The Embrittlement of Blackheart Malleable Iron

Abstract

With the view of investigating the behavior of embrittlement of blackheart malleable iron, Charpy impact tests were carried out for series of specimens. The influences of phosphorus and/or nitrogen content, quenching temperature, holding time, and cooling rate were studied on the brittleness of these irons. Micro hardness test was also carried out on the ferrite grain interiors and its boundaries of irons subjected to a variety of treatments.
Various kinds of surface analyzers such as IMA, ESCA, and AES are utilized for the analysis of the grain boundary fracture surfaces of the embrittled blackheart malleable iron.
The results obtained are as follows.
(1) Phosphorus has a close relationship to the embrittlement of blackheart malleable iron, while nitrogen appears not to give rise to brittle fracture.
(2) Holding at 450°C results in the embrittlement of the iron.
(3) The reversibility between brittle and ductile fracture is confirmed on the impact values.
(4) Quenching from 650°C before 450°C embrittling treatment retards the appearance of brittle fracture in the iron having higher content of phosphorus.
(5) Micro hardness test shows that an embrittled iron has a little increment of hardness at grain boundary, compared with that of grain interior of the same iron.
(6) The remarkable segregation of phosphorus in the grain boundary of the embrittled iron is recognized by means of IMA, ESCA, and AES analyses.