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Study of wear behaviour of ductile iron subjected to two step austempering An investigation was carried out to examine the influence of two step austempering on microstructural parameters and the wear behaviour of austempered ductile iron. Ductile iron was austenitised at 900 8C for 30 min, and then austempered successively at two different temperatures. It was first austempered at 300 8C for different durations from 2 min to 30 min and subsequently austempered at 400 8C for 2 h, after which it was quenched to room temperature. Resulting microstructures were characterised through optical microscopy and X-ray diffraction. Mechanical properties were studied through hardness measurement and tensile testing. Wear studies were carried out using a pin-on-disc machine. Wear rate was found to decrease with increasing time at the first step temperature of 300 8C. At short austempering times at 300 8C, the amount of austenite was instrumental in improving the wear resistance through formation of deformation induced martensite. Wear rate was found to depend on yield strength, austenite content and its carbon content.Keywords: Ductile iron; Austempering; Wear; Austenite IntroductionAustempered ductile iron (ADI) is an interesting engineering material because of its unique microstructure and excellent combination of high strength and ductility [1 -3]. While the microstructure of austempered steel consists of ferrite and carbide called as bainite, that of austempered ductile iron consists of ferrite and high carbon stabilised austenite. Austenite is present because of the presence of large amount of silicon in ductile iron which prevents the formation of carbide. This microstructure is generally called ausferrite to distinguish it from the bainite of steel. The ausferrite microstructure can be varied widely by varying the austempering temperature [4 -6]. When austempered at low temperatures in the range of 280 -320 8C, it exhibits very fine laths of ferrite interspersed with very thin layers of austenite. When austempered at higher temperatures, such as 350 -400 8C, the microstructure consists of coarse ferrite laths within bulky austenite. These microstructures are referred to as lower ausferrite and upper ausferrite respectively. While the former shows high strength and low ductility, the latter exhibits lower strength and higher ductility. Wear properties of ADI have been studied by several investigators [7 -10]. The ADIs austempered at low temperatures such as 300 8C show better wear resistance than those austempered at higher temperatures such as 400 8C because of the much higher hardness of the former. However, ADIs generally show better wear resistance than hardened and tempered steels of comparable hardness. This is due to the presence of substantial amounts of austenite. The austenite imparts improved wear resistance to ADI because of its better strain hardening ability.Recently Daber and Rao [11] as well as Daber, Ravishankar and Rao [12] have shown that interesting microstructures can be obtained through a two step ...

BACKGROUND The mechanical properties of polymers can be improved by electron beam irradiation. The aim of this study is to evaluate the mechanical properties of denture base resins after irradiation with electron beam with an energy dose of up to 25 KGy. METHODS In this study, four different denture base resins were used namely, DPI, Trevalon, Trevalon HI, and Meliodent heat cure acrylic resins. Mechanical properties of the denture base resins after exposure to electron beam post-curing were studied. The irradiated denture base resins are compared with untreated control groups. RESULTS Our study showed that PMMA-based denture resins improved the mechanical properties after irradiation with electron beam. As the radiation dose increases to 25 KGy, the polymeric structure starts to break down, and CC bonds are split off during electron beam irradiation. CONCLUSIONS Mechanical properties such as flexural strength, impact strength, and hardness of DPI heat cure acrylic resin, Trevalon, Trevalon HI, and Meliodent heat cure acrylic resins can be modified by the lower dosage of electron beam irradiation. Denture base resin is not only used for 'unbreakable' dentures but also to construct of skeletally designed heat cure dentures. This is possibly only with high strength polymers. So, research is continuing for higher strength denture base resin. By comparing the flexural strength and impact strength of all heat cure denture base resins (DPI heat cure acrylic resin, Trevalon, Trevalon HI, and Meliodent heat cure acrylic resins) after irradiation, with flexural strength and impact strength of all heat cure denture base resins before irradiation, it was observed that-irradiated heat cure denture base resins had more impact strength and flexural strength than unirradiated heat cure denture base resins. It was also found that on comparing the hardness of all heat cure denture base resins before and after exposure of radiation, radiated heat cure denture base resins were harder than unirradiated heat cure denture base resins.