The biggest misconceptions about cryogenic processing are that it can change the size of parts and lead to brittle components. Those misconceptions can be a stumbling block for people who are undecided about the viability of cryogenic processing, and a lot of people choose to err on the side of caution.
In the early days of cryogenic processing, back in the 1960s and 1970s, the parts to be treated came in direct contact with the liquid nitrogen, and yes, some parts became brittle in the process. In modern cryogenic processing, there is no direct contact between the liquid nitrogen and the parts being treated. Modern machines use a heat-exchanger system to freeze the parts.
“Cryogenic processing is known to increase wear resistance,” said Rick Diekman with Controlled Thermal Processing in Antioch, Ill. “It delays failure of parts due to fatigue, and 90 percent of mechanical failures are due to fatigue. This patented process, because we’re gently cooling the part, it keeps us from overstressing the part due to temperature changes.”
Inside the heat exchanger, the temperatures drop to as low as 300 degrees Fahrenheit below zero when using liquid nitrogen, Diekman said. He added that Controlled Thermal Processing also has begun working with liquid helium, which can go as low as 450 degrees Fahrenheit below zero.
Cryogenic processing improves component life and performance by relieving internal stresses in the material. The National Aeronautics and Space Administration has tested and used the process, so yes, there is a little bit of rocket science to it. In addition, NASCAR, the National Hot Rod Association, IndyCar and other motorsports have used it with measurable success.
In addition to increasing wear resistance, cryogenic processing stabilizes the dimensions of parts. For example, when you put a piston inside an engine and run it for a while, it expands. If you cryogenically treat it, it will change size much less, which gives engine builders a greater measure of control over clearances.
“Another benefit is that the parts are easier to machine to final size,” Diekman said, adding that the heat treating of any part to be cryogenically processed must be done correctly, or brittleness can result. “For instance, the engine blocks machine and hone much better after cryogenic treatment. And again, we’re stabilizing engine blocks so they don’t twist in use.”
Here is how heat treating and cryogenic processing work together to create stronger parts. In heat treating, the metal is heated until the metal forms a particular crystal structure called austenite. When cooled quickly, that turns into a crystal structure called martensite, which is the preferred hard crystal structure in metals. If poorly done, heat treating will not convert all of the austenite. That’s when the treated parts can change size in the cryogenic chamber, but it stems from poor heat treating, not cryogenics.
“The martensitic structure is about 4 percent bigger than the austenitic structure so you end up with a size change,” Diekman said, adding that metals get their metallic properties because they are crystalline in structure, not molecular. “If we end up with a size change on a customer’s part, we’ve just saved him a tremendous amount of money, because basically what would have happened in use is a vibration, and heat of use in a racing engine or transmission or racing component would cause the austenite to change to martensite, but it would be primary martensite, and it would be brittle.”
Clear as pudding, right? Here is a less-complicated example. Diekman said Controlled Thermal Processing worked with Erik Darnell, who used to race the No. 99 Roush truck in the Craftsman Truck series. Before he went to Roush, Diekman said the company cryogenically treated everything it could on his racecar. The result was that the cryogenic processing, although an added expense up front, actually saved money over the season because the parts lasted longer. Diekman explained:
“A good example of what we’ve done for him is that his team would put a set of treated valve springs in at the beginning of a racing season, leave them there for the entire season. They’d check them every race. They used them the entire season,” he said. “His competition put in a new set of valve springs either every race or every other race at $400 a set. Contrast that with $48 to treat the springs and $400 to replace them, it makes a lot of sense.
“I have a lot of people who tell me, ‘We can’t afford that,’” said Diekman. “But I’m getting three and four times the life on engines, transmissions, valve springs, and they really don’t understand that’s cheaper to cryogenically treat it and use it longer.”
Anyone familiar with racing knows the demands placed on valve springs. Cryogenic processing also is used extensively on gears and shafts, even metals that flex in competition — and it could mean the difference between limping back the pits and a podium finish.
“In road racing, where they’re getting two and three races out of a transmission, and we can make it six, that’s something that’s really interesting to people,” Diekman said. “It should amount to big savings in effect. And, because the parts are more reliable, they have a better chance of finishing a race.”
For shops, cryogenic processing makes parts easier to machine, which means cutting tools and bits don’t wear as quickly. Also, if you can sneak some of your machining tools and bits into a batch to be cryogenically treated, they too will benefit from the process.
It’s important to point out that cryogenic processing is not a hardening procedure. It will vary the hardness of the part only by about one Rockwell C point, a standard scale used in metallurgy. It works on lots of different types of metals, including steel, cast iron and aluminum. It also can be used to increase the service life on components in your tow vehicle, chief among them brake rotors, which last three to four times longer than stock when treated. It’s easier on the pads, too.
“For the racing teams, I cannot see why anybody would not use this process,” Diekman said. “It’s going to reduce the cost. It’s going to give you the reliability.”