In order to reduce the susceptibility to embrittlement of steels such as a rotorshaft for power plant, which are to be used at high temperatures, experiments were carried out on the optimum conditions for the removal of tramp elements like Sn, Sb and As by the addition of CaC₂. Industrial scale tests were also carried out, based upon the experimental results obtained. The results obtained can be summarized as follows.
(1) These impurities can be removed by reduction, and the reduction was accelerated by the rapid decomposition of CaC₂ at low initial carbon content and high temperatures.
(2) The amount of impurities removed was found to be proportional to the increase in carbon content during reaction and the initial impurity content. The proportional constant increased in the order of Sn, P, Sb and As.
(3) It was found from the industrial scale tests that the impurities could be favorably removed by using Ar stirring from the bottom of the ladle and by using CaC₂ injection increasing the reaction surface area.