Abstract
In order to clarify the cause of the magnetism at the grain boundary and the slip plane of the work-hardened Hadfield steel, manganese steels of various compositions were examined mainly by the magnetic colloidal method after cold working, In every case, whenever an austenitic manganese steel is work-hardened by impact at room temperature, by static tension at room temperature, or by impact at the liquid nitrogen temperature, a small amount of ferromagnetic products is formed at the traces of slip planes and at grain boundaries. These ferromagnetic products are not formed at every slip plane and grain boundary observed in the etched surface, but formed very partially.
In unstable austenitic steels, both grain boundaries and slip planes become thicker layers in the magnetic colloid patterns, but with increase of the carbon or manganese content in steels, the magnetism at the slip planes is gradually diminished first, and next at the grain boundaries. Ferromagnetic products are not formed at grain boundaries in Fe-Mn alloys. The magnetism at the grain boundaries can be decreased or disappeared by annealing prior to cold working, but the magnetism at the traces of slip planes is not wholly affected.
The ε phase in manganese steels are considered a paramagnetic substance as in the γ phase, but has a slightly stronger magnetism than the γ phase at room temperature. Even when the ε phase coexists in large quantities with the γ phase, the magnetic colloid does not deposit at both phases. It is considered that ferromagnetic products at grain boundaries in the work-hardened Hadfield steels are caused by the segregation of carbon at their grain boundaries, which are accelerated by cold-working and grown up to a complex carbide. It is anticipated that a small amount of very thin martensitic layer is present along the traces of slip planes.
