4142 Steel: Properties and Key Applications Overview

4142 steel is classified as a medium-carbon alloy steel, primarily known for its excellent strength and toughness. It is part of the AISI/SAE 4000 series and is often used in applications requiring high fatigue strength and wear resistance. The primary alloying elements in 4142 steel include chromium (Cr) and molybdenum (Mo), which enhance its hardenability and overall mechanical properties.

Comprehensive Overview

4142 steel is characterized by its medium carbon content, typically ranging from 0.38% to 0.43%, along with chromium (0.9% to 1.2%) and molybdenum (0.15% to 0.25%). These alloying elements contribute significantly to the steel's hardness, strength, and wear resistance, making it suitable for various demanding applications.

The key characteristics of 4142 steel include:

• High Strength: The alloying elements provide enhanced tensile and yield strength.
• Good Toughness: It maintains toughness even at elevated hardness levels.
• Wear Resistance: The steel exhibits excellent resistance to wear, making it ideal for components subjected to friction and abrasion.

Advantages:
- Versatile Applications: Commonly used in the manufacturing of gears, shafts, and other components in automotive and aerospace industries.
- Heat Treatable: Can be heat treated to achieve desired mechanical properties, enhancing its usability in various applications.

Limitations:
- Weldability: The presence of alloying elements can make welding more challenging, requiring specific techniques and filler materials.
- Cost: Generally more expensive than low-carbon steels due to alloying elements.

Historically, 4142 steel has been significant in the development of high-performance components, particularly in the automotive sector, where strength and durability are paramount.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	G41420	USA	Closest equivalent to AISI 4140 with minor differences
AISI/SAE	4142	USA	Commonly used designation
ASTM	A829	USA	Standard specification for alloy steel
EN	42CrMo4	Europe	Equivalent with slight compositional differences
DIN	1.7225	Germany	Similar properties, often used in Europe
JIS	SCM440	Japan	Comparable grade with similar applications

The differences between equivalent grades can affect selection based on specific mechanical properties or heat treatment responses. For instance, while 4142 and 4140 are similar, 4142 typically has a higher chromium content, which can enhance hardenability.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.38 - 0.43
Cr (Chromium)	0.9 - 1.2
Mo (Molybdenum)	0.15 - 0.25
Mn (Manganese)	0.75 - 1.0
Si (Silicon)	0.15 - 0.40
P (Phosphorus)	≤ 0.035
S (Sulfur)	≤ 0.040

The primary role of chromium in 4142 steel is to enhance hardenability and corrosion resistance, while molybdenum contributes to strength and toughness at elevated temperatures. Manganese aids in deoxidation and improves hardenability, while silicon enhances strength and elasticity.

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	850 - 1000 MPa	123 - 145 ksi	ASTM E8
Yield Strength (0.2% offset)	Quenched & Tempered	700 - 850 MPa	102 - 123 ksi	ASTM E8
Elongation	Quenched & Tempered	12 - 18%	12 - 18%	ASTM E8
Hardness (Rockwell C)	Quenched & Tempered	28 - 34 HRC	28 - 34 HRC	ASTM E18
Impact Strength (Charpy)	-40°C	30 - 50 J	22 - 37 ft-lbf	ASTM E23

The combination of high tensile and yield strength, along with good toughness, makes 4142 steel suitable for applications requiring high mechanical loading and structural integrity, such as in automotive and aerospace components.

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	25 °C	45 W/m·K	31 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	25 °C	0.46 kJ/kg·K	0.11 BTU/lb·°F
Electrical Resistivity	20 °C	0.00065 Ω·m	0.00038 Ω·in
Coefficient of Thermal Expansion	20 - 100 °C	11.5 x 10⁻⁶ /K	6.4 x 10⁻⁶ /°F

The density and melting point of 4142 steel indicate its suitability for high-temperature applications, while its thermal conductivity and specific heat capacity are essential for understanding its behavior in thermal environments.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3%	25 °C / 77 °F	Fair	Risk of pitting corrosion
Sulfuric Acid	10%	25 °C / 77 °F	Poor	Not recommended
Sodium Hydroxide	50%	25 °C / 77 °F	Fair	Risk of stress corrosion cracking

4142 steel exhibits moderate corrosion resistance, particularly in atmospheric conditions and certain alkaline environments. However, it is susceptible to pitting in chloride-rich environments and should be avoided in acidic conditions. Compared to stainless steels like 304 or 316, 4142's corrosion resistance is significantly lower, making it less suitable for marine or highly corrosive applications.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400 °C	752 °F	Suitable for high-temperature applications
Max Intermittent Service Temp	500 °C	932 °F	Short-term exposure only
Scaling Temperature	600 °C	1112 °F	Risk of oxidation at high temps
Creep Strength considerations	500 °C	932 °F	Begins to degrade significantly

4142 steel maintains its mechanical properties at elevated temperatures, making it suitable for applications involving heat. However, oxidation and scaling can occur at high temperatures, necessitating protective coatings or careful material selection in high-temperature environments.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
MIG	ER70S-6	Argon + CO2 mix	Preheat recommended
TIG	ER80S-D2	Argon	Requires post-weld heat treatment
Stick	E7018	-	Preheat and post-weld treatment recommended

4142 steel can be welded but requires careful consideration of preheating and post-weld heat treatment to minimize the risk of cracking. The choice of filler metal is crucial for maintaining the integrity of the weld.

Machinability

Machining Parameter	4142 Steel	AISI 1212	Notes/Tips
Relative Machinability Index	60%	100%	4142 is more challenging to machine
Typical Cutting Speed (Turning)	30-50 m/min	60-80 m/min	Use carbide tools for best results

4142 steel presents moderate machinability, often requiring slower cutting speeds and specialized tooling compared to more machinable steels like AISI 1212.

Formability

4142 steel is not particularly known for its formability due to its medium carbon content. Cold forming is possible but may lead to work hardening, necessitating careful control of bend radii and forming processes. Hot forming is more feasible but requires precise temperature control to avoid adverse effects on mechanical properties.

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	Softening, improving ductility
Quenching	800 - 850 °C / 1472 - 1562 °F	30 minutes	Oil or Water	Hardening
Tempering	400 - 600 °C / 752 - 1112 °F	1 hour	Air	Reducing brittleness, improving toughness

The heat treatment processes significantly affect the microstructure of 4142 steel, transforming it from austenite to martensite during quenching, followed by tempering to achieve a balance of hardness and toughness.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Automotive	Gears	High strength, wear resistance	Essential for durability
Aerospace	Shafts	Toughness, fatigue resistance	Critical for safety
Machinery	Crankshafts	High tensile strength	Required for high loads
Oil & Gas	Drill bits	Wear resistance, toughness	Operates in harsh conditions

Other applications include:

• Tooling: Used in the manufacture of dies and molds due to its hardness.
• Construction: Structural components in heavy machinery.

4142 steel is chosen for these applications due to its excellent mechanical properties, which ensure reliability and performance under stress.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	4142 Steel	AISI 4140	AISI 4340	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High strength	Moderate strength	Very high strength	4142 offers a balance of strength and toughness
Key Corrosion Aspect	Moderate	Moderate	Poor	4142 is better than 4340 in corrosive environments
Weldability	Moderate	Moderate	Poor	4142 is easier to weld than 4340
Machinability	Moderate	Moderate	Poor	4142 is more machinable than 4340
Approx. Relative Cost	Moderate	Moderate	High	4142 is cost-effective for high-performance applications
Typical Availability	High	High	Moderate	4142 is widely available in various forms

When selecting 4142 steel, considerations include its cost-effectiveness, availability, and suitability for specific applications. Its balance of strength, toughness, and moderate weldability makes it a preferred choice in various industries. However, for applications requiring superior corrosion resistance or machinability, alternative grades may be more appropriate.

In summary, 4142 steel is a versatile alloy that offers a unique combination of properties, making it suitable for a wide range of demanding applications. Its historical significance and continued relevance in modern engineering underscore its value in material selection.