Steel Hardness

[Dwight Gruber]

Looking at witness marks has brought to mind a question which I hope the Lugersmiths, refinishers, and other machinists here can answer.

Judging by the difference in the "flow" of steel at the edges of witness marks, it appears that the barrel steel of WWII guns may be softer than the steel of the receivers to which they are mated. The nearly identical-appearing edges of the witness marks of Imperial-era Lugers implies that the barrel/receiver steel hardness of these guns is much closer to being the same.

Is this borne out by experience? Does anyone happen to have documetary evidence concerning the steel hardness of different Luger parts?

--Dwight

[Weissen]

It would be interesting to put a Luger up in a Rockwell hardness machine and run a few tests.

In my experience barrel steel is usually much softer than the steel that the action is made from.

Soft steel is easier to machine = faster manufacture = greater thoughput = less cost.

Makes sense really when there is no requirement for a really hard steel for the barrel in the first place as it only gets the occassional soft coppper/lead slug fired through it.

Cheers.

[RockinWR]

Dwight,
* As you may remember, a post on "K Date Luger Hardness" ran 2/17-2/25/03. Thor (Member #3) started the thread which offered some values for the receiver and the frame components. Agreed, it didn't mention barrel hardness. Seems the barrel's shoulder O.D. can be sometimes larger than the receiver's resulting in a deeper line on the barrel to get a line to show on the receiver. May just look like the barrel's softer.

Weissen,
* FWIW: The barrel chamber has to withstand the same pressure as the receiver and breech block. Hence the proof mark on each of these 3 components. I'd guess the barrel would be as hard as the receiver IMO. Been wrong before...maybe that's why we don't see the number of hardness dimples on the barrel O.D. like we do the rcvr./breech link....not to mention appearance considerations.
Respectfully,
WR

[Thor]

Barrels seem softer to me than the receivers on most Lugers. The barrel metal (and sideplate) usually rust blue (rust better) more quickly. The hardest parts usually are ejector, extractor, receiver and breechblock and perhaps the toggle links too. Frame, barrel and sideplate seem softer to me.

[Weissen]

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"> The barrel chamber has to withstand the same pressure as the receiver and breech block. Hence the proof mark on each of these 3 components. I'd guess the barrel would be as hard as the receiver IMO. Been wrong before...maybe that's why we don't see the number of hardness dimples on the barrel O.D. like we do the rcvr./breech link....not to mention appearance considerations. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Steel does not need to be hard to resist pressure, rather, it needs to be tough. These two properties are kind of like opposites. eg Rubber is tough but not very hard, glass is hard but not very tough.
Barrels don't need to be hard (more ruber like)as there is no requiremnt for wear resistance except for the occassional soft bullet going up the spout.
Actions on the other hand require resistance to wear and abrasion hence the need for extra hardness (more glass like)in this area.
Hardening steel costs money 1. for the treatment itself 2. for the after treatment testing.
It would seem strange to me that you would harden something i.e. spend money, on something that didn't require it and slowed your manufacturing process down to boot.
I'd bet that Luger barrels are machined from raw non-heat-treated tool steel billets with no post manufacturing heat treatment either and with just a quick polish and rust blue to finish off.

Anyone got one of those hardness testers?

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[ViggoG]

Weissen,
No hardness tester needed.
The most frequently used steel for Gun Barrels of that era was "1137 free machining steel", a very soft steel usually in the range in Rc 28 to Rc 34 which was the best condition for cutting very thin brittle chips which broke into small scraping like particles, Primarily due to the addition of 0.25 percent lead.
The toughness was comparable to hot rolled steel plate, or hot rolled structural steel, which happened to have much "rolled in scale inclusions", and thereby, very poor machining characteristics, as far as finish was concerned.
Because of the extremely small space available and small cuts allowed by such, the steels had to be of a variety that had a low resistance to cutter penetration and the production of very smooth surfaces without the need of polishing or lapping.
These quality was the basis for the formula of the steel to attain these qualities.
With the Post WW-2 discovery of Sintered Carbide tooling the use of single point and broaching methods rapidly changed to Button Rifling of barrels and allowed the use of higher strength steels of 3100 and 4100 series steels.
Luger barrels being basically of Pre WW-2 design were of the steels of the 1137 series characteristics.
ViggoG

[ViggoG]

Thor,
You are quite correct in your observation that the harder steels are slower to take blueing.
This is caused by the finer crystaline structure of the higher carbon steels and the higher concentration of finer carbon crystals that are trapped in the crystal matrix of the steel, which inhibits the penetration of oxide producing chemicals. And the carbon being high on the replacement scale, steals some of the blueing chemicals for itself.
It can be compared to pouring water on cinder blocks and bricks, the finer bricks allow much less water penetration.
(Please, Excuse the poor comparison)
ViggoG

[Weissen]

Oh...1137...Ok (scratches chin and drifts back into the hazy days of apprenticeship and mis-spent youth).
So the barrel (and action?) material is a sulphurised free maching mild steel that could be heat treated if required, unlike normal mild steel.
So the Luger manufacturers of old had the benefits of an easy to machine yet relatively tough steel giving good surface finishes with the added benefit of it being able to be heat treated if needed, all in one type of steel.
Clever people those Germans.....

Cheers
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[ViggoG]

Weissen,
I think that it would be a bit hasty to credit the Greman Krupp Steel Works with the invention of 1137 steel as I understand it this steel is primarily a Open Hearth type of steel which was primarily an American steel product of Pennsylvania.
As I recall the German Krupp Works were using the Bessimer process.
I could be wrong there I'm just guessing with a "78 year Old's Memory".
ViggoG

[Dwight Gruber]

OK, barrel steel and receiver steel of two different hardnesses. I have observed that barrel flanges are sometimes not exactly the same diameter as the bottom of the receiver they are mated to--more often larger than smaller, it seems.

Could it be that, under these circumstances, there are Lugers whose witness marks simply, physically, -cannot- be struck by a single blow of one instrument?

--Dwight

[ViggoG]

Dwight,
I seriously doubt that the flange diameter would vary more than .25 mm or about .010" this is considering that the tolerance would be in the range of "+ or - .005" or "0.1 mm" which is about standard for non critical mating surfaces.
This amounts to about the thickness of two sheets of high grade writing paper.
Barely perceptable to the feel of the finger tips.
It is probable that the diameters would be set at a figure that would make the largest allowable dimension of the Barrel flange to be equal to the smallest allowable dimension for the Breech face, this would give the best appearance to the joint.
ViggoG