Tempering is a metallurgical engineering heat treatment applied to a metal, most commonly hardened steel, after it has been quenched, in which the metal is reheated to a temperature well below its critical transformation point and then cooled, relieving some of the internal stresses and extreme brittleness that rapid quenching produces while retaining most of the added hardness. By choosing the tempering temperature, an engineer can trade off some hardness for greater toughness and ductility to suit a particular application, from tools that must hold a hard cutting edge to springs and structural components that must flex or absorb impact without cracking. The technique has been practiced by smiths for centuries and remains standard practice in modern steel manufacturing.
Facts
Disputed
Origin YearThe oldest known tempered martensite artifact is a pick axe found in Galilee, dated to roughly 1200 to 1100 BC; the technique was practiced across the ancient world from Asia to Europe and Africa well before it was named or its chemistry understood, and was long confused with quenching itself. Core PrincipleTempering is a heat treatment applied to a quenched, hardened ferrous alloy, reheating it in a controlled way to a temperature below its lower critical temperature so that some hardness is traded for greater toughness and ductility without destroying the hardened martensite structure quenching produced. 1 FAQs
Why is hardened steel tempered instead of being used straight after quenching?
Quenched steel is hard but too brittle to use, and tempering restores toughness at a small cost in hardness.
Quenching leaves steel in a martensite structure that is very hard but much too brittle for most uses. In that condition it is sometimes called glass-hard, and it could break on impact. Reheating it below the transformation temperature lets some of the trapped carbon diffuse out and eases the lattice distortion. The steel loses a little hardness and strength but gains a great deal of toughness, and it stays much harder than it was before quenching.
Connections
Associated With
Field end of a technology member entity grouped under this field
Steel, Materials Quenched steel is tempered to trade some hardness for toughness.
In Field
Source Tempering (Wikipedia)Wikipedia contributors
Preceded By
Source Quenching (Wikipedia)Wikipedia contributors
Sources
1. Tempering (Wikipedia)
Wikipedia contributors, Wikimedia FoundationIntroduction section
Tempering is accomplished by controlled heating of the quenched workpiece to a temperature below its "lower critical temperature"
History section
The oldest known example of tempered martensite is a pick axe which was found in Galilee, dating from around 1200 to 1100 BC
In Field: Metallurgical Engineering, Categories
Metal heat treatments
In Group: Steel Heat Treating and Finishing, Introduction
Tempering is a process of heat treating, which is used to increase the toughness of iron-based alloys.
View the Source Quenching (Wikipedia)
Wikipedia contributors, Wikimedia FoundationPreceded By: Quenching, Heat treatment sectionQuote, Preceded By: Quenching, Heat treatment section
In these cases, another heat treatment technique known as tempering is performed on the quenched material to increase the toughness of iron-based alloys.
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