M398 vs CPM S90V Knife Steel Comparison

M398 vs CPM-S90V – A Complete Comparison for Knife Aficionados

Table of Contents

1. Introduction
2. Overview of M398 Steel
   2.1 Chemical Composition
   2.2 Typical Hardness (Rockwell C) Ranges
   2.3 Key Performance Characteristics
3. Overview of CPM-S90V Steel
   3.1 Chemical Composition
   3.2 Typical Hardness (Rockwell C) Ranges
   3.3 Key Performance Characteristics
4. Detailed Alloy Element Effects
5. Heat Treatment Nuances and Forging
6. Patina Formation and Protective Coatings
7. Side-by-Side Comparison: M398 vs CPM-S90V
   7.1 Edge Retention and Wear Resistance
   7.2 Toughness and Chipping Risk
   7.3 Corrosion Resistance
   7.4 Ease of Sharpening
   7.5 Cost and Availability
8. Ideal Uses and Reasons to Choose One Over the Other
9. Pros and Cons of Each Steel
10. Conclusion and Recommendation

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1. Introduction

For collectors and everyday knife users alike, high-performance steels are often the centerpiece of an excellent blade. Two steels that frequently come up in discussions about premium or “super steel” performance are Böhler-Uddeholm M398 and Crucible’s CPM-S90V. Both are powdered metallurgy steels celebrated for their exceptional edge retention, corrosion resistance, and high hardness. While they share several attributes, they also differ in important ways that can influence your decision for a particular knife or use case.

In this comprehensive guide, we’ll explore these two steels, dissecting their compositions, ideal hardness ranges, heat-treat details, and performance characteristics. By the end, you’ll have the knowledge to decide which steel—M398 or CPM-S90V—best suits your needs.

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2. Overview of M398 Steel

2.1 Chemical Composition

Böhler-Uddeholm M398 is a high-alloy stainless steel formulated to deliver outstanding wear resistance and impressive corrosion resistance. While exact numbers can vary slightly among sources or manufacturer batches, a generally referenced composition is:

• Carbon (C): ~2.0%
• Chromium (Cr): ~19.0–19.5%
• Vanadium (V): ~3.8%
• Molybdenum (Mo): ~1.0%
• Tungsten (W): ~0.7%
• Manganese (Mn): ~0.3–0.5%
• Silicon (Si): ~0.5–0.7%

This high carbon content, combined with substantial chromium and vanadium levels, gives M398 its excellent hardness and extended edge retention capabilities.

2.2 Typical Hardness (Rockwell C) Ranges

M398 is commonly hardened to around 60–64 HRC, with some makers pushing it toward the upper range to maximize wear resistance. As hardness goes up, toughness typically goes down, so knife makers must balance edge-holding with overall blade resilience to minimize chipping.

2.3 Key Performance Characteristics

• Corrosion Resistance: Excellent. M398 contains enough chromium to handle wet or humid environments exceptionally well.
• Toughness: Fair. Its high carbide content makes it more prone to chipping than simpler steels, but it’s still fine for normal EDC and kitchen use.
• Edge Retention: Outstanding. It ranks among the top steels for cutting tasks that require sustained sharpness over long periods.
• Ease of Sharpening: Poor. Like other high-vanadium steels, M398 necessitates diamond or CBN abrasives for efficient sharpening.

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3. Overview of CPM-S90V Steel

3.1 Chemical Composition

Crucible Particle Metallurgy (CPM) S90V is a pioneering super steel renowned for blending excellent edge retention with solid corrosion resistance. Its composition generally includes:

• Carbon (C): ~2.3%
• Chromium (Cr): ~14%
• Vanadium (V): ~9%
• Molybdenum (Mo): ~1%

Large amounts of vanadium create extremely hard carbides, propelling CPM-S90V to the forefront of edge-holding capabilities.

3.2 Typical Hardness (Rockwell C) Ranges

CPM-S90V typically sits in the 59–61 HRC range, with certain custom treatments bringing it up to around 62 HRC. As with M398, higher hardness bolsters wear resistance but can increase brittleness, so most production knives aim for approximately 60–61 HRC for a good balance.

3.3 Key Performance Characteristics

• Corrosion Resistance: Very good. Though it has less chromium than some stainless steels, the CPM process optimizes its corrosion resistance.
• Toughness: Fair. Like M398, it’s not meant for heavy-impact tasks but performs admirably in slicing and day-to-day cutting.
• Edge Retention: Excellent. CPM-S90V holds an edge exceptionally well, especially for detailed slicing.
• Ease of Sharpening: Poor. High vanadium carbide content makes it difficult to sharpen without diamond or CBN stones.

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4. Detailed Alloy Element Effects

• Carbon (C): Elevates hardness and wear resistance. Both M398 and S90V have high carbon content, supporting their ability to reach high Rockwell hardness values.
• Chromium (Cr): Crucial for stainless properties; M398 has around 19% while S90V has about 14%, giving M398 a slight edge in corrosion protection.
• Vanadium (V): Forms extremely hard vanadium carbides that enhance wear resistance. S90V’s ~9% vanadium is notably higher than M398’s ~3.8%.
• Molybdenum (Mo): Strengthens steels at high temperatures and aids corrosion resistance. Both steels contain ~1% Mo.
• Tungsten (W): Present in M398, helps refine grain structure and contributes to wear resistance.

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5. Heat Treatment Nuances and Forging

M398

• Requires careful heat treatment and cryogenic processes to optimize hardness and wear resistance.
• Its high carbide content makes stock removal the more common manufacturing method, as forging is particularly challenging.

CPM-S90V

• The CPM process disperses carbides uniformly, reducing distortion risks.
• Still benefits from pre-heating, controlled cooling, and cryogenic treatments to stabilize the microstructure.
• Also more often stock-removed than forged due to its wear resistance.

Both steels are highly alloyed and require precise control at each stage of heat treatment to avoid warping or sub-optimal carbide formation.

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6. Patina Formation and Protective Coatings

Since both M398 and CPM-S90V contain high levels of chromium, they are classified as stainless steels and do not readily form a patina (unlike 1095 or W2 carbon steels). Most users will never see a patina on these steels under normal conditions. Protective coatings (e.g., DLC, PVD) are optional but may be applied to reduce reflectivity, improve blade aesthetics, or add an extra layer of wear protection.

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7. Side-by-Side Comparison: M398 vs CPM-S90V

Below is a quick-reference table that summarizes key attributes:

Attribute	M398	CPM-S90V
Typical HRC Range	~60–64	~59–61 (up to 62)
Corrosion Resistance	Excellent	Very Good
Toughness	Fair	Fair
Edge Retention	Excellent	Excellent
Ease of Sharpening	Poor	Poor

7.1 Edge Retention and Wear Resistance

Both steels stand out for top-tier edge retention, making them ideal for cutting tasks where the blade must remain sharp over extended usage. M398’s higher attainable hardness may offer an incremental boost in pure wear resistance, though the real-world difference from S90V is usually subtle for most users.

7.2 Toughness and Chipping Risk

Neither steel is aimed at high-impact or prying tasks. They have “fair” toughness compared to more shock-absorbing steels. Used appropriately (for slicing, EDC, and kitchen work), both should perform without significant chipping.

7.3 Corrosion Resistance

• M398: With chromium near 19–19.5%, it provides outstanding rust resistance even in demanding conditions.
• CPM-S90V: Very good stainless performance, sufficient for the vast majority of everyday or outdoor scenarios.

7.4 Ease of Sharpening

In both steels, the high volume of vanadium carbides requires diamond or CBN abrasives for best results. Traditional sharpening stones (aluminum oxide, ceramic) tend to struggle, making the process time-consuming unless you have specialized equipment.

(Note: For those tackling their own sharpening, a slightly higher edge angle—around 20° per side—can offer a touch more durability for these ultra-hard steels, though some prefer more acute angles for push-cutting performance.)

7.5 Cost and Availability

While both come with a premium price tag, CPM-S90V is more commonly found in production models from major brands like Spyderco and Benchmade. M398 is still emerging and often appears in custom or limited-run knives. Expect higher prices and potentially longer waits to find an M398 blade.

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8. Ideal Uses and Reasons to Choose One Over the Other

Ideal Uses for M398

• Heavy Cutting Sessions: Exceptional wear resistance for extended slicing (e.g., cardboard, rope).
• Kitchen Knives: Strong corrosion resistance makes it worry-free in wet, acidic environments.
• Collectibles: Its relative rarity and high-end performance appeal to knife enthusiasts seeking something unique.

Reasons to Pick M398

• You want extraordinary edge retention and robust corrosion protection.
• You’re prepared to invest in specialized, high-grit diamond or CBN stones.
• You appreciate owning a less common steel with “wow factor.”

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Ideal Uses for CPM-S90V

• EDC (Everyday Carry): Balances long-lasting sharpness with good corrosion resistance.
• Tactical/Survival: Fair toughness plus stainless qualities for diverse field conditions.
• High-End Production Knives: S90V is offered by numerous top-tier knife brands, easing market availability.

Reasons to Pick CPM-S90V

• You want a proven super steel that’s easier to find in various production knife models.
• You value excellent edge retention and accept that sharpening requires advanced tools.
• You prefer a steel with a significant track record and wide user feedback.

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9. Pros and Cons of Each Steel

M398 – Pros and Cons

Pros

• Phenomenal edge retention
• Excellent corrosion resistance
• Distinctive, rare steel for collectors

Cons

• Modest toughness (not for heavy prying or striking)
• Demanding to sharpen without advanced abrasives
• Premium or custom-knife pricing and limited availability

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CPM-S90V – Pros and Cons

Pros

• Outstanding edge retention
• Very good corrosion resistance
• Widely available among major knife manufacturers

Cons

• Still challenging to sharpen; requires diamond or CBN stones
• Only fair toughness; not suited to extreme impact
• Higher cost bracket than many standard steels

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10. Conclusion and Recommendation

Both M398 and CPM-S90V exemplify top-tier performance in the world of stainless, high-wear-resistant steels. Their fair toughness levels suffice for ordinary cutting and slicing but won’t excel in heavy-impact tasks or misuse scenarios.

• Choose M398 if you prize the highest possible edge retention at elevated hardness levels, coupled with excellent corrosion resistance—and you’re prepared for specialized sharpening methods. M398’s relative rarity also appeals to collectors seeking something exclusive.

• Choose CPM-S90V if you prefer a well-established steel that delivers nearly equivalent performance, is easier to source in production knife lines, and has ample user feedback confirming its reliability.

In either case, you’ll end up with a top-tier blade capable of exceptional sharpness and longevity. Both steels stand at the cutting edge of modern metallurgy, ensuring you’ll enjoy a knife that keeps performing longer than most competing alloys.