AISI 1320 Steel: Properties and Key Applications

AISI 1320 steel is classified as a medium-carbon alloy steel, primarily known for its balance of strength, toughness, and ductility. This steel grade contains a significant amount of carbon, along with alloying elements such as manganese, chromium, and nickel, which enhance its mechanical properties and overall performance in various applications.

Comprehensive Overview

AISI 1320 steel is characterized by its medium carbon content, typically ranging from 0.18% to 0.23%. The primary alloying elements include manganese (0.60% to 0.90%), chromium (0.40% to 0.60%), and nickel (0.30% to 0.60%). These elements contribute to the steel's hardenability, strength, and resistance to wear and fatigue, making it suitable for a wide range of engineering applications.

The most significant characteristics of AISI 1320 steel include:

• High Strength: The medium carbon content allows for good tensile strength, making it suitable for structural applications.
• Good Toughness: The alloying elements improve the toughness, which is essential for components subjected to dynamic loads.
• Ductility: AISI 1320 exhibits good ductility, allowing for deformation without fracture, which is critical in manufacturing processes.

Advantages:
- Excellent balance of strength and ductility.
- Good machinability and weldability.
- Suitable for heat treatment processes to enhance mechanical properties.

Limitations:
- Moderate corrosion resistance compared to stainless steels.
- Requires careful heat treatment to avoid brittleness.

Historically, AISI 1320 has been used in various applications, including automotive components, machinery parts, and structural elements, due to its favorable mechanical properties and versatility.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	G13200	USA	Closest equivalent to AISI 1320
AISI/SAE	1320	USA	Commonly used designation
ASTM	A29/A29M	USA	General specification for alloy steels
EN	1.7035	Europe	Minor compositional differences
JIS	S45C	Japan	Similar properties, but different applications
DIN	C45E	Germany	Comparable, but with different alloying elements

The AISI 1320 grade is often compared to other medium-carbon steels, such as AISI 1045 and AISI 4140. While AISI 1045 offers higher carbon content for increased strength, AISI 4140 provides enhanced hardenability due to its chromium content. These differences can significantly affect the selection of steel for specific applications.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.18 - 0.23
Mn (Manganese)	0.60 - 0.90
Cr (Chromium)	0.40 - 0.60
Ni (Nickel)	0.30 - 0.60
Si (Silicon)	0.15 - 0.40
P (Phosphorus)	≤ 0.035
S (Sulfur)	≤ 0.040

The key alloying elements in AISI 1320 play crucial roles:
- Manganese: Enhances hardenability and strength while improving the steel's toughness.
- Chromium: Increases corrosion resistance and hardenability, contributing to wear resistance.
- Nickel: Improves toughness and ductility, particularly in low-temperature applications.

Mechanical Properties

Property	Condition/Temper	Test Temperature	Typical Value/Range (Metric)	Typical Value/Range (Imperial)	Reference Standard for Test Method
Tensile Strength	Annealed	Room Temp	580 - 700 MPa	84 - 102 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	Room Temp	350 - 450 MPa	51 - 65 ksi	ASTM E8
Elongation	Annealed	Room Temp	20 - 25%	20 - 25%	ASTM E8
Hardness (Brinell)	Annealed	Room Temp	160 - 210 HB	160 - 210 HB	ASTM E10
Impact Strength (Charpy)	Annealed	-20°C (-4°F)	30 - 50 J	22 - 37 ft-lbf	ASTM E23

The combination of these mechanical properties makes AISI 1320 steel suitable for applications requiring high strength and toughness, such as gears, shafts, and structural components. Its ability to withstand dynamic loads while maintaining ductility is critical in many engineering applications.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	Room Temp	7.85 g/cm³	0.284 lb/in³
Melting Point	-	1425 - 1540 °C	2600 - 2800 °F
Thermal Conductivity	Room Temp	45 W/m·K	31 BTU·in/(hr·ft²·°F)
Specific Heat Capacity	Room Temp	460 J/kg·K	0.11 BTU/lb·°F
Electrical Resistivity	Room Temp	0.00065 Ω·m	0.00038 Ω·in

The density and melting point of AISI 1320 indicate its suitability for high-temperature applications, while its thermal conductivity and specific heat capacity are important for applications involving heat transfer. The electrical resistivity is relatively low, making it suitable for applications where electrical conductivity is required.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-5	25°C (77°F)	Fair	Risk of pitting
Sulfuric Acid	10	25°C (77°F)	Poor	Not recommended
Sodium Hydroxide	50	25°C (77°F)	Fair	Risk of stress corrosion cracking

AISI 1320 steel exhibits moderate corrosion resistance, particularly in environments with chlorides and alkaline solutions. It is susceptible to pitting and stress corrosion cracking in chloride-rich environments, which can limit its use in marine applications. Compared to stainless steels like AISI 304 or AISI 316, AISI 1320's corrosion resistance is significantly lower, making it less suitable for applications where corrosion is a critical concern.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400°C	752°F	Suitable for prolonged exposure
Max Intermittent Service Temp	500°C	932°F	Short-term exposure only
Scaling Temperature	600°C	1112°F	Risk of oxidation beyond this temp
Creep Strength considerations begin	300°C	572°F	Creep may occur at elevated temps

AISI 1320 maintains its mechanical properties at elevated temperatures, making it suitable for applications involving heat exposure. However, care must be taken to avoid prolonged exposure to temperatures above 400°C, as this can lead to oxidation and scaling, affecting the material's integrity.

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	ER80S-Ni	Argon	Requires preheat
Stick	E7018	N/A	Suitable for field welding

AISI 1320 exhibits good weldability, particularly with the appropriate filler metals. Preheating is recommended to minimize the risk of cracking during welding. Post-weld heat treatment can further enhance the properties of the weldment.

Machinability

Machining Parameter	AISI 1320	AISI 1212	Notes/Tips
Relative Machinability Index	70%	100%	AISI 1212 is easier to machine
Typical Cutting Speed (Turning)	30-40 m/min	50-60 m/min	Adjust for tool wear

AISI 1320 has moderate machinability, making it suitable for various machining operations. However, compared to free-machining steels like AISI 1212, it requires more careful handling and tooling to achieve optimal results.

Formability

AISI 1320 can be cold and hot formed, with good ductility allowing for various forming processes. However, care must be taken to avoid excessive work hardening, which can lead to cracking. The minimum bend radius should be considered during forming operations to ensure integrity.

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	Reduce hardness, improve ductility
Quenching	800 - 850 °C / 1472 - 1562 °F	30 minutes	Oil	Increase hardness
Tempering	400 - 600 °C / 752 - 1112 °F	1 hour	Air	Reduce brittleness, improve toughness

Heat treatment processes significantly influence the microstructure and properties of AISI 1320. Annealing softens the steel, while quenching increases hardness. Tempering is essential to relieve stresses and enhance toughness, making it suitable for high-stress applications.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection
Automotive	Gears	High strength, toughness	Ability to withstand dynamic loads
Machinery	Shafts	Ductility, machinability	Ease of fabrication and strength
Construction	Structural components	Strength, weldability	Suitable for load-bearing applications

Other applications include:
- - Aerospace components
- - Tooling and dies
- - Fasteners and fittings

AISI 1320 is chosen for these applications due to its excellent balance of strength, toughness, and machinability, making it a versatile option for various engineering needs.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	AISI 1320	AISI 4140	AISI 1045	Brief Pro/Con or Trade-off Note
Key Mechanical Property	Moderate strength	High strength	Moderate strength	AISI 4140 offers higher hardenability
Key Corrosion Aspect	Fair	Good	Fair	AISI 4140 has better corrosion resistance
Weldability	Good	Fair	Good	AISI 4140 may require preheat
Machinability	Moderate	Moderate	High	AISI 1045 is easier to machine
Formability	Good	Fair	Good	AISI 4140 is less ductile
Approx. Relative Cost	Moderate	Higher	Lower	Cost varies based on alloying elements
Typical Availability	Common	Common	Very Common	AISI 1045 is widely available

When selecting AISI 1320, considerations include its mechanical properties, weldability, and cost-effectiveness. While it offers a good balance of strength and ductility, it may not be the best choice for highly corrosive environments or applications requiring extreme hardenability. Its availability in the market is generally good, making it a practical choice for many engineering applications.

In summary, AISI 1320 steel is a versatile medium-carbon alloy steel that provides a balance of strength, toughness, and machinability, making it suitable for a wide range of applications in various industries.