A108 Steel: Properties and Key Applications Overview

A108 steel is a low-carbon steel grade primarily classified as a medium-carbon alloy steel. It is known for its excellent machinability and is often used in applications requiring good mechanical properties and wear resistance. The primary alloying elements in A108 steel include carbon (C), manganese (Mn), and small amounts of phosphorus (P) and sulfur (S). The carbon content typically ranges from 0.15% to 0.30%, which contributes to its strength and hardness while maintaining good ductility.

Comprehensive Overview

A108 steel is widely recognized for its versatility and is commonly used in the manufacturing of precision machined parts. Its low carbon content allows for good weldability and formability, making it suitable for various engineering applications. The presence of manganese enhances its hardenability and strength, while phosphorus and sulfur can improve machinability but may also affect ductility.

Advantages of A108 Steel:
- Excellent Machinability: A108 is favored for its ease of machining, allowing for high-speed operations and reduced tool wear.
- Good Mechanical Properties: It offers a balance of strength and ductility, making it suitable for a range of applications.
- Cost-Effectiveness: Generally, A108 steel is more affordable compared to higher alloy steels, making it a popular choice in many industries.

Limitations of A108 Steel:
- Corrosion Resistance: A108 steel has limited resistance to corrosion and may require protective coatings in harsh environments.
- Lower Hardness Compared to Alloy Steels: While it has good strength, it may not perform as well as higher alloy steels in applications requiring extreme hardness.

Historically, A108 has been significant in the development of precision machining and manufacturing processes, contributing to advancements in various sectors, including automotive and aerospace.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	A108	USA	Closest equivalent to AISI 1018
AISI/SAE	1018	USA	Minor compositional differences to be aware of
ASTM	A108	USA	Standard specification for cold-finished carbon steel bars
EN	C45	Europe	Similar properties but different applications
JIS	S45C	Japan	Comparable in terms of mechanical properties

The table above highlights several standards and equivalents for A108 steel. Notably, while AISI 1018 is often considered an equivalent, it may have slight variations in carbon content and mechanical properties that could influence performance in specific applications.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.15 - 0.30
Mn (Manganese)	0.60 - 0.90
P (Phosphorus)	≤ 0.04
S (Sulfur)	≤ 0.05

The primary role of the key alloying elements in A108 steel is as follows:
- Carbon (C): Enhances strength and hardness while maintaining ductility.
- Manganese (Mn): Improves hardenability and tensile strength.
- Phosphorus (P) and Sulfur (S): While they can enhance machinability, excessive amounts may reduce ductility.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric - SI Units)	Typical Value/Range (Imperial Units)	Reference Standard for Test Method
Tensile Strength	Annealed	370 - 480 MPa	54 - 70 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	210 - 310 MPa	30 - 45 ksi	ASTM E8
Elongation	Annealed	15 - 25%	15 - 25%	ASTM E8
Hardness (Brinell)	Annealed	120 - 180 HB	120 - 180 HB	ASTM E10
Impact Strength	Charpy V-notch, -20°C	20 - 30 J	15 - 22 ft-lbf	ASTM E23

The mechanical properties of A108 steel make it suitable for applications that require good strength and ductility, such as shafts, gears, and various machine components. Its tensile strength and yield strength provide adequate performance under mechanical loading, while its elongation indicates good ductility, allowing for deformation without fracture.

Physical Properties

Property	Condition/Temperature	Value (Metric - SI Units)	Value (Imperial Units)
Density	Room Temperature	7.85 g/cm³	0.284 lb/in³
Melting Point	-	1425 - 1540 °C	2600 - 2800 °F
Thermal Conductivity	Room Temperature	50 W/m·K	34.5 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	Room Temperature	0.49 kJ/kg·K	0.12 BTU/lb·°F
Electrical Resistivity	Room Temperature	0.0000017 Ω·m	0.0000017 Ω·in

Key physical properties such as density and melting point are critical for applications involving high-temperature environments. The thermal conductivity of A108 steel is moderate, making it suitable for applications where heat dissipation is necessary, while its specific heat capacity indicates how much energy is required to raise its temperature.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	Varies	Ambient	Fair	Risk of pitting corrosion
Sulfuric Acid	Low	Ambient	Poor	Not recommended
Sodium Hydroxide	Low	Ambient	Fair	Risk of stress corrosion

A108 steel exhibits limited corrosion resistance, particularly in environments containing chlorides and acids. It is susceptible to pitting and stress corrosion cracking, especially in humid or saline conditions. Compared to stainless steels like AISI 304, which offer excellent corrosion resistance, A108 is less suitable for applications exposed to harsh environments.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400 °C	752 °F	Suitable for moderate temperatures
Max Intermittent Service Temp	500 °C	932 °F	Short-term exposure only
Scaling Temperature	600 °C	1112 °F	Risk of oxidation beyond this temp

A108 steel maintains its mechanical properties up to moderate temperatures but begins to lose strength and ductility at elevated temperatures. Oxidation can occur at temperatures above 600 °C, necessitating protective measures in high-temperature applications.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
MIG	ER70S-6	Argon + CO2 mix	Good for thin sections
TIG	ER70S-2	Argon	Requires preheat for thick sections

A108 steel is generally considered weldable, but preheating may be necessary for thicker sections to avoid cracking. Post-weld heat treatment can improve the properties of the weld zone.

Machinability

Machining Parameter	[A108 Steel]	[AISI 1212]	Notes/Tips
Relative Machinability Index	70	100	A108 is less machinable than 1212
Typical Cutting Speed	30 m/min	45 m/min	Adjust for tool wear

A108 steel offers good machinability, although it is not as favorable as some free-machining steels like AISI 1212. Optimal cutting speeds and tooling should be employed to minimize wear.

Formability

A108 steel exhibits good formability, allowing for cold and hot forming processes. It can be bent and shaped without significant risk of cracking, making it suitable for various fabrication techniques.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	700 - 800 °C / 1292 - 1472 °F	1 - 2 hours	Air or water	Softening, improved ductility
Quenching	800 - 900 °C / 1472 - 1652 °F	30 min - 1 hour	Oil or water	Hardening
Tempering	400 - 600 °C / 752 - 1112 °F	1 hour	Air	Reducing brittleness

Heat treatment processes such as annealing, quenching, and tempering can significantly alter the microstructure of A108 steel, enhancing its mechanical properties. Annealing softens the steel, while quenching increases hardness, and tempering reduces brittleness.

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, good machinability	Precision and durability
Aerospace	Structural components	Lightweight, good strength-to-weight ratio	Performance under stress
Machinery	Shafts	High tensile strength, ductility	Resistance to fatigue

Other applications include:
* - Fasteners
* - Brackets
* - Machine parts

A108 steel is chosen for applications requiring a combination of strength, machinability, and cost-effectiveness. Its properties make it ideal for components that undergo significant mechanical stress.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	[A108 Steel]	[AISI 1018]	[AISI 4140]	Brief Pro/Con or Trade-off Note
Key Mechanical Property	Moderate	Moderate	High	A108 is less strong than 4140
Key Corrosion Aspect	Fair	Fair	Good	A108 is less resistant than 4140
Weldability	Good	Excellent	Fair	A108 is easier to weld
Machinability	Good	Excellent	Fair	A108 is less machinable than 1018
Formability	Good	Good	Fair	A108 is versatile in forming
Approx. Relative Cost	Low	Low	Moderate	A108 is cost-effective
Typical Availability	High	High	Moderate	A108 is widely available

When selecting A108 steel, considerations such as cost-effectiveness, availability, and specific mechanical requirements are crucial. While it offers good performance for many applications, alternatives like AISI 4140 may be preferred for high-strength applications, while AISI 1018 may be chosen for superior machinability.

In conclusion, A108 steel is a versatile and cost-effective material suitable for a wide range of applications. Its balance of properties makes it an excellent choice for precision machined components, although considerations regarding corrosion resistance and specific mechanical requirements should guide material selection.