420 Stainless Steel: Properties and Key Applications
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Table Of Content
Table Of Content
420 stainless steel is a martensitic stainless steel known for its high strength, moderate corrosion resistance, and ability to be hardened through heat treatment. It is classified under the martensitic stainless steel category, which is characterized by its high carbon content and the presence of chromium as the primary alloying element. The typical composition of 420 stainless steel includes approximately 12-14% chromium and 0.15-0.4% carbon, which significantly influences its properties.
Comprehensive Overview
420 stainless steel is primarily used in applications requiring high hardness and moderate corrosion resistance. The alloying elements in 420, particularly chromium and carbon, play crucial roles in defining its characteristics. Chromium enhances corrosion resistance and contributes to the steel's hardness, while carbon increases strength and wear resistance.
Advantages of 420 Stainless Steel:
- High Hardness: After heat treatment, 420 can achieve a hardness level of up to 50 HRC, making it suitable for cutting tools and blades.
- Good Wear Resistance: Its high carbon content provides excellent wear resistance, ideal for applications involving friction.
- Moderate Corrosion Resistance: While not as resistant as austenitic grades, it performs well in mildly corrosive environments.
Limitations of 420 Stainless Steel:
- Lower Toughness: Compared to austenitic stainless steels, 420 has lower toughness, making it less suitable for applications requiring high impact resistance.
- Limited Corrosion Resistance: In highly corrosive environments, such as marine applications, it may not perform adequately without protective coatings.
Historically, 420 stainless steel has been significant in the manufacturing of cutlery, surgical instruments, and various industrial applications due to its balance of hardness and corrosion resistance. Its market position is well-established, particularly in the cutlery and tool manufacturing sectors.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | S42000 | USA | Closest equivalent to AISI 420 |
| AISI/SAE | 420 | USA | Commonly used designation |
| ASTM | A276 | USA | Standard specification for stainless steel bars |
| EN | 1.4021 | Europe | Equivalent designation in Europe |
| JIS | SUS420J2 | Japan | Similar properties with minor compositional differences |
The equivalence table highlights that while these grades are often considered interchangeable, subtle differences in composition can affect performance in specific applications. For instance, SUS420J2 has a slightly higher carbon content, which may enhance hardness but could also reduce corrosion resistance.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| C (Carbon) | 0.15 - 0.40 |
| Cr (Chromium) | 12.0 - 14.0 |
| Mn (Manganese) | 1.0 max |
| Si (Silicon) | 1.0 max |
| P (Phosphorus) | 0.04 max |
| S (Sulfur) | 0.03 max |
The primary alloying elements in 420 stainless steel include chromium, which provides corrosion resistance and hardness, and carbon, which enhances strength and wear resistance. Manganese and silicon are present in minor amounts to improve toughness and deoxidation during steelmaking.
Mechanical Properties
| Property | Condition/Temper | Test Temperature | Typical Value/Range (Metric) | Typical Value/Range (Imperial) | Reference Standard for Test Method |
|---|---|---|---|---|---|
| Tensile Strength | Annealed | Room Temp | 520 - 700 MPa | 75 - 102 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Annealed | Room Temp | 350 - 500 MPa | 51 - 73 ksi | ASTM E8 |
| Elongation | Annealed | Room Temp | 12 - 20% | 12 - 20% | ASTM E8 |
| Hardness (Rockwell C) | Quenched & Tempered | Room Temp | 40 - 50 HRC | 40 - 50 HRC | ASTM E18 |
| Impact Strength | Quenched & Tempered | -20°C (-4°F) | 30 J | 22 ft-lbf | ASTM E23 |
The mechanical properties of 420 stainless steel make it suitable for applications requiring high strength and hardness. Its tensile strength and yield strength indicate its ability to withstand significant loads, while the elongation percentage reflects its ductility, which is adequate for many applications. The hardness values achieved through heat treatment make it ideal for cutting tools and wear-resistant applications.
Physical Properties
| Property | Condition/Temperature | Value (Metric) | Value (Imperial) |
|---|---|---|---|
| Density | - | 7.75 g/cm³ | 0.28 lb/in³ |
| Melting Point | - | 1450 - 1510 °C | 2642 - 2750 °F |
| Thermal Conductivity | 20 °C | 25.4 W/m·K | 17.5 BTU·in/h·ft²·°F |
| Specific Heat Capacity | 20 °C | 500 J/kg·K | 0.12 BTU/lb·°F |
| Electrical Resistivity | 20 °C | 0.73 µΩ·m | 0.00000073 Ω·m |
| Coefficient of Thermal Expansion | 20 - 100 °C | 15.5 µm/m·K | 8.6 µin/in·°F |
The density of 420 stainless steel indicates a relatively heavy material, which contributes to its strength. The melting point is significant for applications involving high temperatures, while thermal conductivity and specific heat capacity are essential for thermal management in engineering applications. The coefficient of thermal expansion is crucial for applications where temperature fluctuations are expected.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C/°F) | Resistance Rating | Notes |
|---|---|---|---|---|
| Chlorides | 3-10 | 20-60 °C (68-140 °F) | Fair | Risk of pitting |
| Sulfuric Acid | 10-30 | 20-50 °C (68-122 °F) | Poor | Not recommended |
| Acetic Acid | 5-20 | 20-40 °C (68-104 °F) | Good | Moderate resistance |
| Atmospheric | - | - | Good | Suitable for mild exposure |
420 stainless steel exhibits moderate corrosion resistance, particularly in atmospheric conditions and in the presence of acetic acid. However, it is susceptible to pitting corrosion in chloride environments and should be avoided in applications involving strong acids like sulfuric acid. Compared to austenitic grades like 304 or 316, 420's corrosion resistance is lower, making it less suitable for marine or highly corrosive environments.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 400 °C | 752 °F | Suitable for intermittent service |
| Max Intermittent Service Temp | 500 °C | 932 °F | Limited oxidation resistance |
| Scaling Temperature | 600 °C | 1112 °F | Risk of scaling at high temps |
At elevated temperatures, 420 stainless steel maintains its strength but may experience oxidation. The maximum continuous service temperature indicates its capability in high-temperature applications, while the scaling temperature highlights the risk of surface degradation. Care should be taken to avoid prolonged exposure to temperatures above these limits.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| TIG | ER420 | Argon | Preheat recommended |
| MIG | ER420 | Argon + CO2 | Post-weld heat treatment may be necessary |
420 stainless steel can be welded using TIG and MIG processes, but preheating is often recommended to prevent cracking. Post-weld heat treatment can enhance the properties of the weldment, ensuring better performance in service.
Machinability
| Machining Parameter | [420 Stainless Steel] | [AISI 1212] | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 50% | 100% | Use carbide tools for best results |
| Typical Cutting Speed | 30-50 m/min | 60-80 m/min | Adjust for tool wear |
420 stainless steel has moderate machinability, which can be improved with the right tooling and cutting conditions. Carbide tools are recommended for machining to achieve better surface finishes and tool life.
Formability
420 stainless steel is not highly formable due to its martensitic structure, which makes it more suitable for applications requiring cutting and shaping rather than extensive forming. Cold forming is possible but may lead to work hardening, requiring careful control of the process.
Heat Treatment
| Treatment Process | Temperature Range (°C/°F) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Annealing | 800 - 900 °C (1472 - 1652 °F) | 1-2 hours | Air | Reduce hardness, improve ductility |
| Quenching | 1000 - 1100 °C (1832 - 2012 °F) | 30 minutes | Oil or Water | Increase hardness |
| Tempering | 150 - 300 °C (302 - 572 °F) | 1 hour | Air | Reduce brittleness, enhance toughness |
The heat treatment processes significantly affect the microstructure and properties of 420 stainless steel. Quenching increases hardness, while tempering reduces brittleness, making it suitable for various applications.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection |
|---|---|---|---|
| Cutlery | Kitchen knives | High hardness, wear resistance | Edge retention |
| Medical | Surgical instruments | Corrosion resistance, hardness | Sterilization and durability |
| Automotive | Valve components | Strength, moderate corrosion resistance | Performance under stress |
| Aerospace | Landing gear components | High strength, fatigue resistance | Safety and reliability |
420 stainless steel is commonly used in the cutlery and medical industries due to its hardness and ability to maintain a sharp edge. In automotive and aerospace applications, its strength and fatigue resistance make it a suitable choice for critical components.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | 420 Stainless Steel | AISI 304 Stainless Steel | AISI 316 Stainless Steel | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High hardness | Good ductility | Excellent corrosion resistance | 420 is harder but less ductile |
| Key Corrosion Aspect | Moderate resistance | Good resistance | Excellent resistance | 420 is less suitable for harsh environments |
| Weldability | Moderate | Good | Good | 420 requires preheating |
| Machinability | Moderate | Good | Fair | 420 is harder to machine |
| Formability | Poor | Good | Fair | 420 is not suitable for extensive forming |
| Approx. Relative Cost | Moderate | Higher | Higher | 420 is often more cost-effective |
| Typical Availability | Common | Very common | Common | 420 is widely available |
When selecting 420 stainless steel, considerations include its mechanical properties, corrosion resistance, and suitability for welding and machining. While it offers advantages in hardness and wear resistance, its limitations in toughness and corrosion resistance should be carefully evaluated against the specific requirements of the application.
In summary, 420 stainless steel is a versatile material that finds its niche in applications requiring a balance of hardness and moderate corrosion resistance. Its historical significance and established market position make it a reliable choice for various industries.