Steel casting - Melting furnaces

According to statistics compiled by the Syndicat Général des Fondeurs de France, over the past few years, French steel foundries have delivered 150 thousand tonnes of parts, generating sales of e686 million, of which 40% for export markets.

The breakdown of the different categories of cast steels reveals four main alloy families:

• carbon steels ;

• low-alloy steels ;

• high-alloy or stainless steels;

• nickel- or cobalt-based alloys.

These families have completely different chemical compositions, particularly in terms of carbon, nickel, chromium or molybdenum content.

Casting capacities vary enormously from one plant to another, as the mass of steel castings ranges from a few grams to over 200 tonnes. The demand for liquid steel varies greatly from one foundry to another.

The result is a wide variety of manufacturing processes and equipment for steelmaking, the nature and capacity of which must be adapted to the needs of each foundry.

In contrast to the iron and steel industry, where conversion processes from cast iron to oxygen are still widely used, the production of steel castings in France is carried out by some thirty companies, mainly using electric furnaces. Fossil-energy melting processes using coal, fuel oil or gas have all but disappeared, for technical, economic and environmental reasons, as well as to improve working conditions. The same applies to duplex processes involving the refining of liquid pig iron from the blast furnace or cupola furnace, which was then decarburized in Robert-type converters or pure oxygen converters.

In France, electric arc furnaces currently account for around 3/4 of production, with induction furnaces accounting for the remaining quarter. This breakdown is generally respected in most industrialized countries, and the share of induction furnaces, albeit limited, is growing steadily. Other processes, such as cold crucible furnaces and levitation furnaces, are reserved for the production of very high value-added specialties, and their production remains marginal. The capacity of melting furnaces must be adapted to the size of the molded parts, and varies from a few kilograms to a hundred tons.

Some companies also have secondary metallurgy equipment that enables them to produce high-purity steels, as well as very low-carbon chromium stainless steels, under attractive economic conditions. The electric furnace is then considered as a simple melting and pre-refining machine. These include

• the VOD (Vacuum Oxygen...