K340 Steel: Properties and Key Applications Overview

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.