K340 contains approximately 1.10 percent carbon, 8.30 percent chromium, 2.10 percent molybdenum, 0.90 percent silicon, 0.50 percent vanadium, and 0.40 percent manganese, along with trace additions of aluminum and niobium. Carbon allows the steel to harden and supports the formation of wear-resistant carbides. Chromium contributes to hardenability and carbide formation, while molybdenum adds strength and wear resistance. Vanadium introduces hard vanadium carbides and helps restrain grain growth during heat treatment.

Its chromium content is notably lower than that of traditional D2-type cold work steels. Higher chromium levels can produce a greater volume of chromium-rich carbides, improving abrasive wear resistance but potentially reducing toughness when carbide size or volume becomes excessive. K340 uses a lower chromium level and a different alloy balance to maintain strong wear resistance while improving toughness. The addition of aluminum has also played a role, helping promote oxide passivation at the surface and reducing the tendency of material to adhere to tooling under pressure.

Composition
Carbon - 1.1%

Chromium - 8.3%

Molybdenum - 2.1%

Vanadium - 0.5%

Nickel - 0.19%

Manganese - 0.4%

Silicon - 0.9%

Niobium - +

Aluminum - +

Unlike Böhler steels such as K390 MICROCLEAN, K340 is not produced through powder metallurgy. It begins as an air-melted steel and is then processed through electroslag remelting, commonly abbreviated ESR. During ESR, a previously produced steel electrode is remelted through a heated slag layer and allowed to solidify again under controlled conditions. The process reduces segregation, where alloying elements become unevenly concentrated during solidification, while also improving cleanliness and uniformity throughout the material.

Böhler describes K340 ISODUR as having very low levels of micro- and macro-segregation. In industrial tooling, that helps reduce the likelihood that large inclusions or uneven alloy distribution will contribute to premature failure. For knife production, greater uniformity can also make the steel more predictable during heat treatment, grinding, sharpening, and use. ISODUR should not be confused with Böhler's MICROCLEAN powder-metallurgy process, which atomizes molten steel into small particles before consolidating them under heat and pressure. That method allows highly alloyed steels to be produced with fine, evenly distributed carbides, while K340's less extreme composition allows ESR to improve cleanliness and homogeneity without using powder metallurgy.

Electroslag Remelting (ESR) Diagram

For many years, K340 remained primarily an industrial steel, and its adoption by knifemakers appears to have happened gradually. As specialty tool steels became more accessible to custom makers and production manufacturers, K340 offered another option for users who wanted substantial wear resistance without moving toward the very high carbide volumes found in more extreme steels. Its combination of toughness and wear resistance gave makers an alternative to both simpler tool steels and more highly alloyed powder-metallurgy grades.

Australian manufacturer Halfbreed Blades is one company that has regularly used K340 in modern fixed blades. Models such as the MCK-02 Medium Clearance Knife and MIK-03 Gen-2 Medium Infantry Knife use Austrian-made K340 ISODUR in thick, full-tang blades intended for demanding field use. Halfbreed heat treats the steel to 59-60 HRC, a relatively conservative range suited to the durability expected from larger working knives. The MCK-02 uses a 6.5 mm-thick K340 blade in a design developed for active-duty personnel and strenuous outdoor use, while the MIK-03 Gen-2 uses the same blade thickness in a military-oriented fixed blade.

Halfbreed Blades MCK-02 Medium Clearance Knife