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K390 vs M398 Knife Steel Comparison

Introduction

Welcome to our in-depth comparison of two high-performance powdered metallurgy (PM) tool steels: Böhler K390 and Böhler M398. Both are known for pushing the envelope in terms of edge retention and wear resistance, making them highly sought-after by knife enthusiasts, collectors, and professionals alike. In this article, we’ll explore each steel’s chemical composition (including new data on M398’s niobium content), typical hardness, performance characteristics (edge retention, toughness, and corrosion resistance), heat-treatment nuances, and ideal uses. We’ll also discuss their pros and cons, ease of maintenance, and where each steel shines in real-world applications.

1. K390 Steel Overview

1.1 Chemical Composition

K390 is a powdered metallurgy steel with the following approximate composition:

Carbon (C): ~2.47% – Contributes to high hardness and edge retention.
Chromium (Cr): ~4.2% – A moderate amount that improves wear resistance but doesn’t make K390 fully stainless.
Cobalt (Co): ~2% – Often added to increase hot hardness and overall strength.
Manganese (Mn): ~0.4% – Aids in hardness and slightly improves hardenability.
Molybdenum (Mo): ~3.8% – Enhances strength, wear resistance, and toughness.
Silicon (Si): ~0.55% – Helps deoxidize the steel and can add some toughness.
Tungsten (W): ~1% – Adds to the wear resistance and hardness at high temperatures.
Vanadium (V): ~9% – Greatly boosts wear resistance and refines grain structure, contributing to better edge stability.

1.2 Typical Hardness (Rockwell C) Ranges

K390 typically sees hardness levels between 62 and 64 HRC, though specialized heat treatments can push it closer to 65–66 HRC. At these levels, the steel has excellent edge retention and decent (but not outstanding) toughness.

1.3 Key Performance Characteristics

Corrosion Resistance: 4/10 – K390 is not stainless; the relatively low chromium content means it can rust if not properly maintained.
Toughness: 5/10 – Fairly decent toughness for a high-carbide steel but less forgiving than simpler tool steels.
Edge Retention: 9/10 – Excels at holding a razor-sharp edge for extended cutting sessions.
Ease of Sharpening: 3/10 – Relatively difficult to sharpen due to abundant hard carbides. Diamond or cubic boron nitride (CBN) abrasives are recommended.

1.4 Ideal Uses of K390

K390’s high wear resistance and edge-holding capacity make it ideal for:

EDC (Everyday Carry) knives that require long-lasting sharpness.
Bushcraft tasks involving repeated cutting of tough materials like wood or rope.
Tactical or defensive blades where a stable, keen edge is valued.
Light to moderate outdoor/survival tasks where corrosion can be controlled with proper maintenance.

If you prize edge retention above all else and can regularly care for your blade to prevent rust, K390 offers exceptional cutting performance.

1.5 Detailed Alloy Element Effects

High Carbon & Vanadium: Together, they form abundant vanadium carbides, enhancing hardness, wear resistance, and edge stability.
Moderate Chromium: Helps with wear resistance but does not make K390 stainless.
Molybdenum & Tungsten: Improve high-temperature strength and hardness, which is beneficial for difficult cutting tasks and prolonged usage.

1.6 Heat-Treatment Nuances and Forging

K390 can be tricky to heat-treat because of its high carbide content. Proper normalizing cycles and careful hardening/tempering steps are essential to minimize distortion or potential cracking. Knifemakers often rely on vacuum heat-treatment with precise temperature control.

Forging: While forging K390 is possible, it’s rarely done because powdered tool steels are typically best shaped via stock removal. Forging can risk warping or grain coarsening if not managed carefully.

1.7 Patina Formation and Protective Coatings

Because K390 has only about 4.2% chromium, it can form a patina over time—especially in acidic or salty environments. Some users appreciate this natural patina as it can offer mild protective qualities. Others prefer coatings like DLC or Cerakote for improved corrosion resistance.

2. M398 Steel Overview

2.1 Chemical Composition

M398 is another PM steel developed by Böhler. Its approximate composition is:

Carbon (C): ~2.7% – Extremely high carbon content giving exceptional hardness and wear resistance.
Chromium (Cr): ~20% – Classifies M398 as stainless and provides strong corrosion resistance.
Manganese (Mn): ~0.5% – Aids in hardenability and contributes slightly to toughness.
Molybdenum (Mo): ~1% – Improves hardness and enhances wear resistance.
Silicon (Si): ~0.5% – Helps with deoxidation and can contribute to tensile strength.
Tungsten (W): ~0.7–1% – Increases wear resistance, especially at high hardness.
Vanadium (V): ~5–7% – Boosts wear resistance significantly by forming hard vanadium carbides.
Niobium (Nb): ~0.5–0.7% (often present) – Contributes to fine carbide formation, further enhancing edge stability and wear resistance.

Note: Composition percentages may vary slightly by batch or datasheet. Always consult the most recent Böhler or knife-maker specifications for precise numbers.

2.2 Typical Hardness (Rockwell C) Ranges

M398 commonly falls within the 62–64 HRC range, similar to K390. However, with precise heat treatment, it can be pushed toward 65–66 HRC without losing too much stability.

2.3 Key Performance Characteristics (Estimated/Reported)

Corrosion Resistance: ~8–9/10 – Thanks to ~20% chromium, M398 is considered a stainless steel.
Toughness: Moderate to Low – Very high carbide content often results in lower toughness compared to steels with fewer carbides.
Edge Retention: Extremely High – M398 is designed to surpass even M390 in wear resistance, placing it among the top tier for holding an edge.
Ease of Sharpening: Very Difficult – The large amount of hard carbides makes M398 challenging to sharpen without diamond or ceramic abrasives.

2.4 Ideal Uses of M398

High-wear EDC knives where stainlessness is a key factor.
Kitchen knives requiring extended edge life while cutting acidic or moisture-rich foods.
Outdoors and survival tasks in humid or coastal regions where rust resistance is essential (though be cautious of lower toughness).
Tactical blades in environments where moisture is abundant, requiring a combination of stain resistance and lasting sharpness.

2.5 Detailed Alloy Element Effects

Very High Carbon (~2.7%): Creates large amounts of primary carbides, bolstering hardness and wear resistance.
High Chromium (~20%): Ensures stainless properties and contributes to forming chromium carbides for additional wear resistance.
Vanadium & Niobium: Responsible for creating extremely hard carbides that enhance wear resistance and edge stability.
Tungsten & Molybdenum: Help maintain hardness under high heat and heavy use conditions.

2.6 Heat-Treatment Nuances and Forging

M398’s high carbide content requires a precise and specialized heat-treatment protocol, often involving multiple tempering cycles to balance hardness and structural stability.

Forging: As with most PM steels, forging is rare due to the risk of uneven carbide distribution and potential warping. Stock removal is the preferred method.

2.7 Patina Formation and Protective Coatings

Because M398 is stainless, it generally does not form a patina. Some makers still use blade coatings for aesthetic reasons or to add abrasion resistance, but it is not strictly necessary against rust.

3. Side-by-Side Comparison

ATTRIBUTE	K390 (PM)	M398 (PM)
Carbon Content	~2.47%	~2.7%
Chromium Content	~4.2% (Non-Stainless)	~20% (Stainless)
Typical Hardness (HRC)	62–64 (up to ~65–66 possible)	62–64 (can reach ~65–66)
Corrosion Resistance	4/10 (Requires care)	8–9/10 (Stainless)
Toughness	~5/10 (Decent)	Moderate to Low
Edge Retention	9/10 (Excellent)	Extremely High (Top Tier)
Ease of Sharpening	3/10 (Challenging)	Very Difficult (High-carbide content)
Ideal Applications	Heavy cutting, Bushcraft, EDC, Tactical	EDC, Kitchen, High-Wear Tasks

4. Real-World Usage Scenarios

4.1 Bushcraft and Survival

K390: Performs exceptionally well for carving, whittling, and repeated cutting without frequent stropping. However, it will rust if neglected, so consistent oiling or protective coatings are important in wet conditions.
M398: High wear resistance and stainlessness can be advantageous in humid or coastal regions. But be aware of potential chipping due to lower toughness under heavy stress.

4.2 Everyday Carry (EDC)

K390: If you prioritize extreme edge retention and can handle additional care to prevent corrosion, K390 is a top contender. May require consistent wipe-downs in damp climates.
M398: Ideal if you value a knife that remains sharp for an incredibly long time in a stainless package. Challenging to sharpen, but you rarely have to.

4.3 Kitchen Use

K390: Not typically the first choice due to rust concerns with acidic or moist foods. Still, its edge retention is outstanding if you meticulously dry and oil the blade.
M398: A better stainless option in the kitchen. The extremely high carbide content may lead to micro-chipping if used carelessly on bones or very hard materials. Proper technique and a sturdy cutting board are essential.

4.4 Tactical or Defensive

K390: Offers confidence in heavy or repeated tasks due to its wear resistance and sharpness retention. Must be kept clean to avoid corrosion.
M398: Adds stainlessness for harsh environments, though its lower toughness means you should avoid prying or lateral stress on the blade.

5. Cost, Availability, and Maintenance

Cost: Both steels are premium and command higher prices. M398 can be more expensive due to its relative rarity and specialized nature.
Availability:
- K390 has gained popularity (notably through Spyderco) and is more readily found in custom and production knives.
- M398 is newer and less common, so it may require searching specialized or custom knife makers.
Maintenance:
- K390 demands vigilant maintenance to prevent rust—drying the knife and applying a thin coat of oil helps greatly.
- M398 is more user-friendly in terms of corrosion but very difficult to sharpen—diamond or ceramic stones are highly recommended.

6. Pros and Cons

6.1 K390 Pros

Outstanding edge retention (~9/10).
Decent toughness (~5/10) for a high-carbide steel.
More widely available among certain knife makers/brands.

6.2 K390 Cons

Low corrosion resistance (4/10).
Can be difficult to sharpen for beginners.

6.3 M398 Pros

Extremely high wear resistance, surpassing many top-tier steels.
Stainless (~20% chromium), so significantly more rust-resistant than K390.
Great choice for extended use between sharpenings.

6.4 M398 Cons

Lower relative toughness (prone to chipping with improper use).
Rarer, often more expensive, and limited purchasing options.
Very difficult to sharpen without high-end abrasives.

7. Summary and Recommendations

If you’re someone who demands the highest level of edge retention and doesn’t mind regular maintenance against corrosion, K390 is a fantastic all-around performer. Its blend of high hardness, moderate toughness, and long-lasting sharpness suits bushcraft, EDC, and even some tactical roles—provided you keep it clean and dry.

On the other hand, if you need an ultra-premium stainless alternative that can cut for days without going dull, M398 might be your steel. It shines in environments where moisture or acidity is a concern, such as kitchen work or humid outdoor settings. The main trade-off is lower toughness and a more challenging sharpening experience, but for many users who prioritize edge retention and stainlessness, M398 is a dream come true.

Choose Based on Your Priorities

Pick K390 if:
- You want maximum edge retention in a non-stainless package.
- You can commit to regular cleaning and oiling to prevent rust.
- You value slightly better toughness than the most extreme high-carbide steels.
Pick M398 if:
- You need a stainless steel that pushes wear resistance to the absolute limit.
- You’re comfortable with a more difficult sharpening process.
- You’re willing to pay more for a rare, ultra-high-performance steel.

Both steels represent the pinnacle of modern metallurgy for knives. Whichever you choose, you’ll have a blade that stands out in performance. Just be sure you have the right sharpening tools and are prepared for the long haul—these steels are among the best at keeping an edge and can be equally stubborn when it’s finally time to restore it!

Additional Reading & References

Böhler Official Datasheets
Knife Steel Nerds for deeper technical breakdowns
Check specialty knife forums and makers for custom heat-treat protocols

Disclaimer: Always consult official datasheets or trust your knife’s manufacturer for exact composition and heat-treatment protocols, as variations in batches and custom processes can affect real-world performance.