A373 Steel Properties and Key Applications Overview

A373 steel, classified as an obsolete structural steel grade, was primarily utilized in the construction of buildings and bridges. It falls under the category of low-carbon mild steel, characterized by its relatively low alloy content and excellent weldability. The primary alloying elements in A373 steel include carbon (C), manganese (Mn), and small amounts of phosphorus (P) and sulfur (S). These elements contribute to the steel's fundamental properties, such as strength, ductility, and toughness.

Comprehensive Overview

A373 steel is known for its good mechanical properties, which include moderate tensile strength and yield strength, making it suitable for various structural applications. The inherent characteristics of A373 steel include:

• Weldability: A373 exhibits excellent weldability, allowing for easy fabrication and assembly in structural applications.
• Ductility: The low carbon content provides good ductility, enabling the material to deform under stress without fracturing.
• Toughness: A373 steel maintains toughness at lower temperatures, which is critical for applications in colder climates.

Advantages:
- Cost-Effectiveness: A373 steel is generally less expensive than higher alloy steels, making it a budget-friendly option for construction projects.
- Ease of Fabrication: Its excellent weldability and machinability facilitate straightforward fabrication processes.

Limitations:
- Corrosion Resistance: A373 steel has limited corrosion resistance compared to higher alloy steels, necessitating protective coatings in corrosive environments.
- Obsolescence: As an obsolete grade, A373 may not meet modern engineering standards or specifications, limiting its availability and application in new projects.

Historically, A373 was widely used in the mid-20th century for structural applications. However, with advancements in steel technology and the introduction of new grades, its use has declined significantly.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	K02401	USA	Closest equivalent to A36
ASTM	A373	USA	Obsolete; replaced by A992
AISI/SAE	-	-	-
EN	S235JR	Europe	Similar properties, more widely used
DIN	St37-2	Germany	Comparable to A373 with minor differences

The table above highlights some of the standards and equivalents associated with A373 steel. Notably, while S235JR and St37-2 are often considered equivalent, they may exhibit different mechanical properties and chemical compositions that could affect performance in specific applications.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.10 - 0.20
Mn (Manganese)	0.60 - 0.90
P (Phosphorus)	≤ 0.04
S (Sulfur)	≤ 0.05

The primary alloying elements in A373 steel play crucial roles in determining its properties. Carbon enhances strength and hardness, while manganese improves hardenability and toughness. Phosphorus and sulfur, although present in small amounts, can negatively impact ductility and toughness if not controlled.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric - SI Units)	Typical Value/Range (Imperial Units)	Reference Standard for Test Method
Tensile Strength	Annealed	310 - 450 MPa	45 - 65 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	205 - 275 MPa	30 - 40 ksi	ASTM E8
Elongation	Annealed	20 - 25%	20 - 25%	ASTM E8
Hardness (Brinell)	Annealed	120 - 160 HB	120 - 160 HB	ASTM E10
Impact Strength	Charpy V-notch, -20°C	27 J	20 ft-lbf	ASTM E23

The mechanical properties of A373 steel make it suitable for structural applications where moderate strength and ductility are required. Its combination of tensile and yield strength allows it to withstand various mechanical loads, while its elongation percentage indicates good ductility, essential for structural integrity.

Physical Properties

Property	Condition/Temperature	Value (Metric - SI Units)	Value (Imperial Units)
Density	Room Temperature	7850 kg/m³	490 lb/ft³
Melting Point/Range	-	1425 - 1540 °C	2600 - 2800 °F
Thermal Conductivity	Room Temperature	50 W/m·K	34.5 BTU·in/h·ft²·°F
Specific Heat Capacity	Room Temperature	460 J/kg·K	0.11 BTU/lb·°F

The physical properties of A373 steel, such as its density and melting point, are critical for applications involving high-temperature environments. The thermal conductivity indicates how well the material can dissipate heat, which is essential in structural applications exposed to varying temperatures.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Atmospheric	-	-	Fair	Susceptible to rust
Chlorides	Low	20 - 60 °C	Poor	Risk of pitting
Acids	Moderate	20 - 40 °C	Not Recommended	High susceptibility

A373 steel exhibits fair resistance to atmospheric corrosion but is susceptible to rusting in humid environments. Its performance in chloride-rich environments is poor, leading to pitting corrosion. Compared to stainless steels or higher alloy grades, A373's corrosion resistance is limited, necessitating protective coatings or treatments in corrosive applications.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400 °C	752 °F	Beyond this, strength may degrade
Max Intermittent Service Temp	500 °C	932 °F	Short-term exposure only
Scaling Temperature	600 °C	1112 °F	Risk of oxidation at this temperature

A373 steel can withstand moderate temperatures, but prolonged exposure to high temperatures can lead to a decrease in mechanical properties. Its oxidation resistance is limited, making it unsuitable for high-temperature applications without protective measures.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
SMAW	E60XX	Argon/CO2	Preheat recommended
GMAW	ER70S-6	Argon/CO2	Good fusion characteristics

A373 steel is highly weldable, making it suitable for various welding processes. Preheating is recommended to minimize the risk of cracking during welding. The choice of filler metal can significantly affect the quality of the weld, and using a compatible filler is crucial for maintaining the integrity of the weldment.

Machinability

Machining Parameter	[A373 Steel]	AISI 1212	Notes/Tips
Relative Machinability Index	70	100	A373 is less machinable than 1212
Typical Cutting Speed (Turning)	30 m/min	50 m/min	Use sharp tools for better finish

A373 steel has moderate machinability, which can be improved with proper tooling and cutting conditions. It is essential to use sharp tools and appropriate cutting speeds to achieve optimal results.

Formability

A373 steel exhibits good formability, allowing for cold and hot forming processes. Its low carbon content contributes to its ability to be shaped without cracking. However, care must be taken to avoid excessive work hardening during cold forming, which can lead to increased brittleness.

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	Improve ductility and reduce hardness
Normalizing	850 - 900 °C / 1562 - 1652 °F	1 - 2 hours	Air	Refine grain structure

Heat treatment processes such as annealing and normalizing can significantly alter the microstructure of A373 steel, enhancing its ductility and toughness. These processes help relieve internal stresses and improve the overall performance of the material in structural applications.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection (Brief)
Construction	Building Frames	Good weldability, moderate strength	Cost-effective and easy to fabricate
Infrastructure	Bridges	Ductility, toughness	Suitable for dynamic loads
Manufacturing	Machinery Components	Machinability, formability	Easy to machine and shape

A373 steel is commonly used in construction and infrastructure projects due to its cost-effectiveness and ease of fabrication. Its moderate strength and good ductility make it suitable for applications where structural integrity is essential.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	A373 Steel	A36 Steel	S235JR Steel	Brief Pro/Con or Trade-off Note
Key Mechanical Property	Moderate	Moderate	Moderate	Similar properties across grades
Key Corrosion Aspect	Fair	Fair	Good	S235JR offers better corrosion resistance
Weldability	Excellent	Excellent	Good	All grades are weldable, but A373 is superior
Machinability	Moderate	Good	Good	A36 and S235JR may be easier to machine
Formability	Good	Good	Good	All grades exhibit good formability
Approx. Relative Cost	Low	Low	Low	Cost is comparable across grades
Typical Availability	Limited	Widely available	Widely available	A373 is less common due to obsolescence

When selecting A373 steel for a project, it is essential to consider its mechanical properties, corrosion resistance, and availability. While it offers good weldability and formability, its limited corrosion resistance may necessitate protective measures in certain environments. Additionally, the obsolescence of A373 steel may limit its availability compared to more modern alternatives like A36 or S235JR, which are widely used in contemporary engineering applications.

In conclusion, while A373 steel has historical significance and certain advantages, its limitations in corrosion resistance and availability may lead engineers to consider more modern alternatives for new projects.