1995 年 13 巻 4 号 p. 579-584
In order to clarify the factors that affect the creep rupture strength (CRS) of multi-layered welded joints 9Cr-1Mo-V-Nb-N steel, creep rupture tests were performed utilizing either the double cycle of welding heat simulation or electron beam welding. Metallurgical and mechanistic considerations were given to find guides for improving CRS of the welded joints.
The CRS was affected by first cycle temperature (T1) of double-cycled simulated heat affected zone, where T1 were varied from 800 to 1, 400°C, the second cycle temperature (T2) was fixed at 950°C, and then post weld heat treatment (PWHT) was given. When the T1 is lower than 1, 000°C, the CRS is as low as the lowest value of the single cycle test. When T1 is higher than 1, 000°C, the CRS is higher for higher T1. This means that the CRS is improved by multi-layered welding.
When T1 is higher than 1, 000°C, the second cycle of 950°C produces dense precipitation of (V, Nb) N which precipitates during PWHT. This results in the improvement of CRS.
The CRS of welded joint is affected by the angle between the directions of applied stress and fusion interface. With the angle of 45 degrees, the CRS is most degraded ; the creep repture time is almost one-third of the base metal. For the prevention of the degradation of CRS, the bevel angle should be less than 18 degrees.