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Despite their similar names, K390 and M390 ask different things of an owner. K390 has higher abrasive edge retention and toughness, while stainless M390 has much greater corrosion resistance. Your willingness to care for a non-stainless blade is central to this choice.
Performance Ratings
For the science, we turn to Dr. Larrin Thomas of Knife Steel Nerds, who has kindly allowed us to share his ratings here.
| Property | Böhler K390 Microclean | Böhler M390 |
|---|---|---|
| Abrasive edge retention | ||
| Toughness | ||
| Corrosion resistance |
Heat treatment, hardness and geometry affect actual knives.
K390 Favors Abrasive Cutting
K390 rates 7.5 for abrasive edge retention and M390 6.5. We would lean toward K390 when abrasive slicing is a large part of the workload and moisture care is manageable.
The one-point gap is not a cutting-time multiplier. Geometry, heat treatment and the abrasive material all affect how a finished edge wears.
Our K390 steel profile explains its properties and care in more detail.
K390 Also Has the Higher Toughness Rating
K390 rates 6 for toughness, compared with M390 at 3.5. The K390 figure incorporates Dr. Thomas’s written correction to his earlier 5.5 rating.
That combination makes K390 interesting for work where both wear and edge damage matter. It does not remove the need to choose an appropriate knife design or avoid twisting an edge in a cut.
Our M390 steel profile explains its properties and care in more detail.
M390 Has a Much Larger Corrosion Margin
M390 rates 9 for corrosion resistance against K390 at 4. K390 is not stainless and needs more attention to cleaning, drying and storage.
For someone who often carries a damp knife or wants less rust maintenance, M390 may be the better everyday choice despite its lower wear and toughness scores.
What Would We Prioritize?
We would choose K390 for a work knife when its wear/toughness balance is useful and the owner accepts the care. We would choose M390 when corrosion resistance is a major part of the job.
Do not read the shared 390 in their names as evidence that one is a revision of the other. Confirm the maker’s exact material specification and compare the actual knives.
Composition
Our steel composition guide explains the elements and the differences between reported values, ranges and limits.
Böhler K390 Microclean: Böhler K390 Microclean average composition, mass %; not a finished-blade assay. Böhler: K390 Microclean.
Böhler M390: Böhler average composition, mass %; selected elements, not a batch analysis. Böhler: M390 MICROCLEAN.
| Element | Böhler K390 Microclean | Böhler M390 |
|---|---|---|
| Carbon (C) | 2.47% | 1.9% |
| Chromium (Cr) | 4.2% | 20% |
| Molybdenum (Mo) | 3.8% | 1% |
| Vanadium (V) | 9% | 4% |
| Tungsten (W) | 1% | 0.6% |
| Cobalt (Co) | 2% | Not listed |
| Silicon (Si) | 0.55% | 0.7% |
| Manganese (Mn) | 0.4% | 0.3% |
Compare Two Knife Steels
Sources and Update Notes
- Dr. Larrin Thomas: knife steel ratings · Property ratings; the scores describe steels rather than individual finished knives.
- Böhler: K390 Microclean
- Böhler: M390 MICROCLEAN
