40C is a 400 series stainless steel, and is the highest carbon content from 400 stainless steel series. It is usually heat treated to reach hardness of 58–60 HRC. It is a bearing steel, and used in rolling contact stainless bearings, e.g. ball and roller bearings. It is also used to make knife blades. 440C can be oil quenched to achieve maximum hardness.
440C has a carbon (C) content of 0.95–1.20%, chromium (Cr) content of 16.00–18.00%, molybdenum (Mo) content of 0.75%, Manganese (Mn) content of 1.0%, and silicon content of 1.0%.
304 stainless steel also known as A2 stainless steel (not the same as A2 tool steel) or commercially as 18/10 or 18/8 stainless steel, European norm 1.4301, is the most common stainless steel. The steel contains both chromium (between 18–20%) and nickel (between 8–10.5%) metals as the main non-iron constituents. It is an austenitic stainless steel. It is less electrically and thermally conductive than carbon steel and is essentially non-magnetic. It has a higher corrosion resistance than regular steel and is widely used because of the ease in which it is formed into various shapes.
The composition was developed by W. H. Hatfield at Firth-Vickers in 1924 and was marketed under the trade name “Staybrite 18/8”. The Japanese equivalent grade of this material is SUS304.
304 stainless steel has excellent resistance to a wide range of atmospheric environments and many corrosive media. It is subject to pitting and crevice corrosion in warm chloride environments and to stress corrosion cracking above about 60 °C. It is considered resistant to potable water with up to about 200 mg/L chlorides at ambient temperatures, reducing to about 150 mg/L at 60 °C.
304 stainless steel is also very sensitive at room temperature to the thiosulfate anions released by the oxidation of pyrite (as encountered in acid mine drainage) and can undergo severe pitting corrosion problems when in close contact with pyrite- or sulfide-rich clay materials exposed to oxidation.
For more severe corrosion conditions, when 304 stainless steel is too sensitive to pitting or stress corrosion cracking, the 316 stainless steel is the second grade of stainless steel the more commonly used.
304 stainless steel is used for a variety of household and industrial applications such as screws, machinery parts, car headers, and food-handling equipment. 304 stainless steel is also used in the architectural field for exterior accents such as water and fire features. It is also a common coil material for rebuildable vaporizers.
316L grade stainless steel is a standard for an austenic variety of stainless steel given the American SAE designation “316L” which indicates that this steel is low-carbon subtype of marine grade stainless steel containing 16–18% chromium, 10–14% nickel, 2.0–3.0% molybdenum, and no more than 0.03% carbon, 2% manganese, 0.75% silicon, 0.045% phosphorus, 0.03% sulphur, and 0.1% nitrogen by weight, with the remainder consisting entirely of iron (by comparison, regular 316 grade may contain up to 0.08% carbon by weight). For many years it was one of the most highly preferred substances for medical devices and implants, but the greater biocompatibility titanium and cobalt-chromium alloys as well as their greater resistance to corrosion have caused 316L to lose favor.