Cracks in welds

[Dewgilljr]

I am tig welding and I'm finding small hairline cracks in my fresh welds. What can cause these cracks?

[MXtras]

Welding what? Steel? Stainless? Aluminum?

Details. We need details.


Scott

[Rocky D]

Welcome to the forum...as stated we need more info....we can help.
What are you welding? Material, rod, position, machine?

[Dewgilljr]

I was welding a mild steel flat plate to a round piece of acme thread (a nut for the acme thread. Not sure if the nut is hardened or not. Boss found it in the cabinet and wanted it welded. I was using stainless welding rod. We us that most of the time. Cleaned parts with wire brush. they were not perfect but clean. Just wanting to be better welder. Thank you

[Rocky D]

Isn't ACME thread that square thread? Could be then, that it's cast iron. An ordinary nut would not exhibit your description of the problem.

:D you might want to edit your location, Dew...it looks like you are Fighting Illnesses at your home. :D

[Dewgilljr]

Acme thread is the square one. We turned down the size on the lathe and it did not act like cast iron. Isn't cast iron porous? Is the location better. or should I put Home of the late Chief Illiniwek

[hogan]

this is to be expected when welding a nut. try a high ni filler

[Pangea]

When in doubt on ferrous metals, use silicon bronze rod.;)

[Rocky D]

Acme thread is the square one. We turned down the size on the lathe and it did not act like cast iron. Isn't cast iron porous? Is the location better. or should I put Home of the late Chief Illiniwek
It's not always porous.
When you turn cast iron, it spits out granules, not like steel, where you get a ribbon. While sil bronze is good for dissimilar metals, it is not very strong...so be careful how you use it.

[PentaWelder]

What kind of stainless filler material did you use? If you are welding a stainless nut to plain carbon steel, you need to use a 309 filler metal or else you will get weld cracking. I recommend ER309L-16 filler metal. The "L" stands for low-carbon. this is used because of carbon-precipitation in many stainless steels. This happens when you get the stainless hot enough that the carbon molecules combine with the chromium molecules creating chromium carbide. When these molecules combine, it takes away from the amount of chromium in the metal what aids in corrosion resistance. But that's only if the base stainless has enough carbon content to sustain this action from happening. Now if you were welding a plain carbon nut to a plain carbon plate, then the stainless weld will crack almost no matter what.

ACME threads are just the way the threads are configured. They can be made from any type of material not just cast iron. And yes, cast iron is very porous. That is why you should to use a heavy solvent on them before any welding is done on them or they will entrap oils that will contaminate the weld. This is also why cast iron is preferably torch brazed or braze welded.

And, the hardness has nothing to do with the cracking. It is solely the base and filler material's chemical composition.

[PentaWelder]

The granules that you see when you machine cast iron are carbon pockets that are trapped inside the metal itself. This is because of cast iron's high carbon content that ranges from 2.5-4.5 percent which explains the brittleness of the cast iron. The carbon pockets can be explained with at simple experiment. Take a cup of water (this represents steel which is essentially what cast iron is before all of the carbon is added) and start adding sugar (this represents the carbon) to it. The water dissolves the sugar (much like the carbon in the steel) until a certain percent of sugar in the water is reached and then the water is not able to hold any more sugar, so it just sits there on the bottom (representing the carbon pockets). This is known as a saturated solution. Hence the carbon inclusions. These pockets are the reason why cast iron is as porous as it is.

[bobad]

The water dissolves the sugar (much like the carbon in the steel) until a certain percent of sugar in the water is reached and then the water is not able to hold any more sugar, so it just sits there on the bottom (representing the carbon pockets).

That works with coffee too. Trust me, it does. :D


There are many different grades and purities of cast iron. Some are less prone to cracking than others. Pre-heating can help a lot.

[hogan]

where are the cracks? on the nut to weld? or weld to plate? or only in the weld?

[crenshawjm]

ROFLMAO....... i figured it out.... you forgot the axle grease, it works like a flux to bond the threads of the acme rod to the nut

[BBackSoon]

Is the location better. or should I put Home of the late Chief Illiniwek

**** Political Correctness.