The whole Chinese steel story went pretty under the radar. For years people complained. Trump brought it up a lot.
The series Billions had a storyline about a guy cornering his local steel market by greasing the Chinese, the inspectors, and the local gov all to sell incorrectly rated Chinese steel to big contracts. It's the best example I've ever heard provided for how or why a situation like the Chinese steel drama happened.
Trump is probably playing hardball about defective steel and the Chinese are being extra extra extra careful and dragging their feet to make it hurt.