welding a-36 to 4140 6

[conveyorbud]

We have a bull gear 214 tooth (142.667" pd) made of 4140 steel through hardened to 245-285 BHN. We are trying to weld it to a36 5/8" thick steel mixer drum. Both items must remain "very round". any suggestions?

 

[Carburize]

As an Irish policeman once said to me when I asked for directions "If I was you I wouldn't start from here" however since you are here I would suggest that you weld with the lowest strength weld metal you can find which just over-matches the A 36, a material with a yield strength of 40 ksi if you can find one. Then weld with as balanced a technique as you can to even out the stresses.
The 4140 will harden in the weld heat affected zone and will be brittle and prone to cracking unless you carry out a post weld stress relief heat treatment - this in itself is likley to cause some dimensional changes.

 

[metengr]

To add to what carburize had mentioned, you could use a nickel electrode (like Ni99). The tensile strength would match the tensile strength of your steel drum (UTS of around 70 ksi). The Ni99 has good ductility to avoid generating significant residual stresses.

Because of the hardenability of 4140 alloy steel, you could also look at using a temper bead technique to avoid stress relieving. Before attempting this method, I would generate a weld coupon to optimize the welding parameters to verify softening of the heat affected zone.

Preheat of 350 deg F is recommended and staggering the weld passes should be done to balance shrinkage stresses. The concept would be to apply a "butter" layer on the 4140 side of the weld joint and lay subsequent weld passes while remaining on top of the butter layer to temper the 4140 alloy steel heat affected zone. The interpass temperature should not exceed 700 deg F to avoid generating too much heat to affect the gear heat treatment. If the temper bead technique can provide adequate softening, it may help to keep distortion to a minimum.

 

[bklauba]

In addition, a vibratory stress relief treatment done at the end will take a bite out of the remaining stresses that could threaten the dimensional integrity of the gear, a threat that could manifest itself during reassembly and/or during early usage. The treatment will have no effect of a metallurgical nature.

BK

 

[stanweld]

I have successfully made these types of dissimilar welds on numerous occasions with E7018 electrodes; initially buttering the 4140 side of the joint with at least two layers of E7018 and then making the strength weld. Preheat was 450 F min. I have also used metengr's approach, the principal benefit of which is the lower preheat temp.

 

[arto]

Weld on brackets/clips to the drum & pin it through the gear

 

[Carburize]

I like arto's suggestion - is it possible to attach fittings to the drum then mechanically attach the finished gear to the fittings? It would overcome all the issues with regard to welding onto the 4140 gear ring after it is finished.

 

[conveyorbud]

Arto

Excellent suggestion. We will investigate. Thank You

 

[bklauba]

I also like that suggestion, as long as it supplies the mechanical integrity req'd. It might also ease access for service/maintainance/inspection. It could well simplfy the whole job.

BK