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Heat Treating Glossary

Your guide to understanding the terms, processes, and materials we work with every day.

Heat Treating Processes

Annealing

Heating and slowly cooling a metal to soften it, improve machinability, or relieve stress.

Heat treating steel or cast iron and then quenching to a temperature where bainite (steel) or ausferrite (cast iron) is produced to improved toughness and wear resistance.

Adding carbon to the surface of steel to improve hardness and wear resistance.

Diffusing both carbon and nitrogen into the surface to increase hardness.

Hardening only the surface layer of a part while leaving the core tough.

Using electromagnetic induction to heat and harden only selected areas of a component.

Adding nitrogen to the surface to improve wear and corrosion resistance without quenching.

Heating steel above its critical range and air cooling to refine grain structure.

Strengthening alloys by forming precipitates through controlled heating.

Rapidly cooling heated metal in oil, water, or air to set hardness.

Heating metal and cooling slowly to reduce residual stresses from manufacturing.

Reheating hardened steel to achieve a desired final strength/hardness/toughness.

Hardening the entire cross-section of the part, not just the surface.

Metallurgical Concepts

Austenite

A face-centered cubic phase of iron stable at high temperatures.

A microstructure consisting of needle-shaped ferrite and tiny carbides that offers a combination of strength and toughness.

Deformation that is not permanent – once stress is relieved, the component returns to its original shape.

A body-centered cubic form of iron that is soft and ductile.

The arrangement of crystals within a metal that influences its properties.

A measure of a material’s resistance to a depth of penetration or scratching.

A very hard, brittle microstructure formed by rapid quenching of austenite.

Deformation that results in a permanent shape change.

The maximum stress a material can withstand before breaking.

The maximum stress a material can withstand before a permanent shape change occurs.

Equipment & Tools

Atmosphere Furnace

A furnace with a controlled gas environment to prevent oxidation.

Furnace that processes parts in batches rather than continuously.

Furnace where parts move through on a conveyor for high-volume processing.

Furnace using molten salts for uniform heating.

Furnace that operates under vacuum to prevent oxidation and contamination.

A tank filled with oil, water, or polymer solution for cooling parts after heating.

Quality & Testing

Brinell Hardness Test

Uses a 10 mm diameter WC ball indenter to make an indention into a material under high load. The diameter of the indention is measured to determine the hardness.

Measures hardness using a diamond cone or ball indenter under load.

Examining a metal structure under a microscope to verify results.

Measurement of how deep the hardened surface layer extends. The total case depth is the distance from the surface that carbon has diffused to. An effective case depth is the distance from the surface to 50 Rockwell C hardness.

General Industry Terms

Cycle Time

The total time required for a heat treating process.

Change in shape due to uneven heating or cooling.

Oxidized surface layer that forms during heating in air.

The texture or smoothness of a part’s surface after processing.

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