What is the difference between single and double tempering? If a double temper is replaced by single-temper (time*2), what is the difference?
Hi Habib;
it is about the retained austenite carbon content. After the first tempering the amount of carbon would rise in retained austenite and this would increase the probability of martensite formation from retained austenite. So you cannot just remove them by increasing the time of tempering.
please more tell about your material. this means you must describe what is the chemical composition and also initial microstructure. in to way you should recognize tempering temperature and hold time .
When you do the first tempering the Ms & Mf temperatures move toward high values and after cooling you will have untempered martensite, that is very fragil. So, the second tempering is used to temper the untempered martensite formed from the first one.
To do just one tempering with the flat temperature (soaking time) twice more you will not have this efect.
Multiple tempering is used for high-speed steels containing tungsten. Refs may be found elsewhere, for ex.:
http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&LN=RU&NM=57
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