Explained: Stainless vs Carbon Steel.
Before knives were made of steel, they were made of iron. Unfortunately, iron ore rusts and the metal is quite soft, so in the 3rd Century CE, in Damascus, some clever folk came up with a new technique of manufacturing layered steel. This is what knives have been made of for 100s of years, but originally the know-how came out of the Middle East, while the Romans were still running around with swords made of Bronze.
What they learnt in Damascus, was that, by heating iron in a charcoal fire that is carbon rich, some of the carbon entered the surface of the steel. It was then folded over, so the carbon was on the inside of the piece of steel. The process was repeated 100, 200+ times. This meant that the whole piece was impregnated with carbon, and quenching it in water or oil then hardened it. And voila! This is how you make steel. (More on Damascus steel)
From pre-war through to the 50s, all knives were mostly carbon steel, which is very good because it is strong and holds its edge. The disadvantage was that it needed special care. It was called “black steel”, because of the blackish and dull tarnish. This does not detract from the quality, but affects the appearance.
So stainless steel was developed. Originally for knives to be stainless steel, they had to have 13% chromium, which makes it very hard, which also means it does not have the edge retention on the blades. At the time, a lot of kitchen knives that were true stainless were actually useless, blunt articles. Many people reverted back to carbon steel, for its tradition of being easier to sharpen. There is still a market for carbon steel knives, but in the food industry it is no longer legal to use carbon knives, so stainless technology had to evolve.
Stainless knives today, are not true stainless - they have less chrome and more carbon and hence why we find that brands use different terms such as “Rust Free” or “Rust Frei” in German. Victory Knives from New Zealand has – “Non Stain” on their knives, others use “Stain Free”. What they are actually mean is that these knives will not tarnish or rust, but they are not “technically” stainless steel.
For more on stainless vs carbon steel check out this video-