Alternative higher strength steels can be developed by post-forming heat treatment. Retaining the geometry of components during and subsequent to the heat treatment process is a key barrier for the widespread adoption of HSS.
Processing of PFHT Steels
Fixturing the component followed by heating and instantaneous quenching seems to be a solution for production applications. The stamping is created at a lower strength (ellipse 1), and then increased to a very high strength by heat treatment (ellipse 2) (Figure 1).
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Figure 1. The tensile strength-elongation graph of PFHT steels
Air- hardening of alloyed tempering steels is another process, yielding better forming properties in the soft- state (deep-drawing properties) and superior strength subsequent to heat treatment or air-hardening. Besides being used as sheet material, air-hardening steels are ideal for tube welding. These tubes are ideally suited for hydroforming applications.
In-die quenching is another option and is a version of Indirect Hot-Forming. In this process, all forming of the component is completed at room temperatures, followed by heating the component to roughly 850-900ºC. The component is then quenched to martensite using a water cooled die. This process is termed as Form Hardening. The current PFHT steel production grades and corresponding automotive applications are given in the following table:
| PFHT 340/480 |
As-received room temperature |
| PFHT 1050/1500 |
Heat treated after forming |
| PFHT 1200/1900 |
Heat treated after forming |
Download the Advanced High-Strength Steels Applications Guidelines free here, to learn more about the metallurgy, forming and joining of these new steels.
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This information has been sourced, reviewed and adapted from materials provided by WorldAutoSteel (World Auto Steel).
For more information on this source, please visit WorldAutoSteel (World Auto Steel).