Question

what is stainless steel ? what is its composition

Answer 1

Stainless steel chemical composition is vary and depend on a steel grade, but the main property that differ it from carbon steel is that stainless steel has a minimum of 10.5% Chromium content by mass, and can contain Nickel up to 28% by mass. High content of Chrome and Nickel is the main sign of a stainless steel.

Answer 2

the steel having a thin layer of oxide to prevent it from rusting

The three major classes of stainless steel are: Austenitic: Chromium-nickel-iron alloys with 16-26% chromium, 6-22% nickel (Ni), and low carbon content, with non-magnetic properties (if annealed - working it at low temperatures, then heated and cooled). Nickel increases corrosion resistance.