Steel matchup
CPM M4 and CPM 20CV, compared on the five things that decide a blade: toughness, edge retention, corrosion, heat treat and how each one grinds.
A high-speed tool steel with extreme edge retention thanks to a heavy vanadium and tungsten carbide load, popular for hard-use fixed blades where long edge life matters more than rust resistance.
A top-tier powder-metallurgy stainless steel, chemically near-identical to M390, prized for exceptional edge retention and excellent corrosion resistance in premium EDC and outdoor knives.
Dimension by dimension
Each steel's own note, its score out of five, and what separates the two in that one column. The higher score in a row is marked in purple.
| Dimension | CPM M4 | CPM 20CV | What separates them |
|---|---|---|---|
| Toughness | Decent for a steel with this much carbide content, but it trades some toughness for its extreme wear resistance; not in the same class as CPM 3V or CruWear for impact resistance. | The tradeoff for its extreme wear resistance: with a heavy carbide load it is more prone to micro-chipping than tougher steels like CPM 3V or CruWear. On the toughness table in Crucible's MagnaCut data sheet (Charpy C-notch) it is last, 15 ft-lbs at 62 HRC against 25 for CPM S35VN at 61 HRC and 36 for CPM 4V at 62 HRC. That 62 HRC is above the 56-59 HRC Crucible gives as typical service hardness for 20CV; Larrin Thomas's 2140°F test cycle reaches about 61 Rc. | CPM M4 has a real edge here. Its alloy design leans more toward toughness than 20CV's heavier chromium and vanadium carbide load, which trades some toughness for wear resistance. |
| Edge retention | Among the best edge retention available in a non-stainless steel, thanks to a very heavy load of hard vanadium and tungsten carbides. A favorite where long edge life is the top priority. | Exceptional wear resistance from a very heavy chromium and vanadium carbide load, among the best edge retention available in a knife steel. | Essentially tied, both sit at the top of the edge-retention scale among steels covered on this site, and the practical difference in sharpening interval is small. |
| Corrosion resistance | Only 4% chromium, well below the stainless threshold. Needs the same oiling and drying care as a plain carbon steel. | Larrin Thomas rates CPM 20CV 9 out of 10 for corrosion resistance, behind MagnaCut (9.5) and LC200N and Vanax (10) and ahead of Elmax (8) and S35VN and S30V (7.5). About 20% chromium makes it a top-tier stainless: Crucible's 72-hour 1% saltwater spray chart shows only about 2 rust spots on 20CV, and in Thomas's own test a couple of small spots appeared where MagnaCut showed none. It suits wet and humid conditions, but it is not a saltwater steel: wipe it dry after salt exposure, and choose LC200N or Vanax for constant immersion. | CPM 20CV wins decisively. M4 has very little chromium and will rust without diligent care, while 20CV's high chromium content makes it genuinely low-maintenance stainless steel. |
| Heat treat | Preheat at 1500-1550 F, then austenitize between 1900 and 2150 F depending on the desired balance: lower temperatures favor toughness, higher temperatures maximize wear resistance at some cost to toughness. Quench in oil, air, salt, or plate to below 125-150 F. Double or triple temper at 1000-1050 F, holding at least 2 hours per cycle, to fully convert retained austenite through secondary hardening. Typical knife hardness lands around 62-64 Rc, with a maximum near 65 Rc. | Crucible's CPM 20CV data sheet: preheat to 1400-1450°F, heat rapidly to an austenitizing temperature within 1960-2150°F (1071-1177°C) and soak for 30 minutes, using a vacuum furnace between 2050°F and 2150°F; a lower temperature favors toughness and a higher one wear and corrosion resistance. Quench with pressurized gas (4 bar minimum) or warm oil, then temper immediately, typically at 400-800°F for at least 2 hours. Crucible lists a typical service hardness of 56-59 HRC, says higher hardness may be used for more wear resistance, and recommends a cryogenic treatment after the quench when austenitizing at 2100°F or higher. Larrin Thomas's independent test recipe differs from Crucible's: 2140°F austenitize, plate quench, cryo, 365°F temper, which gave about 61 Rc for 20CV (read from his chart). It sits inside Crucible's austenitizing range but tempers below Crucible's typical 400°F minimum. Because this steel demands precise, high-temperature equipment and a controlled quench, it is best suited to makers with a programmable oven or a professional heat-treating service. | Both benefit from precise, professional-grade heat treat to reach their full potential; M4 in particular is known for needing accurate high-temperature control, commonly sent to a professional heat-treat service by hobbyist makers. |
| Grinding | The heavy carbide load makes it noticeably harder on belts than simple carbon or basic stainless steels, though the powder-metallurgy process makes it more workable than conventional high-speed steel. | Demanding to grind and sharpen; typically requires diamond or CBN abrasives to sharpen efficiently once fully hardened, more challenging than most other steels in this database. | Comparable, both are demanding, high-carbide PM steels that benefit significantly from diamond or CBN abrasives for efficient sharpening. |
Best use
CPM M4
CPM M4 suits users who prioritize toughness and are willing to maintain a non-stainless blade carefully, often favored for hard-use fixed blades.
Open the CPM M4 referenceCPM 20CV
CPM 20CV is the better choice for wet, humid, or low-maintenance environments where stainless corrosion resistance matters as much as edge retention.
Open the CPM 20CV reference
The long answer
Both deliver excellent edge retention, but they take almost opposite approaches to corrosion resistance, and that single difference ends up driving most of the practical decision between them.
Keep comparing
Keep reading
CPM 20CV sits alongside CPM S30V and CPM M4 among the more demanding steels in this database to grind and sharpen. The same heavy chromium-vanadium…
CPM M4 sits at the top of this database’s “hardest to grind” list, alongside CPM 20CV and CPM S30V. Its heavy vanadium and tungsten carbide load, adapted…
Every knife steel is iron plus a specific recipe of other elements, and each of those elements pulls the steel’s behavior in a particular direction…
Same bench
Whichever steel wins, the grind is only as flat as the platen behind it. I machine the parts, hand-assemble, track and test Torus grinders in Sterling, Illinois.
Current dual-axis platform with a fiber-laser-cut 6061 chassis and single-knob tracking.
Current dual-axis platform with a steel chassis, more mass and less vibration.
Prior-design aluminum chassis, 90-degree tilt and 1.5-inch tooling arms.
One-man shop
Tell me what the blade is for and how you heat treat, and I will tell you which of these I would put on the bench — including when the answer is neither.
