The effects of V on creep rupture properties and high temperature mechanical properties of 308 stainless steel weld metals for use of the welded joint of pipe and vessel in the fast breader reactor are investigated and the results obtained are sumarized as follows.
1) Tensile strength and rupture elongation of 308V weld metal almost coinside with those for SUS304 stainless steel in the temperature region between 500°C and 600°C.
2) Under certain circumstances the creep rupture strength and creep rupture elongation of 308V weld metal are higher in comparison with those for SUS304 stainless steel.
3) High temperature tensile properties of 308V weld metal are almost same as those for 308 weld metal, on the other hand creep rupture strength and creep rupture elongation of 308V weld metal are higher as compared with those for 308 weld metal.
4) Superior creep rupture properties of 308V weld metal as compared with those for 308 weld metal are caused by the following factors.
i) V contents in the austenite matrix of 308V weld metals are three and a half times to five times as mutch as that of 308 weld metal.
ii) Fine precipitates containing V are formed in the austenite matrix of 308V weld metal in the course of creep rupture test. These fine precipitates are difficult to remelt in the long time creep rupture test. V-less fine precipitates formed in 308 weld metal remelt in austenite in the creep process easily.
iii) When multiplied dislocations locked by fine precipitates, recoverly and recrystallization are delayed in the creep process and high dislocation density is kept on the steady state creep process. Creep strength is strengthened progressed as discribed above.
iv) In proportion as fine precipitates remelt in the austenite, the precipitates in the S ferrite gradually increase in quantity and in size, and the brittleness of the a ferrite is progressed.
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