Masakazu Matsui

Variation in the Type IV cracking behaviour of a high Cr steel weld with post weld heat treatment

In this study creep tests were conducted on P122 steel cross weld specimens at 70 MPa after post weld heat treatment (PWHT) for different durations. Results indicated that the duration of PWHT did not influence the rupture time and all the specimens failed in a typical Type IV manner. However, differences were observed with respect to creep damage and microstructural changes that occurred in the fine grained heat affected zone (FGHAZ), the location of the fracture. It appears that factors other than changes in microstructure also affect the rupture life. One such factor could be the heterogeneity introduced in the weld joint due to the existence of different zones like weld metal, coarse grained HAZ (CGHAZ), FGHAZ and base metal, which differ vastly in their properties.

Development of 25%Cr SMAW welding materials – development of high Cr ferritic overlay welding materials for recovery boiler

ABSTRACT In place of the 18%Cr overlay welding material, which has been used for furnace water wall tubes of recovery boilers, a 25%Cr overlay welding material with good corrosion resistance has been newly developed. In consideration of dilution with a carbon steel tube, the Cr content of the new welding materials are designed to be more than 20%Cr. And in order to fine the grains of the weld metal, some elements, such as Nb, Al and Ti, are added to these welding materials. Mainly two types of welding materials, which have Austenite + Martensite + Ferrite of materials for the three-phase and fully ferritic materials, are examined. As results of weldability tests and bending properties, the fully ferritic welding materials are superior to the three-phase materials, respectively. On the point of the corrosion test, which are exposed into some smelt ashes obtained from the recovery boilers, the corrosion rate of the full ferritic material was confirmed to be the about half of that of 18%Cr overlay welding material. The 25%Cr overlay welding material was found to exhibit excellent corrosion resistance. This study introduces the development of 25%Cr ferritic welding material and methods for reliable overlay welding and examines the weldability, the bend property and the corrosion resistance of the 25%Cr overlay welded metal on tube.