Quotes From Cryogenic Research

We are often told that cryogenic processing is bogus because there is no research to support it. Here are some quotes from research papers from a variety of sources. The headlines are ours, the quotes are from the research with minor clarifications where needed. We've quoted our sources so you can look these up yourself to assure the accuracy and read the papers. We strongly urge you to read the papers to gain a complete understanding of how these conclusions came about and their precise meaning.

1. 50 % Tooling Cost Reduction

The deep cryogenic treatment (-196 degrees C) of quenched and tempered high speed steel tools improves their properties, in particular, it increases the hardness and improves the hardness homogeneity reduces the tool consumption and the down time for the equipment's set up, thus leading to about 50% cost reduction. ...While in the AISI M2 steel the increase can be attributed to the increased hardness, in the case of AISI H13 steel the increased wear resistance can be correlated to the increased toughness.
EFFECT OF DEEP CRYOGENIC TREATMENT ON THE MECHANICAL PROPERTIES OF TOOL STEELS, A. Molinan, M. Pellizzari, S. Gialanella, G. Straffelini, K.H. Stiasny. Journal of Materials Technology 118 (2001), Pages 350-355. The above named researchers are with University of Trento, Trento Italy, and/or GKN Birfield AG. GKN is a world wide manufacturer of automotive drive line parts for OEM and replacement markets.

2. Martensite Changed by Cryo

Our recent research results have proved that the martensite formed in prior heat treatment is further changed during the cryogenic treatment.
"Cryogenic Treatment: The History, The Hype, and The Science", Yuntian Theodore Zhu, Los Alamos National Laboratory, Lecture at Illinois Institute of Technology, June 4, 2001

3. Reduced Residual Stress in Aluminum

The following results were observed for this particular Al(aluminum) alloy after cryogenic treatment:

       1. Residual Stress was reduced by up to 12 ksi in the HAZ of weld specimens and by up to 9 ksi in    the parent metal.
       2. Significant improvements in SCC (stress corrosion cracking) performance were seen for weld specimens.
       3. Minor increases in tensile strength and hardness were noted for the parent metal.
EFFETCS OF CRYOGENIC TREATMENT ON THE RESIDUAL STRESS AND MECHANICAL PROPERTIES OF AN AEROSPACE ALUMINUM ALLOY, Po Chen, Tina Malone, Robert Bond, Pablo Torres: NASA and IIT Research Institute, George C. Marschall Space Flight Center.

4. Increased Fine Carbides, Increase Wear Resistance, Increased Toughness

The effects of this deep cryogenic treatment mechanism are:
A much greater number of fine carbide particals in the microstructure.
A different partition of alloying elements between matrix and carbides, compared with conventionally treated steels.
An improvement in wear resistance of the steel.
An increase in toughness
Little or no increase in hardness.
CRYOGENIC TREATMENT OF TOOL STEELS, David N. Collins, National Heat Treatment Centre, University College, Dublin Ireland; Advanced Materials & Processes, December 1998, H23 to H29.

5. Micro Cracks Eliminated, Carbides Modified

        1. There is distinctive change in the microstructure of AISI T42 High speed steel during Deep Subzero treatment.
             2. The change takes place during the warming up of the steel between 8 and 16 hrs of DSZ
             3. There is change in the morphology of carbides. This change contributes towards ‘rounding off’ of the irregularly shaped carbides at corners and edges in to regular round shape.
             4. The phenomenon of merging / migration / dissolution of finer globular carbides takes place during the process leading to uniform distribution in the matrix.
             5. The micro cracks present due to earlier processing are eliminated completely in the process.
             6. The stress generated dislocations at the interface of the particles and the matrix causes diffusion, which is driven by the concentration gradient.
             7. The soaking time more than 8 and 16 hrs leads excessive contraction of the matrix thereby preventing any diffusion phenomenon.
             8. With the aforesaid changes taking place during the DSZ process, there is improvement in the tool life, which has been experienced by number of researchers.
DEEP SUB ZERO PROCESSING OF METALS AND ALLOYS – PART II EVOLUTION OF MICROSTRUCTURE OF AISI T42 TOOL STEEL, C.L.Gogte1   , Kumar M. Iyer 2,    R.K.Paretkar1, D.R.Peshwe1
1. Department of Metallurgical and Materials Engineering, VNIT, Nagpur, Maharashtra, India.
2. Assab Sripad Steels Ltd., Chennai, India

6. Modification of Carbide Population

In summary, cryogenic treatment cannot only facilitate the carbide formation and increase the carbide population and volume fraction in the matensite matrix, but can also make the carbide distribution more homogeneous. Our results are consistent with previous studies that show increases in carbide density and volume fraction, which may be responsible for the improvement in wear resistance.
Microstructure of cryogenic treated M2 tool steel. J. Y. Huang, Y. T. Zhu, X. Z. Liao, I. J. Beyerlein, M. A. Bourke, T. E. Mitchell: Materials Science and Technlogy Division, Los Alamos National Laboratory, MS G 755, Los Alamos, NM 87545. Publishe in Materials Science and Engineering A339 (2003) pages 241-244

7. Copper Welding Electrodes Last Longer

Cryogenic treatment of copper welding resistance electrodes increases their life by a factor 2 to 9 . Both durability and conductivity were increased although the mechanisms behind the improvement are being further researched. Metallurgists suspect that stress relaxation through recrystallization is responsible for the property improvement.
Sub-zero Treatment of Steels Technology/Processes/Equipment, Linde AG | Linde Gas Division | 82049 Höllriegelskreuth | Germany

8. Cryogenic Treatment and Combination of Nitriding and Cryogenic Treatment of Hot Forging Tools

Conclusions
1. Cryogenic treatment is a process which, compared to steel being quenched and tempered, significantly increases the wear resistance of hot work alloy tool steel. This is confirmed by tribologic tests carried out at elevated temperatures. The achieved growth of the wear resistance depends on the steel grade and on the soaking time of the processed part at the temperature close to that of liquid nitrogen.

2. Due to dilatometric and differential thermal analyses it was possible to state that the reason for a tool steel wear resistance growth are precipitation phenomena taking place during tempering following cryogenic treatment, as at this processing stage a significant amount of very fine and uniformly distributed carbides precipitates; carbides which during work of a tool spall with more difficulty and increase its friction wear resistance under overloads.

3. The phenomenon of significant growth of both the surface hardness and of the depth of internal nitriding and of the hardness measured on the cross-section of nitrated layers achieved for tool steel, which has been subject before to long-term cryogenic treatment, was observed.

4. Comparative research under production conditions of forging dies subjected to toughening and cryogenic treatment and to the combined process of nitriding and cryogenic treatment have demonstrated a wear resistance growth by 20 to 40% as compared to the heat treatment of dies so far applied by manufacturers.

5. In order to better understand the structural transformation taking place inside the internal nitriding zone, the problem of the hardness growth of nitrided layers achieved by combining this treatment with cryogenic treatment must be further researched into.

Cryogenic Treatment and Combination of Nitriding and Cryogenic Treatment of Hot Forging Tools, ZBIGNIEW ŁATAŚ, ALEKSANDER CISKI, Heat Treatment Centre, Institute of Precision Mechanics
Duchnicka 3 Str., 01-796 Warsaw, POLAND;PAVEL ŠUCHMANN COMTES FHT s.r.o. Lobezska E981, 326 00 Plzen CZECH REPUBLIC, psuchmann@comtesfht.cz http://www.coc@imp.edu.pl
Proceedings of the 4th WSEAS Int. Conf. on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT, Elounda, Greece, August 21-23, 2006 (pp133-139)

9. Cryogenic processing of thin metal films

Cryogenic processing has been proven to be efficient in increasing Schottky contact barrier height, and significantly reducing device reverse leakage current. ....... Ag/InGaAs/InP contacts fabricated by a low temperature (LT) processing the Schottky barrier height was found to be as high as 0.64 eV.

L. He and J. E. Siewenie, San Jose State University, Department of Electrical Engineering, San Jose, CA, USA and Northern Illinois University, Department of Electrical Engineering, DeKalb, IL, USA , Surface and Coatings Technology, Volume 150, Issue 1, 1 February 2002, Pages 76-79

(i) All types of sub-zero treatments appreciably improve the wear resistance of the die steels compared to the conventional treated (CONT) ones. However, the improvement in wear resistance
by shallow (SCT) and deep cryogenic treatment (DCT) is significantly higher than that achieved by CT, and the maximum improvement is obtained by DCT. This is attributed to the decrease in the retained austenite content associated with the increasing amount of secondary carbide particles with lowering of temperature of the sub-zero treatments.

(ii) The obtained hardness of AISI D2 steel for CONT and DCT are 759 and 791 VHN, respectively and typical values of their specific wear rates (WS) are 1.03×10−6 and 8.26×10−9mm3 N−1mm−1, respectively, at sliding velocity (SV) of 1.25ms−1.

(iii) Estimation of WS and detailed characterization of worn surfaces, generated debris and subsurfaces of all types of specimens assist to reveal that the severe mode ofwear is associated
with the deformation induced delaminative wear mechanism, whereas the mild mode of wear is associated with the predominantly oxidative wear mechanism coupled with occasional cracking and pull-out of primary carbide particles.

(iv) The modes and mechanisms of wear are synergistically affected by the temperature of sub-zero treatments and the SV of wear tests at a constant normal load. The mild-to-severe wear transition occurs at SV =0.75ms−1 for CONT specimen and at SV =1.00ms−1 for CT specimen, and at SV =1.25ms−1 for both SCT and DCT specimens.

(v) The obtained results unambiguously lead to infer that lower the temperature of sub-zero treatment higher is the improvement in wear resistance. However, the degree of improvement is dependent on the SV of wear tests and/or the temperature of sub-zero treatment, which govern the operative modes and mechanisms of wear.

Influence of temperature of sub-zero treatments on the wear behaviour of die steel
D. Dasa, K.K. Rayb, A.K. Duttac, a Department of Metallurgy and Materials Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711103, India
b Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur 721302, India
c Department of Mechanical Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711103, India∗25 November 2008 WEAR JOURNAL Elsevier B.V.

From this extensive study conducted on the effects of cryogenic treatment and its mechanism on cemented tungsten carbide cutting tools, several findings were made, as listed below:
1) Analysis of the microstructure of cemented tungsten carbide shows that cryogenic treatment significantly alters the microstructure of tungsten carbide, causing the β-phase particles to increase in size and quantity, while the η-phase and γ-phase show a corresponding decrease. The increase in the amount of the binder phase is also supported by evidence of the decrease in thermal conductivity of the cryogenically treated tool as compared to the untreated tool.
2) Cryogenic treatment increases the hardness of the tungsten carbide tools. In this study, the hardness of the tools increased by an average of 7%.
3) Cemented tungsten carbide tools subjected to cryogenic treatment show a decrease in their thermal conductivity. This decrease in thermal conductivity strongly suggests an increase in the binder phase of the tool material.
4) Cryogenically treated tungsten carbide tools in continuous cutting operations show a marked decrease in tool wear during the initial duration of cutting as compared to untreated tools. However as time progresses, the wear resistance of the treated tools decrease, and the flank wear of these tools approach that of, or even exceed, those of the untreated tool inserts.
5) The observation mentioned in the previous point can be avoided if the tools are used to cut for short durations of time, instead of being subjected to a prolonged cutting operation. This suggests that if the tool is allowed to cool such that a certain temperature, know as the threshold temperature, is not reached, the cryogenically treated tool retains its superior wear resistance over the untreated tool. It is also shown that the shorter the duration of cut, the better the wear resistance of the cryogenically treated tool as well.
6) Cryogenically treated tungsten carbide tools perform well in intermittent cutting operations, such as milling operations, as the tool edge does not continuously cut the workpiece. The time when the tool is not performing a cut allows it to cool to a certain extent, such that the temperature at the cutting edge does not reach the threshold temperature too quickly. It is also shown that the application of coolant helps to further increase the wear resistance of the cryogenically treated tool insert, even more so than the untreated tool insert.

7) Cryogenically treated tungsten carbide tools have a certain threshold temperature. This temperature, if exceeded during cutting operations, will cause the tool insert to undergo a morphological change in the microstructure, which causes it to lose the superior wear resistance imparted by cryogenic treatment. This suggests that the state of the microstructure that was created by cryogenic treatment is a metastable one, which is lost when the threshold temperature is reached. This phenomenon is not present in cryogenically treated tool steels. Microstructural analysis of the cryogenically treated and untreated inserts which have been subjected to a controlled heating in a furnace puts the threshold temperature to be within the range of 285°C to 600°C. Turning experiments using a thermocouple measuring the temperature at the bottom of the tool insert estimates the threshold temperature for the tools in this study to be 400°C.
8) Cryogenically treated tungsten carbide tools have their improved wear resistance limited at higher cutting speeds by the threshold temperature, and at lower cutting speeds by lowered resistance to attrition wear.