Heat treatment of a36 steel

Heat treatment of A36 steel, also known as ASTM A36 steel, is a common practice to enhance its mechanical properties and improve its suitability for specific applications. A36 steel is a low-carbon steel widely used in various industries due to its versatility and cost-effectiveness.

While A36 steel is not typically heat treated for hardness, it can undergo certain heat treatment processes to modify its microstructure and mechanical properties. Let’s explore the common heat treatment methods for A36 steel.

Heat Treatment of ASTM A36 Steel

  1. Normalizing of ASTM A36 Steel:
  • Heating temperature: 899°C – 954°C (1650°F-1750°F)
  • Cooling: Air cooling (in still air)
  • Holding time: No specific holding time required; the steel is typically held at the target temperature for a sufficient period to ensure uniform heat transfer before air cooling.
  1. Annealing of ASTM A36 Steel:
  • Heating temperature: 843°C – 871°C (1550°F-1600°F)
  • Cooling: Furnace cooling (slow cooling)
  • Holding time: The steel is typically held at the annealing temperature for a specific duration, usually ranging from 1 to 2 hours, to ensure proper transformation and grain refinement. Afterward, it is slow-cooled in the furnace.
  1. Stress Relieving of ASTM A36 Steel:
  • Heating temperature: 677°C – 927°C (1250°F-1700°F)
  • Cooling: Air cooling (in still air)
  • Holding time: The steel is held at the stress-relieving temperature for a sufficient period, typically ranging from 1 to 2 hours, to allow for stress relaxation. The holding time may vary depending on the thickness and complexity of the part.
  1. Carburizing of ASTM A36 Steel:
  • Heating temperature: 899°C – 927°C (1650°F-1700°F)
  • Cooling: Quenching in oil or water, followed by tempering (depending on the desired hardness and mechanical properties)
  • Holding time: The steel is held at the carburizing temperature for a specific duration, typically ranging from several hours to several days, to allow for carbon diffusion into the surface layers. The exact holding time depends on the desired case depth and carbon concentration.
  1. Hardening of ASTM A36 Steel:
  • Heating temperature: 788°C – 816°C (1450°F-1500°F)
  • Cooling: Quenching in oil, water, or polymer solution (depending on the desired hardness and mechanical properties)
  • Holding time: The steel is typically held at the hardening temperature for a specific duration, usually ranging from a few minutes to several tens of minutes, to ensure proper transformation. The exact holding time depends on the part thickness and the desired hardness depth.
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What is ASTM A36 Steel?

  • ASTM A36 is a mild and hot-rolled carbon structural steel developed by ASTM International.
  • It possesses excellent welding properties and is suitable for processes such as punching, grinding, drilling, tapping, and machining.
  • Compared to higher-performance alloys, ASTM A36’s properties make it versatile and applicable in many different uses.

Advantages and Applications of A36 Steel

  • A36 steel is an affordable carbon steel plate with exceptional strength to withstand various system pressures.
  • It is highly durable and can be recycled entirely, contributing to sustainability.
  • A36 steel serves as the foundational material for constructions and structures and finds applications in warehouses, industrial and commercial buildings, pipes, enclosures, and more.
  • It can be fabricated into various base construction materials.
  • A36 steel is available in different forms, including rectangle bar, square bar, circular bar, angles, H-beams, I-beams, and channels.
  • In Southeast Asia, it is also known as mild steel.

Material Properties and Specifications

  • Chemical Composition: A36 steel plate consists of approximately 0.25-0.29% carbon (C), 0.20% copper (Cu), 98.0% iron (Fe), 1.03% manganese (Mn), 0.04% phosphorus (P), 0.280% silicon (Si), and 0.050% sulfur (S).
  • Mechanical Properties: A36 steel has a tensile strength of 58-80 ksi (400-550 MPa) and a minimum yield strength of 36 ksi (250 MPa). It exhibits an elongation of 20% in 8 inches and 23% in 2 inches for plates and bars.
  • Equivalent Materials: ASTM A36 is often considered equivalent to EN S275 steel plate.
  • Referred Standards: Various ASTM standards (A6/M, A27/M, A307, A325, A325M, A500, A501, A502, A563, A570, A668, F568) specify the manufacturing processes and materials associated with A36 steel.
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Heat Treatment Methods and Performances for A36 Steel

  • Normalizing: A36 steel is subjected to normalization treatment at temperatures between 899°C and 954°C (1650°F-1750°F) after the manufacturing process.
  • Annealing: The steel undergoes annealing treatment at temperatures between 843°C and 871°C (1550°F-1600°F).
  • Stress Relieving: Stress relieving is carried out at temperatures between 677°C and 927°C (1250°F-1700°F).
  • Carburizing: Carburizing treatment occurs at temperatures between 899°C and 927°C (1650°F-1700°F) to introduce carbon into the surface layers.
  • Hardening: Hardening is performed at temperatures between 788°C and 816°C (1450°F-1500°F) to achieve desired hardness and strength properties.
  • Normalization is the final treatment after the manufacturing process.

The properties of ASTM A36 steel plate allow it to deform gradually as stress increases beyond its yield strength, ensuring the safety of structures and allowing occupants to exit safely before collapse occurs. Its high yield strength of 36,000 psi and allowable bending stress of 22,000 psi contribute to its structural integrity.

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