The image below shows how a furnace should be properly loaded with profiles blanks. If you notice, each blank is separated by small pieces of steel which allows the flow of the heat to penetrate each blank. This allows each blank to be correctly stress relieved.
The idea of stress relieving steel profiles is to remove the stress caused in the profiling process. If a blank is to be machined, drilled or fabricated after profiling it is highly recommended to have it stress relieved.