4
The problem that many machining companies are having is that they can’t treat their steels very cost effectively. So many companies are finding out about Deep Cryogenic Treatment also known as DCT. This type of treatment cools the steel to –190 degrees Celsius, which enhances the steels mechanical properties much like heat treatment. The main difference between the two is that DCT is much more cost effective. So you are primarily getting the same type of results without the expensive costs.
The history behind cryogenic processing can be dated back probably 50 years to the occasional use of low temperature treatments in the hardening of steels. Over the past 40 years or so reports have been made of substantial benefits of treating steel at low temperatures. Usually the temperature was around that of liquid nitrogen, which is –196 degrees Celsius. Recently in the United States claims of improvement have been expanded to copper, high temp alloys, carbides, plastics, and nylon. (3,p.6)
DCT is used to enhance the mechanical properties of steel by increasing wear resistance, hardness, and dimensional stability. Many manufacturing companies waste millions of dollars each year on worn out steel tools. For example it is estimated that the Ford Motor Company tooling replacement costs is up around 230 million dollars yearly. So DCT is promises to increase tool life and the overall cost for the company and the end user. The problem with heat treatment is that when the steel is heated up to a phase called austenite and then quenched with oil or water it is usually not a 100% martensite because the steel must reach a much lower temperature then room temp to successfully transform. Another problem that is associated with heat treatment is the internal stresses and the dimensional instability. The DCT process cools the steel down to –196 degrees Celsius, this must not be done to fast or it will induce thermal shock into the steel. So to stay away from this problem rather then immerging the steel in liquid nitrogen people just put the steel in a freezer chamber that has liquid nitrogen floating in the atmosphere, then the material remains in this chamber for 24 hours. After the steel has been in the chamber for 24 hours it is slowly heated back up to room temperature and then conventionally tempered. After the DCT process has been completed it usually increases tool life by 200-600 percent by relieving internal stresses that is from retained austenite. Wear resistance is also increased because the cold temperatures squeeze the carbon atoms out; the new uniform microstructure formed reduces friction and in return reduces the heat involved with friction. Some people that use DCT are for example auto-racing teams use DCT on their engine parts because it increases the longevity of the engine. It is also used for gun barrels because the gun shoots much more accurately when the stresses are relieved. (4,p.6)
One main thing to remember is that DCT does not replace the standard heat treatment, it simply adds another step to the process of treatment of steels. DCT treatment does increase the life of your tools by 200-600% though. (4,p.6)
The effects of cryogenic treatment on other properties are that cryogenic treatment will not effect the hardness of a material such as dies, which have already been heat treated for high hardness. Which means that although cryogenic treatment of steels does prolong life of steels it will not change the properties that were gained during heat treatment. (2,p.5)
The main reason that steel is subjected to this low temperature treating is to refine the molecular structure, which creates a stronger and more durable product. This treatment basically changes the whole molecular structure of the material; this change lasts throughout the entire life of the part because it is not a surface treatment. Even after a number of sharpening the material will not lose strength, although the hardness is not effected by the treatment it will be stronger, more durable, and wear resistant. Cryogenic treatment also increases the tensile strength of the material, which increases the life of the tool. Another thing that cryogenic treatment does is that it takes the brittleness out of materials which makes them less apt to break if they happen to get dropped or hit wrong. This chart below which was done by Dr. Randall F. Barron shows the percent increase of wear resistance in these materials. (1,p.6)
AISI #D-2
52100
A-10
T-1
P-20
430
8620
AQS
S-7
0-1
M-1
CPM-10V
440
303
C-1020
T-2 / Description
High carbon/chromium die steel
Standard steel
Graphite tool steel
Tungsten high-speed tool steel
Mold Steel
Ferritic stainless
Nickel-chromium-moly alloy
Graphitic cast iron
Silicon tool steel
Oil hardening cold work die steel
Molybdenum high-speed steel
Alloy steel
Martensitic stainless
Austenitic stainless
Carbon steel
Tunggsten high-speed steel / % Increase
817 %
420 %
264 %
176 %
130 %
119 %
104 %
97 %
503 %
418 %
225 %
131 %
121 %
110 %
98 %
92 %
So after seeing all this data on cryogenic treatment of steels, I am convinced that it is a great way to extend the heat treatment process, and to increase the life of your tools. This type of treatment would save machine shops millions of dollars a year, all they would have to do is get there tools cryogenically treated. This is not to say that this type of treatment works every time, but as the chart shows that was done by Dr. Barron there was an increase in wear resistance in a variety of different metals. The best thing about this treatment is that it is very cost effective, you figure when you spend about 230 million a year on tools you are losing a lot of your profit. If you get them cryogenically treated it will increase the life of your tools while at the same time gaining you profit. This type of treatment is a huge jump for the machining industry it will save money on replacement costs of parts and make the life expectancy of these parts last longer.