1982 Volume 51 Issue 8 Pages 650-657
Previous paper demonstrated that the C-Mn steels for low temperature service with high Al-low Nmicro Ti could ensure a high weld-HAZ toughness even in high heat input welding. It was assumed that such superior weld-HAZ toughness is attributed to a significant reduction of free-N resulted from reprecipitation of AlN on cooling stage after welding.
To verify the mechanisms which governs correlation between the weld-HAZ toughness and N, Al and Ti contents of steel, the morphologies of N in weld-HAZ were determined by careful phase analysis including hydrogen carrier reduction analysis, iodin methanol alkali fusion analysis and acid decomposition analysis. Results obtained were as follows:
(1) Free-N which is produced by dissociation of nitrides on heating will be caught by Al and.reprecipitates as AlN on cooling stage of welding thermal cycles.
(2) These phenomena will be accelarated by increase in sol. Al content.
(4) Repriecipitation of AlN occures at the temperature range from 850°C to 600°C on the cooling stage of welding thermal cycles.
