Stainless Steel SUS321
Introduction to Stainless Steel SUS321: Titanium-Stabilized Austenitic Alloy
Stainless Steel SUS321 is an austenitic stainless steel alloy that is stabilized with titanium, making it ideal for applications in high-temperature environments where corrosion resistance and stability are critical. SUS321 contains 17–19% chromium, 9–12% nickel, and around 0.4–0.7% titanium, which helps prevent the formation of chromium carbides during welding. This makes SUS321 an excellent choice for industries requiring the alloy to maintain its mechanical properties in extreme conditions, such as aerospace, chemical, and power generation.
SUS321’s ability to resist intergranular corrosion, particularly after welding, is one of its key advantages. CNC machining of SUS321 requires high-performance tooling due to its strength, but it is relatively easy to machine when carbide tools and proper cooling techniques are used. At Neway, CNC-machined SUS321 parts are produced precisely to meet the demanding needs of high-temperature and corrosive applications.
SUS321 Stainless Steel: Key Properties and Composition
SUS321 Stainless Steel Chemical Composition
Element | Composition (wt%) | Role/Impact |
|---|---|---|
Carbon (C) | ≤0.08% | Low carbon content minimizes carbide precipitation and enhances weldability. |
Manganese (Mn) | 2.00% | Improves strength and toughness, especially at high temperatures. |
Chromium (Cr) | 17.0–19.0% | Provides excellent resistance to oxidation and corrosion, particularly in high-temperature environments. |
Nickel (Ni) | 9.0–12.0% | Enhances formability, ductility, and resistance to oxidation in high-temperature environments. |
Titanium (Ti) | 0.4–0.7% | Stabilizes the material against chromium carbide formation during welding, improving weldability. |
Phosphorus (P) | ≤0.045% | Improves machinability and helps reduce surface defects. |
SUS321 Stainless Steel Physical Properties
Property | Value | Notes |
|---|---|---|
Density | 8.00 g/cm³ | Typical for austenitic stainless steels, ensuring durability. |
Melting Point | 1,400–1,450°C | Suitable for high-temperature applications with excellent resistance to oxidation. |
Thermal Conductivity | 16.2 W/m·K | Moderate heat dissipation, suitable for applications with fluctuating temperatures. |
Electrical Resistivity | 7.4×10⁻⁷ Ω·m | Low electrical conductivity, ideal for non-electrical applications. |
SUS321 Stainless Steel Mechanical Properties
Property | Value | Testing Standard/Condition |
|---|---|---|
Tensile Strength | 520–720 MPa | ASTM A240/A240M standard |
Yield Strength | 205 MPa | Suitable for high-temperature and structural applications |
Elongation (50mm gauge) | 40% | Good ductility, allowing for easier forming and welding. |
Brinell Hardness | 150–190 HB | Achieved in a solution-treated state, offering moderate hardness. |
Machinability Rating | 55% (vs. 1212 steel at 100%) | Suitable for machining with carbide tools and low cutting speeds. |
Key Characteristics of SUS321 Stainless Steel: Benefits and Comparisons
SUS321 stainless steel is known for its excellent high-temperature performance, oxidation resistance, and resistance to intergranular corrosion. Below is a technical comparison highlighting its unique advantages over similar materials like SUS304 Stainless Steel, SUS316 Stainless Steel, and SUS430 Stainless Steel.
1. High-Temperature Resistance
Unique Trait: SUS321 offers excellent resistance to oxidation and scaling at temperatures up to 900°C, making it ideal for high-temperature environments.
Comparison:
vs. SUS304 Stainless Steel: SUS304 is less effective than SUS321 in high-temperature applications due to the lack of titanium stabilization.
vs. SUS316 Stainless Steel: SUS316 is more corrosion-resistant but not as suitable for high-temperature environments as SUS321.
vs. SUS430 Stainless Steel: SUS430 lacks the high-temperature resistance of SUS321, making it unsuitable for extreme heat applications.
2. Corrosion Resistance
Unique Trait: SUS321 provides excellent resistance to intergranular corrosion and general corrosion, particularly in the welding zone, due to titanium stabilization.
Comparison:
vs. SUS304 Stainless Steel: SUS321 is better than SUS304 in environments where intergranular corrosion is a concern, such as in welded structures.
vs. SUS316 Stainless Steel: SUS316 offers better resistance to chloride-induced corrosion than SUS321, but SUS321 performs better in high-temperature environments.
vs. SUS430 Stainless Steel: SUS430 offers much lower corrosion resistance than SUS321, especially in high-temperature and welding environments.
3. Weldability
Unique Trait: SUS321’s titanium addition prevents the formation of chromium carbides, which ensures that the material retains its strength and corrosion resistance in welded structures.
Comparison:
vs. SUS304 Stainless Steel: SUS304 may suffer from carbide precipitation during welding, reducing its strength and corrosion resistance compared to SUS321.
vs. SUS316 Stainless Steel: SUS316 is more resistant to chloride-induced corrosion but may not provide the same stability in welded applications as SUS321.
vs. SUS430 Stainless Steel: SUS430 is not as easily welded as SUS321 and is less suitable for critical welded applications due to its lower ductility.
4. Cost-Effectiveness
Unique Trait: SUS321 is a cost-effective solution for high-temperature and corrosion-resistant applications where welding is required, making it a versatile alloy for many industries.
Comparison:
vs. SUS304 Stainless Steel: SUS304 is more affordable than SUS321 but lacks the high-temperature stability and resistance to intergranular corrosion.
vs. SUS316 Stainless Steel: SUS316 is more expensive than SUS321 due to its higher nickel content but provides superior resistance to chloride-induced corrosion.
vs. SUS430 Stainless Steel: SUS430 is the most economical but is unsuitable for high-temperature and corrosion-resistant applications compared to SUS321.
CNC Machining Challenges and Solutions for SUS321 Stainless Steel
Machining Challenges and Solutions
Challenge | Root Cause | Solution |
|---|---|---|
Work Hardening | High alloy content and hardness | Use carbide tools with TiN coatings to improve tool life. |
Surface Roughness | Low carbon content and ductility | Optimize feed rates and use high-speed tools for smoother finishes. |
Tool Wear | High nickel and molybdenum content | Use high-performance tool coatings like TiAlN for reduced wear. |
Dimensional Inaccuracy | Stresses from machining | Perform stress-relief annealing to reduce dimensional variations and improve precision. |
Chip Control Issues | Long, stringy chips | Use high-pressure coolant and optimize tool geometry to break chips. |
Optimized Machining Strategies
Strategy | Implementation | Benefit |
|---|---|---|
High-Speed Machining | Spindle speed: 1,200–1,800 RPM | Increases productivity and reduces heat buildup. |
Climb Milling | Cutting in the direction of tool rotation | Improves surface finish (Ra 1.6–3.2 µm). |
Toolpath Optimization | Use trochoidal milling for deep pockets | Reduces cutting forces, minimizing part deflection. |
Stress-Relief Annealing | Preheat to 650°C for 1 hour per inch | Minimizes residual stress and improves machining accuracy. |
Cutting Parameters for SUS321 Stainless Steel
Operation | Tool Type | Spindle Speed (RPM) | Feed Rate (mm/rev) | Depth of Cut (mm) | Notes |
|---|---|---|---|---|---|
Rough Milling | 4-flute carbide end mill | 1,000–1,500 | 0.15–0.25 | 2.0–4.0 | Use coolant to prevent work hardening. |
Finish Milling | 2-flute carbide end mill | 1,500–2,000 | 0.05–0.10 | 0.5–1.0 | Climb milling for smoother finishes (Ra 1.6–3.2 µm). |
Drilling | 135° split-point HSS drill | 600–800 | 0.10–0.15 | Full hole depth | Peck drilling for precise hole formation. |
Turning | CBN or coated carbide insert | 500–700 | 0.20–0.30 | 1.5–3.0 | Dry machining is acceptable with air blast cooling. |
Surface Treatments for CNC Machined SUS321 Stainless Steel Parts
Electroplating: Adds a corrosion-resistant metallic layer, extending part life in humid environments and improving strength.
Polishing: Enhances the surface finish, providing a smooth, shiny appearance ideal for visible components.
Brushing: Creates a satin or matte finish, masking minor surface defects and improving aesthetic quality for architectural components.
PVD Coating: Boosts wear resistance, increasing tool life and part longevity in high-contact environments.
Passivation: Creates a protective oxide layer, enhancing corrosion resistance in mild environments without altering dimensions.
Powder Coating: Offers high durability, UV resistance, and a smooth finish, ideal for outdoor and automotive parts.
Teflon Coating: Provides non-stick and chemical-resistant properties, ideal for food processing and chemical handling components.
Chrome Plating: Adds a shiny, durable finish that enhances corrosion resistance, commonly used in automotive and tooling applications.
Black Oxide: Provides a corrosion-resistant black finish, ideal for parts in low-corrosion environments like gears and fasteners.
Industry Applications of CNC Machined SUS321 Stainless Steel Parts
Aerospace Industry
Turbine Components: SUS321 is used for turbine blades and parts exposed to high temperatures and oxidative environments.
Chemical Processing
Heat Exchangers: SUS321 is ideal for heat exchangers due to its resistance to corrosion and high-temperature environments.
Marine Industry
Marine Equipment: SUS321 is resistant to marine corrosion, making it suitable for seawater-exposed parts like propellers and piping.
Technical FAQs: CNC Machined SUS321 Stainless Steel Parts & Services
How does SUS321 compare to SUS304 in high-temperature environments?
What welding techniques are suitable for SUS321 stainless steel?
How does SUS321 perform in acidic environments compared to other stainless steels?
What are the recommended heat treatment processes for SUS321?
How does SUS321 perform in aerospace applications compared to other high-temperature alloys?
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