What are the stainless steel grades and how to choose stainless steel grades?

The main requirement for stainless steels is that they should be corrosion resistant in a specific application or environment. Strength and manufacturing characteristics are also taken into account. There are more than 60 grades of stainless steel.
Stainless steel can be divided into four major metallurgical categories. Other mechanical or physical characteristics need to be considered when determining options to achieve overall service performance requirements.

Grades and applications of stainless steel pipes
1: 300 series austenitic – typical grades are T304 and T316
Chromium (17-25%), Nickel (8-25%); non-magnetic, not heat treatable. It can produce high-strength materials by cold working. Addition of molybdenum (up to 7%) improves corrosion resistance. Series 300 resists corrosion and retains its strength at high temperatures, and is easy to maintain. Type 316 contains slightly more nickel and 2-3% molybdenum than Type 304, making it more resistant to corrosion.
Typical uses: Surgical applications, food and beverage equipment, wastewater equipment, chemical equipment, construction applications.

2: 400 Series Martensite - Typical Grade: 410
Pure chromium (12-18%); magnetic, hardenable by heat treatment. Type 410 resists corrosion in mild atmospheric, steam and mild chemical environments.
Typical uses: Fasteners, machine parts, pump shafts.

3: 400 Series Ferrites – Typical Grade 430
Pure chromium (12-18%); low carbon, magnetic, but not heat treatable.
Typical Uses: Highly polished decorative applications, food processing.

4: Precipitation Hardening - Typical Grade: 17-4
Chromium (12-28%), Nickel (4-7%); Martensite or Austenite. The typical grade 17-4 designation comes from the addition of 17% chromium and 4% nickel, also known as grade 630. They have high strength at moderate temperatures, relatively good ductility and good corrosion resistance.
Typical uses: Valves, gears, pump parts, bolts, saws, shafting.

5: Stainless steel suitable for your application
Austenitic stainless steel is the largest category, accounting for two-thirds of stainless steel production. Eagle Stainless stocks 300 series stainless steel seamless and welded pipe for a variety of applications.