1943 D Steel Wheat Penny

If it's been replated it would account for the extra weight for sure can't tell that from these pictures but on the 43 replaying is very common

Sometimes planchetes are outside of normal tolerance limits. It happens.

There are cents struck on planchets intended to be used for foreign coins that were then being struck by the Philadelphia Mint. On quick glance however most appear to be over 3.0g. Your coin is just slightly out of tolerance: Steel cent = 2.689g/2.754g +/- 0.130g (Heavier weight produced in late 1943)

Weight may just be over which happened during this timeframe. According to Roger Burdette, Cheap steel for 1943 cents was coated with zinc by several processes, depending on which company was supplying planchets. Although the Mint specified thickness of zinc, the reality was that no one much cared. Steel strip was electroplated, hot dipped, hot rolled, heated and sprayed with molten zinc then rolled and just about any inexpensive process available. This inconsistency was also why the weight of 1943 cents was increased by 1-grain. This allowed extreme over- and under-weight planchets to be accepted as legal coins.

It's unusual to find an experimental alloy piece in pocket change although that has happened as well. https://www.coinworld.com/news/us-c...ntimony.html So a nondestructive metallurgical analysis XRF (X-ray fluorescence) can always be done generally on a cent if there is no conclusion and you want to know but the initial thought is always that its just slightly over tolerance when it doesn't match up to known foreign planchets and could therefore be nothing more than that since these were strikes for general circulation as well as mentioned that it was wartime and was not always in tolerance as might be today, or struck on a thick rolled planchet but that also may be higher weight generally than what is here. Sometimes we over think hoping for the lottery ticket win.

These coins were from my fathers collection