ANS:B - machinability

Presence of a small quantity of sulfur in low carbon steel improves its machinability. Sulfur is added to low carbon steels as a machining aid. When sulfur is present in low concentrations (typically less than 0.1%), it forms manganese sulfide inclusions in the steel. These sulfide inclusions act as chip breakers during machining operations, which helps to improve the machinability of the steel. Improved machinability means that the steel can be more easily and efficiently machined with cutting tools, resulting in reduced tool wear, shorter machining times, and improved surface finish. This makes sulfur-containing low carbon steels particularly suitable for applications where extensive machining is required, such as in the production of automotive components, bolts, screws, and other machined parts. While sulfur can improve machinability, it may have adverse effects on other properties of the steel, such as its ductility and impact toughness. Therefore, the sulfur content needs to be carefully controlled to achieve the desired balance between machinability and other mechanical properties. So, the correct answer is: machinability.