Huge Stringers

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I was forging on a big bowie from 1075 this morning and noticed some funny dark lines along the back. The steel came from a reputable supplier, and a very popular one with knifemakers. I’d go as far as to say 80% of the knife makers I know use this supplier and that’s being conservative. However, I’m not going to mention his name because that’s not the point. The point here is that no matter who the supplier is,... steel is steel. The notion that steel is homogenous, ideal and free from flaws and inclusions (in this case stringered inclusions), is just wrong. All steel has flaws and inclusions to some degree and should be treated as such. This is why keeping stresses to a minimum during heat treating is so important, and trying to push the steel to it’s absolute extreme theoretic limits, or to “squeeze every last drop of performance out of it” (or beyond) is never a good idea, unless the steel itself were ideal and perfect,… which it isn‘t. We never know for sure what those exacts limits are or exactly how many stress cycles and to what degree any given piece of steel can withstand. Although this is an extreme example, (they run the full length of the blade) this sort of thing is typical. The idea that these types of problems can be solved simply by switching suppliers or steel is just plain false. I’ve seen the same type of thing from numerous reputable suppliers and various types of steels.

It is along the back where it might not be a big problem, but I think it’s heading for the scrap pile anyway. Imagine something like this, or even much smaller, along the edge of a blade, where there is such a small amount of material supporting it, going un-noticed,… which would usually be the case.

I sanded it off to 150 grit and etched it in sodium bisulfate to make it more visible in the bare steel.

DSCN6805-001_zpsb10e7179.jpg
 
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I am curious to see what you are looking at but the picture is blurry to where it looks like shadows - which I am guessing is the issue.
 
Can you see the light and dark lines running parallel to the length of the blade (direction of the rolling) that also roughly conform to the dents from the forging?

It was hard to get a decent pic of...
 
Here's another one, not sure if it's any better. I had to hand hold the blade and try to catch the light just right. You can see the light and dark lines running the length of the blade though right?

... Oh well, I tried... guess you would have had to be there.

DSCN6790_zpsb07687c9.jpg
 
... stresses tend to cause the matrix to tear apart, rip away and separate from those types of inclusions. The steel fatigues faster and is weaker when those are present... which they usually are to some degree.

In the pix it almost looks like the steel is layered... layered with inclusions.

... It's not homogenous.
 
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Here’s a bit better pic of another one, or something similar, I posted a while back, on the edge of a 1095 Kiridashi…. From a different supplier. It ran back a few inches.

DSCN6167.jpg
 
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Because of things like this,… you can’t always expect or predict that the steel will respond, react, perform or appear “ideally”, or the way it is supposed to.

To understand this is as important as it is to understand the drawbacks and disadvantages of just about anything,… which is critical and directly pertinent to getting the most out of it and “optimization“… heat treating or otherwise.

You have to understand the problems, before you can deal with them or begin to solve them…
 
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I think what I'm going to do is see if I can grind them out on this one, and then just baby it along how I normally would with any steel...
 
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I see what you are talking about and understand your concerns and your statements about steel not being homogenous.
Please keep us updated on this project for our own edification.
Question: If I am afraid of steel that is not homogeneous does that make me a homophobe?:biggrin:
 
LOL

O.K.

A few side notes, these usually go un noticed and could be the source of problems attributed to aspects of heat treating, warping, cracking, odd hardness readings etc. They tend not to show up well unless etched. Ferric chloride doesn't show them very well, but the sodium bisulfate does. It tends to eat away at anything that isn't good solid metal, oxides, scale etc. I don't think I would have noticed the inclusion in the little kiridashi if I hadn't descaled it with the sodium bisulfate. I scrapped the Kiridashi because the inclusion was right at the edge. On the big blade I first noticed some darker lines in the surface oxides while forging.

These types of inclusions aren't as serious as fractures or large voids, but definitely something to be aware of. They weaken the steel perpendicular to the direction of the grain flow created by the rolling process… Proper forging, (refinement through reduction in stock thickness and improved grain flow) can help minimize the negative effects of these stringers.
 
There is an opportunity for education and good discussion here, but not of we are going to adhere to absolutes, opinion often consists of absolutes, reality rarely has use for them.

The notion that steel is homogenous, ideal and free from flaws and inclusions (in this case stringered inclusions), is just wrong.

No material is perfect but there are imperfections, and then there are fatal flaws, there is a whole gamut of conditions between perfection and useless. Thus the shortcomings of asolutes.

All steel has flaws and inclusions to some degree…
Agreed, but then comes the absolutes…
…and should be treated as such. This is why keeping stresses to a minimum during heat treating is so important, and trying to push the steel to it’s absolute extreme theoretic limits, or to “squeeze every last drop of performance out of it” (or beyond) is never a good idea, unless the steel itself were ideal and perfect,… which it isn‘t. We never know for sure what those exacts limits are or exactly how many stress cycles and to what degree any given piece of steel can withstand. Although this is an extreme example, (they run the full length of the blade) this sort of thing is typical.

Steel should be treated as steel, if there is a problem in it that the standard procedures cannot handle then those exceptions have to be dealt with on an individual basis, rather than lowering the bar and expectations across the board. That is how the rest of the metalworking world approaches it rather than expecting the worse and treating the most versatile material in the history of mankind with kid gloves. If this absolute held true we would have moved on from steel for a better material long ago, or perhaps stuck with the much more homogenous and predictable bronze.

If absolutes held true then all would share your experience and observations, and I for one have not. I have been squeezing and pushing my steel for most of my life now, and while I have observed many of the same inconsistencies, often microscopically, I have found them to be problematic very small percentage of the time. The vast majority of them can be easily navigated with consistent, standardized methods, and the knowledge necessary to troubleshoot them.

The idea that these types of problems can be solved simply by switching suppliers or steel is just plain false.

No, merely switching to a different batch or run of steel will normally do the trick.

Now, is the steel supply out there getting a bit lax in quality due to creeping trace elements and a wide array of manufacturing standards around the world? It sure is, and we do have to deal with it, so a constructive discussion on how to best do that would be a plus.:thumbup: But it would seem that you are trying to show somebody, or their position, as “wrong” or “false”, by characterizing the position with absolutes, what would traditionally be called a straw man or paper tiger argument, which will be more difficult to glean constructive input from.

If I am to expect the usual pattern this thread will probably soon veer into a crusade about quenchants or the merits of forging, which I see you have already touched on. If you want to have a chat about how to best deal with steel inconsistencies I think that would be a good thing, I have plenty of things I have picked up over the years that I could share in such a discussion, but if something or somebody has set off another episode, I think it would be best to address it or them one on one rather than disappoint all those who look forward to a good thread for objectively troubleshooting steel inconsistencies.
 
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Yes, there are ways to deal with many of the inconstancies, experience with different steels, equipment and procedures not being the least of them.

So, how can we deal with them? I've given a few examples of how I've dealt with them. One thing I haven't mentioned though is that certain steels do tend to be "cleaner" than others. From that standpoint, selecting a steel that suits your forming method, heat treating equipment etc. makes good sense. Cleaner steels would benefit less from forging and these sorts of inclusions would not be as much of a concern. On the other hand, 10xx series steels would probably not be the best choice for stock reduction knives. Conversely, many of the cleaner higher alloy steels, air hardening etc., often do not lend themselves well to the forging process, at least for your average blacksmith shop type set up. They tend to be "hot hard" and "red short" and this is not a big problem with simple steels.

As a general rule, I think minimizing stresses during heat treating also makes sense,… unless you have enough experience with a certain steel etc., to have a better idea of how much it can take. In that case, pushing or squeezing it a bit harder should be fine,... , but I’m not so sure if it would really be any better in the long run.

... good science should leave room for more than one opinion.
 
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… Anyhow, this morning I ground the spine back about 1/8 of an inch, which got rid of the vast majority of it. Lucky in this case I guess. It probably wouldn't have been a big problem along the spine, but did that just for good measure. I'm continuing with the forging and so far haven't noticed anything out of the ordinary.
 
Just wanted to say that this is an interesting discussion and I hope it will continue as long as there is something to be learned from it. I know you guys (One and KC) don't see eye to eye much of the time, and I'll not say that there's anything wrong with that, just that I hope it dosen't put a stop to these discussions before they run their useful course. Feelings run strong sometimes, for me at least, but steel dosen't take account of them so when they enter these discussions it is usually not for the better.
 
Just wanted to say that this is an interesting discussion and I hope it will continue as long as there is something to be learned from it. I know you guys (One and KC) don't see eye to eye much of the time, and I'll not say that there's anything wrong with that, just that I hope it dosen't put a stop to these discussions before they run their useful course. Feelings run strong sometimes, for me at least, but steel dosen't take account of them so when they enter these discussions it is usually not for the better.

Justin, as well as the standard civility policing, I feel my job here as moderator also includes seeing to it that the information you get is of reliable quality. Just as good science shouldn’t even deal with opinion or feelings but provide the most likely hypothesis, and eventually theory, based on the best available data, I want the information here to be easily separated from opinion. When it is hijacked by an agenda is when science does become the biased political tool that it is sometimes seen as. When I can’t have my information agenda free, I at least insist on having it easily separated from opinion, and that is the same courtesy that I am asking for you and the other visitors to this forum. And I feel that is part of my job here, a job that also benefits from separating feelings from it. Let some of my best buds post strong subjective feelings as absolute statements of fact and see if I perform my moderator obligations the same. I would.

To help with the discussion I will give some of my input and observations:

First there are points of agreement that are based on actual fact. No steel is perfect, the fact that every piece of steel has millions of defects in the atomic stacking is what allows us to forge it. On the atomic level is it riddled with vacancies, dislocations, and divergent stacking arrangements; grain boundaries themselves are deviations from a perfect crystalline lattice. On the macro level there are pipe, alloy segregations, slag inclusions etc… they are an inherent part of the material and we deal with them every day whether we know it or not. And this is on our end of the materials evolutionary path, the best it has ever been. The much touted steels of our ancestors were loaded with sulfur, phosphorus out of control deviations in carbon and inclusion levels that make our worst modern stock look pretty darn pure.

Consider this, if an alloy segregation line down the length of homogenous steel renders it so weak that we must walk on pins and needles while heat treating it, how totally useless is every damascus blade ever made? I have done extensive study in this area and after countless hours with damascus, from old swords to my own blades, under the microscope I can safely tell you that the steel pictured at the beginning of this thread is pretty homogenous in comparison. And yet I have found very little difference in most strength based properties, when it is done correctly.

Another point of agreement- forging will indeed help with segregation issues. But theories diverge on the exact cause and effect. I have found the hammer is a distraction from the real benefits of the multiple high temperature thermal cycles during the forging operation, which allow diffusion of the segregations. I base my theory on observations during testing which involved metallographically identifying the problem and then observing the same changes with several normalizing cycles alone. The mill reduced this steel stock from several feet to a fraction of an inch, our deformation is barely worth mention in comparison. But the mill limited the thermal treatments to the bare minimum, so we can easily exceed what they did with heat. You cannot drive alloy atoms through iron with a hammer, but with heat you can get them to simply move on their own.

As previously agreed, the steel supply is getting quirkier. One of the down sides to recycling is the amount of trace elements that are reintroduced to accumulate to levels that now approach alloying. This is probably a larger threat to proper heat treating than slag inclusions, which our ancestors dealt with wonderfully. With the allowable swing in numbers for each given alloy, it is really best to find a batch of steel that really works for you and buy as much of it as you can possibly afford. Getting your steels in small amounts at a time will have you constantly adjusting your heat treatment to match the newest unforeseen chemistry that gets thrown at you. This is not new and the bulk purchasing is how industry has also traditionally dealt with it, but with the looming threat of many simpler steels simply being “phased out” the idea of stockpiling a lifetime supply of good stuff becomes better all the time.

I hope some of this helps and that I have affectively provided input, based on my observations of the data, that can easily be separated from any of my personal feelings that may have crept in with it.
 
Stringers are non metallic inclusions (of various types) classified together according to their morphology. During the forging and/or rolling process (rolling is a type of forging), the stringers get broken up into smaller parts and elongated or “strung out” in the direction of the forging. This is a type of steel refinement and directly relates to steel quality. The higher the degree of this type of refinement the better. It responds better to heat treating it has a higher strength to weight ratio (compared to less refined steel of the same type) and is more predictable.

The benefits of forging are proportionate to the size of the stock. It is true that the rolling process has refined the steel to a point and done the hardest part. However, forging to shape takes these principals a step further. In other words, if we start with a 1/4 inch thick piece of rolled steel and forge the edge down to 1/16 of an inch, we have essentially quadrupled the degree of refinement that we started with, along the edge where it is the most important. It's similar to how the layer count goes up on folded Damascus or pattern welded steel. It takes a lot of folding and drawing to get it up to 500 layers,… but just one more to get to 1000.

These are well established metallurgical principals. However, there is a lot more to say and learn about it all, but it can’t all be explained from every angle in just a few paragraphs. I’m just trying to touch on the basic ideas, raise a few questions and get people to think. It has all been very well studied/documented, is easily verifiable and a topic well worth personal investigation.

Forging is not the only way to help deal with some of these issues or necessarily the best, but it does deserve to be mentioned and understood.
 
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Yes, but this is the heat treating forum, your initial post, despite its issues, was at least on topic for the venue. I will entertain the drift only enough to point out that you omitted the glaring discrepancy in the apples/oranges damascus comparison that one also doubles the thickness with every fold before reduction. But we really need to decide if this is a heat treating thread or a forging thread, for I would be happy to move it to the forging forum where it can get the best play without undo confusion.
 
I think it's all "related" to heat treating and can have an influence on heat treating, but enough on the forging aspect.

They can study more on it themselves if they are interested.
 
... maybe think of it more as the influence of steel quality on heat treating and ways of coping with the inconsistencies and questionable degrees of quality.

... in order to insure that our blades are consistently at least within acceptable standards.
 
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