ANS:A - cast iron

No cutting fluid is normally used while machining cast iron. Cast iron has inherent lubricating properties due to the presence of graphite flakes in its microstructure. These graphite flakes act as solid lubricants during machining, reducing friction between the cutting tool and the workpiece. As a result, cutting fluids are often not necessary when machining cast iron. Additionally, using cutting fluids may lead to issues such as built-up edge formation or reduced surface finish when machining cast iron. In contrast, materials such as aluminum, mild steel, and stainless steel are often machined with the use of cutting fluids to reduce friction, dissipate heat, and improve chip evacuation during the machining process.