There was a good article on this subject in the AISC Engineering Journal, First Quarter, 1998 titled "Integrity of Structural Steel after Exposure to Fire" by R.H.R. Tide.
His final conclusion was "it can be simply stated: 'If it is still straight after exposure to fire - the steel is OK.'"

When steel comes out of a rolling mill it is molten.  We certainly don't throw it away because it was so hot.

When we weld, the weld metal is molten.  Once it cools it has strength.

I agree with AJH1.

Generally mild steel rolled sections will be ok providing they are straight. Be carefull of Cold Worked sections - cold working in effect turns mild steel into high tensile steel which can revert back to mild steel if it gets hot enough. The same can apply to some high tensile steel bolts - check the capacity of the connections assuming that they are ordinary grade bolts and if in doubt replace them.

please forgive my over simplification of terms - remember  that American engineers and British engineers are seperated by a common language - we have different terms for the same things.

Let me put it in thi way. At the time of rolling for required shapes , it is in ideal condition in a controlled teparature. It has its full properties per standards.

Once it is affected with fire under loading conditions, its properties were lost and deformed in to different textures. Better to go for testing with present conditions and decide for reusage. For a physical test and judgement ,  I fully agree with Mr.Ajh1

I would recommend testing if your not sure, it's cheap insurance and simple mechanical tests are not too expensive.
Unless you know specifically the temperature and time the steel was exposed, you really are not sure.

I have seen beams that were "straight" after fire damage that did not comply with the original specification requirements. The beams were supported in a manner that did not divulge deformation to the eye. We cut samples of material in locations chosen by the RDP for that project. I believe his locations were based upon a fire investigators report. Steel in the areas not considered "damaged" (but were still exposed to fire), the material was right were it should have been metallurgically speaking.

Coupons were cut at web or flange of the beams and a few columns. These were sent to a local construction lab for the usual tensile/yield, toughness and hardness. I remember one beam which had 2 coupons removed had one that was satisfactory, the other failed as it had failed the Charpy impact. Both coupons were removed from the center of the web. It was supposed to be our "control" unit as a comparison.

The specific test results were random. Some were satisfactory, some were not. The metallurgical engineer made recommendations to R&R some of these members.

It's cheap insurance.