Producing Martensite & Bainite in Carbon Steel

[tututu87]

How to 'produce' martensite and bainite?

For what i know, martensite formed by rapid cooling from austenite phase of steel, and slow cooling to form back to it's original state. But in order to form bainite, what's the cooling rate? intermediate between rapid and slow cooling? How rapid and how slow is it exactly?

I heated up furnace temp to 760 degree Celsius (1400 F), and put in Fe-0.45C for nearly 20 mins(what phase is this Fe-0.45C falls after i quench it for 20 seconds, with water as quenching media?), but the hardness readings were not equal over the whole test piece.

Is it because of the quenching media, which never equally cool for the test piece, or it is due to the quenching time?

 

[Cerpin Taxt]

I guess the better way to preditc a microstructure result from a heat treatment is looking for the TTT diagram for your alloy.
From the cooling rate you may sketch the curve and analise the initial and final points in the diagram curves for phase transformation.

An example of TTT diagram:
http://www.msm.cam.ac.uk/phase-trans/2000/practicals/AP3/Image5.gif

PS.: The Bainite structure can be obtained from an Austempering heat treatment.

I hope i'd been helpful

regards

Taxt