doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Metallurgy Question

My favorite hammergun circa 1890 came to me more than 25years ago with a left hammer repair to its nose (you could see a weld line). It held up through a lot of shooting over the years. About 2 years ago the repair suddenly failed with the nose flying off into space and never recovered. The craftsman who repaired it, in his words, dripped weld onto the hammer to create a new nose, then shaped it and engraved it to match. That repair lasted about a year when I noticed a crack developing along the repair line. A new repair consisting of filing to the bottom of the crack and laser welding the void is being done.

When the first failure occurred, I could see that the metal structure of the hammer was very coarse and crystalline in appearance. It reminded me of how the broken pot metal of my cap gun looked when I was a kid. My question is what can be done (if anything) to rearrange the metal structure so that it will be strong again and not fail in the future? Would soaking the hammer at high heat for a period of time allow the metal structure to rearrange itself to a more stable form? What should be the final hardness target for the hammer? I assume that the unaffected right hammer might be in the same shape internally and benefit from a similar treatment if there is one.

I appreciate any ideas members might have.

Thanks in advance.

Wally

Wally ;

You omit the origin of your hammergun, but I suspect it is the UK. "rearrange the metal structure so that it will be strong again and not fail in the future" is a Star Trek option not yet available.

Buy two new hammer blanks and fit them or have them fitted. See below suppliers.

Stephen Howell


https://www.peterdyson.co.uk/acatalog/English_guns_and_rifles_hammers.html

https://www.blackleyandson.com/acatalog/English_Flat_faced_Percussion_Hammers.html

First off, unless something has changed, there are no bona-fide metallurists here. And none of us can know the original composition of your broken hammer, why it failed, or exactly how it was repaired in the past.

Welding produces a Heat Affected Zone (HAZ) around the weld that can vary according to the temperature and welding process used. Stress relieving or annealing can even out or change the microstructure, but rehardening or retempering steel of unknown composition involves a lot of guesswork that may or may not be successful.
Here is a brief summary of welding metallurgy that may give you an idea what you're up against:


"Welding metallurgy focuses on the changes that occur in steel's microstructure and properties during and after the welding process. This includes understanding the behavior of different steel types, the impact of heat on the base metal and weld pool, and the formation of the heat-affected zone (HAZ). Welding metallurgy is crucial for ensuring the strength, toughness, and corrosion resistance of welded joints.
Key aspects of welding metallurgy in steel:
Microstructure:
Welding alters the microstructure of the steel, particularly in the HAZ, where the base metal is heated but not melted.
Phase Transformations:
Heat causes phase transformations in steel, such as the formation of ferrite, austenite, and martensite, which can affect the mechanical properties.
Weldability:
Different steel types have varying weldability, depending on their composition and microstructure.
HAZ:
The HAZ is a critical zone where changes in microstructure can lead to defects like cracks if not managed properly.
Post-Weld Heat Treatment (PWHT):
PWHT can help relieve residual stresses, modify the microstructure, and improve the mechanical properties of the weld.
Weld Metal:
The composition and properties of the weld metal, which is a mixture of the filler metal and base metal, also play a role in the overall weld quality.
Defects:
Welding can introduce defects like cracks, porosity, and inclusions, which can be minimized by controlling the welding process and selecting appropriate materials.
Factors affecting the metallurgy of welded steel:
Base metal composition:
The chemical composition of the steel, including the presence of carbon, alloying elements, and impurities, influences its weldability and the resulting microstructure.
Filler metal:
The composition of the filler metal used during welding can also affect the weld's properties.
Heat input:
The amount of heat applied during welding affects the size of the HAZ, the cooling rate, and the resulting microstructure.
Welding process:
Different welding processes, such as shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and gas tungsten arc welding (GTAW), can produce different microstructures and properties.
Cooling rate:
The rate at which the weld cools after welding affects the grain size, phase transformations, and residual stresses."

If the last repair was done by "dripping molten metal" on the end of the broken part, and then reshaping it, I can understand why it failed. If your new laser welding repair is properly done and stress relieved, it may stand a better chance. But I'd be taking a wild assed guess to suggest how it should be hardened. Nothing ventured, nothing gained, so hopefully it holds up for a while. I have an 1850's vintage percussion boot pistol that has a broken hammer nose. I plan to attempt a repair by TIG welding a piece on. I will probably anneal it by burying it in the coals of a wood fire for hours, slowly cooling, and then either rehardening and drawing, or just case hardening. But I know it may fail and I'll end up making a new hammer. You might want to keep your eyes peeled for a suitable replacement.

As for your other unbroken hammer.... if it ain't broke, don't fix it.

Heat treating changes metal microstructure (you'll need to cut & paste the link)
https://jfheattreatinginc.com/2023/08/the-science-behind-metal-heat-treating-understanding-microstructures-and-material-properties/#:~:text=Heat%20treating%20involves%20inducing%20phase,austenite%2C%20and%20pearlite%20to%20martensite.

Metal can be re-heat treated
https://astforgedwheels.com/heat-treating-metals-full-overview-of-the-process-types/

External hammers
https://www.practicalmachinist.com/forum/threads/gun-hammer.254427/

I would go with bushveld's advice, and that of an expert machinist & gunsmith

It is interesting to learn obscure facts about the gun trade from gunmakers who were there during the classic period of gunmaking in the UK, and one of them was the late Jack Rowe who entered the trade just after WWII as a lad. Others of the time of Jack Rowe such as Malcolm Cruxton and Peter Dyson are still plying their skills. Peter is approaching 90 years old. I think that Malcolm and I are about the same age 83.

The obscure facts of how some parts of double barrel shotguns were made and from where the materials came from to make them was commented upon by Jack Rowe during a conversation I had with him in 1998. We were discussing how that some double barrel shotgun trigger guards would eventually turn a plum color, no matter how you blacked them. Jack explained the reason of this. He said that the lads in the gun trade such as him would sweep the floors of the gun making shops gathering the iron and steel filing along with the dirt and grime and collect all this iron/steel/dirt mess into a bucket or barrel. Later the junk man would come by and purchase the barrel or iron/steel/dirt filings and the money the shop received was beer money for the shop workers. The "bucket of grime" was used as the basis for melting and forging then producing strips/bars of "steel" from which trigger guards and other parts were made. Not all guns trigger guards were made of this junk steel but the less expensive ones were.

Wally;

It just may be that your hammers originated from the filings swept up from the floor of the shop and its structure can never be any better than what it is now.

Stephen Howell

Thanks to everyone for their reply. I appreciate all the ideas and comments.
w

Jack Rowe may be a London trained gunmaker, but his explanation of why certain gun parts turn a plum color when blued or blacked seems implausible at best, and based upon pure conjecture. It is a quaint story, but likely has zero basis in fact. I'd hate for this sort of probable misinformation to become accepted as fact, and then endlessly repeated on the internet.

By the 1870's-1880's, steelmaking in England was pretty advanced, and among the best in the world. They were producing over half of the world's steel production, and the days of crude and inefficient processes were over. They knew how to make large quantities of quality steel in such an efficient manner that the price of new manufactured steel had dropped to around 4 Pounds per ton, from over 50 Pounds per ton prior to the invention of the Bessemer Converter in 1856. By 1868 a Metallurgist named Robert Muchet had developed the processes to effectively purify steel, and to then add certain elements to get the desired alloys of steel. They understood the chemistry and were well past the time when it was a seat of the pants affair that produced a sometimes unpredictable result.

Steel soon became one of the most recycled materials on Earth, and it still is today. All manner of steel may be collected as scrap. It is then segregated to the best practical extent, and then added to new steel produced from iron ores of varying quality and chemistry. But there will almost always be a certain amount of contaminants in the scrap, and most of those impurities will be removed during the steelmaking process, or end up floating to the top, so it ends up in the slag ladle as a waste byproduct. Consider the baled and cubed scrap automobiles we see on their way to a steel mill. They are mostly steel of different alloys, but they also contain plastic trim, vinyl, broken windshield glass, aluminum, and perhaps worst of all, copper wiring. Copper contamination is one of the worst and most difficult to remove contaminants, and is best physically removed to the greatest extent possible, and otherwise diluted by the addition of non-copper bearing scrap.

The best explanation I have heard for steel turning a plum color during or after the bluing process is that the steel may have a high nickel content. Gunsmiths have noticed that certain guns containing nickel alloy steel, such as 1930's Winchester Model 12's are prone to this malady. Post 1964 Winchester Model 94's used a different alloy for their receivers, and hot bluing it resulted in a red color. The solution was to first iron plate the frames. Polish that iron plating off during refinishing and you've got problems. I have a Mauser Model 66S rifle in nearly unfired condition that has a plum colored receiver. Everything else is a nice high gloss blue-black. I'd say there is zero chance that it was made from dirt, garbage, filings, and machine chips swept up in some factory. One problem with steel is that all of it is is an alloy of some sort. You can't just select a piece of steel by looks alone, because the chemistry and qualities may be very different due to the elements alloyed into it. Some steel may be hardened for various cutting tools or springs, while another piece that looks identical may not take hardening at all. Some steel welds better than other types. Some wears better and some is more or less corrosion resistant. There are specialty steels that are best for laminated electric motor armatures and transformer cores, because they produce less Eddy currents under the influence of magnetic fields. There are some very specialized steels that contain no radioactivity, since all virtually steel produced after the atmospheric testing of atomic bombs contains traces of radioactive contamination. It all eventually ends up as scrap, and it is all called steel.

It seems far more likely that the trigger guards and other gun parts that turn a plum color when blued or blacked is simply due to use of an unsuitable alloy. The gunmaker needed steel and bought steel... but it wasn't the best steel for gun parts that would be blued or blacked. It would take metallurgical testing by a good Met Lab to know why certain trigger guards, etc., may turn a plum color.