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Embrittlement of cast Mn–Ni–Al bronzes

Abstract A review of the literature of Mn–Ni–Al bronze alloys reveals a sensitivity of these alloys to slow cooling conditions, which has a markedly detrimental effect on impact resistance and failure of large cast components. Investigations of the cause of failures as described in this review have not resulted in solutions. This paper presents a metallurgical study of the phenomenon of the embrittlement of the Mn–Ni–Al bronzes. The study is based on investigations on material of an experimental casting containing 18–21 wt-% manganese and on material of failed ship propeller castings with 11–15 wt-% manganese. The investigations revealed the appearance of a hard and brittle phase in the structure of the material depending on cooling conditions and manganese content. This phase can be identified with the Mn(β) type phase in the Fe–Mn– Al alloys. The Mn(β) type phase has a hard and brittle nature and is assumed to be the cause of embrittlement of the Mn–Ni–Al bronzes.