Best Knife Steel? A Guide for Knife Makers

Knife Steel Categories & Overview

• Carbon Steel (C Steel)
  • rust-prone - not stainless
  • unalloyed & low-alloy steel
• Semi-Stainless Knife Steel
  • rust-prone, but rusts significantly more slowly
  • contains a higher proportion of alloying elements than conventional carbon steel
• Stainless Knife Steel (High-Alloy Chromium Steel)
  • does not rust
  • high chromium content for corrosion resistance
• PM Knife Steel (Powder Metallurgy Steel)
  • state-of-the-art manufacturing method
  • with the same alloy composition, the microstructure is finer, resulting in better performance
  • can be stainless or rust-prone
• Damascus Steel
  • is a special form
  • depending on the material composition, it falls into one of the four categories above

It should be noted that, technically speaking, completely rust-free steel does not exist, but the term is commonly used for a simple classification.
Among high-alloy chromium steels, there are also differences in the level of corrosion resistance. In the knife-making community, a steel is generally considered stainless if it does not rust under normal conditions (exposed to air and left wet with fresh water without being dried). For corrosion resistance in salt water, for example, nickel, molybdenum, or nitrogen can be added and/or the chromium content increased; reducing the carbon content is also possible.

The Most Important Factors of a Knife

• Knife Geometry | Matched to the properties of the knife steel and the intended use
  • Blade Grind | Flat, Hollow, Scandi, Convex, etc.
  • Edge Angle
  • Blade Thickness
  • Material thickness at the cutting bevel (also called edge thickness)
• Good Heat Treatment / Hardening | Also matched to the knife geometry & intended application
• Proper Processing | To prevent warping and loss of hardness
• Hardness (HRC) | Edge retention, edge stability
• Toughness | Resistance to breakage, impact toughness, and chip resistance
• Knife Steel Alloy Composition | Selected based on its properties, workability & intended use
• Corrosion Resistance & Maintenance Requirements

What Does Sharpness Mean? A Look at Razor-Sharp Knives

The term "razor sharpness" is often interpreted in different ways. A knife can already shave at 3,000 grit, but at 12,000 grit it delivers a significantly better shaving result.

In everyday language, a knife is often considered “sharp” once it has been sharpened to around K1000 grit. With high-quality knives, however, true sharpness by our standard only begins at approximately K3000 grit. In addition, fine polishing or stropping with a leather strop and diamond compounds, or using sharpening stones in various grits up to K10000, can produce an even sharper edge.

For straight razors a finish of 12,000 grit is optimal, because a very sharp edge is essential for a comfortable shave. For kitchen or hunting knives, however, such a fine finish is not always necessary. The effort required for such fine sharpening is only justified to a limited extent in these applications. In practice, knives are often sharpened to 2,000 or 3,000 grit and the burr is then removed as needed with a leather strop – often using polishing compound.

So Which Steel Is Suitable for a Knife?

First of all, the higher the alloy content, target hardness, and required properties, the tighter the tolerances become for heat treatment and processing. It is therefore crucial that the knife maker can reliably handle the chosen steel within their own process. A well-understood, seemingly “simpler” steel is, in practice, often the better choice than a theoretically superior steel that is not used to its full potential.

Is Stainless Knife Steel Less Sharp Than Carbon Steel?

If the right stainless steel is used and all parameters are properly matched to it, the achievable sharpness is nearly identical.
For example:
Nitro-V has an extremely fine grain structure among stainless steels, with carbide sizes of approximately 1 to 2 micrometers (1 - 2 µm). A good working hardness for this steel is around 62 HRC.
Fine-grained 1.3505 bearing steel likewise has carbides approximately 1 to 2 micrometers (1 - 2 µm) in size, with a working hardness of 61 HRC.
Because both are very fine-grained, have a relatively low carbide volume, and at the same time offer high hardness and toughness, they can be ground extremely thin.

So what distinguishes these two steels, apart from Nitro-V being stainless and the bearing steel being rust-prone?

• Nitro-V will retain its edge slightly longer due to its fine chromium carbides, because chromium carbide is harder than iron carbide
• Bearing steel will be somewhat easier and faster to sharpen
• Hardening Nitro-V is considerably more difficult and requires significantly more effort
• 1.3505 can be forged and forge-welded very well

Micrograph of the Microstructure

Nitro-V, hardened to 62 HRC

1.3505 bearing steel, hardened to 61 HRC

The result: If Nitro-V is not heat-treated correctly, the bearing steel no longer has a disadvantage in terms of edge retention. Nitro-V can still offer the advantage of corrosion resistance, while the bearing steel benefits from easier hardening, processing/sharpening, and forgeability.

Note: Tungsten-alloyed carbon steel often has a significantly coarser microstructure (and also higher edge retention due to tungsten carbide), so the right carbon steel must also be selected for the finest possible edge. The same applies to stainless & semi-stainless knife steels. Some are true carbide monsters (with lower achievable sharpness), and these should not be ground as thin, because their strengths usually lie in a different geometry.

Unfortunately, there is a common misconception regarding sharpness that stainless steel is significantly less sharp. As explained above, this is not necessarily related to corrosion resistance. Many end consumers are familiar only with stainless blades at 50-56 HRC, or they struggle to sharpen high-alloy steels, which is probably where this assumption comes from. It is also entirely possible that the heat treatment was not carried out well enough. If high-alloy steels contain too much retained austenite, for example, edge retention, stability, and achievable sharpness can suffer enormously. Some blades will not even take a clean edge; at fine grits, the cutting edge simply crumbles away.

Among knife makers, the biggest issue is the demanding heat treatment and the more difficult processing of stainless knife steel. Especially with PM steel, the difference compared with conventional carbon steel is enormous. Many people struggle to carry out the correct heat treatment or to get the knife properly sharp, and chromium steel is then often portrayed as being incapable of taking a sharp edge.