F.F. D2 better than INFI?

morrowj_98 said:
I beg to differ sir......there is some. The same article I referenced earlier and the preceding article in Blade have data you are referring to. I would gladly scan and post the articles if they would be of interest.
Click to expand...

Cool, go ahead and post the tonage that the forging process uses.. I would definitely like to see that.
thanks:thumbup:
 
Cobalt said:
Cool, go ahead and post the tonage that the forging process uses.. I would definitely like to see that.
thanks:thumbup:
Click to expand...


I don't remember seeing anything about force used during the process as this would be part of the manufacturers process and not a lot of info was provided understandably.

What I did see was info that applied to your original post which was this

Cobalt said:
it has yet to be proven whether FF is actually that good. It can cut, but there is no data on edge toughness yet compared to other similar edge profile D2 knives. I won't put my money on the FF bank until I see more conclussive testing.
Click to expand...

I'll scan the articles and get them posted.
 
The down pressure on the shoulder of the CBN stirring tool is 8,000-10,000 lbs.

The DiamondBlade FF process qualifies as forging because it is a solid state process. (Under the melting temperature.) You might call it twist forging because of the way the probe whips it at 300+ rpm. To the best of my knowledge steel has never been whipped, blended and stirred before without melting it. Granted, the process is hard to understand. A whole new chapter is being written to explain the metallurgy of the finished product and how it gets there.

Wayne G
 
Wayne G. said:
The down pressure on the shoulder of the CBN stirring tool is 8,000-10,000 lbs.

The DiamondBlade FF process qualifies as forging because it is a solid state process. (Under the melting temperature.) You might call it twist forging because of the way the probe whips it at 300+ rpm. To the best of my knowledge steel has never been whipped, blended and stirred before without melting it. Granted, the process is hard to understand. A whole new chapter is being written to explain the metallurgy of the finished product and how it gets there.

Wayne G
Click to expand...

Wayne, that makes sense, even though 4-5 tons is not any where near what many presses can do these days (600 to 3000 ton and more) it is by definition a forging because it does not ever get molten even though the metal can be stirred. Yes it is a hard process to grasp. :D

So, Let's assume for a minute that this process imparts localized mechanical properties similar to a 3000 ton forging of the same metal. How is the remainder of the blade stress relieved to prevent internal stresses due from a high hardness local forged area to a softened non-forged area. Without some sort of annealing cycle on the blade. there will be internal stresses induced in the blade. This may not matter in a small hunter size blade, but it would be a big problem on a wide and long bowie style knife.
 
Cobalt said:
Wayne, that makes sense, even though 4-5 tons is not any where near what many presses can do these days (600 to 3000 ton and more) it is by definition a forging because it does not ever get molten even though the metal can be stirred. Yes it is a hard process to grasp. :D

So, Let's assume for a minute that this process imparts localized mechanical properties similar to a 3000 ton forging of the same metal. How is the remainder of the blade stress relieved to prevent internal stresses due from a high hardness local forged area to a softened non-forged area. Without some sort of annealing cycle on the blade. there will be internal stresses induced in the blade. This may not matter in a small hunter size blade, but it would be a big problem on a wide and long bowie style knife.
Click to expand...

Interesting thoughts...

What really matters to first order is the local pressure -- the downward force per unit area. I wonder if it, alone, is sufficient to reduce the metal to a liquid phase?

Then there is the high speed rotary motion and the linear motion of the tool across the surface. Both of these actions impart extra free energy to the metal and probably drive some unusual physical processes. Perhaps these processes serve to reduce local stress -- they might also create a thin zone of high stress material, perhaps in the region between previously liquified metal and metal that remained in the solid phase?

All very interesting. It would be good to see some SEMs of suitable cross-sections of the blade edge.
 
OldPhysics said:
Interesting thoughts...

What really matters to first order is the local pressure -- the downward force per unit area. I wonder if it, alone, is sufficient to reduce the metal to a liquid phase?

Then there is the high speed rotary motion and the linear motion of the tool across the surface. Both of these actions impart extra free energy to the metal and probably drive some unusual physical processes. Perhaps these processes serve to reduce local stress -- they might also create a thin zone of high stress material, perhaps in the region between previously liquified metal and metal that remained in the solid phase?

All very interesting. It would be good to see some SEMs of suitable cross-sections of the blade edge.
Click to expand...

but remember, they state that the metal never reaches liquid phase, otherwise it would not be a forging at all. With the exception of the circulating motion, this process seems to me would impart propertis similar to hot rolled stock, which in itself can be called forging by the solid state definition. The difference is that with hot rolled stock there is no differential Rc and the metal is HT'd with annealing afterwards.
 
OldPhysics said:
Interesting thoughts...

What really matters to first order is the local pressure -- the downward force per unit area. I wonder if it, alone, is sufficient to reduce the metal to a liquid phase?

Then there is the high speed rotary motion and the linear motion of the tool across the surface. Both of these actions impart extra free energy to the metal and probably drive some unusual physical processes. Perhaps these processes serve to reduce local stress -- they might also create a thin zone of high stress material, perhaps in the region between previously liquified metal and metal that remained in the solid phase?

All very interesting. It would be good to see some SEMs of suitable cross-sections of the blade edge.
Click to expand...

I've been watching this thread for the last week. I did not want to comment because I am just the technical geek, but since there are some technical questions... I will chime in a bit.

OldPhysics, you are exactly correct. It is the force per unit area that is important. The tonnage of the press has no implications on what the local forging pressure is. The forging forces we apply in FF are in the range of 8,000-10,000 lbf (thanks for the input Wayne). We have actually applied forces as high as 16,000lbf, but there was no noticeable benefit. The forces in FF are applied to an area of heated metal that is less than 0.25 sq. in.

There is no melting associated with the FF process. The temperatures reached during the FF process are between 1,000-1,200C. I don't have the melting temperature of D2 off the top of my head, but iron melts at 1,523C.

I like the comparison of FF with hot rolling. Both impart a great deal of strain (or deformation, upset) at an elevated temperature. That's about the extent of the similarity. FF induces much higher strain and strain rate. In addition, the FF microstructure is quenched very rapidly as a result of lots of cold metal surrounding and very small volume of heated metal.

The combination of pressure, temperature, and much higher strain rates than traditional forging create dynamic recrystallization (i.e. multiple recrystallizations occurring) during the process. This is what creates the extreme refinement of grain size.

Residual stresses: yes. This process produce some residual stress. However, the recrystallization process helps to reduce these residual stresses. We have seen no problems with residual stress YET. I am sure we will eventually run into some issues. If so, we can apply a stress relief.

As for other steels: FF will refine the grain size, and/or break up carbides of any steel. There is some work required in finding the right processing conditions.

Hope this provides some insight. Please don't hesitate to ask if you want more clarification or have other questions.

Tracy
 
tnelson said:
I've been watching this thread for the last week. I did not want to comment because I am just the technical geek, but since there are some technical questions... I will chime in a bit.

OldPhysics, you are exactly correct. It is the force per unit area that is important. The tonnage of the press has no implications on what the local forging pressure is. The forging forces we apply in FF are in the range of 8,000-10,000 lbf (thanks for the input Wayne). We have actually applied forces as high as 16,000lbf, but there was no noticeable benefit. The forces in FF are applied to an area of heated metal that is less than 0.25 sq. in.

There is no melting associated with the FF process. The temperatures reached during the FF process are between 1,000-1,200C. I don't have the melting temperature of D2 off the top of my head, but iron melts at 1,523C.

I like the comparison of FF with hot rolling. Both impart a great deal of strain (or deformation, upset) at an elevated temperature. That's about the extent of the similarity. FF induces much higher strain and strain rate. In addition, the FF microstructure is quenched very rapidly as a result of lots of cold metal surrounding and very small volume of heated metal.

The combination of pressure, temperature, and much higher strain rates than traditional forging create dynamic recrystallization (i.e. multiple recrystallizations occurring) during the process. This is what creates the extreme refinement of grain size.

Residual stresses: yes. This process produce some residual stress. However, the recrystallization process helps to reduce these residual stresses. We have seen no problems with residual stress YET. I am sure we will eventually run into some issues. If so, we can apply a stress relief.

As for other steels: FF will refine the grain size, and/or break up carbides of any steel. There is some work required in finding the right processing conditions.

Hope this provides some insight. Please don't hesitate to ask if you want more clarification or have other questions.

Tracy
Click to expand...

trace, thank you very much for the very informative post. Since it isn't possible to know all of the internal residual stresses with in treated stock, why not perform annealing cycles to prevent the occurance to begin with. Will annealing cycles reduce the qualities that FF imparts?
 
Cobalt said:
trace, thank you very much for the very informative post. Since it isn't possible to know all of the internal residual stresses with in treated stock, why not perform annealing cycles to prevent the occurance to begin with. Will annealing cycles reduce the qualities that FF imparts?
Click to expand...

Cobalt,

Time and effort. With any new material processing technique, there is a lot of research to be done. Most of our initial research was focused on performance, i.e. what was there and how good is it.

Annealing will not hurt the quality. I have done some preliminary heat treating work and have observed some good results. Just nothing implemented yet.

The initial tests we performed on the FF blades was chopping tests. We made a geometry more suitable for heavy duty work and chopped on desert iron wood, moose antler, moose bone, the finally a brick and a steel anvil. No chips, cracks or edge rolling were observed until we struck the brick. When we struck the brick, we observed a couple of extremely fine chips in the blade. Same occurred with the steel anvil. Based on these results and our bending test results, we were confident that stress relieving was not essential.

Tracy
 
morrow, thanks for the scans. They are just barely readable on my 19" screen. It looks like they got reduced to 260 x 570 in Photobucket.
 
resinguy said:
morrow, thanks for the scans. They are just barely readable on my 19" screen. It looks like they got reduced to 260 x 570 in Photobucket.
Click to expand...

I'm looking at them on a 19'' as well. You should be able to click on the image to enlarge it.
 
tnelson said:
I've been watching this thread for the last week. I did not want to comment because I am just the technical geek, but since there are some technical questions... I will chime in a bit.

OldPhysics, you are exactly correct. It is the force per unit area that is important. The tonnage of the press has no implications on what the local forging pressure is. The forging forces we apply in FF are in the range of 8,000-10,000 lbf (thanks for the input Wayne). We have actually applied forces as high as 16,000lbf, but there was no noticeable benefit. The forces in FF are applied to an area of heated metal that is less than 0.25 sq. in.

There is no melting associated with the FF process. The temperatures reached during the FF process are between 1,000-1,200C. I don't have the melting temperature of D2 off the top of my head, but iron melts at 1,523C.

I like the comparison of FF with hot rolling. Both impart a great deal of strain (or deformation, upset) at an elevated temperature. That's about the extent of the similarity. FF induces much higher strain and strain rate. In addition, the FF microstructure is quenched very rapidly as a result of lots of cold metal surrounding and very small volume of heated metal.

The combination of pressure, temperature, and much higher strain rates than traditional forging create dynamic recrystallization (i.e. multiple recrystallizations occurring) during the process. This is what creates the extreme refinement of grain size.

Residual stresses: yes. This process produce some residual stress. However, the recrystallization process helps to reduce these residual stresses. We have seen no problems with residual stress YET. I am sure we will eventually run into some issues. If so, we can apply a stress relief.

As for other steels: FF will refine the grain size, and/or break up carbides of any steel. There is some work required in finding the right processing conditions.

Hope this provides some insight. Please don't hesitate to ask if you want more clarification or have other questions.

Tracy
Click to expand...


Tracy,
now that I have had some time after work to digest your comments let me ask some more and make comments.

It seems to me that the reason the forces you apply have no need to be greater is because there is still an open area for the squeezed metal to go if you put more pressure on it. When a real forge makes a part, it hammers it in a rough mold and there is no where for the metal to go so it must compact, hence the 3000 ton press is quite a bit more effective than a 4 ton press at compacting the crystaline structure of the steel being forged.


FF induces much higher strain and strain rate. In addition, the FF microstructure is quenched very rapidly as a result of lots of cold metal surrounding and very small volume of heated metal.

Ok, the rapid quenching of this differentially heated metal seems to me to be part of a possible problem. The internal residual stresses have to be there if you have not performed any stress relief, ie. tempering cycles. It seems to me that a fast quench will give a very hard edge, but there is a possibility of crack propagation along the hardness transition zone.

however, based on your test stress relief is not necessary so somehow you have solved it without really having to solve it.
 
Cobalt said:
Tracy,
now that I have had some time after work to digest your comments let me ask some more and make comments.

It seems to me that the reason the forces you apply have no need to be greater is because there is still an open area for the squeezed metal to go if you put more pressure on it. When a real forge makes a part, it hammers it in a rough mold and there is no where for the metal to go so it must compact, hence the 3000 ton press is quite a bit more effective than a 4 ton press at compacting the crystaline structure of the steel being forged.


FF induces much higher strain and strain rate. In addition, the FF microstructure is quenched very rapidly as a result of lots of cold metal surrounding and very small volume of heated metal.

Ok, the rapid quenching of this differentially heated metal seems to me to be part of a possible problem. The internal residual stresses have to be there if you have not performed any stress relief, ie. tempering cycles. It seems to me that a fast quench will give a very hard edge, but there is a possibility of crack propagation along the hardness transition zone.

however, based on your test stress relief is not necessary so somehow you have solved it without really having to solve it.
Click to expand...

Still want to see some SEMs of a carefully prepared cross-section.

I suspect a lot of the free energy goes into creating the greatly increased surface area of these smaller grains. If this were a II-VI or III-V compound we might use electro or photo luminescence to investigate grain quality and crystal structure plus perhaps X-ray crystallography to investigate possible orientation of the grains. Not sure how one would go about this with an iron-based compound -- my training and experience is mostly with semiconductors, semi-metals, and insulators.

Still, with so much free energy readily available, I think there must be some high-stress zones. They might be sequestered and they might be pretty thin. If something like this has occurred, we might not notice any macro-mechanical consequences -- and Cobalt's perplexity might have a fairly straightforward answer. Finally, I think Cobalt's observation that the metal is free to flow locally could mean that the high-stress regions on the edge side could have literally been 'pressed' out of existence (you can see these behaviors in polarization microscopy of dynamic systems -- literally watch phase boundaries move and be driven off of an edge). [We must also remember that this process would appear to be non-equilibrium -- many odd, non-intuitive things can happen when non-equilibrium processes are applied to solids.]

I remember that a number of the HIPped semiconductors (Hot Isostatically Pressed) exhibited greatly enhanced grain purity (essentially high quality single crystal grains) with a strong tendency toward a common grain orientation and a common polytype. However, the grains GREW during the HIP process, since insufficient pressure was applied to prevent this. I wonder if some of the lessons learned in the days of HIPping might be of interest to you. Just do some lit searches -- Raytheon did a fair amount of that in the 80s, I think.
 
OldPhysics said:
and Cobalt's perplexity might have a fairly straightforward answer. Finally, I think Cobalt's observation that the metal is free to flow locally could mean that the high-stress regions on the edge side could have literally been 'pressed' out of existence (). .
Click to expand...

This is true in hot rolling, but remember, that is not what FF is doing here. It is only stirring not flowing out, like in hot rolling.
 
Cobalt said:
This is true in hot rolling, but remember, that is not what FF is doing here. It is only stirring not flowing out, like in hot rolling.
Click to expand...

Frankly, you're probably right.

I'm really just grasping at straws here, wondering what's going on -- without any data. Which, as Sherlock Holmes reminds us, is a 'capital error.'
 
All right, I am going to try and answer your questions without writing a paper here. These are good questions and I will try to enlighten. Please bear with me.

With respect to the forging force, I am going to try a different approach. I am going to try and make a parallelism to the FF process. Lets take a sheet of D2, say 1' X 1'. Now lets rapidly heat a area of 0.25 square inch in the middle of the plate to 1100C. The surrounding metal is only heated by conduction away from the region I am applying heat too.

Once at temperature, lets place a 6 inch diameter WC ball centered on the heated area and press. While applying force I am going to rotate the WC ball. On the surface of the WC ball, I have place a spiral threaded feature. When rotated, this spiral feature acts to draw the metal at the surface of the plate toward the center of the heated area. This action keeps the hot metal contained under the ball while applying force and rotation.

The WC ball and the surrounding cold metal completely contain the hot forged zone. I can keep applying force, but it does little good as it is unnecessary work.

The only major difference between what I described above and the FF process is that I have a small protruding pin on the tool. The pin enable me to process the material to a desired depth. As it rotated under pressure, this pin creates a very small channel around it through which the hot metal is channeled. As the tool traverses the desired process location, the hot metal is forced through this channel very rapidly, i.e. high strain and strain rate. Once through, it rapidly exits the tool and is quenched by the surrounding D2 and anvil below.

Now lets explore a traditional forging process. In open die forging, the entire structure is heated to temperature. Once at temperature, force is applied via a large anvil/hammer. As force is applied, the metal compresses directly under the anvil while simultaneously expanding in a perpendicular direction as it is not constrained (open die). Force remains fairly constant during a given stroke as there is no constraint.

Open die forging is typically used for small volume parts or roughing large structures. The largest forged components I have worked with were 210 ton rotor forgings forged on a 1,000,000 tons press. It was VERY cool (hot?).

Now lets look at closed die forging. There is a die (or sometime a series of dies for complex high aspect ratio parts) into which the metal is pressed into. As the part deforms, it begins to fill the die which. As this occurs, surface area and friction between the die/metal increase rapidly. As a result, forging forces increase rapidly. Depending on the part geometry, final forging pressure can be extremely high. Not because they want to apply high forging force, but because it is required to fill the die.

Higher forging force does not produce finer grain size. Higher forging forces are necessary for larger parts. Even high forces are required in closed die forging to fill the die of smaller parts. Higher forging forces are undesirable because of economics.

Finer grain size is associated with the amount of strain and the strain rate rather than forging pressure. Likewise, temperature and recrystallization play and important roll in grain size.

That was longer than I had hoped. Sorry.

Now for the residual stresses. YES, this process produces residual stresses. Any process which applies deformation to a metal produces residual stresses. There are two things that help us in FF to reduce these stresses.
1. Recrystallization during deformation reduces residual stresses. Hot worked (hot rolled) steel that undergoes recrystallization during rolling has much lower residual stresses than a CW steel that is just annealed. During the FF process, the metal undergoes recrystallization at least once, if not multiple times. I am not implying that the stresses in FF are eliminated by recrystallization, just reduced.
2. The highest residual stresses are typically at the surfaces, e.g. within a couple hundred micrometers of the top and bottom. Both of these regions are machined off during the manufacturing of the finished FF blades.

OldPhysics,

We see no preferred orientation. It is likely that we produce a preferred orientation (texture) in the austenitic temperature range during FF. However, this texture would be eliminated by the continuous dynamic recrystallization during FF. We do see some recrystallization textures in the as processed microstructure, but these are very week.

WOW, that was long.

Tracy
 
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