CPM S45VN by Crucible Industries and M390 by Bohler-Uddeholm are two high-performance stainless steels made using powder metallurgy that offer an excellent combination of properties for knives.
The key difference between these two steels is that M390 has superior wear resistance but lower toughness compared to S45VN more balanced approach.
S45VN derives hardness and edge retention from vanadium and niobium carbides, having an overall carbide content of around 15%.
In contrast, M390 attains its properties through a very high 22% chromium carbide content.
This results in M390 having superior wear resistance but lower toughness compared to S45VN more balanced approach.
S45VN was designed as an upgrade to previous Crucible steels like S30V and S35VN, while Bohler M390 was created to be high wear resistant stainless steel.
M390 Steel is also produced as CPM 20CV by crucible industries and as CTS 204P by Carpenter Technologies.
Manufacturers like Spyderco and Benchmade use both steels, but S45VN is seen as an advancement over past Crucible grades.
M390 remains popular for its sheer cutting and edge retention performance.
S45VN vs M390 Steel At A Glance
| Property | S45VN Steel | M390 Steel |
|---|---|---|
| Toughness | Higher toughness. | Lower toughness |
| Hardness | Hardness up to 64 HRC. Aim hardness 59-61 HRC | Max 64 HRC hardness. Aim hardness 60-62 HRC |
| Edge Retention | Good edge retention but lower than M390. | Excellent edge retention. |
| Ease of Sharpening | Slightly better sharpening than M390 | More difficult to sharpen than S45VN and S30V. |
| Corrosion Resistance | Good corrosion resistance, comparable to M390. | Excellent corrosion resistance, slightly better than S45VN. |
Toughness
Toughness is the ability of a steel to resist shock chipping, breakage, on impact.
CPM S45VN steel demonstrates better toughness compared to M390 steel.
In sub-size Charpy impact testing, S45VN reached 11 ft-lbs toughness when properly heat treated, while M390 scored significantly lower at around 8 ft-lbs.
The higher toughness of S45VN steel is attributed to its finer and lower-volume carbide structure.
S45VN has about 15% total carbides, primarily comprising hard vanadium and niobium carbides, along with some softer chromium carbides.
In contrast, M390 has around 22% carbides by volume, mostly larger chromium carbides.
The high chromium carbide content and coarse carbides in M390 limit its toughness.
The better toughness of S45VN knife steel makes it more resistant to chipping during hard use, allowing thinner edges, and imparts better overall durability.
M390 steel lower toughness requires more robust edge geometries to prevent chipping, and care must be taken to avoid high impacts that could cause a fracture.
Hardness
CPM S45VN and Bohler M390 steels are capable of reaching maximum hardness values of up to 64 HRC.
However, the recommended aim hardness for S45VN knives is 59-61 HRC, while M390 knives target 60-62 HRC for optimal properties.
S45VN blade steel attains high hardness through its carbon content, niobium, nitrogen, and vanadium carbides.
M390 derives its hardness capability through significant chromium carbide formation.
The high chromium at 20% facilitates substantial carbide volume which imparts hardness.
M390 stainless steel also contains 0.60% tungsten that improves its hot hardness, suitable for high wear resistance in high temperatures.
Edge Retention
M390 steel demonstrates better edge retention and wear resistance compared to S45VN steel.
In CATRA cutting tests, M390 scored around 180% relative to 440C steel, while S45VN reached approximately 143% of 440C.
The superior wear resistance of M390 stems from its very high volume of chromium carbides, around 22% total.
Even though the chromium carbides are softer than the vanadium carbides also present in M390, the sheer amount of carbides results in excellent edge retention.
S45VN has a lower carbide volume at 15%, with more reliance on hard vanadium and niobium carbides.
However, the lower overall carbide content reduces wear resistance compared to M390 steel.
For knives, the higher edge retention and wear resistance of M390 translate to better-cutting ability and longer-lasting sharpness during use.
The edge of M390 knives will last longer before requiring resharpening.
However, S45VN achieves good edge retention better than S35VN but slightly lower than S30V from its vanadium carbides.
Ease of Sharpening
S45VN provides slightly better ease of sharpening over M390 with common aluminum oxide stones, facilitating quicker re-establishment of sharp edges after prolonged use.
This is attributed to the lower overall carbide content and volume in S45VN at around 15% versus 22% for M390.
Although M390 derives its edge retention from softer chromium carbides rather than only hard vanadium carbides, the total carbide content still hinders sharpening.
Comparatively, S45VN contains some chromium carbides but has higher amounts of vanadium carbides.
The lower carbide volume reduces resistance to abrasion during sharpening.
Additionally, S45VN is known to be easier to sharpen than CPM S30V, while M390 is typically more difficult than S30V.
The better sharpenability of S45VN knives requires less effort to refresh a sharp edge.
However, when using diamond or CBN abrasives, M390 and S45VN sharpen similarly owing to the hardness of the stones.
Corrosion Resistance
M390 and S45VN are stainless steel with excellent corrosion resistance better than most other steels.
However, M390 steel has a small advantage in corrosion resistance performance over S45VN steel, owing to higher total chromium content.
In corrosion testing, M390 steel performed very well, better than steels like S30V, S35VN, and S90V stainless steel based on its higher chromium content.
However, S45VN still has excellent corrosion resistance due to the addition of niobium and nitrogen in its composition.
The niobium helps increase the amount of chromium in solution, which improves corrosion resistance while nitrogen also helps offset the chromium tied up in carbides.
So while M390 has higher overall chromium, S45VN has optimizations like niobium and nitrogen that increase its corrosion resistance.
The difference in corrosion resistance between M390 and S45VN steel knives will be small, with M390 having a slight advantage.
Final Thoughts on S45VN vs M390 Steel
Having experience with both S45VN and M390 steels in knives, I would highly recommend opting for S45VN over M390 for most uses.
The advancements made by Crucible with S45VN are impressive, as this steel balances properties like toughness, edge retention, and corrosion resistance extremely well.
While M390 outperforms S45VN in ultimate wear resistance and corrosion performance, these advantages are quite small and likely not noticeable for the average user.
However, the markedly better toughness and ease of sharpening of S45VN make a real difference in cutting ability and convenience.
S45VN’s excellent combination of hardness, toughness, edge retention, and corrosion resistance provide very well-rounded capabilities that I find superior to M390’s singular focus on wear resistance.
Unless you constantly process heavy abrasive or corrosive materials, S45VN is likely the better choice over M390 for both performance and practicality.
The refinements in S45VN make it one of my favorite knife steels currently available.