In short Froidur steel is one of the first great all round stainless steels that has all of the qualities we now take for granted; stain resistance, flexibility and good edge retention (you can get it sharp and keep it sharp for a long time). It has been Henckel's steel of choice for years. It has been surpassed in recent years by harder steels (see VG10 and Powder steel) and techniques (laminated steels for instance) but still a great stainless steel for kitchen knives so fear not.
There is a lot of marketing speak surrounding Henckel's knife steel and not much in the way of hard facts. As a result it can be hard to track down all the details about it. A bit like KFC's secret blend of 11 herbs and spices you can guess some of the details (salt and pepper for starters brings it down to 9!) but some of the others get down to gut feeling or hearsay.
It's understandable why Henckel want to keep it under wraps, they invented it so why share it out with the competition?
The ice-hardening is believed to be a technique of literally cooling the steel after forging to get it down to freezing and way beyond. Now I'm not a scientist but from what I've read this cooling changes the way the atoms in the steel settle out making it harder than not cooling it at all. That said it is pretty much guess work as the process is kept under wraps by Henckel.
The trouble is that their marketing claims do end up sounding like the pseudo-science claims you get on hair shampoo adverts "micro-shine-ology pento-peptides give you truer colour and more volume!". Does make you wish they would just explain it a bit more clearly rather than telling us it's magic...
Feel free to google it if you want to know more but take some of what you find with a pinch of salt.