1982 Volume 68 Issue 3 Pages 506-513
In order to investigate the embrittlement of blackheart malleable iron, Charpy impact tests are carried out for series of ferritic graphite steel specimens having the same chemical composition as blackheart malleable iron except for carbon content. IMA analysis has also been employed on the grain boundary fracture surface of the embrittled iron.
The results obtained are as follows :
(1) Quenching from 450°C without holding at this temperature shows some degree of embrittlement, i. e. ΔTr+55°C.
(2) Quenching from 450°C after 1 hour holding at this temperature shows remarkable embrittlement, while quenching from 650°C shows some degree of de-embrittlement. Moreover, it has been clarified that the complex combination of embrittling and de-embrittling treatments changes the behaviour of embrittlement in ferritic graphite steel.
(3) Heat treatment at 300°C after embrittling treatment at 450°C shows considerable degree of de-embrittlement.
(4) IMA analysis has detected the remarkable segregation of phosphorus on the grain boundary fracture surface of embrittled specimen.
(5) It is assumed from results obtained that the segregating behaviour of carbon atoms contributes to the embrittling phenomenon of ferritic graphite steel by larger interaction behaviour of phosphorus atoms in grain boundary zone.