Stainless Steel: Selecting a Grade

Stainless steel, a ferrous alloy, offers high strength and corrosion resistance along with manufacturing flexibility. Often used in pharmaceutical, chemical, industrial, and food applications, stainless steel is valued for its aesthetic, hygienic, and structural qualities.

In 1913, English metallurgist Harry Brearley added chromium to low carbon steel, creating a stain-resistant alloy with a high melting point. Today, stainless steel comes in over 150 different grades, each with varying amounts of chromium, nickel, and other metals.

These different stainless steel grades are classified into three major types based on their crystalline structure:

  • Ferritic stainless steel (400 series) contains 10-20% chromium and has superior corrosion resistance. When an application calls for a thin, lightweight material, this alloy is a good choice. It is less durable than austenitic grades and is available in annealed, pre-hardened and tempered types.
  • Martensitic stainless steel (400 series) contains 11.5-18% chromium and a higher level of carbon. Though not as corrosion resistant as ferritic and austenitic stainless steels, this alloy is extremely strong and highly machinable. It can be hardened by heat treatment.
  • Austenitic stainless steel (300 series) contains 16-30% chromium and 2-20% nickel. Excellent formability and corrosion resistance make this alloy the most popular choice in stainless steel applications. It is wear-resistant and has an excellent surface quality. It will lose its non-magnetic state as it is tempered.

Precipitation hardening (PH Grades) stainless steels combine the properties of both martensitic and austenitic grades, offering strength and corrosion resistance as well as exceptional formability.

  • 17/7-PH is a chromium-nickel-aluminum alloy with excellent fatigue properties. This PH stainless steel is a good option for applications which require heat resistance up to 600° F, and it is a popular choice for springs.
  • PH 15/7 Mo is ideal for applications requiring exceptional strength and corrosion resistance, which is why this alloy is often used for retaining rings and springs in oil field applications. PH 15/7 Mo has minimum distortion on heat treatment.

300 series stainless steels (austenitic) are alloys often used in food, chemical, and pharmaceutical applications. This series offers high corrosion resistance superior durability, and aesthetic appeal.

  • 301 stainless steel is a corrosion resistant alloy available in a variety of tempers. With less chromium and nickel than 302, it offers high strength and good ductility.
  • 302 stainless steel contains more nickel than 301, increasing its corrosion resistance. This alloy is often used when contamination prevention is critical. It has high strength, low weight, and excellent formability.
  • 304 stainless steel is a low carbon, high chromium alloy often used in the food, chemical, and pharmaceutical industries. It is best for soft temper applications, such as spinning and tubing. Considered the most versatile austenitic stainless steel, the widely popular 304 offers more heat and corrosion resistance than 301 and 302.
  • 305 stainless steel has an increased nickel content, making it an excellent choice for deep draw stamping. With its high formability, this alloy works well for cold forming operations.
  • 316 stainless steel works well in marine, pharmaceutical, and chemical applications which require resistance to salt and acids. It contains an addition of 2.0-3.0 % molybdenum, increasing its corrosion resistance. This alloy is durable and easy to fabricate.

400 series stainless steel (ferritic and martensitic)contains more carbon and less nickel than the 300 series. These magnetic alloys are used primarily for indoor applications where moisture exposure is minimal.

  • 410 stainless steel is available tempered or annealed. This general-purpose, pre-hardened alloy is the most commonly used of the martensitic stainless steels, offering good formability with excellent wear and corrosion resistance. It is often used in flat springs for medical and automotive applications.
  • 430 stainless steel is heat and corrosion resistant up to 1500°F. This high-chromium alloy contains little or no nickel. It is often the choice for chemical and oil refinery equipment and is found in interior decorative applications.

Contact Royal Coil’s experienced and knowledgeable staff today to discuss the best stainless steel for your retaining ring and spring applications.