M.T.& C. Engineers - Cryogenic Info Sheet

Metallurgical Testing & Consulting Engineers

Silverdale. NSW. 2752. Australia

(Near Warragamba Dam -Covering Sydney Metro)

Phone/Fax: (02) 4774 1017

Mobile (Stephen Hooker): 0419 498 115

INFO SHEET - CRYO TREATMENT

Metallurgical Testing and Consulting Engineers provide a non-destructive testing and advisory service to the high performance motor-racing industry. We also provide an in-house parts improvement capability including aerospace quality shot peening and cryogenic treatment. Our prompt and professional service ensures that our Customers can operate their business operations at a high level of confidence and reliability.

WHAT IS IT?

Cryo treatment of metal involves controlled cooling below 0° C in order to alter the material microstructure, and enhance its strength and wear properties. Hardened alloy steel parts are particularly responsive to this treatment, as are carburised gears and shafts. Aluminium alloys can also be stress relieved by a process known as "up-hill quenching" from sub-zero temperatures, without the loss of strength normally associated with high temperature stress relieving processes.

Most alloyed steels are rarely fully hardened during normal heat treatment processes, leaving microstructural areas of untransformed austenite (a soft, low strength phase). Cold treatment of steels involves the controlled cooling of the metal to below the 100% martensite (a hard, high strength phase) transformation temperature. After a critical dwell time at this temperature, the metal is reheated slowly to above room temperature for a stress relief treatment. Simply ... the material structure is "blue printed" or optimised to give a resultant structure that satisfies the metallurgical requirements of the alloy.

The whole cycle is customised by MT&C to each individual part on the basis of material, and part configuration. The opposition treat all parts to the same cycle, sometimes with dire consequences. I have a racing pinion that was cryogenically treated in Melbourne that failed quickly by brittle fracture . . . the structure revealed brittle phases that could be attributed to poor treatment practice. It is easy to see why cryo has achieved a reputation for creating brittle parts when the metallurgy of the part is not considered by the cryo treater!

Stress relief of aluminium alloys involves cycling the part below and above room temperature. No microstructural changes are involved in the process. Stress relief is important for parts subjected to cyclic loading (eg. conrods and pistons), or exposed to corrosive environments such as marine atmospheres.

WHAT ARE THE BENEFITS?

Depending on the alloy composition and the prior hardening cycles, the benefits are increased strength, greater dimensional stability or microstructural stability, improved wear resistance, and relief of residual stress. Hardened steels also have fewer tendencies to develop grinding cracks.

Tool steels and carburised gears exhibit improved wear resistance increases between 18% and 560%, depending on the prior hardening cycles.

Careful dressing, cryo treatment and shot peening of gears from a high performance drag racing motorcycle gearbox allowed for an increase in output capability of 200% without pitting or wear of the teeth. The reduction in heat associated with deformation of the gear teeth also resulted in power gains to the rear wheel. In another case cryo treatment and shot peening of a Group A Touring Car differential set allowed the differential to operate at up to 190 degrees C (cooling pump failure) for over 5 hours without evidence of metal flow on the teeth, or cracking. Cryo treatment has also been used successfully in Group A and Group N rally car gearboxes, to extend the life of factory gearbox components. Even the humble Volkswagen, Ozzie 4 speeds, Commodore, Lancer, Daihatsu and Mini gearbox's have benefited from careful grinding and cryo treatment, followed by shot peening. Our customer have high praise for our services, and refer their associates without reservation.

Cast iron disc brake rotors for race cars have responded well to cryo treatment, with customers reporting easier brake pad bedding periods, and an increase in life before cracking of the working surfaces. Our personal experience on the F1 roadracing sidecar and Jedi Formula Libre has also supported these benefits.

The Mazda rotary engine brigade have benefited from cryo treatment of all cast iron rotor seals. Experience has shown that the engines can be tuned to higher power outputs without premature failure of the otherwise brittle cast iron apex seals.

Valve train components that benefit from cryo treatment includes valves, lifters, rockers (especially those Cortina OHC), and retainers.

Uphill quenching of aluminium alloys can result in a reduction of residual stresses in the metal of between 25% and 83% depending on the alloy and the temper condition. The reduction of residual stresses in the material can increase the load bearing capacity of the part.

Contact Stephen Hooker on 0419 498 115 for your cryo treatment and shot peening requirements today. We can also pick-up and deliver in Western Sydney. (PS: it is all done in-house!)

WHAT WON'T IT DO?

I felt I had to add to this . . . negative feedback never comes back direct to us, and is usually spread quickly by hearsay. The cryo process is NOT a miracle cure-all (although other service providers may tell you otherwise) and will not correct the following conditions:

Case hardened steels with massive carbides or ferrite in the structure. These phases are a result of poor initial heat treatment, and result in a dramatic reduction in strength. If this is the condition of your part, then it is destined to fail anyway! In addition, to answer your next question . . . it cannot be readily determined if the part has these defects without partly destroying it.

Alloy steels that have been over-tempered (low hardness) cannot be improved without rehardening and tempering to the correct hardness. Metallurgical fact people! And, if the material is being loaded enough to break within a few load applications your part needs to be redesigned with a higher strength material and larger sections before you look at cryo. Cryo is an OPTIMISATION process that will improve fatigue life and wear properties, and produce smaller gains in bulk strength / hardness. And some mechanical sympathy would help . . . shock loads on any part will reduce its life dramatically . . . it may be wise to review how the loads are applied to the part if you expect it to live longer . . . cheap insurance really!

Materials that have been overheated or overloaded are also destined to fail, and the cryo process will not help them miraculously come back to life either. Bent or deformed parts are beyond stress relief . . . bin them!

If there is any doubt about the effectiveness of the treatment call Stephen. He regularly provides metallurgical backup support to customers to help them solve their material related problems.

The last words . . . there are a number of companies out there with no metallurgical knowledge, a tank of nitrogen and a one-process-does-everything attitude. They can actually do more harm than good to your parts, and I have a differential pinion with less than a race on it here to prove it. One of these companies made a pinion gear that normally lasts three endurance races hard and brittle . . . you have been warned!

This page last updated: 20/11/09