AR400 Steel Welding on a Backhoe Bucket

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Rebuilding a backhoe bucket using AR400 steel on a Caterpillar 325 Excavator that was rebuilt from the ground up, including the sides, grouser bars and wear block .

There is a ton of welding that goes on to rebuild earth moving equipment. Its smokey, hard, time consuming work but there is money in it. When construction was booming, there was a lot more of this work than right now in 2009 but for those who can do it right and charge a fair price, there are still opportunities out there.

This video shows a job done well. When you can make a bucket look like a piece of art, you are doing something right.

The AR400 steel he mentions is a common alloy steel used in earth moving and mining equipment.

The "AR" in AR400 Steel stands for "Abrasion Resistant".

The Carbon content of AR400 steel is only 0.30% but the addition of 0.8-0.9% chromium gives it a lot more hardness and abrasion properties than low carbon steel has. It is often welded with the same procedures and filler metals as mild steel.

Flux Core, Bare wire mig, and stick welding can all get the job done. Depending on whether the work is done in the shop of the field usually determines what process is used.

For Stick, 7018 rod is the ticket. And make sure its new rod or rod that has been kept in an oven.

For bare wire mig, er70s3 or 6 works.

For flux core, ER71T-1 (gas shielded flux core) is recommended.

self shielded fux core like Lincoln nr-212 is used by some but there is some doubt on the toughness.

Remember to check the data sheet for whatever flux core wire you are using because polarity is not always the same. Some flux core is designed to run on DCEN and others DCEP.

There is nothing that will piss you off more than forgetting to swap polarity after you have fought with a welding machine for an hour or more.

Other general recommendations for welding AR400 wear plate?

A wear plate is usually a quenched and tempered steel and is generally a lot more crack sensitive due its chemical composition of carbon, chromium, etc.

The base metal around the weld rapidly heats and cools during welding, resulting in a heat affected zone (HAZ) with high hardness compared to surrounding areas unaffected by heat. Also, Any hydrogen in the weld metal from moisture or old 7018 rods, may diffuse into HAZ and may cause hydrogen embrittlement, resulting in delayed cracking under the weld or at the toes.

To minimize cracking:

1. Use a low hydrogen process and electrode

2. Preheat...but don't get crazy. excessive preheat may soften the base material making it soft like mild steel

data sheets for welding AR400 can be found here.

3. Slow cool.... never speed cool. If its cold outside, you make have to rosebud periodically to keep the preheat

4. Regular mild steel filler metals are better than trying to match the composition of the AR400 plate. even if you have to oversize some welds to make them strong enough.

6. avoid highly restrained welds...that means the part should fit without 3 porta-powers, 2 come alongs, and double jack.

Carbon arc gouging aka arc-air. gouging out the cracks in a backhoe bucket.

I thought you might find this interesting also.

IF you are not familiar with the carbon arc gouging process, It is a down and dirty way to gouge out cracks or to gouge the back side of a weld to be welded for complete penetration without a bevel.

Carbon Arc Gouging is not for pussies.

Fire will go down your neck and every place it can find if you are not careful...But it does work pretty well.

Most welders call carbon arc cutting and gouging "Arc-air" because of the Thermadyne trade name.

Carbon arc gouging uses a special electrode holder that holds a carbon electrode, and an attachment for compressed air that usually has a quick connect air fitting for an air hose. A small orifice on the jaws of the stinger shoots out a stream of air right down the carbon electrode.

A Stick welding machine that can put out pretty high amperage is used for the current that makes the arc and then the compressed air oxidizes the metal and blows it away..if your lucky that is.

What really sucks is when the there is no place for the molten metal to go except back on you.

Imagine if you had to arc gouge inside the bucket.

That might be the time to get the grinder out .
exit AR400 Steel welding and go to shortage of welders article