Maragin behavior of an Fe-19.5Ni-5Mn alloy. III: Mechanical properties

Abstract

A high maraging strength in Fe-Ni-Mn alloys can be achieved at the expense of a marked loss in ductility. Very fine precipitates are observed when peak strength is reached. At peak strength, the Fe-Ni-Mn alloys exhibit brittle failure, mainly along prior austenite grain boundaries, irrespective of the nickel content. The presence of a small amount of retained austenite prior to aging does not improve the ductility. Previous explanation of the embrittlement in Fe-Ni-Mn alloys was attributed to the segregation of Mn to prior austenite grain boundaries. However, this is not fully supported by the present studies. Auger electron spectroscopy reveals no decisive evidence of manganese segregation. Some degree of ductility in the aged martensite may be required in order to prevent brittle fracture. Dual aging recovers part of the ductility and improves the strength slightly. The effect of reversed austenite on ductility may vary, depending on its morphology. Matrix and recrystallized austenite are beneficial to both elongation and reduction of area, but lathlike austenite lowers the elongation, probably because of its lamellar morphology. The lamellar structure of the lath martensite is also detrimental to elongation.