Development of microstructure and crystallographic texture in a double-sided friction stir welded microalloyed steel

S. Rahimi, B. P. Wynne, T. N. Baker

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8 Citations (Scopus)

Abstract

The evolution of microstructure and crystallographic texture has been investigated in double-sided friction stir welded microalloyed steel, using electron backscatter diffraction (EBSD). The microstructure analyses show that the centre of stirred zone reached a temperature between Ac1 – Ac3 during FSW, resulting in a dual phase austenitic/ ferritic microstructure. The temperatures in the thermo-mechanically affected zone and the overlapped area between the first and second weld pass did not exceed the Ac1. The shear generated by the rotation probe occurs in austenitic/ferritic phase field where the austenite portion of the microstructure is transformed to a bainitic ferrite, on cooling. Analysis of crystallographic textures with regard to shear flow lines generated by the probe tool, show the dominance of simple shear components across the whole weld. The austenite texture at Ac1 – Ac3 is dominated by the B{11 ̅2}<110> and ¯B {1 ̅12 ̅ }<1 ̅1 ̅0> simple shear texture components, where the bainite phase textures formed on cooling were inherited from the shear textures of the austenite phase with relatively strong variant selection. The ferrite portion of the stirred zone and the ferrites in the thermo-mechanically affected zones and the overlapped area underwent shear deformation with textures dominated by the D1{1 ̅1 ̅2}<111> and D2{112 ̅ }<111> simple shear texture components. The formation of ultra-fine equiaxed ferrite with submicron grain size has been observed in the overlapped area between the first and second weld pass. This is due to continuous dynamic strain-induced recrystallisation as a result of simultaneous severe shear deformation and drastic undercooling.
LanguageEnglish
Pages362-378
Number of pages17
JournalMetallurgical and Materials Transactions A
Volume48
Issue number1
Early online date24 Oct 2016
DOIs
Publication statusPublished - 31 Jan 2017

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Steel
friction
textures
Textures
steels
Friction
microstructure
Microstructure
shear
ferrites
austenite
Austenite
Ferrite
Welds
Shear deformation
Cooling
cooling
friction stir welding
bainite
Undercooling

Keywords

  • friction stir welding
  • ultra-fine ferrite
  • continuous dynamic strain induced recrystallisation
  • microalloyed steel
  • microstructure
  • crystallographic texture
  • electron backscatter diffraction

Cite this

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title = "Development of microstructure and crystallographic texture in a double-sided friction stir welded microalloyed steel",
abstract = "The evolution of microstructure and crystallographic texture has been investigated in double-sided friction stir welded microalloyed steel, using electron backscatter diffraction (EBSD). The microstructure analyses show that the centre of stirred zone reached a temperature between Ac1 – Ac3 during FSW, resulting in a dual phase austenitic/ ferritic microstructure. The temperatures in the thermo-mechanically affected zone and the overlapped area between the first and second weld pass did not exceed the Ac1. The shear generated by the rotation probe occurs in austenitic/ferritic phase field where the austenite portion of the microstructure is transformed to a bainitic ferrite, on cooling. Analysis of crystallographic textures with regard to shear flow lines generated by the probe tool, show the dominance of simple shear components across the whole weld. The austenite texture at Ac1 – Ac3 is dominated by the B{11 ̅2}<110> and ¯B {1 ̅12 ̅ }<1 ̅1 ̅0> simple shear texture components, where the bainite phase textures formed on cooling were inherited from the shear textures of the austenite phase with relatively strong variant selection. The ferrite portion of the stirred zone and the ferrites in the thermo-mechanically affected zones and the overlapped area underwent shear deformation with textures dominated by the D1{1 ̅1 ̅2}<111> and D2{112 ̅ }<111> simple shear texture components. The formation of ultra-fine equiaxed ferrite with submicron grain size has been observed in the overlapped area between the first and second weld pass. This is due to continuous dynamic strain-induced recrystallisation as a result of simultaneous severe shear deformation and drastic undercooling.",
keywords = "friction stir welding, ultra-fine ferrite, continuous dynamic strain induced recrystallisation, microalloyed steel, microstructure, crystallographic texture, electron backscatter diffraction",
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N2 - The evolution of microstructure and crystallographic texture has been investigated in double-sided friction stir welded microalloyed steel, using electron backscatter diffraction (EBSD). The microstructure analyses show that the centre of stirred zone reached a temperature between Ac1 – Ac3 during FSW, resulting in a dual phase austenitic/ ferritic microstructure. The temperatures in the thermo-mechanically affected zone and the overlapped area between the first and second weld pass did not exceed the Ac1. The shear generated by the rotation probe occurs in austenitic/ferritic phase field where the austenite portion of the microstructure is transformed to a bainitic ferrite, on cooling. Analysis of crystallographic textures with regard to shear flow lines generated by the probe tool, show the dominance of simple shear components across the whole weld. The austenite texture at Ac1 – Ac3 is dominated by the B{11 ̅2}<110> and ¯B {1 ̅12 ̅ }<1 ̅1 ̅0> simple shear texture components, where the bainite phase textures formed on cooling were inherited from the shear textures of the austenite phase with relatively strong variant selection. The ferrite portion of the stirred zone and the ferrites in the thermo-mechanically affected zones and the overlapped area underwent shear deformation with textures dominated by the D1{1 ̅1 ̅2}<111> and D2{112 ̅ }<111> simple shear texture components. The formation of ultra-fine equiaxed ferrite with submicron grain size has been observed in the overlapped area between the first and second weld pass. This is due to continuous dynamic strain-induced recrystallisation as a result of simultaneous severe shear deformation and drastic undercooling.

AB - The evolution of microstructure and crystallographic texture has been investigated in double-sided friction stir welded microalloyed steel, using electron backscatter diffraction (EBSD). The microstructure analyses show that the centre of stirred zone reached a temperature between Ac1 – Ac3 during FSW, resulting in a dual phase austenitic/ ferritic microstructure. The temperatures in the thermo-mechanically affected zone and the overlapped area between the first and second weld pass did not exceed the Ac1. The shear generated by the rotation probe occurs in austenitic/ferritic phase field where the austenite portion of the microstructure is transformed to a bainitic ferrite, on cooling. Analysis of crystallographic textures with regard to shear flow lines generated by the probe tool, show the dominance of simple shear components across the whole weld. The austenite texture at Ac1 – Ac3 is dominated by the B{11 ̅2}<110> and ¯B {1 ̅12 ̅ }<1 ̅1 ̅0> simple shear texture components, where the bainite phase textures formed on cooling were inherited from the shear textures of the austenite phase with relatively strong variant selection. The ferrite portion of the stirred zone and the ferrites in the thermo-mechanically affected zones and the overlapped area underwent shear deformation with textures dominated by the D1{1 ̅1 ̅2}<111> and D2{112 ̅ }<111> simple shear texture components. The formation of ultra-fine equiaxed ferrite with submicron grain size has been observed in the overlapped area between the first and second weld pass. This is due to continuous dynamic strain-induced recrystallisation as a result of simultaneous severe shear deformation and drastic undercooling.

KW - friction stir welding

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KW - continuous dynamic strain induced recrystallisation

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KW - microstructure

KW - crystallographic texture

KW - electron backscatter diffraction

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SN - 1073-5623

IS - 1

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