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Chapter 14. Heat Treatment of Steels. Austenitizing , Quenching, and Tempering • Annealing • Case Hardening • Component Design and Fabrication. Excessively high austenitizing temperatures lead to grain coarsening and loss of toughness.

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Chapter 14

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chapter 14

Chapter 14

Heat Treatment of Steels

Austenitizing, Quenching, and Tempering • Annealing • Case Hardening • Component Design and Fabrication

Burning leads to permanent damage caused by intergranular oxidation or incipient melting along the grain boundaries of the steel.
The severity of quench for a quenching medium must exceed the value required to achieve the minimum allowable hardenability in a steel.
The outer layers of the component transform first and are placed in tension, whereas the inner layers transform last and are placed in compression. With severe quenching, this leads to quench cracking.
At any tempering temperature, a specific maximum amount of residual stress can be removed up to a maximum value.
Tempering takes place in three stages that overlap one another as the temperature is raised.
Austemperingconsists of austenitizinga steel, quenching it into a suitable medium maintained at a temperature in the bainite transformation range, and cooling it in air.
After martempering, the component must be conventionally tempered in order to restore toughness.
The key differences between annealing and normalizing are the holding temperatures and the rates of cooling.
Process annealing of a cold-worked steel causes recrystallization and evolution of fine equiaxed grains.
The majority of the stress relief is obtained after approximately 2 hr at any temperature.
Higher carburizing temperatures or longer holding times at the carburizing temperature result in a deeper carbon-enriched case.
In conventional nitriding processes, the surface consists of a very thin, white layer and a deeper diffusion zone.
Induction hardening is dependent on the frequency of the current and the shape of coils used to produce the current.
During induction hardening, the component is immediately quenched using special designs that incorporate quenching into the equipment.
Machining and grinding operations must be carefully controlled because residual stresses, which lead to cracking before or during heat treatment, will be produced.