Material Technologies, Inc. is and always has been, a metallurgically-based company. Through the years, we have continually added the services and processes our customers have asked for. Surface hardening, diffusion coatings and engineered microstructures are just a few of the things we do. In our world, these are some of the tools we use everyday. To us, “cold” is another one of these tools. So just as you use a wrench in a multitude of ways, we too, use cold in many different ways. For example, it is very effective for pre-machining stress relief, critical shrink-fit applications, microstructure “repairs” and heat-treat diagnostics. And to us, it is a very effective, reliable and consistent tool.

Understanding the variable results is a simple and very complicated task at the same time. The simple part becomes evident when you look at the challenges industry faces as it tries to mass produce heat-treated parts and be cost effective at the same time. Compromises have to be made, there’s no way around it. The net result is parts that are fine for most applications, always seem to have room for improvement. Retained austenite is almost always present when we look at failed parts. All you need to know about that subject is it affects wear and fatigue properties far more than most people realize. Cold is very effective in fixing this problem, but is only the part of the solution. A gear and a drill bit are good examples here. After cryogenic processing, the retained austenite is now converted to “un-tempered martensite”. All that’s necessary here is to know that it results in very brittle part that has poor wear and fatigue properties. Think of it this way, we want the paper clip to bend 100 times before it breaks, not 20 times. To fix this, the parts need to be tempered or “re-heated”. But the gear cannot be re-heated to more than 400 deg. without becoming soft, but the drill sees no response at any temperature below 1000 deg. So, just how you take a drill to that kind of temperature without causing any form of surface oxidation or scale? Well it takes very specialized equipment that protects the drill from any forms of oxygen. How many “cryo processors” do you know out there that have a full line of atmosphere and vacuum furnaces in addition to their cryogenic equipment?

Look, the purpose here is not to make you an engineer. So we are going to spare you the usual “ya-de-ya-de” about “molecular re-alignment”, “wet or dry” processes or the always entertaining, “custom-engineered, unique cycle” that seems to perform miracles on everything from golf balls to panty hose. So, does it result in structural changes in the parts? Yes. Does it help improve wear properties? Yes. Does it work the same way on all parts? No, absolutely not.

Cylinders, Heads & Pistons:
The objective here is deep stress relieving to maintain dimensional stability (rounder cylinders) when things heat up. Cast and forged pistons grow unevenly in use. Those “high spots” are trying their best to weld themselves to the cylinder. Cylinders have a habit becoming “un-round” and this affects ring seal, compression and leak-down. Cranks and cams have both casting (or forging) as well as machining stresses that affect stability. Brake rotors share some of the same problems as well and all of these parts need to be processed differently than the typical gear does.

Interesting side note:
Some years ago we had the opportunity to use a computer measuring machine to “map” the roundness of some Briggs Raptor motors, but with a twist. Because the CMM machine was located next to the heat treat department, we were able to map the cylinders at 100, 200, 300 & 400 degrees before and after cryogenic stress relieving. We were amazed by two things: 1, how “un-round” the cylinders became as the temperature increased (square fins, round cylinder) and 2, how much “rounder” they became after treatment.

Engine & drivetrain parts:
We are usually looking to improve toughness, decrease breakage and increase wear. People quite often refer to surface pitting or flaking of a gear surface simply as wear. To us, it’s an indication of a metallurgical problem. How do we know if it is and what to do about it? We do that by cutting a small piece of failed part and analyzing it in our metallurgical lab before we do anything else. Our opinion on this is, without having a way to diagnose the problem, is like having a broken arm and going to a doctor that doesn’t have an x-ray machine.

Cold is a powerful tool. And like all tools there’s a right way and a wrong to use it. Used correctly, it can be used for a variety of problems. And, believe it or not, it can be very reliable and consistent.