Regarding the welding of quality Wrought Iron:
Please bear with me as Iam on a cursed tablet at the moment.... this post will be edited as I go with links and etc added as I am able ....
True wrought iron is very low carbon with slag threads that act like fiber. It is very rust resistant,
Thus the old ML barrels don?t rust as fast with real BP... the slag produces a natural flux when hammer welded , and often inexperienced welders see the flow slag and think they are puddling metal when they are not ....
See here
https://www.esabna.com/euweb/oxy_handbook/589oxy16_10.htmWrought iron, widely used a century ago, is no longer made in the U. S., but you may be called on to weld it, sincea great deal of wrought iron piping is still in service.Wrought iron has properties much like those of mild steel, but is chemically and structurally much different. It isessentially a mixture of rather pure iron and a slag made up chiefly of iron oxides and iron silicates. The slag isdistributed through the iron in the form of very fine particles which have been stretched, by rolling, into threads orfibers so small that there may be 250,000 or more per square inch of metal cross-section. This structure not onlygives the metal high ductility, but also improves its corrosion resistance.You can weld wrought iron with any good low-carbon steel rod (such as OXWELD No. 1 H.T.) and without usingflux. However, the iron component, which is virtually carbon-free, melts at a higher temperature than carbon steel,while the slag component melts at a much lower temperature. The slag will melt first and give the surface of thewelding vee a greasy appearance. With most base metals, this greasy look is a signal that the metal is ready forfusion with the filler metal, but in the case of wrought iron this is not true. Considerably more heat must be appliedbefore the metal really begins to melt.In welding wrought iron, you can concentrate the flame more on the rod than you should when welding steel, andlet the puddle build up to a fair size before moving the flame from side to side to fuse the base metal with thepuddle. Try to keep the motion of the rod to a minimum, and to melt as little of the base metal as possible.
Wrought iron lends itself to Gas brazing , which is my preferred method of repair... and Gas welding if you know how... Electric welding works fine if you choose the right filler, and have practiced.
For a tiny part like the M&H top latch, I suggested TIG since TIG seems to lend itself to finer work, as opposed to the Farmers Friend, His giant Lincoln welder with the 1/4 inch rods...
I myself would be inclined to cut off the top strap at the middle-ish, fabricate a new tongue and groove latch thingy and nickel silver braze the new latch and top strap on . That would be easier FOR ME to do than rebuild and remachine the latch thingy in place. But that?s because I much better at soldering, high temp soldering, and brazing than I am at welding.
BTW, a nickel silver brazing joint, when properly done , reveals only a thin silver joint, which is stronger than the base metal, whether iron, mild, or high carbon steel.
From welders, here are some advice...
from here
https://www.iforgeiron.com/topic/6997-what-electrode-to-use-on-wrought-iron/There is a great discussion regarding how/what rod to use etc... to repair large immovable load bearing hinges for 600 pound wrought Gates...
From another fellows excerpt from a book:
Snip?
Wrought Iron, It's Manufacture, Characteristics and Applications" James Aston and Edward Story
"In welding WI by the electric arc process the best welds are produced when the welding speed is decreased slightly below that used for the same thickness of soft steel. This procedure is desirable because with reduced speed the pool of molten metal immediately following the arc is kept molten for a longer period of time, thus making for a more complete elimination of the gases and affording the entrained slag an opprotunity to float out of the weld metal.
Also it may be necessary to employ a slightly lower current value than is used with the same thickness of mild steel, particulary in welding thin sections where there is a possibility of burning through the material.
Excessive penetration into the face of the parent metal should be avoided. The penetration should be no greater than that required to obtain a sound bond between the deposited metal and the parent metal, because fusion of an excess quantity of the parent metal tends to carry slag into the weld metal.
Any good quality low carbon rod either coated or bare can be used with wrought iron, but in general the coated rods are used more extensivelly in current installations."
In the O-A welding section it suggests using a rod with the same tensile strength as the WI (27-30 Kpsi)"
There is also tables of suggestions for joint prep, spacing, number of passes, size of electrode, rate of travel, etc.
This book was published by the A. M. Byers Company who commercialized the last major method of making wrought iron--
Endsnip???-
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More links
https://modernwelding.net/welding-wrought-iron/https://www.twi-global.com/technical-knowledge/faqs/faq-can-wrought-iron-be-repaired-by-weldinghttps://www.realwroughtiron.com/about-wrought-iron/what-is-wrought-iron/Turnbull and others can and will repair a presteel wrought iron blow up colt top strap, so it can be done.
One also has to decide one?s goal
Fix it so it looks good as a wall hanger
Fix it so it shoots
Repair it ?properly?
Museum quality restoration
For example, as an amateur weekend blacksmith at Historic Gibbs farm in St. Paul, on a budget of zero dollars, I often made accurate looking and functional cook stove lid lifters, tongs, and spatulas for the ladies in the kitchen out of free found barstock. I made a stronger than original good looking replacement buggy step out of auto coil spring. And I did one museum quality ?authentic frontier repair? on a broken wrought iron piece using forge brazing and a wrought band.. . Cuz my hammer welding sucked then and still sucks now....
Hope this helps
Prof marvel
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