Cryogenic Treatment of Steel: Part One


Cryogenic treatment of materials has been present in the aerospace industry for over 30 years primarily to enhance the service life of the treated steel.
A number of key factors affect the success of sub-zero treatments including time, temperature profile and tempering practice but used in specific combinations can produce excellent results particularly for wear dependent materials such as tool steels.

The word cryogenics is derived from the Greek words Kryos (meaning cold), and Genes (meaning born). The Cryogenics Society of America defines cryogenic temperatures as temperatures below 120K (-244F, -153C). Generally speaking, cryogenic treatment is the process of submitting a material to subzero temperatures (below 0 °C) in order to enhance the service life through morphological changes that occurs during treatment.

Cryogenic processing, originally developed for aerospace applications, has been used for over 30 years to improve the properties of metals.

According to the laws of thermodynamics, there exists a limit to the lowest temperature that can be achieved, which is known as absolute zero. Molecules are in their lowest, but finite, energy state at absolute zero. Absolute zero is the zero of the absolute or thermodynamic temperature scale. It is equal to – 273.15 oC or –459.67 oF. In terms of the Kelvin scale the cryogenic region is often considered to be that below approximately 120 K (-153oC). The common permanent gases earlier change from gas to liquid at atmospheric pressure at the temperatures shown in Table 1, called the normal boiling point (NBP). Such liquids are known as cryogenic liquids or cryogens.

Table 1: Normal boiling points of common cryogenic fluids

Refrigeration of metals to improve performance is divided into two categories: cold treatment and cryogenic treatment. Common practice identifies -120 °F (-84 °C) as the optimum temperature for cold treatment at which parts are held (soaked) for 1 hour per inch of thickness, then subsequently warmed in ambient air. Typical cryogenic treatment consists of a slow cool-down of -5 °F per minute (-3°C per minute) from ambient to -320 °F (-196°C), a soak for 24 to 72 hours, and warm up to ambient temperature. The cryogenically treated parts are then subjected to a temper treatment (300 to 1000°F or 149 °C to 538 °C) for a minimum of one hour. Numerous factors impact how sub-zero treatments affect an alloy. Processing factors like time, temperature profile, number of repetitions and tempering practice, in conjunction with material parameters such as prior heat treatment and alloy composition will alter the final results. Table 2 discusses three sub-zero treatment applications. Sub-zero treatment falls into the broad categories of shrink fitting, cold treatment, and cryo-treatment. Figure 1 shows the differences in the basic processes as regards the time-temperature process cycle.

Table 2: An overview of sub-zero treatment processes for metals

Figure 1: Sub-zero process cycle profiles

Table 3 shows the average useful life of particular tooling pieces with and without the benefit of sub-zero treatment. A parameter called Wear Ratio, defined as the ratio of life after sub-zero treatment/ average tool life without sub-zero treatment, gives a measure of the amount of improvement this process can impart when applied correctly. Differences in wear life, shown in Table 3, between parts cold treated at about –80°C (–110°F), and parts cryogenically treated at –190°C (–310°F) using liquid nitrogen, raised questions about the causes of the improved wear resistance. However, the overall results from these studies could not be disputed and further research has been conducted to gain a better understanding of the underlying mechanisms.

Table 3: Examples of tool life improvements using cryotreatment

* Wear ratio = Life After Treatment / Life before treatment

In Table 4 is showed the comparison of the wear resistance of different materials after cold treatment and cryotreatment.

Table 4: Percentage increase in wear resistance after cold treatment and cryotreatment

기술 자료 검색

검색할 어구를 입력하십시오:

검색 범위



열처리 도표는 Total Materia 데이터베이스 내 많은 재질에서 검토하실 수 있습니다.

열처리 도표는 경화도, 경도 탬퍼링, TTT 및 CCT를 포함하며 모두 규격 데이터에서 검색하실 수 있습니다.

특수 속성 자료를 선택하려면, 고급 검색 모듈에서 특수 검색 기능을 사용하시면 됩니다.

검색 조건을 정의하려면, '국가/규격' 목록에서 귀하에게 관심 국가/규격을 선택하고 특별 검색 영역에 위치한 '열처리 도표' 박스를 체크하는 것입니다. 이는 고급 검색 페이지의 하단 부분에 있습니다.

검색 버튼을 클릭합니다.

관심 소재를 선택 후, 선택된 소재의 열처리 데이터 링크를 클릭하십시오. 열처리 기록의 개수는 링크 옆 괄호 안에 표시됩니다.

선택된 자료의 사용 가능한 모든 열처리 정보가 표시됩니다.

Total Materia 데이터베이스를 사용해 보실 수 있는 기회가 있습니다. 저희는 Total Materia 무료 체험을 통해 150,000명 이상의 사용자가 이용하고 있는 커뮤니티로 귀하를 초대합니다.