Abstract
This article is a response to the state of the art in monitoring the cooling capacity of quenching oils in industrial practice. Very often, a hardening shop requires a report with data on the cooling process for a particular quenching oil. However, the interpretation of the data can be rather difficult. The main goal of our work was to compare various criteria used for evaluating quenching oils. Those of which prove essential for operation in tempering plants would then be introduced into practice. Furthermore, the article describes monitoring the changes in the properties of a quenching oil used in a hardening shop, the effects of quenching oil temperature on its cooling capacity and the impact of the water content on certain cooling parameters of selected oils. Cooling curves were measured (including cooling rates and the time to reach relevant temperatures) according to ISO 9950. The hardening power of the oil and the area below the cooling rate curve as a function of temperature (amount of heat removed in the nose region of the Continuous cooling transformation - CCT curve) were calculated. V-values based on the work of Tamura, reflecting the steel type and its CCT curve, were calculated as well. All the data were compared against the hardness and microstructure on a section through a cylinder made of EN C35 steel cooled in the particular oil. Based on the results, criteria are recommended for assessing the suitability of a quenching oil for a specific steel grade and product size. The quenching oils used in the experiment were Houghto Quench C120, Paramo TK 22, Paramo TK 46, CS Noro MO 46 and Durixol W72.
Highlights
The choice of hardness was motivated by the need to quantify the hardening power of oil, which is relevant to industrial practice
One drawback of EN 42CrMo4 steel is the fact that the hardening power (HP) criterion is calculated for carbon steels, and the values would require correction
The most relevant criterion for the hardening power of an oil is the area under the cooling curve, which characterizes its ability to remove heat from a part
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. This paper responds to the state-of-the-art practice in monitoring the cooling efficiency of quenching oils in industrial practice. Hardening shops only request a quenching process report for a quenching oil. It is rather complicated to interpret the values appropriately. This paper compares various criteria for assessing quenching oils and reviews their relevance to appropriate oil selection. The criteria were compared on the basis of core hardness in an EN C35E steel product. Chemical composition of the steels is on Table 1
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