Friction stir welding of steel: An update for the SMEA · tests tested to BS EN 895:1995 5 FSW...

Copyright © TWI Ltd 2014

Friction stir welding of steel:

An update for the SMEA

Stephen Cater, FRIN MEI

TWI Technology Centre, Yorkshire, England, UK


� Pre-dates fusion welding

� A forging process and thus can enhance material properties

� Highly skilled

Solid state welding


Friction Stir Welding


Principle and Microstructure


FSW in aluminium


FSW of steel

� FSW was never intended for steel.

� Aluminium, magnesium and copper are all relatively difficult to weld and FSW is now almost the process of choice for welding them, producing low cost, high quality welds.

� Customers now demand that in steel.


Steels welded

Carbon steels

� AISI 1018, 1060, 1085

� A36

� S275, S355, S690

� API X 65, X80, L80, X100

� EH36, DH36, EH46

� HSLA-65

� HY-80, HY-100

� D2 , O1

Stainless steels

� 304, 304 L, 316

� 420A, 420B, 420C

� RWL34

� 12C27

� S32205 duplex

ODS & others

� 20Cr5Al, PM2000, MA957

� PH14, PH17

� Others


SAW steel



FSW metallurgy

Advancing


Distortion – 6mm DH36

SAW: 110 mmSAW: 110 mmSAW: 110 mmSAW: 110 mm FSW: 20 mmFSW: 20 mmFSW: 20 mmFSW: 20 mm

Data courtesy BAE Surface Fleet


Mechanical Properties

� Friction stir is a forging process whereas conventional fusion welding is a casting process.

� Testing results seem too good to be true.

� Initial results show that strength, toughness, hardness, corrosion resistance and fatigue are all improved by friction stir !


• Welds overmatch parent plate

• Flat waisted tensiles (average of three tests tested to BS EN 895:1995

5 FSW Steels: Tensile Properties5 FSW Steels: Tensile Properties5 FSW Steels: Tensile Properties5 FSW Steels: Tensile Properties

MaterialMaterialMaterialMaterial UTS, MPaUTS, MPaUTS, MPaUTS, MPa % of Min % of Min % of Min % of Min spec valuespec valuespec valuespec value

RQTRQTRQTRQT----701701701701 831831831831 105%105%105%105%HSLAHSLAHSLAHSLA----65656565 626626626626 107%107%107%107%304L304L304L304L 635635635635 131%131%131%131%Duplex 2205Duplex 2205Duplex 2205Duplex 2205 829829829829 134%134%134%134%S355J2 + N S355J2 + N S355J2 + N S355J2 + N 609609609609 110%110%110%110%


FSW – industrial robustness

� Steel plates have been welded with no surface preparation, and with poor fit up, to test how robust the process is.

� Plates can be welded with sawn, water jet and plasma cut edges without the need for milling the edges.

� Plates with uncleaned surfaces (primed or oxidised) produced good welds

� Welding speeds of up to 500 mm/min attained in 6mm thick plate, but better properties at 350 mm/min


6mm carbon steel, single pass

� Lower distortion than fusion welding

� Cross weld strength over matches parent

� Toughness matches fusion welding

� Welds are asymmetric - retreating side tougher

� All grades of steel weldable, including ODS

� Dissimilar steels can be joined – carbon to stainless

� Process gives good results underwater

� Good indications of enhanced corrosion resistance, especially Duplex stainless

� Good indications of enhanced fatigue strength

� Currently more expensive than fusion welding


FSW – double pass


Double sided weld

� Two sided weld

� Large overlap

� 6mm thick

� Weld line not ground

� Edges not prepared

� Visually defect free weld


Double sided welding

Toughness� Sub-size Charpy

impact specimens, tested at room temp, notched at centreline, +/- 2, 4 & 6 mm

� All specimens intact

� Each side similar

Tensile strength� All tensile samples

failed in parent metal


Toughness (J, -20oC)

Position from weld centre (mm) SAW FS (Single sided) FS (Double sided)

6 (A) 33 44 104

4 (A) 44 39 139

2 (A) 62 60 86

0 54 60 131

-2 (R) 110 56 134

-4 (R) 39 38 130

-6 (R) 30 42 142

Preliminary data– to be confirmedData courtesy BAE Surface Fleet


FSW metallurgy

� Some process parameter conditions do give simple metallurgy variations – though not necessarily the phases we predicted in those zones !

� Other process conditions give us a very complex, almost chaotic, microstructure. This microstructure seems to have the best mechanical properties.

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Friction stir welding of steel: An update for the SMEA · tests tested to BS EN 895:1995 5 FSW...

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