1985 Volume 3 Issue 4 Pages 789-795
A study on the cracking susceptibility of nodular graphite cast irons by means of the implant test in different heat inputs is described. The implant test specimens were mainly smoothed 6 mm in diameter ones. Weld heat inputs, with the use of 4 nun diameter DFCNiFe type electrode (55%Ni-Fe), were changed 18, 000, 21, 000 and 24, 000 joules/cm with 10 cm/min travel speed and 50 mm bead length. After welding, when the temperature of the HAZ cooled to about 400°C, the load was applied.
The implant specimens were fractured at about 100°C, which was below the Ms temperature of the cast irons used. In the heat input variation range of present work when heat input was made higher, the lower critical stress of fracture slightly inrceased; but it went up to only below a half of the strength of the base metal. The implant specimens were fractured at the part of the martensite structure with the highest micro-vickers hardness number, about 900. The fracture surface consisted of mainly intergranular fractures with partly quasi-cleavage fracture mode.
