n Journal of Emerging Trends in Engineering and Applied Sciences - Development of martempered ductile iron by step-quenching method in warm water

Volume 3, Issue 3
  • ISSN : 2141-7016
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Martempering ductile iron (MDI) was produced through the use of salt-bath which is of high cost and non-users friendly because of the elevated temperature of the salt, high energy consumption during production, as well as the increased capital equipment cost for the bath and the equipment that operates it. This hinders the MDI production which becomes a big challenge and needs immediate urgent solution which is the rationale behinds this work. This research investigates the possible use of warm water for the interrupted or step quenching processes which is more users friendly and will minimize energy consumption that is associated with the use of salt-bath because of the elevated temperature of the salt as well as the increased capital equipment cost for the bath and the equipment that operates it. The evaluation of the suitability of warm water for interrupted quenching of ductile cast irons in the production of MDI was carried out. Ductile cast irons used were normalized at a temperature of 850 °C for 60 minutes. The normalized specimens were subsequently heat-treated in muffle furnace to a pre-determined temperature of 850 °C for 30 minutes, then step-quenched in warm water maintained at temperature of 80 °C for 40 seconds followed by tempering at different tempering temperatures (175 °C - 425 °C) and times (30-180 minutes). Hardness test was used to evaluate the mechanical property while the metallographic examinations that produced different microstructures were used to evaluate the transformation behavior. The results showed that the developed MDI has a high average hardness value of 53Rc at the lowest transformation temperature, and 19.6Rc at the highest transformation temperature. Metallographic analysis showed that untempered martensite was obtained at holding temperature below 250 °C, tempered martensite at 250 °C to 325 °C, tempered martensite at holding temperature of 350 °C for short holding times, above which the specimen is over-tempered (depending on the holding time). This showed that warm water is a suitable quenchant for the production of MDI.

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