630 Stainless Steel: Properties, Characteristics, Processing, Applications

Its unique precipitation-hardening properties make 630 stainless steel (17-4PH) stand out for its incredible mix of durability, toughness, and corrosion resistance. Its unique precipitation-hardening properties make it a top choice for demanding industries like aerospace, manufacturing, and chemical processing.

In this article, we’ll walk you through everything you need to know about 630 stainless steel—from its standout properties and heat treatment process to how it’s used and how to keep it performing at its best. Let’s explore why this steel is such a favorite!

What is 630 stainless steel?

630 stainless steel (1.4542, 17-4PH) is a martensitic steel with 15–17.5% chromium, 3–5% nickel, 3–5% copper, and niobium. Also known as precipitation-hardening steel, it resists stress corrosion cracking and offers corrosion resistance similar to AISI 304 in neutral or mildly acidic environments. It can be used in the solution-annealed condition. Per ASTM A564, it is available as bars, plates, flats, and strips. Common applications include aircraft parts, fasteners, and pump shafts.

Properties of 630 stainless steel

630 stainless steel (17-4PH) is recognized for its impressive strength, toughness, and corrosion resistance, improved through heat treatment. This part discusses its chemical makeup, mechanical and physical traits, and comparable grades.

Chemical Composition of SS 630

630 stainless steel (17-4PH) has excellent corrosion resistance and high strength. The key alloying elements, including chromium, nickel, and copper, enhance its durability and mechanical properties, while niobium aids in precipitation hardening.

Chemical Composition Table of 630 Stainless Steel

Mechanical Properties of SS 630

The mechanical properties of 630 stainless steel (17-4PH) change with heat treatment, allowing it to achieve a tailored balance of strength, hardness, and flexibility for diverse applications.

Mechanical Properties Table of 630 Stainless Steel

Physical Properties of SS 630

630 stainless steel (17-4PH) has key physical properties like high density, good thermal conductivity, and electrical resistivity, making it suitable for aerospace components, chemical processing equipment, marine applications, etc. The values below are general and may not apply in all environments, especially extreme temperatures or corrosive conditions.

Physical Properties Table of 630 Stainless Steel

Equivalent Grades of 630 Stainless Steel

630 stainless steel (17-4PH) has equivalent grades in different countries, sharing similar characteristics in composition and properties. These grades enable standardized use across regions and industries.

630 Equivalent Grades Table of Stainless Steel

Characteristics of 630 Stainless Steel

630 stainless steel (17-4PH) is valued for its high strength, hardness, and excellent corrosion resistance, along with good machinability and weldability. Below are its key characteristics:

Corrosion Resistance

In neutral or mildly acidic conditions, 630 stainless steel provides corrosion resistance comparable to 304 stainless steel. Its high chromium, nickel, and copper content ensures durability and resistance to stress corrosion cracking, offering versatility across industries. When treated at higher aging temperatures, its corrosion resistance improves even further.

Note: While it withstands chlorides to some extent, it’s not ideal for warm, chloride-rich environments without additional protection.

Heat Resistance

With good oxidation resistance below 550°C, 630 stainless steel handles exposure to atmospheric conditions, dilute acids, and salts effectively. Heat treatment between 1010°C and 1150°C restores its toughness and strength, making it suitable for high-temperature environments.

Note: Avoid prolonged exposure to 300°C–480°C, as this may lead to the formation of sigma phase, which can cause brittleness and reduce toughness.

Weldability

Standard welding techniques work well with 630 stainless steel without the need for preheating. Post-weld heat treatment is recommended to restore the material’s mechanical properties. In its solution-treated state, it offers machinability similar to 304 stainless steel.

Note: To prevent hydrogen embrittlement during welding, it’s essential to use dry electrodes and maintain proper welding conditions.

Machinability

Despite its hardness, 630 stainless steel is relatively easy to machine, especially in the annealed or non-aged condition. It supports turning, milling, and drilling with excellent results.

Note: Using carbide or high-speed steel tools is recommended, with rough machining at lower speeds and finishing at higher speeds. Adequate cooling is crucial to prevent heat buildup.

Magnetic Properties

630 stainless steel is magnetic in both annealed and hardened states due to its martensitic structure. Its magnetic response is stronger in the solution-treated condition but reduces after aging, making it suitable for applications requiring moderate magnetic properties.

Note: Since magnetic behavior depends on heat treatment, it may not be the best option for non-magnetic requirements.

Shape of 630 Stainless Steel

630 stainless steel is available in various shapes, each suited for specific applications. The different shapes offer versatility for creating parts and components tailored to specific needs in industries like aerospace, manufacturing, and energy.

1. Bars

• Subcategories: Round bars, square bars, hexagonal bars, flat bars.
• Applications: Round bars are used for shafts and fasteners, square and hexagonal bars for precision machining components, and flat bars for structural parts and braces in industrial equipment.

2. Plates

• Subcategories: Hot-rolled plates, cold-rolled plates, precision ground plates.
• Applications: Hot-rolled plates are used in large structural components, cold-rolled plates for parts requiring high strength, and precision ground plates for tooling and machine components.

3. Sheets

• Subcategories: Thin sheets, thick sheets, perforated sheets.
• Applications: Thin sheets are used for cladding, aerospace components, and automotive parts, while perforated sheets serve in filtration and architectural designs.

4. Strips

• Subcategories: Cold-rolled strips, precision strips.
• Applications: Cold-rolled strips are ideal for springs and blades, while precision strips are used in electronic components and fine instrument manufacturing.

5. Tubes

• Subcategories: Seamless tubes, welded tubes, square tubes.
• Applications: Seamless tubes are commonly used in pressure vessels and high-performance systems, welded tubes in piping, and square tubes in structural frameworks.

6. Wires

• Subcategories: Drawn wires, coiled wires, flat wires.
• Applications: Drawn wires are used in fastening and springs, coiled wires for wire mesh, and flat wires in connectors and electrical components.

By offering a variety of shapes, 630 stainless steel can be customized for numerous industrial applications, ensuring both flexibility and performance.

Heat Treatment of SS 630

630 stainless steel requires both solution treatment and aging (precipitation hardening) to achieve its full mechanical properties, a key distinction from other martensitic stainless steels. Solid solution treatment is a prerequisite for aging treatment, these two processes work together to develop the steel’s final strength and hardness.

Necessary Heat Treatment Steps of SS 630

1. Solution Treatment

• Purpose: Dissolves alloying elements to create a uniform, soft structure.
• Process:
  • Heat the steel to 1040-1060°C (1900-1940°F).
  • Hold at this temperature to dissolve the alloying elements.
  • Rapidly cool (air or oil quenching).
• Outcome: The steel becomes soft and ductile, ready for aging.
• Tip: Ensuring consistent temperature control during this step is crucial to avoid uneven dissolution, which could affect the final properties. Rapid cooling prevents unwanted phase formation and keeps the structure uniform.

2. Aging (Precipitation Hardening)

• Purpose: Enhances hardness and strength by precipitating fine particles after solution treatment.
• Process:
  • Heat the steel to 480-620°C (896-1148°F) based on desired properties.
  • Hold for 1-4 hours to allow the precipitation process.
  • Cool either in air or by quenching.
• Outcome: Aging results in a hardened structure with increased strength.
• Tip: Choosing the right balance depends on the specific application. Cooling rates also play a role—controlled cooling is essential to avoid reducing strength or corrosion resistance.

Key Considerations

• Aging Temperature: Lower temperatures are ideal for parts requiring maximum wear resistance. Opt for higher temperatures to boost the toughness of components exposed to impact or stress.
• Cooling Rates: After solution treatment, controlled cooling prevents phase changes that could reduce strength and corrosion resistance.

Heat Treatment State of 630 Stainless Steel

Different heat treatment conditions of 630 stainless steel adjust its strength, hardness, and toughness for specific applications. Below are the main properties of each condition.

H900 Condition

• Aging Temperature: 470-490°C
• Aging Time: 1 hour
• Key Traits: This is the go-to condition for high strength—tensile and yield strength are at their peak, and hardness exceeds HRC 40. It’s perfect for those high-stress applications where strength is non-negotiable.

Tip: For projects that demand the toughest materials, H900 is the way to go.

H925 Condition

• Aging Temperature: 490-510°C
• Aging Time: 1 hour
• Key Traits: A slight dip in strength compared to H900, but the tradeoff is better toughness. If your application needs a balance between strength and durability, H925 is a great choice.

Tip: This is a solid middle ground for parts that need to handle both stress and wear.

H1025 Condition

• Aging Temperature: 540-560°C
• Aging Time: 4 hours
• Key Traits: With this condition, strength takes a backseat, but toughness gets a major boost. It’s ideal for applications where durability is the top priority.

Tip: Choose H1025 when you need a part that’ll last longer and resist damage over time.

H1075 Condition

• Aging Temperature: 570-590°C
• Aging Time: 4 hours
• Key Traits: Here, strength continues to drop, but toughness improves significantly. This is great when toughness is more important than strength, like in parts exposed to impact or vibration.

Tip: This one’s perfect for components that need to endure high impact without cracking.

H1100 Condition

• Aging Temperature: 590-610°C
• Aging Time: 4 hours
• Key Traits: The strength and hardness are lower, but the toughness is off the charts, making it ideal for parts that require both flexibility and moderate strength.

Tip: If your parts need to bend and absorb shock, H1100 offers just the right toughness.

H1150 Condition

• Aging Temperature: 610-630°C
• Aging Time: 4 hours
• Key Traits: This is the softest condition, with the lowest strength and hardness but the highest toughness. If toughness is your primary concern, this is the condition to choose.

Tip: Go for H1150 when flexibility and crack resistance are top priorities.

Selecting the right condition really depends on the specific needs of your project. By adjusting these parameters, you can ensure 630 stainless steel performs exactly as needed, whether you prioritize strength, toughness, or a balance of both.

SS 630 Processing Options You Can Find in SteelPRO Group

At SteelPRO Group, we offer a variety of processing options for 630 stainless steel to meet your specific needs. Each method ensures high-quality results tailored to your project requirements. Below are the smelting, forming, heat-treatment, welding, and machining options we provide.

Smelting Options

1. Electric Arc Furnace (EAF) Smelting
   • Definition: Melting the metal using an electric arc between electrodes.
   • Steps and Effect: The process efficiently melts scrap metal and raw materials, producing high-quality steel with a controlled composition. Perfect for manufacturing significant amounts of material with reliable quality.
2. Vacuum Induction Melting (VIM)
   • Definition: Melting steel in a vacuum to remove impurities.
   • Steps and Effect: This process melts the material in a vacuum chamber, reducing gas content and impurities. It results in cleaner, high-performance steel, perfect for critical applications.
3. Induction Furnace (IF) Smelting
   • Definition: Utilizing electromagnetic induction to warm and liquefy the substance.
   • Steps and Effect: This method is efficient for smaller batches and precise control of alloying elements, leading to uniform, high-quality steel with low contamination.
4. Casting
   • Definition: Pouring molten metal into a mold to shape the material.
   • Steps and Effect: Casting allows for the creation of complex shapes and large components with excellent mechanical properties, suitable for producing custom parts.
5. Protective Atmosphere Electroslag Remelting (PESR)
   • Definition: Refining steel by remelting it under a protective atmosphere.
   • Steps and Effect: PESR removes impurities while maintaining a clean environment, resulting in enhanced purity and homogeneity, ideal for high-end applications requiring superior quality.
6. Vacuum Induction Melting + Protective Atmosphere Electroslag Remelting (VIM+PESR)
   • Definition: Combining VIM and PESR for the highest level of purity.
   • Steps and Effect: The steel is first melted in a vacuum and then remelted under protective conditions. This dual process ensures the highest purity, strength, and reliability for critical components.

Forming Options

1. Hot Forming
   • Hot Rolling:  Performed at high temperatures, this process is ideal for producing large steel sections and complex parts. Our hot rolling process produces 630 (17-4 PH) rods and plates with excellent ductility, strength, and customizable sizes for high-performance applications.
   • Hot Forging: This method is perfect for high-strength, complex parts using advanced equipment like electro-hydraulic presses. It improves mechanical properties and allows for the creation of custom shapes.
2. Cold Forming
   • Cold Rolling: Performed at ambient temperature, this process enhances the steel’s strength and toughness, making it suitable for thin sheets and strips with precise tolerances.
   • Cold Bending: Suitable for bending 630 stainless steel into desired shapes, this must be done in a fully annealed state to prevent brittleness.
   • Cold Stamping: Cold stamping is used to make complex shapes. It is efficient and best performed on annealed material for precise results.

Heat-treatment Options

1. Solution Treatment
   • Process: Involves heating the steel to high temperatures and quenching to achieve a uniform, ductile structure. This prepares the material for further hardening and improves its overall workability.
2. Aging (Precipitation Hardening)
   • Process: Heating the material at specific temperatures for a controlled time to increase its hardness and strength. This process customizes the material’s final mechanical properties.
3. Annealing
   • Process: Makes the steel more pliable by warming it to a medium temperature and gradually lowering the heat. Annealing improves machinability and removes internal stresses.
4. Custom Heat Treatments
   • SteelPRO Group provides customized heat treatment methods to fulfill particular needs, guaranteeing optimal performance for your use.

Welding Options

We offer several welding methods, including:

• Manual Arc Welding (MAW)
• Gas Tungsten Arc Welding (GTAW)
• Gas Metal Arc Welding (GMAW)
• Plasma Arc Welding (PAW)
  Each welding option ensures strong, reliable joints and is suitable for various 630 stainless steel applications.

Machining Options

1. Turning: Perfect for creating shafts and round components with high precision, delivering accurate results in shaping and finishing.
2. Milling: Ideal for producing flat surfaces, grooves, and complex shapes, ensuring precise details for intricate parts.
3. Drilling: Used for creating installation holes and through-holes, this process ensures clean, accurate results for any required perforations in 630 stainless steel.

Surface Treatment Customization

Passivation improves corrosion resistance in mild environments, while PVD coatings offer protection in harsh, chloride-rich conditions. Electropolishing provides a smooth, clean surface for medical and food-grade applications. 

1. Polishing
2. Pickling
3. Passivation
4. Bead Blasting
5. Electropolishing
6. Other Customization Options

At SteelPRO Group, our extensive range of processing options ensures that we can deliver top-quality, customized 630 stainless steel products for any project.

Common Challenges in Processing or Using 630 Stainless Steel

1. Welding Cracks
   630 stainless steel can develop cracks during welding, especially in the H900 condition.
   Tip: Preheat or post-weld heat treatment can reduce cracking.
2. Hydrogen Embrittlement
   During welding, exposure to moisture or hydrogen can cause embrittlement.
   Tip: Use dry electrodes and proper welding conditions to avoid this.
3. Machining Difficulties
   The high hardness of aged 630 stainless steel can make machining challenging.
   Tip: Use carbide tools, lower speeds, and sufficient cooling to improve machinability.
4. Corrosion in Chloride-Rich Environments
   Prolonged exposure to chlorides can lead to pitting and corrosion.
   Tip: Apply a PVD coating or choose a protective surface treatment.
5. Brittleness at Specific Temperatures
   Prolonged exposure to temperatures between 300°C and 480°C can cause brittleness due to sigma phase formation.

Tip: Avoid these temperature ranges during processing and use.   

Applications of 630 Stainless Steel

630 stainless steel (17-4PH) is extensively utilized in multiple sectors because of its blend of durability, toughness, and resistance to corrosion.

It is particularly suited for applications in aerospace, chemical processing, and manufacturing, where durable, high-performance materials are essential.

Maintenance of 630 Stainless Steel

Preserving 630 stainless steel in industrial settings is essential for optimizing its durability and efficiency. Regular maintenance ensures the material retains its high strength, corrosion resistance, and overall reliability, especially in demanding applications.

Regular Cleaning

• Wipe the surface with gentle cleaners to eliminate dust, particles, and impurities.
• Avoid using chloride-containing cleaning solutions to prevent pitting and corrosion.

Are you interested in how to clean stainless steel? Click and read it!

Corrosion Prevention

• Apply protective coatings in chloride-rich environments, especially in marine or chemical industries.
• Frequently check for indications of rust, particularly in joints or regions subjected to pressure.

Inspection of Welded Joints

• Inspect welded joints regularly for cracks or weaknesses, especially after exposure to high temperatures.
• Ensure post-weld heat treatment is properly done to avoid hydrogen embrittlement.

Avoid Prolonged Exposure to Certain Temperatures

• Avoid long exposure to temperatures between 300°C and 480°C to prevent the formation of brittle phases.
• Make certain that thermally processed components are operated within their designated temperature limits.

Stress Relieving

• For components under continuous stress, periodic stress-relieving treatments may help maintain integrity and prevent stress corrosion cracking.

Lubrication of Moving Parts

• For applications with moving parts, apply proper lubrication to reduce wear and tear, minimize friction, and extend the service life of components.

Storage Guidelines

• Store in dry, well-ventilated areas to prevent moisture accumulation.
• Use proper packaging to avoid surface scratches or damage during transportation.

By following these maintenance practices, the performance and durability of 630 stainless steel can be significantly extended in industrial applications.

What is the difference between 630 and 304 stainless steel?

630 is stronger and harder than 304, while 304 offers better corrosion resistance and formability.

Is SS 630 better than SS 316?

SS 630 is stronger, but SS 316 has better corrosion resistance, especially in marine environments.

What is SUS 630 material equivalent to?

SUS 630 is equivalent to 17-4PH stainless steel, known internationally as ASTM A564 Type 630, EN 1.4542, and other standards, depending on the region.

What is the hardness of SUS 630?

The hardness of SUS 630 can vary based on its heat treatment condition, typically ranging from HRC 35 to HRC 44, with the H900 condition reaching the higher end of the scale.

What is ASTM A564 Type 630 equivalent to?

ASTM A564 Type 630 is equivalent to 17-4PH stainless steel, EN 1.4542, SUS 630 in Japan, and X5CrNiCuNb16-4 in Europe.

Proven 630 Stainless Steel Manufacturer

SteelPRO Group is a manufacturer and solutions provider for specialty steel, offering custom services with 100% quality assurance! Choose our 630 stainless steel, we can offer:

• Ample Stock: We maintain a large inventory of 630 stainless steel with custom sizes, finishes, and processing options to meet your needs.
• Global Coverage: Our extensive supply chain ensures we can fulfill 630 stainless steel orders worldwide.
• Quick Response: Expect fast quotes within 24 hours, with expert support and a lifetime warranty on our products.
• Compliance & Certification: Our 630 stainless steel meets ASTM A564 standards and is certified by SGS or TUV for easy traceability.
• Flexible Shipping: Choose from FOB, CFR, or CIF shipping methods for cost-effective, secure delivery.

In addition to our top-quality 630 stainless steel, we also offer 630 Stainless Steel Rods & Plates and so on, designed for applications requiring high strength and excellent corrosion resistance. Whether you’re in aerospace, manufacturing, or energy, our 17-4PH products deliver outstanding performance, with custom sizes and finishes to match your precise needs.

Let SteelPRO Group be your go-to partner for high-performance materials—our 630 stainless steel products are ready to meet the demands of even the most challenging projects.