
Heat treatment of
steels
243
Quenching steels
A hard, strong, steel can be produced by heating the steel to a temperature
greater than the A
3
critical temperature so that the microstructure is entirely
changed to austenite, then cooling quickly so that the austenite is transformed
into martensite. The treatment thus involves continuous cooling. The cooling
rate depends on the medium used for the quenching, water giving a faster
cooling rate than oil.
The TTT diagrams are derived from data obtained for transformations at
constant temperature. However, the diagrams are only slightly modified if
continuous cooling is considered, the effect bein ...