My father recently purchased some Japanese knives off of a facebook ad. I'm proud of him for buying them when they were on a steep sale, as the MSRP is $1200 and he got them $350, but now he's coming to me for knowledge on whether or not he made a good purchase. They feel good in the hand, the sharpening has some minor nicks but nothing I can't fix myself and the balance doesn't seem too bad for an otherwise heavier than average knife. But the main thing I am looking for is whether they are stainless steel or carbon steel? Some research brought up Niigata steel but nothing beyond that. So would anyone have a more detailed answer for me on what Niigata steel is and how it should be cared for?