Microstructure and Impact Toughness of Acicular Ferrite in Low Alloy Steel Weld Joints from Results of Multiple Impact Bending Tests

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Abstract

Analysis of impact bending test results for a large number of specimens is used to investigate fracture of a weld metal consisting predominantly of acicular ferrite. The metal has a very broad ductile-to-brittle transition interval: from +20 to below –60°C. In the temperature range studied, we observe three stable impact toughness levels. Transitions between them with decreasing temperature determine the scatter in the work done to fracture the specimen. According to fractography results, the ductile-to-brittle transition is due to a single-step change from a ductile fracture mechanism to cleavage. Cleavage cracks nucleate at large acicular ferrite grains. Their different arrangements on a cleavage site determine the impact toughness level. Comparison of dynamic fracture curves and the macroscopic structure of fracture surfaces demonstrates that cleavage cracks nucleate at the tip of a stably growing ductile crack. Examination of fracture surfaces makes it possible to identify individual cleavage events observed in the corresponding dynamic curve.

About the authors

M. M. Kantor

Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, 119991, Moscow, Russia

Email: vsudyin@imet.ac.ru
Россия, 119991, Москва, Ленинский пр., 49

V. V. Sudin

Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, 119991, Moscow, Russia

Email: vsudyin@imet.ac.ru
Россия, 119991, Москва, Ленинский пр., 49

V. A. Bozhenov

Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, 119991, Moscow, Russia

Email: vsudyin@imet.ac.ru
Россия, 119991, Москва, Ленинский пр., 49

K. A. Solntsev

Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, 119991, Moscow, Russia

Author for correspondence.
Email: vsudyin@imet.ac.ru
Россия, 119991, Москва, Ленинский пр., 49

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