A thick piece of steel (that is a piece with a high volume/surface area ratio) that got hot enough to soften, would if left alone end up permanently softened because its mass/surface area ratio would prevent rapid heat loss, and it would anneal itself. It wouldn't retain its softness "for a few hours", but permanently*.
If on the other hand it is dropped instantly into quenching water it would end up pretty hard on the outside, pretty tough within.
It is very interesting that when you google "A thick piece of steel (that is a piece with a high volume/surface area ratio) that got hot enough to soften, would if left alone end up permanently softened" or some derivative thereof... you get:
WTC7: Did the fires burn long and hot enough? - Page 6 - Metabunk
Seems like yet another invention.
This appears to be a far better/believable explanation of the processes and results in terms of steel in fire situations .
Critical Temperatures. -- The "critical points" of carbon tool steel are the temperatures at which certain changes in the chemical composition of the steel take place, during both heating and cooling. Steel at normal temperatures has its carbon (which is the chief hardening element) in a certain form called pearlite carbon, and if the steel is heated to a certain temperature, a change occurs and the pearlite becomes martensite or hardening carbon. If the steel is allowed to cool slowly, the hardening carbon changes back to pearlite. The points at which these changes occur are the decalescence and recalescence or critical points, and the effect of these molecular changes is as follows: When a piece of steel is heated to a certain point, it continues to absorb heat without appreciably rising in temperature, although its immediate surroundings may be hotter than the steel. This is the decalescence point. Similarly, steel cooling slowly from a high heat will, at a certain temperature, actually increase in temperature, although its surroundings may be colder. This takes place at the recalescence point. The recalescence point is lower than the decalescence point by anywhere from 85 to 215 degrees F., and the lower of these points does not manifest itself unless the higher one has first been fully passed. These critical points have a direct relation to the hardening of steel. Unless a temperature sufficient to reach the decalescence point is obtained, so that the pearlite carbon is changed into a hardening carbon, no hardening action can take place; and unless the steel is cooled suddenly before it reaches the recalescence point, thus preventing the changing back again from hardening to pearlite carbon, no hardening can take place. The critical points vary for different kinds of steel and must be determined by tests in each case. It is the variation in the critical points that makes it necessary to heat different steels to different temperatures when hardening.