Just for the record Monel is a non magnetic steel, i use very large monel pipes to drill oil wells because it allows us to run magnetometers in the drill string without interferance from magnetized steel.
Actually Monel is not part of the steel or stainless steel family. It does look like some stainless steels (and can sometimes be easily confused with stainless steel), but it is a nickel alloy (up to 67% nickel). It contains very little iron and therefore is not at all part of the steel family.
Monel is a proprietary name for a whole family of nickel alloys. It is similar to Inconel, Incoloy, Hastaloy (sp?), etc. All of the above are proprietary names for families of basically nickel alloys.
Nickel alloys are known for being very corrosion resistant and very strong for a very large range of temperatures. Depending on the alloy they can have a lot of great characteristics, but they are also known for being relatively expensive.