Hi folks, I was wondering if some basic cleaning + oil is enough to avoid rusting on a high-carbon steel blade with no coating? Or do I need something more "complicated" than that? Is WD-40 good for that? Also, recommend me some good grease/oils and maintenance products.
You're in luck. These days, there's lots of good options.
First, WD-40. WD-40 is less of a lubricant, and more of a solvent (WD stands for Water Displacing). It works well for cleaning a knife, but isn't that great at preventing corrosion. I used to use it frequently as a first stage for knives that are really dirty, especially folders with grit deep in their guts. I generally wipe it away entirely, however, and use something else for protection.
Oil or grease is another traditional option. It's very effective while it's on the blade, but it's biggest problem is that it won't stay there under use. If you intend to reapply after use, or you're dealing with a piece that will mostly be for show or storage, it works quite well. The other problem I have with these, is that they tend to attract dirt, dust, and other particulates.
Modern metal protectants are your next option. There's a bunch of these that have come out in the last 10-15 years, and most of them work quite well. Among the ones I've used and had excellent luck with are Tuf-Cloth/Tuf-Glide, Militec-1, Breakfree CLP, and White Lightning. I've also heard really good things about Eezox, but haven't personally tried it yet. In a pinch, a dry teflon/silcone based lubricant from any hardware store can offer some protection.
Most of these were originally designed as lubricants and protectants for use with guns, but their application with knives is also excellent. White Lightning is the obvious exception there, having been designed as a wax-based lubricant for bicycle chains. Additionally, most of these will leave a dry lubricating coating on the metal, offering continued protection that won't wipe off as easily as oil or grease, and won't attract particulate matter like dust and dirt.
My personal preference is the modern options. Either alone, or in combination with some mineral oil.
If I'm going to be storing a piece for a long period of time, then I'll usually treat it with one of the modern lubricant/protectants, and then follow that with a thin layer of mineral oil (I usually go for the non-toxic mineral oil available in almost any pharmacy, and I avoid vegetable oils because they can o rancid).
For daily users, I usually just go with a thorough wipe down with a cloth soaked in whichever modern lubricant/protectant I have on hand. If I'm going to be in a particularly harsh environment (like around salt water with anything other than my Spyderco Salt 1), I'll soak a cloth in the lubricant and put it in a zip top bag to take with me. Otherwise I just wipe down my knives with the same thing every week or so, or after heavy use that may be corrosive (salt water, acidic food, etc).
White Lightning has been my recent favorite among the many choices, although I've been meaning to sit down and do some real comparative corrosion tests to see which one really protects best. I'm of the opinion that any one of the options listed above will work just fine for most people and most uses, though.
. I remember buying an Imperial hunting knife some 30 years ago that had a gorgeous mirror finish. I had it for 2 days and was very proud of it. I made a sandwich and spread mustard using the knife, and to my horror the finish went gray in just a few minutes before my eyes.