heat treats & edges

[DennisStrickland]

members have wondered if the factories send out knives with edges that are brittle due to fact the main part of blade receives a slightly different effect during heattreat than the much thinner edge. maybe this has been addressed earlier but i can think of no person more qualified to answer this query than Phil Wilson. hopefully he will answer & give us the facts. i remember yrs. back pardue the custom maker said he heat treated the blade before grinding the final edge since it made a more homogenous product. many earlier factories from the 19th century seemed to favor this method after blade was forged & hear t.also many custom makers wrap the blades in stainless foil to prevent decarbination at the edge. members comment that after reprofiling & sharpening several times that edge holding is improved. hopefully glasser or wilson can clear up this conception .thanks for any info. dennis

 

[DennisStrickland]

follow up --Cotdt [phillip] is also very qualified to shed light on this process.

 

[mete]

Decarburization is a major consideration for doing final grind after HT.Typically and edge about the thickness of a dime is used. Foils is used for stainless steel and other high alloy steels where hardening times are long. Even using salt for hardening they do final grind after HT. Some of that is to avoid handling damage during HT.Final grind can do damage BTW. I've had even good quality knives that had a soft edge or tips break off do to the damage !! Grinding heat can temper back the edge softening it and if severe can reharden the edge making it brittle.Sharpening once or twice usually takes care of that.

 

[Phil Wilson]

Dennis, It is difficult to say whether one process is better than another with out a metallurgy lab to actually investigate the different states. In my heat treat process I grind both before and after. I use foil to prevent de-carb as Mete describes above. Depending on the temp, time at heat and the steel there is going to be some de-carb on the surface with this method. The steels most sensitive to this are the high vanadium. Vanadium is very active at high temps. The production companies have access to either inert gas or vacuum furnace's. These tools should eliminate or minimize the effect of de-carb. I grind to about .030 on the edge before heat treat to lessen the amount I have to grind and finish in the hard state. This small amount of decarb is thus ground away. The other reason is that some of these steels are quench rate sensitive. The thin edge is going to cool faster than the rest of the blade and that insures that I get a good hard full martensite edge to temper back. This does cause some stress in the blade but with the cryo cycle and subsequent tempers I feel that this all evens out. I also do a final temper for stress relief after all final grinding and finish and before I put on the handle. Yes it is possible to overheat the thin edge on a hardened blade while finish grinding or sharpening or even buffing. Normally this would just draw the temper a bit in that area. If it gets too hot, red hot, for example and there is some retained austenite it could be transformed to new martensite ( very brittle) and then cause a chipping problem later. Only re tempering could correct this. Hope this helps some,, Phil

 

[Gabe Newell]

Hey, Phil - have you tried S35VN yet?

Gabe

 

[nevermind35]

Very informative thread and posts thanks for sharing.

 

[DennisStrickland]

thanks phil i could see how effective inert gas & cryo quench could offset negative processes. admirable that you do a final temper on your blades before attaching the handles. at present i do'nt require any custom knives, however if i need a custom blade you will be the guy to call. thanks, dennis.

 

[Jason B.]

People blame the HT when they should blame the sharpening.

 

[RevDevil]

@knifenut1013 - Not sure that is the case across the board. I wouldn't make a blanket statement about that without first knowing what methods production companies use.

 

[Jason B.]

@knifenut1013 - Not sure that is the case across the board. I wouldn't make a blanket statement about that without first knowing what methods production companies use.

I've seen very few factory edges that the edge grind would be higher than a 320 grit belt and a finish polish. The excessive plastic deformation caused by the high speed belt basically turns the metal into a liquid and pushes this liquid like metal to the edge. This metal is not in the same state as if the edge were to be sharpened by hand on stones. Given that the factory is no better than a XC or C diamond stone this adds into the issue of why factory edges do not show proper performance, the coarse edge has "teeth" that bend and break making the edge much wider than a fine polished as it wears.

The reason you hear most say that after they sharpened the edge is was OK is because they are taking the edge to a much finer level therefor reducing the size of the scratch pattern making it harder for the object being cut to deform the edge.

This pic shows that "flow" of metal I was talking about.

 

[Phil Wilson]

Gabe, I have not worked with 35VN yet. I talked with a rep from Crucible-Niagrara about it during the Oregon show last month. They modified S30V by taking out a little Vanadium and adding some Niobium. Niobium makes a very fine carbide and the idea is that this will increase toughness a bit. The trade off is that wear resistance goes down some since there is less Vanadium carbide in the mix. These are small changes and my guess is that it would be hard to tell the difference in knife blade in normal use. I make a lot of fillet blades, hard thin, with CPM S30V and it works very nice for that application. I have a good stock of 30v so probably would not move to put that aside and opt for the new stuff till that is used up. I have been using a lot of CPM S110V, this one has Niobium and Vanadium in about equal amounts, is very stain resistant, reasonably tough even at RC 64 and holds an incredible edge --in the same category as 10V and M4 at the same hardness. Good stuff but in short supply right now. The other recent steel I have tried is Bohler-Uddeholm M390. Its a particle steel, high chrome and vanadium and heat treats and works nice. It takes a nice belt finish. I haven't done comparison cutting tests with it but looks like it would hold its own with S30V and others in that category.. Phil

 

[DennisStrickland]

hot damn its always great to hear from one of the legends in the alphabet alloys. many formites may not be aware that Phil Wilson wrote a column in blade magazine for some time & was one of the first to really produce knives from many of the really exotic metals. he has worked out many of the complicated heattreats on these newer alloys by trial & error. boldly gone where few have tread.

 

[RevDevil]

Thank you Phil, Dennis, and mete for explaining this concept with a little more detail. It's nice to be able to understand these thigns in better detail. :thumbup:

I've seen very few factory edges that the edge grind would be higher than a 320 grit belt and a finish polish. The excessive plastic deformation caused by the high speed belt basically turns the metal into a liquid and pushes this liquid like metal to the edge. This metal is not in the same state as if the edge were to be sharpened by hand on stones. Given that the factory is no better than a XC or C diamond stone this adds into the issue of why factory edges do not show proper performance, the coarse edge has "teeth" that bend and break making the edge much wider than a fine polished as it wears.

The reason you hear most say that after they sharpened the edge is was OK is because they are taking the edge to a much finer level therefor reducing the size of the scratch pattern making it harder for the object being cut to deform the edge.

I figured that the different production companies use different diamond grades for sharpening. This seems like a given variable. The other variables that stand out to me are: forging process, heat treat / quenching process. I'm sure some companies/knifemakers take this into account more than others - and would correct for the heat generated during sharpening (my guess would be by sharpening slower), but this may not be the case.
Tanks for sharing your knowledge on this too, I'm always happy to learn more for those with something to share. :thumbup:

 

[DennisStrickland]

RevDevil the only way one can acquire a blade that has the maximum heattreats is to go to the custom knifemakers.factories cannot take the time required to tweak the optimal performance of alloys. i do'nt mean to imply that factories ca'nt achive this but that it makes knives so much more expensive.most major suppliers certainly turn out decent products. if you really are picky then a custom maker can supply knives with true super attributes. some makers can tweak 1095 & 01 to give legendary results.of course these knives are going to be more expensive but some individuals are willing to opt for this stellar performance. in this class of knives sisal rope & hard dry bamboo can be cut for hours & still shave hair, however expect to pay hundreds of dollars for this quality.

 

[Superdave1]

RevDevil the only way one can acquire a blade that has the maximum heattreats is to go to the custom knifemakers.factories cannot take the time required to tweak the optimal performance of alloys. i do'nt mean to imply that factories ca'nt achive this but that it makes knives so much more expensive.most major suppliers certainly turn out decent products. if you really are picky then a custom maker can supply knives with true super attributes. some makers can tweak 1095 & 01 to give legendary results.of course these knives are going to be more expensive but some individuals are willing to opt for this stellar performance. in this class of knives sisal rope & hard dry bamboo can be cut for hours & still shave hair, however expect to pay hundreds of dollars for this quality.

Maybe I'm not understanding this--but why couldn't couldn't a production co heat treat for 'optimal'properties? Maximum hardness isn't optimal for all users. A harder,more wear resistant blade steel may be more expensive to grind or sharpen. I suspect the higher price for custom knives has more to do with fit and finish time,low production volume and economies of scale and not so much with the heat tratment of 1095 for example.

Dave

 

[samhain73]

I think it's because it would be next to impossible for a production companies to utilize salt pots, or cryo treatments. It wouldn't be cost effective.

 

[Superdave1]

I think it's because it would be next to impossible for a production companies to utilize salt pots, or cryo treatments. It wouldn't be cost effective.

Could be...sort of like spending too many bucks on pimping a Ford Escort when you could just move up to a Mustang.

 

[DennisStrickland]

crusader forge triple tempers s30v to create blades that are super tuff. dozier tweaks d2 to create legedary cutters. it's not that factories ca'nt make heattreats that accomplish what the custom makers do ; its the simple fact that the average knife user is'nt going to pay a hundred $ for a pocketknife. custom heattreats can take days not a few hours like the majority manufactuers perform.this has nothing to do with engraving,gold inlays, & rare woods but with the amount of effort it takes to achive a super knife. most knife users are quite happy with our major knife producers since the knives are quite good.the point i'm trying to convey is that a person whom desires the upmost an alloy can give & is willing to pay the expense will need to go to a custom maker. an example is the 1095 hunter produced at a factory may cut sisal rope 50 or 60 times however that same 1095 in the hands of a custom man might cut the same rope 250 times.

 

[Superdave1]

crusader forge triple tempers s30v to create blades that are super tuff. dozier tweaks d2 to create legedary cutters. it's not that factories ca'nt make heattreats that accomplish what the custom makers do ; its the simple fact that the average knife user is'nt going to pay a hundred $ for a pocketknife. custom heattreats can take days not a few hours like the majority manufactuers perform.this has nothing to do with engraving,gold inlays, & rare woods but with the amount of effort it takes to achive a super knife. most knife users are quite happy with our major knife producers since the knives are quite good.the point i'm trying to convey is that a person whom desires the upmost an alloy can give & is willing to pay the expense will need to go to a custom maker. an example is the 1095 hunter produced at a factory may cut sisal rope 50 or 60 times however that same 1095 in the hands of a custom man might cut the same rope 250 times.

And MY point is that one could just pay for M4 or S30V...I like 1095 my Schrades are hair whittling sharp, and easy to sharpen...I'm not married to 1095, could get D2...
Maybe production heat treat for 1095 IS optimal and the others are more of a specialty treatment...
Marginal rerturns

 

[knarfeng]

I think it's because it would be next to impossible for a production companies to utilize salt pots, or cryo treatments. It wouldn't be cost effective.

Nonsense. It is quite feasible to include cryo on a commercial scale.

Only a big company can do a salt pot economically.
My company used to use heat treat salt baths. When our production rates fell, we shut them down and used other methods. Too much thermal mass to turn on and off. Too expensive to leave hot and only use it a bit.