A Study of Fracture Toughness and Microstructures in the Weld Heat-Affected Zone of QLT-Processed 9% Ni Steel

  • J. Jang
  • Y. Yang
  • W. Kim
  • D. Kwon
Part of the Advances in Cryogenic Engineering book series (ACRE, volume 44)


The objective of this study, based on the concept of fitness-for-purpose, is to evaluate the fracture toughness in X-grooved weld HAZ(heat-affected zone) of QLT(quenching, lamellarizing and tempering)-processed 9% Ni steel, qualitatively and quantitatively, and analyze the relation between the fracture toughness and microstructure. In general, CTOD test is widely used to determine the fracture toughness of steel weldments. But several problems of accuracy have been brought up. To avoid those, in this paper, modified CTOD testing method is proposed and used for weld HAZ for 9% Ni steel. In addition, microstructure of HAZ is observed and analyzed by OM, SEM and XRD.

From the results, HAZ toughness of QLT-9% Ni steel decreased as the evaluated region approaches the fusion line from base metal. The decrease in toughness was apparently partly caused by the reduction of the retained austenite content resulting from the decrease in nucleation sites for α→γ reverse transformation due to the increasing fraction of coarse-grained region. On the other hand, due to the poor stability of retained austenite in the mixed zone of weld metal/base metal, toughness drop in F. L.~F. L.+3mm was larger than that in F. L.+5mm and F.L.+7mm with decreasing test temperature.


Fracture Toughness Fusion Line Welding Residual Stress Crack Propagation Path Retain Austenite Content 
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Copyright information

© Springer Science+Business Media New York 1998

Authors and Affiliations

  • J. Jang
    • 1
  • Y. Yang
    • 2
  • W. Kim
    • 2
  • D. Kwon
    • 1
  1. 1.Division of Materials Science and EngineeringSeoul National UniversitySeoulKorea
  2. 2.Research and Development CenterKorea Gas CorporationAnsanKorea

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