M390 Knife Steel Overview

Bohler M390 Steel

Introduction

Bohler M390 stainless steel is one of the recent wave of “super steels” heralded by knife makers all over the world. It has characteristics of high hardness and excellent corrosion resistance. This means you’re going to get a very fine edge that retains its sharpness even through hard use, with little to no patina. Introduced and manufactured by Bohler-Uddeholm, M390 is a powdered steel utilizing 3rd generation technology. 

In industrial applications, it is often used in screws, barrels, and in injection molding. Bohler’s specifications claim a Rockwell hardness of 60 – 62HRC, putting it in the higher echelon of stainless knife steels. 

M390 Steel Chemical Composition

M390 is called “micro clean” steel and takes a mirror finish very well. It has minimal dimensional changes and is very resistant to vibrations and mechanical shock. The chemical makeup is as follows:

M390 Properties

Hardness

Bohler specifications of the M390 stainless steel specifies that this steel hardens and tempers to a Rockwell hardness of 60-62HRC. This is a considerably high hardness level and provides a perfect balance between toughness, wear resistance, and great edge retention.

You do not have to worry about the surface of your M390 knife getting destroyed or chipped away easily.

Toughness

A tough steel blade resists chipping and complete breakdown when subjected to impact, beating, twisting, and torsion. Tough blades are perfect for camping and outdoor use in the wild. Where a normal steel blade might chip or even break down, tougher steel blades are able to withstand that and much more such as batoning sessions, steel strapping, and much more!

The M390 steels make highly tough knives. The M390’s steel chipping resistance is quite high compared to other steel knives which have the same Rockwell hardness. The steel provides high toughness levels for knife-making.

Some people might argue that M30 is not the toughest steel available, but we cannot ignore that that it manages to provide a decent amount of toughness for knives while at the same time maintaining high hardness, corrosion resistance, and grindability.

You can put your full trust in your M390 steel knife to last an outstandingly long period of time with minimum maintenance and without showing any signs of chipping or cracking under stress.

Edge retention

The edge retention is the knife’s ability to hold its sharpness while in use. Whether it is cutting up nylon ropes, cutting fresh meat, sharpening wood, or cutting up cardboard boxes, no one wants to deal with a dull knife. The performance you can observe during cut tests is quite remarkable when you compare high-end steels to lower-end ones.

Edge retention and hardness typically go hand in hand. The M390 steel has been given the title of a super-steel which means that it delivers outstanding edge retention. This particular aspect can be called the force behind its growing popularity. 

The high amount of carbide content plus the addition of 4% of Vanadium in its composition makeup account for the great sharpness retention.

After sharpening your M390 knife steel, you can be sure as hell that it will retain its sharpness for a really long period of time. This is a great factor as this will lead you to decrease the frequency of sharpening your steel, and subsequently, preserve the steel’s quality.

Corrosion resistance

Are you someone who tends to venture out into the wild, salty, wet, and humid environments? Do you often use your knife for prepping meals with acidic ingredients such as tomatoes or lemon? 

Certain steels are pretty good at resisting rust and corrosion and can be left uncleaned for hours without any complications or ill effects. Carbon steel knives will easily pit and rust in wet, humid environments if not looked after properly. Usually, knives with a low corrosion resistance can be protected with a thin layer of mineral oil.

As we already know, Chromium is the essential factor for controlling corrosion resistance in a steel alloy, besides additional chemical elements like Nitrogen and Molybdenum. Keeping that in mind, the amount of Carbon in M390 is quite high – as much as 20% – which results in overall great corrosion resistance. 

This is one of the main reasons why the M390 stainless steel is chosen for making knives for use in saltwater conditions with high humidity where rust vulnerability is sky-high.

Ease of sharpening

Usually, the most overlooked aspect of blade steel is its sharpenability and sharpness. Touching up or sharpening certain steels with a sharpening stone can be quite a simple, easy, and relaxing process whereas harder steels can make the process much tougher, tedious, and not so relaxing. 

Achieving the right amount of sharpness can be a life-or-death matter when you are out in the wild, as it determines your ability to cut up and cook food as well as other tasks. It is crucial to keep in mind that an easy to sharpen knife usually indicates low edge retention.

For steel that exhibits such sort of hardness and wear resistance, one would expect it to be equally hard to sharpen. But surprisingly, M390 steel is quite reasonably easy to sharpen and does not require you to break your back over it.

The steel holds within itself more Chromium Carbides than Vanadium Carbides. The former is easier to sharpen than the latter as they are much softer than the common Aluminium oxide sharpening belts.

Heat treatment of M390 Stainless Steel

Step 1 – Full annealing

Full annealing for M390 stainless steel is done at temperatures ranging between 750 – 800 C after which it is slowly cooled down in the furnace at about 550 C and then air-cooled down to room temperature. It can also be heated at temperatures ranging between 735 – 785 C and then slowly cooled down in the furnace until it reaches room temperature.

Step 2 – Hardening

The M390 steel is heated once again at temperatures ranging between 1112 – 1176 C and then quenched in warm water or oil. Thicker sections of the steel should be quenched in oil to allow a faster and uniform temperature decrease, whereas thinner sections can be quenched in air.

Step 3 – Tempering

The steel is tempered at temperatures ranging between 250 – 370 C where multiple levels of hardness and mechanical properties are obtained. Tempering at temperatures between 425 – 565 C will lead to lower corrosion and impact resistance, and tempering between the temperatures 590 – 675 C will result in high impact resistance lower hardness. 

M390 vs. other steels

M390 vs. S35VN

From the above table, it is fair to deduce that M390 stainless steel provides improved edge retention whereas S35VN steel provides improved ease of sharpening. Both of them rank equally in terms of toughness and corrosion resistance.

M390 vs. Elmax

From the above table, it is fair to deduce that the M390 stainless steel provides improved corrosion resistance whereas the Elmax steel provides improved ease of sharpening. Both of them rank equally in terms of toughness and edge retention.

M390 vs. CPM20CV

From the above table, it is fair to deduce that the M390 stainless steel and CPM20CV rank equally in terms of edge retention, toughness, corrosion resistance, and ease of sharpening.

M390 vs. D2

From the above table, it is fair to deduce that the M390 stainless steel offers improved edge retention and corrosion resistance whereas the D2 steel offers slightly improved ease of sharpening. Both of the steels rank equally in terms of toughness.

M390 vs. CPM30V

From the above table, it is fair to deduce that the M390 stainless steel offers slightly improved edge retention and toughness whereas the CPM30V steel offers slightly improved ease of sharpening. Both of the steels rank equally in terms of corrosion resistance.

M390 vs. N690

From the above table, it is fair to deduce that the M390 stainless steel offers improved edge retention and toughness whereas the N690 steel offers improved ease of sharpening. Both of the steels rank equally in terms of corrosion resistance.

M390 vs. CPM-M4

From the above table, it is fair to deduce that the M390 stainless steel offers improved corrosion resistance whereas the CPM-M4 steel offers slightly improved ease of sharpening and toughness.

Fun fact: Bohler M390 is almost identical to Latrobe DuraTech 20CV stainless steel. The corrosion resistance is superior to 420C stainless and it has twice the cutting edge retention. This does make it more difficult to sharpen, though not as difficult as S90V, a close cousin.

The reason for this is the fine grain size, small carbides, and superior cleanliness of the powder metallurgy (PM) microstructure.

M390 STEEL FALLS INTO THE GENERAL RANGE OF ABOUT 62 HRC

Favorites using Bohler M390 Stainless Steel

My favorite knife utilizing Bohler M390 Steel is the Steel Will Knives Cutjack Urban Flipper Knife. It has a 3.5″ satin-finish drop point blade that is 0.12″ thick. The excellent cutting ability is due to the high flat grind on the blade. The handle scales are black G-10 Micarta. Ergonomics of the Cutjack are just incredible. There is a finger groove on the handle that matches a choil just beyond it. This gives you the ability to lock into the choil and the finger groove at the same time, giving you unparalleled control and stability. The flipper, combined with the blades ball bearings allow a one-handed opening with just a slight flick of the wrist. It has a rock-solid lock up and zero sticking. A reversible, tip-up pocket clip completes the Cutjack Urban model’s design. This version of the Cutjack features an extended tang that curves beautifully into a cutout where a lanyard can be attached. Steel Will is an American company with the knives being made in Italy. Each Cutjack Urban model is boxed and individually serial numbered for the serious collector.

Steel Will Cutjack C22 Linerlock Black

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It has a 3.5″ satin-finish drop point blade that is 0.12″ thick. The excellent cutting ability is due to the high flat grind on the blade. The handle scales are black G-10 Micarta. Ergonomics of the Cutjack are just incredible. There is a finger groove on the handle that matches a choil just beyond it. This gives you the ability to lock into the choil and the finger groove at the same time, giving you unparalleled control and stability. The flipper, combined with the blades ball bearings allow a one-handed opening with just a slight flick of the wrist. .

Conclusion

Bohler M390 is undoubtedly in a class all its own, being almost as corrosion resistant as H1. While the hard blade will require some owners to use a bit more elbow grease to sharpen than other stainless steels, the blade will keep that edge long after others have failed. Many bladesmiths and large knife making companies are utilizing M390 more and more thanks to these characteristics. Some online forums have even hailed this as the “holy grail” of knife steel. The truth is, as always, the perfect knife steel is the one used in the knife you choose to carry.