431 Stainless Steel: Properties, Characteristics, Uses

431 stainless steel is a flexible, durable martensitic alloy recognized for its outstanding rust resistance, toughness, and ease of shaping. Widely used in industries, 431 stainless steel offers a balance of toughness and durability. 

In this guide, we explore its properties, applications, equivalent grades, and processing options to help you understand why it’s a reliable choice for demanding environments.

What is 431 Stainless Steel?

431 stainless steel (UNS S43100) is 80-85% iron, 15-17% chromium, and carbon and nickel. It’s martensitic stainless steel that meets ASTM A276 standards, offering strength, corrosion resistance, and machinability. Processing 431 stainless steel at 600°C to 800°C optimizes its performance. Processed by heat treatment, 431 stainless steel is used in aerospace, marine, and automotive sectors for shafts, bolts, and fasteners. Cold working can increase its hardness and strength. 

Properties of 431 Stainless Steel

431 stainless steel is notable for its superior durability, outstanding rust resistance, and solid toughness. Its chromium and nickel content boost durability and oxidation resistance. It also provides excellent resilience and wear resistance, making it perfect for challenging conditions.

Chemical Composition of SS 431

SS 431’s composition is characterized by its high chromium content, which provides superior corrosion resistance, along with moderate levels of carbon and nickel for enhanced strength. For specific figures, please consult the table below.

Mechanical Properties of 431 Stainless Steel

SS 431 is most notable for its high tensile strength and hardness, even after heat treatment, making it suitable for demanding mechanical applications. For specific values at different annealing conditions, see the table below.

Physical Properties of 431

The physical properties of ss 431 are highlighted by its high density and good thermal conductivity, making it suitable for high-stress environments. These values represent general properties under standard annealing conditions and may vary with different heat treatments.

Equivalent Grades of 431 Stainless Steel

431 stainless steel shares similar chemical composition and mechanical properties with equivalent grades used in other countries. These grades provide comparable performance across various applications. Below is a table of equivalent grades from different regions.

Possible Alternative Grades to 431 Stainless Steel

Several stainless steel grades can be alternatives to 431 due to their similar composition or applications:

1. Grade 410: Martensitic stainless steel with chromium. It has good corrosion resistance and strength but slightly lower toughness compared to 431.
2. Grade 420: Higher carbon content than 431. It offers better hardness after heat treatment, suitable for wear-resistant applications, but with lower corrosion resistance.
3. Grade 304: Austenitic stainless steel with higher nickel content. It has excellent corrosion resistance and can replace 431, where corrosion resistance is more important than strength.
4. Grade 316: Contains more molybdenum than 431. Offers better corrosion resistance, especially in marine environments, but has lower strength.

These options can be selected depending on the particular requirement for durability, rust resistance, or strength.

Characteristics of 431 Stainless Steel

431 stainless steel is recognized for its strong tensile durability, outstanding rust resistance, and solid toughness, making it ideal for challenging conditions.

1. High Tensile Strength

431 offers significantly higher tensile strength than many other stainless steels, making it ideal for applications requiring strong, durable materials, such as in aerospace and marine components.

2. Excellent Corrosion Resistance

Due to its high chromium content, 431 stainless steel provides excellent resistance to corrosion, especially in mildly corrosive environments like marine and industrial settings.

3. Good Hardness

431 can reach significant hardness through heat treatment, making it ideal for parts needing wear resistance, like shafts, bolts, and fasteners.

4. Magnetic Properties

Unlike austenitic stainless steels, 431 is magnetic, which can be advantageous in certain mechanical and electrical applications.

5. Heat Treatment Performance

431 responds well to hardening and tempering, allowing for tailored mechanical properties to suit various applications.

6. Quenchability

• Hardness Increase: After quenching and tempering, the hardness of 431 stainless steel can reach 360 to 480HB, equivalent to Rc44.
• Cooling Method: Small sections can be air-cooled, while larger sections require oil quenching to achieve optimal through-hardening.

7. Low-Temperature Characteristics

• Lower Brittle Transition Temperature: 431 stainless steel becomes tougher in low temperatures, allowing it to resist impact without breaking.
• Microstructure: At low temperatures, the structure includes martensite and some ferrite, improving strength and toughness.

Limitations

• Difficult Welding: Due to its high carbon content, 431 stainless steel is challenging to weld and requires pre- and post-weld heat treatment to avoid cracking.
• Vulnerability to Strong Acids: While corrosion resistant, 431 is prone to pitting and crevice corrosion in strong acidic environments, limiting its use in aggressive chemical exposure.

How is Stainless Steel 431 Produced?

The production of stainless steel 431 involves several key steps, each critical to ensuring its final properties such as strength, hardness, and corrosion resistance.

1. Melting: The raw materials, primarily iron, chromium, carbon, and nickel, are melted in an electric arc furnace (EAF) at high temperatures.

2. Casting: The liquid steel is poured into molds to form billets or slabs, which are then cooled and hardened.

3. Hot Rolling: The solidified slabs are heated again and rolled to decrease their thickness and shape the steel into plates, bars, or other required forms.

4. Annealing: The rolled steel is heat-treated to release internal stresses, soften the material, and enhance machinability. This process involves heating the steel to a set temperature and gradually cooling it.

5. Hardening: To enhance hardness and strength, 431 is subjected to a quenching process, where the steel is rapidly cooled after being heated to high temperatures.

6. Tempering: After hardening, the steel is tempered by reheating to a lower temperature and then cooling it again to adjust the final hardness and toughness.

7. Descaling: After heat treatment, the surface scale formed during processing is removed through pickling or mechanical cleaning.

8. Finishing: The steel is machined and finished to precise dimensions, typically through grinding or polishing, to achieve the desired surface quality.

9. Inspection and Testing: The final product undergoes rigorous inspection and testing to ensure it meets the required mechanical and chemical properties, such as tensile strength, hardness, and corrosion resistance.

These processes guarantee that 431 stainless steel attains the required strength, toughness, and rust resistance for its specific applications.

Processing Options We Provide for SS 431

At SteelProGroup, we offer a full range of processing and product customization options for SS 431 stainless steel, designed to meet specific performance requirements and application needs.

Machining

Below are the detailed processing options we offer:

Melting

• Electric Arc Furnace (EAF): Produces high-quality steel by melting raw materials using electric arcs, ensuring precise control over composition.
• Vacuum Induction Melting (VIM): Removes impurities in a vacuum, creating a cleaner, more uniform material with fewer inclusions, ideal for critical applications.
• Argon Oxygen Decarburization (AOD): Argon Oxygen Decarburization (AOD) refines steel by reducing carbon, improving corrosion resistance, and achieving the desired composition, ideal for producing high-quality stainless steel like 431, as it controls alloy content and improves performance.

Heat Treatment

• Annealing:Reduces the hardness of 431 stainless steel to enhance machinability and release internal stresses, typically done at 815-900°C, making it easier to work with in later stages.
• Hardening: Increases strength and wear resistance by heating 431 stainless steel to 980-1065°C and then rapidly cooling it, ideal for high-strength applications.
• Tempering: Adjusts hardness and toughness after hardening, improving durability and reducing brittleness, typically done at 600-650°C for 431 stainless steel, for applications that require both strength and flexibility.
• Quenching: Quickly cools 431 stainless steel after heating to lock in hardness and mechanical properties, essential for ensuring consistent performance in demanding environments.

Cold Working

• Cold Rolling: Reduces thickness and refines surface quality without heating, resulting in a stronger, smoother finish.
• Cold Drawing: Increases strength by pulling the steel through a die, providing tight dimensional control for precise applications.
• Stretch Forming: Stretches the material without heat, improving mechanical properties while shaping it into complex geometries.

Other Cold Working Options Not Recommended for 431 Stainless Steel

• Deep Drawing: 431’s limited ductility makes it prone to cracking during deep drawing, making it unsuitable for this process.
• Bending at Low Temperatures: Due to its higher strength and lower ductility, bending without sufficient heat can lead to cracking.
• Cold Swaging: The hardness and brittleness of 431 after cold working make it unsuitable for swaging, as it can result in fractures.

Mechanical Machining

• Cutting: We offer precision cutting using saws or lasers, providing clean and accurate cuts to match custom specifications with minimal material loss.
• Milling: High-precision milling ensures the creation of intricate parts with accurate dimensions that are suitable for complex shapes and designs.
• Drilling: Custom drilling to achieve exact hole sizes and depths, ensuring a perfect fit for bolts, fasteners, or other joining methods.

Surface Treatment

• Grinding: Smoothens rough surfaces and ensures a uniform finish, improving the overall appearance and performance of the steel.
• Polishing: Adds a reflective, high-gloss finish, enhancing corrosion resistance and aesthetic appeal, especially for visible components.
• Pickling: Removes surface impurities, such as oxides or scale, ensuring a clean surface and improving the adhesion of coatings.
• Passivation: Improves rust resistance by creating a protective oxide coating, making it perfect for use in aggressive environments.

Welding

• TIG (Tungsten Inert Gas) Welding: Provides high-quality, precise welds with minimal contamination, suitable for thin sections or critical applications.
• MIG (Metal Inert Gas) Welding: Efficient for joining thicker sections with high deposition rates, suitable for industrial and structural applications.
• Resistance Welding: Uses heat and pressure to join steel without filler materials, producing clean, strong joints for a variety of applications.

Other Welding Options Not Recommended for 431 Stainless Steel

• Gas Welding and CO2 Welding: These methods are difficult with 431 stainless steel.
• Low-Temperature Welding: Welding at extremely low temperatures can reduce toughness and strength.
• No Preheating: Skipping preheat treatment raises the risk of brittleness and cracks, so preheating is advised for 431 stainless steel.

Shape and Forms We Have

Below are the shape and form options we offer:

• Bars:
  • Shape: Round bars, square bars, flat bars, hexagonal bars.
  • Form: Polished bars, pickled bars.
• Sheets and Plates:
  • Shape: Thin sheets, thick sheets.
  • Form: Pickled sheets, sheet coils, flat plates, perforated plates, checker plates.
• Wires and Strip:
  • Shape: Round wire, flat wire, square wire.
  • Form: Drawn wire, coiled wire, stranded wire.
• Coils:
  • Shape: Narrow coils, wide coils.
  • Form: Cold-rolled coils, hot-rolled coils, annealed coils.
• Rods:
  • Shape: Round rods, square rods.
  • Form: Hot-rolled rods, cold-drawn rods, polished rods.
• Tubing:
  • Shape: Round tubing, square tubing.
  • Form: Seamless tubing, welded tubing, polished tubing.
• Pipes:
  • Shape: Round pipes, rectangular pipes.
  • Form: Seamless pipes, welded pipes, pickled pipes.
• Custom Machined Forms: We offer custom machining and shaping services to suit your specific industrial requirements.

With our comprehensive processing capabilities and diverse range of available forms, we guarantee that our 431 stainless steel products meet top industry standards.

Applications of 431 Stainless Steel

431 stainless steel is commonly utilized in industries that demand high strength, durability, and rust resistance. It is especially well-suited for aerospace, marine, automotive, and industrial uses.

1. Aerospace Industry

431 stainless steel is frequently employed in the aerospace sector for its superior strength and ability to resist wear and fatigue.

• Aircraft Landing Gear: The strength and durability of 431 make it perfect for parts that face heavy stress and impact.
• Fasteners: Its corrosion resistance and mechanical properties are suitable for critical fasteners in aircraft construction.
• Turbine Parts: Its ability to withstand high temperatures and maintain strength is crucial for turbine components.

2. Marine Industry

Thanks to its excellent resistance to corrosion in marine environments, 431 is widely used in the marine sector.

• Shafts: 431 is often utilized for propeller shafts because of its strong durability and excellent resistance to seawater corrosion.
• Boat Fasteners: Corrosion-resistant bolts and screws made from 431 are ideal for use in saltwater environments.
• Pump Components: The material’s toughness and corrosion resistance make it suitable for marine pump parts that require long-lasting durability.

3. Automotive Industry

431 stainless steel’s strength and machinability make it a good choice for demanding automotive applications.

• Axles: Its high strength and fatigue resistance are ideal for automotive axles that endure heavy loads and stress.
• Gears: Gears made from 431 are able to handle high torque and wear without sacrificing performance.
• Engine Components: Parts like valve seats and fuel injection systems benefit from the material’s hardness and corrosion resistance.

4. Industrial Equipment

In industrial applications, 431 stainless steel is used in parts that require wear resistance and the ability to withstand harsh conditions.

• Valves: The material’s toughness and corrosion resistance make it ideal for valve stems and components in chemical and oil industries.
• Pumps and Pistons: 431’s durability under stress and exposure to corrosive fluids makes it suitable for pump shafts and piston rods.
• Cutting Tools: 431 stainless steel’s capacity to retain sharpness and resist wear under heavy stress makes it ideal for producing cutting tools.

431 stainless steel is also used in the oil and gas, medical, food processing, and pharmaceutical industries for its corrosion resistance, toughness, and cleanliness.

What is the difference between 316 and 431 steel?

316 is an austenitic stainless steel with elevated chromium and nickel levels, providing excellent corrosion resistance, particularly in marine environments. 431, a martensitic steel, offers greater strength and hardness but has lower corrosion resistance compared to 316.

What is the difference between 420 and 431 stainless steel?

420 contains more carbon, making it harder and more wear-resistant after heat treatment but with lower toughness. 431 has greater overall toughness and enhanced corrosion resistance thanks to its higher chromium content, making it well-suited for more demanding environments.

Can 431 stainless steel be hardened?

Yes, 431 stainless steel can be hardened through heat treatment, specifically by quenching and tempering, which enhances its hardness and strength.

What is the difference between 430 and 431 stainless steel?

430 is a ferritic stainless steel known for its good corrosion resistance and ease of forming, but it has lower strength compared to other grades. 431 is martensitic, offering higher strength, hardness, and better corrosion resistance, making it suitable for tougher applications.

What is the equivalent of 431 stainless steel?

Equivalent grades include SUS 431 in Japan, 1Cr17Ni2 in China, X17CrNi16-2 in the EU, 1.4057 in Germany, and 14Kh17N2 in Russia.

Professional 431 Stainless Steel Manufacturer

SteelPRO Group is a manufacturer and solutions provider for specialty steel, offering custom services with 100% quality assurance! Choose our 431 stainless steel, we can offer:

• High Strength And Durability: Our 431 stainless steel has excellent tensile strength, making it ideal for high-stress applications.
• Excellent Corrosion Resistance: Ideally suited for marine and chemical environments, 431 stainless steel has excellent corrosion resistance.
• Precision Machining: Our 431 stainless steel has a shape that lends itself to precision machining, ensuring a top-quality end product.
• Customizable Finishes: Options like polished, pickled, and annealed can be customized to fit your specific application needs.
• A Wide Range Of Shapes To Choose From: Bars, rods, plates, sheets, coils, tubing, and more to meet a variety of industrial needs.
  Advanced Heat Treating Options: Customized heat-treating processes to enhance material performance and service life.
• Global Supply Chain: Reliable global delivery with competitive transportation options.
  Industry Compliance And Certifications: ASTM-compliant products, SGS/TUV certified for quality and traceability.

Contact us today to submit your project requirements and experience our 431 stainless steel solutions and customized services!