Why bucket of stainless steel soup rusts not easily

Rust not easily, because it contains chromium,be. Chromic content is normally indispensible achieve 13~25% (weight is compared) , ability changes the condition that steel surface is oxidized. But stainless steel is not true won't rusty, if use microscope observation, its surface has fine really much smaller rust spot, look again carefully, these contain sulfur in fleck, and avoidable is not had in the process that the existence of sulfur element is production iron and steel. The thing that is not these sulfur atom to become vitriolic and so on in water so is brought about erode, make in stainless steel however, in cooling process, the chromic shift in iron and steel reachs certain place, the branch replaces the position of the manganese in vulcanization manganese, create the place then all around chromic content becomes low, and the content when chromium under 13% when, stainless steel can rust.