"There are three key temperature which may affect the properties of steel. As mentioned in the accepted answer the recrystallization temperature is the most significant as it can potentially affect any steel, especially ones which have been cold worked to improve their properties or have a high alloy content eg stainless, chrome-moly steels and some castings.

The second consideration is the tempering temperature. This only applies to steels which have been heat treated, generally cutting tools, dies, springs and certain other very high strength/hardness parts. The tempering range can vary between 180 and 300 C or up to 600C for high speed steels. Heating above the tempering temperature will remember the steel and consequently soften it. this is usually only a concern for finished components although some types of stock are supplied hardened and tempered, typically high alloy tool steels.

The final concern is that very high temperatures, approaching the melting point of the steel may cause the growth of very large crystals of even deep oxidation of the surface. This is a concern for all grades but particularly those containing chromium.

Finally, while many hot rolled steel grades can be hot worked without any loss of mechanical properties some have a narrow working window (red short) and the manufacturers data should be consulted in all cases."