Welding in the World

, Volume 62, Issue 2, pp 339–350 | Cite as

Influence of microalloy design on heat-affected zone toughness of S690QL steels

Research Paper


Three high-strength Nb-, Ti- and Ti + V-bearing S690QL steels were welded to investigate and compare the effects of microalloy addition on heat-affected zone (HAZ) toughness. Charpy V notch impact tests from three microalloyed welds under different cooling rates have been performed. Fractographic examination shows that several factors, including large-sized grain, upper bainite or hard second phase, interact to determine brittle fracture and impaired toughness in Nb-bearing weld with high heat input. In contrast to this reduced toughness, Ti-bearing welds exhibits satisfied toughness regardless of at fast or slow cooling. This is attributed to its limited austenite grain and refined favourable intragranular acicular ferrite structure. Moreover, in the case of such refined structure as matrix, TiN particles are found to be irrelevant to the fracture process. The crystallographic results also confirm that high-angle boundaries between fine ferrites plates provide effective barriers for crack propagation and contribute to improved toughness.


High-strength steels Microalloyed steels Toughness Cooling rate Microstructure 



The authors thank R. S. Neumann, M. Buchheim, S. Brunow, D. Schroepfer and E. Steppan from Federal Institute for Materials Research and Testing (Germany) for their kind support. One of the authors (Lei Zhang) also appreciates the funding support from China Scholarship Council.


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Copyright information

© International Institute of Welding 2018

Authors and Affiliations

  1. 1.Federal Institute for Materials Research and TestingBerlinGermany

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