Nak55 Steel: Properties and Key Applications in Molding
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Table Of Content
Nak55 steel, also known as mold steel, is a high-performance tool steel primarily classified as a medium-carbon alloy steel. It is characterized by its excellent machinability, wear resistance, and toughness, making it a preferred choice for various tooling applications, particularly in the manufacturing of molds and dies. The primary alloying elements in Nak55 steel include carbon (C), chromium (Cr), and molybdenum (Mo), which significantly influence its mechanical properties and performance characteristics.
Comprehensive Overview
Nak55 steel is specifically designed for applications requiring high wear resistance and the ability to withstand high temperatures. The carbon content typically ranges from 0.5% to 0.6%, which contributes to its hardness and strength. Chromium enhances corrosion resistance and hardenability, while molybdenum improves toughness and stability at elevated temperatures.
The most significant characteristics of Nak55 steel include its high hardness, excellent wear resistance, and good machinability. These properties make it suitable for producing complex shapes and intricate designs in molds and dies. However, Nak55 steel also has limitations, such as its susceptibility to cracking during hardening and the need for careful heat treatment to achieve optimal properties.
Advantages (Pros):
- High wear resistance, ideal for tooling applications.
- Good machinability, allowing for efficient manufacturing processes.
- Excellent toughness, providing durability in demanding applications.
Disadvantages (Cons):
- Susceptible to cracking if not properly heat-treated.
- Limited corrosion resistance compared to stainless steels.
- Higher cost compared to lower-grade steels.
In terms of market position, Nak55 steel is widely used in the mold-making industry, particularly in regions with advanced manufacturing capabilities. Its historical significance lies in its ability to meet the evolving demands of precision tooling and mold production.
Alternative Names, Standards, and Equivalents
| Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
|---|---|---|---|
| UNS | S7 | USA | Closest equivalent with similar properties |
| AISI/SAE | AISI D2 | USA | Minor compositional differences; higher carbon content |
| ASTM | A681 | USA | Tool steel specification |
| JIS | SKD11 | Japan | Similar performance but different heat treatment requirements |
| DIN | 1.2379 | Germany | Equivalent with slight variations in composition |
The table above outlines various standards and equivalents for Nak55 steel. Notably, while grades like AISI D2 and JIS SKD11 are often considered equivalent, they may exhibit differences in hardenability and toughness, which can affect their performance in specific applications.
Key Properties
Chemical Composition
| Element (Symbol and Name) | Percentage Range (%) |
|---|---|
| C (Carbon) | 0.50 - 0.60 |
| Cr (Chromium) | 5.00 - 6.00 |
| Mo (Molybdenum) | 1.00 - 1.50 |
| Mn (Manganese) | 0.20 - 0.50 |
| Si (Silicon) | 0.20 - 0.50 |
| P (Phosphorus) | ≤ 0.030 |
| S (Sulfur) | ≤ 0.030 |
The primary alloying elements in Nak55 steel play crucial roles in determining its properties. Carbon is essential for hardness and strength, while chromium enhances corrosion resistance and hardenability. Molybdenum contributes to toughness and stability at high temperatures, making Nak55 suitable for demanding applications.
Mechanical Properties
| Property | Condition/Temper | Test Temperature | Typical Value/Range (Metric) | Typical Value/Range (Imperial) | Reference Standard for Test Method |
|---|---|---|---|---|---|
| Tensile Strength | Quenched & Tempered | Room Temp | 1,200 - 1,400 MPa | 174 - 203 ksi | ASTM E8 |
| Yield Strength (0.2% offset) | Quenched & Tempered | Room Temp | 1,000 - 1,200 MPa | 145 - 174 ksi | ASTM E8 |
| Elongation | Quenched & Tempered | Room Temp | 10 - 15% | 10 - 15% | ASTM E8 |
| Hardness (HRC) | Quenched & Tempered | Room Temp | 58 - 62 HRC | 58 - 62 HRC | ASTM E18 |
| Impact Strength | Quenched & Tempered | -20°C | 20 - 30 J | 15 - 22 ft-lbf | ASTM E23 |
The mechanical properties of Nak55 steel, particularly its high tensile and yield strength, make it suitable for applications involving significant mechanical loading. The hardness achieved through heat treatment allows for effective wear resistance, while the elongation percentage indicates good ductility, essential for preventing brittle failure.
Physical Properties
| Property | Condition/Temperature | Value (Metric) | Value (Imperial) |
|---|---|---|---|
| Density | Room Temp | 7.85 g/cm³ | 0.284 lb/in³ |
| Melting Point | - | 1,400 - 1,500 °C | 2,552 - 2,732 °F |
| Thermal Conductivity | Room Temp | 25 W/m·K | 14.5 BTU·in/h·ft²·°F |
| Specific Heat Capacity | Room Temp | 0.46 kJ/kg·K | 0.11 BTU/lb·°F |
| Electrical Resistivity | Room Temp | 0.0001 Ω·m | 0.0001 Ω·in |
The density of Nak55 steel indicates its substantial mass, which contributes to its durability in applications. The melting point is critical for processes involving high temperatures, while thermal conductivity and specific heat capacity are essential for understanding heat treatment processes and thermal management in tooling applications.
Corrosion Resistance
| Corrosive Agent | Concentration (%) | Temperature (°C/°F) | Resistance Rating | Notes |
|---|---|---|---|---|
| Chlorides | 3-5 | 25°C/77°F | Fair | Risk of pitting |
| Acids | 10-20 | 20°C/68°F | Poor | Susceptible to corrosion |
| Alkaline Solutions | 5-10 | 25°C/77°F | Fair | Moderate resistance |
| Atmospheric | - | - | Good | Performs well in mild conditions |
Nak55 steel exhibits moderate corrosion resistance, particularly in atmospheric conditions. However, it is susceptible to pitting in chloride environments and can corrode in acidic conditions. Compared to stainless steels, Nak55's corrosion resistance is limited, making it less suitable for applications exposed to harsh environments.
Heat Resistance
| Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
|---|---|---|---|
| Max Continuous Service Temp | 300°C | 572°F | Suitable for prolonged exposure |
| Max Intermittent Service Temp | 400°C | 752°F | Short-term exposure |
| Scaling Temperature | 500°C | 932°F | Risk of oxidation beyond this limit |
Nak55 steel maintains its mechanical properties at elevated temperatures, making it suitable for applications involving heat. However, care must be taken to avoid oxidation and scaling, which can compromise its integrity.
Fabrication Properties
Weldability
| Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
|---|---|---|---|
| MIG | ER70S-6 | Argon + CO2 | Good for thin sections |
| TIG | ER80S-Ni | Argon | Requires preheating |
| Stick | E7018 | - | Suitable for general applications |
Nak55 steel can be welded using various processes, though preheating is often necessary to prevent cracking. The choice of filler metal is crucial to ensure compatibility and maintain mechanical properties in the weld zone.
Machinability
| Machining Parameter | Nak55 Steel | AISI 1212 | Notes/Tips |
|---|---|---|---|
| Relative Machinability Index | 70% | 100% | Nak55 is machinable but requires careful tooling. |
| Typical Cutting Speed (Turning) | 30 m/min | 50 m/min | Adjust speeds based on tooling and conditions. |
Nak55 steel offers good machinability, though it requires specific tooling and cutting conditions to optimize performance. The relative machinability index indicates that while it is machinable, it is not as easy to work with as some lower-grade steels.
Formability
Nak55 steel exhibits moderate formability, suitable for cold and hot forming processes. However, due to its hardness, it may require special considerations for bending and shaping, particularly in complex geometries. Work hardening can occur, necessitating careful control of the forming process to avoid cracking.
Heat Treatment
| Treatment Process | Temperature Range (°C/°F) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
|---|---|---|---|---|
| Annealing | 600 - 700 °C / 1,112 - 1,292 °F | 1 - 2 hours | Air or oil | Reduce hardness, improve machinability |
| Quenching | 1,000 - 1,050 °C / 1,832 - 1,922 °F | 30 minutes | Oil or water | Increase hardness and strength |
| Tempering | 500 - 600 °C / 932 - 1,112 °F | 1 hour | Air | Reduce brittleness, enhance toughness |
Heat treatment is critical for Nak55 steel to achieve desired mechanical properties. The quenching process increases hardness, while tempering reduces brittleness, allowing for a balance between strength and toughness. Understanding these transformations is essential for optimizing the steel's performance in specific applications.
Typical Applications and End Uses
| Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection |
|---|---|---|---|
| Automotive | Injection molds | High wear resistance, toughness | Durable molds for high-volume production |
| Aerospace | Die casting | High strength, heat resistance | Precision components under stress |
| Consumer Goods | Plastic molds | Excellent machinability, wear resistance | Complex shapes and designs |
| Electronics | Stamping dies | Good toughness, dimensional stability | High precision in component manufacturing |
Other applications include:
- Medical devices: Precision molds for surgical instruments.
- Packaging: Molds for creating packaging materials.
- Construction: Tools and dies for forming structural components.
Nak55 steel is chosen for these applications due to its excellent balance of hardness, toughness, and machinability, making it ideal for producing high-quality molds and dies.
Important Considerations, Selection Criteria, and Further Insights
| Feature/Property | Nak55 Steel | AISI D2 | JIS SKD11 | Brief Pro/Con or Trade-off Note |
|---|---|---|---|---|
| Key Mechanical Property | High hardness | High hardness | High hardness | Similar hardness but varies in toughness |
| Key Corrosion Aspect | Fair | Poor | Fair | Nak55 offers better corrosion resistance than D2 |
| Weldability | Moderate | Poor | Moderate | Nak55 is more weldable than D2 but still requires care |
| Machinability | Good | Excellent | Good | D2 is easier to machine than Nak55 |
| Formability | Moderate | Poor | Moderate | Nak55 has better formability than D2 |
| Approx. Relative Cost | Moderate | High | Moderate | Cost varies by region and supplier |
| Typical Availability | Common | Common | Common | Widely available in tooling markets |
When selecting Nak55 steel, considerations include its mechanical properties, cost-effectiveness, and availability. While it offers excellent performance in tooling applications, its susceptibility to cracking during hardening and moderate corrosion resistance must be weighed against the specific requirements of the application. Additionally, understanding the trade-offs with alternative grades like AISI D2 and JIS SKD11 can guide engineers in making informed decisions based on performance needs and economic factors.
In summary, Nak55 steel stands out as a versatile and reliable choice for mold and die applications, balancing hardness, toughness, and machinability, making it a staple in the tooling industry.