FAQ's About Deep Cryogenic Treatment
Won't cryogenic processing make things brittle?
We process automotive valve springs for racing engines. If we made them brittle they would not last for long. There are two sources of brittleness caused by cryogenic temperatures.
1. Many metals and plastics do get brittle when down at cryogenic temperatures. That brittleness goes away as the temperature returns to ambient so it is not a factor in the use of the treated part.
2. The primary martensitic structure produced when retained austenite is transformed is brittle. That is one reason for the tempering cycle at the end of cryogenic process. The tempering cycle tempers the martensitic structure the same as it does in the quench and tempering when hardening steel.
A metallurgist told me that all cryogenic processing does is convert retained austenite to martensite.
It is not unusual for metallurgists to say this, as they really have not been taught much about cryogenic processing. Yes, on hardened steels, cold temperatures will induce retained austenite to convert to martensite. But whatever is going to convert is usually converted by about -140F, which is not even into the cryogenic range which starts at about -244F. If you read the research into the field of cryogenic processing you will find other things happening. They have to, because cryo processing causes parts that do not have retained austenite to exhibit changes. For instance, automotive brake rotors increase their life between two and four times when processed. The microstructure of brake rotors is pearlitic; it contains no austenite. Resistance welding electrodes made of copper alloys also exhibit significantly increased life and also have no austenitic structure.
Does the nitrogen used in the process pollute the air?
No, it does not pollute the atmosphere. Liquid nitrogen is made by cooling atmospheric air down below the temperature of below -320F. So by using liquid nitrogen, it is just returns it to the atmosphere. The atmosphere is about 78% nitrogen. There is a danger if you release enough nitrogen in a closed room that you will dilute the oxygen in the closed room. So use adequate ventilation.
Does the vacuum insulation need an expensive vacuum pump?
No. No vacuum pump is required. Think of the vacuum insulation as a Thermos® bottle. Your coffee is inside a double walled container. The vacuum is between the double walls. And you don't need a vacuum pump to keep your coffee hot.
Is your machine junk if the vacuum is lost?
Although loss of the vacuum is rare, it can be fixed by the same people who fix the dewars that nitrogen is shipped in. These dewars are banged around in loading them into trucks, knocking against other other dewars and equipment on the trucks when road hazzards are encountered and then unloaded. They seem to survive that beating quite well for decades. If they develope a vacuum leak they are simply fixed, much like you would fix a flat tire.
Our competition makes the case that "When you start to place a vacuum in a situation where it needs to cycle between –300°F and 1200°F the inevitable leak occurs, just due to metal fatigue alone." This is really strange for a company that does cryogenic processing to claim. Cryo processing makes the welds and the metal of the dewar last longer in fatigue, and nothing gets more cryo processing than a cryo processing dewar. We have machines in the field that are cycled three times a week with heavy loads. They've been out there for five years without losing their vacuum. We have machines in the field over twenty years without losing vacuum.
Our competitors also state "...everyone that manufactures vacuum insulated products knows about it and they go to great lengths to solve the problem through the use of "getters". Getters absord the free molecules that result from the out-gassing of the stainless. The only problem is that as the getters get warm, they release what they absorbed. And the hotter they get the more they release, becoming ineffective. " What they fail to mention is that as the getter is re-cooled during refrigeration, the getter re-absorbs the few organic molecules that got free during heating (cryo pumping) and the vacuum is optimum at the temp. where you really need the best insulation.
Why isn't cryogenic processing used more?
This is a great question with no definite answer. We've heard a lot of excuses. (see our web page on myths) We have a hard time understanding why companies would not like to make the best possible products at the lowest possible costs. We cannot fathom why racers would not want the best possible chances of winning.
What is the difference between cryogenic processing and cold treatment?
Cold treatment is performed by heat treaters to convert retained austenite to martensite. It usually takes place at about -140F. There is no specific profile to follow. Cold treatment does not seem to have any effect on cast iron or aluminum. Experiments show that cold treatment is nowhere near as effective as proper cryogenic treatment.
Why can't I just dip a part in liquid nitrogen?
Research indicates that dipping in liquid nitrogen is successful about 10% of the time. Think of it this way. If you dip a part into liquid nitrogen the surface wants to contract to the size it would be when it is -320F. The inside of the part is still at room temperature and therefore at the size it would be at room temperature. This creates stresses, and the stresses at the surface are there at temperatures where the metal is brittle. This is an invitation to disaster. Our system of slow cooling eliminates the extreme temperature differentials created by dipping the part or by having a nitrogen spray hit the surface.
There are other reasons to avoid dipping. Some the things that are happening in the metal take time and happen within certain temperature ranges. Blasting through these temperature ranges by quick cooling or dipping does not allow enough time for these changes to take place.