Are CPM ( Powder Steels ) More prone to chipping?

[rbmcmjr]

Charpy results are not formulated by lateral flexing(sideways bending). Powder steels will not flex and return to true like ingot steels can. They will shear.

Reading this makes me wonder if you do not understand how Charpy testing is conducted. Even ingot steels fracture under the correct test conditions. That is the whole point of the exercise.

 

[Ankerson]

Are these parts highly stressed?
Are they critical parts that have to endure impact and flexion to keep the plane in the air? If so, which powder steels are employed? I'd be interested in knowing, as my two favorite ingot knife steels are 154 CM and BG-42; which are both utilized by the aerospace industry.

Research is a good thing before posting.

Google is your friend, the information is out there about what steels are used.

 

[hardheart]

If this is the case, then why are turbine engine blades, firearm barrels/chambers, revolver cylinders, railroad tracks, vital pieces of infrastructure, etc. produced from ingot steel?

While Charpy test results may look impressive on paper, how well do they really represent real-world scenarios? Until skyscrapers are erected with powder steel I beams and aircraft carriers hulls are constructed from powder steel, I am personally not convinced.

Because none of those things requires the alloy content that benefits from PM.

Are these parts highly stressed?
Are they critical parts that have to endure impact and flexion to keep the plane in the air? If so, which powder steels are employed? I'd be interested in knowing, as my two favorite ingot knife steels are 154 CM and BG-42; which are both utilized by the aerospace industry.

RWL-34, CPM-154, CTS-B75P have the same alloy content, but in PM. So same wear resistance, same heat treat with better response, and higher toughness.

 

[knarfeng]

If this is the case, then why are turbine engine blades, firearm barrels/chambers, revolver cylinders, railroad tracks, vital pieces of infrastructure, etc. produced from ingot steel?

While Charpy test results may look impressive on paper, how well do they really represent real-world scenarios? Until skyscrapers are erected with powder steel I beams and aircraft carriers hulls are constructed from powder steel, I am personally not convinced.

Frank, You got everything gerflunkled.
The original question was for similar cutlery alloys. In that case, PM steels are tougher.

PM steels are really only of a significant advantage when you have a high carbide loading, or have a composition which won't melt together properly. And they are orders of magnitude more expensive than melt alloys. Rule of thumb for engineers: If you don't need it, don't pay extra for it.
--IIRC, Turbine engine blades are exotic single crystal alloys. Not in the same ballpark in cost or performance as either PM or melt alloys.
--The steels used for structural reinforcement in skyscrapers don't have enough carbon to form carbides. Same goes for Aircraft carriers. Changing to PM steels would be fiendishly expensive. Since the current alloys are good enough to do the job, why pay astronomical amounts for a higher performing steel?

 

[Buck_110]

Reading this makes me wonder if you do not understand how Charpy testing is conducted. Even ingot steels fracture under the correct test conditions. That is the whole point of the exercise.

I fully understand what Charpy results represent...squat, unless employed as received from the foundry.

Once heat treated, these numbers account for less than nothing.
knarfeng's quote below reflects Charpy results published by Crucible.
Noctis3880's post below states 154 CM chipped when the edge was subjected to metal, and M390 had the edge roll when subjected to cardboard. Do Charpy results not favor M390 to 154 CM?

If you take Charpy numbers and hearsay to heart, then why can 154 CM walk away unscathed from what it endured in the two threads below? M390 clearly has more favorable Charpy data backing its impact strength.

http://www.scrapyardknives.com/ubbthreads/showflat.php?Cat=0&Number=202608&page=38&fpart=1&vc=1

http://www.scrapyardknives.com/ubbthreads/showflat.php?Cat=0&Number=451415&page=0&fpart=1&vc=1&nt=3

The two threads above prove the only data that accounts for anything is that derived from the finished product. If Noctis3880's M390 knife had the edge roll going up against cardboard, how do you think it will fare when put through the same paces as that 154 CM?

http://www.crucible.com/PDFs\DataSheets2010\dsS35VNrev12010.pdf
Notice the toughness table in which Charpy values for S30V and S35V are compared to those for 440C and 154CM. The PM steels are tougher by a factor of at least 4.

All I know is, I found bigger chips on softer 154CM steel at Rc 57-59(Emerson CQC-7) than I did on CPM-154(Galyean Pro Turbulence) at Rc 60-62 when I accidentally ran the edge onto metal. Also found that M390 at Rc 62 still tends to roll rather than chip on thick cardboard. So I suppose fine grain structure is a plus to toughness.

 

[Buck_110]

Because none of those things requires the alloy content that benefits from PM.

Any alloy can be created from powder, no?
These things don't require carbides, but if greater toughness can truly be attained by employing powder, why not use a powder which is not carbide-rich?

 

[hardheart]

This is similar to when you said PM steels are not solid.

Charpy tests are conducted on heat treated samples. The numbers do not count for less than nothing after heat treat, they ONLY count after heat treat. As received annealed from the foundry test results would be less than worthless in any tooling application.

Impact testing is sensitive to sample size, surface finish, weather conditions, and of course microstructure. You somehow think completely different blade designs, manufactured and heat treated by different companies, used by different people, in different tasks, in different locations, gives you a basis for comparison? And no, M390 does not 'clearly' have more favorable charpy data. There is overlap in impact force across the working range of the alloys, and you don't know the geometry, hardness, and microstructure of the knives used in your anecdotal evidence.

As for low alloy steel without primary carbides gaining greater toughness, like mete said, don't confuse grain size with carbide size. Grain size can be reduced in martensitic steel through thermal cycling, you do not need PM to influence toughness in that way. But if your steel has large primary carbides when produced as ingot cast, then PM can reduce carbide size and give consistent grain size, helping increase toughness in that way.

 

[Buck_110]

Charpy tests are conducted on heat treated samples. The numbers do not count for less than nothing after heat treat, they ONLY count after heat treat.

But, the numbers are derived from the foundry's heat treat, NOT the manufacturer's/maker's. After heat treated by the manufacturer/maker, the foundry's numbers for the foundry's heat treat do in fact become moot.

Impact testing is sensitive to sample size, surface finish, weather conditions, and of course microstructure. You somehow think completely different blade designs, manufactured and heat treated by different companies, used by different people, in different tasks, in different locations, gives you a basis for comparison?

Absolutely! Different heat treat protocols will yield different results. Anybody can take delivery of raw materials, but not everbody can execute perfection. If pallets containing identical metals were delivered to GM and Porsche, one company would create transportaion, and one would create a driving machine. Execution is everything! Execution of anything ultimately determines success or failure.

And no, M390 does not 'clearly' have more favorable charpy data. There is overlap in impact force across the working range of the alloys, and you don't know the geometry, hardness, and microstructure of the knives used in your anecdotal evidence.

I never stated I knew the geometry, hardness, or microstructure. Hence the reason I stated only data derived from finished products is the only data that matters. What they eyes see is anything but anecdotal. You parrot published data without the ability to confirm or deny it. While you take that at face value, I'll continue to believe what I see.

But if your steel has large primary carbides when produced as ingot cast, then PM can reduce carbide size and give consistent grain size, helping increase toughness in that way.

I agree with you about grain size affecting toughness, but reducing carbide size? A single carbide is a single carbide is a single carbide.

 

[hardheart]

I agree with you about grain size affecting toughness, but reducing carbide size? A single carbide is a single carbide is a single carbide.

http://www.hypefreeblades.com/files/schneiden.pdf

This pdf has been available for years. You can see the clumping in 440C and D2 creates carbides up to 42+ microns, while the S90V carbides do not aggregate and stay under 7. All PM manufacturers point out this effect of PM, as do the peer reviewed papers testing the properties.

A single water molecule is a single water molecule, but an ocean is bigger than a raindrop.

 

[Buck_110]

http://www.hypefreeblades.com/files/schneiden.pdf

This pdf has been available for years. You can see the clumping in 440C and D2 creates carbides up to 42+ microns, while the S90V carbides do not aggregate and stay under 7. All PM manufacturers point out this effect of PM, as do the peer reviewed papers testing the properties.



A single water molecule is a single water molecule, but an ocean is bigger than a raindrop.

A single water molecule is the same physical size, no matter if it's in a raindrop or the ocean.

Clumped together carbides equates to a mass of carbides.
While they may be clustered together, the size of the individual carbides do not change in physical size.

 

[Noctis3880]

I agree with you about grain size affecting toughness, but reducing carbide size? A single carbide is a single carbide is a single carbide.

The way I understood it, the carbides are more or less clumped together, and the carbide "chunk" is where the weak link is. Which makes sense given that pure carbide is very hard and brittle. The PM process makes the "chunks" smaller with plenty of iron binder in between. Thinking about it in those terms, it's not hard to imagine why that would increase toughness.

I fully understand what Charpy results represent...squat, unless employed as received from the foundry.

Once heat treated, these numbers account for less than nothing.
knarfeng's quote below reflects Charpy results published by Crucible.
Noctis3880's post below states 154 CM chipped when the edge was subjected to metal, and M390 had the edge roll when subjected to cardboard. Do Charpy results not favor M390 to 154 CM?

If you take Charpy numbers and hearsay to heart, then why can 154 CM walk away unscathed from what it endured in the two threads below? M390 clearly has more favorable Charpy data backing its impact strength.

http://www.scrapyardknives.com/ubbthreads/showflat.php?Cat=0&Number=202608&page=38&fpart=1&vc=1

http://www.scrapyardknives.com/ubbthreads/showflat.php?Cat=0&Number=451415&page=0&fpart=1&vc=1&nt=3

The two threads above prove the only data that accounts for anything is that derived from the finished product. If Noctis3880's M390 knife had the edge roll going up against cardboard, how do you think it will fare when put through the same paces as that 154 CM?

Actually the CPM-154 blade ran up against metal, I'm not sure what my brother chipped the 154CM blade on. He insists that he rarely uses it, and it's mostly to cut plastic ties and cardboard.

While I would be eager to volunteer running M390 against metal, I don't sharpen my knives to exact angles, and I suspect the blade grinds themselves would be important.

As well, heat treat is certainly important. Emerson did the heat treat of the 154CM I used, and I suspect Scrapyard knives would have a much more costly and thorough heat treatment of their knives. I never felt all that excited about D2(one reason why I avoided the HEST folder), and yet my Dozier Buffalo River Hunter went through cutting onion roots full of dirt and still sliced paper fine, something my M390 BM 710 failed to do.

Still, I'd like to think there's a good reason that most custom makers opt to use CPM-154 over 154CM. I'm just psychotic that way.

 

[hardheart]

A single water molecule is the same physical size, no matter if it's in a raindrop or the ocean.

Clumped together carbides equates to a mass of carbides.
While they may be clustered together, the size of the individual carbides do not change in physical size.

You are arguing semantics to try to support a point that is untenable. The individual atoms in steel do not change in size, the metallic bonds between them do not change properties, the fundamental forces of the universe do not change, either. And yet 52100, 154CM, and M390 do not perform the same. Composition and distribution matter, and structures differing by a factor of ten to a hundred have an effect on impact strength.

the size of individual carbide molecules remaining constant is irrelevant since that is hundreds/thousands of times smaller than the scale we are dealing with when looking at the carbides in steel. From sub-micron eta carbide to the monsters in steels like D2, 154CM, 440C, etc.

 

[Buck_110]

You are arguing semantics to try to support a point that is untenable. The individual atoms in steel do not change in size, the metallic bonds between them do not change properties, the fundamental forces of the universe do not change, either. And yet 52100, 154CM, and M390 do not perform the same.

Not quite. You stated carbide size decreases. I stated the size of the carbide cluster, not individual carbide size decreases. If this is what you meant, then I honestly misunderstood your earlier statement.

I never stated those three steels performed the same, nor is M390 automatically tougher because it is a powder steel.

Composition and distribution matter, and structures differing by a factor of ten to a hundred have an effect on impact strength.

They can. Anything is possible. You want it cut and dry and in easy to read chart form. Chemistry doesn't work this way. Too many variables exist, and a small tweak can change everything; sometimes for better, sometimes for worse. As I stated earlier, this is the reason I only concern myself with the finished product. In the end, it's the only thing that matters.

 

[flatface77]

All this discussion of carbide sizes made me think of something I had just read: http://www.bladeforums.com/forums/showthread.php/897429-ZDP-189...-yeh-or-nah/page2

Click the link on post#36. It's a guy from Carpenter Steels going on about this issue.

 

[hardheart]

You want it cut and dry and in easy to read chart form. Chemistry doesn't work this way.

 

[Ankerson]

Frank, You got everything gerflunkled.
The original question was for similar cutlery alloys. In that case, PM steels are tougher.

PM steels are really only of a significant advantage when you have a high carbide loading, or have a composition which won't melt together properly. And they are orders of magnitude more expensive than melt alloys. Rule of thumb for engineers: If you don't need it, don't pay extra for it.
--IIRC, Turbine engine blades are exotic single crystal alloys. Not in the same ballpark in cost or performance as either PM or melt alloys.
--The steels used for structural reinforcement in skyscrapers don't have enough carbon to form carbides. Same goes for Aircraft carriers. Changing to PM steels would be fiendishly expensive. Since the current alloys are good enough to do the job, why pay astronomical amounts for a higher performing steel?

Yeah the metals used in the Aerospace industry are much more advanced than the typical knife blade steel.

Then the treatment of those alloys in the manufacturing process and treatment process is much more advanced than for the typical knife blade, railroad rail, steel I-Beam ect.

That would be a whole different topic completely.


People trying to do a cross relationship between the steel applications really isn't realistic.

 

[mete]

There are many confused people here !! Typical steel has significant difference between transverse and longitudinal impact strength.Powder steels raises the transverse impact strength.
Aircraft carriers need steels with much higher impact strength and a low brittle transition temperature .That's why HY-80 and HY-120 were developed. Jet engine blades are often made of alloys very difficult to machine so may be investment cast .Those alloys require high temperature creep resistance .
Carbides are carbides ?? Large carbide size steel fractures usually are carbide to carbide , small carbide size steel tends to be trans-granular. Therefore small carbide => tougher ! Smaller carbides also tend to have some coherency which is lost with large carbides.
Deal with facts not assumptions !

 

[Steel130]

Wow haha. You guys have laid out a lot for me to try and take in. From what I understood PM is stronger due to finer grain size and a more even distribution of carbides right? I understand that free carbon in a blade makes it very brittle. I assume free carbon is like a clump or gathering rather than a spread of them? Also from what I understood 154cm and CPM154 are the same makeup just CPM154 starts out as a powder. I am not sure what ingot steel is. From my understanding the way a blade is heat treated can make the same steel perform differently? Baby steps haha.

 

[David Martin]

Good stuff guys. Thanks for your efforts. HardHeart, I couldn't get the chemistry table to interact. DM

 

[mete]

Typical steels are made in a furnace ,many tons worth. The steel is then poured into a series of ingot molds to form ingots of steel which are on the order of 20" diameter and 10' or so long.Solidification of the ingot causes various problems of segregation of elements and a carbon and alloy rich center.
I have no idea what "free carbon " is.
The blademaker's HT makes a big difference in properties !