welding question

[Nick O]

I have this melting pot that I think is made from iron. I was using it trying to melt some brass that would not melt and instead the pot began to melt. The pot was at a orange heat when i pulled it out of the forge and since I know that its not cast iron I cooled it in my quench bucket. When I quenched the pot it did not break nor leak water so I thought I would try to fill in the hole using my arc welder. Since I was using a new rod I had to break the flux off the end of the rod to strike the arc. I taped the rod on the pot and it exploded with sparks and to my amazement there was a crater in the pot were I taped my electrode. The pot has a vary grainy look to it were I taped the rod. The welder was at about 90 amps then I turned the welder down to 80 amps and I had the same results. Then I tried a nickel rod because that is what you are supposed to use when welding cast iron and I had the same results. I've herd and have read in books that when people try to forge weld a piece of iron and steel together the iron will melt much faster than the steel. The pot is also very hard but i think that is because it was quenched. I would like to find out how i can weld this but i think a tig welder would work.     

[JME1149]

Brass melts at 1700F, Copper at 1981F, Cast Iron at 2200F, Steel at 2500F. If your pot started to melt before the brass, my guess is the pot is Bronze (1675F) or Aluminum (1218F) or some other low melting point metal. Is it magnetic? Is it heavy or light? Take a file to the surface, what color is the base metal and how do the shavings come off? Pictures might be helpful.

Not sure how any of these metals would respond to the welder. What settings and rod were you trying?

[Kozzy]

Thermal conductivity of cast iron is roughly half that of brass (very roughly depending on types) so in theory you can be putting heat into the outside of an iron crucible much faster than it can transfer that heat to the contents--so it's heat can easily rise above the melting point while the contents are basically still solid.  There are a ton of other factors involved so it's not a simple single answer.

As to the welding issue, way too many factors involved to answer with more than wild speculation.  My wild guess would be that the quench induced internal stresses which in caused failure when you re-heated a small section with the welder rather than an even overall heat.  If you've ever had a weld "pop", you've seen how much energy can be stored in a stressed object.  Yes, such things can also shatter like glass.

Proper crucibles are worth the expense.

[arftist]

1 hour ago, Nick O said:

I have this melting pot that I think is made from iron. I was using it trying to melt some brass that would not melt and instead the pot began to melt. The pot was at a orange heat when i pulled it out of the forge and since I know that its not cast iron I cooled it in my quench bucket. When I quenched the pot it did not break nor leak water so I thought I would try to fill in the hole using my arc welder. Since I was using a new rod I had to break the flux off the end of the rod to strike the arc. I taped the rod on the pot and it exploded with sparks and to my amazement there was a crater in the pot were I taped my electrode. The pot has a vary grainy look to it were I taped the rod. The welder was at about 90 amps then I turned the welder down to 80 amps and I had the same results. Then I tried a nickel rod because that is what you are supposed to use when welding cast iron and I had the same results. I've herd and have read in books that when people try to forge weld a piece of iron and steel together the iron will melt much faster than the steel. The pot is also very hard but i think that is because it was quenched. I would like to find out how i can weld this but i think a tig welder would work.     

How do you know it isn't cast iron?

Sure sounds like cast iron to me. 

Read up on welding cast iron, vee grooving, pre and post heat etc.

Then realise that any circular shape is the most difficult to weld in cast iron.

You could possibly bronze weld it using silicon bronze rod and a TIG or oxy-gas torch but you will not be  melting metal in it any more except lead or zinc. 

As to why it is responding so, you burnt the iron. Generally burnt cast iron cannot be repaired by welding at all.

Finally, why do you think you need to chip flux off a new rod?

You don't. You just need to strike using the bare end of the rod. 

[Steve Sells]

I have to ask is why did you quench an unknown ? that is never a good idea, its funny how when we ge in a rush to finish in a hurry the first time, we always find time to do it again a second time

[Nick O]

4 hours ago, JME1149 said:

Brass melts at 1700F, Copper at 1981F, Cast Iron at 2200F, Steel at 2500F. If your pot started to melt before the brass, my guess is the pot is Bronze (1675F) or Aluminum (1218F) or some other low melting point metal. Is it magnetic? Is it heavy or light? Take a file to the surface, what color is the base metal and how do the shavings come off? Pictures might be helpful.

Not sure how any of these metals would respond to the welder. What settings and rod were you trying?

the brass turned out to be some kind of alloy 

3 hours ago, arftist said:

How do you know it isn't cast iron?

Sure sounds like cast iron to me. 

Read up on welding cast iron, vee grooving, pre and post heat etc.

Then realise that any circular shape is the most difficult to weld in cast iron.

You could possibly bronze weld it using silicon bronze rod and a TIG or oxy-gas torch but you will not be  melting metal in it any more except lead or zinc. 

As to why it is responding so, you burnt the iron. Generally burnt cast iron cannot be repaired by welding at all.

Finally, why do you think you need to chip flux off a new rod?

You don't. You just need to strike using the bare end of the rod. 

if it were cast iron it would have busted when I quenched it at an orange heat

[Dogsoldat]

have you tried preheating your melting pot before welding.  and just because its cast iron doesn't mean it will explode when quenched,  just means that it has the potential to fail.