Anti-dumping duties on imports are sought by a trade group or producer(s) in a country or trading bloc. They do so when the goods are believed to be being sold at significantly below their home market price – or even below their cost of production – and as a result cause, or threaten, significant economic injury (material injury) to domestic producers of similar goods.
Countervailing duties on imports are sought when the supplying country’s production and/or exports are directly or indirectly subsidised to the extent that they cause or threaten material injury to domestic producers of these goods.
Both duties are allowed under WTO rules, but are only imposed after an investigation which may reject them. The US market is attractive to steel exporters most of the time, and this has meant that over the years these duties have been a noticeable feature of that country’s steel trade. But AD and CV duties are also used elsewhere, including by the EU, Canada, Mexico, Southeast Asian countries etc. And for more detail click and see this and this wikipedia entries.