Cryogenic treatment significantly enhances the service life of steel components through controlled exposure to extremely low temperatures. This methodology, established in aerospace applications over 30 years ago, produces remarkable improvements particularly for wear-dependent materials like tool steels. The success of cryogenic processing depends on precise control of critical parameters including temperature profile, treatment duration, and subsequent tempering practices. This article examines the fundamental principles of cryogenic treatment, compares cold treatment versus deep cryogenic processing, and provides evidence of substantial performance improvements in treated materials as demonstrated by increased wear resistance and extended service life.
The word "cryogenics" derives from the Greek words "Kryos" (meaning cold) and "Genes" (meaning born). According to the Cryogenics Society of America, cryogenic temperatures are defined as those below 120K (-244°F, -153°C). Cryogenic treatment refers to the process of subjecting materials to subzero temperatures (below 0°C) to enhance service life through beneficial morphological changes that occur during treatment.Originally developed for aerospace applications, cryogenic processing has been utilized for over 30 years to improve the properties of metals. This treatment has proven particularly valuable for extending tool life and enhancing wear resistance in various steel components.
According to thermodynamic laws, absolute zero represents the lowest theoretically achievable temperature, where molecules reach their minimum energy state. Absolute zero equals -273.15°C or -459.67°F, which forms the zero point of the Kelvin thermodynamic temperature scale. In practical terms, the cryogenic region is typically considered to be below approximately 120K (-153°C).Common gases transform from gaseous to liquid state at atmospheric pressure at specific temperatures known as normal boiling points (NBP), as shown in Table 1. The resulting liquids are called cryogenic liquids or cryogens.
Table 1: Normal boiling points of common cryogenic fluids
Metal refrigeration treatments fall into two distinct categories: cold treatment and cryogenic treatment. These processes differ significantly in their application parameters and results:
Multiple factors impact how sub-zero treatments affect an alloy. Processing parameters such as time, temperature profile, number of repetitions, and tempering practice interact with material factors including prior heat treatment and alloy composition to determine final results. Table 2 outlines three different sub-zero treatment applications.
Table 2: An overview of sub-zero treatment processes for metals
Figure 1 below illustrates the significant differences in time-temperature cycles among these processes.
Figure 1: Sub-zero process cycle profiles
Table 3 demonstrates the average useful life of various tooling components with and without sub-zero treatment. The "Wear Ratio" parameter—defined as the ratio of life after sub-zero treatment divided by average tool life without treatment—quantifies the improvement this process delivers when correctly applied.
Table 3: Examples of tool life improvements using cryotreatment
The substantial differences in wear life between parts cold treated at approximately -80°C (-110°F) versus parts cryogenically treated at -190°C (-310°F) using liquid nitrogen have prompted further research into understanding the underlying mechanisms of improved wear resistance.Table 4 below provides a comparison of wear resistance improvements in different materials after cold treatment versus cryogenic treatment.
Table 4: Percentage increase in wear resistance after cold treatment and cryotreatment
Total Materia Horizon contém detalhes de tratamento térmico para centenas de milhares de materiais, diagramas de temperabilidade, têmpera de dureza, diagramas TTT e CCT e muito mais.
Obtenha uma conta de teste GRATUITA na Total Materia Horizon e junte-se a uma comunidade de mais de 500.000 usuários de mais de 120 países.