Union Sidérurgique du Nord de la France ( USINOR ) was a French steel group headquartered in Paris, together with the Spanish Aceralia SS and the Luxembourg Arbed S. A. From 2002, the European steel group Arcelor was formed, which was acquired by the competitor Mittal Steel Company in 2006.

Usinor was formed in 1948 as a state-owned company through the merger of metallurgical, steel works and rolling mills of the North and East and the blast furnaces, foundries and steel mills of Denain - Anzin. Usinor had production facilities in Calais, Roubaix, Nivelles and Charleville- Mézières, which lay adjacent to the northern French -Belgian coalfield. In Usinor was cast iron and steel, but also produces flat steel.

In the same year, the Société Lorraine de Laminage Continu SA was ( SOLLAC ), headquartered in Paris as a joint venture by the family de Wendel, the steel industry created in the 18th century, together with eight other Lorraine company founded, who continued the flat steel and brass industry of Lorraine with a capacity of 1 million tons per year. Here is the raw material for the French automotive and electrical industry was created. Sollac had production facilities in Dunkirk, in Rombas, Hagondange, Gueugnon and Longwy in Lorraine, but also in the department of Bouches -du -Rhône. To Sollac included the Dillinger Hütte in Germany.

1950 was also the Metz in Lorraine Union Sidérurgique SA ( SIDELOR ) based in Paris founded, another steel company owned by the de Wendel family, which had production facilities in Rombas, the blast furnaces and foundries in Pont -à -Mousson, Homécourt and Micheville in Lorraine, where minette iron ore were mined. The Rombacher metallurgical plants were originally founded by Carl Later Koblenz Group. During the Second World War they were adopted by Otto -Ernst Flick in trusteeship. Sidelor 1968 absorbed by the family de Wendel.

1964, the other major French steel group SACILOR was founded and took over the steel plants in Lorraine. In the early 1970s accounted for a Driitel the French steel production to Usinor.

1971 campaigned Usinor in a prospectus for the capital increase thus, have increased six-fold that its sales increased since 1968 by about 80% and the cash flow. Under the assumption that the next five years would take the same course as 1970, the company saw able to be 4 billion francs strong investment program to fully fund itself. While the steel crisis of the 1970s, a variety of steel jobs was mined in Lorraine and in neighboring Belgium-Luxembourg area. The long, tough but ultimately unsuccessful struggle of the steel workers of Longwy excited for this mid-1970s, international attention and solidarity.

After the election of François Mitterrand, the new government Usinor and Sacilor, which were merged in 1986 to Usinor Sacilor nationalized. Four years later, the third French companies in the sector, Sollac was acquired by Usinor. The following year also Ugine Sacilor was integrated. In 1994, the stainless steel producers have been restructured in the Aster - Holding.

In Germany Usinor acquired in 1980 initially accounted for 25 % of the wire work of Ludwig in Lampert home, which she topped up in 1990 to 100 %. In 1993, Usinor Sacilor in Neuves Maisons a subsidiary of structural steel, the Société des Acier d' Armature pour le Concrete (SAM ), which supplied the wire Werke Ludwig from his electric steel plants Neuves Maisons and Montereau on the water of the Moselle and the Rhine with starting material. 2000 sold Usinor the SAM along with its German subsidiary of the Italian Riva Group.

Privatized in 1995, the conservative French government Usinor Sacilor SA In 1997 the company changed its name again to and changes his name again Usinor SA In France Usinor busy 1997, around 50,100 people and generated sales of 72,000 million francs. In 1998, the Belgian competitor Cockerill -Sambre SA adopted what in 1999 had a new organization of the group result, until it was incorporated in 2002 in multinational companies.