Welding and Re-machining Cast Iron 1

[BrysonRD]

I have a client that has received several cast iron pieces from a vendor that are slightly undersize in one location. I understand that a good weld can be stronger than the base material itself. Is it a generally accepted practice to weld or braze gray cast iron, and then possibly machine or grind back down to size? If so, what type of weld would be preferable? Based on other readings, it seems like brazing would be the way to go, but I'd appreciate any feedback.

Thanks

 

[TugboatEng]

Welding cast iron is almost always the worst option. It requires expensive nickel rods and the weld is not always machinable. I use silicon bronze to build up and join cast iron items. Depending on how much thickness you need to add, hard chrome is another option.

 

[EdStainless]

Either build up with braze or machine back further and braze a steel piece in to make up the dimension.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[0707]

“The most common arc welding electrodes for grey cast iron are nickel and nickel-iron types. These electrodes have been used with or without preheating and/or post weld heat treatment. Cast iron and steel electrodes must be used with high preheats (550°C) to prevent cracking and the formation of hard deposits.”

“Braze welding should only be used to repair old casting because of the poor color match achieved with newer castings. Braze welding is suitable for grey, austenitic and malleable cast irons. However joint strength equivalent to fusion welds are only possible with grey cast iron. A neutral or slightly oxidizing flame should be used.
Braze welding has advantages over oxy welding in that the consumable melts at a lower temperature than the cast iron. This allows lower preheat (320-400°C). As with other forms of welding the surface must be properly cleaned so that carbon doesn't contaminate the weld deposit. The application consumables to use are AWS RBCuZn-C (Aufhauser 681 Low-Fuming Bronze) Types and AWS RBCuZn-D (Aufhauser 773 Nickel Silver) Types.”

 

[Tmoose]

"I understand that a good weld can be stronger than the base material itself."

Possibly true for some materials, but not the various generic cast irons, and definitely not for the nastier abrasion resistant ASTM A 532 cast irons.
A small spot on an edge of a gray iron part Tig melted will cool rapidly and form a HRC 50 plus nugget. Possibly some underbead cracking thrown in for good measure.

The as yet unknown size and value of the casting, the function of the undersize feature, whether the feature is a diameter or a plane surface, operating temperature, location on the casting ( high or low stress area) will may conspire to severely limit the repair options.

Belzona/Chesterton/Devcon filled epoxies, Speed-sleeves, or a steel bushing pressed into machined bore or onto a machined diameter are among the possible good quality repairs that will not muck with the metallurgy.

 

[TugboatEng]

Flame-spray is another option for CI. This is especially effective in round shafts.

 

[gtaw]

If you can find it, an oxy-acetylene welded repair using cast iron rod should give you a pretty good match with regards to the mechanical properties. Preheat is a must and a post weld heat treat is recommended. I typically preheat up around 700 degrees F and once the welding is complete, put the entire casting into a charcoal fire that was started about the same time as the preheating takes place. You don't want the pat to cool down between welding and placing the casting on the coals of the charcoal. Cover the casting and let it "roast" until the charcoal has burned itself out.

Best regards - Al

 

[Tmoose]

OP ain't been back since Nov 6. That's only a couple of days, but ............

 

[BrysonRD]

Unfortunately, I haven't been able to get a lot of details from my client about where the issue is. Here's what I know:
- It's gray cast iron
- It's a brand new casting in good condition
- The problem area is some sort of protrusion (not a planer surface)
- The protrusion is approximately .25-.50 diameter

Thank you all for your time and input. I've shared some of these things with my client and will hopefully be hearing good news from him soon.

 

[TugboatEng]

Give us details about about geometry because that has a big influence on the suggested repair. I know I have mentioned silicon bronze which is a great all purpose repair but gets challenging if you need to add substantial thickness. You can also consider attaching an entirely new piece if it's a protrusion. Silicon bronze works great if fit up is poor and 50N or 56 silver alloys are better if the fit up is tight. You can use any material for the new piece.

 

[CWB1]

IME the success or failure of welding iron castings depends largely on the cast material, method, and geometry of the part itself. There's nothing inherently troublesome about welding cast, I do grey iron regularly with high nickel filler and both pre&post heat. That said, I also would not put much faith in welds on low-quality castings, welds done without thorough pre&post heating, and I always keep internal stresses/relieving in mind when dealing with geometry that expands/contracts significantly.

 

[BrysonRD]

I wanted to let you all know how much I appreciate your input. Unfortunately, I can't really give any more details at the moment. My client hasn't shared any more details with me, and his customer is the military, so I wouldn't be able to share more anyway.

Thank you all.

 

[Tmoose]

I'm thinking if "military" means Navy the cast iron is actually a ductile/nodular variety with some useful ductility.
MIL STD 278 might have something to offer.

 

[gtaw]

I would not bet dinner on NAVSEA S9074-AR-GIB-010/278 addressing the repair of cast irons. Cast steels, maybe, but not cast iron. The Navy is rather conservative on issues related to welding and the materials used to fabricate shipboard equipment.

The HAZ of the ductile iron pretty much reverts to gray iron when one attempts to weld it without the prescribed post weld heat treatment. If in fact one has to weld ductile iron a visit to the Ductile Iron Pipe Research Association. Do a Google search using "Ductile Iron Pipe Research Association Welding" and you see an article of welding of ductile iron.

Best regards - Al

 

[Tmoose]

Hi GTAW,

I also was under the impression even steel castings and materials with less than maybe 10% elongation were not allowed on Military ships.

Then I stumbled on this -

MIL-I-24137(SHIPS)
MILITARY SPECIFICATION - IRON CASTINGS, NODULAR GRAPHITIC (DuCTILE IRON) AND NODULAR GRAPHITIC
(CORROSION RESISISTING ,AUSTENITIC, LOW MAGNETIC PERMEABILITY)
(FOR SHIPBOARD APPLICATION)

Page 3 from 24137 attached. It references MIL-STD-278" Welding and casting repair"
I have not reviewed 278 for how it might apply to 24137.

 

[EdStainless]

Welding the high Ni austenitic cast irons (NiResist) is a piece of cake compared to regular CI.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[gtaw]

Referring to MIL-STD-278 is like referring an ancient manuscript. It has been replaced by NAVSEA S9074-AR-GIB-010/278 some twenty years ago.

Nodular iron has good ductility because the carbon forms nodules instead of graphite platelets. The problem is, once it is welded, it reverts to a cast iron with rather poor ductility. The difference can be seen when one purchases a vice for the workbench. The cast iron vice will be on the order of $100 and will break in short order. The ductile iron vice will cost 6 or 7 times as much, but you'll hand it off to your grandson after twenty or thirty years of hard use.



Best regards - Al

 

[Tmoose]

MIL STD 278 was only cancelled in 1998.
Nearly all my cars are older than that so that vintage technology is cutting edge to me.

NAVSEA S9074-AR-GIB-010/278 seems to actually refer back to MIL-STD-278 in a section about recording welds and maintaining weld maps. Probably a typo.
Searches for "iron" "cast iron" and "castings" in both documents only pulled up fancy alloyed chrome etc irons.

I'm back to thinking guessing the OP's casting ain't some lowly cast iron.