doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Disaster struck yesterday

First & foremost I realize Dr Gaddy, has studied this much more than I & has much greater knowledge of the subject than I. However a few of his statements do not stack up with my limited knowledge. "If" quenched below the critical temp, carbon steel does not harden, so the only hardness gained is from the increased amount of carbon. RE a piece of low carbon steel & one of high carbon, both in the annealed state, will have different hardness. The high carbon will be harder, but not to the extent of the case hardened gun frames I am familar with. As far as I can tell the makers "Did" quench from above the critical temp. However one other thought on this & perhaps Oscar for some reason missed it, or perhaps I am not underestanding what he is saying. 1400°F "Is" above the critical temperature for "High" carbon steel, but below it for "Low" carbon steel. This from "Machinery's Handbook". Critical temp varies according to the % of carbon, higher %'s having a lower CT than low %. It would seem to me Oscar was quenching at a temp above the critical temp of the case but below that of the core. This however is not what I understand he was saying, it seems he was saying when he dropped the temp to 1400° he was completely below the critical temp. This "Between Temp" may well be the secret of his success. I had incidently started a PM discussion of this matter with him, but "Unfortunately" too late. I hope everyone takes this in the right light, for I certainly had great respect for Oscar & his knowledge & abilities.

Thanks for everyone's interest in this. I obviously won't name the person who casehardened it ( bone and charcoal ) as there is no proof that his process was flawed and I won't harm a man's reputation based on a possibility. I've been moaning about this for several days now and as my wife keeps reminding me, no one got hurt and she even told me to buy a new gun. I closely examined the fired hulls after this incident. Absolutely no difference that I can see. No evidence of excessive pressure. I know anything can happen but I am as confident in my reloading process that I can be that nothing was wrong with those shells. And I also examined numerous other shells that were loaded in the same batch and not a one of them look out of place. The barrels appear okay and maybe I can part out some of the gun at some point and recoup some of my loss. Thanks for everyone's imput.

The Gunsmith said wall thickness was not the cause of the barrel failure of the LC.
He did say he had repaired some guns that the owner had used a case color kit or "do-it-yourself" case color system. I won't mention the seller here.
Deltaboy

Miller,

From a metallurgical perspective, you are correct. Not sure what Dr. Gaddy was thinking of when he wrote this. I'll have to give it a try one of these days and see what structure is formed - likely something called bainite (named for Edgar C. Baine, the director of research for U.S. Steel.) Softer and tougher than martensite or tempered martensite, but harder than a normalized medium/high carbon steel. I'm not sure I would call it "file hard", however. Forming the bainite depends almost entirely on the quench rates employed.

I just re-read Oscar's posts that I had re-posted earlier in this thread. (Your partial quote, Miller, looks to be from a different one of Oscar's posts -- not better, not worse, just different.) It looks to me like he was saying, as you infer, that he quenched from a temperature above the critical temp of the case, but below that for the core. He always did a careful pre-anneal.

He also had a very precise temp controller that he built, precise within a few degrees.

Gil - Case hardening and the coloring associated are two different processes, as I understand it. You can case harden without a trace of color and you can color without hardening; the fact that are often combined has lead to the belief that they are one and the same process. The trick going on here seems to be that some of the better technicians are using the lower temperature coloring process without affecting the hardness. If you are familiar with tempering colors, you will know that color forms on polished steel at temperatures way below the critical temperature. So, in theory, color can be restablished without warpage, shrinkage or softening of the reciever.

If I understood OG correctly, he recommended quenching from a temperature just low enough to avoid martensitic formation; he was trading some hardness for dimensional stability. The case he recommended was much harder than low carbon steel surfaces, but not as hard as a martensitic surface. In gun service conditions, this was a very good trade.

I guess the main question to be answered here is "What is the Purpose?" of the case hardening. "If" it is unnessesary for the integrity of the gun, then it is of little consequence, whether it is "Cased" or "Colored". On a piece of heat treated carbon steel hardness starts to be drawn (tempered) @ about 300/350°F & the higher it is heated the more it is drawn (Softened). When a tempering temp just below the critical temp has been reached it is "Almost" as soft as in the fully annealed state. My personal opinion is the makers put that "Hard Case" on their guns for a purpose, I don't want it destroyed on "Mine". My questions I had for Oscar, which unfortunately did not reach a culmination, was that while he stated he was quenching from a point below which martensite is formed, the temp he listed would have been above that temp, for the high carbon "Case, Only", although the low carbon core would have been below it's critical temp.

Deltaboy,

Regarding your failed LCS barrel: There is a very professional project underway to characterize, and understand much more thoroughly, antique barrel steels. Zircon (VP of metallurgy for an internationally-respected producer of very specialized high strength tubing) is the principal investigator, and Chuck H and I are lending a hand. Around 3 dozen bbls will be characterized metallurgically, for tensile strength in two axes, and in key cases chemically. We aren't releasing results piecemeal, but some findings made to date will be very interesting. I tell you this because as new participant, you may not have seen considerable prior traffic concerning it.

Failure analysis is not the project's purpose, but in limited, very relevant cases Zircon is able to determine failure modes and likely causes. That is the case for the two Parker bbls, one steel and one Damascus, deliberatly tested to destruction by Sherman Bell and Tom Armbrust, which have been about 80% processed to date.

We have, and will analyze another LCS homogeneous steel bbl, similar to yours, with a very similar-appearing failure. Rabbit has seen a third, also.

Because these three failures are of a very uncommon type and are so similar, there may be a common (systematic) cause. To determine this, we would appreciate your donation of the failed portion plus about 8" toward the muzzle, and an inch or two toward the breech, if possible. (I understand that you will probably have the failed tube replaced.) This should allow Zircon to determine if it, and the one we already have failed the same way, and probably identify an underlying defect if one exists.

I'm guessing that your gunsmith will probably monobloc a new tube into the breechmost several inches of the failed tube. If so it may be most convenient to send the entire forward portion he will cut off.

If you need more info, I'll provide it. If you can make the donation, PM me and I'll provide shipping instructions.

Thanks for considering this!

Fred, I have PM'd you. I think!

Fred, I have lost the business card of the Roanoke gunshop I visited in summer 05. Gun definitely an LCS w/ steel barrels and same longitudinal rip. I don't think there'd be much buyer interest as I don't believe the action bar indicated a higher grade gun.

What salutary effect does case hardening action bars have, Miller? I've heard postulated a bimetal spring effect and also resistance to abrasion, nicks and dents.

jack