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Steel M390
This manufacturer makes steel types that are incredibly wear-resistant, the so-called “special steels”.
It might be quite surprising though for some obvious, but almost all types of steel we know today were not developed as knife steel.
Many types of steel have been developed for ball bearings or for parts of jet engines.
The same goes for the Böhler M390.
Although the Böhler M390 is one of the most popular and performing steel grades on the market, Böhler developed it for use in moulds for the injection moulding industry.
If we consult Böhler’s datasheet, we can still see that it is listed as the primary purpose.
The fact that it is also great for use in knives is considered an alternative purpose.
For these molds, the steel must also be extremely wear-resistant.
If you want to be able to maintain the same shape of a mold about 100,000 times, this should not wear out between the first and 100,000th plastic injection or beaten if it is sheet metal.
That is why these molds are made from high-quality steel grades.
It is therefore not so surprising that M390 is used as steel for molds where the industrial market is much larger.
Böhler can sell many more kilos of steel to this industry than to the knife industry, where relatively small and lightweight steel plates are mentioned.
The PM process, combined with the high chromium content gives M390 good workability and excellent polishability.
It has excellent edge retention, corrosion resistance and very high hardness for excellent wear resistance.
Chromium, molybdenum, vanadium and tungsten are added to promote sharpness and exceptional edge retention.
The M390 is a fantastic steel and is one of the most commonly used “supersteels” around.
As with any steel, however, it has its advantages and problems.
The M390 is first of all an exceptional steel for wire retention.
You will not see much wear of the thread even through a rather approximate and care less caring use of the blade.
With a higher chromium content, it tends to form slightly larger carbides, what does this translate into? which is harder to get some sort of mind-blowing thread that cuts like a super razor, that rests a hair and splits in two.
As a tip it needs about 15° of lateral inclination as a sharpening angle to get the best performance and tightness of the wire.
By the way forget to sharpen it with a field sharpever, it is annoying to sharpen, since its high wear resistance results in resistance to sharpening stones,especially the highest grain.
The excellent cutting sealing capabilities, maintaining it is very simple, another thing that is worth noting in fact is the absence of resistant burr formations during sharpening; as a result, there is also no risk of forming a false wire.
It also has a rather respectable robustness and can withstand a good blow.
Corrosion? with 20% chromium, it is also very resistant to corrosion!
Unlike other stainless steels, most carbides are made of vanadium and molybdenum, leaving more than chromium free to prevent corrosion.
It can be polished for an extremely high surface finish.
Bohler calls this steel “Microclean” and can be polished to get a real mirror but it is a steel that provides excellent performance with both finishes, rough or very polished.
Propietà of Steel M390
- Extremely high wear resistance
- High corrosion resistance
- Mirror polishing
- Excellent toughness
- High dimensional stability
- Improved resistance to vibration and mechanical shocks
Why is Böhler M390 so famous?
The answer is the preservation of sharpening.
M390 steel is so wear-resistant that it also properly maintains the shape of the sharp edge and this allows an M390 steel knife to maintain its sharpening for a long time.
This means that you don’t have to sharpen your knife so often.
It’s not only great because sharpening the knife takes time, but also because it means your knife will last longer.
Remember that the more often you sharpen a knife, the faster it will wear out.
Remember that it is not possible to sharpen a blade on its entire extension because the blade will become too thick behind the edge and consequently you will have greater sharpening angles that make the blade less sharp.
This also means that it won’t be so easy to sharpen if you don’t have the right equipment or stones.
Why is the M390 so wear-resistant?
To answer this question we must look at the chemistry and production process of this steel.
First of all, the way Böhler produces its M390.
M390 is produced according to a powder metallurgical process.
This requires some explanation.
Normally a manufacturer combines several elements into one alloy, pours large blocks and flattens them to finish with sheets that can be used by knife manufacturers.
Böhler, however, levels up.
After putting these elements together, they put them in a gas atomization machine that sprays the molten steel as a kind of diffuser.
The result is that the structure becomes much finer at the molecular level.
There are, of course, other manufacturers who have mastered this process.
Take, for example, Crucible with the CPM or Carpenter method who called it Micro Melt.
Below you can check the chemical composition of steel.
Chemical analysis (average%)
| C | Si | Mn | Cr | Mo | V | W |
|---|---|---|---|---|---|---|
| 1,90 | 0,70 | 0,30 | 20,00 | 1,00 | 4,00 | 0,60 |
1.9% carbon, 20% chromium, 1% molybdenum, 4% vanadium, 0.7% silicon, 0.3% manganese and 0.6% tungsten are added for excellent resistance and thread tightness.
This is what the M390 looks like:
| Carbon | 1.9 |
| Chrome | 20.0 |
| Molybdenum | 1.0 |
| Tungsten | 0,6 |
| Vanadium | 4.0 |
| Manganese | 0,3 |
| Silicon | 0.7 |
Heat treatment
We talked about the type of steel and its composition but this is a more important part of making a special knife steel and it is heat treatment.
There is a saying that says that the type of steel is the body, but that the heat treatment determines the core of the steel.
That is, there are different methods to harden the same type of steel and it depends on the intended use.
For example, it may happen that the M390 does not retain its sharpening for so long with some makers, but that it is harder and more resistant to corrosion.
Or that others make knives with an M390 that is extremely wear-resistant but that are more sensitive to rust.
Are some better than others? It depends on the purpose It is a matter of choices and several times if you follow the blog I have told you about this aspect..
- The more durable version will work best during the most demanding tasks.
- The harder version will work best if you have to pay attention only to wear and preservation of sharpening.
This choice can be made with the design of the knife, the sharpening angle and especially with the heat treatment.
Recommendations for heat treatment
Heat treatment from the supplier
- Supply status: max. 280 HB
- Optimal sweet annealing is possible only after hot molding.
Relieves stress
- 650°C (1200°F)
- After heating, soak for 4 hours in a neutral atmosphere.
- Oven cooling up to 300°C (570°F), followed by air
Hardening
- 1100 to 1180°C (2010 – 2155°F) / oil, N2
” Waiting time:- After total heating:
– 20-30 minutes for a hardening temperature of 1100-1150 °C (2010-2100 °F)
– 5-10 minutes for a hardening temperature of 1180 °C (2155 °F)
- After total heating:
Tempering for maximum corrosion resistance
- Subzero treatment for the processing of retained austenite
- Slow heating at tempering temperature
- Oven time 1 hour for every 20 mm (0.79 inches) thick of the piece, but at least 2 hours
- Refer to the tempering table for information on hardness that can be obtained after quenching.
- Tempering: 200 to 300 ° C (390-570 ° F)
Tempering for maximum wear resistance
- Recommended subzero treatment
- Subzero treatment immediately after quenching leads to tempering hardness values increased to austenitization temperatures ≥ 1150 °C
(≥ 2100 °F), [Rischio di rottura da stress] - Slow heating at tempering temperature
- Oven time 1 hour for every 20 mm (0.79 inches) thick of the piece, but at least 2 hours
- Refer to the tempering table for information on hardness that can be obtained after quenching.
- Triple tempering 20 ° C (68 ° F) above the secondary hardening maximum is necessary to obtain a complete transformation of the retained austenite.
Austenitization is a transformation of the crystalline structure of steels, consisting in obtaining in the steel itself an austenitic structure.
Since austenite is a metastable crystalline form, it cannot exist at room temperature; Austenitisation is therefore the first stage of the treatment of:
hardening, in which case it is followed by rapid cooling, aimed at freezing the austenitic structure and precipitating the iron-carbon alloy in the form of martensite.
respray, when it is followed by a more or less slow cooling, tended to solve the austenite in ferrite and cemented.
Advantages of Böhler M390
M390 has a good tightness of the sharpening because it can be hardened up to a relatively high hardness without making it too fragile but it does not mean that M390 is very resistant if hardened in this way that prefers the knife thread.
But this means that the M390, compared to other types of steel, can be sharpened a little thinner, with lower sharpening angles.
Thanks to the large amount of chromium, M390 steel is also relatively stainless, rust will have no chance of forming.
Especially when compared to other types of steel that reach high hardness and that are known for their preservation of sharpening, but can still be damaged by rust.
Disadvantages of the Böhler M390
M390 steel is relatively expensive, I say relatively because I would not recommend it for those who want to make their first knives where perhaps a steel like ma5MV is better.
I’m not only talking about the purchase price per kilo, but also in terms of modifying the blade because being wear-resistant also means difficult to modify, you need more time to process it and your abrasive belts will wear out much faster.
A knife made of M390 steel is therefore often more expensive than a knife made of another type of steel.
M390 is not so easy to sharpen.
You won’t get very far using a simple Arkansas stone.
M390 prefers stones with diamond cover or ceramic options.
Preferably under a very fixed angle.
The M390 is not incredibly durable, of course I am not saying that it is fragile, but it must be taken into account and that is why it is more suitable for small knives.
When making a larger knife you need a much stronger type of steel, something the M390 often doesn’t excel at, so I would personally opt for an N690 steel which is for larger knives a much better option.
The price?
The price can be a problem, because M390 is significantly more expensive than 154CM and S30V, to understand us about the prices:
- Thickness 3.5X40X300 mm. (€49.00)
- Thickness 3.5X40X600 mm. (€98.00)
- Thickness 3.5X40X900 mm. (€147.00)
- Thickness 3.5X40X1200 mm. (€196.00)
- Thickness 4.3X40X300 mm. (€62.80)
- Thickness 4.3X40X400 mm. (€85.50)
- Thickness 4.3X40X600 mm. (€125.70)
- Thickness 4.3X40X900 mm. (€188.50)
- Thickness 4.3X40X1200 mm. (€251.40)
- Thickness 4.3X50X300 mm. (€79.30)
- Thickness 4.3X50X400 mm. (€108.20)
- Thickness 4.3X50X600 mm. (€158.60)
- Thickness 4.3X50X800 mm. (€216.30)
- Thickness 4.3X50X900 mm. (€238.00)
- Thickness 4.3X50X1200 mm. (€317.20)
- Thickness 4.3X60X300 mm. (€81.90)
- Thickness 4.3X60X600 mm. (€161.80)
- Thickness 4.3X60X900 mm. (€241.70)
- Thickness 4.3X60X1200 mm. (€319.60)
- Thickness 5.3X50X400 mm. (€129.80)
- Thickness 5.3X50X800 mm. (€259.60)
- Thickness 5.3X60X300 mm. (€112.30)
- Thickness 5.3X60X400 mm. (€159.70)
- Thickness 5.3X60X600 mm. (€224.60)
- Thickness 5.3X60X800 mm. (€319.30)
- Thickness 5.3X60X900 mm. (€336.80)
- Thickness 5.3X60X1200 mm. (€449.10)
Steel types that look a lot like Böhler M390
At the chemical level there are a couple of types of steel that look a lot like M390.
Take, for example, CPM 20CV and Carpenter CTS-204P.
The components and the production process are similar.
If you take into account all the cutting tests that we have carried out we can also say that also, in terms of performance they are similar.
Is one of these types of steel better than the other? No.
The differences are so small that no user will ever notice them.
Conclusions
This steel is called “super steel” for a reason.
It surprisingly uses third-generation metal powder technology which is then developed for knife blades.
Bohler calls this steel “Microclean” and can be polished to get a real mirror.
Definitely a high-end knife steel suitable for experienced makers.
Overall, it is one of the best steels in terms of corrosion and wear resistance and for this reason it is a favorite choice for the high end and for limited edition knives.
It has been developed for knife blades that require good corrosion resistance and high hardness and excellent wear resistance.
M390 is a fine-grained alloy and is the preferred choice for high-end closables and small fixed blades.
The M390 excels when used for smaller knives, see it more suitable for pocket knives or smaller stationary knives.
When making a larger knife you need a much stronger type of steel, something the M390 often doesn’t excel at, so I would personally opt for an N690 steel which is for larger knives a much better option.
Are You Experience?
Andrea
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