H1 and work hardening

[sircantaloupe]

I'm wondering - what exactly constitutes the "work" that leads to hardening? Reason I ask is I recently spent some time with a coarse stone and turned the hollow grind on my Salt 1 into a flat saber grind. Now, I was assuming that all this would lead to a harder edge afterward due to all the work I put into it, but now I'm worried that I actually removed steel hardened by the factory grinding and exposed softer metal at the edge.

 

[EricV]

I'm fairly certain that if sharpening contributes to work hardening, then reprofiling by hand certainly should as well You should be good.

 

[RevDevil]

I'm wondering - what exactly constitutes the "work" that leads to hardening? Reason I ask is I recently spent some time with a coarse stone and turned the hollow grind on my Salt 1 into a flat saber grind. Now, I was assuming that all this would lead to a harder edge afterward due to all the work I put into it, but now I'm worried that I actually removed steel hardened by the factory grinding and exposed softer metal at the edge.

The way I understand it, any stress (sharpening/cutting) on the blade in turn increases the overall hardness at that point. Wait doesn't the Salt 1 come with a saber grind already? I think your initial assumption is accurate. Keep in mind you cannot expose new steel without submitting it through the stress of grinding or honing it anyway. :thumbup:

 

[Itch Blade]

The way I understand it, any stress (sharpening/cutting) on the blade in turn increases the overall hardness at that point. Wait doesn't the Salt 1 come with a saber grind already? I think your initial assumption is accurate. Keep in mind you cannot expose new steel without submitting it through the stress of grinding or honing it anyway. :thumbup:

My Saver is a hollow grind.

I'm not sure why you would want to go to a saber from a hollow unless the knife is really going to get beat on.

 

[richard j]

you didnt hurt the blade any and you didnt made it any harder from the work you done to the blade. work hardening steel is used in excavating equipment. for example the teeth on a backhoe bucket are made from work hardening steel. each time the teeth impact a rock or similar material they get harder.

 

[RevDevil]

you didnt hurt the blade any and you didnt made it any harder from the work you done to the blade. work hardening steel is used in excavating equipment. for example the teeth on a backhoe bucket are made from work hardening steel. each time the teeth impact a rock or similar material they get harder.

That is what H1 does, maybe not by hand sharpening - but if you throw the knife in a beltsander that is a different story:
http://spyderco.com/forums/showpost.php?p=258981&postcount=2

 

[richard j]

thats why i said he didnt hurt or change anything since he done the work by hand.

 

[erichsen]

I'm wondering - what exactly constitutes the "work" that leads to hardening? Reason I ask is I recently spent some time with a coarse stone and turned the hollow grind on my Salt 1 into a flat saber grind. Now, I was assuming that all this would lead to a harder edge afterward due to all the work I put into it, but now I'm worried that I actually removed steel hardened by the factory grinding and exposed softer metal at the edge.

According to Wikipedia, and my own vague recollection on this topic, work hardening occurs when the item is cold formed or hot forged, not by the small amount of force and friction associated with passing a blade over an abrasive.

The pertinent portion of the Wikipedia page reads thusly:
"Work hardening, also known as strain hardening, is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements within the crystal structure of the material.[1] Any material with a reasonably high melting point such as metals and alloys can be strengthened in this fashion[citation needed]. Alloys not amenable to heat treatment, including low-carbon steel, are often work-hardened. Some materials cannot be work-hardened at normal ambient temperatures, such as indium,[citation needed] however others can only be strengthened via work hardening, such as pure copper and aluminum.[2]"

For example, Egyptians and Sumarians used copper tools which were progressively hardened by hammering to shape, then re-annealing and then repeatedly beating them with stone hammers until a final usable hardness was achieved.

Cheers,

-E

 

[Noctis3880]

I'm a little curious to know if H1 can be artificially work hardened by the end user? Say, by running it repeatedly over a smooth steel rod or by mashing the edge into a slotted paper wheel(which in its own right acts a bit like smooth steel)?

 

[Dr Heelhook]

Wait doesn't the Salt 1 come with a saber grind already?

All Salt knives are hollow ground, because it's impossible to flat grind them on a factory production level, since you need to grind both sides of the blade at the same time in order not to mess up the hardening.

 

[unit]

All Salt knives are hollow ground, because it's impossible to flat grind them on a factory production level, since you need to grind both sides of the blade at the same time in order not to mess up the hardening.

I am not sure this is technically true. It *may* be, but I understood Sal's statement to mean that Spyderco has not found a way that makes sense from a production stand point (relative to Spyderco's current abilities and relative to the desired price point of the final product). I would imagine that the same thing could have been said 20-30 years ago about any number of the "super" steels we see on the market today (for different reasons).

My point is, as the industry evolves with superior tools and practices, previously "impossible" things start to become available at reasonable prices.

 

[Michael Janich]

All Salt knives are hollow ground, because it's impossible to flat grind them on a factory production level, since you need to grind both sides of the blade at the same time in order not to mess up the hardening.

The simultaneous hollow grind in the production of H-1 ensures that both sides of the blade are stressed/hardened at the same time to prevent warping.

My experience has been that even hand sharpening of the edge increases its edge-holding properties over time, particularly on plain edges. Serrated H-1 edges are about as aggressive as a knife edge can possibly get, right out of the box.

Stay safe,

Mike

 

[Broos]

As stated above, work hardening is caused by plastic deformation (as opposed to elastic deformation). So unless you are permanently deforming the edge, you are not work hardening it when sharpening. Maybe on some microscopic level you have work hardened an extremely thin layer by sharpening, but I question whether this would even be picked up from a hardness test. It would be interesting to hear more of Spyderco's theory - might do some research...

 

[jekostas]

As stated above, work hardening is caused by plastic deformation (as opposed to elastic deformation). So unless you are permanently deforming the edge, you are not work hardening it when sharpening. Maybe on some microscopic level you have work hardened an extremely thin layer by sharpening, but I question whether this would even be picked up from a hardness test. It would be interesting to hear more of Spyderco's theory - might do some research...

Spyderco had Crucible Specialty Metals do a report on H1 - that's where a lot of the information comes from.

http://spyderco.com/forums/showpost.php?p=258981&postcount=2

 

[Broos]

Thanks for the link, I took a look at that post yesterday. Friction and the resultant heat cannot cause work hardening - it can cause hardening if the blade gets hot enough, but not work hardening. I'll look around for some of the crucible info referred to...

edit...

Did some looking around - so this is a precipitation hardened steel that is cold rolled at the mill and then simultaneously double ground (tempering affect there?) at Spyderco. So the proper terms to describe any hardening post production is precipitation hardening or age hardening. An interesting knife steel, though I am with Mr. Landes in that thread on messerforums about it getting to 68 HRc.

Sorry I know this stuff came out a long time ago...

 

[Noctis3880]

Thanks for the link, I took a look at that post yesterday. Friction and the resultant heat cannot cause work hardening - it can cause hardening if the blade gets hot enough, but not work hardening. I'll look around for some of the crucible info referred to...

edit...

Did some looking around - so this is a precipitation hardened steel that is cold rolled at the mill and then simultaneously double ground (tempering affect there?) at Spyderco. So the proper terms to describe any hardening post production is precipitation hardening or age hardening. An interesting knife steel, though I am with Mr. Landes in that thread on messerforums about it getting to 68 HRc.

Sorry I know this stuff came out a long time ago...

It's a shame that Spyderco doesn't seem to have done more extensive testing of this steel(i.e. artificially hardening desirable portions of the blade). I'd be interested to see this steel in a kitchen knife or perhaps even a katana.

Still, the two things you'll find about grinding blades on a belt sander is abrasion and heat. So I think it's safe to say that similar acts would harden the steel further. I'll be interested in taking this knife to my paper wheels to see if I can harden the edge on the slotted wheel.

I don't really have the tools and materials to test the edge retention before and after, but I suppose I can cut on some hard plastic and see if the edge rolls. I'll also try to put a scratch on the blade with a razor blade, buff it to a mirror finish, and try it again:thumbup:.

If I really can harden the blade artificially, it'll end up being one heck of a magic metal.

Also I would be kind of curious to know if there's some sort of upper limit to how much it can be hardened in this manner before chipping becomes an issue.

 

[jekostas]

Thanks for the link, I took a look at that post yesterday. Friction and the resultant heat cannot cause work hardening - it can cause hardening if the blade gets hot enough, but not work hardening. I'll look around for some of the crucible info referred to...

edit...

Did some looking around - so this is a precipitation hardened steel that is cold rolled at the mill and then simultaneously double ground (tempering affect there?) at Spyderco. So the proper terms to describe any hardening post production is precipitation hardening or age hardening. An interesting knife steel, though I am with Mr. Landes in that thread on messerforums about it getting to 68 HRc.

Sorry I know this stuff came out a long time ago...

I understand. From the reading I've done, the impression is that standard sharpening will provide some hardening of H1 steel, but the actual change is so minuscule as to be unnoticeable without years of constant use by the end user.

I'm not sure the Crucible report can be dismissed quite so easily as the messerforum thread would like to believe, but on the other hand Spyderco doesn't sell H-1 steel on the edge retention or hardness properties, but rather on the corrosion resistance.

 

[Noctis3880]

I understand. From the reading I've done, the impression is that standard sharpening will provide some hardening of H1 steel, but the actual change is so minuscule as to be unnoticeable without years of constant use by the end user.

I'm not sure the Crucible report can be dismissed quite so easily as the messerforum thread would like to believe, but on the other hand Spyderco doesn't sell H-1 steel on the edge retention or hardness properties, but rather on the corrosion resistance.

Still, it's not as though the knife needs to be dull before you sharpen it.

You can cut down from years to minutes with a bench grinder and a set of paper wheels.

And actually, I believe Spyderco DOES sell H-1 on edge retention and hardness:

A big myth in the knife world is that out there somewhere is a knife that seriously cuts but cannot rust. Knives claiming these super powers are usually made with steels that are unable to hold a cutting edge for any measurable amount of time. Finally a steel foundry in Japan called Myodo Foundry makes this myth a reality with the introduction of a new steel called H1. H1 steel is a PH steel, meaning it is a precipitation-hardened steel. "Huh" you ask? Utilizing .1% nitrogen instead of carbon to harden the steel, it reaches a Rockwell hardness of 57-58rc. Spyderco uses H1 on its new C91 Pacific Salt model.

The selling point being that edge retention/hardness will be better than traditional titanium diving knives, which is true. Now we just need people to thoroughly test out the work-hardening properties of the steel.

 

[erichsen]

As stated above, work hardening is caused by plastic deformation (as opposed to elastic deformation). So unless you are permanently deforming the edge, you are not work hardening it when sharpening. Maybe on some microscopic level you have work hardened an extremely thin layer by sharpening, but I question whether this would even be picked up from a hardness test. It would be interesting to hear more of Spyderco's theory - might do some research...

I seriously doubt this based on the description from Wikipedia and a book on mechanical properties of common structural alloys I checked after my original posting.

Bashing with a hammer is about the only sure-fire way of dislocating crystalline structure in the manner described. If you sharpen a bit of H1 the way you might a piece of pig iron or pure copper by heavy hammering, that would be work hardening. Applying mere hand pressure to a tool steel does not induce plastic deformation per the definition to (permanently) indent the blade.

-E

 

[Broos]

Looking at the edge as a whole, obviously there is not plastic deformation of the whole edge during sharpening. So there is no work hardening from this.

Regarding work hardening from sharpening, it does not occur when it comes to low speed abrasive wear with hardened, tempered, martensitic steel. See third paragraph of the link below. The failure mechanism for low speed abrasion is brittle failure due to the brute force removal of material, not brittle failure due to microscopic deformation & the resultant strain hardening (work hardening).

http://resources.metapress.com/pdf-preview.axd?code=qh36vk634q2w3p38&size=largest

They used an ESM to inspect the affects of the abrasion in the above, & plastic deformation was observed even with steels that do not work harden with abrasion (they saw plastic deformation at the bottom of the gouge from the abrasive, and brittle failure & cracking perpendicular to the direction of the abrasive particles at the ridges).

But work hardening from abrasive wear does occur with austenitic steels. The mechanics of wear I would guess also to be brittle fracture, but after deformation and the resultant work hardening (this mechanism is discussed in the 1st link, but not with an austenitic precipitation hardening steel like H1).

http://www.outokumpu.com/pages/Page____5763.aspx

The above link is more relatable to machining, but sharpening is basically machining. So work hardening of the surface of an austenitic steel from sharpening does occur, but what I'm not sure about is the measure of hardness that can be obtained, the extent of hardening, & the thickness of penetration of the hardening - they will depend on numerous factors and are debatable without testing (they are all testable & measurable). (see second column of the link below-lots of good info here I'm trying to digest)

http://books.google.com/books?id=Or... wear work hardening austenitic steel&f=false

This topic is very applicable to the oft-heard conjecture about how an edge dulls in use - If you understand the mechanics of abrasive wear for a steel (some good info in the 1st link on this), you can relate it to the portion of the dulling equation dependent on abrasive wear.