Abstract
Experiments were performed to make clear the true nature of harmful effects of sulfides on mechanical properties and workability etc. of high-sulphur steels such as S-type or S-Pb-type free-cutting steels, and to solve these problems from the results. Various experimental specimens were melted by an atmosphere-controlling high-frequency furnace, and then studies were made on the morphology, deformation of sulfides by working and their effect for the toughness in the length and breadth direction of steels.
The results obtained were as follows; (1) Excess Al or Si in steels elongated sulfides remarkably by working, and this tendency was found also on increase of Mn/S ratio in steel.
(2) There was a large difference between the toughness in the length and breadth direction in such materials, and the toughness in the breadth direction was very inferior to the length direction. (3) On the contrary, decrease of Mn/S ratio or existence of oxygen in steel restrained the elongation of sulfide due to working. (In this case, MnS presumably dissolved FeS or (Fe, Mn) O, or they existed together.) (4) However, the small Mn/S ratio materials was liable to be cracked by hot working. The fact was ascribed to high temperature brittleness. (5) Each problem abovementioned could be solved by a displacement of part of the Mn with the Zr.
