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

 

[oswaler]

To produce martensite and bainite in carbon steel, the cooling rate and temperature are crucial factors. Martensite is formed by rapid cooling, also known as quenching, from the austenite phase of steel. This rapid cooling allows the carbon atoms to be trapped in the crystal structure, creating a hard and brittle microstructure. The cooling rate for martensite formation is typically on the order of 10-100°C per second.

On the other hand, bainite is formed by slower cooling from the austenite phase. The cooling rate for bainite formation is intermediate between that of martensite and pearlite, typically around 1-10°C per second. The exact cooling rate will depend on the composition of the steel and the desired microstructure.

In your experiment, heating the steel to 760°C and quenching it for 20 seconds in water would likely result in the formation of mostly martensite. However, the uneven hardness readings on the test piece could be due to variations in the cooling rate or the quenching media not cooling the entire piece evenly. It is important to control both the cooling rate and the quenching media to produce consistent and desired microstructures in carbon steel. Additionally, the quenching time can also affect the final microstructure, as a longer quenching time may allow for some austenite to transform into pearlite instead of martensite. Further experimentation and control of these factors may help to improve the consistency of your results.