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Open AccessArticle

MAG Welding Tests of Modern High Strength Steels with Minimum Yield Strength of 700 MPa

1
Department of Mechanical Engineering, Aalto University, 02150 Espoo, Finland
2
Materials Science and Environmental Engineering, Tampere University, P.O. Box 589, FI-33014 Tampere, Finland
3
SSAB, Rautaruukintie 155, P.O. Box 93, FI-92101 Raahe, Finland
*
Author to whom correspondence should be addressed.
Appl. Sci. 2019, 9(5), 1031; https://doi.org/10.3390/app9051031
Received: 15 January 2019 / Revised: 4 March 2019 / Accepted: 6 March 2019 / Published: 12 March 2019
(This article belongs to the Special Issue Welding of Steels)
The modern high strength steel plates have an excellent combination of strength and toughness based on micro-alloying and complex microstructure. Retaining this combination of properties in the weld zone is a major challenge for applications in high-demanding structural construction. This work investigates the weldability of three different modern high strength steel plates, with a thickness of 8 mm. Two of the test materials were produced by a thermo-mechanically controlled process (TMCP) and one by a quenching and tempering method (Q&T). Two-passes MAG (metal active gas) welding was used with four different heat inputs. The tests implemented on all the materials included tensile, hardness profiles (HV5), Charpy-V impact toughness tests, and microstructure analysis using scanning electron microscope (SEM). For one of the TMCP steels, some extended tests were conducted to define how the tensile properties change along the weld line. These tests included tensile tests with digital image correlation (DIC), and 3-point bending tests. The most notable differences in mechanical properties of the welds between the materials were observed in Charpy-V impact toughness tests, mostly at the vicinity of the fusion line, with the Q&T steel more prone to embrittlement of the heat affected zone (HAZ) than the TMCP steels. Microstructural analysis revealed carbide concentration combined with coarse bainitic structures in HAZ of Q&T steel, explaining the more severe embrittlement. During the tensile tests, the DIC measurements have shown a strain localization in the softest region of the HAZ. Increasing the heat input resulted in earlier localization of the strain and less maximum strength. The tensile properties along the weld line were investigated in all welding conditions, and the results emphasize relevant and systematic differences of the yield strength at the transient zones near the start and end of the weld compared with the intermediate stationary domain. View Full-Text
Keywords: high strength steel; weldability; thermo-mechanically controlled process; quenched and tempered; metal active gas welding process; Charpy-V; tensile; digital image correlation; bending; hardness; microstructure high strength steel; weldability; thermo-mechanically controlled process; quenched and tempered; metal active gas welding process; Charpy-V; tensile; digital image correlation; bending; hardness; microstructure
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MDPI and ACS Style

Lahtinen, T.; Vilaça, P.; Peura, P.; Mehtonen, S. MAG Welding Tests of Modern High Strength Steels with Minimum Yield Strength of 700 MPa. Appl. Sci. 2019, 9, 1031.

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