The amount of tempering required depends on the particular application in which the steel will be used. In some cases, toughness is not important, so tempering at a low temperature for a short period of time is acceptable. In cases where very strong and tough steel is required a high carbon steel tempered at a high temperature might be used. More information about steel heat treating is in our online, on-demand courses Principles of Metallurgy or Metallurgy of Steel Heat Treating.
The book Steels: Processing, Structure, and Performance by George Krauss provides a comprehensive discussion of steel heat treating. Need help with a steel component failure or quality problem?
See our failure analysis page. Reach him at mike imetllc. Tempered martensite Tempering is used to improve toughness in steel that has been through hardened by heating it to form austenite and then quenching it to form martensite. Previous post Residual Stress May 28, The following tempering characteristics were discussed:. This article will now discuss how tempering affects the mechanical and metallurgical properties of the steel being tempered.
Hardness is perhaps the first noticeable change that takes place during the tempering operation. Based on the selected tempering temperature and the time at that particular temperature, the final hardness will be determined. The final tempered hardness will depend on: selected temperature, residence time of the steel at the tempering temperature, material chemistry carbon content and carbide-forming elements , type of martensite present in the microstructure and retained austenite if present after quenching.
The type of martensite that is present will be determined by the carbon content of the steel. It can be stated that there are two types of martensite that can form: lath martensite steels with low carbon content and plate martensite steels with carbon content above 0. This website requires certain cookies to work and uses other cookies to help you have the best experience.
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Parts which are quenched usually must be aged, tempered or stress relieved to achieve the proper toughness, final hardness and dimensional stability. Alloys may be air cooled, or cooled by quenching in oil, water, or another liquid, depending upon the amount of alloying elements in the material and final mechanical properties to be achieved.
Hardened materials are tempered to improve their dimensional stability and toughness. Tempering is done to develop the required combination of hardness, strength and toughness or to relieve the brittleness of fully hardened steels.
Steels are never used in the as quenched condition. The combination of quenching and tempering is important to make tough parts. This treatment follows a quenching or air cooling operation. Tempering is generally considered effective in relieving stresses induced by quenching in addition to lowering hardness to within a specified range, or meeting certain mechanical property requirements.
Tempering is the process of reheating the steel at a relatively low temperature leading to precipitation and spheroidization of the carbides present in the microstructure.
The tempering temperature and times are generally controlled to produce the final properties required of the steel.
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