Alloy banding in A2?

[james terrio]

I' a bit of an over-thinker, too. That's just part of the addiction. If you like CPM-154 and S35VN, you're gonna love Elmax and CTS-XHP... get ready for another round of sticker-shock, though.

Honestly though, if you offer your main model(s) in a great tool steel (I prefer 3V), a fine stainless like S35VN or CPM-154, and mayyybe a good well-known low-alloy steel like O1 or 52100, you've got the whole market pretty well covered.

 

[aarongough]

A Timesaver is a large belt sander. Generally around 48" wide. Given that you're unlikely to have larger than a 0.001" taper in the area the size of a knife blade, I think that I'll continue to plan on that for my next sheet. Even if the sheet varies by the full tolerance, I'm not going to be concerned about the slight variations in thickness. More than likely the sheet will be within 0.002" in deviation from its average, with the +/-.010 tolerance applying to the average size VS nominal.

Good enough for me, I make each sheathed for each knife specifically anyway.

Cool, good to know!

I' a bit of an over-thinker, too. That's just part of the addiction. If you like CPM-154 and S35VN, you're gonna love Elmax and CTS-XHP... get ready for another round of sticker-shock, though.

Honestly though, if you offer your main model(s) in a great tool steel (I prefer 3V), a fine stainless like S35VN or CPM-154, and mayyybe a good well-known low-alloy steel like O1 or 52100, you've got the whole market pretty well covered.

I'll have to ask Bohler/Uddeholm about Elmax as well, that's one I forgot about!

 

[james terrio]

I'll have to ask Bohler/Uddeholm about Elmax as well, that's one I forgot about!

I really love Elmax and CTS-XHP. The only problem is finding them in the sizes I want.

 

[aarongough]

Ok guys, I'm going to say that I think I've accidentally called wolf on this. Today when I was polishing up the blades in this batch to see if they were salvageable I realized that I've seen this carbide segregation (or whatever it is) in A2 before, in probably all the knives I've made from it in fact. In the past I would see little ghosts of it during finishing and inspection, but I never thought much of it as I've seen much worse orange peel in other steels.

Thinking back though I've never acid-etched an A2 blade before, and the results of that were what startled me so much...

I took one of the knives from the batch all the way up to a mirror finish on one side to see if I could highlight the carbide segregation:

You can see it as streaks of 'orange peel' in the finish in the next 2 photos:

Full size: http://i.imgur.com/DGSNnPT.jpg

Full size: http://i.imgur.com/FobaeK4.jpg

Everything is much easier to see after just a few seconds in Ferric Chloride:

This carbide segregation stands out pretty clearly in a mirror finish, and would definitely not be suitable for a knife intended to be finished that way. But I only ever take my knives to a ~600 grit satin finish in which case the issue pretty much disappears.

This blade will be getting broken tomorrow after doing edge retention testing just to satisfy myself that these blades will perform the same as others I've made. All the reading I've done so far says that carbide segregation should not negatively impact the performance of the blade, so I assume the testing will go just fine. Especially given that this carbide segregation was likely also present in every previous A2 blade I've made and tested.

I will be polishing and acid-etching the A2 test blade that I used during the original steel testing process to confirm this.

So: Seems like A2 is not the steel to use for fine finishes (which is what Stacy noted in his previous post), it also seems that A2 is not the steel to use if you plan on doing acid etched finishes, which is a bit of an issue for me right now, but one I'm sure I will work around.

Provided the sample blade passes my tests and proves itself identical to my past blades then this carbide segregation will not be an issue for me with my satin finished blades. I will have to find another option for a current customer that wanted an acid-etched finish but that's fine.

Going forward I think I'm likely going to change steels pending further tests.

Thanks to everyone who contributed in the thread so far! Lots of great stuff to consider!

-A

 

[AVigil]

Glad it is working out.

I love A2 and have had great experiences with it since I met Phil Hartsfield who swore by it.

 

[Matthew Gregory]

Good to hear, Aaron, however I want further clarification about how carbide banding ISN'T deleterious to performance. That seems entirely contrary to conventional wisdom...

 

[aarongough]

Good to hear, Aaron, however I want further clarification about how carbide banding ISN'T deleterious to performance. That seems entirely contrary to conventional wisdom...

I've read that in a few tool and die books (which granted talk about a different application) and Stacy seemed to think it wasn't harmful either.

More info will come tonight when I test that blade to destruction. I'll also be etching the original A2 test blade that I made (which was made from Uddeholm steel) to see if that contains the same banding.

 

[Nathan the Machinist]

Good to hear, Aaron, however I want further clarification about how carbide banding ISN'T deleterious to performance. That seems entirely contrary to conventional wisdom...

As you're aware, carbon moves but alloy doesn't. A2 really doesn't have a huge primary carbide fraction. After the steel has been processed and the carbon is doing what it's supposed to do, areas where you once had a large carbide become alloy rich and are, in effect, a somewhat different steel and etch differently.

Imagine a pattern welded O1 and L6. Done properly and without inclusions that banding has no negative effect. I imagine this might be somewhat similar.

I can't think it's a good thing and I wouldn't want it, but I expect it's probably not as bad as it appears.

 

[Matthew Gregory]

As you're aware, carbon moves but alloy doesn't.

Right, but that's why getting alloy disbursement right in the beginning is important, one of the advantages of PM technology, no?

I can't think it's a good thing and I wouldn't want it, but I expect it's probably not as bad as it appears.

Although I agree that it's unlikely to create an issue, or else we'd be hearing about it with A2 all the time, I agree that it's not something I'd want.

 

[aarongough]

As you're aware, carbon moves but alloy doesn't. A2 really doesn't have a huge primary carbide fraction. After the steel has been processed and the carbon is doing what it's supposed to do, areas where you once had a large carbide become alloy rich and are, in effect, a somewhat different steel and etch differently.

Imagine a pattern welded O1 and L6. Done properly and without inclusions that banding has no negative effect. I imagine this might be somewhat similar.

I can't think it's a good thing and I wouldn't want it, but I expect it's probably not as bad as it appears.

I've been thinking about this for the last few days, and especially last night and this morning on the way to work. I'm going to scrap these blades and move to another steel regardless of the outcome of my testing tonight.

I've already spent too long dealing with an issue that's clearly present in a lot of A2 from different sources. Yes, I can likely get clean A2 from *somewhere*, but how clean and will it stay clean. It seems that none of the potential suppliers have a policy about how much of this type of banding is acceptable in their steel, which means that I'll constantly be dealing with a level of uncertainty that isn't particularly comfort inducing.

The smart thing for me to do then is to move to a steel that's simply not going to have these issues. Likely candidates right now are CPM3V or CPM154. I've always wanted to offer a stainless so CPM154 will be the primary steel I'll be testing. This will open up a lot of options for me in terms of finishing options and refining my heat-treat process. It also makes sense from the perspective that I want to get into folders and kitchen knives, and being able to use one steel for all of these would be great.

I've been very happy with A2 in the past in terms of performance, and I've heard nothing but good feedback from my customers and from other makers who are using my heat-treat for A2. All that said I don't want to have to deal with any uncertainty in my steel so I'm going to make the call.

Thanks for keeping me grounded guys. Good to have so many knowledgeable people as a sounding board.

Update:

After testing one of these blade to destruction I'm still amazed at the performance of A2 even at high hardnesses. The blade was hardened to about 62HRC and still took multiple hits with a crowbar to the edge before chipping. Pretty crazy in my book.

With that in mind I think it would be wasteful to scrap the A2 blades I have on hand. I'll continue using A2 for satin finish blades while I investigate other potential steels, with a focus on CPM154 and CPM3V. They'll get compared to A2 and we'll go from there.

 

[mete]

The real way to get away from banding is to use a CPM type . For a stainless one you wouldn't be disappointed in CPM 154.!!

 

[aarongough]

The real way to get away from banding is to use a CPM type . For a stainless one you wouldn't be disappointed in CPM 154.!!

That's what I'm hoping! My minimal experience with CPM154 has so far been very positive. Re-ground one of the test blades made from it last night and was certainly very happy with the way it was cutting. More testing will tell on that front.

Will have to experiment with some different heat-treats as well.

 

[Kloepper Knife Works]

I look forward to reading about your further exploits as you test CPM154 and CPM 3V more extensively. I can say that the knives I've finished in 3V at 60Rc were still ductile enough to exhibit deformation instead of cracking when abused hard. I am however battling surface rust on the blanks I am currently working on. After I finish coarse shaping them I plan to hit them briefly in an acidic solution after washing with soap and a scotchbrite pad to see if they were just contaminated from surface grinding on borrowed equipment.

The funny thing is that I have yet to see rust on my finished 3v knives, no oiling, rarely cleaned, and to top it off a sandblasted finish (notoriously the most rust prone). Totally unexpected, and I'll be curious to see if it was a fluke. If CPM154 really does end up nearly as durable as 3v in your testing, it should prove to be a beast of a material.

 

[aarongough]

So guys, a quick update. I went to the shop tonight and etched every old A2 test blade I could find. All of them exhibited the same banding. This is an old test blade that I made during the steel testing I did, I believe this was Uddeholm steel:

Full size: http://i.imgur.com/p13LLEB.jpg

This is the blade that was made from Starrett steel after going through destructive testing:

The blade bent to about 40º before breaking, which is not quite as good as the standard my original test blade set (55º) but I take my blades to a higher hardness now and that's likely responsible for the change. My blades now come out at about 62-63HRC, whereas the original test blade was 60HRC.

The edge of the blade was ground to only 0.010" so it was very thin. It still took multiple blows from a crowbar (both inline with the blade and also at an angle) before chipping. It chipped after a very firm blow from the crowbar that struck the blade at 45º.

Overall I'd say the performance in terms of toughness wasn't quite as good as the original test blade, but that's likely down to this new blade likely being ~2-3 rockwell points harder than the original test blade.

A blade at 62+ HRC taking a beating like this (from a crowbar no less) is pretty darn impressive from what I've seen, so I think it's unlikely the alloy banding has any negative impact on the performance of the steel, and as shown above it seems that all the A2 steel I've ever received has had the same banding!

For me at least that pretty much answers the question of whether the banding has a performance impact...

If any of you guys have A2 on hand as well as ferric chloride it would be great if you could etch some blades to see if the banding is also present!

 

[aarongough]

I look forward to reading about your further exploits as you test CPM154 and CPM 3V more extensively. I can say that the knives I've finished in 3V at 60Rc were still ductile enough to exhibit deformation instead of cracking when abused hard. I am however battling surface rust on the blanks I am currently working on. After I finish coarse shaping them I plan to hit them briefly in an acidic solution after washing with soap and a scotchbrite pad to see if they were just contaminated from surface grinding on borrowed equipment.

The funny thing is that I have yet to see rust on my finished 3v knives, no oiling, rarely cleaned, and to top it off a sandblasted finish (notoriously the most rust prone). Totally unexpected, and I'll be curious to see if it was a fluke. If CPM154 really does end up nearly as durable as 3v in your testing, it should prove to be a beast of a material.

Yeah my corrosion testing in the past showed that 3V was surprisingly rust resistant. It pitted more than it surface rusted, which is apparently a thing it's fairly well known for.

I think taking a CPM3V blade to 62+HRC would really change the character of the blade (in a good way!), if A2 can be usable at that hardness (and I'm not nice to my knives!) then I'm sure CPM3V would be just as good or better!

I ordered a an extra 3' bar of CPM154 and a 3' bar of CPM3V today, they should arrive next week. Will get started with the testing after that!

Thanks for keeping up with the thread!

 

[james terrio]

{re:3V} ... After I finish coarse shaping them I plan to hit them briefly in an acidic solution after washing with soap and a scotchbrite pad to see if they were just contaminated from surface grinding on borrowed equipment.

You're absolutely on the right track. :thumbup: As Aaron said, 3V is kinda picky that way (it doesn't really patina or rust deeply, but it will get orange "bloom" on it if you neglect it long enough, and it's weird about pitting), and etching it just to get it good and clean definitely helps. I don't have the links handy, but if you google "3V passivication" you will find lots of info on the topic, including some really helpful threads by reknowned maker Jerry Hossom.

 

[james terrio]

Here's the thread I did on my first 3V prototype, regarding corrosion-resistance. It includes some good links about passivating.

I still use that very same knife almost daily, in the kitchen, in my shop, at the dinner table, in the garden, and in the boonies. It has cut a heckuva lot of stuff and shows no sign of wearing out. It exhibits no further corrosion or pitting to this day, with only the bare minimum of maintenance. (Sometimes I remember to wipe it clean after getting it dirty. That's all I've ever done to it except hone the edge. No oil, no wax, no nothin')

 

[aarongough]

You're absolutely on the right track. :thumbup: As Aaron said, 3V is kinda picky that way (it doesn't really patina or rust deeply, but it will get orange "bloom" on it if you neglect it long enough, and it's weird about pitting), and etching it just to get it good and clean definitely helps. I don't have the links handy, but if you google "3V passivication" you will find lots of info on the topic, including some really helpful threads by reknowned maker Jerry Hossom.

Funny that passivation should come up. I acid etched some CPM154 the other day, then left it wrapped in a wet rag for a day and a half to see how much corrosion would form. I was pretty surprised not to find any!

Took me a moment to realize that the grey oxide that CPM154 forms is likely chromium oxide rather than the black magnetite that a carbon steel would produce. So the blade was passivated by the ferric chloride and is likely even more corrosion resistant now than it started out as! I'm doing some reading to confirm that... Playing with new steels is always fun.

Also: after my testing last night with the A2 I think it would be wasteful to not use the blades I have on hand (16 of them) given how well they performed. I'm going to exhaust my on-hand supply of A2 while investigating other steels.

I was definitely shaken by A2's strange appearance after etching, but that seems to be something that's always been present, I've just never noticed it. It's definitely not a steel that takes a clean mirror finish, but a 600-800 grit satin finish looks great on it.

After the testing last night I would personally be quite happy to stick with A2 for my fixed blades. But given that CPM3V and CPM154 came up and turned out to be more affordable than I thought I think I should also investigate them again, especially with regards to finding one steel that I can use for fixed blades, folders and kitchen knives (not sure yet if that's really feasible or sensible). I think CPM3V and CPM154 are two very good candidates there. They'll get tested up against A2, as even with the minor cosmetic issues that A2 brings to the table, I still think it's performance at high hardness is pretty amazing.

 

[aarongough]

Here's the thread I did on my first 3V prototype, regarding corrosion-resistance. It includes some good links about passivating.

I still use that very same knife almost daily, in the kitchen, in my shop, at the dinner table, in the garden, and in the boonies. It has cut a heckuva lot of stuff and shows no sign of wearing out. It exhibits no further corrosion or pitting to this day, with only the bare minimum of maintenance. (Sometimes I remember to wipe it clean after getting it dirty. That's all I've ever done to it except hone the edge. No oil, no wax, no nothin')

Cool thread mate! It's cool that 3V is so rust/stain resistant. A2 would have definitely stained and rusted given your test conditions.

Any of you guys have tips for getting 3V to high hardness in heat-treat? Best I managed was about 61.5HRC, and the charpy c-notch tests show that CPM3V @ 62HRC will absorb 40J of energy, the equivalent number for A2 is 40J @ 60HRC. With that in mind I'd say that 3V can/should be taken even higher for my purposes, probably 63-64 even. Have no clue how to get it that much harder though...

That's one thing I would miss when going to a steel from Crucible, real datasheets with full CCT graphs and so on. The nice datasheets from Uddeholm make life so much easier when designing a heat treat!

 

[james terrio]

By all means, do not throw your existing A2 blades away Clearly, you've shown that it works pretty dang well for knife blades, as have many, many other makers.

I'm really looking forward to your comparison testing between A2/CPM-154/CPM-3V and whatever else you decide to try out. :thumbup: