Cryogenic Hardening versus Heat-Treating Hardening 3

[Lovison]

Metal hardening processes have me running in circles. I can't believe all the methods available for hardening and yet there are many.

Lately we've been looking into cryogenic hardening what are the pluse's and minus's of this process. Good points and bad.

How does it compare to Heat-Treating a long time standard of hardening? Good points and bad.

When would you use one over the other is rather a delema I'm having. They both can't be ideal and one or the other must have some drawbacks?

Appreciate any pointers and experience. Also where can I get something in writing about both processes that is generalized to some degree but yet sufficient information can be ascertained from the materials.

service-parts@naglepumps.com

Wayne

 

[Chinnia]

That is why metallurgists are employed in industries - to take the headache away from designers! Enough on boosting my profession.

Generally, as-received carbon or low alloy steels come in pearlite and ferrite microstructure. When you heat to around 900 C (Please convert to F), you form austenite. When quenched in water or oil, it forms martensite. This is hard and brittle. To make is tough (requires ductility but loss of litle hardness), it is tempered between 200 to 600 C for an hour or so. But in steels alloyed, not all austenite is converted to martensite when quenched to room temperature. It may require what si called cryogenic treatment.

Cryogenic treatments in steel converts remaining austenite (soft phase) to martensite (hard phase) in some alloy steels as their martensite finish (Mf) is lowered by alloying. This won't be the case for all steels.

Refer to a basic metallurgy/materials engieering book. These things are more clearly explained.

On a global basis, please ask the basic questions:
1. what is the application requirement - wear resistance (sliding, abrasive, erosive, corrosive type), fatigue resistance or corrosion resistance?

2. why do you need hardened surface - life, protect the counter surface, tolerence, etc?

3. what do others do in similar applications? Many a time, this is much quicker and easier (cheaper too)

You seem to be coming from valve industry and I assume yu require erosion resistnce of valve components. There are bulk material solutions (alloyed cast iron or hard materials) and surface engineered solutions (coatings and surface hardened methods).

Refer to ASM Handbook on Surface Engineering or Wear Control Handbook. There are so many books on this subject.

best wishes

Chinnia

 

[Lovison]

01-29-2002

Chinnia,

I will need to discuss this more with you. I have
a few questions. I appreciate your feed back and
it was helpful. Let me gather my thoughts and I
will get back to you.

Thanks Again

Wayne Wayne E. Lovison
service-parts@naglepumps.com

 

In addition to Chinnia's comments, you will need to do a second temper after cryogenic (cold stabilizing) in order to temper the transformed martensite. You also need to consider that the first tempering operation is not desireable, for some materials, because the retained austenite is partially stablized and will not transform during cryogenic treatment. For applications where dimensional stability is critical, you should develop a detail heat treatment procedure, including times and temperatures and cooling rates. The amount of retained austenite for some materials is significantly effected by the austenitizing temperature. Recommend you call in an expert unless you have lots of development money to spend. Been there and done that. Bob

 

[gdodd]

If you know the material then look up the time temperature transformation diagram (TTT diagram) for the alloy and it will give you Ms and Mf temperature to determine optimum heat treatment procedures.
Alternatively, consult with a contract heat treater in your area.

 

[Lovison]

Shippmet

Appreciate your feedback. It's the little details that get
you in trouble. Is there a written specification that is used by one supplier than another? Where could I find a generic overview of a typical cryogenic hardening procedure?

I need more material to review before I could recomend one process from another. It's difficult to know which process to use at any time. If one were hardening only metals would one specific specification apply or would I find that this would vary from source to source?

Does the thickness of the metal object have anything to
do with the specification? I would assume (bad choice of words) that more or less time would apply depending on the wall thickness you are tyring to harden - do you agree?

Thanks Again





Wayne E. Lovison
service-parts@naglepumps.com

 

[rustbuster1]

My experience with most common heat-treatable carbon steels is the cryogenic hardening has very little practical use. In some cases it may - as referred above - help with dimensional stability. Otherwise the results are usually insignificant as far as making a quenched part made of low alloy steel harder or better in any other practical way.

You should do what we have done: take examples of the parts you are dealing with and harden them by Q&T and with Cryogenic treatment to see if you can detect any useful effect. On slitter blades and other cutting edged parts, doctor blades and bearing parts we have never seen any improvement worth the effort/cost of cryogenic treatment, but you can make your own judgment. Remember, one test is often worth a thousand opinions!!

 

[Kenneth]

A simple version:

http://www.ln2cryo.com/howitworks.html

A more scholarly version:

http://cvip.csufresno.edu/~rlk16/cryo.html

 

[rustbuster1]

I rest my case.

 

[Lovison]

rustbuster1 and kenneth

I appreciate your feedback. I've been collecting research and attempting to get a better understanding both of you have helped.

We are getting test pieces together to send out and have hardened. Many of you have replied and to that I am grateful.

I won't pretend to tell you I know whats going on with this process since no ones else knows either. But its been interesting to say the least. It seems this process has been going on since WWII and since then has evolved into a colder process.

Thanks Again Wayne E. Lovison
service-parts@naglepumps.com