Originally Posted by
jgwilliams
The magnetic element of steel is a crystal called martensite. Higher quantities of alloying elements - Chromium and Nickel amongst others - the less martensite tends to form. So high alloy steels - such as is used to make spoons and forks - are not magnetic at all. However, it's the martensite which gives the steel its strength so high alloy steels are also rather soft. For this reason they aren't used to make kitchen knives...
Correct so far. The "high alloy" stainless steels you are referring to are the "300-series", generically 18/8 Cr/Ni, the most common of which are 303, 304 and 316. They are high in Cr and Ni content and low in carbon. They are non or only weakly magnetic and can't be heat treated for hardness. As noted they aren't suitable for knives, tools, etc. but are used to make bike cables and spokes and they are very corrosion resistant.
Originally Posted by
jgwilliams
Once upon a time we didn't know how to make stainless steel which would also keep its edge which is why antique steel knives tend to rust. You obviously couldn't use a high alloy steel for brake cables either.
There is a whole family of heat treatable and hardenable cutlery and tool stainless steels, the "400-series" that has been around since the early 1900's. Typical grades are 410, 416, 440, etc. and they that contain 12% or more Cr and up to 1.2% carbon. There are also more exotic Stainless Tool Steels but they aren't commonly found in consumer items. These are used to make knives, tools and other items where hardness and edge keeping ability is required and some corrosion resistant is sacrificed. They are indeed magnetic and strongly so. These are not used for cables or spokes but the 300-series are as noted above.