Stainless Steel Grade 403 (AISI/UNS S40300) — Properties, Composition & Applications
A 12% chromium martensitic stainless steel engineered for high-precision forged components — compressor blades, steam turbine buckets, and nuclear control parts. Supplied by Ambica Steels in bars, rods, hexagons, and custom sections.
General Properties:
Type 403 has a metric density of 7.80 g/cm3. A martensitic kind of alloy, Type 403 stainless steel has lower silicon and chromium content than the type 410. It gives it apt strength, toughness and ductility leading to its use as compressor blades, rods and other turbine parts. It scores 80 on the Rockwell B scale, and it has a tensile strength of 485 MPa.
The modulus of elasticity lies in between 190-210 GPa. Type 403 has a specific heat capacity of 0.460 J/g-°C. In comparison to the austenitic 300 series, the Grade 403 is overall high on-resistance, but it is not as resistant to corrosion and oxidation as the 300 series. This alloy is also prone to rust under specific conditions. It is also magnetic by property.
The stainless steel type 403 bar is available in many shapes- round, rectangular, square, flat, billet, hex and custom shapes. It is used, for steam turbine buckets, valves and bucket covers, blades, pump parts, nuclear reactor control, gas turbine compressor, fasteners, shafting.
Chemical Composition:
| Element | Symbol | Min % | Max % |
| Carbon | C | - | 0.15 |
| Chromium | Cr | 11.5 | 13 |
| Manganese | Mn | - | 1 |
| Silicon | Si | - | 0.5 |
| Phosphorus | P | - | 0.04 |
| Phosphorus | S | - | 0.03 |
| Phosphorus | Fe | Balance | ~86% |
Mechanical Properties
| Property | Value | Unit |
| Tensile strength | 485 | MPa |
| Yield strength (0.2%) | 275 | MPa |
| Elongation (50 mm) | 20 | % |
| Reduction in area | 60 | % |
| Hardness (Rockwell) | 80 | HRB |
| Density | 7.8 | g/cm³ |
| Elastic modulus | 190-210 | GPa |
Physical & thermal Properties
| Property | Value | Unit |
| Density | 7.8 | g/cm³ |
| Specific heat capacity | 0.46 | J/g·°C |
| Thermal conductivity | 24.9 | W/m·K at 100°C |
| Thermal expansion | 9.9 | µm/m·°C (0–100°C) |
| Electrical resistivity | 570 | nΩ·m |
| Oxidation resistance (max) | 760 (1400°F) | °C continuous |
| Forging temperature range | 1095–1205 | °C |
Forging:
This metal can be, easily forged both headed or upset. It requires more weight to be forged and therefore, the hammer required for it is heavy. It also requires more blows compared to mild steel. The right temperature for its forging is 2000°F/2200°F (1095°C/1205°C). The correct temperature among the range depends on the deformation.
Post the deformation; it is forged and then air-cooled. If the forging is huge, then it has to be cooled in the furnace or by using dry lime. This type of steel should not be, forged below 1650°F (900°C).
Heat Treatment:
Annealing: All the parts of alloy should be heated uniformly. The correct temperature lies between 1200°F (650°C) and 1400°F (760°C). After heating it to the given temperatures, it is air-cooled. It becomes an important step for its machinability as well.
If the metal is annealed, at a lower temperature, it gives it an optimum hardness for the machinability. If softening is required, the temperature is raised to 1500°F/1650°F (815°C/900°C). It is followed by cooling slowly at the furnace. It gives it 155 BHN. Softness is often required, for cold forming and cold heading.
Hardening: Unlike the 300 stainless steel series, type 403 can be hardened, with heat treatment. It can be attributed to the 11% increase in Chromium and a 1% increase in Manganese when compared to the 300 series.
The hardening will transform the microstructure of the material. However, the extent of hardness depends on the carbon content of the particular material. With this step, the heat elevates the hardness of Grade 403.
Tempering: Tempering completely depends upon the mechanical properties that are being, expected out of the steel. It has to be immersed into water, for at least an hour or two. For larger chunks, it has to be soaked for more time followed by air-cooling. The consequence on the metal is as follows:
If the metal is, tempered between the range of 750°F (400°C) and 1050°F (565°C), this will decrease the strength and corrosion resistance. It is based on the medium circumstances. If this the required strength and ductility, it can be tempered, in this way. But the corrosion resistance might be reduced in this case.
Machinability: Type 403 stainless steel is durable, hard and strong even in its softest condition. Therefore, it can be transformed into tough chips and maintain durability wherever they are, used. It builds upon tools. The heat-treated condition or the drawing in the cold working process can be, used to obtain a better finish. Its material can be machined up to Rc 35 to ensure higher mechanical properties.
Weldability: For welding type 403, the required part must be preheated, at 350/400ºF (180/205ºC). It prevents any cracking that can occur in heavy sections. Annealing is an important step that must be done right after welding as the alloy is air hardening.
Applications of Type 403:
In compressor blades: Type 403 retains its strength even at extremely high temperatures and is ideal for being used in compressor blades. The industry requires a corrosion-resistant material, which makes this alloy a suitable choice.
Automobile exhausts: Type 403 has high-temperature characteristics. The high corrosion resistance specific to rust ensures clean exhaust gases that contribute to the social responsibility of an individual.
Bucket covers: With its convenient flexibility to adapt into a tapered shape, type 403 contributes to the ease of pouring, collecting and cleaning. It also helps in sterilization as it is corrosion-resistant. Moreover, these covers are very reliable and durable as the hardness of type 403 reduces the chances of any damage.
Turbine engines: The power generation industry has to be very careful in choosing the material involved. Type 403 is a good choice as it sustains extreme heat, is resistant to corrosion and maintains its strength.
FAQ:
Q1. Is stainless steel 403 magnetic?
Yes — Grade 403 is magnetic in all conditions. As a martensitic stainless steel, it has a body-centred tetragonal (BCT) crystal structure after hardening, which is inherently ferromagnetic. This is a key difference from austenitic 300-series grades (like 304 or 316), which are non-magnetic in the annealed state.
Q2. What is the difference between SS 403 and SS 410?
Grade 403 has a lower silicon limit (max 0.50% vs 1.00% for 410) and is designed specifically for precision forging of turbine and compressor parts. Grade 410 is a more general-purpose martensitic grade suitable for cutlery, valves, and structural applications. Both are heat-treatable, but 403 offers superior forgeability and ductility due to lower Si content.
Q3. Can SS 403 be hardened by heat treatment?
Yes — Unlike austenitic grades, SS 403 can be through-hardened by heat treatment. The process: heat to 950–980°C (1740–1800°F), then oil or air quench. Temper between 150–370°C for desired hardness. Higher carbon content in the specific heat gives higher hardness potential. Tempering at 400–565°C range reduces strength and corrosion resistance (avoid this range).
Q4. What is the forging temperature for Grade 403?
The recommended forging range is 1095°C to 1205°C (2000°F to 2200°F). Do not forge below 900°C (1650°F) as this causes internal stresses and cracking. After forging large sections, cool slowly in dry lime or furnace. Post-forge annealing at 760–900°C is recommended to relieve stress and restore machinability.
Q5. What are the equivalent grades for SS 403 internationally?
International equivalents: Europe (EN): 1.4000 / X6Cr13 · UK (BS): 403S17 · Japan (JIS): SUS403 · India (IS): X7Cr13 · Russia (GOST): 12X13. Note that equivalence is approximate — always verify the specific compositional limits for your application standard.
Q6. Is SS 403 suitable for marine or chloride environments?
Not recommended for severe marine or chloride-rich conditions. Grade 403's corrosion resistance is moderate — superior to carbon steel but significantly lower than 316L or duplex grades. For marine environments, consider 316L (2% Mo) or duplex 2205. Grade 403 works well in atmospheric and mildly corrosive environments where its strength advantages are needed.
Q7. What sizes and forms does Ambica Steels supply in SS 403?
Ambica Steels supplies Grade 403 in: Round bars (bright, precision, hot-rolled), Flat bars (HRAP and cold-drawn), Hexagon bars, Square bars, and Custom forged sections. We maintain ready stock in New Delhi and Maastricht (NL). Minimum order quantity and pricing available on request — contact dm@ambicasteels.com or call +91 (11) 47034400.
