Mechanical and microstructural characterization of dissimilar welded joints between S355J2 + N and S690QL steels using G69 and T46 filler wires
Abstract
<jats:p> This study evaluates and compares the mechanical performance and microstructures of dissimilar welded joints made from S355J2 + N and S690QL steels, using G69 and T46 fillers. Tensile, Charpy V-notch (CVN) impact, and hardness tests were conducted, along with optical microscopy and scanning electron microscopy (SEM) for microstructural and fractographic analysis. Average ultimate tensile strengths reached <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mn>540</mml:mn> <mml:mo>±</mml:mo> <mml:mn>2.5</mml:mn> <mml:mspace width="0.25em"/> <mml:mrow> <mml:mi mathvariant="normal">MPa</mml:mi> </mml:mrow> </mml:math> </jats:inline-formula> for T46 and <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mn>524</mml:mn> <mml:mo>±</mml:mo> <mml:mn>2.5</mml:mn> <mml:mspace width="0.25em"/> <mml:mrow> <mml:mi mathvariant="normal">MPa</mml:mi> </mml:mrow> </mml:math> </jats:inline-formula> for G69 joints, with all specimens fracturing within the weaker base metal (S355J2 + N) that had an ultimate tensile strength of 479 MPa, indicating successful overmatching with joint integrity. Hardness examination showed a peak value of <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mn>282</mml:mn> <mml:mo>±</mml:mo> <mml:mn>3</mml:mn> <mml:mspace width="0.25em"/> <mml:mspace width="0.25em"/> <mml:mrow> <mml:mi mathvariant="normal">HV</mml:mi> </mml:mrow> </mml:math> </jats:inline-formula> in the S690QL-HAZ, attributed to the formation of martensite laths and localized tempered martensite. The G69 filler wire exhibited higher energy absorption ( <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mn>94</mml:mn> <mml:mo>±</mml:mo> <mml:mn>13</mml:mn> <mml:mrow> <mml:mspace width="1pt"/> </mml:mrow> <mml:mspace width="0.25em"/> <mml:mrow> <mml:mi mathvariant="normal">J</mml:mi> </mml:mrow> </mml:math> </jats:inline-formula> at <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mn>20</mml:mn> <mml:mrow> <mml:mo>∘</mml:mo> <mml:mi mathvariant="normal">C</mml:mi> </mml:mrow> </mml:math> </jats:inline-formula> ) compared to the T46 wire ( <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mn>67</mml:mn> <mml:mo>±</mml:mo> <mml:mn>23</mml:mn> <mml:mspace width="0.25em"/> <mml:mrow> <mml:mi mathvariant="normal">J</mml:mi> </mml:mrow> </mml:math> </jats:inline-formula> ). The T46 weld zone showed a higher density of brittle cleavage facets, likely due to the presence of M-A constituents. Despite the variances, all tested specimens fulfilled the minimum impact toughness requirement of <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mn>27</mml:mn> <mml:mspace width="0.25em"/> <mml:mrow> <mml:mi mathvariant="normal">J</mml:mi> </mml:mrow> </mml:math> </jats:inline-formula> at <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mn>20</mml:mn> <mml:mrow> <mml:mo>∘</mml:mo> <mml:mi mathvariant="normal">C</mml:mi> </mml:mrow> </mml:math> </jats:inline-formula> according to EN 10025-2 standard for S355J2 + N structural steel, demonstrating that both filler wires are appropriate for high-strength dissimilar steel applications under the investigated conditions. </jats:p>