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A678 | High Strength Structural Steel

A678 | High Strength Structural Steel

A678 is a high-strength, low-alloy structural steel. The “A” follows ASTM standards, with grades (A, B, C, D) indicating mechanical differences. Equivalent grades include EN S355JR and GB Q345B. It offers high tensile strength, toughness, and weldability, making it ideal for bridges, pressure vessels, and construction equipment.

According to ASTM A678/A678M, we offer products in grades A to D with thicknesses ranging from 6 to 75 mm, 900~4800 mm width, and 3000~25000 mm length to ensure versatility for various structural applications.

Description

What is A678 Steel

A678 is a high-strength, low-alloy structural steel made of about 98% iron with carbon, manganese, and copper. Produced as solid plates through hot rolling, it offers excellent tensile strength, toughness, and weldability. Available in grades A, B, C, and D, it is used in bridges, pressure vessels, and heavy machinery for its durability under heavy loads and harsh conditions.

Characteristics of A678 Steel

A678 steel is a high-strength, low-alloy structural steel known for excellent tensile strength, toughness, and weldability. It is resistant to impact and performs well under heavy loads, making it suitable for bridges, pressure vessels, and construction equipment. The hot rolling process ensures enhanced durability and toughness, ideal for demanding environments. In cases where higher corrosion resistance or better low-temperature performance is needed, A588 or A514 steels can be considered. For even better fatigue strength, A709 may be a suitable alternative.

Chemical Compositions

ElementContent (%)
Carbon, C≤ 0.16 – 0.22
Manganese, Mn1.00 – 1.60
Silicon, Si0.15 – 0.50
Phosphorus, P≤ 0.035
Sulfur, S≤ 0.040
Copper, Cu0.20 – 0.35
Nickel, Ni≤ 0.25
Chromium, Cr≤ 0.25
Molybdenum, Mo≤ 0.08
Vanadium, V≤ 0.11

Physical Properties

PropertyMetricImperial
Density7.85 g/cm³0.284 lb/in³
Melting Point1450 – 1520 °C2642 – 2768 °F
Boiling Point~3000 °C~5432 °F
Thermal Conductivity45 – 50 W/(m·K)26 – 29 BTU·in/(h·ft²·°F)
Electrical Conductivity6.99 MS/m6.99 MS/m
Specific Heat Capacity486 J/(kg·K)0.116 BTU/(lb·°F)
Thermal Expansion Coefficient11.5 × 10⁻⁶ /K6.4 × 10⁻⁶ /°F
Electrical Resistivity14 × 10⁻⁸ Ω·m14 × 10⁻⁸ Ω·m

Mechanical Properties

PropertyMetricImperial
Tensile Strength490 – 850 MPa71,000 – 123,000 psi
Yield Strength314 – 793 MPa46,000 – 115,000 psi
Brinell Hardness170 – 321 HB170 – 321 HB
Rockwell Hardness84 – 95 HRB84 – 95 HRB
Vickers Hardness180 – 340 HV180 – 340 HV
Elongation12 – 33%12 – 33%
Elastic Modulus200 – 210 GPa29,000 – 30,500 ksi

Data After QT(Quenching and Tempering) Processing

 

PropertyMetricImperial
Tensile Strength650 – 780 MPa94,000 – 113,000 psi
Yield Strength520 – 600 MPa75,000 – 87,000 psi
Brinell Hardness220 – 280 HB220 – 280 HB
Rockwell HardnessHRC 40 – 45HRC 40 – 45
Vickers Hardness210 – 260 HV210 – 260 HV
Elongation15 – 18%15 – 18%
Elastic Modulus210 GPa30,500,000 psi

Industries & Applications

IndustriesProducts
ConstructionBeams, Columns, Frames, Reinforcements, Plates
BridgesBridge Decks, Trusses, Girders, Supports, Barriers
Pressure VesselsTanks, Boilers, Heat Exchangers, Cylinders, Pipes
Heavy MachineryCrane Arms, Excavator Buckets, Chassis, Tools, Lifting Equipment
EnergyWind Turbine Towers, Pipelines, Offshore Structures, Supports, Frames
ShipbuildingHull Structures, Bulkheads, Deck Plates, Frames, Fuel Tanks
MiningConveyor Systems, Mining Trucks, Drilling Rigs, Support Beams, Structural Platforms
RailwayRail Tracks, Bridge Structures, Rolling Stock, Support Columns, Switchgear

Machining

A678 Steel Heat Treatment 

  1. Heating: Heat the steel to 850–900°C (1560–1650°F) to achieve uniform austenitization.
  2. Soaking: Hold the steel at the target temperature for 1–2 hours, depending on thickness, to ensure even heating throughout.
  3. Quenching: Rapidly cool in water or oil to harden the steel and enhance strength.
  4. Tempering: Reheat to 540–680°C (1000–1255°F) for 1–2 hours to reduce brittleness and improve toughness.
  5. Cooling: Allow the steel to cool slowly in air to stabilize the microstructure.

A678 Surface Finish

  1. Galvanizing: Coats the steel with zinc to enhance corrosion resistance.
  2. Painting: Adds a protective layer and improves appearance for outdoor use.
  3. Powder Coating: Provides a durable, decorative finish resistant to chipping and fading.
  4. Shot Blasting: Cleans the surface and improves adhesion for subsequent coatings.
  5. Pickling: Removes scale, rust, and oxides to prepare the surface for further treatment.
  6. Anodizing: Enhances surface hardness and corrosion resistance (less common for steel).
  7. Electroplating: Applies a metal layer (such as chrome or nickel) to improve wear and corrosion resistance.
Custom surface treatment requirements can be accommodated upon request.
Disclaimer
The above heat treatment instructions and surface finish processing methods for Mn13 steel are provided for informational purposes only. Actual results may vary based on specific conditions and equipment used. Testing is recommended, and a metallurgical expert or material supplier should be consulted to ensure the processes are suitable for your specific application. The user assumes all risks and liability for the use of this information.

Our Service

SteelPRO Group – manufacturer and solution provider for special steel, offering multi-industry application solutions and customised services, 100% quality free, accompanying customers in their growth!

Our Quality Control

  • Roundness
  • Tolerance
  • Microstructure
  • Non-Destructive Testing
  • Destructive Testing
  • Process Control

Service Integration Processing

  • Welding
  • Metal Fabrication
  • CNC Machining
  • Lathe
  • Forming

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