By Yashar Mousavand • Lead Instructor
This article is written from a bushcraft and survival training perspective at Yashar Survival Academy. It focuses on microstructural causes of corrosion in knife-grade stainless steels and on practical controls a buyer or maker can use: heat treatment parameters, carbide management, surface condition, and carry discipline. Technical claims are backed by the references listed at the end. [1]
1) What stainless really means for a bushcraft knife
In the field, “stainless” does not mean “never stains.” It means the alloy can form and maintain a protective passive film, typically chromium oxide, that slows corrosion. In knife steels, the critical variable is not just nominal chromium content but how much chromium remains available in the steel matrix to support that passive film. Knife Steel Nerds summarizes that corrosion rate drops significantly as chromium is added until around the low teens percent, and notes that the stainless cutoff is often described as roughly 10.5 to 12 percent chromium depending on the definition. [6]
For knife users, the key concept is matrix chromium. If chromium is tied up in carbides, it is not contributing to the passive film in the matrix. That is why two blades labeled “stainless” can behave differently in wet sheaths or salty sweat.
2) Carbides: the wear benefit that can tax corrosion resistance
Carbides are hard particles formed when carbon bonds with alloying elements. In martensitic stainless knife steels, chromium carbides are common. Carbides help wear resistance and edge retention, but they also consume chromium that would otherwise remain in solid solution in the matrix.
2.1 Chromium tie up and passive film quality
Alleima explains the mechanism in knife specific terms: carbides tie up chromium, and when enough carbides are dissolved during hardening, chromium (and molybdenum when applicable) is released into the matrix so it can form a protective passive film on the surface. [2]
2.2 Carbide size matters because dissolution is not equal
Alleima also points out that carbide size affects corrosion resistance because large primary carbides do not dissolve to the same degree during hardening as small carbides. If carbides remain undissolved, chromium stays locked in those particles, leaving less chromium in the matrix to support passivation. [2]
What this means in practice:
- High wear stainless steels often rely on higher carbide volume. That can be excellent for abrasive wear but increases the risk of chromium being tied up in carbides.
- Fine carbide microstructures generally give a more uniform matrix chemistry after heat treatment, which supports more uniform passivation.
- Two knives with the same steel can differ in corrosion performance if one has a microstructure with more undissolved carbides due to its heat treatment window.
3) Heat treat is the corrosion switchboard
For martensitic stainless knife steels, corrosion resistance is strongly shaped by how the maker runs three linked steps: austenitizing, cooling after hardening, and tempering. Manufacturer guidance explicitly warns that incorrect parameters can reduce corrosion resistance.
3.1 Austenitizing: dissolve enough carbides, but do not overshoot the window
Austenitizing temperature and time determine how much carbide is dissolved and therefore how much chromium returns to the matrix. Alleima’s 14C28N datasheet states that a low hardening temperature gives low hardness and reduced corrosion resistance. [4]
That statement is important because it links corrosion resistance to hardening parameters, not to alloy name alone. The same datasheet also warns that incorrect time at the hardening temperature affects retained austenite and hardness. [4] For corrosion, the practical point is to stay inside the datasheet window so the microstructure is what the steel was designed to deliver.
3.2 Cooling rate after hardening: a direct corrosion risk lever
Cooling rate is one of the most common hidden reasons a “stainless” knife stains early. Alleima’s 12C27 datasheet states that a high cooling rate after hardening is necessary to avoid brittleness and reduced corrosion resistance. It even provides a target: 600 C should be reached within 1 to 2 minutes and room temperature within 30 minutes. [3]
This matters because insufficient cooling rate can allow chromium rich carbides to precipitate in ways that reduce corrosion resistance. The stainless steel sensitisation literature describes the core mechanism: precipitation of chromium rich carbides at grain boundaries depletes adjacent zones of chromium, increasing the likelihood of localized corrosion. [11]
You do not need to treat your knife like a welded pressure vessel to benefit from this concept. The knife specific takeaway is simpler: if the datasheet calls for fast cooling to avoid reduced corrosion resistance, the maker must be able to execute that cooling rate uniformly on the blade geometry. [3]
3.3 Tempering: corrosion can be traded for wear at high temperatures
Tempering is required to reduce quench stresses and stabilize the steel, but tempering temperature changes carbide behavior. Uddeholm states that precipitation of secondary carbides occurs when tempering highly alloyed steel at high temperature, and that this will be detrimental to corrosion resistance while giving somewhat higher wear resistance. [5]
This is a clear statement of an engineering tradeoff: corrosion resistance and wear resistance can pull in opposite directions depending on tempering strategy. If a maker is tuning for maximum wear, the corrosion penalty may show up later as staining, pitting, or crevice attack, especially in chloride exposure.
4) Stainless in the wild: the corrosion modes bushcrafters actually see
4.1 Pitting in chloride exposure
Pitting is localized breakdown of the passive film, commonly accelerated by chlorides from sweat, sea spray, or salty food prep. Once a pit initiates, local chemistry inside the pit becomes more aggressive, so pits can grow even when the rest of the blade looks fine.
4.2 Crevice corrosion: why sheaths defeat stainless
Crevice corrosion is a localized form of attack where the passive surface layer breaks down in crevices or shielded areas beneath deposits. The British Stainless Steel Association describes it as breakdown of the surface passive layer in crevices or on shielded areas. [9] A ScienceDirect review similarly defines crevice corrosion as localized accelerated dissolution after breakdown of the protective passive film. [10]
Knife relevant crevices include the inside of a wet sheath, under a guard, around fasteners, or under stubborn deposits. In bushcraft, the most common crevice is simple: a blade put into a sheath while damp, especially after salt exposure.
Field indicator:
- Pitting often shows as isolated dark dots or craters, frequently along scratches or near deposits.
- Crevice corrosion often appears where oxygen renewal is restricted: under handle scales, in the sheath contact zone, or under dried mud or sap.
5) Surface finish and thermal damage can dominate corrosion initiation
Even with correct alloy and heat treatment, surface condition can decide whether corrosion initiates. Finish changes both the number of initiation sites and how easily deposits and chlorides remain trapped on the surface.
5.1 Finish roughness and corrosion: quantified evidence
The British Stainless Steel Association reports that variations in dull polished finishes on the same grade can produce significant differences in corrosion resistance, and notes development of well defined polished finishes such as EN 10088-2 2K with a specified maximum roughness of 0.5 microns Ra. [7]
Peer reviewed work shows the same direction of effect. A 2024 study on 304 stainless in seawater reported that as average roughness Ra increased, pitting potential decreased linearly, and the smoothest surface condition in the study showed higher corrosion resistance. [8]
5.2 Grinding and localized overheating risk
Any localized thermal event that changes near surface microstructure can reduce corrosion resistance. For knife makers, that means controlling finishing heat input and avoiding conditions that can locally alter carbide precipitation or passive film quality.
Practical buyer guidance:
- If corrosion resistance is a priority, prefer a cleaner, smoother finish over a deep coarse belt finish. [7][8]
- Treat deep scratches as corrosion accelerators because they hold chlorides and act as initiation sites.
- If you do your own refinishing, keep temperatures controlled and avoid localized overheating.
6) What to ask a maker if you care about corrosion resistance
Steel name is not enough. Ask process questions that map directly to corrosion mechanisms.
- What is the hardening temperature and hold time for this steel, and why? (A low hardening temperature can reduce corrosion resistance in 14C28N.) [4]
- How do you control and verify cooling rate after hardening? (12C27 guidance ties cooling rate directly to reduced corrosion resistance.) [3]
- What tempering temperature range and number of cycles do you use, and what tradeoffs are you targeting? (High temperature tempering can reduce corrosion resistance via secondary carbide precipitation.) [5]
- What finishing steps happen after heat treatment, and how do you prevent localized overheating or surface damage?
- What sheath materials and drainage features do you recommend for wet carry? (Crevice corrosion is driven by shielded, oxygen restricted zones.) [9][10]
7) A field protocol that keeps stainless stainless
Corrosion is a system problem: environment plus time plus crevices. In bushcraft you can control the time part.
- After salt exposure or sweaty carry, rinse with clean water and wipe dry. Chlorides are a high leverage trigger for localized attack.
- Do not sheath the knife wet unless you accept crevice conditions. If you must sheath wet, remove the knife later, dry it, and let the sheath drain and dry. [9][10]
- Keep the blade surface reasonably smooth if corrosion is your problem. A smoother finish reduces pitting risk compared with rougher finishes. [7][8]
- Inspect the sheath contact band for early dots or staining. That is where crevice conditions develop first.
- For storage after wet trips, apply a thin protective oil film and store the knife out of the sheath.
8) A decision framework for bushcraft buyers
Use this order of operations to avoid steel marketing traps:
- Define your environment: constant humidity, river work, and coastal salt demand stronger corrosion control than dry inland use.
- Define your worst acceptable failure mode: cosmetic staining is annoying; pitting at the edge or in a sheath band is performance relevant.
- Select a maker, not just a steel. Look for process transparency on austenitizing, cooling rate, and tempering. [3][4][5]
- Select finish and sheath system to match the environment. Drainage and drying discipline can matter as much as alloy choice. [7][9][10]
You Might also like: Edge retention vs toughness vs corrosion resistance
About the author
Yashar Mousavand is a survival instructor and the founder of Yashar Survival Academy. The Academy exists to make outdoor skills understandable, reliable, and usable when it matters most, combining field tested techniques with evidence based guidance. [1]
References
[1] Yashar Survival Academy, About page (author and training philosophy). https://yashar-survival.ir/en/about-me/
[2] Alleima technical article: microstructure, carbides tie up chromium; carbide size affects dissolution and corrosion. https://www.alleima.com/en/news-media/technical_articles_blogs/2024/01/is-the-secret-to-high-quality-knife-steel-in-the-microstructure/
[3] Alleima 12C27 datasheet PDF: high cooling rate after hardening needed to avoid brittleness and reduced corrosion resistance; 600 C in 1 to 2 min. https://www.alleima.com/contentassets/f19934a765084f1c9c5e21081325275b/datasheet-alleima-12c27-en-v2025-05-12-1022-version-1.pdf/download
[4] Alleima 14C28N datasheet page: low hardening temperature gives reduced corrosion resistance; time and temperature effects. https://www.alleima.com/en/technical-center/material-datasheets/strip-steel/alleima-14c28n/
[5] Uddeholm Heat Treatment guide PDF: high temperature tempering precipitates secondary carbides, detrimental to corrosion resistance, increases wear. https://www.uddeholm.com/app/uploads/sites/216/2024/05/Tech-Uddeholm-Heat-treatment-EN.pdf
[6] Knife Steel Nerds: corrosion resistance vs hardness in knife steels; stainless cutoff discussion; chromium and passive film basics. https://knifesteelnerds.com/2025/07/14/corrosion-resistance-vs-hardness-in-knife-steels/
[7] British Stainless Steel Association: Importance of Surface Finish in the Design of Stainless Steel (EN 10088-2 2K max Ra 0.5 microns; finish affects corrosion). https://bssa.org.uk/wp-content/uploads/2021/02/surfacefinishbssaVer2.pdf
[8] Journal of Materials Engineering and Performance (Springer): surface roughness vs pitting behavior of stainless in seawater; higher Ra lowers pitting potential. https://link.springer.com/article/10.1007/s11665-024-10527-1
[9] British Stainless Steel Association: Principles and prevention of crevice corrosion; passive layer breakdown in crevices and under deposits. https://bssa.org.uk/bssa_articles/3-principles-and-prevention-of-crevice-corrosion/
[10] ScienceDirect review: crevice corrosion is localized dissolution after breakdown of protective passive film. https://www.sciencedirect.com/science/article/pii/S1350630722009220
[11] British Stainless Steel Association: Sensitisation of stainless steels PDF; chromium rich carbide precipitation depletes adjacent zones and increases localized corrosion risk. https://bssa.org.uk/wp-content/uploads/2024/09/Stainless-Steels-Sensitisation.pdf
