E350 Steel (S355JR): Properties and Key Applications

E350 Steel, also known as S355JR, is a structural steel grade widely used in construction and engineering applications. Classified as a low-carbon mild steel, E350 is characterized by its excellent weldability, good machinability, and moderate strength. The primary alloying elements in E350 include carbon (C), manganese (Mn), and silicon (Si), which collectively contribute to its mechanical properties and overall performance.

Comprehensive Overview

E350 steel is primarily used in structural applications due to its favorable balance of strength, ductility, and toughness. With a yield strength of approximately 350 MPa, it is suitable for a variety of engineering applications, including bridges, buildings, and other structures where load-bearing capabilities are essential. The low carbon content enhances its weldability, making it a preferred choice for welded constructions.

Key Characteristics:
- Strength: E350 offers a good yield strength, making it suitable for structural applications.
- Ductility: The steel exhibits excellent elongation properties, allowing it to deform without fracturing.
- Weldability: The low carbon content facilitates easy welding, which is crucial for construction applications.

Advantages:
- High strength-to-weight ratio, allowing for lighter structures.
- Excellent weldability and machinability, reducing fabrication costs.
- Good toughness, even at low temperatures, making it suitable for various environmental conditions.

Limitations:
- Limited corrosion resistance compared to higher alloy steels, necessitating protective coatings in certain environments.
- Not suitable for high-temperature applications due to reduced mechanical properties at elevated temperatures.

E350 steel holds a significant position in the market due to its versatility and reliability, making it a staple in the construction industry.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S355JR	International	Closest equivalent to E350
ASTM	A572 Grade 50	USA	Similar mechanical properties, but different chemical composition
EN	S355J2	Europe	Minor compositional differences; better impact resistance
DIN	St 52-3	Germany	Comparable strength, but different alloying elements
JIS	SM490A	Japan	Similar properties, but with different toughness requirements

The table above highlights various standards and equivalents for E350 steel. While these grades may exhibit similar mechanical properties, subtle differences in chemical composition can affect performance in specific applications. For instance, S355J2 offers improved impact resistance, making it more suitable for low-temperature environments.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.12 - 0.20
Mn (Manganese)	1.20 - 1.60
Si (Silicon)	0.10 - 0.40
P (Phosphorus)	≤ 0.035
S (Sulfur)	≤ 0.035

The primary alloying elements in E350 steel play crucial roles in determining its properties:
- Carbon (C): Enhances strength and hardness but can reduce ductility if present in high amounts.
- Manganese (Mn): Improves hardenability and tensile strength while enhancing toughness.
- Silicon (Si): Contributes to deoxidation during steelmaking and improves strength.

Mechanical Properties

Property	Condition/Temper	Test Temperature	Typical Value/Range (Metric)	Typical Value/Range (Imperial)	Reference Standard for Test Method
Yield Strength (0.2% offset)	Normalized	Room Temp	355 MPa	51.5 ksi	ASTM E8
Tensile Strength	Normalized	Room Temp	470 - 630 MPa	68 - 91 ksi	ASTM E8
Elongation	Normalized	Room Temp	≥ 21%	≥ 21%	ASTM E8
Reduction of Area	Normalized	Room Temp	≥ 30%	≥ 30%	ASTM E8
Hardness (Brinell)	Normalized	Room Temp	≤ 200 HB	≤ 200 HB	ASTM E10
Impact Strength (Charpy)	Normalized	-20°C	≥ 27 J	≥ 20 ft-lbf	ASTM E23

The mechanical properties of E350 steel make it suitable for structural applications where high strength and good ductility are required. Its yield strength and tensile strength provide the necessary load-bearing capacity, while its elongation and reduction of area indicate good ductility, allowing for deformation without failure.

Physical Properties

Property	Condition/Temperature	Value (Metric)	Value (Imperial)
Density	Room Temp	7850 kg/m³	490 lb/ft³
Melting Point	-	1425 - 1540 °C	2600 - 2800 °F
Thermal Conductivity	Room Temp	50 W/m·K	34.5 BTU·in/h·ft²·°F
Specific Heat Capacity	Room Temp	460 J/kg·K	0.11 BTU/lb·°F
Electrical Resistivity	Room Temp	0.0000017 Ω·m	0.0000017 Ω·ft

The physical properties of E350 steel, such as density and melting point, are critical for understanding its behavior in various applications. The high density contributes to its strength, while the melting point indicates its suitability for high-temperature applications.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C)	Resistance Rating	Notes
Chlorides	Varies	Ambient	Fair	Risk of pitting corrosion
Acids	Varies	Ambient	Poor	Not recommended
Alkalis	Varies	Ambient	Good	Moderate resistance
Atmospheric	-	Ambient	Fair	Requires protective coating

E350 steel exhibits moderate corrosion resistance, particularly in atmospheric conditions. However, it is susceptible to pitting in chloride environments and should not be used in acidic conditions without protective measures. Compared to higher alloy steels, such as stainless steels, E350's corrosion resistance is limited, necessitating careful consideration in corrosive environments.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400 °C	752 °F	Suitable for structural use
Max Intermittent Service Temp	500 °C	932 °F	Limited exposure only
Scaling Temperature	600 °C	1112 °F	Risk of oxidation
Creep Strength considerations	400 °C	752 °F	Reduced performance at high temps

E350 steel maintains its mechanical properties up to approximately 400 °C, beyond which its strength and ductility may diminish. It is not recommended for continuous service above this temperature due to potential oxidation and scaling issues.

Fabrication Properties

Weldability

Welding Process	Recommended Filler Metal (AWS Classification)	Typical Shielding Gas/Flux	Notes
MIG	ER70S-6	Argon + CO2	Good for thin sections
TIG	ER70S-2	Argon	Excellent for precision work
SMAW	E7018	-	Suitable for general use

E350 steel is highly weldable, making it suitable for various welding processes. Preheating may be required for thicker sections to avoid cracking. Post-weld heat treatment can enhance the properties of the weld zone.

Machinability

Machining Parameter	E350 Steel	AISI 1212	Notes/Tips
Relative Machinability Index	70	100	Moderate machinability
Typical Cutting Speed (Turning)	30 m/min	50 m/min	Use high-speed steel tools

E350 steel has moderate machinability, making it suitable for various machining operations. Optimal cutting speeds and tooling should be selected to minimize wear and achieve desired surface finishes.

Formability

E350 steel exhibits good formability, allowing for both cold and hot forming processes. It can be bent and shaped without significant risk of cracking, making it suitable for various structural applications. However, care should be taken to avoid excessive work hardening during cold forming.

Heat Treatment

Treatment Process	Temperature Range (°C)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	600 - 700	1 - 2 hours	Air	Softening, improved ductility
Normalizing	850 - 900	1 - 2 hours	Air	Refined grain structure
Quenching	800 - 850	30 minutes	Water/Oil	Increased hardness

Heat treatment processes such as annealing and normalizing can significantly enhance the mechanical properties of E350 steel. These processes refine the microstructure, improving ductility and strength.

Typical Applications and End Uses

Industry/Sector	Specific Application Example	Key Steel Properties Utilized in this Application	Reason for Selection
Construction	Bridge construction	High yield strength, good ductility	Load-bearing capacity
Automotive	Chassis components	Excellent weldability, moderate strength	Lightweight structures
Heavy machinery	Frames and supports	Good toughness, machinability	Structural integrity

Other applications include:
- Structural beams and columns
- Industrial equipment
- Shipbuilding components

E350 steel is chosen for these applications due to its favorable mechanical properties, which provide the necessary strength and durability required in demanding environments.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	E350 Steel	S235JR Steel	S355J2 Steel	Brief Pro/Con or Trade-off Note
Key Mechanical Property	Yield Strength	Lower	Higher	E350 offers a balance of strength and ductility
Key Corrosion Aspect	Fair	Good	Better	E350 requires protective measures in corrosive environments
Weldability	Excellent	Good	Excellent	E350 is easy to weld, suitable for various processes
Machinability	Moderate	Good	Moderate	E350 requires careful machining to avoid wear
Formability	Good	Good	Excellent	E350 can be formed easily, but care is needed in cold forming
Approx. Relative Cost	Moderate	Lower	Higher	E350 is cost-effective for structural applications
Typical Availability	High	High	Moderate	E350 is widely available in the market

When selecting E350 steel, considerations such as cost-effectiveness, availability, and specific application requirements are crucial. Its balance of properties makes it a versatile choice for many engineering applications, while its limitations in corrosion resistance and high-temperature performance should be carefully evaluated based on the intended use.

In conclusion, E350 steel (S355JR) is a reliable and versatile structural steel grade that offers a combination of strength, ductility, and weldability, making it suitable for a wide range of applications in construction and engineering.