球状黒鉛鋳鉄溶接部の限界破断応力に対する後熱の効果

球状黒鉛鋳鉄の溶接割れに関する研究(第3報)

抄録

A study on the postheating effect for increasing the strength of heat-affected zone of nodular graphite cast irons (FCD 60) 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 reports. Weld heat input is 25, 000 Joules/cm. When the temperature near bond line was cooled down to 200°C, postheating using propane burner was started and was lasted to reach the temperature; 300°C, 400°C and 500°C. To study the postheating effect of multilayer sequence, two layer welding was also examined.
When postheating temperature was set higher, the critical rupture stress of the heat-affected zone increased: It went up to about 80% of the tensile strength of base metal with postheating at 400°C and 500°C while it showed only about a half of that strength with postheating at 300°C and without postheating. In case of postheating at 400°C and 500°C, bainite structure was formed at the true heat-affected zone. This fact was the reason of postheating effect. In case of two layer welding, the critical rupture stress increased to 410 MPa by the postheating effect of second layer bead.