Influence of deep cryogenic treatment on heat treatment of steel and Cu–Be alloy

Abstract

Deep cryogenic treatment (DCT) is claimed to be an efficient technique to improve the properties of steels and non ferrous alloys. A lot of benefits related to this treatment are reported in the scientific literature and probably even more in Internet. The process has a wide range of applications from industrial tooling to improvement of musical signal transmission. Some of the benefits of cryogenic treatment include longer part life, less failure due to cracking, improved thermal properties, better electrical properties including less electrical resistance, reduced coefficient of friction, less distortion, improved flatness and easier machining. Sometimes, the influence of subzero treatment could be directly ascribed to a specific metallurgical transformation. It is the case of the transformation of retained austenite into martensite, causing a general increase in hardness and higher wear resistance (but lower toughness). In other cases, however, the increase in wear resistance is not supported by a higher hardness and a lot of theories have been proposed to justify the observed results. To the author's best knowledge, the most reliable is the so called 'low temperature conditioning of martensite' occurring in steels during prolonged soaking in liquid nitrogen (–196°C), and affecting the precipitation of secondary carbides on tempering. However, poor experimental evidence has been reported in the literature for this phenomenon. The lack of published evidence is even more pronounced for non-ferrous alloys. It is the aim of the present paper to present and discuss some of the results collected at Trento University in the last few years. Specific attention is paid to the influence of subzero treatment carried out just after quenching in the conventional heat treatment cycle of three steels (1%C steel, X110CrMoV8 2 cold work and a X40CrMoV5 1 hot work tool steel.) and after solution treatment in a Cu–Be alloy.

Keywords:

• DEEP CRYOGENIC TREATMENT
• STEEL
• CU–BE
• PRECIPITATION HARDENING