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Welding steel castings

F

falcon556

NAXJA Forum User
Location
Tulsa
I'd like to share my experience regarding the welding of steel castings.
A few months ago I had a pair of knuckles with wear from the brake pads.
Took them to a guy to fill the wear by heliarcing them.
The weld turned very hard which is fine by me because it will prevent furhter wear.
Later on I had to have some other steel cast parts welded. Again the weld turned real hard even though the filler rod was mild steel. I was told that the base metal influences the welded area, metal from both gets mixed up creating a hard weld.
The base metal is soft, the filler is soft, the weld turns real hard.
Asked around a bit and it seems that there is no way to have a steel casting welded with the welded area to be like the original.
At least that's what I was told.
 
A weld will get hard unless you do some sort of heat treatment after the fact. You're heating the metal to the melting point, and then allowing it to cool relatively quickly, as opposed to cooling gradually.

From what I've heard and seen, it's best to have a "torch man" handy when welding cast. Preheat the weld area to ~500-750*F, keep it warm while welding, and let it cool gradually over a couple hours or so. That will help to anneal the weld.

You can also anneal after-the-fact, but it will take more effort. You'll have to heat to ~1400*F, and allow it to cool roughly overnigt (very slowly...)

You're going to get localised hardening in the Heat Affected Zone from welding - it's going to be hardest at the weld bead, and gradually decrease over the next three to four inches - to the hardness of the base casting.

5-90
 
tealcherokee said:
high nickle filler will help
Click to expand...

I heard about the high nickel rod. What is the result of using it, does it stay soft?
Do you know the alloy number? I may have to do another couple of parts.
 
5-90 said:
A weld will get hard unless you do some sort of heat treatment after the fact. You're heating the metal to the melting point, and then allowing it to cool relatively quickly, as opposed to cooling gradually.

From what I've heard and seen, it's best to have a "torch man" handy when welding cast. Preheat the weld area to ~500-750*F, keep it warm while welding, and let it cool gradually over a couple hours or so. That will help to anneal the weld.

You can also anneal after-the-fact, but it will take more effort. You'll have to heat to ~1400*F, and allow it to cool roughly overnigt (very slowly...)

You're going to get localised hardening in the Heat Affected Zone from welding - it's going to be hardest at the weld bead, and gradually decrease over the next three to four inches - to the hardness of the base casting.

5-90
Click to expand...

Are you discribing cast iron or cast steel?
Is the method the same for both?
 
falcon556 said:
I heard about the high nickel rod. What is the result of using it, does it stay soft?
Click to expand...


Well, without it about 90% of the time the weld will crack when it cools.

Check your welds for hairline fractures. Dye-pen them even. I bet you'll find they're fuct.


It's the only CORRECT rod to use for welding cast steel/iron.


I always pre-heat with a propane torch, and don't worry about post heating. But, I backtrack the welds doing only an inch at a time. It has worked fine so far.
 
DirtyMJ said:
Well, without it about 90% of the time the weld will crack when it cools.

Check your welds for hairline fractures. Dye-pen them even. I bet you'll find they're fuct.


It's the only CORRECT rod to use for welding cast steel/iron.


I always pre-heat with a propane torch, and don't worry about post heating. But, I backtrack the welds doing only an inch at a time. It has worked fine so far.
Click to expand...

Will the above produce a soft weld or just a weld that will not crack.
I have two problems, cracking and hardness of the finished weld.
Thanks.
 
falcon556 said:
Are you discribing cast iron or cast steel?
Is the method the same for both?
Click to expand...

Yes.

Yes.

The temperatures may be a bit different, but that should give good results.

The problem is the amorphous grain structure of the cast metal vice wrought "mill stock." Mill stock is going to end up being a bit harder than cast anyhow, which is why you don't notice it as much.

Also, ferrous alloys (irons and steels) get harder when they are heated past the "transformation point" (about 2/3 of melting, but I'd have to look it up to be sure) and are cooled relatively quickly. To eliminate that, you have to let it cool gradually - over a period of a couple of hours (if you're working directly from the heated state,) or overnight (if it's already hardened and you have to anneal from the hardened state and ambient temperature.)

In fact, there are some grades of tool steel (A2 being fairly common) that will get VERY hard when heated to, say 1400-1600*F and allowed to cool in air naturally. There are also "W" grades (for quenching in water) and "O" grades (for quenching in oil) available.

I should probably work up a materials primer, right after I finish my fasteners primer.

Also, bear in mind that this is for ferrous alloys only - different base metals respond to head in different ways (brass, for instance, is directly opposite of steel in its response to heat...)

5-90
 
5-90 said:
Yes.

Yes.

The temperatures may be a bit different, but that should give good results.

The problem is the amorphous grain structure of the cast metal vice wrought "mill stock." Mill stock is going to end up being a bit harder than cast anyhow, which is why you don't notice it as much.

Also, ferrous alloys (irons and steels) get harder when they are heated past the "transformation point" (about 2/3 of melting, but I'd have to look it up to be sure) and are cooled relatively quickly. To eliminate that, you have to let it cool gradually - over a period of a couple of hours (if you're working directly from the heated state,) or overnight (if it's already hardened and you have to anneal from the hardened state and ambient temperature.)

In fact, there are some grades of tool steel (A2 being fairly common) that will get VERY hard when heated to, say 1400-1600*F and allowed to cool in air naturally. There are also "W" grades (for quenching in water) and "O" grades (for quenching in oil) available.

I should probably work up a materials primer, right after I finish my fasteners primer.

Also, bear in mind that this is for ferrous alloys only - different base metals respond to head in different ways (brass, for instance, is directly opposite of steel in its response to heat...)

5-90
Click to expand...
Thanks, great info. I now know enough to ask questions before I let somebody to touch my steel castings.
In a couple of weeks I'll have to repeat my failed experiment, I hope I have better luck next time.
 
falcon556 said:
Will the above produce a soft weld or just a weld that will not crack.
I have two problems, cracking and hardness of the finished weld.
Thanks.
Click to expand...



How hard is your finished weld? I know that doing it this way produces a hard weld, but I doubt it is excessivly so.


Are you sure that it is failing because it is too hard? Like I said, if you weld it not using a high-nickel rod, it's probably going to develope hairline cracks...


I only know the basics of metullgury, but I do know that nowhere does it say you should try to weld cast steel/iron using anything but a high-nickel rod.



What are you trying to weld up?
 
DirtyMJ said:
How hard is your finished weld? I know that doing it this way produces a hard weld, but I doubt it is excessivly so.


Are you sure that it is failing because it is too hard? Like I said, if you weld it not using a high-nickel rod, it's probably going to develope hairline cracks...


I only know the basics of metullgury, but I do know that nowhere does it say you should try to weld cast steel/iron using anything but a high-nickel rod.

What are you trying to weld up?
Click to expand...

I am trying to weld the mounting holes of a brake bracket so that I can redrill them. The first attempt was a failure, produced cracks and hard welds that can be drilled with carbide only. That's OK so far because those brackets were trash to start with and I was never planning to use them.
The next set that I get welded has to work or I'll be looking for new brackets.
There is a welder in town that is supposed to be real good. I'll talk to him on Monday.
BTW I am amazed that the base metal has such an effect on the soft filler rod.
 
It's not so much the base metal that causes the problem - it's the heating/cooling cycle that gets you.

I've assisted on welding cast iron (things like engine mount ears and the like) and it was only welded because it was either too broke to use a Heli-Coil/bushing, or because the hole was no longer compleat (part broken off.)

Given a choice, I'll use a Heli-Coil or a threaded bushing - and it sounds like you're dealing with a hole that's too large to use a Heli-Coil effectively. A decent selection of threaded bushings can be had from MSC Direct (www.mscdirect.com) The advantages of the bushings are twofold - they can use a standard tap to make the hole accept the bushing, and they are rather thicker than a Heli-Coil, and you have somewhat more margin for hole wear.

Drilling welds is a HUGE pain in the arse - and you'll definitely need to post-heat-treat if you want a useable hole. Probably easier to see about using a threaded bushing instead, so peruse MSC Direct before you talk to another welder (to save yourself a headache...)

5-90
 
what your doing is pretty much impossible. that being said I've done it, but on something like brakes, its not a safe thing to do. welding cast to something else is fine, ive never preheated, post heated, or used nickle rod, and (knock on wood) ive never had an issue. welding cast to cast, i use a nickle rod, and do multiple beads depending on the thickness, high heat, and a good post heat to cool it down, usually in an oven over 1-12 hours depending on what it is
 
5-90 said:
Given a choice, I'll use a Heli-Coil or a threaded bushing - and it sounds like you're dealing with a hole that's too large to use a Heli-Coil effectively. A decent selection of threaded bushings can be had from MSC Direct (www.mscdirect.com) The advantages of the bushings are twofold - they can use a standard tap to make the hole accept the bushing, and they are rather thicker than a Heli-Coil, and you have somewhat more margin for hole wear.
Click to expand...

I need to relocate the holes a little. They are not stripped.
 
falcon556 said:
I need to relocate the holes a little. They are not stripped.
Click to expand...

Got access to a mill? That's going to be the easiest way to do the work - you can mill the new hole (not something I'd want to do with a drill press...) set the bushing, and then fill what's left after you install the bushing.

I wouldn't trust a weldment for something like holding brakes, either...

5-09
 
If it's just a brake caliper bracket, could you not try sending it out to be annealed/normalized professionally?


But, the better solution it to make new brackets. Depending on how complicated the caliper setup you want to use is, this might be rather involving.
 
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