18-8 STAINLESS STEEL (302, 303, 304 Series) ASTM F593A
The number 18-8 refer to the percentages of chromium and nickel in the stainless steel Alloy. The 18 refers to the chromium content, which provides rust-resistance properties, and the 8 refers to the nickel content, which gives a silver-like shine and some rust-resistance. 18-8 is probably the most commonly used stainless steel. This stainless steel is also known as 304 in the American AISI grade designation system or 1.4301 in the European BS EN 10088 standard.
The specification below for ASTM F593A covers the requirements for 18-8 (302, 303 304) series stainless steel bolts, hex cap screws, and studs 0.25 to 1.50 in., inclusive, in nominal diameter in a number of alloys in common use and intended for service applications requiring general corrosion resistance.
- Mechanical Properties
Head Marking F593A
Diameter 1/4 to 1-1/2
Tensile 65 to 85
Rockwell B85 max
Manganese, min 2.00%
Phosphorus, max 0.045%
Sulfur, max 0.030%
Chromium, 18.0 to 20.0%
Nickel, 8.0 to 10.5%
Type 302 is the basic type of the 300 series, 18% chromium— 8% nickel group. It is the renowned 188
Stainless and is the most widely used of the chromium nickel stainless and heat resisting steels.
Type 303 contains added phosphorus and sulfur for better machining characteristics. Corrosion resistance is slightly less than 302/304.