While ASTM A36 is commonly used in the as-rolled (hot-rolled) condition, it can undergo various heat treatments for specific purposes, often to modify properties for machining or service:
Annealing: Heating to 843–871°C (1550–1600°F) and slow cooling. This is done to soften the steel, relieve internal stresses, and improve ductility and machinability, especially if the material has been cold-worked.
Normalizing: Heating to 899–954°C (1650–1750°F) followed by air cooling. This refines the grain structure, resulting in more uniform and slightly improved mechanical properties compared to the as-rolled state. It relieves stresses and homogenizes the microstructure.
Stress Relieving: Heating to 677–927°C (1250–1700°F) and slow cooling. The primary goal is to reduce residual internal stresses from machining, welding, or cold forming without significantly altering the hardness or strength. This minimizes distortion in precision components.
Hardening (Quenching & Tempering): While not typical for A36 due to its low carbon content, it can be surface hardened. Processes like carburizing (adding carbon to the surface at 899–927°C / 1650–1700°F) followed by quenching (rapid cooling from 788–816°C / 1450–1500°F) can create a hard, wear-resistant case over a tough, ductile core. This is used for parts like gears or pins requiring wear resistance.
It's important to note that for structural applications, A36 is almost always used in the as-rolled or normalized condition, as these treatments are not required by the base specification.