Tadashi Nemoto

Carbon Migration in Dissimilar Welded Joint

The present study was carried out to make clear the C migration in dissimilar metal welded joint at high temperature. To prepare test pieces, C steel and 2 1/4 Cr-1 Mo steel plates were welded with eight kinds of ferritic electrodes, 1/2 Mo, Cr-Mo Cr-Mo-V etc. and eight kinds of ferritic steel plates were welded with two kinds of sustenitic electrodes and 2 1/4 Cr-1 Mo steel was welded with Inconel electrode. These dissimilar welded joint specimens were heated at 500-800°C for 1-3, 000 h and then observed microscopically. The results are summerized as follows :(1) C in lower Cr steel migrated to higher Cr steel and carbides precipitated in higher Cr steel along fusion line. At higher temperatures, the ferrite grains coarsened in decarburized zone.(2) C migration was promoted with increase of Cr content in higher Cr steel and addition of V.(3) C migration was reduced with increase of Cr content in lower Cr steel and addition of V.(4) In the welded joints of Cr-Mo weld metals to C steel, the width of carbides precipitated zone increased with increase of Cr content in Cr-Mo weld metals up to 3 Cr-1 Mo steel and decrease with the increass of Cr content more than 3 Cr-1 Mo steel. The distribution density of carbides increased with the increase of Cr content in Cr-Mo weld metals.(5) The extent of C migration with 25 Cr-20 Ni weld metal was slightly more than 16 Cr-8 Ni-2 Mo weld metal. The extent of C migration with Inconel weld metal was less than those with 16 Cr-8 Ni-2 Mo and 25 Cr-20 Ni weld metals.

High Temperature Strength of Dissimilar Welded Joint

The present study was carried out to examine the tensile strength, creep rupture strength and cyclic creep rupture strength of dissimilar metal welded joint. To prepare test pieces, 2 1/4 Cr-1 Mo steel and 18 Cr-8 Ni-Cb steel or 18 Cr-8 Ni-Ti steel plates were welded with Inconel, 50 Ni-10 Cr-2 Mo, 25 Cr-20 Ni, 19 Cr-8 Ni-1 Mo and 16 Cr-8 Ni-2 Mo electrodes. These various dissimilar welded joints were tested as welded and after post heat treatment at 650°C for 3 hours and at 720°C for 1 hour. The results are summarized as follows:1) The specimen welded with 50 Ni-10 Cr-2 Mo electrode fractures at the weld metal or 21/4 Cr-1 Mo base metal, but those specimens welded with other electrodes fracture at 214 Cr-1 Mo base metal in the tensile test at room temperature and 600°C.2) Creep rupture strength of an as-welded specimen is higher than that of a post heat treated specimen in a shorter time test at 600°C, but in a longer time test, the creep rupture strength of a post heat treated specimen is higher than that of the as welded specimen.3) Creep rupture strength of 720°C×1 h post heat treated specimen with Inconel is the highest of all other specimens in long time tests.4) When temperature and load cycle are imposed in a creep rupture test, the rupture strength of an as-welded specimen is higher than the ordinary creep rupture strength, but the rupture strength of 720°C×1 h post heat treated specimen is lower than the ordinary creep rupture strength.