The Strength of Stainless Steel Welded Joints of Types 321 and 347 at Elevated Temperatures

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• The present study was carried out to clarify the high temperature properties of stainless steel welded joints of AISI types 347 and 321 in as-welded condition, and the effect of post-heating on the creep rupture properties of these joints.To prepare test pieces, stainless steel plates of types 347 and 321 with 25mm thick were welded using 16 Cr-8Ni-2Mo and 19 Cr-8Ni-1Mo electrode, Some of these welded joints were given post-heating at 1050°C for 1hr and at 900°C for 2hrs.In the tension test, specimens as-welded fractured at base metal, and their tensile strength was equal to that of base metal. Tensile strength of specimen post-heated was slightly lower than when it was left as-weld. (Fig. 4, 5)Type 321 stainless steel welded joint using 16-8-2 electrode had the best fatigue properties among the joints in as-welded condition. (Table 2)In creep rupture test, type 347 stainless steel welded joint as-welded fractured at the heat-affected zone of base metal and its rupture strength was very poor. However type 347 stainless steel welded, joint recovered considerable rupture strength by post-heating at 900°C and 1050°C. (Table 4) It seems that this decay of the heat-affected zone is caused by the strain, near the weld groove. By post-heating at 1050°C, coarsening of grain and softening occurred at the heat-affected zone. (Fig. 3, Photo. 1, 2) It seems that this zone has been slightly hot-cold worked during weld by thermal stress caused from temperature gradient and contraction of weld metal. On the other hand, type 321 stainless steel welded joint as-welded fractured at base metal and showed no decay such as shown by type 347 stainless steel welded joint in the rupture test. 1050°C post-heating make its weld boundary so weak, that the creep specimen ruptured at the boundary along the bond. But, 900°C post-heating didn't produce such a decay. (Table 4, Photo. 4, 5) It is not clear why such a decay occur in type 321 stainless steel welded joint.

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