Metal Treatment

[Samarjit Sen]

Are their any one who has done some work on hardening of metals by chilling the same down to -80oC or lower. I read somewhere that hardening of tools and other critical parts such bearings etc are better achiebed by chilling the metal parts.

Please do let us have your opinions.

[US Iceman]

Samarjit,

This is probably similar to using a heat treatment oven for stress relieving the base materials after fabrication.

The temperature changes cause the crystalline structure of the metals to decrease in size, thus making them more dense and harder to penetrate, thus the term hardening.

Here are some links I could find quickly...
http://www.infoplease.com/ce6/sci/A0822694.html

http://www.citysteelht.com/heat_treating.html

[Samarjit Sen]

This is a process which has been adopted in a number of places in the Western World. A couple of years ago I did some work on it and found a very big demand for the same.

Heating and then quenching the metal in oil or air is the general process. By heating the molecules expand and their are spaces in between the molecules. At the time of quenching they contract, but some spaces remain.

While freezing the metal, the molecules contract and that creates a better binding and the hardening is more. The only thing is that the lowering of the temperatures has to be done in steps, otherwise the metal will crack.

I had collected a lot of documents on this and I feel this a very interesting field. I will collect the documents and information and put up in the forum for the members to suggest after studying these.

[smpsmp45]

We had done similar project for one Accurate Gauges for such a low temperture The idea was to fit in the bearing by cooling the surfaces.

There are few companies , with whom I did some proejcts ( like for Cummins) who are using such chambers for -80 deg c.

[Samarjit Sen]

Hi smpsmp45,

The system is basically a simple cascade. But the important part in this system is to regulate the drop in temperature to ensure that the complete job is getting an uniform temperature before dropping further. Otherwise the metal shall crack.

Could you please let me know as to how you did it. I have been considering various ways, but there is a problem in getting the suitable controls.