Hot-rolling is the defining production process for ASTM A36 and profoundly impacts its final state.
Process: The steel is shaped (rolled into beams, plates, etc.) at extremely high temperatures, typically above 1700°F (925°C), which is above its recrystallization temperature.
Effects on Properties and Characteristics:
Microstructure and Residual Stress: The slow, natural cooling in still air after rolling results in a relatively stress-free, normalized-like condition. This generally eliminates the need for subsequent stress-relief heat treatment.
Surface Finish: The high-temperature process causes oxidation, resulting in a characteristic bluish-gray mill scale on the surface, which is rough to the touch.
Dimensional Tolerances: Tolerances are looser (±) compared to cold-rolled products. There can be more variation in thickness and less precise "squareness" or straightness.
Mechanical Properties: The process refines the grain structure, improving toughness and ductility compared to the as-cast state. However, yield and tensile strengths are generally lower than what can be achieved through cold working.
Cost: It is generally cheaper than cold-rolled steel due to fewer processing steps.
Formability: The as-rolled state is more ductile and better suited for bending and forming than high-strength or cold-worked steels.