S350 Steel: Properties and Key Applications Overview

S350 Steel is a structural grade steel that falls under the category of medium-carbon alloy steels. It is primarily characterized by its balanced composition of carbon, manganese, and other alloying elements, which contribute to its mechanical properties and versatility in engineering applications. The primary alloying elements in S350 steel include carbon (C), manganese (Mn), and silicon (Si), with typical compositions that enhance its strength, ductility, and weldability.

Comprehensive Overview

S350 steel is classified as a medium-carbon structural steel, typically containing around 0.25% to 0.35% carbon. This composition provides a good balance between strength and ductility, making it suitable for various structural applications. The presence of manganese enhances hardenability and improves toughness, while silicon contributes to deoxidation during steelmaking and can improve strength at elevated temperatures.

The significant characteristics of S350 steel include:

• High Strength: Offers excellent tensile and yield strength, making it suitable for load-bearing applications.
• Good Ductility: Allows for deformation without fracture, which is critical in structural applications.
• Weldability: Can be welded using standard techniques, making it versatile for construction and fabrication.
• Machinability: Generally good, although it may require specific tooling and conditions for optimal results.

Advantages (Pros):
- Excellent mechanical properties for structural integrity.
- Versatile for various applications, including construction and manufacturing.
- Cost-effective compared to higher alloy steels.

Limitations (Cons):
- Moderate corrosion resistance, requiring protective coatings in harsh environments.
- Not suitable for extremely high-temperature applications without proper treatment.

S350 steel holds a significant position in the market due to its balance of properties and cost-effectiveness, making it a popular choice in construction, automotive, and manufacturing sectors.

Alternative Names, Standards, and Equivalents

Standard Organization	Designation/Grade	Country/Region of Origin	Notes/Remarks
UNS	S35000	USA	Closest equivalent to EN 10025 S355
ASTM	A572 Grade 50	USA	Similar properties, often used interchangeably
EN	S355	Europe	Minor compositional differences; widely used in Europe
DIN	St52-3	Germany	Comparable in strength but may differ in toughness
JIS	SM490	Japan	Similar applications but with different standards

The table above highlights various standards and equivalents for S350 steel. While these grades may be considered equivalent in many applications, subtle differences in composition and mechanical properties can affect performance. For instance, S355 steel may offer slightly higher yield strength, while St52-3 may have better toughness at low temperatures.

Key Properties

Chemical Composition

Element (Symbol and Name)	Percentage Range (%)
C (Carbon)	0.25 - 0.35
Mn (Manganese)	1.0 - 1.5
Si (Silicon)	0.15 - 0.40
P (Phosphorus)	≤ 0.035
S (Sulfur)	≤ 0.035

The primary alloying elements in S350 steel play crucial roles:
- Carbon (C): Increases hardness and strength but can reduce ductility if too high.
- Manganese (Mn): Enhances hardenability and toughness, critical for structural applications.
- Silicon (Si): Improves strength and acts as a deoxidizer during steel production.

Mechanical Properties

Property	Condition/Temper	Typical Value/Range (Metric - SI Units)	Typical Value/Range (Imperial Units)	Reference Standard for Test Method
Tensile Strength	Annealed	470 - 570 MPa	68 - 83 ksi	ASTM E8
Yield Strength (0.2% offset)	Annealed	350 - 450 MPa	51 - 65 ksi	ASTM E8
Elongation	Annealed	20 - 25%	20 - 25%	ASTM E8
Hardness (Brinell)	Annealed	150 - 200 HB	150 - 200 HB	ASTM E10
Impact Strength	Charpy V-notch @ 20°C	27 - 40 J	20 - 30 ft-lbf	ASTM E23

The mechanical properties of S350 steel make it suitable for applications requiring high strength and good ductility. Its yield strength allows it to withstand significant loads, while its elongation indicates a capacity for deformation, which is essential in structural applications.

Physical Properties

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

Key physical properties such as density and thermal conductivity are significant for applications where weight and heat transfer are critical. The density of S350 steel makes it suitable for structural components, while its thermal conductivity allows for effective heat dissipation in certain applications.

Corrosion Resistance

Corrosive Agent	Concentration (%)	Temperature (°C/°F)	Resistance Rating	Notes
Chlorides	3-5	20-60 / 68-140	Fair	Risk of pitting corrosion
Sulfuric Acid	10-20	20-40 / 68-104	Poor	Not recommended
Atmospheric	-	Variable	Good	Requires protective coating

S350 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 stainless steels, S350's corrosion resistance is limited, making it less suitable for marine or highly corrosive environments.

Heat Resistance

Property/Limit	Temperature (°C)	Temperature (°F)	Remarks
Max Continuous Service Temp	400 °C	752 °F	Suitable for structural applications
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	400 °C	752 °F	Begins to degrade at elevated temps

S350 steel performs well at elevated temperatures, making it suitable for structural applications where heat exposure is expected. However, care must be taken to avoid prolonged exposure to temperatures above 400 °C, as this can lead to loss of mechanical properties and oxidation.

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	Preferred for clean welds
Stick	E7018	-	Requires preheat for thick sections

S350 steel is generally considered weldable using standard processes such as MIG and TIG. Preheating may be necessary for thicker sections to prevent cracking. Post-weld heat treatment can enhance the properties of the weld area.

Machinability

Machining Parameter	S350 Steel	AISI 1212	Notes/Tips
Relative Machinability Index	60	100	Moderate machinability
Typical Cutting Speed	30-50 m/min	60-80 m/min	Adjust tooling accordingly

S350 steel has moderate machinability, which can be optimized with appropriate cutting speeds and tooling. It may require specific tools to achieve desired surface finishes.

Formability

S350 steel exhibits good formability, allowing for both cold and hot forming processes. It can be bent and shaped without significant risk of cracking, although care should be taken to avoid excessive work hardening.

Heat Treatment

Treatment Process	Temperature Range (°C/°F)	Typical Soaking Time	Cooling Method	Primary Purpose / Expected Result
Annealing	600 - 700 / 1112 - 1292	1-2 hours	Air	Improve ductility and reduce hardness
Quenching	850 - 900 / 1562 - 1652	30 minutes	Water/Oil	Increase hardness and strength
Tempering	400 - 600 / 752 - 1112	1 hour	Air	Reduce brittleness and improve toughness

Heat treatment processes such as annealing, quenching, and tempering significantly alter the microstructure of S350 steel, enhancing its mechanical properties. During quenching, the steel transforms to martensite, which is then tempered 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)
Construction	Beams and Columns	High Strength, Ductility	Load-bearing structures
Automotive	Chassis Components	Toughness, Weldability	Structural integrity
Manufacturing	Machinery Frames	Machinability, Strength	Durability and performance

Other applications include:
- Bridges and infrastructure
- Heavy equipment manufacturing
- Structural components in buildings

S350 steel is chosen for these applications due to its excellent mechanical properties, which provide the necessary strength and durability required in structural components.

Important Considerations, Selection Criteria, and Further Insights

Feature/Property	S350 Steel	A572 Grade 50	St52-3	Brief Pro/Con or Trade-off Note
Key Mechanical Property	High Strength	Similar	Higher Toughness	S350 is cost-effective
Key Corrosion Aspect	Moderate	Similar	Better Resistance	S350 may require coatings
Weldability	Good	Excellent	Good	S350 is versatile
Machinability	Moderate	High	Moderate	S350 requires specific tooling
Formability	Good	Excellent	Good	S350 is suitable for forming
Approx. Relative Cost	Moderate	Higher	Similar	Cost-effective for structural use
Typical Availability	Common	Common	Less Common	S350 widely available

When selecting S350 steel, considerations include cost-effectiveness, availability, and specific mechanical properties required for the application. Its moderate corrosion resistance necessitates protective measures in harsh environments, while its weldability and machinability make it suitable for various fabrication processes.

In summary, S350 steel is a versatile structural grade that balances strength, ductility, and cost, making it a popular choice in many engineering applications. Its properties can be optimized through heat treatment and careful fabrication practices, ensuring that it meets the demands of modern construction and manufacturing.