Answer and explanation:
The people who would be angry about Japanese steel dumping are the American steel producers/manufacturers. If Japanese steel costs much lower than American steel, that means American manufacturers will lose clients and, consequently, money. If the product is the same, if there are no differences in quality, then buyers will simply go for the cheapest one.
The people who would benefit are companies and factories that need steel to make their products. Manufacturers of appliances, cars, machinery, and even construction companies would greatly save money due to the low costs of such an essential material. That could also benefit their clients, since low costs of production can mean lower prices when the products are sold.