K340 Steel: Properties and Key Applications Overview
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Table Of Content
K340 steel, also known as Bohler Tool Steel, is a high-performance tool steel primarily classified as a high-carbon alloy steel. It is designed for applications requiring exceptional wear resistance and toughness. The primary alloying elements in K340 include chromium, molybdenum, and vanadium, which significantly enhance its hardness, wear resistance, and overall mechanical properties.
Comprehensive Overview
K340 steel is characterized by its high carbon content, which typically ranges from 0.9% to 1.1%, along with a balanced mix of chromium (4.0% to 5.0%), molybdenum (1.0% to 1.5%), and vanadium (0.5% to 1.0%). These alloying elements contribute to the steel's ability to maintain hardness at elevated temperatures, making it suitable for high-speed cutting tools and dies.
The significant characteristics of K340 steel include:
- High Hardness: Achievable hardness levels can exceed 60 HRC after appropriate heat treatment.
- Excellent Wear Resistance: The alloying elements provide superior resistance to abrasion and wear, making it ideal for tooling applications.
- Good Toughness: Despite its hardness, K340 maintains a level of toughness that allows it to withstand impact without fracturing.
Advantages:
- Exceptional wear resistance makes it suitable for high-performance tooling.
- High hardness retention at elevated temperatures allows for prolonged tool life.
- Versatile applications across various industries, including automotive and aerospace.
Limitations:
- Prone to brittleness if not properly heat-treated.
- Requires careful machining and fabrication due to its hardness.
- Higher cost compared to lower alloy steels.
K340 steel holds a significant position in the tool steel market, often chosen for applications where performance and durability are paramount. Its historical significance lies in its development for high-performance cutting tools, which has evolved alongside advancements in manufacturing technologies.
Alternative Names, Standards, and Equivalents
Standard Organization | Designation/Grade | Country/Region of Origin | Notes/Remarks |
---|---|---|---|
UNS | T42040 | USA | Closest equivalent to K340 |
AISI/SAE | AISI D2 | USA | Minor compositional differences; D2 has lower toughness |
ASTM | A681 | USA | Standard specification for tool steels |
EN | 1.2379 | Europe | Equivalent with similar properties |
JIS | SKD11 | Japan | Similar performance but varies in toughness |
The differences between K340 and its equivalents, such as AISI D2 and JIS SKD11, can affect selection based on specific application requirements. For instance, while D2 offers good wear resistance, K340's higher toughness may be preferable in applications subject to impact loading.
Key Properties
Chemical Composition
Element (Symbol and Name) | Percentage Range (%) |
---|---|
C (Carbon) | 0.9 - 1.1 |
Cr (Chromium) | 4.0 - 5.0 |
Mo (Molybdenum) | 1.0 - 1.5 |
V (Vanadium) | 0.5 - 1.0 |
Mn (Manganese) | 0.2 - 0.5 |
Si (Silicon) | 0.2 - 0.5 |
P (Phosphorus) | ≤ 0.03 |
S (Sulfur) | ≤ 0.03 |
The primary role of the key alloying elements in K340 steel includes:
- Chromium: Enhances hardenability and corrosion resistance.
- Molybdenum: Improves toughness and high-temperature strength.
- Vanadium: Increases wear resistance and refines grain structure, contributing to overall toughness.
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 | 1800 - 2200 MPa | 261 - 319 ksi | ASTM E8 |
Yield Strength (0.2% offset) | Quenched & Tempered | Room Temp | 1500 - 1900 MPa | 217 - 276 ksi | ASTM E8 |
Elongation | Quenched & Tempered | Room Temp | 5 - 10% | 5 - 10% | ASTM E8 |
Hardness (HRC) | Quenched & Tempered | Room Temp | 58 - 62 HRC | 58 - 62 HRC | ASTM E18 |
Impact Strength (Charpy) | Quenched & Tempered | -20 °C | 20 - 30 J | 14.8 - 22.1 ft-lbf | ASTM E23 |
The combination of these mechanical properties makes K340 steel particularly suitable for applications involving high mechanical loading and structural integrity requirements, such as cutting tools, dies, and molds.
Physical Properties
Property | Condition/Temperature | Value (Metric) | Value (Imperial) |
---|---|---|---|
Density | Room Temp | 7.85 g/cm³ | 0.284 lb/in³ |
Melting Point | - | 1425 - 1450 °C | 2600 - 2642 °F |
Thermal Conductivity | Room Temp | 25 W/m·K | 14.5 BTU·in/(hr·ft²·°F) |
Specific Heat Capacity | Room Temp | 460 J/kg·K | 0.11 BTU/lb·°F |
Electrical Resistivity | Room Temp | 0.0006 Ω·m | 0.0004 Ω·in |
The practical significance of K340's physical properties includes:
- Density: Affects the weight and balance of tools made from K340, crucial for precision applications.
- Thermal Conductivity: Important for heat dissipation in high-speed cutting applications, preventing overheating.
- Melting Point: Indicates the steel's ability to withstand high temperatures without losing structural integrity.
Corrosion Resistance
Corrosive Agent | Concentration (%) | Temperature (°C) | Resistance Rating | Notes |
---|---|---|---|---|
Chlorides | 3-10 | 20-60 | Fair | Risk of pitting corrosion |
Sulfuric Acid | 10-30 | 25-50 | Poor | Not recommended |
Sodium Hydroxide | 5-20 | 20-60 | Good | Moderate resistance |
K340 steel exhibits moderate corrosion resistance, particularly in environments with chlorides and alkaline solutions. However, it is susceptible to pitting in chloride-rich environments and should be avoided in acidic conditions. Compared to other tool steels like D2 and SKD11, K340 offers better toughness but may not perform as well in corrosive environments, necessitating protective coatings or surface treatments in specific applications.
Heat Resistance
Property/Limit | Temperature (°C) | Temperature (°F) | Remarks |
---|---|---|---|
Max Continuous Service Temp | 500 | 932 | Suitable for prolonged use |
Max Intermittent Service Temp | 600 | 1112 | Short-term exposure only |
Scaling Temperature | 700 | 1292 | Risk of oxidation beyond this temp |
Creep Strength considerations | 400 | 752 | Begins to degrade at this temp |
At elevated temperatures, K340 steel maintains its hardness and strength, making it suitable for applications involving high thermal loads. However, oxidation can become a concern, particularly at temperatures exceeding 600 °C (1112 °F). Proper heat treatment and surface coatings can mitigate these issues.
Fabrication Properties
Weldability
Welding Process | Recommended Filler Metal (AWS Classification) | Typical Shielding Gas/Flux | Notes |
---|---|---|---|
TIG | ER80S-D2 | Argon | Preheat recommended |
MIG | ER70S-6 | Argon/CO2 | Post-weld heat treatment advised |
Stick | E7018 | - | Requires preheating |
K340 steel can be welded, but care must be taken to avoid cracking. Preheating and post-weld heat treatment are recommended to relieve stresses and improve toughness. Common defects include porosity and cracking if not properly managed.
Machinability
Machining Parameter | K340 Steel | AISI 1212 | Notes/Tips |
---|---|---|---|
Relative Machinability Index | 50 | 100 | K340 is more challenging to machine |
Typical Cutting Speed | 20 m/min | 40 m/min | Use carbide tools for best results |
K340 steel's hardness presents challenges in machining, requiring specialized tooling and slower cutting speeds. Optimal conditions include using carbide tools and appropriate coolant to manage heat.
Formability
K340 steel is not particularly suited for extensive forming processes due to its high hardness. Cold forming can lead to cracking, while hot forming is more feasible but requires careful temperature control to avoid losing hardness.
Heat Treatment
Treatment Process | Temperature Range (°C/°F) | Typical Soaking Time | Cooling Method | Primary Purpose / Expected Result |
---|---|---|---|---|
Annealing | 800 - 850 / 1472 - 1562 | 1 - 2 hours | Air | Reduce hardness, improve machinability |
Quenching | 1000 - 1100 / 1832 - 2012 | 30 minutes | Oil | Increase hardness |
Tempering | 500 - 600 / 932 - 1112 | 1 hour | Air | Reduce brittleness, improve toughness |
The heat treatment processes significantly impact K340's microstructure and properties. Quenching increases hardness, while tempering balances hardness and toughness, making it suitable for demanding applications.
Typical Applications and End Uses
Industry/Sector | Specific Application Example | Key Steel Properties Utilized in this Application | Reason for Selection (Brief) |
---|---|---|---|
Automotive | Cutting tools | High hardness, wear resistance | Prolonged tool life |
Aerospace | Molds for composite parts | Toughness, thermal stability | High-performance requirements |
Manufacturing | Dies for stamping | Wear resistance, strength | Durability under stress |
Other applications include:
- Precision machining tools
- Injection molds
- Shear blades
K340 steel is chosen for these applications due to its exceptional wear resistance and ability to maintain performance under high-stress conditions.
Important Considerations, Selection Criteria, and Further Insights
Feature/Property | K340 Steel | AISI D2 | SKD11 | Brief Pro/Con or Trade-off Note |
---|---|---|---|---|
Key Mechanical Property | High hardness | Good wear resistance | Moderate toughness | K340 offers superior toughness |
Key Corrosion Aspect | Moderate resistance | Poor in acidic environments | Fair in chlorides | K340 is better in tough conditions |
Weldability | Moderate | Poor | Moderate | K340 requires careful handling |
Machinability | Challenging | Easy | Moderate | K340 needs specialized tooling |
Formability | Limited | Good | Moderate | K340 is not ideal for forming |
Approx. Relative Cost | Higher | Moderate | Lower | Cost reflects performance benefits |
Typical Availability | Moderate | High | High | K340 may be less available |
When selecting K340 steel, considerations include its cost-effectiveness, availability, and specific application requirements. While it may be more expensive than alternatives, its performance in demanding applications often justifies the investment. Additionally, K340's magnetic properties are minimal, making it suitable for applications where magnetic interference is a concern.
In conclusion, K340 steel is a versatile and high-performance tool steel that excels in applications requiring durability and resistance to wear. Its unique properties and careful selection criteria make it a valuable choice for engineers and manufacturers in various industries.