Tempering of steels takes place in four distinct but overlapping stages: 1. First Stage of Tempering: (Though mild steels as a rule are not hardened and tempered in industry, it is of academic interest to see the changes occurring in such steels during tempering after hardening). The tempering reactions in steels, containing carbon less than 0.2%, differ somewhat from the [...]
In this article we will discuss about:- 1. Introduction to Tempering 2. Aim of Tempering 3. Stages 4. Classification 5. Effects 6. Time and Temperature Relationship 7. Calculation of Hardness of Tempered Steels Based on Composition 8. Industrial Practice. Contents: Introduction to Tempering Aim of Tempering Stages of Tempering Classification of Tempering Effects of Tempering Time and Temperature Relationship in [...]
Normally, as the tempering progresses, the hardness and the strength decrease, but the ductility and impact strength increase. But in certain steels, there is an unexpected decrease of the impact strength in certain ranges of temperatures as schematically illustrated in Fig. 7.13. This indicates that there are two main types of embrittlement during tempering: 1. Tempered martensite embrittlement (TME), 2. [...]
The presence of alloying elements effects substantially, the tempering behaviour of the steels depending on the nature, amount and simultaneous presence of number of alloying elements. Most common elements (except cobalt) shift the CCT curve to longer times, which essentially result in the increase of hardenability of the steels, so that pearlitic transformation can be avoided easily to obtain martensitic [...]
As tempering is the process of reheating a hardened steel up to a temperature, maximum A1, it is a low temperature process. It can be performed in a: (a) Oil-bath furnace (b) Salt bath furnace (c) Lead bath (d) Forced-air circulation furnace. 1. Oil-Bath Furnace: Oils can be used as a medium for quick transfer of heat for tempering, or [...]