5%Ni-0.5%Mo鋼溶接熱影響部の組織と靱性

抄録

A study has been made of the microstructure and toughness of the heat affected zone (HAZ) in 5%Ni-0.5%Mo steels with the original structures of which were tempered martensite and bainite.
These properties depend strongly on carbon contents in steels and cooling rate after rapid heating to 1350°C. With decreasing in the cooling rate the microstructure changes from martensite to bainite, and the increase of carbon content tends to retard this change. However, the optimum toughness is obtained in duplex structure of martensite and lower bainite regardless of carbon content. The microstructure and toughness of the partially-transformed region in HAZ are affected by original microstructures, since the aspect of austenitization is different in them. When the original microstructure is tempered martensite, the aspect depends on the tempering temperature and carbon content. On the other hand, when the structure is bainite, it depends on the roughness of the ferrite lath structure which is related to carbon content.