Heat Treating Processes TSM 233 Unit 12

What is Heat-treating? Changing the physical and mechanical properties of metal by using heating and cooling processes. Changes the nature of the grain structure of the metals. Almost all metals can be heat treated in some form. Generally, the heat treating process are commonly used for steel products with greater than 0.30 percent Carbon.

How to Quench Harden steel. The following process is used for steels with 0.30% or higher carbon content: Heat to slightly above the critical temperature, Red heat, about 1400 deg. F. Cool quickly. Water quench is the fastest, but can crack, very brittle, must “stir”, can form a slag coating. Oil quench is often preferred for a more uniform structure and a more finished appearance, but is a possible environmental and safety hazard.

What is Annealing? Heat treating processes that “soften” a metal. There are several different annealing processes, we will use the “Full Annealing” process for steel. For steel products: Heat above the critical temperature, Allow to cool slowly, use a dry cooling material (sand) or a furnace. This process reduces the internal residual stresses in the steel, “softening” the steel. In the manufacturing process, some tool steel products are annealed so they can be machined and then heat treated to the desired hardness.

What is Normalizing? Produces a uniform metal structure, For steel products: Heat above the critical temperature, Cool by “still” air. This process allows the structure of the metal to return to a “moderate” state of residual stress.

How steel products are Quench Tempered: Used to get a desired degree of hardness, Heat to slightly above the critical temperature, Quench (harden). Reheat, slowly, Quench again at desired hardness (temperature/color) A tempering oven is the best heat source. Both coal and gas forges can be used, it is difficult to control the volume of heat. A torch can be used, but it is difficult to get the heat throughout the material at an even rate.

Tempering Chart: Colors Temp. F Uses Yellow 425 Steel-cutting tools, files Straw 462 Punches, dies Brown 490 Hammer faces, cold chisels, center punches Purple 500 Axes, wood-cutting tools Violet 540 Springs, screwdrivers. Blue 580 Springs Gray 620 Annealed, cannot be used for cutting tools.

What is thermal stress relieving? Heat treating process to reduce the stress within metal. For steel products: Heat to slightly below the critical temperature, Cool slowly, the grain structure realigns.

What is Spheroidizing? A heat treating process for high carbon steel. Enough carbon is present to form spheres of cementite, Heat high carbon steel to just below the critical temperature, Cool slowly, High carbon steel then can be more easily machined, formed, etc.

General Process for Forging and Heat treating steel project: Cut stock to desired length (5 – 7 inches). Heat stock in heated metal forge to red heat (about 1400 deg. F) Forge hot metal on the anvil, do not allow metal to cool below red heat (about 1100 deg. F) When forged to desired shape, cool slowly for 24 hours in dry sand. Grind to desired shape. Heat cutting end to red heat (forge or O-A torch) Quench the cutting end of project. Allow heat to transfer from the stock end to the tool end until desired temperature/color. Quench cool entire project. Clean and polish project.