S30V: What are your experiences with this steel?

[Cliff Stamp]

I wouldn't be surprised if S30V's high wear resistance causes an 'overcooking' of the edge with power sharpening.

This was one of the reasons given by Crucible, however they promoted S30V for ease of grinding over 440C. The companies using it had also used hard to grind steels like D2. The real problem is in the reported hardness, they have been checked and found to vary from 55 to 63 HRC. You would expect such a wide swath to generate a pretty radical spread in performance.

My question is: does the chipping that occurs in some S30V blades become any less after several uses (dulling of the edge) and re-sharpenings?

Sometimes it goes away, some times it doesn't some times it actually is fine for awhile and then starts chipping. My small Sebenza for example was fine for a long time but now if I attempt to hone it on the Sharpmaker the edge just fractures.

Are you talking about variation in all steels (from the same mfg), or just variation in S30V.

I would assume there is significant variation in all steels. This has to be the case because otherwise you have to assume a lot of people are lying. For example Thom and Sodak have described to me very different behavior of VG-10 at low angles than what I have seen. I would find it much more likely that there is a difference in the steels we are using than both of them are engaged in a conspiracy to defame the steel. I have also checked this personally by comparing several S30V and ZDP-189 blades from Spyderco and there is enough variance that while on average the ZDP-189 blades cut significantly better on cardboard, the groups actually overlap so it would be reasonable to assume that some customers could get equal performance or that rarely even some could see better performance from S30V.

I've seen your threads on S30V chipping. Have you seen other steels chip under similar levels of stress?

Not even close.

I'd also like to know more about the chipping problem. I have one S30V fixed blade that I've really beat on, chopping at a hard oak pallet. I couldn't get it to chip, and I think that's about as extreme as I will ever get with a knife. There must be some unknown variation in the steel or heat treat if chipping is happening with normal use.

The chipping happens at times even when sharpening and at other times under very light use like cutting cardboard, light vegetation and plastics. Edge geometry of course plays a large role, if you make the edge thick and obtuse enough then anything will be durable.

-Cliff

 

[HoB]

I am going to see if I can't convince Cashen to take some micro-graphs of some S30V blades I have as it isn't like I have a shortage of pieces. With some direct visual results of the grain/carbide structure it would eliminate some guesswork.
-Cliff

Not that I wouldn't like to see the micrographs, but really this discussion makes me doubt more and more that the issue with S30V is its microstructure. I believe Roman Landes pointed out that the size and structure of primary carbides does not change appreciably during the heattreat and the carbide fraction is not THAT different from the other high-alloy stainless steels like BG-42, VG10 or even ATS-34 and 440C for that matter. And in principle the carbides should be smaller in S30V than in ingot steels. So there must be something else that makes S30V so much more hit and miss than other ledeburitic (did I spell that right?) steels. So either, the heattreat got totally botched in those knives that exhibit problems, or there is something going on in the meso-structure (well technically, the carbides are all meso-structure, but I think you get what I want to say) of the steel. I don't know, you talk about secondary hardening and carbide aggregation, maybe, S30V shows a bad case of that, when the heattreat is not right. I have no idea, really, but I would love to know.

 

[Cliff Stamp]

So there must be something else that makes S30V so much more hit and miss ...

I would be interested in the martensite grain structure and the amount of precipitation of secondary carbides along those grains. Both of these significantly effect toughness and they are very dependent on how it is hardened. Plus I would also like an independent confirmation of the carbide size/volume. Note the micro-graphs Landes took of S60V for example paint a very different picture than the common promotion of that steel which just notes the average carbide size is small and ignores the fact that there are large aggregates due to the very high volume fraction.

-Cliff

 

[misque]

If this chipping problem is manifest only in products from the bigger companies, it might be in the heat treat. I believe they do their HT in batches. That means a large number of blades go in the oven at the same time. Unless the ovens they are using have heating elements on all six sides, there might be some blades in the batch that do not get enough heat, like those at the very center of the batch, or those that get too much heat, like those blades toward the outside edges of the batch, closer to the heating elements.

This is just idle speculation on my part because I honestly have no experience as to how the big makers perform their heat treat, other than pictures I've seen in the past.

Mike U.

 

[a223cat]

Could it be that the edge is overly thick? Perhaps it needs a reprofile. I believe CRK aims for 17-18 degrees but since they are sharpened by hand they are sometimes over 20 degrees. Also, if you don't get it very sharp in the first place after your sharpening it will of course dull quicker since it was not that sharp to begin with. Does it get very sharp after you are done sharpening it?

yes it is scary sharp when finished fighting with it. But that takes an hour or so. I find myself not wanting to spend so much time fighting with the one blade for that long. It has the original grind and angles, and I have not tried to reprofile it. I figured that would take way too much time.

I also am concerned that if I make the edge a narrower angle it might start the chipping thing. Maybe it is just my specimens of the steel, but I dont want to keep buying it waiting to get comfy steel for me.

 

[Larrin]

I would be interested in the martensite grain structure and the amount of precipitation of secondary carbides along those grains. Both of these significantly effect toughness and they are very dependent on how it is hardened. Plus I would also like an independent confirmation of the carbide size/volume. Note the micro-graphs Landes took of S60V for example paint a very different picture than the common promotion of that steel which just notes the average carbide size is small and ignores the fact that there are large aggregates due to the very high volume fraction.

-Cliff

Asking Crucible I've heard anything from 16-20 ASTM grain size, but no one has told me more coarse than 16, including Dick Barber, who no longer works for the company, so he may or may not have any interest in hyping the CPM process.

 

[Cliff Stamp]

Asking Crucible I've heard anything from 16-20 ASTM grain size ...

The grain size depends on how it was heat treated, specifically it is critically influenced by the temperature and rate of heating/cooling. The references you find in tool steel books are what you get with the industry standard treatments which can often be exceeded by a small scale maker who can simply afford to put more money into the process and refines the process to optomize the performance for a knife and not a mold/die.

-Cliff

 

[HoB]

The grain size depends on how it was heat treated, specifically it is critically influenced by the temperature and rate of heating/cooling. The references you find in tool steel books are what you get with the industry standard treatments which can often be exceeded by a small scale maker who can simply afford to put more money into the process and refines the process to optomize the performance for a knife and not a mold/die.

-Cliff

Correct me if I am wrong, but as I said, I thought that the carbide grain size is NOT affected by heattreat? So strictly speaking carbide grainsize should be independent on how it was heattreated. However, carbide aggregation might occure and martensite grain structure is affected. Not trying to be nitpicky here, just to understand what is really going on here. In the end it probably doesn't matter in praxis whether you have large grains or large aggregates of small grains.

 

[Cliff Stamp]

Correct me if I am wrong, but as I said, I thought that the carbide grain size is NOT affected by heat treat?

Carbide size is strongly effected by heat treatment, however the range of heat treatement used by most knifemakers won't produce a significant effect. This is usually more of an issue for forgers because they are actually doing the rolling/normalizing themselves where stock makers are all starting from the same point and basically all use the same austenizing temperature to within a range that won't significant effect the size of the primary carbides on most steels.

You could soak S30V so hot it dissolved the chromium carbide and thus effected the nature of the primary carbide. This would not make very much sense however because why put all that carbide in the steel if you are just taking it out again in the soak. This also makes it much harder to actually transform the austensite to martensite and makes it much more likely that the steel will be brittle due to carbide precipitation during the cooling plus the greater amount of carbon dissolved will make it more brittle directly. The only real reason would be to create a high secondary hardness and there are much more effective ways to do that anyway by simply using a more suitable steel.

So in short, yes it can, but no it usually don't. However the nature of the carbide will be significantly influenced because you can get secondary carbide precipitation during the cooling after the austenization and this will strongly influence behavior. It makes the steel much more brittle, increases the tendancy to burr and reduces corrosion resistance.

-Cliff

 

[HoB]

You could soak S30V so hot it dissolved the chromium carbide and thus effected the nature of the primary carbide. -Cliff

Ok, that I kind of see as a "trivial" case (like a null-solution), and not really as a heattreat.

So what is exactly, on grain size level, secondary carbide precipitation? I thought that was an aggregation of carbides at the grain boundaries (mainly)? In that case the nature of the carbides is unchanged, only their "position" in the matrix is altered. Well, "only" with respect to a mechnistic behavior, obviously this greatly alters the performance of the material, but right now I am not so interested what the actual change in properties is, but more what is exactly going on at the grain level.

 

[Cliff Stamp]

Ok, that I kind of see as a "trivial" case (like a null-solution), and not really as a heattreat.

In that extreme yes, but for example Wilson soaks very hot and according to Crucible will dissolve molybdenum carbide which isn't done at the 1950F soak so it is possible that his hardening is effecting the primary carbides, so it would be interesting to see definately. In some steels it has a dramatic effect. The range of soaks for AEB-L for example drastically change the primary carbide structure. I can email you the paper if you want.

However what tends to happen in most of the heavy carbide steels, which is the majority of the current cutlery steels, is that the smaller carbides dissolve and the structure is dominated by the large aggregated chunks which stay around for a long time due to a low dissolution speed due to the tiny surface area/volume ratio. It is likely that by the time you dissolve them significantly you would have blown the austenite grain size.

So what is exactly, on grain size level, secondary carbide precipitation?

Carbides in general precipitate on heterogenous sites; dislocations, existing carbides and grain boundries. They do this as soon as the temperature is high enough to allow them to move (or conversely, low enough that they are no longer in solution). When you buy a steel in bar form it can contain both primary carbides from the initial casting as well as secondary carbides that formed as the steel was cooling during any post processing.

When you austensize the steel, the smaller secondary carbide will dissolve very rapidly and thus the carbide structure that remains tends to be the larger primary pieces of carbide. Now the temperature you soak will influence how much of this carbide is dissolved as that is where the alloy comes from that goes into the austensite but as noted, since most makers use pretty much the same temperatures, the primary carbide would be expected (in most cases) to look very similar.

However, during the cooling things can have a strong influence on the carbide structure. In a stainless steel you want the chromium to stay dissolved in the austenite until it turns to martensite because if it carbides out then two very bad things will happen. First it reduces the free chromium, and second, one of the places it tends to precipitate is on grain boundries and this massively makes the steel very brittle regarding impact toughness and it also lowers the edge stability. This is why you should always cool the steel as fast as possible without going so fast it cracks.

There is an exception to this which is intentionally getting the carbide to precipitate which is done in steels with a secondary hardness responce as you are in them generally more concerned with hardness, strength and wear resistance vs toughness/corrosion resistance. This is why there was a debate about ATS-34 for example because it has a strong secondary hardening responce and thus you have two sets of properties to pick from. There are makers on both sides of this issue as to which one is the best. Bos for example used primarily the secondary hardening cycle and his work was praised for years, Mayer was one of the first makers to say that was a really bad idea.

-Cliff

 

[knarfeng]

Guys, I'm a little out of my league here, but bear with me a bit while I ask what may be a stupid question.

I am a materials engineer for an aerospace company. My own specialty is chemicals and polymers, but I work with metallurgists. My company makes parts that go around jet engines, so we deal in steel as well as aluminum. I talked to one of our metallurgists who specializes in steel about chipping of S30V.

He commented that, while the particle metal process gives some unique properties to steel, it also has weak points. When the metal goes through the HIP process, there is always a danger that not all the micro-voids will be removed from the metal. There is also a danger that some of the particles may not join perfectly. His comment was that taking a piece of particle metal to a fine edge would be the very thing that would most expose any such weakness in the metal.

So now my stupid question. I would guess that the HIP processing parameters must be optimized for each alloy. So is it possible that those for S30V may not be fully optimized and could possibly produce metal ingots that may occasionally contain small flaws. Flaws that are not evident until one tries to achieve a fine edge? So that some parts of the ingot are flawless and form excellent blades and some parts of some ingots do not? If this were the case, I do not think variations in heat treat would remove the problem.

Again, this is not my specialty, nor is particle metal the specialty of the metallurgist I talked to. I was just wondering if this had been considered.
Sorry, I just had to ask.

add:
I was wondering because, judging by the threads I have read, it seems that most knife makers make both good and chippy S30V blades, even within the same model. Since these are top line companies, one would think that there would not be that much variation within a single company's heat treat process. So one possible cause that would account for the variation within a company's product would be issues with the base material. Like I said, just wondering.

 

[misque]

knarfeng,

There is absolutely no reason to apologize. This is a forum and interjecting differing ideas, opinions and/or observations is encouraged.

Your questions are relevent and I look forward to the replies.

All the best,
Mike U.

 

[JCaswell]

Some of the behavior described so far causes me to think of something discussed in another thread, namely heat affected zones resulting from laser cutting. Of course many knife companies use laser cutting for blanking parts and, depending upon a host of variables which will differ between laser cutting vendors, laser cutting is known to produce undesirable material conditions along the cut edges.
I would be interested to know how many of the chipping blades were laser cut rather than waterjet or cut using another 'cold' proceedure.

 

[M Wadel]

knarfeng

afaik the metal is pressed to 100% density before sintering or while they sinter it (or atleast should be)

 

[M Wadel]

Asking Crucible I've heard anything from 16-20 ASTM grain size, but no one has told me more coarse than 16, including Dick Barber, who no longer works for the company, so he may or may not have any interest in hyping the CPM process.

astm 16 would equal 32768 grains per square inch

and astm 20 would equal 524288 grains per square inch

can somone calculate how large the grains will be

 

[puukkoman]

I've got nothing but love for S30V.
My Spyderco Military was made with it, and that's hands-down my favorite "tactical" folding knife. Cuts like no other, stays sharp forever despite the thin, flat grind, has never chipped, hasn't rusted no matter where I've taken it, blah, blah, blah.

 

[Alex p. Schorsc]

I, also, have nothing but praise for this steel. I think it holds a great edge. I have a Sebenza and think this steel is great, although I don't do any real hard chopping or striking. I just do more plain cutting. I feel that Arkansas Translucent stones are the best for putting a real sharp edge on this steel.

 

[will_77]

I've only used s30v extensively in two of my Spyderco knives, the military and the dodo. My military is sharpened with a really steep back bevel, and touched up at 30 degrees on the sharpmaker. It is sharp and I haven't experienced any chipping. This military has been carried for years and seen its fair share of use. The s30v dodo has the factory back bevel and has been sharpened many times on the sharpmaker. It gets razor sharp and stays sharp for quite some time with use. I was worried about the thin delicate-looking tip on this one, but it has held up well.

 

[Cliff Stamp]

M Wadel, the common ASTM defination is

n=2^(G-1)

where n is the number of grains in an inch at 100 times magnification and G is the grain size number. Converting :

grain micron diameter = sqrt(2.54e4^2/100^2/n)

The 2.54e4 converts inches into microns and the 100 gets rid of the magnification. This reduces to :

grain diameter = 254/sqrt (n)

or

grain diameter =360*2^(-G/2)

So a grain size of ten has a micron diameter of 10 which is an amusing coincidence if you are a math geek. HSS is about 9.5 which gives a grain size of about 15. For G values of 16 and 20 the grain sizes would be tiny; 1.5 and 0.5 microns, which leads me to believe they were not citing G values.

-Cliff