jad0110
Member
Next time an anti says we are just a bunch of gun loving, stupid, ignorant hicks, I'm whipping this thread out!
A great read everyone, I've really enjoyed it.
A great read everyone, I've really enjoyed it.
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?
You ask me that as if you think they are different things…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:
Quote:
Assuming two bolt-action receivers of identical dimensions andweight -- one constructed in forged steel and other in cast steel(both of the best steel, process, and QC) -- would anybody hereassert 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)?
Cast-Steel
We won’t waste much time discussing cast-steel rods because they’re poorly suited to any type of serious performance use. Though the casting process is very inexpensive and results in “near net” shapes that require minimal machining, the lack of a cohesive grain pattern and compromised molecular binding yields brittle parts. Trust us, brittle connecting rods are the last thing you want in a performance engine.
In the ’60s and ’70s, American Motors, Cadillac, Buick, and Pontiac all used cast rods in a wide variety of engine designs. In an effort to improve molecular binding and strength, the molten metal was injected into the mold cavity under high pressure. The resulting castings may have been good enough for use in everything from GTOs to Jeeps, but they have no place in anything other than the most fanatical numbers-matching restoration effort. Worst of all, these cast parts had to be made heavier than comparable forged rods to maintain strength. When you consider that a cast “Arma-Steel” Pontiac 455 rod weighs 31.7 ounces and a stock Chevy 454 forged rod weighs 27.4 ounces, you’ll agree they’re the automotive equivalent of recycled cardboard.
http://www.hotrod.com/techarticles/choosing_the_right_connecting_rods/index.html
You've been saying that anecdotally, but without any offered. . . I know that the Win wouldn't of held.
And the Ruger is strongest......Ed
Would have calculated out?. . . would have calculated out . . .
the lack of a cohesive grain pattern and compromised molecular binding yields brittle parts
Regarding the "Ruger 77 long action as 42 oz", that is likely the MkI
given the 1st edition of Haas's book. What do the MkII actions weigh?
I'm away from my library, so I cannot now check this.
OK, Daniel, these near-net shape investment cast parts are:
1) slowly cooled down to annealed (or normalized) pearlite/ferrite, then
2) machined (if necessary) to net shape, then
3) reheated back up to austenite transformation temp, then
4) quenched into martensite, then
5) tempered
I follow that perfectly. I think we all do by now.
However, assuming, arguendo, that when the molds were poured
the carbons were (somehow) very nicely distributed in austenite
solution, that carbon content later segregates in stage #1
(as laminar cementite Fe3C strips in pearlite/ferrite).
When that pearlite/ferrite is reheated into austenite, any previous
quality carbon distribution (i.e., in the first austenite phase
during the investment casting) is lost as this second austenite
phase is derived from pearlite/ferrite (with its carbide segregated
in cementite strips).
And how are those carbides randomly distributed in the (second)
austenite then?
The second austenite solution has none of the benefits that the
first austenite solution enjoyed, such as (you mentioned) of induction
furnace churning, gating, pouring, or ultrasonic vibration. Near-net
shape pearlite parts are simply reheated to austenite and then quenched
into martensite. (Rather, it's re-melted but not re-stirred.)
If you counter that such processes (induction furnace churning,
gating, pouring, or ultrasonic vibration, etc.) are not necessary for
a well-mixed second austenite solution, then why were such
even done at all the first time during the original casting?
I.e., if simply reheating pearlite into austenite #2 effectively "stirs" the
solution, then why bother (very elaborately) stirring it in austenite #1?
which in the context of the alloys we're talking about is utter nonsense.McClung's point has been that attempts to drive pearlite segregated
carbides into austenite solution are notably unsuccessful.
Hence,
investment casting relying on austenite-->pearlite-->austenite-->martensite
process will have, according to his thesis, segregated carbides in the
grain boundaries. In short, mere heat treat of pearlite does not create
a well-mixed austenite (#2) and thus you can't avoid carbide strings in
your martensite.
If you have specific countering evidence on this very issue, please post
it because we've arrived (finally) at the very crux of the dispute.
btw, the strongest bolt-action that author Haas could find
was an Arisaka. It was almost impossible to blow up.
A forged steel action . . .
.btw, the strongest bolt-action that author Haas could find
was an Arisaka. It was almost impossible to blow up.
A forged steel action . .
All forgings?Not only that but forgings of these alloys undergo precisely the same cycle: they are forged in the austenitic condition at elevated temperature, normalised to form ferrite + pearlite so as to allow machining, and then back up to austentising temperature, quench to martensite and temper.
Can you post any micrographs to support that?In the case of this transformation the diffusion distances the carbon travels are pretty small though, and when you heat it up again the carbon just has to diffuse back these same small distances to dissolve into a new and at least equally uniform (if not even more uniform) austenite.
Regarding my cast-steel receiver SA M1, Ron spoke of
the cast steel being the issue vs. the heat-treat.
Stretching indicates the steel was soft, and that almost certainly has nothing to do with whether it was cast or forged. More than likely a heat treatment issue, or perhaps the wrong steel.
I guess that what I am trying to say is that if you respect me enough to ask me for an engineering opinion on something, at least respect me enough to believe what I tell you.
Let me be the first to commend you for your very impressive intellectual honesty in re-opening this thread to post this update and also to thank you for the information.
Let me be the first to commend you for your very impressive intellectual honesty in re-opening this thread to post this update and also to thank you for the information.
I'll second this.
This polished section shows two features: a longitudinal crack and sulfide inclusions in the steel. The steel used in the barrel appears to be a re-sulfurized steel. The inclusions seen in the figure have been elongated as a result of the forging/rolling of the barrel. They enhance the machineability of the steel. These inclusions are well spaced and reasonably fine sized and do not form any noticeable network to act as a source of the failure. Shown in the top of the figure is an incipient crack. A number of these cracks were examined. The cracks appear to initiate at the surface, dive straight in and then turn to run parallel to the bore axis. The cracks seen in the transverse section, Figure 5, are these cracks as they appear from the end on. These specimens were etched to reveal the microstructure of the steel. This is shown in Figures 7 and 8.
Figure 7: Microstructure of barrel steel showing ferrite/pearlite structure and crack propagating through the ferrite grains Again, a crack can be seen running parallel to the bore axis. The dark areas are pearlite and the white areas are ferrite. These are the two major constituents of the steel. It should be notice that the ferrite forms a coarse network around the pearlite. Also notice that the cracks run through the ferrite. They appear to initiate in one end of the ferrite grain where it meets the surface, propagate down through the grain, follow it along the axis and then go back to the surface where the ferrite grain again surfaces.
Figure 8: Typical microstructure of failed M14 barrel showing elongated grains. A little background on steel; steel is pretty amazing stuff because it so versatile in the properties that can be produced. One of the reasons is the allotropic phase trans*for*ma*tion that takes place when iron is heated above a certain temperature. It changes its crystal structure, the arrangement of atoms. Above this temperature, the austenitizing temperature, it can dissolve carbon. However, as the steel is allowed to cool and the phase transformation occurs the solubility of carbon in iron decreases. Think of making rock candy; as the water is heated, more and more sugar can be dissolved. As the water cools, sugar begins to precipitate out and form solid sugar crystals. In much the same way, this is how steel works. In steel, the way the carbon precipitates (comes out) is largely dependent on temperature and time. Cool it fast and the carbon can't get out fast enough and is trapped in the iron. Cool it very slowly and it can come out uniformly. All the different phases seen in steels are basically governed by this reaction. It largely evidences itself in the hardness and mechanical properties of the resultant steel. The two phases seen in this steel are ferrite and pearlite. The ferrite is nearly pure iron. The pearlite is a combination of two phases that contains most of the carbon, trapped inside. Ideally, one would want a nice uniform grain size and uniform distribution of the two constituents. This results in uniform properties. The steel used in these barrels is rolled from a starting billet to produce a rod which is than bored out to make the barrel. The rolling or forming process causes these grains to become elongated as the bar is deformed from a large diameter to a smaller one. This is normal. The problem with this barrel2 is that the ferrite grains are quite large and interconnected through the pearlite grains. Because ferrite has so little carbon in it, it has roughly the strength of iron. It is the weaker constituent of the steel. Because the grains are large, interconnected and many sit on the surface of the bore, they are prime sites for cracks to form.
"This steel was most likely held at too high a temperature for too long."
That is what happened here. The other factors to consider are that the forces or stresses in the barrel which are tangential, i.e., want to cause radial cracking, are the highest at the bore sur*face and the bore surface is also the location of the stress concentrations at the land and groove interfaces. The ferrite grains are governed by the grain sizes in the steel while it is held at the high temperatures above the austenitizing temperature. This steel was most likely held at too high a temperature for too long. This allowed the austenite grains to grow too large and resulted in the large ferrite grains. Hardness measurements were also made of the sections removed from the barrel; they average out at about Rc 30. This would be typical for this type steel as processed for a rifle barrel. However, hardness measurements don't always pick up the anisotropy seen in this material. In summary, the failure of the M-14 barrel was the result of a poorly formed microstructure in the steel.
There was no evidence of excessive inclusions that would have contributed to the failure. The cause of the observed non-uniformity in the microstructure was most likely due to poor quality control during the austenitizing/rolling operations. The appearance of the microstructure is indicative of a 4xxx high strength low alloy steel. This is certainly an appropriate steel alloy. There should not have been any problems if conventional practices had been followed. Most likely, the effects of the large grain size after processing could have been detected by conducting mechanical property tests on a sample of the barrels prior to machining. The highly deformed microstructure resulting from the anisotropy would result in different mechanical properties depending on whether the test specimen was cut such that it aligned with the barrel axis or was cut transverse to the barrel axis. Higher toughness and ductility would be measured parallel to the axis and lower toughness and ductility for the transverse specimens in this case.
Dang, long going thread