Actually the only truly rust proof stainless steel has an "L" in the number series. If you have metal bolts in marine environment any SS will corrode unless it has an L. I suppose for fresh water pools 3000 series is good enough. L SS is very expensive.
Type 304
The most common of authenticate grades, containing approximately 18% chromium and 8% nickel. It is used for chemical processing equipment, for food, dairy, and beverage industries, for heat exchanges, and for the milder chemicals.
Type 316
Contains 16% to 18% chromium and 11% to 14% nickel. It also has molybdenum added to the nickel and chrome of the 304. The molybdenum is used to control pit type attack. Type 316 is used in chemical processing, the pulp and paper industry, for food and beverage processing and dispensing and in the more corrosive environments. The molybdenum must be a minimum of 2%.
Type 317
Contains a higher percentage of molybdenum than 316 for highly corrosive environments. It must have a minimum of 3% “moly”. It is often used in stacks which contain scrubbers.
Type 317L
Restricts maximum carbon content to 0.030% max. and silicon to 0.75% max. for extra corrosion resistance.
Type 317LM
Requires molybdenum content of 4.00% min.
Type 317LMN
Requires molybdenum content of 4.00% min. and nitrogen of .15% min.
Type 321
Type 347
These types have been developed for corrosive resistance for repeated intermittent exposure to temperature above 800 degrees F. Type 321 is made by the addition of titanium and Type 347 is made by the addition of tantalum/columbium. These grades are primarily used in the aircraft industry.
Martensitic Grades
Martensitic grades were developed in order to provide a group of stainless alloys that would be corrosion resistant and hardenable by heat treating. The martensitic grades are straight chromium steels containing no nickel. They are magnetic and can be hardened by heat treating. The martensitic grades are mainly used where hardness, strength, and wear resistance are required.
Martensitic Grades of Stainless Steel
Figure 2 - Martensitic Grades
Type 410
Basic martensitic grade, containing the lowest alloy content of the three basic stainless steels (304, 430, and 410). Low cost, general purpose, heat treatable stainless steel. Used widely where corrosion is not severe (air, water, some chemicals, and food acids. Typical applications include highly stressed parts needing the combination of strength and corrosion resistance such as fasteners.
Type 410S
Contains lower carbon than Type 410, offers improved weldability but lower hardenability. Type 410S is a general purpose corrosion and heat resisting chromium steel recommended for corrosion resisting applications.
Type 414
Has nickel added (2%) for improved corrosion resistance. Typical applications include springs and cutlery.
Type 416
Contains added phosphorus and sulphur for improved machinability. Typical applications include screw machine parts.
Type 420
Contains increased carbon to improve mechanical properties. Typical applications include surgical instruments.
Type 431
Contains increased chromium for greater corrosion resistance and good mechanical properties. Typical applications include high strength parts such as valves and pumps.
Type 440
Further increases chromium and carbon to improve toughness and corrosion resistance. Typical applications include instruments.