M390 toughness?

T

TigFur

Joined
Oct 25, 2016
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I tried to read up on all the different knife forums and reviews about the M390 steel and there seem to be two very different opinions about its toughness.
Some say its not tough at all and they wouldnt use it for bones or hardwood, some compare it to D2 and more and that difference really bothers me.
all agreed on its super edge retention though.
I saw a few videos of M390 knives in action and havent found any failures so far (if you have some id love to see that)

Could it be that the people that claim that this steel isnt tough just looked at the 20% Cr content and made it up? Or is there some truth behind it?

i think it should get cleared up once and for all so that there is at least one thread that explains this steel clearly and completely.


So please post your opinions and experiences here


(btw i wanted to put this in a steel topic forum on here but didnt find any, so i hope this is allright)
 
It's not tough in comparison to some carbon and tool steels. Pending hardness, it can be better or worse than other stainless PM steels. In a general sense, it is not tough at all.
 
Blues Bender said:
It's not tough in comparison to some carbon and tool steels. Pending hardness, it can be better or worse than other stainless PM steels. In a general sense, it is not tough at all.
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well of course its not as tough as steels made to be tough for certain stough (pun allowed?) But we're talking knives here, the worst ive seen a knife had to handle was batoning, diging the knife into a wwood and standing on it or prying wood with the tip or throwing it. most of the tough steels ive seen outside of knife world dont hold an edge at all
 
TigFur said:
well of course its not as tough as steels made to be tough for certain stough (pun allowed?) But we're talking knives here, the worst ive seen a knife had to handle was batoning, diging the knife into a wwood and standing on it or prying wood with the tip or throwing it. most of the tough steels ive seen outside of knife world dont hold an edge at all
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I am talking about knives, in a general sense. I wouldn't want a chopper with M390 @ 60+ hrc. For what many of us use folders for, toughness is almost a moot point.
 
TigFur said:
well of course its not as tough as steels made to be tough for certain stough (pun allowed?) But we're talking knives here, the worst ive seen a knife had to handle was batoning, diging the knife into a wwood and standing on it or prying wood with the tip or throwing it. most of the tough steels ive seen outside of knife world dont hold an edge at all
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You can take a piece of low toughness steel and make it an inch thick with half am inch primary grind and it can do all that. Does not mean it is still the right steel for the intended application.

M390 is a good balanced steel between properties but if you want a thin knife for slicing and still want toughness you can get better options.

It all comes down to choosing your steel and heat treatment cycle for intended use.

You can heat treat M390 with corrosion and wear resistance in mind or with toughness and wear resistance in mind. Both would have the same hardness but completely different properties.
 
For some context; according to crucible s90v has a higher impact toughness than 440c. M390 is tougher tha s90v at same hardness. 440c has always nbeen a decent knife steel so i would say m390 woild be adequate for most edc needs. If you want more toughness, consider elmax; nice toughness increase without sacrificing much edge retention. Check out bohler website, they have catra and charpy toughness compsrisons.
http://www.bucorp.com/knives.htm
 
see we already have some differences, first one says its not tough at all, second one says it depends on the blade (which is indeed true and i agree) and third one says its tougher than other steels...

yes geometry thickness and so on all belong to the calculation, of course. In my opinion knives are a cutting tool, they should be made with the intention of cutting and the heat treat too. but then again a certain toughness is necesary so that it doesnt break even with a hard use. kitchen knives doesnt need to be as tough as bushcraft knives, but there is about double thickness difference to make up for it so in the end it comes back to the steel. Thats how i see it.

i have a knife in D2 and i couldnt do anything bad to it, i think after it has a certain toughness, the extra toughness on top is unnoticable under regular use (batoning and stuff)

just gonna throw this in
http://www.cliffstamp.com/knives/forum/read.php?17,12501
 
I have a knife being made in 1/4" CPM 10V hardened to 62RC and cryo'd. It's a bowie with a 6.5" sharpened length. Toughness of CPM 10V is equal to D2 and M4. That being said, I'm not worried at all.
 
Charlie Mike said:
I have a knife being made in 1/4" CPM 10V hardened to 62RC and cryo'd. It's a bowie with a 6.5" sharpened length. Toughness of CPM 10V is equal to D2 and M4. That being said, I'm not worried at all.
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Thats a common thickness with this type of knives, probably for a good reason too.

Im starting to think that toughness in knife steels is a completely useless fact. Geometry, size, hardening.. so many different variables and in the end all we want/need is a knife that wont break or bend easily while keeping the sharpest edge for the longest time possible...
 
TigFur said:
Thats a common thickness with this type of knives, probably for a good reason too.

Im starting to think that toughness in knife steels is a completely useless fact. Geometry, size, hardening.. so many different variables and in the end all we want/need is a knife that wont break or bend easily while keeping the sharpest edge for the longest time possible...
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I tend to agree
Even with a lower toughness steel it isn't easy to break a 1/4 inch blade
I think the geometry and HT are the major points
 
highestpoint said:
It's tough enough.
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This is my experience too. In a folder, for the stuff I typically cut, it is tough enough.

I am talking about a relatively thin convexed edge, about 10 dps, with a 15 dps micro. I've hit a staple in cardboard once with this knife. I was fearing the worst the moment it happened, because I was putting some speed and force behind the cut, but it only rolled slightly. That's good enough for me.

20150307_143302_zpsdd0upqq9.jpg
 
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I have been trying to find comparable charpy data for m4, elmax, 204p and 3v for a good long while with little to no success, someone said m390 is as tough as 1095 at 60hrc which is a highly interesting statement
 
M390 is no where near as tough as steels designed for shock. People make a mistake in cross comparison steels outside of its category. This is covered by literature.

D2 by any means is not a tough steel for construction or as a jack hammer bit, but people have used in knives for years (though it still has its own limitations)

Is M390 good enough for general use. Sure. Does it have its limitations. Jip. At extremely low angles it suffers similar fate as most high carbide steels. It chips.

If you want charpy data for all steels. Good luck as 'datasheets' barely indicate what orientation was used for the sample heat treatment involved etc.
 
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highestpoint said:
It's tough enough. Get a folder with M390 and report back with your experiences
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Im actually looking at fixed blades right now.

well i dont expect any steel at a very sharp angle to handle much abuse, even if it was cool if it did. all i want is a knife i can shave my face with in the morning, fall a tree and repeat the next day :cool:

i think 20-30 angle included should do just fine with m390
 
Fixed blade I would look no further than 3v.

I don't think m390 would still be a bad alternative based on its other qualities that help equal it out but depending on other uses might limit it.

Sent from my SM-N910V using Tapatalk
 
highestpoint said:
Fixed blade I would look no further than 3v.

I don't think m390 would still be a bad alternative based on its other qualities that help equal it out but depending on other uses might limit it.

Sent from my SM-N910V using Tapatalk
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i chose m390 for its ability of polish and very good edge retention with shaving edges. But its also tough for any other use, at leasst thats what id hope.
 
Chart from Crucible:

chooseimpacttough.gif


Of course, geometry and hardening matter, but if D2 and similar are considered "tough," what are S7 and H13? XXXL-tough lol.

Are they tough enough for cutlery and worth it for the edge retention, corrosion resistance, etc.? Usually, but I wouldn't pick 10v, D2, or M4 for a demolition tool. Just depends on what you want and what you're doing with it.
 
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