steel plate emdeded in reinforced concrete

I wouldn't normally worry about similar metals. For galvanic corrosion, you need moisture, dissimilar materials, and electrolyte. If you have steel to steel the corrosion rate will be minimal. In addition, the high pH of concrete passivates the steel to some extent.

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-Dik

The key here is dissimilar. When they are the same there is no difference in potential and no accelerated corrosion.

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P.E. Metallurgy, consulting work welcomed

The weld metal used will be slightly different (more noble due to additional alloys) from the plate and rebar steel materials.
However once embedded into concrete, water ingress is difficult (unless the concrete is porous, i.e. badly made and poured). Also the anode to cathode ratio is at the benefit of the weld metal and won't easily corrode galvanically.

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The weld metal is absolutely more sacrificial than the base metal. Higher strength steel alloys will tend to corrode at a higher rate than low strength alloys under the same conditions.