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Satrang and CPM question
- Thread starter Cobalt
- Start date
Cobalt
Platinum Member
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- Dec 23, 1998
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- 17,894
So my questions are as follows:
How large is each container used to heat and pressurize the powder?
If the large containers are heated you have no way of knowing that the bond in the inner most section of the container has fused and bonded equally to the outer regions?
Does crucible make std formula steels the same way to compare to rolled steel? Say like ATS34 done by CPM versus ATS34 done the std way? Apples to appples comparison?
How do you determine at what point the bond is equivalent to smelted steel bonds?
I am obviously no authority on CPM steels or any other steel, but these are just my observations over years of use and being around steel. I'd like to get some answers. I have had 440V, 420V, S30V and 3V, fail me, all by different manufacturers, which leads me to believe that it was not the maker of the knife. The heat treaters were different in a few cases, but one is well known and I believe it was done right, so this takes me back to my original idea that the bond at the 200 micron level (I am assuming powder particle size here) is weak.
How large is each container used to heat and pressurize the powder?
If the large containers are heated you have no way of knowing that the bond in the inner most section of the container has fused and bonded equally to the outer regions?
Does crucible make std formula steels the same way to compare to rolled steel? Say like ATS34 done by CPM versus ATS34 done the std way? Apples to appples comparison?
How do you determine at what point the bond is equivalent to smelted steel bonds?
I am obviously no authority on CPM steels or any other steel, but these are just my observations over years of use and being around steel. I'd like to get some answers. I have had 440V, 420V, S30V and 3V, fail me, all by different manufacturers, which leads me to believe that it was not the maker of the knife. The heat treaters were different in a few cases, but one is well known and I believe it was done right, so this takes me back to my original idea that the bond at the 200 micron level (I am assuming powder particle size here) is weak.
Here is some primary resource you can look into yourself, from Madeleine Durand-Charre's La microstruture des acies et des fontes (Microstructure of Steels and Cast Irons) originally published in 2003 in French and translated by James H Davidson:
http://files.filehosting.org/cs10.pdf
or if that fails,
http://www.filecoast.com/?pg=file&c1=2309621876&c2=V96gVmr5
"Sintering essentially involves two operations, which can be performed either separately or
simultaneously, depending on the case concerned. The first step is to agglomerate the
powders to a "green" compact, with sufficient strength to allow subsequent handling. The
powders are mixed with a wax-type binder, later eliminated by heating, and hot or cold
pressed in a mould to obtain a shape close to the final component geometry. The second
step is hot consolidation of the green compact to allow diffusion bonding between the
powder particles, leading to an increase in strength and density. The two steps are
performed simultaneously when the powders are hot compacted under high pressure. A
more sophisticated technique is hot isostatic pressing (HIP), in which the powders are
placed in a sealed container which is exposed to a gas pressure of the order of 100 MPa in
a high temperature autoclave. The container deforms as the powder contracts, making it
possible to achieve 100 % theoretical density."
...
"The principal characteristic of a powder is that it consists of small particles with a high
surface area to volume ratio, and therefore a large total surface energy. At sufficiently high
temperatures, the system will tend to reduce this surface energy by welding together of the
individual particles. This provides the major driving force for sintering."
...
"A typical average particle size is about 80 um."
http://files.filehosting.org/cs10.pdf
or if that fails,
http://www.filecoast.com/?pg=file&c1=2309621876&c2=V96gVmr5
"Sintering essentially involves two operations, which can be performed either separately or
simultaneously, depending on the case concerned. The first step is to agglomerate the
powders to a "green" compact, with sufficient strength to allow subsequent handling. The
powders are mixed with a wax-type binder, later eliminated by heating, and hot or cold
pressed in a mould to obtain a shape close to the final component geometry. The second
step is hot consolidation of the green compact to allow diffusion bonding between the
powder particles, leading to an increase in strength and density. The two steps are
performed simultaneously when the powders are hot compacted under high pressure. A
more sophisticated technique is hot isostatic pressing (HIP), in which the powders are
placed in a sealed container which is exposed to a gas pressure of the order of 100 MPa in
a high temperature autoclave. The container deforms as the powder contracts, making it
possible to achieve 100 % theoretical density."
...
"The principal characteristic of a powder is that it consists of small particles with a high
surface area to volume ratio, and therefore a large total surface energy. At sufficiently high
temperatures, the system will tend to reduce this surface energy by welding together of the
individual particles. This provides the major driving force for sintering."
...
"A typical average particle size is about 80 um."
Cobalt
Platinum Member
- Joined
- Dec 23, 1998
- Messages
- 17,894
that still does not proove that a sintered bond is going to equal a smelted bond. And the performance from what I have seen does not show it either. I'd like to see some comparisons by independent steel testers showing how the same formula the CPM way showed a marked improvement over the std.
The reason I say this is becuase the steel formulas CPM uses are much better than average, so the steel should perform better. 440V would cut like crazy and hold an edge frever, even though it would take forever to resharpen it. However, where is a CPM version of ATS34 and how does it fare against hitachi ats34, lets say or 154cm. This is where it would get interesting.
The reason I say this is becuase the steel formulas CPM uses are much better than average, so the steel should perform better. 440V would cut like crazy and hold an edge frever, even though it would take forever to resharpen it. However, where is a CPM version of ATS34 and how does it fare against hitachi ats34, lets say or 154cm. This is where it would get interesting.
I just remembered I saw this from the Crucible site, from ASM, Hot Isostatic Pressing of Metal Powders:
http://filecoast.com/?pg=file&c1=2309661644&c2=VBDtJcT6
Page 13 and 14 gives you an idea of the ingot size possible.
http://filecoast.com/?pg=file&c1=2309661644&c2=VBDtJcT6
Page 13 and 14 gives you an idea of the ingot size possible.
Cliff Stamp
BANNED
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- Oct 5, 1998
- Messages
- 17,562
Cobalt said:
Powder metallurgy isn't new, and is *NOT* unique to Crucible, in general I don't think I have ever seen a reference which showed powder steels are inferior to ingot steels aside from cost. I have seen lots of problems with CPM steels as well but this is simply because they are in generally really high alloy and used for knives not suitable for the steel. Better is a hard work to apply to a steel, is the Ratweiler is a better knife than a Temperance - better for what?
Much of the misinformation about powder steels comes from the idea that the powder process alone is critical like all powder steels are finer/tougher than all ingot steels. RWL34 for example is a powder steel but the primary carbides are *far* greater in size than AEB-L which is an ingot steel, so RWL34 is more coarse and segregated, not less. The properties come from the manufacturing process and the alloy and the heat treatment. Note Landes work for example where he critizes powder steels like S60V as they are too coarse for knives and give low edge retention and praises ingot steels like 440A. Now how would Crucible respond to a question of which is the "superior" knife steel.
Phil Wilson is working with CPM-154CM and has worked with 154CM. He isn't a "tactical" style maker though so most his perspective will be on its use as a cutting steel not on a prybar/chopper. He has made some comments recently and hopefully will have an update to share soon. He tends to be fairly frank and non-promotional about steels, open to what they do well as well as what they don't. R. J. Martin is also pretty level as well, unfortunately he isn't that active, he is email responsive though.
-Cliff
Cobalt,
Let's start at the basics of PM and go from there. All PM starts the same way as an ingot casting process. A melt is generated in an arc furnace to get you the basic molten starting material. Chemistry is also deternined at this stage. (This is stage 1). Stage 2 for some makers is to transfer this melt to a ladle for further refining of the metal (cleanliness). Stage 3 or stage 2 depending on the maker is to pour the melt into the atomizer. The atomizer is just high pressure gas nozzles which break up the melt into very small droplets. Imagine putting your thumb over a garden hose type effect.
The droplets fall and solidify and there is your basic starting material for PM.
Each droplet is essentially a microscopic ingot.
Digest this a little, ask any questions up to this point and we'll go on from here.
Let's start at the basics of PM and go from there. All PM starts the same way as an ingot casting process. A melt is generated in an arc furnace to get you the basic molten starting material. Chemistry is also deternined at this stage. (This is stage 1). Stage 2 for some makers is to transfer this melt to a ladle for further refining of the metal (cleanliness). Stage 3 or stage 2 depending on the maker is to pour the melt into the atomizer. The atomizer is just high pressure gas nozzles which break up the melt into very small droplets. Imagine putting your thumb over a garden hose type effect.
The droplets fall and solidify and there is your basic starting material for PM.
Each droplet is essentially a microscopic ingot.
Digest this a little, ask any questions up to this point and we'll go on from here.
Cobalt
Platinum Member
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- Dec 23, 1998
- Messages
- 17,894
Satrang said:
Thanks, this is all the part I already knew. Now from there when the powder is made into a casting, that is what I am interested in. I just read a link from RJ MArtin that shows a 52 inch diameter container, using say S3V and S30V, what is the temp and press used to make the powder bond into a metal format. and how do you know that this happened when the lad unit is only 7.5 inches in diameter?
The major thing to remember about the powder vs the ingots is that the carbide size of the powder particles is much smaller than the large poured ingots. This is the basis of the process. The trick is to get the powder into a usable form. This is done by putting the powder into a container. The container is made from carbon or stainless steel. When shaken the powder denisty falls between 65 and 80 percent dense. Air is purged from the container and it is welded shut to seal it.
At this point it is put into a Hot Isostatic Press (HIP unit). These are large autoclaves that are used for things other than PM production but the steel manufacturers use them directly to consolidate the containers. The containers are heated either externally from the HIP unit or heated up within the HIP unit. The choice is up to the manufacturer or the type of HIP unit.
The temperatures used are between 2000 F to 2300F depending on the alloy. You don't want to melt the alloy. The pressure is raised to 25 -50 tons per square inch of pressure. This essentially forge welds the powder particles together with air pressure. The container will then be removed and will be 100% dense at this point. The difference between HIPing and sintering is that sintering does not have the massive pressure to densify the particles. After the container is removed it is now an ingot that will be forged and rolled to whatever size is needed. The forging and rolling after HIPing imparts some additional toughness in the materials. Contrary to what is typically seen, PM steels do have grain flow. The homogenous carbide distribution hides this fact. Even PM steels will be tougher in the rolling direction vs across the grain. As a side note, HIP units are used to densify castings, ingots, and to apply claddings of powder to other materials. Quite a versitile technology if you get the chance to look at it more closely.
At this point it is put into a Hot Isostatic Press (HIP unit). These are large autoclaves that are used for things other than PM production but the steel manufacturers use them directly to consolidate the containers. The containers are heated either externally from the HIP unit or heated up within the HIP unit. The choice is up to the manufacturer or the type of HIP unit.
The temperatures used are between 2000 F to 2300F depending on the alloy. You don't want to melt the alloy. The pressure is raised to 25 -50 tons per square inch of pressure. This essentially forge welds the powder particles together with air pressure. The container will then be removed and will be 100% dense at this point. The difference between HIPing and sintering is that sintering does not have the massive pressure to densify the particles. After the container is removed it is now an ingot that will be forged and rolled to whatever size is needed. The forging and rolling after HIPing imparts some additional toughness in the materials. Contrary to what is typically seen, PM steels do have grain flow. The homogenous carbide distribution hides this fact. Even PM steels will be tougher in the rolling direction vs across the grain. As a side note, HIP units are used to densify castings, ingots, and to apply claddings of powder to other materials. Quite a versitile technology if you get the chance to look at it more closely.
Cobalt
Platinum Member
- Joined
- Dec 23, 1998
- Messages
- 17,894
Satrang, thanks for the explanation. That was quite clear. Now for my question.
Are you saying that powder particles can be made smaller than the ingot or the actual metal in it's molten state?
The other comment/question is that the forge welding of the powder particles can be no where near as strong as the molten bond of the liquid molten metal particles. This is a known fact. Does the fact that the microconstituents are mixed better throughout CPM steel make up for the weaker bonds?
So in other words is the homogenous nture of CPM's 154CM make for a better steel than ATS34, which has stronger molecular bonding? I know you will say yes, but have steels shaped into knife blades been compared? I have not seen this. Charpy tells you what a rectangular profile will test out like, but grinding down a knife to an edge can lay hell with the molecular structure of a steel.
Satrang thanks for your patience in this.
Are you saying that powder particles can be made smaller than the ingot or the actual metal in it's molten state?
The other comment/question is that the forge welding of the powder particles can be no where near as strong as the molten bond of the liquid molten metal particles. This is a known fact. Does the fact that the microconstituents are mixed better throughout CPM steel make up for the weaker bonds?
So in other words is the homogenous nture of CPM's 154CM make for a better steel than ATS34, which has stronger molecular bonding? I know you will say yes, but have steels shaped into knife blades been compared? I have not seen this. Charpy tells you what a rectangular profile will test out like, but grinding down a knife to an edge can lay hell with the molecular structure of a steel.
Satrang thanks for your patience in this.
There really is no separate metallic particles in the larger ingots. There are crystal structures (grains) but they change as the material is hot worked down from the large ingots. The powder particles also have that same crystal structure, just much smaller. You raise a good question on the bond between the particles. If the powder particles are not oxidized the resultant bond will make a seamless metallurgical bond that has no detrimental effect on the toughness of the end steel. The bond between the particles, if the contact is clean, will form a matrix as tough as the parent material. This goes into the basics of welding metallurgy. It's quite complicated but the best way to look at this is with the damascus guys. Given a clean bond they can weld even disimillar metals with seamless bonds as tough as or tougher than the individual materials. The true test of PM vs conventional is the simple fact that the impact toughness increases with PM materials. The bond, plus the smaller grain size, plus the smaller homogenous carbides make PM tougher than ingot cast. The better structure is the main reason for the advanced properties. The bond between the particles just need to be sound and defect free as to not hurt the advantages of the better structure.
On a side note. The PM tool steel process from a metallurgical standpoint is very new (1970's). This and the fact that the technical information was patented and very competitive has made information regarding this process very scarce. The best information available is from the manufacturers if they will release it. Even academics with high knowledge of metallurgy such as Verhoeven have very little experience if any with PM tool steels and their manufacture.