Stainless Steel –
Stainless Steel is an iron-based alloy that must contain at least 10.5% chromium. This chromium creates a surface film that resists oxidation. This surface is considered passive, or corrosion resistant.
Three types of stainless steel:
- Austenitic – This category includes the 18-8 stainless that is approximately 18% chromium and 8% nickel. 18-8 is the most common stainless used in industrial fasteners.
- 304 – The most popular stainless for hex head cap screws. It is a low carbon and higher chromium stainless steel with improved corrosion resistance.
- 304L – Is a lower carbon version of type 304 which is slightly lower in strength but has increased corrosion resistance and welding capacity.
- 316 – Improved corrosion resistance when exposed to seawater and many types of chemicals. It also has a higher tensile strength at higher temperatures.
- Martensitic – A class of stainless that contains 12 – 18% chromium. They can be hardened through heat treatment, are considered magnetic and have poor corrosion resistance compared to the 300 series stainless.
- 410 – A chromium alloy containing no nickel. Commonly used for self-drilling and tapping screws
- Ferritic – Contains 12 -18% chromium and less than 0.2% carbon. It is magnetic, non-hardenable through heat treatment and has poor weld characteristics. It should not be used in high corrosion environments.