Help welding cast steel

Hi.
Recently noticed a crack in the boom support on my Volvo EC55B.
I ground the crack out which went all the way through.
Preheated.Tig welded the root run with supasteel wire.stick welded with 3.2mm 7016 low hydrogen rods.
The repair seemed successful but when it cooled a crack appered right at the join of the weld to parent material.
Ground it all out again. Got some advice from a engineer who said." No preheat,keep it cool as possible and peen each run".
Followed this procedure and it still keeps cracking.
I contacted Volvo but they don't have a repair procedure only replace, but at $2500 I would prefer to repair over replace.
Any suggestions would be appreciated.

Cheers.

hmmm, cast steel? Generally I'll preheat the part to 350 degrees for 15-20 minutes, cracking is the differential cooling, let the part get nice and toasty warm, ususally even warm up the welding bench, wrap the uninvolved parts of the piece in a welding blanket or two to help retain the heat. My usual rod is straight stick 9018 or 11018, make a pass and chip / wire brush then put down another pass, keep it all hot. A needle scaler can be used to help peen and minimize welding stresses. If the repair spans a distance, move around to keep the heat even. I'm thinking stick is putting down more heat than tig so maybe that'll help but you can always add more heat with fire. Once you're done welding, reheat the entire part, 350 and keep it there for a while, few hours at least and then let it cool slowly. If the part will fit in a kitchen oven and the ladies aren't around, that'll work. Post welding cool down I typically see five hours or more before its back to room temperature.

My preheater was a big propane weed burner fed off a 100 pound tank, it'd put out a lot of heat over a very large area without chewing up my torch tanks, softer than a rosebud as well.

My big question is what caused the crack? Also I think there's one on ebay for 800

I'd say you were on the right track with your original approach, however it is possible that there was insufficient pre heat, excessive joint restraint or the cooling rate was too fast.
Let's start at the beginning. Cast steel is primarily a reference to the method of forming the component and tells you nothing about the possible composition of the component other than informing you that it is steel, rather than iron and thus implying a reasonable degree of weldability. A photo of the component would be handy when you get sufficient posts up to be able to upload one.
I don't know your experience level, so forgive me if I state the seemingly obvious.
In order to perform the more critical forms of welding such as this, you will need some method of accurately measuring the pre heat and interpass temperatures. Temperature crayons or non contact infra red thermometers are the two most common methods that spring to mind. Without knowing the exact composition of the component, I'll make a bit of an assumption and work on quite a high Carbon Equivalent (a measure of the weldability of steels). Based on this you could be looking at preheat temperatures of anywhere from 170 deg C for a 10mm material thickness up to 260 deg C if the component is 40mm thick. For a highly restrained joint (one unable to freely expand and contract while welding and cooling), you would possibly add another 50 deg C to those temperatures. Generally, too much pre heat is better than too little. Electrodes should be used from a hot box to ensure they are dead dry and truly Low Hydrogen. Your TIG root run is optional, but make sure you achieve 100% penetration so you don't allow a crack to propagate from an unfused root. It may not hurt to use a higher classification electrode than a 7016 such as 8018 or even 9018, but based on what you have said, I believe your issues are more procedure related than consumable related. As far as pre heat goes, a down and dirty method for gauging temps is to remember that at 100 deg C, water will quickly evaporate from the surface (nearly instantly), while at 200 deg C the drop of water will dance around on the surface in a very energetic fashion as it boils off. You will want to heat a generous area so that the cold metal doesn't rapidly suck the pre heat away from the weld zone. It doesn't hurt to check the temperature during longer welding jobs and adding heat as required as 3.2 electrodes don't put much heat in and therefore heat loss may be greater than heat input. If you can run them, some 4mm sticks may be a better option. I would definitely grind each run back to shiny metal so as to eliminate potential inclusions and slag traps and would also peen each run as you progress as well as the final capping pass. A cheap air chisel with the edge blunted is a really good tool for this otherwise hammering will achieve the same result. Once you are satisfied that all welding is complete then you will want to cool the component slowly and evenly to eliminate thermal shock and resultant stresses. A fiberglass welders blanket is ideal to pack around the joint so as to exclude wind and slow the cooling rate.
I recommend you download this book, some 212 pages long (only 2.7Mb though) that apart from listing the various Welding Industries of Australia consumables, has a large technical section detailing various steel grades and the procedures and consumables to weld them. http://www.welding.com.au/news/view/australian-welding-guide-available-to-download
Hope this helps, but having limited information to go on, there are many unknown factors.

Eutectic 680 all the way, no preheat, weld as per Eutectic instructions.

Was this piece originally welded from the factory or strictly a bolt on part? I ask because there was another thread about a Cat backhoe that had a cracked swing tower made of cast/nodular iron. Cast steel doesn't usually pose too much of a problem welding. Using too high a tensile of rod like 11018 can cause cracking too. 7016/7018 shouldn't though. Things like crane booms usually specify an 8018-C3 (1% nickel) to add toughness to the weld. Temp sticks for preheat are more accurate than infrared thermometers. Some pics would definitely help if you could post some. Eutectic 680 looks to be similar to other high tensile rods for welding difficult to weld steels, like supermissle rod, Blueshield Xtreme,etc. I think Eutectic 9598CEC is the same thing as the 680 with a different name for another market (Canada as it's in French on the website). 312 stainless is similar as well. Preheat on steel should never hurt but first thing is to determine just what type of cast it is.

after welding a small amount you need to peen the weld to release and built up stress from welding, this will help with cracking, also some heavy equipment parts have tags right on them that state" NO WELDING"..do you see anything like that on your machine?

Yair . . .

Eutectic 680 all the way, no preheat, weld as per Eutectic instructions.

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With you all the way on that one lantraxco but bloody hell they're spendy.

Over the years, out of necessity I have welded many things that probably should never have been welded with varying success

I have received (and acted on) advise and technique sheets as detailed up thread by Karl Robbers and even the most rigorous following of methods will not guarantee success. Some "cast steel" components cannot be welded back to original strength and spec.

However some judicious plating and reinforcing and perhaps drilling and tapping for some grade eight bolts to mechanically take some stress and then a good melting together around the bolt heads and the edges often seems to work.

I have never used preheat, just wound up the amps and pour low hydrogen in there, clean it out and peen it if possible smooth it off real pretty, bury it in lime and again if possible don't touch it for a week . . . in the real world with unknown metallurgy I always reckon the real slow cooling was half the battle.

Cheers.

One caution that must be added is to consider what the worst possible outcome may be in the event of a catastrophic failure in the component. For example, it may be easily possible to do more than the $2500 price for the new boom support in damage to the machine and surrounds plus downtime if the component fails catastrophically. If you use your machine as part of a business, then you will need to consider your liability exposure level in the event of a failure. I notice you are a fellow Aussie, so you will be well aware of how Workcover will savage you if somebody were to get hurt or even look like getting hurt.

Hobbytime said:

after welding a small amount you need to peen the weld to release and built up stress from welding, this will help with cracking, also some heavy equipment parts have tags right on them that state" NO WELDING"..do you see anything like that on your machine?

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Once you take that tag off you're good to go!

www.ebay.com/itm/281958986445

has some good pictures of the part, man that looks like a rather nasty casting.

photo upload

How do i post photos?

In the "quick reply" box, click "Go advanced"
Once there, scroll down below where you would type your post
and look for "attachments".

This also works.

fast_st said:

www.ebay.com/itm/281958986445

has some good pictures of the part, man that looks like a rather nasty casting.

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That is an ugly little sucker from a welding perspective, probably still fixable, but to give yourself a fighting chance you would be best to remove the component from the machine and deal with it on the bench which is no small task.
If it were me, I'd look carefully at the one on EBAY as it may well be the most cost effective solution all things considered.

fast_st said:

www.ebay.com/itm/281958986445

has some good pictures of the part, man that looks like a rather nasty casting.

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That casting does look rough for cast steel. It might be a cross between cast steel and cast iron. Seeing the crack and the grain structure could give some clues to what it is. If it is cast steel peening can help some to reduce stresses but isn't as critical as if it was cast iron. Peening on cast iron is because the filler rod has different expansion and contraction than the cast iron. Over peening puts stresses back in too. That's why brazing is a good option if high temperatures aren't encountered or O/A cast iron welding.

If it cracked along the weld I would say its cast iron,not cast steel. Completely different welding procedure and consumables. Cast steel is generally grinding a weld prep and welding with a low hydrogen of S6 wire after a preheat. Cast iron is a completely different creature and I would be bronzing it or using a nickel rod or wire.
Any welding rod or wire with iron in it is going to have issues in the long term. Best of all is find someone who specialises in welding cast iron and has a furnace and can heat the whole thing red and fusion weld it with cast iron rods.

pics

Pics

Some of the weld looks decent but in the bottom pic looks like some of it is just piled on top of the piece which might indicate is some type of cast iron. Preheated cast steel, the weld should wet out on the sides like normal steel. The weld piled up like that creates a notch effect at the edge that can cause cracking. Did you do a spark test or see if it would cut with a cutting torch?

fast_st said:

Once you take that tag off you're good to go!

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LOL...sshhhhhhhhh....I done that once, or maybe twice....

time to make a camp fire and throw that chunk of metal in it, and when it gets a nice glow to it, weld the crap out of it and throw it back in the fire with some more wood and let it burn out overnite..if it still cracks, put in scrap pile and buy a replacement...putting in the fire will burn off any contaminating oil and junk, also peen the welds, and the slow cooling of overnite should be slow enough to prevent cracks, if it still does then its a mix of metal thats not weldable.. I know the feeling to want to fix and not spend $$$$, but if it fails when your using it, what will be the cost and liability to you??