CK75 Steel: Properties and Key Applications Overview

CK75 steel is a medium-carbon steel grade that falls under the category of high-carbon steels. It is primarily characterized by its carbon content, which typically ranges from 0.65% to 0.75%. This steel grade is known for its excellent hardness and wear resistance, making it suitable for various applications where strength and durability are paramount. The primary alloying element in CK75 is carbon, which significantly influences its mechanical properties, particularly its tensile strength and hardness.

Comprehensive Overview

CK75 steel is classified as a medium-carbon alloy steel, which means it has a higher carbon content compared to low-carbon steels, leading to improved strength and hardness. The presence of carbon enhances the steel's ability to harden through heat treatment processes, making it a popular choice for applications requiring high strength and wear resistance.

The most significant characteristics of CK75 steel include:

• High Hardness: Due to its carbon content, CK75 can achieve high hardness levels, especially after quenching and tempering.
• Good Wear Resistance: The steel's hardness translates into excellent wear resistance, making it ideal for components subjected to friction and abrasion.
• Moderate Ductility: While it offers good strength, CK75 has moderate ductility, which may limit its use in applications requiring extensive deformation.

Advantages and Limitations

Advantages	Limitations
High strength and hardness	Limited ductility
Excellent wear resistance	Susceptible to cracking during welding
Good machinability when properly treated	Requires careful heat treatment to avoid brittleness

CK75 steel is commonly used in the manufacturing of springs, cutting tools, and various mechanical components. Its historical significance lies in its widespread use in the automotive and machinery industries, where high-performance materials are essential.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	G10750	USA	Closest equivalent to AISI 1075
AISI/SAE	1075	USA	Similar properties but may have slight compositional differences
DIN	C75	Germany	Minor differences in carbon content
JIS	S75C	Japan	Equivalent with similar mechanical properties
EN	C75	Europe	Closest equivalent with minor variations

The differences between these equivalent grades can affect selection based on specific application requirements, such as hardness, ductility, and weldability. For instance, while AISI 1075 and CK75 are similar, the slight variations in carbon content can lead to differences in hardness and machinability.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.65 - 0.75
Mn (Manganese)	0.30 - 0.60
Si (Silicon)	0.15 - 0.40
P (Phosphorus)	≤ 0.025
S (Sulfur)	≤ 0.025

The primary role of carbon in CK75 steel is to enhance hardness and strength through heat treatment. Manganese contributes to hardenability and improves toughness, while silicon helps in deoxidation during steelmaking and enhances strength.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric - SI Units)	Typical Value/Range (Imperial Units)	Reference Standard for Test Method
Tensile Strength	Quenched & Tempered	800 - 1000 MPa	1160 - 1450 ksi	ASTM E8
Yield Strength (0.2% offset)	Quenched & Tempered	600 - 800 MPa	870 - 1160 ksi	ASTM E8
Elongation	Quenched & Tempered	10 - 15%	10 - 15%	ASTM E8
Hardness (HRC)	Quenched & Tempered	55 - 65 HRC	55 - 65 HRC	ASTM E18
Impact Strength	-	30 - 50 J at -20°C	22 - 37 ft-lbf at -4°F	ASTM E23

The combination of high tensile and yield strength, along with significant hardness, makes CK75 steel suitable for applications that require high mechanical loading and structural integrity, such as in automotive components and machinery parts.

Physical Properties

Property	Condition/Temperature	Value (Metric - SI Units)	Value (Imperial Units)
Density	-	7.85 g/cm³	0.284 lb/in³
Melting Point	-	1425 - 1540 °C	2600 - 2800 °F
Thermal Conductivity	20 °C	50 W/m·K	34.5 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	20 °C	0.46 kJ/kg·K	0.11 BTU/lb·°F
Electrical Resistivity	20 °C	0.0000017 Ω·m	0.0000017 Ω·in

The density of CK75 steel indicates its mass per unit volume, which is important for weight-sensitive applications. The melting point signifies its thermal stability, while thermal conductivity and specific heat capacity are critical for applications involving heat treatment and thermal processing.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Atmospheric	-	-	Fair	Susceptible to rust without protective coatings
Chlorides	Low	Ambient	Poor	Risk of pitting corrosion
Acids	Dilute	Ambient	Poor	Not recommended for acidic environments
Alkalis	Dilute	Ambient	Fair	Moderate resistance, but protective measures advised

CK75 steel exhibits moderate corrosion resistance, primarily due to its carbon content. It is susceptible to rusting in humid environments and requires protective coatings for outdoor applications. Compared to stainless steels, CK75's corrosion resistance is significantly lower, making it less suitable for applications in highly corrosive environments.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	300 °C	572 °F	Above this temperature, properties may degrade
Max Intermittent Service Temp	400 °C	752 °F	Short-term exposure can be tolerated
Scaling Temperature	600 °C	1112 °F	Risk of scaling at elevated temperatures

At elevated temperatures, CK75 steel maintains its strength but may begin to lose hardness and toughness. Oxidation can occur, leading to scaling, which can compromise the material's integrity. Therefore, it is essential to consider the operating temperature when selecting CK75 for high-temperature applications.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
MIG	ER70S-6	Argon + CO2 mix	Preheat recommended
TIG	ER70S-2	Argon	Requires post-weld heat treatment
Stick	E7018	-	Not recommended for thick sections

CK75 steel presents challenges in welding due to its high carbon content, which can lead to cracking. Preheating and post-weld heat treatment are recommended to mitigate these risks. Proper filler metals should be selected to ensure compatibility and strength in the weld joint.

Machinability

Machining Parameter	CK75 Steel	Benchmark Steel (AISI 1212)	Notes/Tips
Relative Machinability Index	60	100	Moderate machinability
Typical Cutting Speed (Turning)	30 m/min	50 m/min	Use carbide tools for best results

CK75 steel has moderate machinability, which can be improved with appropriate cutting tools and speeds. The use of carbide tools is recommended to achieve better surface finishes and tool life.

Formability

CK75 steel is suitable for cold and hot forming processes. However, due to its higher carbon content, it exhibits work hardening, which can make extensive deformation challenging. Recommended bend radii should be larger to avoid cracking during forming operations.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	600 - 700 °C / 1112 - 1292 °F	1 - 2 hours	Air or furnace	Softening, improving ductility
Quenching	800 - 900 °C / 1472 - 1652 °F	30 minutes	Oil or water	Hardening, increasing strength
Tempering	150 - 300 °C / 302 - 572 °F	1 hour	Air	Reducing brittleness, improving toughness

During heat treatment, CK75 undergoes significant metallurgical transformations. Quenching increases hardness through the formation of martensite, while tempering reduces brittleness and enhances toughness, making the steel more suitable for dynamic applications.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Automotive	Leaf springs	High strength, excellent wear resistance	Required for load-bearing applications
Machinery	Cutting tools	High hardness, good machinability	Essential for precision cutting
Aerospace	Landing gear components	High strength, fatigue resistance	Critical for safety and performance

Other applications of CK75 steel include:

• Manufacturing of gears and shafts: Due to its strength and wear resistance.
• Production of knives and blades: Where hardness is crucial for cutting performance.
• Construction of heavy machinery: For components that require durability and strength.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	CK75 Steel	AISI 1075	AISI 4140	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High hardness	Similar hardness	Lower hardness	CK75 offers better wear resistance
Key Corrosion Aspect	Fair resistance	Fair resistance	Good resistance	AISI 4140 is better for corrosive environments
Weldability	Challenging	Moderate	Good	CK75 requires careful handling during welding
Machinability	Moderate	Good	Moderate	AISI 1075 is easier to machine
Formability	Moderate	Good	Moderate	AISI 1075 offers better formability
Approx. Relative Cost	Moderate	Moderate	Higher	CK75 is cost-effective for high-strength applications
Typical Availability	Common	Common	Less common	CK75 is widely available in various forms

When selecting CK75 steel, considerations such as cost-effectiveness, availability, and specific application requirements must be evaluated. While it offers excellent mechanical properties, its limitations in weldability and corrosion resistance should be carefully considered based on the intended use. Additionally, CK75's magnetic properties make it suitable for applications where magnetic interference is a concern.

In summary, CK75 steel is a versatile medium-carbon steel that excels in applications requiring high strength and wear resistance, making it a preferred choice in various industries.