Investigation of structure and properties of high-machinability low-carbon steels with pb, bi, s and cu additives

A comparative study of the structure and properties of three experimental lead-free steels alloyed with sulfur, copper and bismuth (0.28S + 0.4Cu; 0.2S + 1.3Cu; 0.28S + 1.3Cu + 0.1Bi), and free-cutting lead steel AC14 (0.2Pb + 0.2S + 0.2Cu) has been carried out. It is shown that machinability of steel AC14 is considerably higher than that of lead-free steels. To improve machinability of lead-free steels, alloying with bismuth is the most preferable, alloying with sulfur is less effective, and copper is the least effective in this regard. No influence of such structural factors as texture, shape factor and hardness anisotropy on machinability were found. It has been established that the effectiveness of low-melting additives such as lead and bismuth depends on the technological history of material and may differ for cast and deformed products, and it is important whether it was hot or cold deformation.