N690 Steel: Properties and Key Applications Overview
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Table Of Content
Table Of Content
N690 steel, also known as Bohler N690, is a high-performance stainless steel that falls under the category of martensitic stainless steels. This steel grade is primarily alloyed with chromium, molybdenum, and vanadium, which significantly enhance its hardness, corrosion resistance, and overall mechanical properties. N690 is particularly known for its excellent edge retention and wear resistance, making it a popular choice in the manufacturing of high-quality knives and cutting tools.
Comprehensive Overview
N690 steel is classified as a martensitic stainless steel, which is characterized by its high carbon content and the ability to be hardened through heat treatment. The primary alloying elements in N690 include:
- Chromium (Cr): Typically around 17%, which provides corrosion resistance and contributes to the steel's hardness.
- Molybdenum (Mo): Approximately 1.1%, enhancing resistance to pitting and crevice corrosion.
- Vanadium (V): About 0.2%, which improves wear resistance and contributes to the fine grain structure.
The combination of these elements results in a steel that exhibits remarkable hardness, typically achieving a Rockwell hardness of 58-60 HRC after proper heat treatment.
Advantages and Limitations
| Advantages (Pros) | Limitations (Cons) |
|---|---|
| Excellent edge retention and wear resistance | More challenging to machine compared to lower alloy steels |
| Good corrosion resistance, suitable for various environments | Can be prone to brittleness if not heat-treated properly |
| High hardness and strength, making it ideal for cutting tools | Requires careful handling to avoid chipping or cracking |
| Retains sharpness well, making it popular in knife applications | Limited ductility compared to austenitic stainless steels |
N690 steel has carved a niche in the market, particularly in the knife-making industry, where its properties are highly valued. Its historical significance is tied to its development by Bohler, a company known for producing high-quality tool steels, which has established N690 as a benchmark for performance in various applications.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | S69030 | USA | Closest equivalent to N690 |
| AISI/SAE | 440C | USA | Minor compositional differences; 440C has higher carbon content |
| ASTM | A276 | USA | General specification for stainless steel bars |
| EN | 1.4528 | Europe | Equivalent grade in European standards |
| JIS | SUS440C | Japan | Similar properties but different heat treatment response |
While N690 is often compared to 440C, it is essential to note that the higher chromium content in N690 provides better corrosion resistance, while 440C may offer slightly higher hardness due to its carbon content. This distinction can influence the selection of steel for specific applications, particularly in environments where corrosion resistance is critical.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| Carbon (C) | 0.90 - 1.00 |
| Chromium (Cr) | 16.0 - 17.0 |
| Molybdenum (Mo) | 1.0 - 1.2 |
| Vanadium (V) | 0.1 - 0.3 |
| Manganese (Mn) | 0.5 - 1.0 |
| Silicon (Si) | 0.5 max |
| Phosphorus (P) | 0.03 max |
| Sulfur (S) | 0.03 max |
The primary role of the key alloying elements in N690 steel is as follows:
- Chromium: Enhances corrosion resistance and hardness.
- Molybdenum: Improves resistance to pitting and enhances overall toughness.
- Vanadium: Contributes to wear resistance and helps refine the grain structure, leading to improved mechanical properties.
Mechanical Properties
| Property | Condition/Temper | Test Temperature | Typical Value/Range (Metric - SI Units) | Typical Value/Range (Imperial Units) | Reference Standard for Test Method |
|---|---|---|---|---|---|
| Tensile Strength | Quenched & Tempered | Room Temperature | 1000 - 1100 MPa | 145 - 160 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Quenched & Tempered | Room Temperature | 800 - 900 MPa | 116 - 130 ksi | ASTM E8 |
| Elongation | Quenched & Tempered | Room Temperature | 12 - 15% | 12 - 15% | ASTM E8 |
| Hardness | Quenched & Tempered | Room Temperature | 58 - 60 HRC | 58 - 60 HRC | ASTM E18 |
| Impact Strength | Quenched & Tempered | -20 °C | 30 - 40 J | 22 - 30 ft-lbf | ASTM E23 |
The combination of high tensile and yield strength, along with good hardness, makes N690 steel suitable for applications that require high mechanical loading and structural integrity. Its ability to maintain these properties under various conditions is critical for tools and components subjected to wear and impact.
Physical Properties
| Property | Condition/Temperature | Value (Metric - SI Units) | Value (Imperial Units) |
|---|---|---|---|
| Density | - | 7.8 g/cm³ | 0.282 lb/in³ |
| Melting Point/Range | - | 1400 - 1450 °C | 2552 - 2642 °F |
| Thermal Conductivity | 20 °C | 25 W/m·K | 14.5 BTU·in/(hr·ft²·°F) |
| Specific Heat Capacity | 20 °C | 500 J/kg·K | 0.119 BTU/lb·°F |
| Electrical Resistivity | 20 °C | 0.75 μΩ·m | 0.0013 Ω·in |
The practical significance of N690's physical properties is evident in its applications. For instance, its high density contributes to the weight and balance of knives, while its thermal conductivity allows for effective heat dissipation during cutting operations. The melting point indicates its suitability for high-temperature applications, although care must be taken to avoid overheating during processing.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C/°F) | Resistance Rating | Notes |
|---|---|---|---|---|
| Chlorides | 3-10 | 20-60 °C / 68-140 °F | Good | Risk of pitting corrosion |
| Acids (Sulfuric) | 10-30 | 20-40 °C / 68-104 °F | Fair | Susceptible to SCC |
| Alkaline Solutions | 5-20 | 20-60 °C / 68-140 °F | Good | Limited resistance |
| Atmospheric Conditions | - | - | Excellent | Good for outdoor applications |
N690 steel exhibits good resistance to various corrosive environments, particularly in atmospheric conditions and mild chlorides. However, it is susceptible to pitting corrosion in high chloride environments, which can be a concern for marine applications. Compared to other stainless steels like AISI 440C and 154CM, N690 offers superior corrosion resistance due to its higher chromium content, making it a preferred choice for applications requiring durability and longevity.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 300 °C | 572 °F | Suitable for high-temperature applications |
| Max Intermittent Service Temp | 350 °C | 662 °F | Can withstand short-term exposure to higher temperatures |
| Scaling Temperature | 600 °C | 1112 °F | Begins to lose mechanical properties beyond this temperature |
At elevated temperatures, N690 steel maintains its mechanical properties up to a certain limit. However, prolonged exposure to high temperatures can lead to oxidation and a decrease in hardness. It is essential to consider these factors when selecting N690 for applications involving heat.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| TIG | ER 316L | Argon | Preheat recommended |
| MIG | ER 308L | Argon + CO2 | Post-weld heat treatment advised |
| Stick | E308-16 | - | Careful control of heat input |
N690 steel can be welded using various processes, but it requires careful control of heat input to avoid cracking. Preheating is often recommended, and post-weld heat treatment can help relieve stresses and improve toughness. The choice of filler metal is crucial to ensure compatibility and maintain corrosion resistance.
Machinability
| Machining Parameter | N690 Steel | AISI 1212 | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 50% | 100% | More difficult to machine due to hardness |
| Typical Cutting Speed (Turning) | 30-40 m/min | 80-100 m/min | Use carbide tools for best results |
N690 steel presents challenges in machining due to its hardness. Optimal conditions include using carbide tooling and maintaining lower cutting speeds to prevent tool wear. Proper cooling and lubrication are essential to achieve desired surface finishes.
Formability
N690 steel is not particularly known for its formability, as it is a hard steel that can be challenging to shape. Cold forming is possible but may lead to work hardening, requiring careful control of bending radii and forming processes. Hot forming is more feasible, but temperatures must be monitored to avoid compromising the steel's properties.
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 or Oil | Reduce hardness, improve ductility |
| Quenching | 1000 - 1100 °C / 1832 - 2012 °F | 30 minutes | Oil or Water | Increase hardness |
| Tempering | 200 - 600 °C / 392 - 1112 °F | 1 hour | Air | Reduce brittleness, enhance toughness |
The heat treatment process for N690 steel involves quenching and tempering to achieve the desired hardness and toughness. During quenching, the steel is rapidly cooled to lock in the martensitic structure, while tempering helps relieve internal stresses and improve ductility. Understanding these transformations is crucial for optimizing the steel's performance in various applications.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection (Brief) |
|---|---|---|---|
| Knife Manufacturing | High-end kitchen knives | Excellent edge retention, corrosion resistance | Ideal for culinary applications |
| Tool Making | Cutting tools | High hardness, wear resistance | Essential for durability |
| Medical Instruments | Surgical tools | Corrosion resistance, strength | Safety and hygiene requirements |
| Aerospace | Components in aircraft engines | High strength-to-weight ratio, heat resistance | Critical for performance |
N690 steel is widely used in industries requiring high-performance materials. Its excellent edge retention makes it a favorite among knife makers, while its strength and corrosion resistance are vital for surgical instruments and aerospace components.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | N690 Steel | 440C | 154CM | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High hardness | High hardness | Moderate hardness | N690 offers better corrosion resistance than 440C |
| Key Corrosion Aspect | Good | Fair | Good | N690 is superior in chloride environments |
| Weldability | Moderate | Poor | Moderate | N690 requires careful welding techniques |
| Machinability | Challenging | Moderate | Good | N690 is harder to machine than 154CM |
| Formability | Limited | Moderate | Good | N690 is less formable than 154CM |
| Approx. Relative Cost | Moderate | Low | Moderate | N690 is generally more expensive due to alloying elements |
| Typical Availability | Moderate | High | Moderate | N690 may be less readily available than 440C |
When selecting N690 steel, considerations include its cost-effectiveness, availability, and specific application requirements. While it may be more expensive than some alternatives, its superior properties often justify the investment, particularly in high-performance applications. Additionally, its magnetic properties are minimal, making it suitable for applications where magnetic interference is a concern.
In summary, N690 steel is a versatile and high-performance material that excels in various applications, particularly where hardness, corrosion resistance, and edge retention are critical. Understanding its properties, advantages, and limitations is essential for making informed decisions in material selection.
