Abstract
The influence of austempering holding time on the mechanical properties and microstructures of high carbon (AISI 1070) steel using epoxidized transesterified cotton seed oil (ETO) as quenchant has been studied. Initially, steel samples were austenitized at 850°C for 1 hour, then quenched interruptedly in an oil bath maintained at 280°C at different holding times from 15-75 minutes at regular interval of 15 minutes. Subsequently, the samples were removed and air cooled to room temperature. Mechanical properties test and microstructural examination were carried out. Obviously, except at 75 minutes austempering period; the results revealed significant enhancement in tensile strength (1580 MPa) at long holding time. Additionally, higher improvement in hardness value (430 HBN) and impact strength (12.7 J/mm) at short time was noticed. In the SEM (scanning electron microscope) images, bainitic structure (acicular), retained austenite and martensite were observed. Accordingly, 15 minutes austempering condition produced austempered high carbon steel (HCS) with the best mechanical properties.
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