Preheating 4130 Chrome-moly

[ClassicXJ]

Well I just got done reading another welding book and a short section of the book discussed why not to preheat chrome-moly before welding it.

1) because you have no way to know what temperature the metal is with just hitting it for 5 minutes with a torch

2) because the steel would cool back to ambient temperature before you could complete 20% the weld

I was just wondering what some of you guys thought about this. I mean I've had a ton of people tell me to preheat something with a torch before starting my weld. And these 2 reasons are pretty general and would pretty much stand true for any type of metal.

Thoughts?

 

[5-90]

Mildly amusing. As I recall, 4130 and 4340 were orignally formulated for torch-welding - you used oxy-acetylene with a slightly rich flame (in place of arc welding and flux,) and you got ROCK SOLID welds from it - even better than arc or resistance welding!

As far as preheating, that should only really be necessary on very thick sections (say, 1" or more,) or castings - and you'll use Tempil pellets or sticks to set up your temperature. I've done torch help on cast iron welding before, and that was what I did. It's still not a "fine" control, but it's loads better than just hitting it with a torch and guessing...

5-90

 

[RCP Phx]

X2 on the temp sticks!
https://weldingsupply.securesites.com/cgi-bin/einstein.pl?Next::1:UNDEF:OR:terms:P7

 

[Weasel]

we weld 4130 tube all the time (0.049, 0.035, 0.093") and from our lab test of the welds, preheat the tubes by it's self doesn't do anything. Same with post heat by itself. As for them together, for some stupid reason I can't get anyone to preform this test, they seem to think it doesn't matter.

 

[MudDawg]

we weld 4130 tube all the time (0.049, 0.035, 0.093") and from our lab test of the welds, preheat the tubes by it's self doesn't do anything. Same with post heat by itself. As for them together, for some stupid reason I can't get anyone to preform this test, they seem to think it doesn't matter.

I have welded up a lot of tubing in this thickness range as mods on dragbike frames without pre or post heating with no failures or problems.

 

[txredxj]

i just did a chopper frame with 4130 tig and all i did was run it a little hot.
really only thick aluminum and any magnesium need pre heat and maybe cast. the temp stick work fine.

 

[Weasel]

I have welded up a lot of tubing in this thickness range as mods on dragbike frames without pre or post heating with no failures or problems.

We've not really had any problems either but were just doing tests so that we can have data to jusitfy our welding process and seem if there were any worthwile improvements using pre/post heat. Using the right rod is working well.

 

[Weasel]

i just did a chopper frame with 4130 tig and all i did was run it a little hot.
really only thick aluminum and any magnesium need pre heat and maybe cast. the temp stick work fine.

That may actually make the weld slightly worse. The increased heat was the HAZ zone bigger then it needs to be.

 

[txredxj]

well with the increased heat you have to go faster and use more gas. with the smaller parts i ran it regularly but with a 4 inch or bigger pass i wanted to go faster to cut down heat