Metals strengthened by cryogenic treatment? 1

[Chamblin]

Cryogenic treatment of materials is a new topic for me and I was wondering what type of metals are strengthened by cryogenic treatments and would cryogenic treatment strengthen welds made in those metals as well?

 

[mcguire]

The value of crygenic treatment is in completing the transformation of austenite to martensite in carbon, alloy and tool steels, and martensitic stainless steels. Yes, it would work on their welds as well.
It could be detrimental to austenitic stainless steels where you don't want to transform the austenite.
It's hard to imagine any effect at all on aluminum, titanium, or copper based alloys.

 

[Frederick]

Cryogencic processing will work to increase wear resistance and fatigue resistance of most metals, including austenitic stainless steels. I know because I have been working in the field for over 6 years. It doesn't give a significant increase to the tensile strength of metals unless there was a lot of retained austenite, and that would indicate inadequate heat treating to start with.

As for aluminum, copper, brass, etc., the process works just fine on them. Practical tests show significantly increased life of many components that are made of these metals. Why? We believe that it has some affect on the crystal structure of the metal, but this is not proven, and nobody in the field has had the resources to prove this.

 

[JimMetalsCeramics]

Cutting tool steels are often treated cryogenically in liquid nitrogen. This increases the martensite volume percent which hardens the tool's surface. For many cutting applications the tool life will markedly increase.

 

[Frederick]

The conversion of retained austenite to martensite is only one of the ways cryogenic processing changes the wear resistance of metals (both ferrous and non ferrous.) We know this because non ferrous and even single metal systems are affected by cryogenic treatment. Also, cryogenic processing is more than a surface treatment, as treated tools can be sharpened without losing the cryogenics.

Research indicates that in the iron/carbon system there are very fine carbides that precipitate during the cryogenic process. These add to the wear resistance. Resicual stresses are also reduced. Several researchers (for instance at University of Trento, Italy, and Los Alamos National Laboratory) have noted that there is something happening in the sub microstructure that is not well understood.

The point is that cryogenic processing has been shown to reliably increase the wear resistance of virtually all metals and some plastics. The results are repeatable and are a valuable way to reduce wear.

 

[shooter45]

Call me an old fashioned sceptic if you like but I have a hard time with "something happening in the sub microstructure that is not well understood". Fifty years ago metallurgists could say that sub-microscopic particles were responsible for mechanisms such as age hardening but with modern TEM and STEM techniques which can reveal detail down to the molecular level I'm afraid that unless you can show me an image I remain unconvinced by the explanation.

 

[Frederick]

Shooter45. You asked for it. You are old fashioned. And out of date. First of all, "molecular structure"? Metals are crystalline. They have no molecular structure. Their crystalline structure is what gives them their metallic properties. So the submicrostructure of metals does not necessarily include particles. It includes the interactions of the atoms with each other in the metallic bond. This would not always show up with a TEM.

Secondly: Los Alamos and IIT have some marvelous toys and resources. If you read the research, you will find that there were attempts to find microstructure differences with EMs and these attempts failed.

If you did all within the scope of your research and failed to find a micrstructural change that would explain your results, what would you do? These three researchers independently came to the same conclusion. This is not proof, but it is evidence.

What is your theory to explain the results of cryogenic processing, and on what do you base your theory? Please don't come out with the tired explanation of retained austenite to martensite transformation. That doesn't work for non ferrous metals. Same with carbide formation.

 

[shooter45]

Fred
Apologies - I used the word "molecular" to describe the scale of possible observations not any particular kind of structure.
Maybe I should have worded my comments as follows - with my relatively antiquated electron microscope I can see the atoms and crystallographic structure of the heavier elements and can observe the movement of dislocations in alloy steels.
On examining materials which have been subjected to cryogenic treatments using the same instrument I see only transformation products - no "sub-structures" - no "cells" just regular metallurgical structures.
Until peer reviewed scientific papers are published presenting real evidence I remain sceptical. It is not sufficient to say "it works, trust me. Send me your panty hose and I will make them last longer"

 

[Frederick]

There are plenty of peer reveiwed studies out there that flatly state that cryogenics works, going all the way back to the original work of Dr. Randall Barron. The work of Dr. David Collins is magnificent. The afformentioned studies by IIT, Los Alamos National Labs, and the US Army Aviation and Missile Command, The University of Trento, Italy and others all state the process works and works well and works as advertised by the more responsible practioners. The American Society for Materials, International says it works. The Cryogenic Society of America says it works. What do you want, a new book in the Bible about it?

Your studies point to a conclusion that everyone is making. We do know it works, we do not know why. But your conclusion seems to be that you do not know why it works, therefore you are skeptical that it does work. Does not knowing why something happens mean the process should not be used? Show me any study that shows how gravity works. Do you distrust gravity? In today's competitive market, we need to use every advantage we have. And this process provides a HUGE advantage in tooling performance and in component performance.


You need to separate having to understand a process from being able to profit by it. Until the early part of the 20th century, we did not understand why steel got hard by quenching and tempering. That did not stop us from using hardened steels. We did not understand exactly why airplanes flew for the first 25 years of flight. (The Wright brothers observed the way wings created lift, but did not have any idea why they created lift. Their work was strictly empirical.) But not understanding how the aircraft worked did not ground all aircraft. And people watching them fly began to see that it was no illusion.

People who refuse to use cryogenic processing because they cannot explain its mechanism are not being rational. The research by careful, prestigious organizations is overwhelming. The practical uses are overwhelming. We are beyond the point of being skeptical about WHETHER it works. If you want to help us find out why cryogenic processing works, hail and welcome. If you want to denigrate the work of learned researchers with an opinion, then don't waste our time.

 

[unclesyd]

Our main use of Cryogenic treat was in the heat treatment of tools components, mainly D2,A2, and H11. We used Cryogenics to stabilize the materials due to running tight tolerances 0.0005" on parts. This had been done previously by multiple tempers, up to 9 times. The first cryogenic treatment was done in the sixties using Liquid Air coming of a LH2 line at an unloading station.

Our H11 socket head cap screws were at one time quenched directly to LN2 then tempered once to give 235,000 psi tensile strength. We didn’t use the high tensile strength as we tempered back to 200,000 and used then at 150,000 psi bolt stress. The fastener manufacturer said that the 235,000 psi tensile strength was about a 10% increase on his normal heat treatment.

On of the most significant improvements was with wear improvement in very small 0.0090" diameter broaches and drills down to 0.0015" dia. The wear improvement on the 0.0090" broach was phenomenal, well over 3000% in holes broached based on a measured hole size and measuring the broach. We were broaching a 0.0090"D x 0.015"L hole. The improvement was essentially the same on broaches made from A2, S2, O1. The testing was very accurate as we made the broaches in lots of all the same heat of material.
The increase in drill life was not checked as close since a lot other variables were involved in the life, but an informal test revealed a 50-60 increase in holes produced per drill.

We saw some improvements on fatigue life from 6061 Aluminum parts quenched directly into LN2. Nothing was ever done to quantify this.

I was doing work on 17/4 PH S/S properties with cryogenics in the early 80's which was never completed. The work looked very promising up to the point of stopping.

 

[grumpyphil]

I probably shouldn't even be posting here as I am not an engineer but only a lowly toolmaker. However...
My question has to do with what I might expect cryogenic treatment to do for carbide tooling (drills, lathe cutters, etc.)Will the process significantly effect carbide tools? I've been very impressed by treated HSS drills and I'm wondering if having my carbide reamers etc. treated will yeild similar results.

 

[JimMetalsCeramics]

Cryogenic treatment is of benefit to steel for specific metallurgical reasons. I had actually heard some anecdotal comments that strangely enough the process also showed benefit for carbide tooling. But you should ask a company doing that work.

 

[grumpyphil]

My experience with "companies" of this sort is that they will promise you anything to get your money. If you work for a huge concern you can make 'em prove it but barring that, you can take their word and, more often than not, get screwed.

 

[Frederick]

To lump all cryogenic processing companies into the the mold of trying to get your money is stupid and narrow minded. There are those of us who have worked hard to give our customers exceptional value for their money. In most cases, we are the ones who get screwed, when we do a lot of research, show exceptional results and don't get paid because we can't prove why cryogenics works.

I am sure that grumpyphil has gotten lousy results from heat treating and probably from machine shops and he doesn't call them all shysters. Yes there are those out there after only money, but there are a lot of us out here with legitimate, growing businesses. Shop carefully, make sure you and the shop you choose understand metallurgy, and everyone will benefit. Otherwise, crawl back into a hole and pull the styrofoam lid back down to cover it.