Nippon Steel plans to spend about $3 billion on a new hot rolling mill at US Steel's Mon Valley Works in Pennsylvania. The current equipment has been running for about 90 years. The new mill should start operating in the second half of 2029 & will produce much higher-quality steel. The project is part of an $11 billion investment pledge that Nippon Steel made when it bought US Steel in 2025. The company also plans to double its American steel output within three to five years.