 7307.21 | 7307.21.5000 | 7307 21 00 |
Tariff class: stainless steel (by chemical composition, under the Chapter 72 Notes and Section XV Note 5).
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
ASTM A276 / A479 (S40300)
| Element | Range (%) |
|---|---|
| C | ≤ 0.15 |
| Mn | ≤ 1.00 |
| Si | ≤ 0.50 |
| P | ≤ 0.040 |
| S | ≤ 0.030 |
| Cr | 11.5 – 13.0 |
| Fe | balance |
Mechanical properties
Annealed (ASTM A479); quenched and tempered values depend on the temper
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 275 MPa (annealed) |
| Tensile strength | ≥ 485 MPa (annealed) |
| Elongation | ≥ 20% |
| Reduction of area | ≥ 45% |
| Hardness | ≤ 223 HB (annealed, A479) |
| Quenched and tempered | Rm ≈ 690–900 MPa depending on temper (typical) |
Typical physical properties
| Property | Value |
|---|---|
| Density | 7.75 g/cm³ |
| Melting range | 1,480 – 1,530 °C |
| Modulus of elasticity | 200 GPa |
| Thermal conductivity (100 °C) | 24.9 W/m·K |
| Thermal expansion (20–100 °C) | 9.9 µm/m·K |
| Electrical resistivity | 57 µΩ·cm |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | Oxidation resistance up to ≈ 700 °C (continuous), but mechanical strength drops above ≈ 480–540 °C; typical structural use up to ≈ 450 °C. |
| Heat treatment | Full annealing 830–885 °C, slow furnace cooling (≤ 223 HB). Hardening: austenitize 925–1,010 °C, cool in oil or air. Tempering 565–760 °C according to strength; avoid tempering between 370 and 565 °C (embrittlement and loss of corrosion resistance). |
| Welding | Weldable with care: preheat 200–300 °C, interpass ≥ 200 °C, post-heating/tempering 650–760 °C. Consumables AWS E410/ER410 (same strength) or E309/ER309L when there is no post-weld treatment. |
| Machining | Fair machinability (≈ 55% of free-cutting steel B1112); best in the annealed condition or tempered below 30 HRC. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Steam turbine and compressor blades
- Turbine discs and components
- Bolts and nuts
- Shafts and valve stems
- Pump parts in water and steam
- Blades and finned tubes
Alternatives: 410 for general use (cheaper); 416 when machining is the priority; 422 or 13-4 (F6NM) when more hot strength or toughness is needed; 431 for more corrosion resistance.
AISI 403: complete guide
What AISI 403 stainless steel is
403 belongs to the family of martensitic and ferritic stainless steels. It is a 12% chromium steel of the same class as 410, from which it differs in silicon, limited to 0.50% instead of 1.00%, and in chromium, limited to 13.0%. This narrower composition gives 403 more consistent toughness, which is why it is the classic grade for steam turbine blades.
Chemical composition and microstructure
With carbon up to 0.15% and chromium of 11.5 to 13%, 403 forms austenite above ≈ 900 °C and transforms to martensite on cooling in air or oil. Iron is the balance, about 85 to 88%.
Welding
403 hardens in air, so welding requires preheating to 200 – 300 °C and post-weld tempering at 650 – 760 °C. The consumables are E410 / ER410, or an austenitic 309 when joint strength is not critical.
Corrosion and temperature limits
With a PREN of 11.5 to 13, 403 resists atmosphere, fresh water, steam and petroleum products well, but not chlorides or acids. Corrosion resistance is highest in the quenched and tempered, polished and passivated condition.
Applications
Steam turbine blades and discs, compressor blades, valve stems and seats, pump shafts, bolts and components of furnaces and chemical plants in mild media.
Supply forms and Dustre services
Round bars and blocks forged in open die, cut to size on a band saw, with rough or finish machining, heat treatment (quenching and tempering, annealing, solution annealing and aging) in our own furnaces and hardness, tensile and impact testing. All material is supplied with a 3.1 inspection certificate and heat traceability.
Frequently asked questions
What is the chemical composition of AISI 403?
Per ASTM A276 / A479 (S40300): C ≤ 0.15; Mn ≤ 1.00; Si ≤ 0.50; P ≤ 0.040; S ≤ 0.030; Cr 11.5 – 13.0.
Which standards cover AISI 403?
Bar: ASTM A276 / A479 (403); AMS 5611. Forging: ASTM A473 (403); AMS 5611. Plate: ASTM A240 (403, on request). Wire: ASTM A580.
Up to what temperature can AISI 403 be used?
Oxidation resistance up to ≈ 700 °C (continuous), but mechanical strength drops above ≈ 480–540 °C; typical structural use up to ≈ 450 °C.
Which materials can replace AISI 403?
410 for general use (cheaper); 416 when machining is the priority; 422 or 13-4 (F6NM) when more hot strength or toughness is needed; 431 for more corrosion resistance.
Is AISI 403 martensitic or ferritic?
Martensitic. With carbon up to 0.15% and chromium of 11.5 to 13%, it forms austenite above ≈ 900 °C and becomes martensite on cooling, which is why it hardens by quenching. It is magnetic in all conditions.
