Stainless steel Also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5[1] or 11% chromium content by mass.[2] Stainless steel does not stain, corrode, or rust as easily as ordinary steel, but it is not stain-proof.[3] It is also called corrosion-resistant steel or CRES when the alloy type and grade are not detailed, particularly in the aviation industry. There are different grades and surface finishes of stainless steel to suit the environment to which the material will be subjected in its lifetime. Stainless steel is used where both the properties of steel and resistance to corrosion are required. For more information about the topic Stainless steel, read the full article at Wikipedia.org
There are about 50 stainless steel grades recognized by the American Iron and Steel Institute (AISI) .Three general classification used by AISI to identify steel are:

• metallurgical structure  
• the AISI numeric system(200,300,400 series numbers)
• the unified numeric system developed by American Society for Testing Materials(ASTM) and the Society of Automotive Engineers(SAE) to apply to all commercial metals and alloys.