Martensite finish in Elmax steel

N

Nico Cappelli

Joined
Apr 20, 2019
Messages
27
Good morning guys. I have just finished the changes to my cold machine, which works with a refrigeration cycle. Now it is able to reach the temperature of - 88 ° c (-126f). Unfortunately it is far from the temperature that can be reached in liquid nitrogen, but it has some advantages such as ease of use, low operating cost and the possibility of electronically controlling the temperature with a pid, therefore programming cooling ramps. By the way, I was wondering, - 88celsius are enough to reach the Mf temperature in elmax steel? Is it cold enough to get a good cold treatment? Thanks
 
The Mf temp for Elmax is well below zero and changes depending on how high the austenitizing temperature is. The higher the austenitizing temperature the lower the Mf goes.

Cold treatments are used to reduce retained austenite, with your current set up you should be able to eliminate a good portion of it. If you use the upper tempering temperature most or all of the RA will be eliminated. With upper tempering temps you will sacrifice some toughness and some corrosion resistance though.

The sooner after the quench you get it into the subzero treatment, the greater the benefit. You should gain a couple of points of hardness using your set up.

Hoss
 
Thanks everyone for the info, although there seem to be conflicting opinions.
Scaniaman said:
N Nico Cappelli I would love to see and hear more about this "cold machine" of yours, Sounds interesting!
I've been eyeballing ULT freezers, but they are darn expensive.
Click to expand...

my machine is nothing more than a refrigerator, self-built by recycling Reciprocating compressors from old refrigerators. It is not difficult to build, just need refrigeration equipment and a basic thermodynamic knowledge. By making several compressors work together, it is possible to obtain a high compression ratio, which a large pressure drop, which in turn will produce a high temperature difference. The refrigerant I used is r410a, with more suitable refrigerants it is possible to reach lower and more efficient temperatures, but they have much heavier environmental impacts, for this reason are expansive and difficult to find. The efficiency of my machine is poor, it consumes about 500 watts to obtain a cooling of about 30 watts .. but fortunately the heat capacity of a medium-sized knife is small, and keep about 30 minutes from +20c to - 80 celsius.
 
Nico Cappelli said:
Thanks everyone for the info, although there seem to be conflicting opinions.


my machine is nothing more than a refrigerator, self-built by recycling Reciprocating compressors from old refrigerators. It is not difficult to build, just need refrigeration equipment and a basic thermodynamic knowledge. By making several compressors work together, it is possible to obtain a high compression ratio, which a large pressure drop, which in turn will produce a high temperature difference. The refrigerant I used is r410a, with more suitable refrigerants it is possible to reach lower and more efficient temperatures, but they have much heavier environmental impacts, for this reason are expansive and difficult to find. The efficiency of my machine is poor, it consumes about 500 watts to obtain a cooling of about 30 watts .. but fortunately the heat capacity of a medium-sized knife is small, and keep about 30 minutes from +20c to - 80 celsius.
Click to expand...

Thank you for your reply, very interesting! I'll look further into this in the future. Right now I freeze to -44 Celsius with AEB-L, 14C28N and RWL 34. It lands me between 61 and 63 Hrc depending on steel and temper. I austenize at 1065 Celsius for all of them.
 
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