Oxidation of vegetable oils and its impact on quenching performance

Traditionally, mineral oils have been one of the most important quenchants used. However, their substantial deficiencies with respect to environment friendliness and toxicity as well as long-term, low-cost supply necessitate the search for alternative replacement media. Quenching performance of petroleum oils is limited by the oxidative degradation properties, which are composition dependent. Upon repeated exposure to the relatively high interfacial temperatures between the steel surface and the oil, petroleum oils undergo thermal and oxidative degradation leading to significant variation in their quenching performance. Therefore, this is a particularly important performance parameter that must be examined for any alternative quenching medium. One class of alternative fluids is vegetable oils, which are typically biodegradable and non-toxic. However, vegetable oils typically exhibit relatively poor oxidative stability properties, and therefore it is important to determine the potential impact of oxidation on quenching performance. The results reported here are the first step in a larger study. In this work, uninhibited vegetable oils were studied using a laboratory apparatus and procedure previously reported to promote premature oxidation of petroleum oils to approximate actual use conditions. Experimental fluids are examined and compared to typical petroleum quench oil compositions using viscosity, infrared spectroscopy, 13 CMR spectroscopy and cooling curve performance according to ASTM D 6200. The results obtained indicate that vegetable oils are promising alternatives to petroleum oils as quenchants but that to be commercially feasible, appropriate antioxidants must be used.