The Effect of σ-Phase Formation on Long-Term Durability of Welding Joints in SUPER 304H Steels
J. Horváth a,b, P. Král c and J. Janovec a
aCTU in Prague, Faculty of Mechanical Engineering, Department of Materials Engineering, Karlovo náměstí 13, 121 35 Prague, Czech Republic
bUJP PRAHA a.s., Nad Kamínkou 1345, 156 00 Prague, Czech Republic
cInstitute of Physics of Materials, ASCR v.v.i., Žižkova 22, 616 62 Brno, Czech Republic
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Article presents results on the analysis of secondary phases formed in the medium-term static isothermal ageing welding joints of a SUPER 304H (675°C/2×104 h). The investigations of the precipitates were focused on the occurrence of σ-phase because its formation leads to significant deterioration of mechanical properties. The microstructure was investigated on microscopic level by scanning/transmission electron microscopy. The distribution and quantification of brittle σ-phase were studied on macroscopic level by color etching method using light optical microscopy. The effect of microstructural changes (σ-phase formation) on the impact strength of an aged base material was investigated. For comparison impact tests on received state material were also performed. The results showed that long-term ageing led to the significant reduction of impact strength as a result of the formation of the σ-phase. It was found that the σ-phase distribution is influenced by welding process. The influence of brittle σ-phase on long-term durability of the degraded steel regarding its insufficient impact strength has been discussed.

DOI: 10.12693/APhysPolA.130.960
PACS numbers: 81.70.Jb, 68.37.Ma, 81.30.Mh, 81.20.Vj, 62.20.mj