What is S390 Steel?
Bohler S390 steel is high-speed tool steel manufactured by Bohler through the powder metallurgy process. S390 Microclean steel is a red hot hardness tool steel with extremely good edge stability and compressive strength.
Based on the heat treatment, S390 Microclean steel is a high performer used to make cutters, knives, taps, drill bits, broaches, and cold work applications. We should also note that the steel features a fine carbide microstructure that positively impacts its properties.
S390 knife steel was hugely popularized by Switzerland Kase Knives in their knives that had awesome edge retention compared to other knives made from hard steel like Maxamet steel knives.
S390 Steel Composition
- Carbon C 1.64%: Increases edge retention, hardness, and tensile strength. It also improves steel resistance to wear, abrasion, and corrosion.
- Chromium Cr 4.80%: The formation of Chromium carbide Increases the hardness, tensile strength, and corrosion resistance of the blade.
- Tungsten W 10.40%: used as an alloying ingredient due to its high melting point, hence improving the performance of steel in high heat.
- Molybdenum Mo 2.00%: It improves corrosion resistance, machinability, and hardness.
- Vanadium V 4.80%: inhibits grain growth during elevated temperature processing and heat treatment, which enhances the strength and toughness of steel. It also forms carbides that increase wear resistance.
- Cobalt Co 8.00%: Increases the strength of steel and hot hardness temperature.
- Silicon Si 0.60%: Increases strength and heat resistance.
Properties of S390 steel
S390 Steel Hardness
Bohler S390 steel can achieve a Rockwell hardness of up to 69HRC, the level of hardness differs depending on the heat treatment used by the manufacturer and the tempering technique applied, S390 Rockwell hardness can range between 65HRC to 69HRC.
68 HRC is impressive hardness and is associated with high levels of carbon, molybdenum, vanadium, and Tungsten in its composition. The high hardness of Tungsten makes S390 very hard and increases its wear resistance and heat treatment temperature.
Cobalt is added in huge amounts about 8% to improve the hot hardness of Bohler S390, which is the ability to stay hard even in high operating temperatures. This is also why other knife steels like VG 10 steel and N690 steel contain Cobalt in their alloy composition.
S390 Steel Edge retention
Edge retention is another area of excellence for Bohler S390 steel. The steel stays sharp longer than most steels on the market. The credit for the outstanding edge retention goes to the high hardness range. S390 edge retention can outdo that of popular Maxamet knife steel.
Secondly, it contains high amounts of vanadium, which aids in the formation of vanadium carbides, the amazing part is that the carbides formed are very fine unlike other high alloy steel with lots of coarse carbides.
The fine hard carbides ensure that S390 blades maintain their edge stability and do not become dull fast, The fine carbide is attributed to the powder metallurgy production process.
S390 Steel Wear resistance
The wear resistance of steel is directly proportional to its hardness. Being very hard steel, S390 offers excellent wear resistance. Bohler S390 steel knives will serve you for a long time, even when used for everyday applications or on abrasives.
The high wear resistance is associated with the combination of Tungsten, Vanadium, and Chromium in its composition resulting in a high Rockwell Hardness. S390 knives are very durable and can be used across generations.
S390 Steel Toughness
S390 steel offers decent toughness. Being very hard steel, we expect it to offer a low hardness level, but it provides a high level of toughness. The steel offers a perfect hardness and toughness balance, although it does not have the best toughness level out there.
With decent toughness, S390 steel does not break or chip easily when used for tough applications. You can carry the blades to the wild and be confident that they will not disappoint when used for challenging outdoor applications.
S390 Steel Corrosion resistance
S390 is not stainless steel because it contains 4.80% chromium which is not enough to make it stainless steel. The steel is highly susceptible to rust, but the Chromium and Tungsten in its composition fight corrosion to some levels.
Knives made from S390 steel will rust if used in highly corrosive environments like high humidity areas with salty water. However, proper care and maintenance will help to keep corrosion at bay. Therefore, clean and dry your knives after every use and apply a coat of oil before storage to keep rust at bay.
Sharpening S390 Steel
Another downside of S390 steel is that it is very difficult to sharpen. Sharpening S390 knives are difficult even with diamond sharpeners because it contains high amounts of hard carbides.
Take S390 knives for professional sharpening to save time and energy and prevent disappointments. The good news is that once the blade gets a sharp edge, it will stay for a very long time without the need to resharpen.
S390 Steel Comparison
S390 vs M390 steel
The significant difference between S390 steel and M390 steel is that M390 steel is a stainless steel, that offers extremely good corrosion resistance while S390 is non-stainless steel.
S390 steel also offers better edge retention and stability than M390 steel, it does this due to its high attainable Rockwell hardness. The high hardness also contributes to higher wear resistance.
Despite M390 steel being hard steel and hard to sharpen, it generally beats S390 knife steel in ease of sharpening.
S390 vs S30V Steel
Bohler S390 beats Crucible S30V stainless steel in edge retention, and wear resistance due to the higher Rockwell hardness and the addition of high wear resistance in its alloy composition.
On the other hand, S30V shines in corrosion resistance as it is stainless steel while S390 is not. S30V is also easier to sharpen and offers a more balanced approach in all aspects, this is why it is so popular in most knives.
Is S390 good knife steel?
Bohler S390 steel is great knife steel, It stands out on the market for offering excellent wear resistance, outstanding edge retention, and edge stability.
It is also respected because it strikes a good balance of hardness and toughness. It offers high toughness level considering that it is very hard steel.
The major downside of Bohler S390 steel is that it is not stainless steel. It is also hard to sharpen, this issue can be solved by taking your knives for professional sharpening. It will cost you to get a sharp edge, but the edge will last for a long time.
My name is Jonathan M, and I’m a passionate Mechanical Engineer, a knife enthusiast, and the author of this website. I have a bachelor's degree in Mechanical engineering with a specialization in material science. I am particularly interested in researching knife steel, knife properties, and brands. I hope you will find value in the articles on this website. Contact me if you have any questions or input!