Heat Treating - 8: Alloy and Unalloyed Heat Treated Steels
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
There are three basic types of unalloyed carbon steels which have different hardenability characteristics. They are:
  • Low carbon Steel: Composed of mainly iron and from .1 to .3% carbon, this steel cannot be heat-treated but is easily welded.
  • Medium carbon Steel: Composed of mainly iron and from .3 to .6% carbon, this steel can be heat-treated and gain toughness and hardness.
  • High carbon Steel: Composed of mainly iron and from .6 to 1.7% carbon. The steel that contains from .6 to 1% carbon is the unalloyed steel that is often heat-treated. Steel that has a carbon content greater than 1% is seldom used.

Alloy steels that can be heat treated are:

  • Tool Steels, which contain up to 1.3% of carbon
  • Alloy Steels, which contain a few percent of alloying elements that enhance their heat-treat ability.

The table (right) shows annealed, maximum, and minimum values of tensile strength (in pounds per square inch) that a selected few materials can be heat treated to

Low Carbon (1020)

Medium Carbon (1040)

High Carbon (1095)

Alloy Steel (4130)

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label: heat treating, annealing, normalizing, stress relieving,. qunench, quench temper, tool steels, hardness, Brinell, rockwell, alloyed steel, carbon contenet