Steel used in the first smokeless gun barrels?

[Iron Song]

Hi, this is just another obscure question that I can't get out of my head and need help answering, Google ain't what it use to be, not sure if this is the right place, but I know guys here know a thing or two about steel. Maybe you can answer this riddle for me?

So, I'm trying to find out what sort of steel the gunsmiths were using for their barrels when smokeless powders first came out, barrels that were actually meant to take the pressure of the new propellants without blowing up in your face. This would be at around the 1880-1900~? period, with rifles such as the Norwegian/Danish/American Krag-Jørgen, French Model 1886 Rifle, and the German Gewehr 98, and British Lee-Enfield coming into play.

From what I can dig up, the original smokeless cartridge for the Krag-Jørgen reached 40,000 psi of max pressure when fired. Cartridges on the other military rifles of the time would had been similar, or possibly even higher, from what I gather. Combined with longer "high" in duration of pressures, the old wrought-iron barrels and mild steel barrels just couldn't handle these pressures safely. The Lee-Enfield was the direct result of the British military's need to "bulk up" the previous BP-loaded Lee-Metfords for smokeless ammunition.

Question is, what grade of steels did they exactly find to use? At first, I thought it might had just been a medium-grade carbon steel, like 1045, that was heat treated to increase its tensile strength. But after looking at charts, I started to doubt that a plain carbon steel can handle that sort of pressure without either being too brittle after a heat-treat or too soft if used normalized/annealed. Correct me on this if I'm wrong.

4140 would be the typical steel grade used for modern firearms. It has a yield strength around 90,000 psi after heat treating, giving a huge margin of safety for whatever ammunition used today. I'm basing most of my assumptions around this number, but I guess whatever used back then might had been somewhat lower.

It couldn't had been a chrome-moly alloy like those used today, these weren't developed until the early 1930s. Which meant everything shooting in the trenches of WW1 was using something else as well.

Winchester in 1895 looked for something to smokeless-proof their Model 1894s, they came up with a nickel-steel alloy, 5% nickel content, and it proved strong and tough enough for the 30-30 and 32 Special rounds. They also messed around with a 1-2% low nickel "extra" steel for easier machining, but it couldn't stand up to erosion from shots so it was abandoned. No hard numbers on the tensile strength on this 5% nickel-steel, but a chart from an INCO publication shows a 5% nickel- 0.17% carbon steel, normalized and temper, gives a yield of about 55,000 psi. Nothing on heat treated, but a different chart showed that 2-3% nickel-steel could be water-quenched to above 85,000 psi of yield strength, 110,000 psi ultimate tensile strength.

Butttt, on the same page I got all this info, stated that the American military wasn't using nickel-steel in their own rifles until 1927. So again, what the heck were they using? Also, it seemed Winchester attempted to make stainless steel barrels in the 1920s, but again failed because of machining and cost issues.

There was a forum post stating that the early Springfield 1903 rifles might had been made from maraging steel (which is another nickel alloy, but that contradicts with the earlier finding), iffy confirming this one.

My last bet would be a manganese-steel, since maganese was already well known and needed for the Bessemer-process steelmaking. Hadfield steel was used for making British helmets, it could be casted without worries about air-pockets or blow holes because of its manganese content (13%) - it increases impact and wear-resistance of the steel without affecting toughness. Problem with this alloy is an apparent difficulty in machining, and the inability to soften the alloy by annealing. Invented in 1886.

Thoughts?

 

[arftist]

Yeah, two thoughts. 

The pressures are not directly comparable, which is why nothing is making sense to you. You are not even comparing apple to oranges when comparing pressures this way. 

Second; you are not taking into account other dimensions. So, a tube with a 5/16 i.d. and a wall thickness of 5/16" will hold how much pressure if the material has a tensile strength of 90k pounds? 

 

Since I am too lazy to do calculations before coffee I refer you to the 6th line in the following chart; http://www.tubeweb.com/Stainless-Steel-Tube/theoretical-bursting-collapsing-pressures-for-pipes.html

Where we discover that a tube with a strength of 75,000 pounds tensile with a bore of just under 5/16" and a wall thickness less than 1/8" has a burst strength of well in excess of 30,000 PSI. Double the wall thickness to less than a 1/4" and the burst pressure is well in excess of 44,000 psi and add in the higher tensile strength of 1045 vs s.s. and I think you can see why 1045 is more than sufficient. 

Clear as mud? 

 

Edited February 24, 2015 by arftist

[HWooldridge]

I found this in a search related to the 30-40 Krag:

"From Brophy's book pages 32-33, there is a description of substandard steel received in fiscal year 1894. The spec for the steel at the time was ultimate tensile strength 100,000 psi (100ksi); yield strength 60 ksi. Max C 0.5%, Mn (max) 0.6%; Si (max) .16%, S (max) .034%, P (max).045%. The report also indicates experiments were being conducted with nickel steel to obtain 80 ksi yield.
"Hatcher's Notebook" 1st edition pg 225 & 226 confirms barrels of both Krags and 03s were made of Ordnance Barrel Steel, and the "double heat treated 03s) were made of same Springfield Armory Class C steel as the Krag was. Note that Hatcher's chemical compositions are slightly different than the 1895 report quoted by Brophy. For high numbered double heat treated 03 receivers, of course, the heat treatment was different."

Another notation about Krupp steel.

Quote: 1905 Krupp Chrome Nickel Steel Brand D

0.5% Carbon
3.26% Chromium
0.16% Manganese
1.26% Nickel
0.04% Phosphorus
0.11% Silicon
0.03% Sulphur

Tensile strength was near 106.5k lbs
Elastic limit near 92.5k lbs/in^2 End quote:

Both spec at 50 points carbon but the German steel has the addition of nickel and chromium.  It looks similar to what we might call an AISI-SAE 3xxx "nickel steel" today - although not exactly the same composition.

[ThomasPowers]

Coming at it sideways did the weight/length of the weapons change indicating using more steel to deal with increased pressures?

[Iron Song]

Great findings Wooldridge! Looks like normalized 1045 would had been pretty close to what Brophy stated. Searching up "Ordnance Steel" comes up with a few shotgun forum posts that state around the same tensile and yield points for Remington products at that time period. So I guess it was just a medium carbon steel after all?

That finding on Krupp steel is eye-opening, it seems they were getting close to a chrome-moly with chrome-nickel alloys by the start of the 1900s. This kind of steel would been needed for the cordite-firing big-guns being produced for battleships at that time.

--------------------------------------------

Hi Arftist, understand that the maximum pressure a cylinder walled "pipe" can handle is related to its maximum tensile strength. There comes a point in a non-autofrettage or compression pre-stressed pipe or gun barrel where adding more thickness does not increase the pressure limit of the pipe or barrel (this max thickness is stated around x1.5 diameter of bore by one of my sources). Since the magnitude of the stress decreases as it radiates away from the inner wall of the pipe, ultimately the inner wall would start to at least fracture or deform once the pressure goes beyond the yield or failure point of the material. You can see this in your own link you posted, notice how all the pressures listed never exceed the 75,000 psi of the TP304 stainless steel used? The dimensions you stated could actually handle even greater pressures than the 33,000 psi, the manufacturer is using Barlow's formula to calculate pressures, but this formula gets a bit inaccurate for thick walled cylinders with OD:thickness ratios greater than 20 times. Using Lame's equation, the pipe could actually handle upwards of 56,500 psi before failure, but again see how it doesn't reach the 75,000 psi limit. Auto-frettaging and pre-stressing was invented to get around this limit for large-caliber guns, and I suppose button rifling does the same benefits for small-arms.

Lame's equation for hoop stress (interior pressure only) states:

Pressure = Tensile Strength x (Outer Radius^2 - Inner Radius^2) / (Outer Radius^2 + Inner Radius^2) --- Notice this gives us a fraction in the radius portions which is always <1, meaning the maximum pressure for a given material can never exceed its tensile strength.    

Also, the 75,000 psi limit denotes the material's ultimate tensile strength, but the tensile strength of TP304 stainless is only around 30,000 psi. This means the pipe or tube would start to stretch permanently well before the 75,000 psi burst pressure is reached. For a gun, repeatedly firing at above the "operating pressure" (which is determined by yield point of material) would stretch the bore of the barrel, up until it starts to crack or the bore becomes too big to engage the bullet. This is why a high yield strength is needed, since we don't want a barrel that stretches appreciatively and we want a margin of safety (don't we?). Of course for artillery guns of the period, stretching was expected (some of the firing pressures were right at where the yield point is) and dealt with by retiring or refurbishing pieces once they past a certain service life. Part of this question is to answer how much stretching for gun barrels was tolerated. Hope this clarifies things.

By the way, does anyone have any data on quenched/tempered 1045? I can only find find annealed or normalized.

-------------------------------

Thomas, I think weight only became an issue with the big naval guns. The British 12 inch Mk VIII weighed about 46 tons, this gun used wire-winding to reinforce the barrel, and the weight was enough to cause barrel to droop over time since it wasn't exactly rigid with its construction :/ . The military loves to flirt with danger.

Edited February 24, 2015 by Iron Song