CPM S30V, S35VN, S45VN: Steel Invented Specifically for Knives

Almost all knife steel is borrowed. It was developed for bearings, dies, cutting tools, medicine and aviation, and knifemakers then took whatever was at hand and happened to fit. The S30V series is a rare exception: it was made for knives, and made together with knifemakers.

There are not many exceptions like it. If we mean kitchen knives specifically, then apart from S30V the only steels developed for the purpose are the Japanese Shirogami and Aogami. Everything else on your board is steel that used to have another profession.

How it was designed

CPM S30V was released in 2001. The task was framed not as “make the hardest” but as “make the balanced”: acceptable ease of sharpening, toughness, corrosion resistance and edge retention all at once. Development was carried out jointly with knife companies, makers and heat treatment specialists — that is, with the people who would later be working with this steel. The lead metallurgist was Dick Barber, drawing on Crucible’s earlier experience with stainless steels.

The engineering logic inside is simple. The base is CPM 3V, a very strong and wear-resistant steel that rusts, to which chromium was added to make it stainless. They took 14% chromium — deliberately less than the 16–20% of earlier stainless steels. The reason is that excess chromium binds into chromium carbides, and chromium carbide is softer and coarser than vanadium carbide, so it degrades both wear resistance and toughness. Corrosion resistance was made up not with chromium but with molybdenum (over 2%) and nitrogen (around 0.2%). A separate goal was to make the steel predictable when hardened in different furnaces.

The word “balanced” here is technical, not promotional. Every requirement you put on a steel takes properties away from somewhere else. High-speed steels need a lot of molybdenum and tungsten to hold hardness when hot — and that limits everything else. Stainless steel needs a lot of chromium — same story. A knife needs a combination of high hardness, toughness and wear resistance, and every additional condition narrows the space in which that combination can be looked for. S30V is an attempt to search inside that space deliberately, rather than to pick something ready-made.

The result came out exactly as ordered: edge retention better than Elmax, S35VN, CPM-154 and BG42, and slightly worse than S90V and M390. Toughness is good. Corrosion resistance is “above average” — enough for most knives.

How the popularity ended

In the early 2000s S30V was a fashionable steel, and that did it harm. Its heat treatment is not the simplest, and it is hard to harden at all — the ceiling is around 62 HRC. Some manufacturers, including specialist ones, put out knives that turned out either too soft or too prone to chipping. The steel’s reputation was ruined not by its properties but by other people’s furnaces. Many have since preferred to play safe and harden to 58–60 HRC.

That is probably the main lesson of the whole S30V story, and it goes wider than one grade: the line “S30V” on a blade tells you less about the knife than the name of whoever hardened it.

S35VN and S45VN: two attempts to refine it

S35VN came out in 2009 as a modification of S30V with improved strength and machinability. The key addition is about 0.5% niobium. Niobium is a stronger carbide former than vanadium: it forms its own carbides even where there is plenty of chromium, and thereby reduces the amount of chromium carbides. Niobium carbides are also finer, because they coarsen more slowly during hot working.

An honest description of S35VN goes like this: it stands out in no category and fails in none. Machinability was improved primarily for the manufacturer, not for the owner.

S45VN is the next step. It has 16% chromium, but also 0.5% niobium and around 0.17% nitrogen, and thanks to that pair it contains not much more chromium carbide than S30V and S35VN with their 14%. The microstructure came out better than in either predecessor. On properties: against S30V, better toughness and corrosion resistance at comparable edge retention; against S35VN, slightly less toughness, but better corrosion resistance and edge retention.

Who needs this

The S30 series is above all a material for folders and pocket knives; in the kitchen it turns up rarely, and mostly from one-off makers. If you are choosing between the three alphanumeric options anyway, it helps to understand the scale: the difference between S30V, S35VN and S45VN is a set of steps within one family, not a change of class. S45VN looks like a tidy improvement on both earlier grades; S35VN gives a little more toughness.

But if toughness is genuinely your limiting factor — if the knife chips — then looking for a solution inside the S30 series is pointless. Steels with substantially higher toughness exist, and they are not stainless. The choice between “doesn’t rust” and “doesn’t chip” is still a choice here, not a compromise somebody has already found for you.