Now a day’s many industries have interest to develop lightweight material to reduce weight of existing material without negotiating their mechanical properties. In the automotive industries, attempts have been made to replace cast iron, steel and aluminium components with austempered ductile iron. ADI is basically nodular or ductile cast iron which is subjected to heat treatments called austempering, as it has access to achieve desire mechanical properties by changing treatment parameters.
Machining of ADI conducted prior to heat treatment, offers no significant difficulty. Machining post heat treatment is demanding due to maintaining tight tolerances and requirement of better surface finish.
This often avoided because of phase transformation (SIT) of retained austenite to martensite, this phenomenon making hurdle for the further applications of ADI. It has been found that, mechanical and metallurgical properties of ADI component depends on initial microstructure of ductile iron, selected austempering parameters, media for quench, section size of component and addition of alloying elements. Austempering offer an access to achieve desired mechanical properties by selecting proper heat treatment cycle. Over the years, the temperature of 350 °C acting as a threshold for various mechanical properties of ADI. Selection of proper austempering parameters is the key part to achieve desire mechanical properties. Austenitizing temperature play vital role for the control of carbon content of austenite, this affects structure and properties of austempered casting. It has been found that, the austempering temperature range 350- 400 °C will give an ADI with lower strength and hardness but higher elongation and fracture toughness (coarse ausferrite matrix). While, below 350°C will produce an ADI with higher strength and greater wear resistance. To achieve the optimum mechanical properties, in present work ADI rods austenitised at 850 °C for 2 hr soaking period and austempered at 350°C for 1 hr soaking period. According to Polishetty, high rate of plastic deformation and generation of high heat or combination of both are responsible for strain induced transformation while machining ADI. It is expected to machine ADI before the formation of martensite, by using ultra hard cutting tools at low cutting speed with high penetration (feed rates); or to use different machining approaches to minimize or completely eliminate the formation of martensite, by avoiding strain induced transformation.
Analysis of variance (ANOVA) shows depth of cut is important parameter for main cutting force followed by feed rate. Increased depth of cut and feed generated higher cutting forces due to increased shear area.
Main cutting force has been found to vary from 52.87 N to 264.6 N. The R-squared value for main cutting force has found to be 0.9590. 2. Cutting speed and feed play vital role for surface roughness, ANOVA shows cutting speed has greater influence on values of surface roughness. Greater cutting speed and lower feed exhibited superior surface finish, due to the elimination of built up edge at higher cutting speed. The R-squared value for Ra was found to be 0.9288. 3. At lower depth of cut hardness of the surface increased than bulk hardness, this indicates occurrence of SIT. At higher depth of cut tool avoid facing newly formed surface, causing relatively low hardness.