the billet to be obtained which is intended to undergo thixoforging naturally in the case of addition of arsenic during the production of the liquid metal all the necessary precautions must be taken so that the toxic vapours released are collected in such a manner that they do not poison the staff at the steelworks in fact the presence of arsenic most frequently results from the addition of copper or tin which arsenic generally accompanies by way of an impurity as arsenic is an element which is very highly segregating it is necessary to take it into account to be sure that in combination with the other segregating elements it does not lead to effects which are prejudicial to the hot transformation which have been cited table 1 sets out the compositions of a first pair formed by a reference steel and a steel according to the invention which is derived therefrom relative to the reference steel it will be seen that apart from the very significant addition of silicon the manganese content has been substantially increased so as to re establish a ratio mn si in accordance with the preferred requirements of the invention 0073 fig1 represents the proportion of liquid phase as a function of the temperature in these two steels the measured solidus temperatures are 1315 u00b0 c for the reference steel and 1278 u00b0 c for the steel according to.