Cities get titles for either good or bad reasons. One example would be Philadelphia as the "City of Brotherly Love." On the downside, Philadelphia has been negatively nicknamed as "Killadelphia." The reason for the negative nickname is because of the high crime rates and murders in Philadelphia. There are many reasons a city would get a bunch of positive or negative nicknames.
Why does Pittsburgh, Pennsylvania have the tile of the "Steel City?" The answer is obvious: steel. Pittsburgh is known for its steel mills and steel production companies. A good deal of American steel is produced out in Pittsburgh, Pennsylvania. By the early nineteenth century, Pittsburgh was producing massive quantities of iron, brass, tin, and glass products. That would be the first start of the origins of Pittsburgh getting its title of the "Steel City."
Steel manufacturing let alone from Pittsburgh was stimulated and triggered by the cutoff of supplies by Britain during the War of 1812. Almost halfway into the nineteenth century, there were many Welsh people working in the steel mills. After the chaos of the Merthyr Riots, many of them would migrate to Pittsburgh. This is proof that steel is in the lifeblood of Pittsburgh, Pennsylvania.
Pittsburgh's steel economy would get a boost with the American Civil War. More iron and armaments would get produced. Andrew Carnegie would then found the J. Edgar Thompson Steel Works. That would be when steel production would begin. The company would transform into the Carnegie Steel Company.
At the beginning of the twentieth century, the U.S. Steel Corporation would be formed. Thirty to fifty percent of America's steel would be produced in Pittsburgh. By World War II, Pittsburgh would produce tons of steel in the millions. This is how Pittsburgh got its name of the "Steel City." Unfortunately, the industry imploded with many steel mills getting closed down and many workers getting laid off.
However, the steel industry is still honored. U.S. Steel is still operating in Pittsburgh. It is a Fortune 500 Corporation. There is also Wheeling-Pittsburgh Steel which is a Fortune 1000 Corporation.
Overall, the origins of Pittsburgh's nickname lie in steel, steel production, and steel mill. One cannot deny that most of the nation's steel during the time came from Pittsburgh, Pennsylvania. There is much historical significance that surrounds the Steel City. As a result, Pittsburgh is called the Steel City.
In NFL, there is the football team called the Pittsburgh Steelers. Also in Pittsburgh, there is a yearly anime convention called Tatsucon. Tatsu means "metal" in Japanese. Steel is a metal. Tatsucon is considered a fitting name for a yearly anime convention in the Steel City.