Properties of carbon and alloy steels vary with their composition and microstructures, which are dependent on the heat treatment and quenching process used.
Typically, steel is heated to its austenitization temperature and then cooled sufficiently fast to avoid pearlite transformation and obtain maximum hardness and strength. The critical cooling rate is dependent on both the specific heat capacity and thermal conductivity of both the steel and the quenchant in addition to quench-bath temperature and agitation.
Among the most common quenchants used is water. However, petroleum-oil-derived quenchants are used when lower cooling rates and more uniform cooling is desired for better distortion control and crack prevention. In addition to being susceptible to global supply issues and price volatility, petroleum oil possesses a number of other significant disadvantages, including: poor biodegradability, toxicity and flammability. Therefore, it is of continuing interest to identify a viable alternative to petroleum oil as a basestock for quenchant formulation.
Currently, vegetable oils are one of the most commonly identified renewable, biodegradable and non-toxic basestocks. In addition to their relatively narrow viscosity range, vegetable oils exhibit considerably lower thermal-oxidative stability relative to petroleum oil, which has been a significant factor inhibiting its use in the industry.
This paper will provide an overview of the recent history of the use of vegetable oils as quenchants for steel. A brief comparison of the quenching performance exhibited by vegetable oils relative to petroleum oil will be illustrated. Also discussed is the effect of antioxidants on thermal-oxidative stabilization of soybean oil.