Split the hub above the key, drive 2 wedges in the kerf, one inboard - one outboard, and get on with the show. This one runs just like you see it. Never welded back. Or weld a nut on the hub and screw a cap screw in to push the axle.
In the 50 years I've worked with this type of repair I've found penetrants to be a waste of time just like you've discovered.
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