Blade chipping

M

ma tumba

Joined
Apr 5, 2014
Messages
125
Hello folks,

Some time ago I bought a Guardian 3/M390 from Bradford knives and I really like this knife, ergonomics is great. From what I heard, M390 steel excelled in almost any respect and indeed I was able to get a very sharp edge but as I dont cut cardboard or rope too often. I'd say I need to open a can with a knife more often then cut a rope.

So I decided to put the knife to a different test. I slowly thrusted the tip to a beer bottle cap and then very carefully picket the hole open. No impact at all. The blade chipped, it was not a micro chip, the size of the defect is about 1mm. I repeated this "test" and the blade chipped again. Tried to show it in the pic, but actually it looks worse than you may guess from the pic.

chip.jpg
Well, this made me wonder. The edge was 36 degrees inclusive, which doesnt look too aggressive. The task was very mild in my opinion, far cry from prying a car door or crushing a cinder block.

So my questions:
1. what kind of edge retention is the ability to withstand this kind of abuse?
2. how good m390 is supposed to be as far as this kind of edge retention is concerned. In other words, how much better could be another steel for this type of use?
3. what kind of improvement in this kind of edge stability I would get if I go from 36 inclusive to, say, 40 degrees?

Thanks for any input!
 
It chipped because M390 isn't tough...its wear resistance and corrosion resistance that this steel excels at.
 
Blues Bender said:
It chipped because M390 isn't tough...its wear resistance and corrosion resistance that this steel excels at.
Click to expand...

Well, from what I could pick up reading numerous posts here, toughness was related to impact, while in this "test" I did everyting VERY carefully and slowly. So was my understanding of toughness incomplete?
 
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Toughness can be related to impact resistance, in that a knife can be used to chop things and the edge will remain stable. However, a steel that isn't tough can be brittle when taken to a high hardness, that means the edge can chip if enough stress is applied.

A lack of toughness can also translate to the edge chipping and not rolling or deforming under use. Cut a very abrasive material with a brittle steel, and you'll chip the edge. Impact is only one part of the equation.
 
Thanks BB, is there a kind of edge stability so that the edge would neither chip nor deform (in relative terms) under this kind of stress (at the expense of other properties such as abrasions resistance, for example)? And how this kind of edge stability is correctly referred to, or it is just toughness?
 
Hard brittle steel will chip if it lacks toughness. Tough steel will roll if used under too much stress or deform if it lacks abrasive resistance (aka wear resistance).

Regarding M390, look at this chart to see how it stacks up to other steels (CPM-20CV is Americas answer to M390). Please note, that this is when hardening 20CV to 58 hrc. When at a higher hardness, toughness will decrease.

95F49FB2-7C35-4669-B743-ABA99D10437D_zpsl2m93q5h.png
 
Thanks for the graphs!

So in order for a blade not to deform and not to chip the steel should be both hard and tough. From what I picked, these properties are just inversly correlated so you cant generaly have both at once. But nevertheless is the right way, to take the toughest steel, like 3V, and bring it to the highest RC, like Nathan does for his blades?
 
ma tumba said:
Thanks for the graphs!

So in order for a blade not to deform and not to chip the steel should be both hard and tough. From what I picked, these properties are just inversly correlated so you cant generaly have both at once. But nevertheless is the right way, to take the toughest steel, like 3V, and bring it to the highest RC, like Nathan does for his blades?
Click to expand...

To some degree, yes. You can't have all the properties excell in one steel; 3V will never be wear resistant like S90V and S90V will never be tough like 3V (that's just one example). Of course, heat treat has a heavy influence on performance and should not be forgotten about, but then things get more complex. Generally, these graphs just give us an idea of what a steel was designed for and doesn't necessarily predict their performance when in use.
 
People should also note that 3v and other tough steels are not adamantium. These steels are tough, but not invincible. You can damage any blade even with reasonable use.
 
How does Aus-8 stack up against other metals. This is what my daily carry is made from. It is a Camillus from the Carbonitride Titanium series. It was relatively cheap to buy at $30 Americans dollars and it's really durable. I originally had the Beast which was a much larger blade and came with the price of $80. That knife I ran over with a fork lift and only flattened out the pocket clip, and it was open at the time. I loved that knife and hated the fact that it got stolen. I haven't heard anyone mention anything about Camillus yet in any of the post. Is there a reason for this?
 
Foot442 said:
How does Aus-8 stack up against other metals. This is what my daily carry is made from. It is a Camillus from the Carbonitride Titanium series. It was relatively cheap to buy at $30 Americans dollars and it's really durable. I originally had the Beast which was a much larger blade and came with the price of $80. That knife I ran over with a fork lift and only flattened out the pocket clip, and it was open at the time. I loved that knife and hated the fact that it got stolen. I haven't heard anyone mention anything about Camillus yet in any of the post. Is there a reason for this?
Click to expand...

Camillus concentrates mostly on entry level blades aimed at the average consumer. That doesn't mean they're bad, just that they're easy for knife enthusiasts to overlook while we concentrate on brands that cater more to our wants. AUS8 is a decent steel that will take a very fine edge and hold it for a bit, but there are certainly steels that completely outclass it in almost every regard. If, however, AUS8 was doing everything you needed it to, then I'd say stick with it. The Ontario Rat 1 is a very popular folder around here with AUS8 steel and a price comparable to the Camillus that was stolen from you. You might want to check it out.
 
ma tumba said:
Thanks for the graphs!

So in order for a blade not to deform and not to chip the steel should be both hard and tough. From what I picked, these properties are just inversly correlated so you cant generaly have both at once. But nevertheless is the right way, to take the toughest steel, like 3V, and bring it to the highest RC, like Nathan does for his blades?
Click to expand...

I'd go for something more like the latest spyderco mule in 4V. If they did the heat treatment right 4V is more than capable enough to handle those kinds of tasks and they're about the same size as the bradford.

Other than that I'd look at something more along the lines of 52100 heat treated by a legit heat treater at something over 61 and under 64 with a decently obtuse edge of say 20 degrees per side. That should be plenty.

Fwiw I haven't seen a smaller edc type of knife from Nathan the machinist. And it's not so much the steel as what he's doing to bring out specific attritrubes the steel CAN have.
 
bodog said:
I'd go for something more like the latest spyderco mule in 4V. If they did the heat treatment right 4V is more than capable enough to handle those kinds of tasks and they're about the same size as the bradford.

Other than that I'd look at something more along the lines of 52100 heat treated by a legit heat treater at something over 61 and under 64 with a decently obtuse edge of say 20 degrees per side. That should be plenty.

Fwiw I haven't seen a smaller edc type of knife from Nathan the machinist. And it's not so much the steel as what he's doing to bring out specific attritrubes the steel CAN have.
Click to expand...

Getting a 4V Mule is a great idea! I wanted to try one of the Mules anyway, so just ordered the 4V version. Thanks much for the hint.

I've never seen a Nathan's EDC sized knife either, but his larger blades are really impressive. Hope that he would eventually make more in different sizes.
 
I recently had my Manix2 in s30v chip terribly in 2 spots along the edge. I was pull cutting fairly thick boat rope. I believe it to be a brittle edge from the factory sharpening as I had not yet sharpened it, is this normal for Cpm s30v? I have read that it's more likely to roll along the edge rather than chip.
 
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