M398 is a high-performance, powder-metallurgy (PM) tool steel developed by Böhler-Uddeholm. While precise introduction dates are not always publicized, it emerged during the late 20th and early 21st centuries—an era when powder-metallurgy processes were transforming the knife industry. Powder metallurgy allows for extremely fine microstructures and uniform carbide distribution, enabling steels like M398 to achieve exceptional wear resistance and hardness.
The chemistry of M398 sets it apart for those seeking maximum edge retention. Knifemakers, from custom workshops to mid-tech manufacturers, have experimented with M398 to create blades capable of retaining a razor-sharp edge through demanding cutting tasks. Its enduring appeal stems from a compelling balance of:
As a premium steel, it often carries a higher price tag, but the performance benefits can justify the investment for discerning users and enthusiasts.
Below is the typical composition of M398 by weight. Note that official references from Böhler-Uddeholm may list slightly varying percentages (e.g., 2.7–2.95% C, 18.9–20% Cr, 7–8.7% V).
Typical Composition of M398 (by weight, approximate):
Carbon (2.7–2.95%)
High carbon levels significantly boost hardness and wear resistance. Much of the carbon forms carbides with elements such as vanadium and tungsten.
Chromium (19–20%)
Enhances corrosion resistance and helps the steel through heat treatment (hardenability). This high chromium content is why M398 excels in humid or wet conditions.
Manganese (~0.3–0.5%)
Improves depth-hardening and tensile strength, supporting overall toughness in the steel matrix.
Molybdenum (~1%)
Contributes to hardness retention at high temperatures and aids corrosion resistance.
Silicon (~0.4–0.5%)
Increases strength and helps deoxidize the steel. It can offer minor wear resistance benefits.
Tungsten (~0.6–0.7%)
Forms very hard tungsten carbides, further boosting abrasion resistance.
Vanadium (~7–8.7%)
Critically important for forming extremely hard vanadium carbides, which drive M398’s impressive edge retention.
The powder-metallurgy process yields a dense structure with a fine dispersion of carbides in a martensitic matrix after heat treatment. This results in outstanding wear resistance but also makes M398 more challenging to sharpen and reduces its toughness relative to simpler alloys.
M398 is primarily produced via powder metallurgy and is most often used in stock-removal applications due to its high hardness and carbide content. Nevertheless, some specialty makers may consider forging under specific conditions:
Hot Forging
Conducted at temperatures above ~2000 °F (about 1093 °C). Precision in temperature control is vital to prevent excessive grain growth and carbide segregation. Improper or overly aggressive practices at high temperatures can lead to large carbide clusters and increase the risk of cracking.
Cold Forging
Uncommon because M398’s high hardness (especially after preliminary heat treatments) makes it extremely difficult to deform without micro-cracking. The substantial carbide content also causes significant wear on tooling.
Warping
Rapid or uneven heating and cooling can result in warping due to M398’s high hardness potential and alloy content. Preheating and careful step-cooling protocols help mitigate this risk.
Cracking
If worked too aggressively or at improper temperatures, micro-cracks can form around carbide clusters. This is another reason many makers avoid forging M398 altogether.
Note: Most makers opt for stock-removal methods to shape M398, as it is more consistent and less risky than forging for this high-carbide steel.
A carefully managed heat-treatment process is essential for maximizing M398’s performance. While specifics vary by manufacturer and shop experience, general industry guidelines include:
Preheating
Typically in one or two stages (e.g., 1500–1600 °F / 815–870 °C) to minimize thermal shock before reaching austenitizing temperature.
Austenitizing
Commonly in the 2050–2150 °F (1120–1177 °C) range. Higher temperatures can increase hardness but raise the risk of grain coarsening if soak times are not controlled.
Quenching
Rapid quenching (oil or fast-moving air/gas) is crucial to form the desired martensitic structure. However, the high hardness potential means extra care is needed to prevent cracks.
Cryogenic Treatment (Optional)
Some knifemakers add a cryogenic cycle (e.g., -300 °F / -184 °C in liquid nitrogen) to refine the grain, reduce retained austenite, and improve dimensional stability before tempering.
Tempering
Commonly at 400–600 °F (204–316 °C). Multiple tempering cycles may be used to dial in the balance of hardness, toughness, and stress relief.
Below is an illustrative table correlating austenitizing temperature, tempering temperature, and typical hardness values. Actual results can vary based on soak time, quench rate, and batch size.
| Austenitizing Temp (°F) | Tempering Temp (°F) | Approx. Hardness (HRC) |
|---|---|---|
| 2050 | 400–450 | 60–62 |
| 2100 | 400–450 | 61–63 |
| 2150 | 400–450 | 62–64 |
Tip: Soak times and multiple temper cycles can shift hardness by 1–2 HRC points. Consistent temperature control is paramount for reliable results.
Edge Retention
M398 excels in holding a sharp edge for extended periods, thanks to abundant vanadium and tungsten carbides. It shines in abrasive cutting tasks.
Toughness
Though not brittle to the point of being unusable, M398’s toughness is relatively moderate. Users should avoid heavy prying or significant lateral stress, as chipping is more likely than with simpler or shock-resistant steels.
Corrosion Resistance
With ~19–20% chromium, M398 offers excellent protection against rust in most common environments. Routine cleaning and drying further preserve the blade’s finish.
Ease of Sharpening
M398 is challenging to sharpen by traditional means because of its high volume of very hard carbides. Many hobbyists and professionals rely on diamond or ceramic abrasives. Regular honing with a ceramic rod can extend the interval between full sharpenings.
M390 or CPM-20CV
M398 often provides even higher edge retention (due to slightly higher vanadium and carbon content) at the cost of tougher sharpening and potentially less overall toughness.
CPM-3V
Known for its outstanding toughness, CPM-3V cannot match M398’s wear or corrosion resistance. M398, in turn, is more vulnerable to chipping than CPM-3V.
AEB-L
A simpler stainless steel with excellent toughness and easier sharpenability. AEB-L cannot reach the extreme wear resistance of M398 but is more forgiving for general use or when frequent sharpening is acceptable.
EDC (Everyday Carry) Folding Knives
Ideal for users seeking extended time between sharpenings. Be prepared for a more time-intensive sharpening routine.
Hunting and Skinning Knives
M398’s high edge retention is beneficial for processing game. Its corrosion resistance is an asset in outdoor and potentially wet conditions.
Bushcraft or Survival Knives
While it performs well for slicing or fine tasks, caution is advised if prying or batonning through hardwood is expected. A more impact-resistant steel may be preferable.
High-End Kitchen Knives
Chefs appreciate minimal downtime for resharpening. However, specialized diamond or ceramic sharpeners are often necessary to manage M398’s high hardness.
Thanks to its elevated chromium content, M398 is relatively easy to maintain regarding corrosion. Still, it’s wise to keep the blade clean and dry, especially in saltwater or acidic environments. Since M398 has moderate toughness (rather than high), avoid heavy impact or bending forces.
M398 is considered a premium steel due to the advanced powder-metallurgy process and high-alloy composition. It typically carries a higher price point than simpler or more conventional ingot steels. However, for knife enthusiasts, professionals, or collectors seeking:
…the investment can be well worth it. M398’s “sweet spot” is in roles where abrasion resistance and durability against corrosion matter more than outright toughness or ease of sharpening.
Although not as mainstream as M390 or CPM-S30V, M398 appears in select boutique runs and custom blades:
Availability: Bar stock is less common than more established steels, which means M398 knives can be harder to find and come at a premium price.
M398’s position in the knife industry stems from its remarkable wear resistance, robust corrosion resistance, and good (though not extreme) toughness. Powder metallurgy and a carefully balanced composition of high-carbon, high-vanadium, and tungsten content create a blade that excels in edge retention.
On the flip side, the very factors that gift M398 its durability and razor-sharp performance also make it more difficult to sharpen and less tolerant of lateral abuse. Still, for users focused on edge longevity—be it in everyday carry, hunting, or high-end kitchen contexts—M398 is a formidable choice. Despite its premium cost, many find the benefits in extended cutting performance and reduced maintenance to be well worth the investment.
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