Opinions please S5 "shock steel"

[oldnbusted]

Why do we need to compare it to another steel?

S5 is the original steel questioned but S7 was also brought up. These numbers show the tempering temperature that gives a specific hardness level and toughness level for S7. HOW HARD IS THAT TO UNDERSTAND?

Cliff adressed a particular question,namely the similarities between S5 or 7, and a crucible steel, hence the othr steels involved.

Why is it meaningless? Why do you always talk in circles? Why, Why Why Cliff do you always try to find fault in someones post?

Without wanting to get into the middle of this, you started it with the comment

Hey Cliff why don't you be more specific for the people who don't understand the lingo of heat treating, tempering and toughness levels.

And yet, you just posted up some numbers, yes, all the information in the thread is useful, but the numbers you posted weren't helpful to a pleb like me. I understand temp, i understand rockwell hardness, but the toughness was not quantified, and it took another post before you explained the point, even now i have to take your word for it that the lower numbers mean tougher steel.

 

[Alpha Knife Supply]

I understand temp, i understand rockwell hardness, but the toughness was not quantified, and it took another post before you explained the point, even now i have to take your word for it that the lower numbers mean tougher steel.

The higher the charpy number the tougher the steel.

I forgot to mention, lots of jackhammer bits are made from S5 & S7. They are very tough steels.

 

[Gossman Knives]

The higher the charpy number the tougher the steel.

I forgot to mention, lots of jackhammer bits are made from S5 & S7. They are very tough steels.

Thanks Chuck. That's why when a blade has a high rockwell hardness the edge is more likely to chip when under alot of stress. D2 is a good example of this because most blades run 60-61 RC.
Scott

 

[Cliff Stamp]

The lower the rockwell the tougher the blade.

No. Impact toughness doesn't have that simple relationship, even the table you posted contradicts this and you listed it.

That's why when a blade has a high rockwell hardness the edge is more likely to chip when under alot of stress.

This usually more to do with ductility than impact toughness, and even then the relationship isn't as simple as you noted. Tom Brogran recently got a number of S30V blades rehardened and they are now more durable not less.

Why didn't you compare S7 at HRC 47 ...

Because the hardness would be so low the tensile strength would be an issue leading to lower edge retention so you would not run it in knives at that hardness. At their peak values which would be optimal for knife use S7 is more than 50% tougher so that is where they would be compared.

The chart explains the tempering of S7 pretty clearly. Why is it meaningless?

Because charpy values change depending on size of sample and nature of block piece. You need at least another steel to judge the size of the numbers unless they also give the exact size and nature of the test block of course.

My mian point was that you complained I didn't explain issues like temper and then you posted a chart which would be completely meaningless unless someone understood the materials background, as oldnbusted noted. It isn't meaningless in general, just to the "people who don't understand the lingo of heat treating" which you noted.

It also doesn't address the origional post at all, which would be better served by a direct comparison of S5/S7 to other steels, not a simple list of its properties without a corrosponding set of other values for other steels.

-Cliff

 

[Alpha Knife Supply]

Because the hardness would be so low the tensile strength would be an issue leading to lower edge retention so you would not run it in knives at that hardness.

Now you changing the comparison to edge retention.

Edge Retention of 3V at charpy 85 = 6
Edge Retention of S7 at charpy 125 = 1

When comparing edge retention for 3V and S7 for the charpy values you listed, 3V has 6 times or since you used percentages 600% more edge retention than S7.

 

[Gossman Knives]

Well let's see............. if I response to Cliff again, he'll have a come back like he always does. Then we'll just go back and forth and back and forth until this thread is 15 or 20 pages long. No sense in wasting good bandwidth. I have to remember here at BF..... don't feed the trolls.
Scott
BTW, Cliff, if you really want to know what I think of your reviews and testing , come over to Whine and Cheese and I'll let you know what I think. The General Discussion forum is not the place.

 

[Cliff Stamp]

Now you changing the comparison to edge retention.

No, as noted, when comparing steels for materials properties the optimal values are used either peak values for the steel, or for the specific application.

Of course if you adjust the tempering temperature you can generate any ratio you want, you can easily soften D2 so it is weaker with lower abrasion resistance than AUS-6A as it is normally ran in knives, ~ 56 HRC.

However if someone asked about a comparison between the two steels at what point would be reasonable to use, how about both when ran at optimal hardness for knife steels. Seems sensible to me.

When using such a comparison S7 is *much* tougher than 3V.

3V has 6 times or since you used percentages 600% more edge retention than S7.

Six times is actually a 500% increase.

However that data isn't meaningful to knives which S7 would be made out of however because those knives would not primarily blunt by wear, they would blunt by deformation and fracture and thus S7 would likely have better edge retention not less.

-Cliff

 

[thombrogan]

ERDept,

What they're all trying to say is that S5 makes one heck of a chopper or field knife, but you shouldn't clamor to have it put gent's folder or slipjoint. Also, that Robert Hankins character makes some beautiful knives.

Scott/Razorback Knives,

I've never heat-treated a blade (unless ruining a temper or two counts) and I know, first-hand, that S30V heat-treated to RC61 by Phil Wilson is stronger and stays sharp longer than that same steel hardened to RC58 or 59. Knives from my own collection and money from my own pocket went into testing that assumption.

Haven't tried testing that assumption with tool steels yet, but those pesky folks at the American Society for Metals publish data showing that a lot of steels have a non-linear behavior for hardness versus toughness. That is, AISI 1095 is tougher at RC53 than at RC55, but it's also tougher than RC55 when it's hardened to RC60.

Also, a lot of qualification has to be made with those charts and graphs. A whole huckabucka qualification.

For toughness, which test was used and how do its results apply to a knife with similar values? How did the steel obtain a level of hardness or toughness (a little bird told me that O1 marquenched to RC65 can be tougher than O1 hardened to RC60 with a more severe quenching method)? Does the company publishing the data have a financial interest in the results of the data? Unless these sorts of details are explained, charts are just pretty pictures.

 

[Cliff Stamp]

Haven't tried testing that assumption with tool steels yet ...

The "softer = tougher" arguement comes up on rec.knives every now and again, awhile ago Alvin took a M2 HSS hawksaw blade and drew the temper and thus made it softer. He then put it in normal use compared to one left full hard, and guess which one suffered broken teeth? I'll give you a hint, it wasn't the full hard one.

Toughness / durability in general when applied to cutting instruments is a mixture of a bunch of properties, (hardness, ductility, and impact toughness) just like edge retention isn't restricted to one simple property (same things + wear/corrosion resistance). It depends on what is being cut and how as to the importance of each property.

-Cliff

 

[tallwingedgoat]

I don't know why some guys are criticising Cliff. Steels do not have a linear increase in toughness with a corrosponding drop in hardness. Take A2 for example, according to Crucible A2 has a charpy C-notch of 41 ft-lbs at 57 HRC and 60 HRC. Yet it's much less tough in between.

Take S7 for another example. At 53 HRC it's 105 ft-lbs but it actually peaks at higher hardness of 55-57 where it's 125 ft-lbs. Yet move it up to 59 HRC and toughness drops sharply to 85 ft-lbs. Now someone pointed out CPM-3V at 58 HRC also happens to be at 85 ft-lbs, implying both steels are equally tough. But this does not take into account S7's sweet spot at 55-57 HRC which is in another league in toughness. This is the point I think Cliff Stamp is trying to make. CPM-3V can never match 125 ft-lbs at any hardness.

 

[tallwingedgoat]

From my point of view, S5 is as the industry advertises - "a shock resistant tool steel." If I may extrapolate from the expereince with other steels used to make knives, the chemical makeup of S5 means that it could be similar in performance to 5160 and could potentially have a slight advantage over 5160 because of the modest molybdenum and vanadium content.

I use this comparison because a HECK OF A LOT of knifemakers use 5160 and make great knives from it. The edge holding isn't as good as 1095, O1 or 52100, but the compromise in carbon content and hardness gives you the value of toughness.

My sentiment exactly. A lot of blademakers speak highly of 5160 yet say they don't like S5 because it doesn't hold an edge. Huh? S5 should hold as good or better an edge than 5160.

On paper I like S5 much more than S7. Yes it seems they're both just as tough. However S7 falls off after 57 HRC, but S5 remains super tough at 59 HRC where it has a charpy c-notch of an incredible 138 ft-lbs! There are no other steel that I know of with that kind of toughness at that hardness.

Another well known tough steel for example L6, reach a sweetspot of 68 ft-lbs at 57 HRC, any harder and toughness drops appreciably. In fact at 61 HRC both L6 and S5 are pretty low in the 40ish ft-lbs and some may mistake this to mean both steels are similiarly tough.

Yet S5 should be far tougher than L6 at the optimal hardness both are designed for and you can't tell me S5 at 59 HRC isn't going to be competitive edgeholding wise against L6 at 57 HRC.

 

[thombrogan]

On paper I like S5 much more than S7. Yes it seems they're both just as tough. However S7 falls off after 57 HRC, but S5 remains super tough at 59 HRC where it has a charpy c-notch of an incredible 138 ft-lbs! There are no other steel that I know of with that kind of toughness at that hardness.

That's the silicon in the S5 which is missing in S7. My S7 knife from Justin Gingrich sneers at S5 knives for that reason:

"Those martensite crystals aren't even real"

Tough, but jealous, that S7 is.

 

[Cliff Stamp]

...you can't tell me S5 at 59 HRC isn't going to be competitive edgeholding wise against L6 at 57 HRC.

Too many people just assert as Chuck did in the above that wear resistance = edge retention.

For knives this is never 100% true, and in some cases wear resistance is actually largely irrelevant.

In lots of knives S5 would easily have better edge retention than L6 in the above as it is harder and tougher.

M2 at 65 HRC has excellent edge retention in a light utility knife, would have horrible edge retention in a wood chopping blade.

-Cliff

 

[TLM]

Impact toughness figures are notoriously hard to decipher, the standard test block is way larger than typical knife geometry. Toughness improves as size gets smaller. The phenomenon is also not continuous or linear with size and Charpy figures can be manipulated if the notch is not quite the standard or if the better option of fatigue notch is used. All in all I would not read all that much into the Charpy figures unless very specific test conditions are given and preferably the tests are done with a representative test piece size.

TLM

It gives an indication but not much else and in serious work fracture tougness figures are prefered.

 

[Cliff Stamp]

Fracture toughness tests a different, though related, property, which is the resistance to crack propogation under a load whereas charpy tests a sudden impact. It would be nice to see fracture toughness data as well for the various knives steels.

-Cliff

 

[the possum]

Now you changing the comparison to edge retention.

Edge Retention of 3V at charpy 85 = 6
Edge Retention of S7 at charpy 125 = 1

When comparing edge retention for 3V and S7 for the charpy values you listed, 3V has 6 times or since you used percentages 600% more edge retention than S7.

Again, this depends on what the edge is going up against. The above may be true in a contest where you're cutting dirty rope or something, but it seems we all agree we wouldn't be using these steels for that application. (Well, actually, 3V not only has great impact toughness, but is also about as wear resistant as D2, so this steel really could be used for a wide range of applications. In fact, it aught to be about perfect for what most people do with bowie knives, though my own uses focus more on the shock/impact side of things.)
These steels are for big choppers that will take a lot of shock. If you're out clearing weeds in a junkyard, the S7 blade would likely have several hundred percent better "edge retention". As in, the 3V blade may be severely chipped, dented, or rolled from accidental contact with the junk, whereas the S7 blade just needs a good resharpening. (and just to put things into perspective, in that same application many lesser steels and stainless would be utterly destroyed) I have stated many times that I don't even care about wear resistance on my big blades.

I've gotten into very confusing discussions before, because everyone had a different idea of "edge retention". We all meant "the ability to retain an edge", but some of us were talking about wear resistance, while others were talking about impact resistance.

And this is where the origional poster needs to evaluate his own use. If you do a lot of slicing on soft materials, the knife may not be worth it to you. However, I would just LOVE to have a big knife made of this steel, to try out. If you have ever actually broken knives during genuine hard use, this one will pay for itself many times over. (I didn't see the specs on the knife in question, but I'll give the benefit of the doubt to the maker that he knows what he's doing with this steel.)

...The standard test block is way larger than typical knife geometry. Toughness improves as size [of the stock] gets smaller. The phenomenon is also not continuous or linear with size and Charpy figures can be manipulated if the notch is not quite the standard or if the better option of fatigue notch is used. All in all I would not read all that much into the Charpy figures unless very specific test conditions are given and preferably the tests are done with a representative test piece size.

Though I understand what you're getting at, I hope that some of the newbies in question don't totally discount Charpy figures for this reason. Sure, the factory doesn't tell you how your knife will perform, but they're a good place to start when evaluating generalities of steel performance. For example, it would be completely illogical to look at the impact resistance figures for S5 and S30V, and then still choose S30V for a big chopping blade. (I suppose if you just wanted to nit-pick my post, you could say something about needing corrosion restistance, or whatever.) Just because they weren't testing a knife, doesn't make the tests worthless.

 

[Cliff Stamp]

I have stated many times that I don't even care about wear resistance on my big blades.

Pretty much, most of such blades tend to be sharpened from damage not wear. If you can get wear resistance, why not, but usually it comes with the cost of lower machinabiliy and thus for a dedicated large brush knife has little value and is often just detrimental.

-Cliff

 

[TLM]

Fracture toughness tests a different, though related, property, which is the resistance to crack propogation under a load whereas charpy tests a sudden impact

Sudden impact? What do you mean. Charpy tests the propagation of a crack under fairly high strain rates. Standard K1c test the same under quasi static load. The difference is just strain rate that can be varied if needed.

Its not quite that easy but not that difficult or different either. Most ways of knife use do not involve strain rates comparable to Charpy rates so fracture mechanics approach might actually be more relevant.

TLM

 

[the possum]

Though the two are often related, they don't have to be.
Some time ago, Kevin Cashen talked about this- he did a demonstration as part of a bladesmithing class to illustrate the difference. (if I'm not remembering this correctly, someone please correct me.)
He heat treated a big blade so that it easily passed the lauded 90 degree flex test. Then he chopped a pine 2x4 with it, and the edge chipped out badly.

I believe he was doing this partly in response to the popularity of the 90 degree flex test, being misrepresented as proof of a tough blade.

 

[Cliff Stamp]

Sudden impact?

Charpy tests have the sample hit with a hammer, and you measure how much kinetic energy was dissipated, fracture toughness tests have the sample bent to open up a crack and you measure how much load it takes to crack the sample.

On a basic level a load and impact are just strains of course, but they induce failures differently. Prying with a file takes a lot of effort to actually break it, but a sharp impact can shatter it with little effort. I have seen this happen to machetes in use.

Most ways of knife use do not involve strain rates comparable to Charpy rates ...

Batoning and heavy chopping, which tend to be primary uses for knives where that property is referenced. Fracture toughness would be more for prying. Relevant of course as are most material properties to various applications.

-Cliff