Influence of Ti on the toughness of the FGHAZ and the CGHAZ of high-strength microalloyed S700MC steels

The influences of titanium on the microstructure and the mechanical properties of three microalloyed steels were investigated. Light optical microscopy as well as scanning electron microscopy were used to determine any changes in microstructure and precipitations. Charpy V-notch impact and tensile t...

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Bibliographic Details
Published in:Welding in the world 2017-11, Vol.61 (6), p.1117-1131
Main Authors: Spachinger, Stefan Johannes, Ernst, Wolfgang, Enzinger, Norbert
Format: Article
Language:English
Subjects:
Chemistry and Materials Science
Coarsening
Ferrite
Heat affected zone
High strength low alloy steels
Impact strength
Impact tests
Martensite
Materials Science
Mechanical properties
Metallic Materials
Microalloying
Microscopy
Microstructure
Optical microscopy
Optical properties
Research Paper
Solid Mechanics
Tensile tests
Theoretical and Applied Mechanics
Titanium base alloys
Transition temperature
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Summary:The influences of titanium on the microstructure and the mechanical properties of three microalloyed steels were investigated. Light optical microscopy as well as scanning electron microscopy were used to determine any changes in microstructure and precipitations. Charpy V-notch impact and tensile tests were performed to examine the mechanical properties. Only the low titanium alloyed steel showed the formation of granular bainite/ferrite in the fine-grained heat-affected zone at 15-s t 8/5 time. All other steels showed a microstructure consisting of tempered and untempered martensite, leading to very similar strength values in all samples. Particle analysis showed the formation of coarse titanium containing precipitations in the two steels with an overstoichiometric titanium-to-nitrogen ratio. These lead to a decrease of the maximum impact energy in the coarse-grained heat-affected zone as well as to an increase of the T 27 transition temperature when compared to the fine-grained heat-affected zone. The drop in impact energy was less in the low titanium alloyed steel, showing the harmful impact of these coarse titanium-containing precipitations. Finally, the comparison between 2- and 15-s t 8/5 times showed that with the right (softer) matrix structure, the detrimental influences of the coarse titanium-containing precipitations can be lessened.
ISSN:0043-2288
1878-6669
DOI:10.1007/s40194-017-0480-7