These are alloy steels containing at least 10% chromium and offer much improved corrosion resistance over plain or alloy steels. Stainless steels will stain and corrode (slowly) in severe environ­ments such as seawater. Some stainless-steel alloys have improved resistance to high temperature. There are four types of stainless steel, called martensitic, ferritic, aus­tenitic, and precipitation hardening. The latter two types are commonly used in springs.

• 300 Series Stainless Steel
  
  Austenitic stainless steel is alloyed with 17 to 25% chromium and 10 to 20% nickel. It has better corrosion resistance due to the nickel, is nonmagnetic, and has excellent ductility and toughness. It cannot be hardened except by cold working. It is classed as 300 series stainless steel.

• Stainless Steel Type 301 
  
  Stainless Steel 301 is capable of attaining high tensile strength and ductility by cold working. It is not hardenable by heat treatment. Type 301 is essentially nonmagnetic in the annealed condition and becomes magnetic with cold deformation. 

• Stainless Steel Type 302
  
  Stainless Steel 302 is widely used because of its corrosion resistance and physical properties.
  SS 302 obtains its spring temper condition by cold working. Though it is categorized as being a nonmagnetic stainless, SS 302 becomes slightly magnetic as a result of cold working. It is not hardenable by heat treatment. SS 302 has a silver-gray color.

• Stainless Steel Type 316
  
  Stainless Steel 316 is nearly identical in physical properties and heat resistance to SS 302.
  SS 316 provides additional corrosion resistance, particularly against pitting, due to its molybdenum chemical content. SS 316 is generally used in food, chemical and sea water applications. SS 316 has lower magnetism than Type 302. This stainless grade is also not hardenable by heat treatment. Type 316 Stainless Steel has a silver-gray color.