Section 232 Investigations: Overview and Issues for Congress [Updated April 7, 2020] [open pdf - 2MB]
From the Introduction: "The Trump Administration has conducted five investigations, two of which have led to presidential proclamations imposing tariffs on U.S. imports of certain steel and aluminum products, using presidential powers granted under Section 232 of the Trade Expansion Act of 1962. Section 232 authorizes the President to impose restrictions on certain imports based on an affirmative determination by the Department of Commerce (Commerce) that the targeted products are being imported into the United States 'in such quantities or under such circumstances as to threaten to impair the national security.' The Constitution gives Congress primary authority over international trade matters. In the case of Section 232, Congress has delegated to the President broad authority to impose limits on imports in the interest of U.S. national security. The statute does not require congressional approval of any presidential actions that fall within its scope."
CRS Report for Congress, R45249
Congressional Research Service: https://crsreports.congress.gov/