Because it covers a variety of complex processes, heat-treating is not easily described. Many metalworking procedures shape or give external finishes to metals-such as rolling, forming, machining, and plating-but only heat-treating can significantly change the ultimate condition of these shapes.

Grinding can sharpen the edge on a knife, but heat-treating makes the edge stay hard and sharp.

Forging and machining can produce a crankshaft, but heat treating gives it strength and makes the journals resistant to wear.

Stamping can produce a coiled shape, but heat-treating gives the part its spring.

What is it?

In general, heat-treating is the controlled use of time and temperature to produce predictable chances in the internal structure of metals. Materials other than metals-plastics, glass and ceramics-also may be heat-treated.

Without the word internal, the definition could be construed literally to include welding ,flame cutting and even melting, but heat-treating in the classic metallurgical sense has to do with the atomic and improvements that can be made by altering them. Heat-treating involves little outward physical change and applies only to solid, never molten, metals.

It does, however, deal with metals as solid solutions; that is, while the object being heat-treated always retains its essential shape, it can be in a state of internal flux in which vast atomic rearrangements take place.

Heat-treating is performed on metals after they have been given some sort of shape, such as plate, sheet, bar or wire. Heat-treating can be the first process following the initial shaping of metal, or it can be the last process prior to direct use of the part or its incorporation into a component, or both.

Heat-treating is a broad term encompassing a wide variety of treatments intended to accomplish different ends-softening or hardening.

Pure and alloyed metals-including iron,aluminium,copper,nickel,lead,chromium,tin,titanium,steel,brass,and bronze-can be heat-treated.

It’s not true, however, that all metals and alloys that can be heat softened also can be heat hardened. Heat-treating is commonly misconceived as only a hardening process and is often erroneously thought applicable only to heat hardened metals. Metal can be alloyed to become heat treatable for hardening, but it is not true that because a metal is an alloy it can be hardened by heat treatment.

Although it can take many forms, annealing generally serves to soften metals. It is often used after cold working metals that is subjecting them to physical changes such as hammering, cutting and bending. This cold working can mechanically alter their crystalline structures, causing them to harden. A simple example of this is the repeated bending of a paper clip or nail until it hardens and fractures.

By the proper application of heat, as in annealing, these work-hardened metals can be made to recrystallize, making them softer, more ductile and more amenable to further manufacturing processes.

Steel is not only the most commonly used metal but also the metal most subject to the kinds of end usage that necessitate heat-treating.