Different types of knife steel

Sandvik produces martensitic stainless chromium knife steels. These steels become stainless only after correct hardening, when carbides have been dissolved.

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There are also many other types of stainless steels, but these are different in composition and structure and are rarely used in edge applications, since the edge properties are inferior to those of martensitic stainless steel grades.

Difference between carbon steel and stainless steel

There are two main differences between carbon knife steel and stainless knife steel. The first is that stainless steels have much higher corrosion resistance, due to the protective chromium oxide layer that covers the steel surface after heat treatment. The second difference relates to the alloying elements that form carbides. Stainless steels contain at least 10.5% by weight of chromium. The carbide particles provide the steel with significant wear resistance. The carbides are bonded together by the steel matrix.

The importance of carbide size

A knife steel with large carbides is generally very difficult to regrind, since the carbides crumble out of the edge and cause a 'saw edge' instead of a razor-sharp edge. Sandvik produces knife steels with fine carbides which enable excellent edge sharpness. The pictures below show the microstructures of the three classes of stainless steel on the market.

Coarse-carbide tool steel grades

Medium-size carbide powder-metallurgic grades

Fine-carbide knife steels

Combination of knife steel properties

The table shows combinations of knife steel properties for different classes of steel. Note that corrosion is detrimental for the cutting edge. Consequently the lack of sufficient corrosion resistance also affects knife performance and not only the esthetics of the blade.

Edge performance
Steel typeSharpnessEdge stabilityWear resistanceToughnessCorrosion resistance
Coarse- carbide steels1)
Poor
Poor
Excellent
Poor
Very good
Powder-metallurgical grades2)
Very good
Average
Excellent
Average
Very good
Fine-carbide knife steels3)
Excellent
Excellent
Very good
Excellent
Very good
Carbon steels4)
Excellent
Excellent
Poor
Excellent
Insignificant

Material examples:
1) ASTM 440A, 440C, D2; 9Cr18MoV; Sandvik 19C27
2) Powder-metallurgical steels for knife applications
3) Sandvik 14C28N, 13C26, 12C27, 12C27M, 7C27Mo2
4) ASTM 1095, 1075