Study on JIC Fracture Toughness in the Weld Heat-Affected Zone of a Structure Steel

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The fracture toughness in a simulated weld heat-affected zone (HAZ) of the high tensile strength steel (HT80) was evaluated through JIC values using a Charpy-size three point bending specimen in a temperature range between 180゜C and - 150゜C. The effect of the microstructure on crack initiation was iavestigated by a fractographic method using the scanning electron microscope (SEM). In the temperature range from about -50゜C to 18゜C, for the base metal and HAZ whose cooling time from 800 to 500゜C (Tc) was 17 sec, the JIC values increased with a decreasing test temperature. The SEM examination showed that area fraction of martensile-austenitc constituent (M-A) in the microstructures mentioned above was less than 4%. The fracture occurred by stable crack extension after the formation of a stretched zone at the precrack tip. On the other hand, the JIC values decreased with a decreasing test temperature on HAZ microstructure whose To were 89 and 223 sec. In these microstructures, which had more than 8 % of area fraction of M-A, a cleavage fracture occurred immediately frter the formation of the stretched zone. JIC values in the microstructures which included more than 8 % of area fraction of M-A were nearly a quarter of those in the microstructures whose M-A were less than 4% at about -50゜C. The critical stretched zone width (SZWc) and JIC were found to be related as follows: JIC=α・σ_y SZWc whereσ_y is the yield stress of steel and αis an experimental constant which was found to be 8.5.
社団法人溶接学会の論文
1983-10-01

Study on JIC Fracture Toughness in the Weld Heat-Affected Zone of a Structure Steel

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