Abstract
Type IV cracking in heat affected zone (HAZ) of weldment is a problem for advanced high Cr ferritic steels. The present paper investigates the creep properties and microstructures of W strengthened P122 steel weldment at 923K. From the investigation of creep properties of simulated HAZ, it is clarified that heating up to around Ac3 during welding minimized the grain size and creep strength. Most of the welded joint specimens were type IV fractured in fine-grained HAZ and resulted in shorter creep lives than those of the base metals. Electron beam welded joint with very narrow HAZ also showed the brittle type IV fracture due to the formation of creep voids and cracks. The growth of intergranular precipitates was faster for pine-grained HAZ. On the basis of experimental results, the FEM code that simulates type IV crack growth behavior has been developed. The vacancy diffusion under multi-axial stress condition in HAZ of weldment is analyzed.
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