Microstructural analysis of the as-welded heat-affected zone of a Grade 91 steel heavy section weldment

Y. Wang, R. Kannan, L. Zhang, L. Li

Research output: Contribution to journalArticlepeer-review

34 Scopus citations

Abstract

A 5-in. (127-mm) ASTM A182F91 Grade 91 steel heavy section was gas tungsten arc and flux cored arc welded. The nonequilibrium substructure of the as-welded heataffected zone (HAZ) was characterized in multiscales. The HAZ included a narrow coarsegrained HAZ (CGHAZ) and a wide intercritical HAZ (ICHAZ). The as-welded ICHAZ exhibited the largest structural inhomogeneity with the finest grain structure, the largest fraction of the high-angle grain boundaries, and the highest local strains. Delta (δ) ferrite grains originating from the base metal were found undissolved in the HAZ. The thermodynamic simulation and composition analyses seem to suggest formation of δ-ferrite grains in the base metal were due to microsegregation of Cr, Mo, V, and Nb. These ferrite-stabilizing elements in the retained δ-ferrite grains in the HAZ had a lower concentration than that in the 8-ferrite grains of the base metal. The rejected elements may have promoted the precipitation of carbides along the interface between the 5-ferrite grains and tempered martensite.

Original languageEnglish
Pages (from-to)203s-219s
JournalWelding Journal
Volume96
Issue number6
StatePublished - Jun 2017
Externally publishedYes

Keywords

  • Delta ferrite
  • Grade 91 steel
  • Heat-affected zone
  • Heavy section weldment
  • Microstructure
  • Phase transformation

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