311 / 352
307
Besides, carbonitrides precipitates MX coarse became rough and coagulated, which
reduced their hardening effect. Due to the phenomena specified, FGHAZ corresponding
to simulation-temperature interval from 900°C to 950°C had the smallest hardness. With
an increase of simulation temperature above 950°C, hardness increased due to higher
solubility of carbides.
7. CONCLUDING REMARKS
According to the investigations, the weldability of the heat resistant material P91 can
be described as very satisfactory although there is a drop in the creep resistance in the
HAZ. The investigations have shown that this drop in the creep resistance occurred in the
FGHAZ where the peak temperature reached a level of about 900-950°C. At stresses
lower than 150 MPa, the fracture location shifts from the parent steel into the softened
FGHAZ. At operating temperature of 600°C, the data points of the weldments are below
those of the parent steel by more than 25%.
This effect must be taken in account when designing the welded components made
from P91.
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