Forged???

[Stinkyshoe]

Shear_Stress

This I heard from a very credible member of the American Pistol Smiths Guild. I assume he'd know.

Ss

 

[harrydog]

Ash,
I think you're the one who brought up the longevity issue in that forged parts wore out more quickly based on what happens in a race car engine. I was merely pointing that forged cranks are also used in many production road cars where longevity is important.
My original point was that forged parts, cranks and connecting rods in particular, are generally stronger than their cast counterparts and that is why they are used. In many racing applications a cast crank would end up cracking under the high stress.
The only real advantage of cast parts over forged or machined from bar stock parts is the manufacturing cost.

Slamfire,
Some of those big diesel engines may have cast cranks but they are very low RPM engines.
It's high RPM that really stresses a crankshaft. But even so, I did a search and it appears that many diesel engines including Cummins and Caterpillar are using forged steel cranks.

 

[Slamfire]

Slamfire,
Some of those big diesel engines may have cast cranks but they are very low RPM engines.
It's high RPM that really stresses a crankshaft. But even so, I did a search and it appears that many diesel engines including Cummins and Caterpillar are using forged steel cranks

I can believe that. I would love to have seen a forging press large enough to stamp out some of the cast iron cranks I saw. They were huge. And those engines, they are designed to run 1500 rpm for forever. Not to say the loads don't vary, but they are not high rpm.

If you want to see the world's largest diesel, take a look at the pictures on this site.

http://people.bath.ac.uk/ccsshb/12cyl/

 

[harrydog]

Holy crap! Now that's a huge engine. At 1660 gallons of fuel per hour, imagine how much fuel it has to carry to cross the Pacific or Atlantic!

 

[Ash]

"I think you're the one who brought up the longevity issue in that forged parts wore out more quickly based on what happens in a race car engine."

No, I actually did not. My point merely was that using a race car is not a good example of longevity or superiority of forged parts. Indeed, I said “They (race car parts) are wonderfully strong and capable for short-term use, but they are worn out very quickly. Of course, a cast part might just wear sooner."

The point is, race cars are bad examples for any kind of longevity comparisons, whether they be tires, engine oil, or metals.

Ash

 

[daniel (australia)]

In relation to crankshafts and rods I said this back at post #58 in this thread

If we compare a forged steel crankshaft or con-rod with one of conventional spheroidal graphite or nodular cast iron the forged steel will generally be significantly better, at least for racing and high duty. That is not because of strength though but resistance to fatigue failure, which is admittedly much better for forged steel than any cast iron or even the general run of cast steel.

Fatigue is a big factor for cranks and rods, but not rifle receivers: a crank and rods will undergo more load cycles in a few seconds at full noise than a rifle receiver will undergo in its entire service life. That is why as well as specifying a forged crank your tuner will also be obsessive about radiusing all corners, shot peening and polishing, crack testing, and balancing, all to reduce the likelihood of fatigue cracks being initiated. None of this is relevant to rifle receivers.

There are better materials than these for racing car components too, such as Metal Matrix Composites, already seen and then banned from use in F1 pistons. MMCs are generally produced by casting or else powder metallurgy, and have particular advantages for pistons due amongst other things to the thermal loads.

F1 engines do use investment castings in the form of valves, valve-train components, blocks, gearbox housings and a myriad of others. The rules specify a steel crank though, so that is what is used.

Generally cranks and rods aren't running at stresses anywhere near their maximum strength, unless something goes seriously wrong. Nor do they wear much, even in race engines, unless bearings and/or lubrication are inadequate. The main thing that will bring their service life to an end, often in the form of an expensive unplanned reorganisation of the engine design, is fatigue. Fatigue is where a crack gets a start, perhaps in a sharp corner or defect, and under the enormous number of load cycles these components undergo it gradually progresses acoss the section, until there's not enough left to support the load and the whole thing lets go in a cloud of oily smoke and swearing.

Now fatigue life depends on a number of factors, including the material chosen, how well it is radiused, peened etc to minimise or eliminate possible crack initiation sites, and the applied stress. Now of course a race engine crank runs at fairly high stress, especially as it will generally be specced to be fairly light, but you can also reduce the stresses by good balancing and a few other tricks. Frequent tearing down and inspection including crack testing also helps you to keep an eye on things, and (ideally) swap out components before fatigue cracks can do damage.

In the case of the big diesel it has a massive crank running comparatively slowly, so fatigue is much less a factor. It probably also has pretty massive conrods too, and fairly low piston velocity, as well as running at a fairly constant speed without sudden accelerations. The net effect is that the big diesel can well get away with a nodular iron crank (one of a size which would be exceptionally difficult to produce by forging too), and very long maintenance intervals/service life.

In the case of the race car, even if the rules didn't specify it, the steel crank would be better than the iron largely because the steel is better able to resist fatigue. There are potentially even better materials too, though for F1 at least steel is mandatory.

Point is though, that all of this is entirely irrelevant to the use of investment cast components in firearms. No one is talking about making a receiver from nodular or SG iron, just for starters. More importantly though fatigue resistance is just not a factor in the case of sporting firearms. As I said a couple of weeks ago

a crank and rods will undergo more load cycles in a few seconds at full noise than a rifle receiver will undergo in its entire service life.

In any design, you have to look at the properties the material needs to have for that application, not how well suited it is to some other, entirely different application.

 

[harrydog]

Caspian sells excellent cast steel 1911 receivers. They have proven to be every bit as durable as forged or bar stock receivers and carry a lifetime warranty against cracking. However, for their slides they use forged steel because a cast slide would not last nearly as long. Slides endure greater stress and impact than receivers.
Cast parts may be perfectly fine for many applications but they are almost always specified only because they cost less to manufacture, not because they are better.

 

[Boston T. Party]

Cast parts may be perfectly fine for many applications but they are almost always specified only because they cost less to manufacture, not because they are better.

That seems an excellent and accurate encapsulation of the issue, thanks.

Regarding McClung's contribution to my book Safari Dreams, it was
in context of cast steel receivers in dangerous game rifles. For such
a gun, you want every possible odd in your favor, such as controlled-feed,
M98 extractor, fixed ejector, ample caliber, etc. I still agree with McClung
that a forged-steel receiver adds to your odds, and that a cast steel
receiver does not (and possibly lowers your odds).

If you don't have to take an unnecessary chance, why do it when a
forged Win M70 or CZ550 Magnum is available for the same price?

Regarding daniel's contention that 4140 steel has a sufficiently low
carbon content to avoid the dendrite paths from the casting process,
I'm sure McClung will respond to that when he has a moment.

Thanks to all so far for your comments.
I'm always up for learning something, or correcting my own misinformation.

btw, my book Safari Dreams is in, and turned out very nicely.
If you're keen to hunt in Africa, it will be a great use to you.

$36 cash gets you a signed postpaid copy.
352 pages, 100 color photos

Javelin Press
POB 31
Ignacio, Co. 81137-0031

Regards,
Boston

 

[Boston T. Party]

Kevin McClung's reply

Quoted below in full is McClung's email.

Boston

Boston,
My response, and then I am done with this:

One has only to view the scrap piles of visibly flawed and
mis-cast pieces behind Ruger's casting plant, which is proximal to
my own place of business, or interview several hundred current and
former Ruger employees who will candidly discuss the goings on
there in terms unseen in Ruger's promo videos... to get the idea
that their manufacturing, casting and QA process subsets do not
necessarily guarantee top quality results.

Watching them begin the re-grind/re-melt recycling process of all
of this scrap, tons of it, (not always perfectly sorted for alloy content
but then, dilution does wonders for that...right?), is entertaining in the extreme.

In response to the smugly pedantic "Daniel", the cooling rate must be
optimized to prevent the formation of dendrites and other cooling
related issues. It is apparent after examining many samples of Ruger
castings that their cooling process is not what we would call "consistently
optimized". But again, Ruger's sentiment on casting quality seems to be
that what you can't hit consistently through precision and repeatability,
you can hit haphazardly often enough to make it worthwhile to keep on
plugging away at it. Fortunately for them, casting is a cheap foundry
process and "do overs" are easy.

But for Daniel or anyone else who may be emotionally invested in their
investment cast guns or have a personal interest in promoting/selling them:
If you like that stuff, fine. Buy it, sell it, whatever.
It's your money, your life on the line and as always, YMMV.

Mine doesn't. It's a science thing.

Stay Sharp,
Mad Dog

 

[JohnKSa]

the smugly pedantic "Daniel",

Cheap shot.

Posting an email from someone else that insults a member on THR when you can't do it yourself per the forum rules.

But again, Ruger's sentiment on casting quality seems to be that what you can't hit consistently through precision and repeatability, you can hit haphazardly often enough to make it worthwhile to keep on plugging away at it.

This is why Rugers are known for breaking...

But for Daniel or anyone else who may be emotionally invested in their investment cast guns or have a personal interest in promoting/selling them:

Naturally, anyone who disagrees with the esteemed Mr. McClung must be doing so out of emotion or personal interest. Apparently he finds it unfathomable that there could be a disgreement based on any thing technical.

 

[Slamfire]

One has only to view the scrap piles of visibly flawed and
mis-cast pieces behind Ruger's casting plant, which is proximal to
my own place of business, or interview several hundred current and
former Ruger employees who will candidly discuss the goings on
there in terms unseen in Ruger's promo videos... to get the idea
that their manufacturing, casting and QA process subsets do not
necessarily guarantee top quality results.

Scandal mongering employees seldom have nice words to say about their employer. In fact, with a little prompting you can get from any employee of any business a long litany of why things are messed up at work.

And the fact there is a pile of rejects means a least there is a QA process, maybe not to the satisfaction of disgruntled former employees.

As to the complaints; yes, overall the earth is messed up and the country is going down a rat hole, but what specifically are the incidents that they are complaining about? Dollar coffee machines?, not enough parking spaces at work?, etc? I have heard any number of employees dog the products that their employer makes, and yet I have never heard any employee admit that they personally, with malice and forethought, sent out product that was dangerous or defective.

Disgrunted employees find out later they had it good when their jobs are off shored.

 

[harrydog]

This thread has taken a turn for the worse which I don't really want to get caught up in, but I do have a question regarding Ruger castings.
My question is, are Rugers really known for breaking? I thought it was just the opposite. I know that Caspian has never had a 1911 receiver returned to them due to cracking or breaking, and they are cast by Ruger. Also Ruger revolvers and rifles are known for being extremely strong and durable. More so than some of their competition. So I'm wondering where the "known for breaking" comes from.
By the way, I don't own or never have owned a Ruger, so I really don't have a vested interest in this at all.

 

[daniel (australia)]

My response, and then I am done with this...

Well, yeah, whatever…

I have to laugh though, especially at this bit:

for Daniel or anyone else who may be emotionally invested in their
investment cast guns or have a personal interest in promoting/selling them

I have no financial or personal stake in this argument at all. Sure, I did write an Honours thesis on the production of high integrity castings, and I did spend a bit of time in researching, testing and developing this sort of stuff for defence and other applications, but that was a fair while ago. I spent rather more time as a metallurgical consultant, mainly investigating failures, and I’ve seen them in all sorts of products, so I don’t think I’m “emotionally invested” in any particular production method either. I’ve moved on even from there though, and my interest in all of this is in the “science thing”, and nothing else.

I note with some amusement though that Mr McClung in fact does have a financial stake in forged receivers, given that they are sold by his company – as of course does the fellow who chose him to provide “technical” input to a book he keeps mentioning.

The “science thing” too, I had to smile a wry smile at that.

For starters:

the cooling rate must be optimized to prevent the formation of dendrites and other cooling related issues.

McClung claimed earlier that you’d get dendrites of carbide, so assume that is what he is talking about here.

The credibility gap is yawning wider though: with the steels we’re talking about it doesn’t actually happen that way at all. This is all fairly basic metallurgy, and there are vast atlases of diagrams based on enormous amounts of empirical data showing precisely what does happen with different alloys as they solidify slowly (phase equilibrium diagrams) and as they are cooled at varying rates from slow furnace cooling to rapid quenching (TTT diagrams). With a medium carbon (“hypoeutectoid”) steel such as you might use for a receiver, cooled slowly from liquid, the steel doesn’t solidify all at once, but in fact the first thing to solidify is the ferrite, not the carbide. Ferrite is essentially pure iron (with a very small amount of dissolved carbon). Carbon is concentrated in the remaining liquid until it reaches about 0.8%, and this solidifies as a phase called pearlite, consisting of laminations of carbide and ferrite. You’ll see the resulting microstructure in cast steel and you’ll also see it in annealed forged steel of the same composition.

What about dendrites though? Well, by and large metals solidify by forming dendrites. Steel is one of them. Dendrites are no more than the name for what you see in the development of the crystal structure from the liquid as the metal cools, as a sort of branching framework which grows until the whole structure is solidified

You see the same type of crystallisation at work in snowflakes. Saying you'd prevent the formation of dendrites as you make steel is a bit like saying you can prevent a tree from containing wood. Moreeover, as I’ve said, the ferrite actually forms first in the steels we’re talking about, not the carbide, so the dendrites from which the crystals start to grow consist of this ferrite.

As for "cooling related" issues, you get these with forgings too. Quench cracking for example, or distortion, or wrong hardness. All of these are "cooling related". You avoid them with good process control, and the same applies to castings.

One has only to view the scrap piles of visibly flawed and
mis-cast pieces behind Ruger's casting plant…
…Watching them begin the re-grind/re-melt recycling process of all
of this scrap, tons of it, (not always perfectly sorted for alloy content
but then, dilution does wonders for that...right?), is entertaining in the extreme.

You’ll always have some scrap, with any casting process, mainly in the form of sprues, risers etc. You’ll get rejects too, for any number of reasons. Same with any process. It says nothing of the comparative merits of the product, and I suspect is being grossly exaggerated here.

In foundry practice you simply recycle the metal back into the furnace. As to segregation according to alloy again I’d be surprised if Ruger wasn’t doing this, as it is standard practice in any foundry I've been in, but in any case it is also standard practice to analyse each heat immediately before pouring and make any adjustments to bring it to spec. I’ve done this myself, many times (though a long time ago): it takes a matter of minutes to carry out a spectrographic analysis and calculate the alloy additions to bring an off-spec. heat to spec again, before you pour.

As for disgruntled employees well, I take such hearsay with a substantial grain of salt. It wouldn’t prove anything about the relative merits of forging and casting anyway. In any case it is no secret that there’s been a significant shake up at Ruger's factory over the past year or so. They sought to reduce inventory significantly and it exposed problems in their manufacturing systems which they've had to bite the bullet and address. That has nothing to do with the relative merits of forging and casting either.

I don’t place all that much credence in one firearm supplier running down another’s product either, but that is all I see here. Where's the "science"?





.

 

[Slamfire]

I don’t place all that much credence in one firearm supplier running down another’s product either, but that is all I see here. Where's the "science"?

Daniel: Knock em dead mate:

We all know that vendors always fairly rate the products of their competitors. Rubbish!

All I read from the critics of casting is unsubstantiated mud slinging. Almost at their last stand. The final stand will be that they don't like casting because they don't like the people who make castings.

These guys trust their lives daily on the cheapest cast components in one of the deadliest games around: Cars. Like 50,000 US citizens die per year and there are 600,000 vehicle injuries.!!

But what they emphasize is a cast receiver failing during a what, a maybe once in the lifetime hunt against lions and tigers and bears!

 

[JohnKSa]

My question is, are Rugers really known for breaking?

The little "eye-rolling smiley= " is indicative of sarcasm.

You are correct. In spite of all the innuendo about QA issues and casting problems from our "expert", Rugers have a well-deserved reputation for extreme durability.

I don’t place all that much credence in one firearm supplier running down another’s product either, but that is all I see here. Where's the "science"?

Agree, the email is several paragraphs of attacks and innuendo with maybe a couple of sentences of technical information (being generous).

I'm always terribly unimpressed with people who claim to be experts but when pressed choose to resort to pomposity, innuendo, and insults rather than responding technically.

 

[Boston T. Party]

Cheap shot.

Posting an email from someone else that insults a member on THR when you can't do it yourself per the forum rules.

I understand the point, but didn't consider "smugly pedantic"
to have crossed the line of insulting. It certainly wasn't my
intention to insult or facilitate such. From here on, I'll post
only what I have to say.


from Daniel:

I note with some amusement though that Mr McClung in fact does have a financial stake in forged receivers, given that they are sold by his company – as of course does the fellow who chose him to provide “technical” input to a book he keeps mentioning.

Actually, I've no financial stake in any forged steel product.
I wrote a book containing the opinions of myself and others.
I've never found any reason to doubt Kevin's technical
expertise in my 16 years of knowing him. He exposure of the
Zylon material failure in bullet-resistant vests points to his
wide understanding of material properties.

Before I published Kevin's essay on the subject, I searched
diligently for facts and discussion on the forged vs. cast issue,
but this thread did not come up. (I found it only post-publication
when I was running down whether or not Montana rifles were
cast, and posted on it that same day.)

Kevin, to my knowledge, has nothing personal against Ruger
that would color his stance against cast steel receivers.


_____________
Regarding the veracity of Ruger's former employees, I cannot
comment to that with any knowledge, though I take the point
that some may be bitter and have an agenda.


_____________
from Daniel:

With a medium carbon (“hypoeutectoid”) steel such as you might use for a receiver, cooled slowly from liquid, the steel doesn’t solidify all at once, but in fact the first thing to solidify is the ferrite, not the carbide.

Is it your contention that cast receivers of “hypoeutectoid” steel
are slowly cooled?

If, however, they are cooled fast, does that tend to collect
carbides in a fern-like lattice vs. randomly distributing them?


_____________
In order to constrain this thread within technical bounds,
I pose the following question:

Assuming two bolt-action receivers of identical dimensions and
weight -- one constructed in forged steel and other in cast steel
(both of the best steel, process, and QC) -- would anybody here
assert that the cast version is of equal or superior tensile strength?

(Interestingly on this very point are two virtually identical rifle
receivers: the forged Win M70 Classic and Montana's cast version
of it. The Montana action may be heavier, however.)

Thank you all for your posts.
My only reason for posting is to further understanding of this issue.
May true science win.

Boston

 

[JesseL]

Assuming two bolt-action receivers of identical dimensions and
weight -- one constructed in forged steel and other in cast steel
(both of the best steel, process, and QC) -- would anybody here
assert that the cast version is of equal or superior tensile strength?

(Interestingly on this very point are two virtually identical rifle
receivers: the forged Win M70 Classic and Montana's cast version
of it. The Montana action may be heavier, however.)

I would assert that until they do some serious real-world testing and analysis of both receivers, nobody is qualified to state definitively which receiver is stronger. No science exists in a vacuum (except maybe pure mathematics).

 

[Boston T. Party]

Surely a test of two otherwise identical steel cavity forms
has been done to ascertain the strength of casting vs. forged.
If so, where?

Remember, my question is not whether a cast receiver can be
sufficiently oversized to equal the strength of a (thinner) forged
receiver, but, rather, the comparative strength of equal weight
and thickness of the two.

Boston

 

[hubel458]

A false premise-It should be stated how much thicker forged
reciever has to be to match investment one.

Don't do no good badmouth investment cast, heat treated stuff .
I have stressed tested the Ruger 77, and emphatically
state that they are stronger than the forged Win 70.
And the Win 70 and many others are thicker at the side of
reciever ring in same place as the flat side of the Ruger 77, where
the 77 is thinnest where if it was going to split, that's the place.
I overloaded, not by plan, a 77 in 458, so bad it bulged chamber ahead
of the reciever about ..060, flowed the brass case around bolt,
but it didn't blow out the corners of the case, or shear the lugs
or shear the lug seats. Took out barrel with lathe, tested action, put
in other barrel still going after another thousand rounds, I know that
the Win wouldn't of held. The investment casting can be treated to higher
strength than forged. Can be treated more uniformly throughout
thus giving a much higher strength all through the material.
They both have same diameter barrel thread
but the Win is about .025" bigger OD than Ruger on the sides, and
the Win wouldn't have held like the Ruger. Ed

 

[Slamfire]

I would assert that until they do some serious real-world testing and analysis of both receivers, nobody is qualified to state definitively which receiver is stronger. No science exists in a vacuum (except maybe pure mathematics).

I agree. I can recall reading something in the 70's where Ruger shear tested the lugs on their bolts and found they took twice the shear of forged bolts. But, if memory was right, the forged bolts were like M1903 bolts. The material technology and process technology was decades different, so it was not an apples to apples comparison. The tests were not published in the open literature.

But I want to say, at some point the tensile and ultimate of the receiver becomes meaningless. Steel is far stronger than brass. At some pressure point the cartridge ruptures. I personally think action strength is really a measure of how well the action design supports the cartridge case. If the action properly supports the case, than a plain carbon steel action, like the M38 Japanese, will prevent cartridge rupture far better than the more massive M1917. Which was made of nickel steel. P.O Ackleys’ tests show this.

Once the cartridge ruptures, the next issue is how well the action protects the user in what is, essentially, a destructive incident.

I don’t think anyone ever designed an action with the idea that after a “catastrophic” failure, that all the user had to do was screw on a new, intact barrel. It is just good fortune that some have useable receivers after such events. If I were the designer, I would consider the safety margin of the action to have been used up. If these were not individuals, but were rather companies or Armies, I have no doubt that even though the receiver was still intact, it would have been scrapped. Individuals don’t have such deep pockets so ……..

In the book "Technical Notes" from Armalite, the load of a 30-06 on the bolt face is between 4000 and 6,600 pounds, for a couple of milliseconds. I will bet the wheel bearings on my truck experience more than that on some big pot holes.

I think the focus on cast versus forged is a distraction, created by corporate advertising, from what is the real issue: Good action design.

And for that, go read Stuart Otteson’s books on “The Bolt Action”. Good action design is far more complicated than material choice.

 

[hubel458]

Thr reciever besides being intact was also tested.
No weaknesses showed up. Total loads fired through it
is about 2000, half before the overload and half after.
Proper investment, alloyed and treated steel isn't going to
stress away so to speak, unless you subject it to many
tens of thousands of pressure cycles, may take hundreds
of thousands. Now it may fail in a few hundred of my stupid
overloads, but that would be awful expensive for barrels to
find out.Ed

 

[Boston T. Party]

from Daniel:

With a medium carbon (“hypoeutectoid”) steel such as you might use for a receiver, cooled slowly from liquid, the steel doesn’t solidify all at once, but in fact the first thing to solidify is the ferrite, not the carbide. Ferrite is essentially pure iron (with a very small amount of dissolved carbon). Carbon is concentrated in the remaining liquid until it reaches about 0.8%, and this solidifies as a phase called pearlite, consisting of laminations of carbide and ferrite.

You contend that steel alloy with <0.83% carbon does not form
carbides because up to 0.83% carbon is dissolved in the
austenite (gamma iron in liquid phase).

This is a partial truth.

Hypoeutectoid alloys contain less carbon content than the maximum
dissolvable in the parent material of austenite. (The introduction of carbon
into austenite lowers its temperature of stability, but that effect peaks
at about 0.83% carbon content.)

Such alloys with <0.83% carbon will indeed form carbides, though only with
ferrite (called cementite, or Fe3C) because the austenite first dissolves carbons
until its saturation point of 0.83%. Cementite plus ferrite -- and slowly cooled --
is what creates the phase of pearlite (+ free ferrite), beginning at 0.20% carbon.
Beyond 0.83% carbon, you get free ferrite, pearlite, and non-ferrite carbides
(i.e., with the other alloys such as vanadium, tungsten, etc.).

No gun manufacturer wants pearlitic steel because the very definition
of pearlite means that the once-dissolved-in-austenite carbons were
foolishly allowed to precipitate out of the austenite solution to form
segregated cementites (Fe3C). The whole point of a rapid cooling of
AISI 4140 gun receiver steel (which is oil quenched for 30 minutes from
an initial temp of some 1525°F/1625°F, by the way, not "slowly cooled"
as in your model) is to trap individual carbon atoms within the austenite
crystals, creating tough martensitic steel.

http://info.lu.farmingdale.edu/depts/met/met205/tttdiagram.html

(If you quench too slowly, you end up with a phase between pearlite and
martensite called bainite, but that's a matter irrelevant to our discussion.)

Yes, quench stresses can form from the formation of martensite, but that
is why such are relieved through subsequent tempering.

The fact that gun receiver steels such as AISI 4140 are <0.83%/hypoeutectoid
alloys is really immaterial regarding the issue of carbides segregating into
dendrites. By definition, steel is iron with at least 0.20% carbon, else the
iron could not be formed into martensite (i.e., hardened). And even such
a low carbon content of 0.20% will precipitate out if the austenite
were allowed to be "slowly cooled" as per your example.

I am trying to imagine further your point, to wit, that 4140 cast steel's
carbon will necessarily form into pearlite cementite layers vs. dendrites,
but that is not a given at all. Such in part must assume not only a forged
steel quality of alloy distribution, but also no internally disparate cooling
(i.e., crystallization) of the cast piece within its mold.

Moreeover, as I’ve said, the ferrite actually forms first in the steels we’re talking about, not the carbide, so the dendrites from which the crystals start to grow consist of this ferrite.

Not exactly:

The area along which crystals meet, known as the grain boundary, is a region of mismatch. The boundaries are formed by materials that are not part of a lattice, such as impurities, which do not show a specific grain pattern. This leads to a noncrystalline (amorphous) structure at the grain boundary with the atoms irregularly spaced. Since the last liquid to solidify is generally along the grain boundaries, there tends to be a higher concentration of impurity atoms in that area.

http://info.lu.farmingdale.edu/depts/met/met205/crystallization.html

If carbon solidifies last, then that helps to prove my point that carbides will
tend to accumulate along the grain boundaries, especially during internally uneven
parts crystallization.


I will grant you that >0.83% carbon content austenite (hypereutectoid steel),
all other things being equal, is more prone to grain boundary carbide dendrites,
but I do not at all agree that such dendrites are impossible or even rare in
hypoeutectoid steels (especially such cast instead of forged).

Does forging more effectively distribute dissimilar alloys within the austerite?
Of course it does, that's one reason for the operation. There really can
be no disagreement about that.

Quality hot forging of carbon steel distributes the alloys, and the oil quench
"freezes" this distribution in place for optimal strength. After nearly many
hours of research into all this, I'm really astounded that the matter can
seriously be called into question at all.

Regards,
Boston

 

[daniel (australia)]

Looking back at my last post I should correct something I wrote – not that it changes the thrust of the argument but because I misstated something inadvertently, and it should be fixed: it is of course the generally the metastable austenite which nucleates first. Ferrite then appears as a transformation product from the austenite with decreasing temperature, and finally at about 720 degrees C the remaining austenite undergoes an isothermal transformation to pearlite.

Hypoeutectoid alloys contain less carbon content than the maximum
dissolvable in the parent material of austenite. (The introduction of carbon
into austenite lowers its temperature of stability, but that effect peaks
at about 0.83% carbon content.)

Such alloys with <0.83% carbon will indeed form carbides, though only with
ferrite (called cementite, or Fe3C) because the austenite first dissolves carbons
until its saturation point of 0.83%. Cementite plus ferrite -- and slowly cooled --
is what creates the phase of pearlite (+ free ferrite), beginning at 0.20% carbon.
Beyond 0.83% carbon, you get free ferrite, pearlite, and non-ferrite carbides
(i.e., with the other alloys such as vanadium, tungsten, etc.).

Well, yeah, but in the hypoeutectoid alloy, cooled slowly enough to avoid transformation to martensite or bainite, the carbide is all in the form of pearlite, which is a fine laminated structure – fine layers of hard carbide and soft ferrite combining to make a comparatively strong and tough structure.

No gun manufacturer wants pearlitic steel because the very definition
of pearlite means that the once-dissolved-in-austenite carbons were
foolishly allowed to precipitate out of the austenite solution to form
segregated cementites (Fe3C).

No, no, no! In the annealed or normalised condition you are going to have the same percentages of pearlite and ferrite for any given composition, regardless of whether the steel was forged, machined from bar stock or produced as a casting. You then heat treat. Further, the carbide in these grades isn’t precipitated out of the austenite, nor does it form segregated cementites. Instead the remaining austenite transforms isothermally to the new structure, pearlite.

The whole point of a rapid cooling of
AISI 4140 gun receiver steel (which is oil quenched for 30 minutes from
an initial temp of some 1525°F/1625°F, by the way, not "slowly cooled"
as in your model) is to trap individual carbon atoms within the austenite
crystals, creating tough martensitic steel.

You are confusing a couple of important points here. First, investment castings are, in my experience, poured into investments (moulds) which have been preheated in a furnace to about 1000 degrees Celsius or so, and allowed to cool over a period of hours. It is not equilibrium cooling but nor is it anywhere near being quenching. You then clean off the mould material, do any finish machining and of course you are then at liberty to heat treat them any way you like. The same is true of forgings: you forge at temperatures above the austenite transformation temperature, cool slowly, and generally do your machining in the same normalised state, before heat treating to develop the final hardness. The reason is fairly simple: it is easier to do any machining before hardening. In either case though whenever you are ready you can quench and temper the product, or use some other heat treatment, to get the final properties you want.

The fact that gun receiver steels such as AISI 4140 are <0.83%/hypoeutectoid
alloys is really immaterial regarding the issue of carbides segregating into
dendrites.

Except to the extent that, in direct contradiction of your earlier claims, carbides just don’t “segregate into dendrites” in these alloys.

Quote:
The area along which crystals meet, known as the grain boundary, is a region of mismatch. The boundaries are formed by materials that are not part of a lattice, such as impurities, which do not show a specific grain pattern. This leads to a noncrystalline (amorphous) structure at the grain boundary with the atoms irregularly spaced. Since the last liquid to solidify is generally along the grain boundaries, there tends to be a higher concentration of impurity atoms in that area.http://info.lu.farmingdale.edu/depts...llization.html
If carbon solidifies last, then that helps to prove my point that carbides will
tend to accumulate along the grain boundaries, especially during internally uneven
parts crystallization.

The carbide appears as the result of an isothermal transformation in the solid state. It is a different mechanism from that which causes impurities to tend to concentrate at grain boundaries. In fact the carbide is exceptionally finely distributed within islands of pearlite, not at grain boundaries. As you approach 0.8%C the pearlite % increases to 100%.

Here’s a 0.3%C steel, normalised: the ferrite grains are white, the pearlite darker – you can see the laminated structure:

At 0.4%, again normalised, you can see theres rather more pearlite, and less ferrite:

And at 0.8% C, its pretty much all pearlite:

Does forging more effectively distribute dissimilar alloys within the austerite?
Of course it does, that's one reason for the operation. There really can
be no disagreement about that.

More effectively than what? The austenite is a solution, not dissimilar alloys, and the metal is effectively mixed in the case of modern castings by a number of factors, including the churning which takes place in an induction furnace,gating and pouring processes etc. Any minor degree of segregation is easily attended to by heat treating anyway. There’s also processes like ultrasonic vibration to nucleate a fine structure, as well as various alloy additions to nucleate grains, pin growth, modify or remove inclusions etc– quite a bit is going on in fact.

Quality hot forging of carbon steel distributes the alloys, and the oil quench"freezes" this distribution in place for optimal strength. After nearly many
hours of research into all this, I'm really astounded that the matter can
seriously be called into question at all

Well I suppose that is one way of putting it. It just isn’t a very accurate way of putting it.

Let us not lose sight of the point though, that there are other processes besides forging which can give rise to a product equally suitable in terms of strength and other properties. Modern investment casting is one such process, and as I have previously said there is no technical reason why an investment cast receiver, all else (in terms of heat treatment, QA etc) being equal should be any less serviceable and safe than a forged one.

I do hope that the research you’ve done has sparked a bit of an interest, even though it is a bit late for your book

 

[Boston T. Party]

Thanks, Daniel, for your reply.

I do hope that the research you’ve done has sparked a bit of an interest, even though it is a bit late for your book

Since McClung's thesis in my book (and thus its discouragement
of cast steel receivers) points to the side of caution, even if such
is ever proven technically to have been in error, my readers will not have
been deprived of any safety or value because of that error.


___________
Are you contending that gun parts/receivers are generally made of
softer pearlitic steel (subsequently heat treated) vs. martensitic steel?

Further, are you contending that heat treating transforms pearlite into martensite?

I will respond to the rest of your reply when I can, but meanwhile reiterate
to you my previously unanswered question:

Assuming two bolt-action receivers of identical dimensions and
weight -- one constructed in forged steel and other in cast steel
(both of the best steel, process, and QC) -- would anybody here
assert that the cast version is of equal or superior tensile strength?

To me, this is the real question.

Neither I nor McClung disallow that a sufficiently heavier cast
receiver can have a similar working strength as a lighter forged one -- just
that such is 1) heavier, and 2) less robust over time. Your disagreement
with 2) is certainly noted, but are you also disagreeing with 1)?

Regards,
Boston

 

[hubel458]

Properly investment cast, heat treated, alloy recievers
and bolts are as strong as a forged ones, of the
same dimensions. Winchesters are a little thicker on
the side compared to Ruger and not even a Winchester nut
would say it would hold as much as a Ruger. Ed