What can a file test be used to determine about steel?

A file test is used primarily to assess the hardness of a material, particularly metals. When conducted on steel, the file is dragged across the surface, and the way the file interacts with the steel indicates its hardness. For instance, if the file scratches the surface easily, the material is relatively soft; if it does not, the steel is harder. Thus, the correct choice is about its hardness, not carbon content.

The carbon content of steel is typically determined through chemical analysis or specialized metallographic examination, rather than a simple mechanical test like a file test. Additionally, ductility refers to how easily a material can deform under tensile stress, which requires a tensile test, rather than a file test. Tensile strength indicates the maximum stress a material can withstand while being stretched or pulled before failing, which is also determined through a tensile test and not through the file test. Therefore, the file test is specifically related to assessing the hardness of steel.