"Metalurgy" Notes

[Bruce_in_Oz]

I have not yet seen any original documents that precisely describe the process(es) of heat-treating the bolt body of any Lee Enfield.

There would have been several such processes, as all four bearing surfaces of the lugs should have been sufficiently hard to minimise wear, but not to be brittle.

The main "body" of the lugs should have been "tough" to support this hardened skin and , particularly, to have some elasticity to cope with the forces transmitted during the shock of firing.

If this process were not done correctly, especially in the days before pyrometers etc, and given that, to the end, SMLES were made from various grades of CARBON steel, (NO "fancy alloys" allowed except under very special circumstances), the potential for "over-cooking" the metal was very much present.

The bolt body started out as a straight bar of steel and was FORGED into an "L" shape before being machined to final form. The forming of the long "tail" on earlier LE bolts must have been REAL fun!

The 1903 Spec (S.A. 242 (1903)) for the Mk1 SMLE states that the bolt body was made from "56A42 Crucible steel, oil-hardened, tempered and browned".56A42 is actually a low-carbon (0.67 to 0.77") steel and the stuff used in the bolts was to have vanishingly small traces of Manganese, Phosphorus, Sulphur and Silicon.

The 1938 Spec (S.A. 462P) specifies "D.D.8" steel, oil-hardened, tempered, polished and browned (blued" or oil-blacked.Both recipes seem to rely on selected Swedish ore for the base material. One source of problems is in the coal used to produce the coke in the furnace. Some coal contains significant traces of Phosphorus and Sulphur, neither of which are desirable.

Interestingly, at some, as yet unknown date, Lithgow started using what I suspect was "electric" heating for the heat-treating of the locking shoulders in the body. If you are lucky enough to have a "MINT" Lithgow SMLE (usually WW2 or later), or one of the WW2 XP carbines, take a close look at the exterior of the left and right sides, just behind the locking shoulders.

There you should find a small circle of discolouration and surface distortion, a bit like tiny "spot-welding" scars. I understand that these marks were left by the application of Carbon electrodes that delivered the current to "spot" heat the metal before quenching.

Thus, the remainder of the body would be in a "toughened" (strong, but NOT brittle) condition, and thus able to withstand the "shock load" of firing.

Later "FTR" activity seems to erase these little heat-treatment marks.

Information

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[jmoore]

The 1903 Spec (S.A. 242 (1903)) for the Mk1 SMLE states that the bolt body was made from "56A42 Crucible steel, oil-hardened, tempered and browned".56A42 is actually a low-carbon (0.67 to 0.77") steel and the stuff used in the bolts was to have vanishingly small traces of Manganese, Phosphorus, Sulphur and Silicon.

I'm guessing that 0.67 to 0.77 number is "percent"? Not what I'd call a "low carbon" steel! That much carbon would put it well into the "high carbon" classification. Given the ductile nature of most SMLE receivers, I would have to guess that the heat treatment was somehow localized by slowing the cooling rate away from the locking surfaces. Spot hardening or induction hardening those areas would be later innovations, I'm thinking not generally used before the 1920s, but I am making a SWAG based on examples of such tech seen elsewhere.

[Bruce_in_Oz]

"jmoore":

Thanks for the reply and corrections.

I guess it is fairly obvious that I am NOT a metalurgist; just an enthusiast with an enquiring mind.

[jmoore]

The reason I asked is that it's not hard to misplace the decimal point if you are not familiar with such things. It's barely conceivable that the numbers were 0.067 to 0.077%, which would be a very low carbon alloy. But highly unlikely! Too close a control, for one thing. And without other strengthening elements it would be way soft and virtually "un heat treatable". 6.7 to 7.7% is right out as well.

Like lots of things, there's specifications within specifications. What would be the next step would be to find is any documentation of the oil quench specs for this alloy, and any processing notes for the receiver. (Partial quench to a certain depth, or clay masking, etc.)

[Detroit-1]

Interestingly, at some, as yet unknown date, Lithgow started using what I suspect was "electric" heating for the heat-treating of the locking shoulders in the body. If you are lucky enough to have a "MINT" Lithgow SMLE (usually WW2 or later), or one of the WW2 XP carbines, take a close look at the exterior of the left and right sides, just behind the locking shoulders.

There you should find a small circle of discolouration and surface distortion, a bit like tiny "spot-welding" scars. I understand that these marks were left by the application of Carbon electrodes that delivered the current to "spot" heat the metal before quenching.

I have a all matching non FTR'ed 1945 Lithgow that on the left side behind the charging bridge is the circle that you are talking about.

[303Guy]

My 1944 Lithgow has them. They look like punch marks with a 'disturbance' around them. Mine is a Sportco 25/303. Thanks for the information. I would like confirmation on the steels used in later Lee Enfields including the No4. I've been told that the American built No4's used a stronger alloy than the British and these alledgedly withstood 7.62 NATO proof loads better than the Brit made ones.

[Peter Laidler]

Your last sentence is yet another myth 303guy. What we in REME circles call 'a load of old boll-..............' I'm struggling to find the word I'm looking for again! They were all made to a strict criteria, made to our spec, for us! And if any of your old shooting friends tell you that the Indian 7.62's were also made from a tougher steel, then tell them that that is also a load of old whatsit too.

Can any of you less refined forumers help me find these words that keep slipping from my memory banks. Maybe my lingustic skills are fading now that I have left an Infantry/REME workshop environment

[Thunderbox]

(Quote PrinzEugen) "Personally I've been watching a glut of metal obsessed postings on milsurps of late with something of a feeling of deja-vu, wondering if some of our old friends have returned again."

[muffett.2008]

Yep Pete, we have done all this recently with the same bloke.
303Guy, reread those old posts, what you were told then is still pertinant a month later.
I am beginning to think there is a problem with Kiwi's(not you 5th.) it may have something to do with a shortage of sheep.

Back to Bruce's original, in my files I have the Lithgow SAF requirements for all metals, but this is the one you are interested in.Attachment 46221

Just ask if you want the rest.

[5thBatt]

I am beginning to think there is a problem with Kiwi's(not you 5th.) it may have something to do with a shortage of sheep.

No worries, plenty of sheep around this area