[weldin mike 27]

We use heavy wall Chromolly tube at work. 6.4 (1/4) wall thickness. We weld it with pulse mig and 80s8d2 wire. With the mig we use a pre heat of 80°c minimum.

My question is in regards to tig welding of same material. We use the tig for blending /fixing undercut and the like. We are not required to pre heat the material when tigging. 15 °minimum ambient temperature. This doesn't sit right with me. (I preheat when tigging) Just wondering if anyone has any theories on this? Or is it just because the guy who wrote the welding procedure is an escaped mental patient.

All the best, Mick.

[Coldman]

I think any thickness over 3mm requires preheat.

[BugHunter]

The 15° minimum ambient is probably 15 C. Basically comfortable room temperature.

Maybe the idea is that when you TIG there is no way to get the heat quite as localized as you can when you Mig. The thought might also be that once you are blending the mig weld with tig, you already have a mixed base metal, so it's no longer really 4130. It's 4130 mixed with 80s8 filler wire. All except the very small amount where the undercut is at the surface.

I'm guessing there but that kind of makes sense.

[Coldman]

There still is a boundary where 80s meets moly, that's where cracking will occur without preheat on thick material.

[weldin mike 27]

Coldmans Point is where I find the issue. There is a large grey area in this job, that I think is going to bite us later on down the track.

[Poland308]

Coldmans Point is where I find the issue. There is a large grey area in this job, that I think is going to bite us later on down the track.

Totally possible but it will definitely be the responsibility of whoever wrote the procedure to show there engineering work, and after that whoever approved of the procedure. Others who might be held accountable would be anyone with documented training equal to or exceeding those of said procedure writers, and also full knowledge of the work being done. Other than that your just following the directions of your supervisor. If it endangers someone’s safety or life then file a written concern with your employer, have then sign it date it and give them a copy.

[weldin mike 27]

That's how it would work in the real world. I work for a you're not smart enough to question me company.

Ah well. I keep preheating and tell others to do the same.

[Kuki89]

I would use er 70s_2 or if it is well clean er70s_3 (not the er70s_6 which contains a lot of silicon and becomes brittle) and 80 celsius should work well or maybe 100 better, to avoid hardening in the heat affected zone. The 80s_d2 would make a stronger but brittle weld is my humble opinion.

[weldin mike 27]

I can't vouch for the filler metal selection. One can only hope that the God like figure who is in charge actually talked to the company supplying the base metal.

[BugHunter]

How large are these parts that you are doing? Are they something that is going later to a heat treat facility? Maybe that's why they don't care. But I would think there would be a limited amount of time to leave the steel under stress before that became a big problem. I mean if indeed they are going into an oven to resolve any problems the weld caused, there is generally a Time. Called out on the material data sheet saying how long you can leave the stuff in any particular condition without going back in a draw oven.

At work it seems lately I can't buy 4140 which I have good solid data sheets for. All I can get is 4130. It absolutely does not act the same in the heat treat oven. Even though the temperatures called out in the documentation I can find, are exactly the same, the mechanical properties that I end up with are certainly not the same.

I rarely have to weld the stuff and if I do it generally very small parts. I'm much more likely to simply machine pieces and bolt them together. I have plenty of empirical data about how it reacts to Machining, welding or heat treat. But from a code standpoint I know zero.

[weldin mike 27]

They are vehicles sub frames. Front and rear frame bolted to a central cab. They are heat treated post welding.

[BugHunter]

If they are heat treated after welding then I would say almost nothing you do matters. You certainly can't cause a problem by doing a preheat, but it may just be a waste of time.

4130 has less carbon than 4140 so it will be more forgiving. With other types of steels I have seen things happen that would blow your mind. At work I have seen where when the data sheet says quench to 150 degrees Fahrenheit and immediately bring to a normalizing temperature of between 300 and 800 for a minimum of 1 hour, it doesn't mean wait until the next morning. LOL

[weldin mike 27]

So, underbead cracking isn't as big an issue with 4130 as it is with other low alloy steels? Like you quenched and tempered steels?

[BugHunter]

The only comparison I made was to 4140 which has a higher carbon content and is more hardenable. I'm not saying it's not a worry, only that it's more forgiving than 4140. And it's a lot less of a concern than many other tool steels (stuff that gets much harder).

Also, if the part leaves your welding booth and goes to an oven where it is normalized, it's entirely likely there's zero concern. But that's impossible for anyone to know reading only what's been posted above.

Like you quenched and tempered steels?

Not sure I"m following you here.

With some steels I've worked with, there is a definite time frame under which you must complete the cycle of events to have the steel retain it's intended properties. If you ignore that time limit, it can get ugly. It varies by what steel you're working with. In one particular case, I saw an A2 part of roughly 7" diameter, 3/4" thick with many sharp points, literally explode overnight when not normalized. It was like tempered glass hit with a bullet. little 3/8" pieces all over the shop, some stuck in the ceiling and walls. I'd seriously doubt 4130 will ever do that, but that doesn't mean there aren't concerns.

I seem to recall a 4140 datasheet at work that told about welding and follow-up treatment, but I can't recall if that was the one I'm thinking of or not. I've not found a 4130 datasheet that gives me consistent results. Either the info is wrong, or the 4130 steel I've purchased is not 4130. But mine doesn't react as intended.

[weldin mike 27]

Thanks for your detailed responses to my questions. I am a welder, have been for a long time. But I just have to go weld this. No extra technical knowledge required, as long as I do what they say. What I refer to as quenching an tempered steels are the kind of low alloy steels that are used in mining equipment and some impact resistant applications. Supplied from the factory in a hardened state that has to have pre heat and interpass temperature adhere to. I am trying to ascertain whether 4130 is as susceptible to cracking as some of these steels. Hence the issue. Doesn't matter what happens down the track if it's cracked under your weld as you are doing it.

The steels I am referring to are Bisalloy 80 and bisalloy high hardess armour

https://www.bisalloy.com.au/product/armour/

Thanks again for the replies.

[BugHunter]

Thanks for your detailed responses to my questions. I am a welder, have been for a long time. But I just have to go weld this. No extra technical knowledge required, as long as I do what they say. What I refer to as quenching an tempered steels are the kind of low alloy steels that are used in mining equipment and some impact resistant applications. Supplied from the factory in a hardened state that has to have pre heat and interpass temperature adhere to. I am trying to ascertain whether 4130 is as susceptible to cracking as some of these steels. Hence the issue. Doesn't matter what happens down the track if it's cracked under your weld as you are doing it.

The steels I am referring to are Bisalloy 80 and bisalloy high hardess armour

https://www.bisalloy.com.au/product/armour/

Thanks again for the replies.

At the bottom of the datasheet for 80 there's a note saying that for fabrication procedures to contact them. Likely, there are so many variables they can't even document what all the tradeoffs are. Thickness matters, ambient temp, type of weld process, type of filler, type of shield, I mean the list just goes on and on. At no point do they even mention the word "weld".

Here's a datasheet for 4140/4142 that I've used. When I've bought this stuff, these graphs are spot on with temps I set. Much like any other tool steel I've worked with. Do what the sheet says, test the finished result and they are dead on. Well, all except the supposed 4130 I've purchased. It doesn't harden anywhere close to what the online datasheets say, and the vendor of the material (a steel reseller company) does not provide certs nor a datasheet. In other words, I doubt it's really 4130. It's been ok for the maintenance stuff I've done with it, but the one time I wanted a serious hardened tool, it failed miserably and was actually better off using as purchased.

https://fordtoolsteels.com/wp-content/u ... 4142HT.pdf

Take note, they never mention the word "Weld" in that datasheet either.

Also, down in the section headed "Tempering", take note they have in italics the part about "Temper immediately after quenching." That's because it's not optional.

In your case, it's entirely possible you're working with a special recipe not available to anyone else. Maybe something added specifically to negate the need for a preheat just to save time and money. Seems unlikely, but ya just never know. Again, I machine steels, heat treat steels, but I'm not involved in welding alloy steels but very rarely. I know just about enough to question stuff that seems off. You already did that with the preheat question. The 4140 I've worked with in the past would make me think your concerns were valid. But the stuff that is supposed to be 4130??? Between this thread and the datasheets online not working, it's convincing me it's not really 4130.

[sbaker56]

BugHunter is quite a bit more qualified than I am to speak on the subject given that it's part of his job. But I would agree the post welding heat-treat would reduce or eliminate certain issues that you'd otherwise encounter with not preheating.

The most common issue with not preheating 4130 before welding is that while the rest of the piece stays relatively cool your weld and the immediate area surrounding your weld will cool so fast that'll quench no different from if you'd heated it in a forge and dunked it in oil. This leaves you with a very hard and brittle spot compared to the rest of the part that'll crack very easily.

When it's heat treated it'll bring everything to the same hardness and relieve any stressors that may have built up upon welding.

[weldin mike 27]

Thanks fellas. It does, in fact answer my questions. I got lost in the transition from my previous project on hardened steels with no post welding heat treatment to this one with a heat treatment at the end.

Thank you for your time. All the best, mick