Abstract
Sub-zero treatment of tool steels is included within the cycle of conventional heat treatment. This kind of heat treatment has been reported to improve wear resistance of tools. The improvement is attributed to precipitation of fine carbide particles, but is depending on a number of the other factors as well. This paper follows the previous works, in which the effect of sub-zero treatment on the mechanical and structural properties of P/M tool steels was evaluated. Two types of P/M cold work tool steels were used in the research: Vanadis 6 and high speed steel Vanadis 30. They were austenitized, nitrogen gas quenched and tempered. The 4 hours long sub-zero period of dwell at -196°C was also incorporated between quenching and tempering. Wear evaluation was carried out using a pin-on-disk method. The observed values of wear resistance have been collated with the values of hardness and the bending strength. The results of the work are supplemented by a detailed analysis of the carbide particles of both monitored conditions.
Highlights
IntroductionSub-zero treatment ( referred to as cryogenic treatment) is a way of treatment at low temperatures (lower than -80°C) added to the Conventional Heat Treatment (CHT)
Sub-zero treatment is a way of treatment at low temperatures added to the Conventional Heat Treatment (CHT)
Three point bending strength of Vanadis 30 steel after Deep Cryogenic Treatment (DCT) remains almost unchanged within the standard deviation
Summary
Sub-zero treatment ( referred to as cryogenic treatment) is a way of treatment at low temperatures (lower than -80°C) added to the Conventional Heat Treatment (CHT). The fact that the presence of high alloying elements content decreases the temperature of martensitic transformation start and finish, thereby increasing the fraction of retained austenite in the structure after hardening, is known To reduce this undesirable amount of the retained austenite, the cryogenic treatment can be used. The authors of summary articles [1,2,3,4] and our own work [5,6] published in 2005-2015 addressing this issue agree on a finding that cryogenic processing of tool steels causes precipitation of very fine carbides in the structure Superposition of both effects leads to a change of properties such as hardness, toughness, wear resistance and dimensional stability
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