First the four Iowa class Battleships that were completed were not scrapped, as others have stated all four still exist as museum ships. Two incomplete Iowa class ships, USS Illinois (BB-65) and USS Kentucky (BB-66) were scrapped, but these ships were never finished. A proposal was made to convert Illinois and Kentucky to carriers, but this was abandoned after the design team realized that compared to the Essex class carriers being built, the converted battleships would carry fewer aircraft, be significantly more expensive and take longer than building new Essex-class carriers.
As far as I know, there was only one WW2 Battleship that was converted to a carrier, that would be the IJN Shinano (above). The largest carrier built up to that time, she was also the largest warship ever sunk by a submarine. She was a Yamato class battleship and was still under construction when the decision was made to convert her to a carrier, but the advanced state of her construction prevented her conversion into a fleet carrier, so the IJN decided to convert her into a carrier that supported other carriers, she would have been a glorified aircraft transport. It was unfortunate that she put to sea before all the water tight doors were installed, she sunk after being hit by four torpedoes from USS Archerfish.
Only two other ‘battleships’ I know of that were converted into Aircraft carriers, but they were both ships from first world war, specifically the British HMS Eagle and the French Béarn, which compared to WW2 fleet carriers were not up to par, both carried around 30 aircraft and could only make 24 and 21 knots of speed.
There were several battle cruisers that were successfully converted in the 1920’s, but those are not WW2 ships.