A mill certificate showing the full chemical composition — including chromium, nickel, molybdenum, and carbon percentages by heat number — is required to substantiate stainless classification and to respond to any CBP or Commerce Department inquiries under AD/CVD proceedings. Country-of-melt and country-of-manufacture may both be relevant if the product was processed in multiple countries.

For customs purposes, origin is generally determined by the country of last substantial transformation, which for semifinished steel is typically where the steel was melted and cast. However, antidumping and countervailing duty orders may define the scope of covered merchandise differently, sometimes capturing products melted in one country and processed in another. Importers should review the specific order language and consult a trade attorney or customs broker when multi-country processing is involved.