1985 Volume 3 Issue 4 Pages 796-801
A study on the preheating effect for preventing cracking of heat-affected zone of nodular graphite cast irons (FCD 50) is made by means of the implant cracking test. The apparatus for the implant test, dimensions of the smoothed test specimens and DFCNiFe (55%Ni-Fe) electrodes used for the present study are the same as in the previous report. Weld heat input is 21, 000 Joules/cm.
When preheating temperature was made higher, the critical rupture stress of the cracking increased: It went up to about 90% of the tensile strength of base metal with preheating at 300°C and 450°C, while it showed only about a half of that strength without preheating. In case of preheating at 300°C and 450°C, the implant specimens were fractured in the unmixed zone which had ledeburite structure. From the studying for the CCT diagram of cast iron used for the present work, the critical cooling time, when the troostite structure appeared at the partially melted zone and true heat-affected zone, from 800°C to 500°C was about twelve seconds. In the present work, this condition was obtained with preheating at 300°C.
