The Steinway piano company has a new owner. This fall, the investment firm Paulson & Co. — led by billionaire John Paulson — spent about $500 million and bought all of Steinway & Sons, the venerated piano maker. The deal includes a foundry in Springfield, Ohio, where the Steinway pianos are born in fire. The O.S. Kelly Foundry has been making Steinway's plates since 1938. The plate is the cast-iron heart of…