Magnetic blow doesn't exist when welding with AC (alternating current). Is it possible to use AC in your case?
Giovanni S. Crisi
Sao Paulo - Brazil
Happy New Year to all the frequentors of this Forum.

You could try moving the ground clamp.Say if the ground is clamped on the monel try clamping it on the HY-80 plate or vice versa.

"This is from my failing memory" The reason it is more evident when half of the electrode is consumed is as the rod gets hotter the resistance in the rod decreases. You could try decreasing the amps which would make it take longer for the heat to build up in the rod and that might make the arc blow not as noticeable or it could stop your problem all together.

Question: Does the slag line start at the halfway point of the rod or does in exist all through the weld?

You may need to demagnitize the HY-80 steel plate before continuing. Once the HY-80 steel plate is demagnitized, use multiple work leads connected to opposite ends of the joint or along the joint to reduce the current density passing through any one point. In this case I would try connecting two work leads to opposite corners, i.e., one lead to the monel and the other to the carbon steel as far from each other as practical.The intensity of the magnetic field is proportional to the current, thus, in general, by reducing the current through a point of contact you will reduce the field intensity by 50% as well.

The fact that the arc is being pushed to the monel is a function of the polarity of the magnetic field that has developed in the HY-80 steel plate. You will have to "destroy" the magnetic field that already exists before the use of multiple work leads will help.

Degausing or demagnetizing the plate can be accomplished by wrapping the HY-80 with several turns of the welding cable. Energize the cables with AC current and slowly step down the amperage of the alternating current. Finally, remove the wraps of welding cable, one at a time while the current is flowing. You can determine the direction of the "magnetic poles" of the HY-80 by suspending a paper clip by a thread and holding it near each side of the HY-80. The paper clip will be attracked more strongly toward the poles of the HY-80. You wrap the leads parallel to the axis of the magnetic poles. The resulting magnetic field (once energized by AC) will overpower the existing remanent magnetic field thus destroying it. The step down technique will prevent the formation of a remanent magnetic field perpendicular to the initial filed.

Hope this helps you.

Good luck - Al