What slag inclusions look like

Z

ZebDeming

Well-Known Member
There seems to be alot of talk lately about "slag inclusions" or metal having a "grain" direction. In a comercial steel, this is probably unlikely. It is something else that someone is seeing, while I can't comment on what exactly it is, I can almost certainly guarantee that it isn't slag.
I work with alot of bloomery material that I make myself, THIS material may benifit from forging to shape over stock removal, as it definatly contains slag "stringers". I'm sure that this is where the myth that forging creates a better blade comes from, as the material certainly needs forge folding and working to get it to behave like a bar of steel. After about a year of working bloomery material, I find it very funny when people complain about stringers in their comercial steel, almost to the point that I feel that it's an insult to those of us who choose to work with the "old" material.
Simple fact, if you're working comercial steel that you feel has a problem, contact the supplier or steel mill, I'm sure that the "problem" will be fixed. If you really want to see what working a slagged up metal is like, build yourself a stack and get to work chopping charcoal and crushing and roasting ore, tis alot of work, but the steel is beautiful, and probably not as strong of a blade as you could make from some 1075.
Here's a pic of a blade forged from some bloom steel, you can see the little specks in it that are the slag, and it takes alot of work to get it this far.

blade.jpg

I've yet to see any pics from comercial steel that look like that :)
This post isn't a stab at anyone, just my opinion that what some people are seeing in their steel isn't slag, or an inclusion. I see the real thing every time I work bloomery material, some has more, some has less.

Zeb
 
Yes Zeb,
I would have to say that you are a glutton for punishment :biggrin: with the amount of True Slag etc you must deal with!

While I admire your devotion to the craft of beating out your blooms of steel. I am quite happy grinding away modern stainless steel with all of those terrible slag spots in it! LOL

Laurence

www.rhinoknives.com
 
So funny people talking about "slag inclusions" when they seem to only use modern steels Zeb, good on you to show them the real thing :D

nice blade!
 
Here’s what the “grain flow” looks like in a piece of modern steel. It's a little different than the "slag inclusions", (more refined etc.), in Zeb's pic, but still a good illustration of the grain direction in steel.

Click to enlarge:

http://upload.wikimedia.org/wikipedia/commons/5/5c/ForgedConrodShowingEtchedSection-s.jpg

Any “forgable” steel/iron/metal can benefit from forging. They even forge super alloys/"clean" steels in the aerospace industry for improved grain flow and refinement,… higher strength to weight ratio.
 
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What people are calling slag inclusions in modern steel is not imaginary, it is mislabeled alloy banding. I have a bar of 1075 in my shop as I speak that is full of it, and will show a nice grainy pattern if subjected to a lot of low-temperature cycling and then hardened and etched. It is alloying elements and impurities that segregated themselves along grain boundaries in the interior of the original ingot, and were extruded during the subsequent rolling process. It does have an effect on the behavior of the steel but not nearly as drastic as very high amounts of actual slag as pictured in the original post.

The mislabeling of this as slag inclusions is a bit misguided, but is not a total dislocation from reality, and I'm sure it isn't done with the intent of insulting anybody.

All that aside, I admire anyone who goes to the length of making their own bloomery steel and am a little envious of the ability to do it. I can imagine the amount of work that went into the example pictured.
 
The anisotropy or “directionality” of forged/rolled steel, can not be created, manipulated or changed (short of melting it) through thermal treatment alone,...

... it's the "nature" of the material.
 
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Justin King said:
What people are calling slag inclusions in modern steel is not imaginary, it is mislabeled alloy banding. I have a bar of 1075 in my shop as I speak that is full of it, and will show a nice grainy pattern if subjected to a lot of low-temperature cycling and then hardened and etched. It is alloying elements and impurities that segregated themselves along grain boundaries in the interior of the original ingot, and were extruded during the subsequent rolling process. It does have an effect on the behavior of the steel but not nearly as drastic as very high amounts of actual slag as pictured in the original post.

The mislabeling of this as slag inclusions is a bit misguided, but is not a total dislocation from reality, and I'm sure it isn't done with the intent of insulting anybody.

All that aside, I admire anyone who goes to the length of making their own bloomery steel and am a little envious of the ability to do it. I can imagine the amount of work that went into the example pictured.
Click to expand...

I agree 100% I'm not trying to say that there isn't something there, just trying to say that it isn't slag. The alloy banding, IIRC, can be made better or got rid of by proper thermal cycling? I would think that moving the carbide banding around by forging (similar to creating patterns in "wootz") would only be a band aid. Tai, barstock as delivered, IS forged already, and if a knife would "benifit" from forging it, I believe it's being used as an instrument other than a knife, remember we are making fine cutting instruments, not crankshafts. The end use of the material dictates the acceptable process to create it. I believe alot more tips of knives are broken because of improper forging and heat treat, than the anisotropy of steel. And also, there is no need to put slag inclusions in quotes, that IS what is in my pic.

Zeb
 
The alloy banding becomes more visible when the steel is cycled such that carbon precipitates to it to form carbides. The carbon can be made to move back where we want it with the right heat treatments, but most of the other alloying elements and impurities that cause the banding are pretty much stuck where they are. Once the carbon has moved to those areas to form large carbides in the banding, the issue becomes worse, both visually and in it's implications for the properties of the steel. Slow cooling from above critical temp. is usually the culprit when this occurs. This is one of the reasons that sub-critical annealing is desireable with highly alloyed steels.
 
There are a variety of deformable non metallic inclusions or stringers,... sulfides, oxides, silicates, nitrates, and phosphides. Inclusions bonded with oxygen are further broken down into free oxides, spinels and silicates. These are all associated with casting.

Slag is also a general term,... a byproduct of the smelting process. Fluxes etc., form slag in the smelting process.

It would be hard to say exactly what the chemical composition of a “stringer” is just by looking at it, but none of them are considered desirable in steel. They tend to have negative effects on the steel, which applies across the board, knives included. The smaller and fewer the inclusions the less of a problem they are.
 
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A few clarifications... I never used the word "slag" in reference to any of the illustrations I showed and I'm not suggesting in any way that stock reduction knives are inferior to forged knives in general, or vice versa. However, there are structural differences between the two that can play a role in performance.

There are lots of other variables to consider and it's how they all work together to create a superior knife. Inclusions are just part of the picture.

The alloy banding and large carbides are another matter, a different subject. I don't think they are being confused with inclusions here. They typically look different and are indicative of alloying and heat treating rather than forging/rolling. However, the alloy banding can be incorporated into the grain flow of the steel, become part of it and manipulated through forging like "damascus" steel.. Stringered Inclusions being confused with alloy banding is a weak argument,... bordering on desperate, but I'm sure it's been used before,.. not blaming anyone in particular for it or know for sure where it first came from.
 
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One said:
A few clarifications... I never used the word "slag" in reference to any of the illustrations I showed and I'm not suggesting in any way that stock reduction knives are inferior to forged knives in general, or vice versa. However, there are structural differences between the two that can play a role in performance.

There are lots of other variables to consider and it's how they all work together to create a superior knife. Inclusions are just part of the picture.

The alloy banding and large carbides are another matter, a different subject. I don't think they are being confused with inclusions here. They typically look different and are indicative of alloying and heat treating rather than forging/rolling. However, the alloy banding can be incorporated into the grain flow of the steel, become part of it and manipulated through forging like "damascus" steel.. Stringered Inclusions being confused with alloy banding is a weak argument,... bordering on desperate, but I'm sure it's been used before,.. not blaming anyone in particular for it or know for sure where it first came from.
Click to expand...

This entire thread is based on a disagreement and/or misunderstanding on a semantic level. Somewhat like your use of the terms "stock reduction" and "forged" to distinguish between different methods of blade production. "Stock removal" is the terminology I use to describe the shaping of a knife by grinding, because the term "removal" is quite self explanatory. "Stock reduction" is a term I associate with forging or rolling a piece of stock to decrease it's thickness, because that is the context in which I most often see it used.
Your use of terms in the above post makes it clear that we use different words to describe the same thing, which causes endless and rather pointless misunderstandings when highly technical subjects are discussed by people using less than precise terminology. Most of us are guilty of that at times.
 
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I agree 100% that semantics and terminology can muddy the waters. Valid points and opinions do often get misinterpreted and lost in the mud.
 
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