This French steel giant has a long and turbulent history. The factory, which primarily produced 'long steel products', was one of the most important steel mills in the region in the 1970s. It complemented a nearby steel mill, which in turn specialized in 'flat products'. In the mid-1970s, the company was not only hit by the general crisis in the steel industry but also fell victim to the poor technological choices it made itself.

The steel company was founded around 1890 by a German industrialist. He acquired all the land needed to build the factory and oversaw the development of the infrastructure and the railway and road network. In 1890, the company started with two blast furnaces. Later, capacity was expanded to a total of seven blast furnaces.

By 1903, the factory was already a complete facility comprising 2,745 hectares of iron mines, seven blast furnaces, a Thomas steel plant, a Martin steel plant and various rolling mills. There was also a cement plant, a gas plant supplying a thermal power plant. Furthermore there were of course all supporting services, such as slag mills, a brick factory, lime kilns, a foundry, general workshops, a laboratory…

In the mid-1960s, the steel plant was extensively modernized. Management made the strategic decision to switch to a different production process. The first oxygen steel plant, based on the Kaldo process, started operations in 1969. The plant astonished the world with its gigantism: the building, 100 meters high, 430 meters long, and 150 meters wide, was designed to produce 7 Mt (metric tons) per year using 6 converters.

It took only a few months to realize that the gamble on the Kaldo process was a major strategic mistake. The monstrous 1,000-ton converters, twice the size of any other Kaldo converter, proved to be just as unreliable as they were economically unviable. The race for size killed the process. Instead of saving money, costs increased with size, whereas the opposite was expected.

In the early 1980s, they moved away from the Kaldo process. Unfortunately by then, it was already too late. In 1999, the steel plant was sold for a symbolic franc to the then still unknown Lakshmi Mittal. He implemented a number of restructurings, reducing the workforce to the bare minimum. However, when the plant was still not profitable in 2008, the now-constituted ArcelorMittal Group decided to shut down the plant.

In early 2009, the fire at Forge Lunaire went out for good. Ten years later, demolition and remediation works were commenced.