Hot forming is a critical fabrication process for shaping A515 Gr.65 pressure vessel steel plates into complex components like heads and shells. Proper execution is essential to maintain the material's mechanical properties and ensure code compliance.
Key Process Parameters
The success of hot forming hinges on precise temperature control. The steel must be uniformly heated to within the proper hot working temperature range, typically between 1650°F and 1750°F (900°C to 950°C). Forming should be completed while the metal temperature remains above a critical threshold, generally not below 1550°F (845°C), to prevent excessive strain hardening and the formation of undesirable microstructures. The component must then be allowed to cool in still air after forming is complete.
Critical Post-Forming Heat Treatment
Due to its normalized supply condition, A515 Gr.65 requires full re-normalization after hot forming if the final forming temperature falls below the material's original normalization range or if severe deformation occurs. This heat treatment cycle involves reheating the component to a temperature typically between 1550°F and 1650°F (845°C and 900°C), holding for a sufficient time (usually 1 hour per inch of thickness), followed by air cooling. This step is mandatory to restore a uniform, fine-grained microstructure and the specified mechanical properties required by the ASME Boiler and Pressure Vessel Code.
Quality Control and Documentation
Strict process records are essential. A detailed Hot Forming Procedure (HFP) and Post-Forming Heat Treatment (PFHT) record must document all critical parameters: heating rates, soaking times, actual forming temperatures, and cooling rates. These records, along with updated material traceability, become part of the vessel's permanent documentation for code compliance and future integrity management.
