M390 Knife Steel: History, Properties, and Practical Insights
Introduction (Historical and Practical Context)
M390 is a powder metallurgy stainless steel that has earned a prominent position in the knife industry for its excellent balance of wear resistance, corrosion resistance, and edge retention. Originally developed by Böhler-Uddeholm—and sometimes referred to as “M390 Microclean”—this steel was intended for use in cutting tools and industrial applications requiring long-lasting, sharp, and corrosion-resistant edges. Over time, knife manufacturers and custom bladesmiths recognized its potential in high-end, high-performance blades, leading to widespread use in the premium knife segment.
Today, M390 remains a favored choice among collectors, enthusiasts, and professionals who demand reliability and performance. Its unique combination of properties allows it to maintain keen edges for extended periods, even under rigorous use. Though it is not without limitations—particularly in terms of forging complexity and moderate toughness—M390’s reputation as a premium steel continuously attracts users looking for a reliable balance between hardness, corrosion resistance, and overall durability. M390’s chemical design and powder metallurgy technology set it apart from more conventional steels, positioning it alongside other “super steel” counterparts like CPM-20CV and CTS-204P.
Chemical Composition and Metallurgical Properties
Like most high-performance tool steels, M390’s properties are directly tied to its chemical makeup. It is produced using powder metallurgy (PM), which allows for a highly uniform distribution of carbides—hard particles formed by the combination of carbon and alloying elements. This uniform carbide structure significantly influences edge retention and wear resistance.
Below is a representative breakdown of M390’s composition (in approximate weight percentages):
- Carbon (C): ~1.9%
- Chromium (Cr): ~20%
- Manganese (Mn): ~0.3%
- Molybdenum (Mo): ~1%
- Silicon (Si): ~0.7%
- Tungsten (W): ~0.6%
- Vanadium (V): ~4%
Each element contributes unique properties:
- Carbon (1.9%) – Increases hardness and wear resistance. Higher carbon content directly boosts edge retention but must be balanced against potential brittleness.
- Chromium (20%) – Elevates corrosion resistance and helps form chromium carbides. High chromium is key to M390’s exceptional corrosion resistance.
- Manganese (0.3%) – Assists in hardenability but is kept low to avoid excessive brittleness.
- Molybdenum (1%) – Improves toughness, high-temperature strength, and pitting resistance.
- Silicon (0.7%) – Enhances overall strength and acts as a deoxidizer during production.
- Tungsten (0.6%) – Contributes to red hardness (resistance to softening at high temperatures) and wear resistance by forming complex carbides.
- Vanadium (4%) – Increases hardness, wear resistance, and grain refinement. Small, well-distributed vanadium carbides improve edge stability.
The powder metallurgy process ensures this chemical blend forms an even distribution of fine carbides, crucial for M390’s ability to maintain very good edge retention while still offering a serviceable level of toughness. M390 belongs to the same family of “super steels” as CPM-20CV (Crucible) and CTS-204P (Carpenter), which share near-identical compositions and thus exhibit very similar overall performance.
Forging Processes and Considerations
Although M390 can be forged, it is a challenging steel due to its high alloy content and relatively narrow forging window. Most manufacturers and bladesmiths opt for stock removal methods using bar stock produced via the powder metallurgy process. However, for those who prefer forging:
- Hot Forging: Typically performed above 2000°F (1093°C). Strict control over both temperature and duration is crucial. Excessive or uneven heat can lead to decarburization and carbide segregation, as well as grain coarsening.
- Cold Forging: Involves working the steel at or near room temperature. Given M390’s high hardness potential, this can be extremely difficult and bears a risk of cracking. Lengthy or aggressive cold working also increases the likelihood of warping if the microstructure is not carefully managed.
Common pitfalls include overheating during the forging process and overly rapid cooling, which may cause cracking. Because of M390’s composition—particularly high vanadium and chromium—any deviation from recommended temperature ranges can compromise the fine carbide structure. Less experienced bladesmiths often skip forging altogether to avoid these challenges, relying instead on stock removal.
Heat Treatment Nuances
Proper heat treatment is critical for getting the best performance out of M390. Manufacturers, custom bladesmiths, and heat-treating specialists typically follow a specific protocol for austenitizing (heating the steel until it transforms into austenite and dissolves carbides), quenching, and tempering:
- Austenitizing Temperature: Usually between 2100°F (1149°C) and 2150°F (1177°C). While higher temperatures up to about 2200°F can increase hardness, they can also cause excessive grain growth.
- Quenching: An oil or forced-air quench is recommended to cool the steel rapidly, “locking in” the dissolved carbon and alloying elements. This forms a martensitic structure.
- Tempering: Commonly done in two cycles to stabilize the microstructure. Tempering temperatures typically range from 350°F (177°C) to 450°F (232°C), based on the desired balance of hardness and toughness.
Below is a simplified table illustrating generalized hardness outcomes relative to austenitizing temperature (actual results may vary):
| Austenitizing Temperature (°F) | Typical Hardness (HRC) |
|---|
| 2100 | 60–61 |
| 2150 | 61–62 |
| 2200 | 62–63 |
A cryogenic (sub-zero) treatment step between quenching and tempering can further reduce retained austenite, increasing hardness and wear resistance. Many professional heat treaters use liquid nitrogen at around -300°F (-184°C) for this phase, fully optimizing M390’s microstructure.
Performance Characteristics and Properties
M390’s popularity in high-end knife circles largely stems from its well-rounded performance profile:
- Corrosion Resistance: With approximately 20% chromium, plus added molybdenum, M390 provides excellent corrosion resistance—ideal for humid or marine environments.
- Toughness: Considered fair. It handles typical cutting tasks but may not withstand heavy prying or repeated impact as well as certain lower-alloy steels like CPM-3V.
- Edge Retention: M390 excels at retaining a sharp edge, thanks to its fine carbide dispersion and high hardness potential—making it stand out among many stainless steels.
- Ease of Sharpening: While not as easy to sharpen as simpler alloys, M390 is more user-friendly than some other ultra-high-wear steels (e.g., CPM-S110V). Quality diamond products or ceramic rods can quickly restore a razor-sharp edge.
These attributes make M390 especially appealing to users who need a blade that cuts for extended periods without frequent maintenance or resharpening.
Comparisons to Other Steels
M390 differs from other steels according to user needs and preferences:
- M390 vs. CPM-3V: CPM-3V offers outstanding toughness but is less corrosion-resistant. M390 provides a more stainless option with superior long-term edge holding under regular cutting tasks.
- M390 vs. AEB-L: AEB-L boasts excellent toughness and is easy to sharpen, but it cannot match M390’s wear resistance or higher-end hardness range.
- M390 vs. 154CM: 154CM is a more affordable stainless steel with a decent balance of properties. M390, however, surpasses it in edge retention and corrosion resistance.
- M390 vs. CPM-20CV / CTS-204P: These three steels are extremely similar in composition and performance, often considered interchangeable. Subtle differences arise mostly from proprietary heat treatments rather than the steel itself.
Overall, M390 stands out for its high corrosion resistance, extended edge retention, and a hardness range that remains manageable for experienced hobbyists and professionals alike.
Practical Applications
The properties of M390 make it suitable for various knife designs:
- Everyday Carry (EDC): Folders benefit from M390’s minimal maintenance needs and sharp edge retention, reducing the frequency of resharpening.
- Hunting and Field Knives: M390’s fair toughness suffices for typical tasks like skinning and processing game. The steel shrugs off corrosion from blood and fluids, ensuring easier cleanup.
- Bushcraft and Survival: Although not the top choice for heavy-duty chopping, M390 can handle medium-duty tasks if used sensibly. Steels like CPM-3V might be more appropriate for extreme impacts or prying.
- Kitchen Knives: Some high-end kitchen knives use M390, valued for its corrosion resistance and ability to hold a keen edge through extensive slicing or dicing sessions.
While abusive uses may expose M390’s moderate toughness limits, it excels in most cutting-focused roles.
Maintenance and Care
One of M390’s prime advantages is its strong corrosion resistance, making upkeep simpler compared to many other high-performance steels. Recommended practices include:
- Cleaning and Drying: Although M390 is resistant to rust, rinsing and drying promptly after contact with saltwater or acidic materials helps preserve a flawless finish.
- Lubrication: A light coat of oil or a rust-inhibiting lubricant is advisable for extra protection in humid environments or long-term storage.
- Sharpening Tools: Diamond plates, ceramic rods, or premium whetstones are ideal for M390. Consistent, light touch-ups keep the edge in peak shape without exhaustive sharpening sessions.
Since M390 inherently resists patina formation, blades typically retain their original finish with only minimal cosmetic changes over time.
Cost and Value
Positioned in a premium tier among knife steels, M390 generally carries a higher price tag due to its powder metallurgy production and advanced performance:
- Long-Term Investment: Users seeking a blade that remains sharp with minimal corrosion risks and only occasional maintenance often find M390’s cost worthwhile.
- Comparison to Ultra-High-Wear Steels: M390 sits slightly below certain exotic steels (like CPM-S110V) in price, while offering a substantially easier sharpening experience.
Consequently, many production and custom knife makers position M390-based models at the upper echelon of their product lines, balancing cost-effectiveness and top-level performance.
Popular Knives Featuring M390
Several notable production and custom models use M390 to leverage its corrosion resistance and edge performance:
- Benchmade 940-1 (Limited/Special Runs): Though the classic 940 series often uses other steels, certain versions feature M390 for enhanced cutting performance.
- Microtech Ultratech: Various runs utilize M390 to improve edge retention in this iconic out-the-front (OTF) knife.
- Zero Tolerance (ZT) Models: Limited editions and high-end production lines frequently showcase M390, pairing advanced features with superior steel.
- Custom/Mid-Tech Knives: Many boutique makers select M390 for its mix of premium aesthetics and performance.
These examples highlight M390’s status as both a prestigious and practical steel that appeals to discerning collectors and avid knife users alike.
Conclusion
M390 has rightfully earned its distinction as a premier knife steel. Originating from an advanced powder metallurgy process, it combines an outstanding balance of wear resistance, corrosion resistance, high achievable hardness, and approachable sharpening needs. When heat-treated correctly—often with a cryogenic step—M390 typically attains a Rockwell hardness of 60–62 HRC (or slightly higher), providing remarkable edge retention in everyday and specialized applications.
While its toughness does not rival certain lower-alloy steels and forging M390 remains challenging, it shines in most cutting tasks, retaining sharp edges for far longer than many alternatives. For enthusiasts and professionals prioritizing reliable, high-performance blades that resist corrosion and minimize maintenance, M390 represents a top-tier choice in today’s premium knife market.
Key Takeaways
- High-End Powder Metallurgy Steel: M390 is produced via PM technology, yielding an exceptionally uniform carbide structure for excellent wear and corrosion resistance.
- Optimal Heat Treatment is Essential: Proper austenitizing, quenching, cryogenic treatment, and tempering maximize M390’s edge retention and resilience.
- Part of the “Super Steel” Family: M390 compares closely to CPM-20CV and CTS-204P, all prized for their top-tier performance in premium knives.
- Balanced Performance: M390 offers superb edge retention and outstanding corrosion resistance, balanced by moderate toughness.
- Premium Tier Pricing: While more expensive than many mid-range steels, M390’s long-term durability and minimal maintenance often justify the investment.
By incorporating these considerations into your purchasing or crafting decisions, you can fully appreciate M390’s remarkable capabilities and decide whether it suits your particular needs—whether in an EDC folder, a hunting blade, or a specialty kitchen knife.