Technological aspects of production of environmentally-friendly free-cutting steels without lead

Abstract

Possibility of producing corrosion-resistant steel AVTs14Kh17N2 alloyed with bismuth and calcium is estimated. The steel is intended for cutting operations at automatic mills in mass production. Steel quality was estimated by chemical composition (via X-ray microprobe), macrostructure, surface quality of ingots and billets, mechanical properties and resistance to intercrystalline corrosion after sensibilization annealing at 700 °C. Machinability in cutting operation and the type and shape of non-metallic inclusions were also determined. It was found that bismuth distribution in ingot height and width and rod length is homogeneous. Bismuth exists in steel as metallic inclusions that do not affect the structure of martensite-ferrite steel. Mechanical properties of the corrosion-resistant steel containing bismuth and calcium are at the same level as for the steel without lowmelting elements. Bismuth does not affect resistance to intercrystalline corrosion. Addition of bismuth and calcium enhances machinability of the steel: the number of machined parts resulting in 0.1 mm flank wear of cutting tool becomes 13 % greater, and the roughness of machined surfaces decreases from 2.5 to 1.6 Ra. The chips of bismuth-calcium steel has the shape of short and easily breaking spirals having several times smaller volume than those of the base steel.