Reddit and even the World of Warships forum is posting this picture. Supposedly part of the Yamato's armor (26 inches thick), pierced by a US Navy 16-inch gun. Said to be on display at the US Navy Museum (where I don't know.)
Well, this site History and Technology - Ballistic Tests on the IJN Shinano's Turret Face Armor - NavWeaps says the test was conducted in 1946 using the turret face for the Shinano. I'm guessing this was found somewhere in Japan and didn't sink with the Shinano which was already a carrier.
Ballistic Tests and Metallurgical Examination of Japanese Heavy Armor Plate Accession Number: ADA955281 Title: Ballistic Tests and Metallurgical Examination of Japanese Heavy Armor Plate Descriptive Note: [paste:font size="6"]Corporate Author: NAVAL PROVING GROUND DAHLGREN VA[/paste:font] Personal Author(s): DeRocher, H. L. Meyers, W. W. Report Date: 1947-11-01 Pagination or Media Count: 102.0 Abstract: Descriptors: *ARMOR PLATE PROJECTILES BALLISTICS ARMOR PIERCING AMMUNITION METALLURGY Subject Categories: Armor Distribution Statement: APPROVED FOR PUBLIC RELEASE https://apps.dtic.mil/sti/pdfs/ADA955281.pdf