1988 年 6 巻 1 号 p. 41-46
Crack Tip Opening Displacement (CTOD) properties in the HAZ of 50 kgf/mm2 (490 MPa) class steels were investigated from the view point of fracture facet size and fraction of M-A constituent. The C-Mn microalloyed steels with carbon content of 0.025 to 0.19 wt. % were selected in this study. The results obtained were as follows:
(1) The CTOD properties in the HAZ were strongly affected by the carbon content which varied both the fracture facet size and fraction of M-A constituent in the local brittle zone near fusion line.
(2) The fracture facet size got small and the fraction of M-A constituent was increased by increasing the caron content.
(3) The distributions of carbon content in the HAZ were analyzed by the EPMA. The peak points in carbon content corresponding to the M-A constituent were 1.07-1.32 wt.% in spite of that the carbon contents in the bulk of base metal were 0.025 to 0.19 wt.%.
(4) The cementite as well as the M-A constituent were observed in the HAZ of the steel plate containing carbon more than 0.06 wt. %.
(5) The mechanism of the M-A constituent formation was discussed in condensing the carbon atoms.
(6) The CTOD properties, as compared with the Charpy impact properties, were greatly influenced by the M-A constituent.