As far as I know, in most of metals, IR radiation is reflected almost entirely and is not absorbed by metals. How does a metal become warmed under IR radiation? or does reflection, on its own, can warm up a metal?
You would need to look up the spectral characteristics, and impurities and roughened surfaces could affect the reflectivity, but if the reflectivity is in the 95% range or higher, most of the heating is probably coming from other regions of the spectrum. With a very bright source with a lot of IR (such as the sun), even 5% absorption could cause appreciable heating.Do you mean that IR, on its own, doesn't warm up a metal?