Environmental Aspects of Lead-Free Free-Machining Steels Production

Abstract

The paper presents the results of comparative studies of working area air pollution during the production of three alloy steels containing bismuth and calcium as machinability-enhancing additives: AVTs40Kh13 (0.4 %C + 13 %Cr + Bi + Ca), AVTs14Kh17N2 (0.14 %C + 17 %Cr + 2 %Ni + Bi + Ca) and AVTs19KhGN (0.19 %C + 0.9 %Mn + 0.9 %Cr + 0.9 %Ni + Bi + Ca). Experimental studies were performed in industrial conditions at Zlatoust Electrometallurgical Plant, Ltd. According to the technology developed and used at the enterprise, bismuth was introduced in the form of shot to the steel stream during casting of 0.5 t ingots at a special casting site. Air samples (of statistically reliable volume) were taken using standard techniques in the working areas at principal moments of technological processes. Bismuth content in air samples was then determined by polarography method. The results demonstrate that bismuth introduction to the steel stream during top casting results in bismuth concentration in the air of the working areas exceeding the maximum permissible concentration of 0.5 mg/m3 only in the first 10 min after casting start. Bottom casting and hot forming of free-machining steels containing bismuth and calcium is not accompanied by pollution of the air in the working area with harmful substances in amounts exceeding maximum permissible concentration, unlike leaded free-machining steels.