780MPa 級鋼の母材と再現 HAZ の強度・靭性に及ぼす Ti, N の影響

概要

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Influence of Ti and N on strength and toughness of base plate and HAZ in 780MPa class steels with ultra-heavy thickness of over 150mm was examined using a thermal-cycle simulator. (1) Relationship between Ti content and mechanical properties of the base plate under as-quenched condition varies depending on N content. While, toughness of medium-N steels (N=40ppm) is improved by adding Ti due to microstructural change, toughness of low-N steels (N=20ppm) deteriorates with increasing Ti content due to precipitation hardening by TiC. (2) Influence of Ti and N on simulated HAZ toughness is more significant for double cycle condition than that for single cycle. Ti addition gives remarkable improvement in simulated HAZ toughness of the medium-N steels for double cycle condition. On the other hand, simulated HAZ toughness of the low-N steels deteriorates with increasing Ti content. The governing factors of the simulated HAZ toughness in double-cycle condition are the same as those of the toughness of base plate. (3) It is concluded that the low-N steel without Ti addition and medium-N steels with Ti addition of 0.005∿0.01% attain both high simulated HAZ toughness and high strength and toughness of base plate.
社団法人日本鉄鋼協会の論文
1997-03-01