Steel is an alloy of iron and other elements, primarily carbon, that is widely used in construction and other applications because of its high tensile strength. Steel's base metal is iron, the element that rusts when in direct contact with oxygen. There are three ways to cope with this property: block direct contact with the air (e.g. by galvanising), replace a certain amount of iron with carbon (e.g. stainless steel), or use rust as a finish (e.g. weathering steel).
Steel may rust sooner or later, so try to keep surfaces clean and dry, and in any case do not leave metal objects outside on top of any other steel surface. A chemical reaction occurs that will affect the other surface. As soon as rust has been noticed, act immediately and accordingly, as rust accelerates rusting.