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Quenching is the most common method of hardening metals, which involves continuous cooling from a given austenite temperature to achieve full transformation into martensite structure to produce optimal mechanical properties. The quenching media contain base oil and different types of additives according to application requirements. The cooling rate mainly depends on thermal characteristics of metals, section thickness of workpieces and the quenching medium heat-removal properties. As the base oil, it is possible to use mineral oils, synthetic and natural oils separately or in combination. Mineral base oils are widely used because of their advantages in stability in comparison to natural oils, or lower prices in comparison to synthetic oils. There are numerous compounds available for use but, besides of functional properties, the environmental and safety requirements have a strong influence on the components selection. Based on that the barium additives must be replaced with less harmful compounds. Petroleum derivatives should be changed with renewable base stocks that are biodegradable, as general trend in lubricant development. By changing the composition of quenching oils, base oils or additives, heat transfer characteristics are also changed. In this study are presented the examination results of physical-chemical properties and also cooling characteristics of quenching oils formulations with different types of additives. Cooling curves of tested oils have been evaluated according to ISO 9950 standard. |
