Weld hardened after welding cast iron on milling machine.. What happened?

[pmccand]

A question for you metallurgists...

I have a cheap manual Sieg micro milling machine made with a fairly soft cast-iron steel, easy to cut and machine with HSS bits. Two 6.0x1.0 mm holes were easily drilled and tapped into the vertical column to which I mounted a custom designed aluminum adapter for a CNC stepper motor upgrade.

Unfortunately, I drilled the holes slightly out of alignment. My plan to fix the mis-aligned holes was to weld them closed using E71t-gs flux-cored wire and grind/file the surface flat so that I could start with fresh new holes in proper alignment.

Welding the holes went without a problem and the excess weld was ground flush with the column using a electric grinder. However, I noticed that when I dragged a new file across the surface, the file WOULD NOT cut into the weld material. I then tried to drill the weld material with a HSS drill bit and found that the drill would not cut into the weld. It wouldn't even scratch the weld!

For some reason, the weld became INSANELY hard and I am unable to machine the weld. I can still file and cut the metal surrounding the welds, but I cannot machine the weld that was filled with E71t-gs wire. Looking at the manufacturer's description of E71t-gs, it states that it is a general all purpose wire for mild steel, including galvanized and sheet metal...

Can someone please tell me what happened and why I cannot machine the repaired metal? If I have to grind the material out again, can someone please tell me how to make a proper weld that more closely approximates the metal composition of the original cast iron material? Will brazing the holes be better in this case? Thanks in advance...

 

[Rob F.]

Sounds like a classic case of you didnt know what you didnt know....
Do a search, this has been discussed MANY times. Here is another thread that will get you started.

https://www.practicalmachinist.com/vb/general/welding-cast-iron-401775/?highlight=weld+cast+iron

 

[pmccand]

Sounds like a classic case of you didnt know what you didnt know....
Do a search, this has been discussed MANY times. Here is another thread that will get you started.

https://www.practicalmachinist.com/vb/general/welding-cast-iron-401775/?highlight=weld+cast+iron

You are correct. I didn't know what I didn't know. (Actually, I DID know, I learned this in 1978 metal shop class when I was in high school.) I had not welded (brazed) CI since then.. so this is a classic case of I didn't know what I didn't remember.

Thanks for the link tho'

 

[Rob F.]

After doing some research you may want to heat up the weld area and let it cool very slowly. I can not say if that will soften the alreeady hard weld area or how hot it will need to be, my immediate thought is dull red and a very slow cool down might do it. Be sure to sconsider the heat may warp or distort your casting if not heated evenly. Brazing might be better if you could get the brass to stick in the bottom of the hole. Threading the hole and screwing in a soft bolt might have been best in your case. There are tapered threaded plugs made just for this and crack repair, lock & stitch might be the name?

 

[eKretz]

What happened is that the carbon in the iron migrated/diffused into the liquid weld puddle, then rapidly cooled, effectively quenching what had now become medium to high carbon steel. It will be brutal to cut. Carbide may or may not be able to cut it. Your best bet to soften the weld is probably to bring the whole casting up as hot as you can get it and cool slowly. You will definitely see some distortion if you do this though. A better idea might be to grind it flush and alter your design to move the bracket elsewhere so you can avoid any further distortion. It's of little use to consider other repair methods of the holes at this point, the damage is done.

 

[pmccand]

What happened is that the carbon in the iron migrated/diffused into the liquid weld puddle, then rapidly cooled, effectively quenching what had now become medium to high carbon steel. It will be brutal to cut. Carbide may or may not be able to cut it.

This is the answer I wanted, but not happy about the options for a solution.

With the patience of Job, I was able to grind out the old slab and place a washer and nut behind the repair to hold the adapter to the cast iron part in place.

I am really a LOT SMARTER having gone through this. Thanks guys.

 

[Scruffy887]

A question for you metallurgists...

I have a cheap manual Sieg micro milling machine made with a fairly soft cast-iron steel, easy to cut and machine with HSS bits. Two 6.0x1.0 mm holes were easily drilled and tapped into the vertical column to which I mounted a custom designed aluminum adapter for a CNC stepper motor upgrade.

Unfortunately, I drilled the holes slightly out of alignment. My plan to fix the mis-aligned holes was to weld them closed using E71t-gs flux-cored wire and grind/file the surface flat so that I could start with fresh new holes in proper alignment.

Welding the holes went without a problem and the excess weld was ground flush with the column using a electric grinder. However, I noticed that when I dragged a new file across the surface, the file WOULD NOT cut into the weld material. I then tried to drill the weld material with a HSS drill bit and found that the drill would not cut into the weld. It wouldn't even scratch the weld!

For some reason, the weld became INSANELY hard and I am unable to machine the weld. I can still file and cut the metal surrounding the welds, but I cannot machine the weld that was filled with E71t-gs wire. Looking at the manufacturer's description of E71t-gs, it states that it is a general all purpose wire for mild steel, including galvanized and sheet metal...

Can someone please tell me what happened and why I cannot machine the repaired metal? If I have to grind the material out again, can someone please tell me how to make a proper weld that more closely approximates the metal composition of the original cast iron material? Will brazing the holes be better in this case? Thanks in advance...

I am not sure I would modify that hobby toy. It prob would have been better to fill the holes with bondo or liquid steel mixed from a tube and make a drill guide. What are you talking about here, mount for a 23 series stepper? Good that you learned about welding a casting. Maybe now learn about polishing a turd?

 

[Strostkovy]

Drill holes in a different location and machine a bracket to match

 

[52 Ford]

A question for you metallurgists...

I have a cheap manual Sieg micro milling machine made with a fairly soft cast-iron steel, easy to cut and machine with HSS bits. Two 6.0x1.0 mm holes were easily drilled and tapped into the vertical column to which I mounted a custom designed aluminum adapter for a CNC stepper motor upgrade.

Unfortunately, I drilled the holes slightly out of alignment. My plan to fix the mis-aligned holes was to weld them closed using E71t-gs flux-cored wire and grind/file the surface flat so that I could start with fresh new holes in proper alignment.

Welding the holes went without a problem and the excess weld was ground flush with the column using a electric grinder. However, I noticed that when I dragged a new file across the surface, the file WOULD NOT cut into the weld material. I then tried to drill the weld material with a HSS drill bit and found that the drill would not cut into the weld. It wouldn't even scratch the weld!

For some reason, the weld became INSANELY hard and I am unable to machine the weld. I can still file and cut the metal surrounding the welds, but I cannot machine the weld that was filled with E71t-gs wire. Looking at the manufacturer's description of E71t-gs, it states that it is a general all purpose wire for mild steel, including galvanized and sheet metal...

Can someone please tell me what happened and why I cannot machine the repaired metal? If I have to grind the material out again, can someone please tell me how to make a proper weld that more closely approximates the metal composition of the original cast iron material? Will brazing the holes be better in this case? Thanks in advance...

What diameter holes? How deep do they need to go?

If you want to anneal it, you need go get it pretty hot. You can heat it with a torch. Localized heating isn't ideal, but it's a whole lot less localized that welding. Maybe try 6 or 7 hundred degrees Fahrenheit. Dark blue if you go by temper color. Cool it very slow. Wrap it in welding blankets, burry it in sand, whatever ya gotta do.

Edit: this won't get it dead soft. You need to get the metal glowing to do that. For example, 1095HCS needs to get up around 1,600F to fully anneal it.
Sent using Morse code on - .- .--. .- - .- .-.. -.-

 

[memphisjed]

a good center punch, slow rpm on a good hss bit or sharpened masonry bit with all the push the drill can handle and you will be able to drill into the weld. I doubt it will be that deep- flux core gasless wire is always gooey and doesn't flow.
The Milwaukee bits at lowes depot are not bad, not the best but good for roughneck work in a hand drill.
I am not sure if it would be better to drill out the weld to remove stress or let it ride. Next time just move the holes in the bracket instead of the mill.

You can buy a ##### cnc machine and end up with two things for the same dollar as retrofitting your existing machine.

 

[52 Ford]

a good center punch, slow rpm on a good hss bit or sharpened masonry bit with all the push the drill can handle and you will be able to drill into the weld. I doubt it will be that deep- flux core gasless wire is always gooey and doesn't flow.
The Milwaukee bits at lowes depot are not bad, not the best but good for roughneck work in a hand drill.
I am not sure if it would be better to drill out the weld to remove stress or let it ride. Next time just move the holes in the bracket instead of the mill.

You can buy a ##### cnc machine and end up with two things for the same dollar as retrofitting your existing machine.

Your Lowe's has Milwaukee??

I own Bosch and Milwaukee "impact drill bits" and frankly, they're awesome. They last a long time and they seem to be really well ground and made of good steel. I imagine DeWalt impact bits are just as good. My impact driver bits are DeWalt and Bosch and the DeWalts hold up as good, if not better, than the Bosch. I've driven THOUSANDS of screws with a single DeWalt bit. I've done the same with Bosch, but I've owned the DeWalt bit long... so probably more use.

By the way, Milwaukee is owned by a Chinese company, nowaday. Bosch is German (I think? I own new Bosch tools that are made in Germany), and DeWalt is still USA owned and some of their tools are USA made... not most, though.

 

[eKretz]

a good center punch, slow rpm on a good hss bit or sharpened masonry bit with all the push the drill can handle and you will be able to drill into the weld. I doubt it will be that deep- flux core gasless wire is always gooey and doesn't flow.
The Milwaukee bits at lowes depot are not bad, not the best but good for roughneck work in a hand drill.
I am not sure if it would be better to drill out the weld to remove stress or let it ride. Next time just move the holes in the bracket instead of the mill.

You can buy a ##### cnc machine and end up with two things for the same dollar as retrofitting your existing machine.

Not likely. Have you ever tried to center punch a bad iron weld deposit? I have flattened more than a few center punch points that way. If the file won't cut it, a HSS drill won't fare well at all. I've tried to cut poorly done iron welds that carbide could barely cut, and certainly not well enough to get a precise surface. A really badly done weld basically creates a hardened steel weld deposit with chilled iron just past the interface. You won't be doing much cutting of chilled iron with carbide either.

But you never know I guess. Could get lucky.

 

[DDoug]

I have a cheap manual Sieg micro milling machine

So no real loss....

 

[Scottl]

What happened?

"
I have a cheap manual Sieg micro milling machine made with a fairly soft cast-iron steel"

Not trying to be rude or funny, it's just that China made stuff use some really nonstandard materials. Who knows what scrap the "cast iron" was made from and the welding process likely created a local spot of hardenable alloy.

Most likely the weld material absorbed some material with an affinity for iron that leaves hard particles of iron-whatever. In future when working on such "overseas" stuff drill and tap to a larger size. Bond in threaded rod with epoxy or Loctite and then face off and re-drill.

 

[tylersteez]

Heating and cooling to get the hardness out of it is your best bet at saving the original hole location. Once you heat and cool it, go slow with a drill and lots of pressure and oil. You may find that you need to repeat the heating process the deeper you drill.

since you'll be heating cast iron, things can get wacky and cracking can happen without warning, even if you're careful. This is why this repair is kind of a crap shoot. Next time you weld cast that you want to be able to machine, use a 99 cast iron rod or SI.

 

[DDoug]

Heating and cooling to get the hardness out of it is your best bet at saving the original hole location. Once you heat and cool it, go slow with a drill and lots of pressure and oil. You may find that you need to repeat the heating process the deeper you drill.

since you'll be heating cast iron, things can get wacky and cracking can happen without warning, even if you're careful. This is why this repair is kind of a crap shoot. Next time you weld cast that you want to be able to machine, use a 99 cast iron rod or SI.

The machine will fit in a standard kitchen over, Easy Peasy.

Or try the microwave for faster heating !

 

[pmccand]

Thanks for all the input folks! I really knew it was a dumb move, but did it anyway. Good thing is that the welds are small (<6mm dia x 4mm deep) in a non-critical location.

I FINALLY ground through the old weld with one sharp 1/8" carbide burr, and about 45 minutes later had both holes reamed to accommodate two 6mm bolts with nuts behind the plate. Plenty strong...

What did I learn?

1) Metallurgy 101. Carbon migrates into the weld from CI. (Whoda thunk?)
2) Don't weld it.

What else can I learn from this episode?

1) What other common metals other than Cast Iron do I want to avoid welding that will result in hardening? I dunno. Maybe someone can enlighten me.

 

[eKretz]

Thanks for all the input folks! I really knew it was a dumb move, but did it anyway. Good thing is that the welds are small (<6mm dia x 4mm deep) in a non-critical location.

I FINALLY ground through the old weld with one sharp 1/8" carbide burr, and about 45 minutes later had both holes reamed to accommodate two 6mm bolts with nuts behind the plate. Plenty strong...

What did I learn?

1) Metallurgy 101. Carbon migrates into the weld from CI. (Whoda thunk?)
2) Don't weld it.

What else can I learn from this episode?

1) What other common metals other than Cast Iron do I want to avoid welding that will result in hardening? I dunno. Maybe someone can enlighten me.

You can weld it, but it has to be done properly with a lot of pre-heat, in-process heat and slow cooling if you want it readily machinable afterward - and that includes welding using nickel rod also. That means the process is generally ruled out from the start on something like a machine tool unless you plan to refinish all the precision surfaces.

Avoid welding any iron or medium to high carbon steel without knowing what you're doing... Those are pretty much it for any common metal you might be welding.

 

[pmccand]

You can weld it, but it has to be done properly with a lot of pre-heat, in-process heat and slow cooling if you want it readily machinable afterward - and that includes welding using nickel rod also. That means the process is generally ruled out from the start on something like a machine tool unless you plan to refinish all the precision surfaces.

Avoid welding any iron or medium to high carbon steel without knowing what you're doing... Those are pretty much it for any common metal you might be welding.

Here is a wild story about welding cast iron...

Years ago, I took my 1982 Ford Fairmont into a welding shop to have some work done on the exhaust manifold which was cracked. So, the welder came out, took one look at it and asked how much I was willing to sell the car for. I said I'd let it go for $500. He said, "OK" and handed over $500 on the spot. The next thing I know, he started the car, warmed the engine to operating temperature, and proceeded to arc weld the crack with a "mystery" rod while it was running. The car sounded like new before the weld was finished in less than 20 seconds - totally quiet. He ran the car a bit longer and took it through a few cycles of start/stop/and restart to cool it down slowly. As far as I heard, it was running years later with no recurrent leak or crack. Guess I should have asked him how much was the repair gonna cost.

 

[rogertoolmaker]

Heat the entire casting. Bury it in powdered lime and leave it there until it cools.
Must cool "very slowly" to anneal. Will take days to cool.

Roger