China’s pledge to reduce overcapacity in its steel industry has eased tension with the U.S. but probably won’t be enough to head off a trade clash between the world’s two biggest economies over whether the Chinese have truly embraced market forces.

Treasury Secretary Jacob J. Lew has been pressing China in recent months on the issue of its excess capacity, arguing in the past week that it has distorted global markets for steel and aluminum and may have a “corrosive” effect on the country’s growth. Lew’s arguments echo those made by U.S. steel and aluminum makers, who say state-supported Chinese producers are feeding a global glut of the commodities…