Overheating

Overheating 

(metallurgy), a defect that results from heating metals and alloys to high temperatures; the defect is most pronounced when the heating time is extremely long. Steel overheats between 1000° and 1300°C.

After cooling, an overheated metal’s crystal structure is coarse-grained, with distinct, linear boundaries between the components; furthermore, the metal’s resilience is reduced. Overheating can occur during furnace treatments and around seams that have been electrically welded.

In many cases, overheating may be eliminated by a second heating, usually to a temperature 20°-30°C above the recrystallization temperature. This procedure serves to reduce grain size. With alloys of nonferrous metals and with austenitic and ferritic steels, all of which are usually not subjected to recrystallization, overheating cannot be eliminated by repeated thermal treatment; thus, the overheated samples must be rejected as scrap.

The tendency of steels toward overheating depends on their chemical composition and is significantly reduced by adding small amounts of vanadium, titanium, aluminum, or boron.

V. M. TYMCHAK