An installation for producing stainless steel for all stainless steel products both in the austenitic and the ferritic range, based on liquid pig-iron and FeCr solids, without using a supply of electrical energy. The liquid pig-iron, after being pre-treated in a blast furnace, is subjected to a DDD treatment (dephosphorization, desiliconization and desulphurization), is heated, finished or alloyed and deoxidated. The quantity of slag-free liquid pig-iron that has been pre-treated in the blast furnace and a DDD device is separated and introduced into two classic “twin” AOD-L converters, where the required chemical process steps (of the heating, decarburization and alloying stages) take place in parallel contrary processes using autogenous chemical energy. The heating stage is carried out first in the first twin AOD-L converter and the decarburization is carried out first in the second twin AOD-L converter.