Stainless Steel, Martensitic
431 Stainless Steel (S43100) Bar
A high chromium, low nickel high hardenability martensitic stainless steel.
431 stainless steel is a martensitic precipitation-hardening stainless steel known for its high strength, good corrosion resistance, and excellent mechanical properties. It is a versatile alloy widely used in applications requiring a combination of strength, toughness, and moderate corrosion resistance.
1.4057 (Type 431) is a hardenable martensitic stainless steel alloy which combines high tensile strength and torsional strength. The material is well suited to shaft manufacture due to these characteristics.
Of all the stainless steels, 1.4057 it has one of the best combinations of high strength, corrosion resistance, and good impact toughness.
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Range
| Product Form | Condition | Imperial Sizes | Metric Sizes |
| Round Bar | QT800 | 1⁄8" - 6" | 4.0mm - 30.0mm |
| Round Bar | Condition P | 1⁄8" - 6" | 4.0mm - 30.0mm |
PLEASE NOTE
If you do not see what you are looking for, please contact your local service centre with your specific requirements.
431 Stainless Steel Related Specifications
| System / Standard | Country / Region | Grade / Designation |
| AISI | USA | 431 |
| UNS | International | S43100 |
| EN / W.Nr. | Europe | 1.4057 |
| EN Name | Europe | X17CrNi16-2 |
| ASTM A276 | USA | 431 (bars, shapes) |
| ASTM A182 | USA | F431 (forgings, flanges, fittings) |
| ASTM A314 | USA | 431 (forged/rolled bars for piping) |
| GB | China | 1Cr17Ni2 |
| JIS | Japan | SUS431 |
| BS | UK | 431S29 |
Properties
Chemical Composition
| Chemical Element | % Present |
| Carbon (C) | 0.00 - 0.20 |
| Manganese (Mn) | 0.00 - 1.00 |
| Silicon (Si) | 0.00 - 1.00 |
| Phosphorous (P) | 0.00 - 0.04 |
| Sulphur (S) | 0.00 - 0.03 |
| Chromium (Cr) | 15.00 - 17.00 |
| Nickel (Ni) | 1.25 - 2.50 |
Mechanical Properties
| Mechanical Property | Value |
| Elongation A50 mm | 11 % |
| Tensile Strength | 850-1000 MPa |
| Proof Stress | 665 MPa |
| Hardness Brinell | 248-302 HB |
General Physical Properties
| Physical Property | Value |
| Density | 7.8 g/cm³ |
| Modulus of Elasticity | 200 GPa |
| Thermal Conductivity | 20.2 W/m.K |
Applications of 431 Stainless Steel
431 stainless steel is a martensitic stainless steel known for its high strength, good corrosion resistance, and excellent hardness. It is widely used in applications requiring high mechanical strength and moderate corrosion resistance.
1. Aerospace and Automotive Components
Aircraft structural parts and fasteners
Automotive engine components, shafts, and valve parts
High-strength springs and connecting rods
2. Mechanical and Industrial Applications
Pumps, valves, and fasteners in moderately corrosive environments
Gears, bushings, and bearings requiring wear resistance
Hydraulic and pneumatic components
3. Oil, Gas, and Petrochemical Industry
Equipment and components exposed to moderate corrosion and high stress
Shafts, pins, and valve stems in chemical processing equipment
4. Marine and General Engineering
Marine fasteners and hardware requiring strength and corrosion resistance
Precision engineering parts subjected to mechanical stress and moderate corrosion
Summary
431 stainless steel combines high strength, good hardness, and moderate corrosion resistance, making it suitable for aerospace, automotive, industrial, oil and gas, and marine applications. It is ideal for components requiring durability under stress in moderately corrosive environments.
Characteristics of 431 Stainless Steel
431 stainless steel is a martensitic stainless steel known for its high strength, excellent hardness, and good corrosion resistance. It is widely used in applications that require mechanical durability and moderate resistance to corrosion.
1. Chemical Composition
Chromium: 15–17% – provides corrosion resistance and hardenability
Nickel: 1.25–2.5% – improves toughness and corrosion resistance
Carbon: 0.12–0.25% – enables high hardness after heat treatment
Minor elements like manganese, silicon, and molybdenum enhance mechanical properties
2. Mechanical Properties
High tensile strength and yield strength
Can be hardened to 50–55 HRC after heat treatment
Excellent wear resistance and fatigue strength
3. Corrosion Resistance
Good resistance to oxidation and mild corrosive environments
Superior to standard carbon steels but lower than austenitic stainless steels (304/316)
Suitable for marine, chemical, and industrial applications with moderate corrosion
4. Fabrication and Machinability
Machinable in annealed condition
Can be welded carefully, though post-weld heat treatment is recommended to restore hardness
Cold working is possible but may require stress relief
5. Applications
Aerospace and automotive components
Pump, valve, and fastener parts
Shafts, springs, and structural components
Oil, gas, and petrochemical equipment
Summary
431 stainless steel is characterized by high strength, excellent hardness, and moderate corrosion resistance. Its combination of properties makes it ideal for aerospace, automotive, industrial, and marine applications requiring durable, wear-resistant components.
Additional Information
Fabrication
Fabrication of 431 Stainless Steel
431 stainless steel is a martensitic precipitation-hardening stainless steel known for its high strength, good corrosion resistance, and excellent mechanical properties. Its fabrication requires careful handling due to its hardening capability and strength.
1. Forming
Hot Working:
Can be performed in the annealed condition.
Typical hot working temperature: 950–1050°C (1740–1920°F).
Avoid overheating to prevent grain growth, which reduces toughness.
Cold Working:
Cold forming is possible in the annealed state.
Increases strength via strain hardening, but excessive deformation may cause cracking.
Cold rolling, bending, and stamping are common processes.
2. Machining
Easier to machine in the annealed condition.
Hardened 431 is difficult to machine, requiring carbide tooling and slower speeds.
Good surface finish can be achieved with proper tooling and coolant.
3. Welding
Weldable, but preheating and post-weld heat treatment are recommended to reduce stress and prevent cracking.
Use matching or low-carbon filler materials to maintain corrosion resistance and mechanical properties.
4. Heat Treatment
Annealing, solution treatment, and precipitation hardening are part of fabrication to achieve desired hardness, strength, and dimensional stability.
Proper heat treatment is essential after forming or welding.
5. Surface Treatment
Can be polished or passivated to improve corrosion resistance.
Surface finishing is important for aerospace, automotive, and precision applications.
6. Applications Benefiting from Fabrication
Automotive shafts, fasteners, and valve components
Aerospace hardware
Pump shafts, springs, and high-strength mechanical components
Summary
Fabrication of 431 stainless steel is typically performed in the annealed condition, with careful hot and cold working, machining, and welding procedures. Post-fabrication heat treatment and surface finishing ensure optimal strength, corrosion resistance, and dimensional stability, making it ideal for high-strength, precision applications in automotive, aerospace, and industrial fields.
Weldability
Weldability of 431 Stainless Steel
431 stainless steel is a martensitic precipitation-hardening stainless steel known for its high strength, good corrosion resistance, and excellent mechanical properties. While it is weldable, special precautions are needed due to its tendency to harden and the risk of cracking.
1. General Considerations
Preheating is recommended to reduce thermal stresses and prevent cracking.
Welding should ideally be performed in the annealed or solution-treated condition.
Avoid excessive heat input to minimize distortion and loss of mechanical properties.
2. Preheating
Typical preheat: 150–200°C (300–390°F).
Reduces the risk of cold cracking in the heat-affected zone (HAZ).
3. Welding Methods
TIG (GTAW) and MIG (GMAW) are commonly used.
Stick welding (SMAW) is possible with low-hydrogen electrodes.
Precise control of welding parameters is critical to avoid cracking and loss of corrosion resistance.
4. Filler Materials
Use matching 431 filler metal for optimal mechanical properties and corrosion resistance.
Low-carbon martensitic or precipitation-hardening fillers can be used to reduce cracking risk.
5. Post-Weld Heat Treatment
Stress relief or precipitation hardening is often required after welding.
Heat treatment typically involves heating to 480–500°C (900–930°F) to restore strength and toughness.
Ensures that welded areas maintain mechanical properties similar to the base metal.
6. Limitations
Welding in the fully hardened condition is not recommended due to the risk of cracking.
High-strength welded joints may require careful control of heat input and post-weld treatment.
Not as easily weldable as austenitic stainless steels like 304 or 316.
7. Applications Benefiting from Welded 431 Stainless Steel
Automotive shafts, fasteners, and valve components
Aerospace hardware
High-strength industrial components
Summary
431 stainless steel is weldable with precautions, ideally in the annealed or solution-treated condition. Proper preheating, controlled welding, matching filler metal, and post-weld heat treatment are essential to achieve high-strength, corrosion-resistant, and crack-free welds, making it suitable for automotive, aerospace, and high-strength industrial applications.
Machinability
Machinability of 431 Stainless Steel
431 stainless steel is a martensitic precipitation-hardening stainless steel known for its high strength, toughness, and corrosion resistance. Its machinability depends on the heat treatment condition, with the annealed state being easier to machine than the hardened or aged condition.
1. General Characteristics
Annealed 431:
Relatively easy to machine with standard high-speed steel (HSS) or carbide tools.
Provides good surface finish and dimensional control.
Hardened or aged 431:
Difficult to machine due to high hardness (up to ~50 HRC).
Requires carbide tooling, slower cutting speeds, and proper coolant.
2. Recommended Cutting Parameters
Cutting Speed: Lower speeds for hardened or precipitation-hardened material.
Feed Rate: Moderate, balancing surface finish and tool life.
Depth of Cut: Shallow for hardened steel to reduce tool wear.
Coolant: Use water-soluble oils or cutting fluids to reduce heat and friction.
3. Tooling
Annealed condition: High-speed steel (HSS) tools can be used for general machining.
Hardened/aged condition: Carbide or ceramic tools are recommended for drilling, turning, and milling.
Threading and tapping: Slow speeds and sharp tooling to avoid galling or cracking.
4. Effects of Machining
Strain hardening may occur in the machined surface if proper speeds are not maintained.
Good dimensional precision can be achieved in the annealed condition.
Hardened 431 requires careful handling to maintain surface quality.
5. Applications Benefiting from Machinability
Automotive shafts and fasteners
Aerospace components
Precision valves and pump parts
High-strength mechanical parts
6. Limitations
Hardened 431 is challenging to machine without specialized tools.
Excessive heat during machining may reduce hardness or damage the surface.
Requires careful cooling, tooling, and feed rate control.
Summary
Machinability of 431 stainless steel is moderate in the annealed condition and difficult in the hardened or aged condition. Proper tool selection, cutting speed, feed, and coolant use are essential to achieve accurate dimensions, good surface finish, and long tool life, making it suitable for automotive, aerospace, and high-strength industrial components.
Corrosion Resistance
Corrosion Resistance of 431 Stainless Steel
431 stainless steel is a martensitic precipitation-hardening stainless steel that combines high strength, toughness, and moderate corrosion resistance. Its corrosion resistance is better than most carbon steels but lower than austenitic stainless steels like 304 or 316.
1. General Properties
Exhibits good resistance to atmospheric corrosion and mild oxidizing environments.
Maintains resistance to freshwater, mildly acidic conditions, and some chemical exposures.
Less resistant to chloride-rich environments or marine applications, where pitting and crevice corrosion may occur.
2. Factors Affecting Corrosion Resistance
Heat treatment: Hardened or precipitation-hardened conditions may slightly reduce corrosion resistance.
Surface finish: Smooth, polished, or passivated surfaces improve resistance.
Environment: Performs well in low-corrosion, indoor, or mildly humid conditions; avoid continuous exposure to aggressive salts.
3. Enhancing Corrosion Resistance
Polishing: Reduces surface roughness and corrosion initiation points.
Passivation: Nitric or citric acid treatment forms a protective oxide layer.
Regular maintenance: Cleaning and drying prevent corrosion and staining.
4. Applications Benefiting from Corrosion Resistance
Automotive components exposed to moderate conditions (shafts, fasteners)
Aerospace hardware
Precision industrial parts and valves
Components in mildly corrosive environments where strength is critical
5. Limitations
Not recommended for marine or highly acidic environments without protective coatings.
Susceptible to pitting and crevice corrosion in chloride-rich environments.
Welding without post-weld treatment may reduce localized corrosion resistance.
Summary
431 stainless steel provides moderate corrosion resistance, suitable for automotive, aerospace, and industrial applications where high strength and toughness are essential. Its corrosion resistance can be enhanced by polishing, passivation, and proper maintenance, but it is less suitable for highly corrosive or marine environments.
Cold Working
Cold Working of 431 Stainless Steel
431 stainless steel is a martensitic precipitation-hardening stainless steel known for its high strength, toughness, and moderate corrosion resistance. Cold working can be used to increase strength and hardness, but it requires careful control due to the steel’s high strength and work-hardening tendency.
1. General Characteristics
Cold working increases strength and hardness via strain hardening.
Ductility decreases as the amount of cold deformation increases.
Work is typically performed in the annealed or solution-treated condition to reduce the risk of cracking.
2. Recommended Practices
Anneal or solution-treat the steel before cold working for improved ductility.
Apply gradual deformation rather than aggressive forming to avoid fractures.
Lubrication can reduce tool wear and surface defects.
For extensive deformation, intermediate annealing may be necessary to restore ductility.
3. Effects of Cold Working
Increased strength and hardness proportional to deformation.
Reduced ductility, making further forming more difficult.
Surface finish and dimensional accuracy can be improved in some processes.
4. Applications Benefiting from Cold Working
Automotive shafts, fasteners, and springs
Aerospace components requiring high strength
Precision mechanical parts and industrial tools
Components that will undergo final hardening after shaping
5. Limitations
Hardened or overworked 431 stainless steel is brittle and prone to cracking.
Requires careful control of deformation and temperature.
Cold working alone cannot achieve final hardness—post-working heat treatment is usually required.
Summary
Cold working of 431 stainless steel is most effective in the annealed or solution-treated condition, allowing shaping and forming while increasing strength and hardness. Excessive cold deformation reduces ductility, so controlled deformation and intermediate annealing are critical. After cold working, heat treatment is typically applied to achieve the desired mechanical properties, making it suitable for automotive, aerospace, and high-strength industrial components.
Heat Treatment
Heat Treatment of 431 Stainless Steel
431 stainless steel is a martensitic precipitation-hardening stainless steel known for its high strength, toughness, and corrosion resistance. Heat treatment is critical to achieve optimal mechanical properties, including hardness, strength, and dimensional stability.
1. Annealing
Purpose: Softens the steel for forming, machining, or cold working.
Process:
Heat to 840–900°C (1545–1650°F).
Hold to achieve uniform microstructure.
Slow cooling in furnace or still air.
Result: Produces a soft, ductile, and machinable steel.
2. Solution Treatment
Purpose: Dissolves precipitates to prepare for aging.
Process:
Heat to 980–1020°C (1800–1870°F).
Quench rapidly in air or oil.
Result: Forms a homogeneous martensitic structure ready for precipitation hardening.
3. Precipitation Hardening (Aging)
Purpose: Achieves high strength and hardness.
Process:
Heat to 480–500°C (900–930°F) for 1–4 hours, depending on section size.
Air cool to room temperature.
Effect: Precipitates strengthen the martensitic matrix, producing high tensile strength and hardness.
4. Effects of Heat Treatment
Annealed 431: Soft, ductile, suitable for forming and machining.
Solution-treated: Prepares steel for aging with uniform structure.
Aged/precipitation-hardened: High strength (~930–1000 MPa), high hardness, and good corrosion resistance.
5. Applications Benefiting from Heat Treatment
Automotive shafts, fasteners, and springs
Aerospace components
Industrial tools and precision components
Components requiring a combination of strength, toughness, and corrosion resistance
6. Limitations
Overheating during aging can reduce toughness.
Uneven heating or quenching may cause distortion or residual stresses.
Requires controlled temperatures and times to achieve optimal mechanical properties.
Summary
Heat treatment of 431 stainless steel involves annealing, solution treatment, and precipitation hardening to achieve a balance of high strength, hardness, and corrosion resistance. Proper control of temperature and time ensures that the steel meets the mechanical and functional requirements for automotive, aerospace, and industrial applications.
Heat Resistance
Heat Resistance of 431 Stainless Steel
431 stainless steel is a martensitic precipitation-hardening stainless steel known for its high strength, good corrosion resistance, and toughness. Its heat resistance is moderate, sufficient for many industrial applications but lower than that of austenitic stainless steels like 304 or 316.
1. General Properties
Suitable for intermittent service up to 425–450°C (800–840°F).
Continuous exposure to higher temperatures may lead to softening and reduced mechanical properties.
Exhibits good oxidation resistance under moderate temperatures but may scale in prolonged high-heat environments.
2. Effects of High Temperature
Loss of hardness: Martensitic and aged structures may soften if exposed to excessive heat.
Reduced tensile strength and toughness when used continuously at elevated temperatures.
Oxidation and scaling: Occurs above recommended service temperatures, particularly in air or oxidizing environments.
3. Practical Considerations
Best used in moderate-temperature industrial, automotive, or aerospace applications.
Avoid continuous exposure to high temperatures exceeding 425°C (800°F).
Heat-treated 431 retains strength better than annealed steel but is not suitable for furnace or flame-exposed components.
4. Applications Benefiting from Heat Resistance
Automotive components such as shafts, gears, and fasteners
Aerospace parts exposed to moderate heat
Industrial valves and mechanical components
Applications requiring a combination of strength and corrosion resistance under moderate temperatures
5. Limitations
Not suitable for continuous high-temperature applications above 450°C.
Prolonged exposure to heat can lead to softening, dimensional changes, and surface oxidation.
Heat-treated 431 is preferred when mechanical properties at moderately elevated temperatures are critical.
Summary
431 stainless steel offers moderate heat resistance, capable of handling intermittent temperatures up to ~425°C (800°F). While it maintains strength, hardness, and corrosion resistance at these levels, it is not intended for continuous high-temperature service, making it suitable for automotive, aerospace, and industrial components exposed to moderate heat.
Hot Working
Hot Working of 431 Stainless Steel
431 stainless steel is a martensitic precipitation-hardening stainless steel known for its high strength, good corrosion resistance, and toughness. Hot working is generally performed in the annealed or solution-treated condition to enable shaping while avoiding cracking and excessive hardening.
1. General Guidelines
Hot working temperature: 900–1050°C (1650–1920°F).
Steel should be in the annealed or solution-treated condition prior to hot working.
Avoid overheating to prevent grain growth, which reduces toughness.
2. Common Hot Working Processes
Hot rolling: Produces bars, plates, and sheets.
Hot forging: Shapes shafts, blades, or other high-strength components.
Hot extrusion: Forms complex profiles and precision parts.
3. Advantages of Hot Working
Reduces strength and hardness temporarily, making deformation easier.
Minimizes brittleness and cracking risk compared to cold working.
Promotes uniform microstructure and better mechanical properties after subsequent heat treatment.
4. Post-Hot Working Considerations
Annealing or solution treatment may be applied to relieve internal stresses.
Machining is easier after hot working in the annealed state.
Final precipitation hardening (aging) is performed after shaping to achieve high strength and hardness.
5. Limitations
High-carbon content limits ductility compared to austenitic stainless steels.
Requires careful temperature control to avoid surface oxidation, scaling, or distortion.
Hot working in the hardened or aged condition is not recommended.
6. Applications Benefiting from Hot Working
Automotive components (shafts, fasteners)
Aerospace hardware
High-strength industrial tools and precision components
Components that require final heat treatment for maximum strength
Summary
Hot working of 431 stainless steel is performed in the annealed or solution-treated condition at 900–1050°C (1650–1920°F). This process allows rolling, forging, and extrusion while minimizing brittleness and promoting a uniform microstructure. After hot working, stress relief, machining, and precipitation hardening are applied to achieve the desired strength, hardness, and corrosion resistance, making 431 stainless steel suitable for automotive, aerospace, and high-strength industrial applications.
