英语时差：不锈钢为什么不生锈？（下）

The best way to avoid rust is to use stainless steel. Like all steel, stainless steel is mostly iron, but it also contains nickel and chromium. These are not just a protective coating, but are melted into the steel itself. The mixture must contain at least ten percent chromium, because it’s the chromium that protects stainless steel from corrosion. What happens is this: Like a sacrificial metal, the chromium rusts first. Unlike iron however, rusting chromium doesn’t crumble apart. Instead, it forms an invisibly thin layer that protects the iron underneath. The nickel in stainless steel helps hold this protective layer of chromium rust in place. Remember that chromium and nickel are present throughout stainless steel, not just on the surface. Because of this, the microscopic layer will form itself anew, even when the steel is cut or scratched.