Press Hardening

Thermal Cycle

Heating occurs in a furnace at temperatures exceeding nine hundred degrees Celsius to ensure a complete phase transformation. Press hardening requires a very fast transfer from the furnace to the press to prevent the metal from cooling down before the forming begins. The dwell time in the die is carefully controlled to ensure the part reaches a temperature low enough for the martensite to be stable.

If the cooling is too slow, softer phases like bainite or pearlite will form and reduce the final strength of the component.

Microstructural Development

Final properties of the part are a direct result of the cooling rate and the chemical composition of the steel. Press hardening produces a material with a tensile strength of approximately fifteen hundred megapascals, which is significantly higher than conventional cold stamped parts. This strength allows for a reduction in the thickness of the structural components, which helps offset the weight of the battery cells.

The resulting microstructure is very uniform, leading to consistent performance across the entire part.

Dimensional Control

Cooling the metal while it is held under pressure in the die prevents the springback that typically affects high strength steels. Press hardening achieves much tighter dimensional tolerances than cold forming, which simplifies the assembly of the battery enclosure. The surface of the steel is often protected by an aluminum silicon coating to prevent the formation of scale during the heating phase.

If the coating is damaged, the part may be subject to corrosion or reduced weld quality. This technique is now the standard for producing the critical safety components in the chassis of modern electric vehicles.