While there are many grades of stainless steel available for fasteners, we will focus on three of the highest performing grades used: Super Duplex, A-286 and 17-4PH.When comparing these materials to 316 stainless steel, their properties – of corrosion resistance, strength and high temperature stability – are significantly improved.
Corrosion Resistance
The term “corrosion resistance” is a very much a relative term as it is dependent on the application’s corrosive media, temperature and concentrations. In comparison to 316 stainless steel fasteners, one most corrosion resistant stainless steel grades to be aware of is super duplex stainless steel or alloy 2507. Due to its higher content of chromium, nitrogen and molybdenum, super duplex stainless steel fasteners offer reliable resistance to localized and uniform corrosion.
Key Characteristics:
Good resistance to uniform corrosion
Good resistance to pitting and crevice corrosion
Good resistance to stress corrosion cracking and corrosion fatigue
Applications Examples:
Pulp & paper equipment
Desalination plants
Chemical process equipment
However, if super duplex does not satisfy your needs, there are a variety of other specialty alloys that will provide you greater corrosion resistant horsepower. To learn more about other corrosion resistant fasteners, see our Extreme Bolt & Fasteners, “Corrosion Resistant Material Guides” for more information on our specialty alloys, engineered polymers and advanced ceramic fasteners.
High Temperature Stability
At elevated temperatures, 316 stainless steel fasteners will oxidize relatively quickly in air and mechanically weaken. One of the best stainless steel alloys to counter these effects is alloy A-286. This iron-nickel-chromium alloy (once age-hardened) provides A-286 fasteners with high levels of strength from room temperature up to about 1300°F (700°C).
Key Characteristics:
Good high temperature oxidation resistance
Excellent strength, even at elevated temperatures
Application Examples:
High temperature exhaust streams
Turbines
Manifolds and flue gas streams
High Strength
Compared to 316 stainless steel, all the specialty stainless alloys provide significantly improved strength, with super duplex being about 2x stronger and A-286 being about 2.5x stronger. However, 17-4PH, a specialty grade of stainless steel surpasses them all. Fasteners made from 17-4PH can have a yield strength that is up to 4.5x strong than 316 fasteners.
17-4PH is a precipitation hardened alloy with 8 different methods of heat treating. Depending on the heat treatment desired the yield strength could range from 2 – 4.5x that of 316 stainless steel. This chart shows the different heat treatments available and their respective strengths (click chart for more details).
Key Characteristics:
Superior strength
Maintains good mechanical properties up to 600°F
Application Examples:
High torque applications
High pressure valves and process equipment