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September 13, 2011 Material Considerations when Welding Dissimilar Combinations Morgan Gallagher, Ph.D. Applications Engineer, Materials Group

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Presentation on theme: "September 13, 2011 Material Considerations when Welding Dissimilar Combinations Morgan Gallagher, Ph.D. Applications Engineer, Materials Group"— Presentation transcript:

1 September 13, 2011 Material Considerations when Welding Dissimilar Combinations Morgan Gallagher, Ph.D. Applications Engineer, Materials Group Email: mgallagher@ewi.orgmgallagher@ewi.org Phone: 614.688.5134

2 Objective Provide an understanding of the importance of materials science in dissimilar materials joining Focuses: Metallurgy Fusion Welding Processes Structural Materials and Corrosion-Resistant Alloys Carbon and Low-Alloy Steels Stainless Steels Ni-Based Alloys

3 Meet Joe … Joseph Schweissen – BSWE from Ohio State (2011)

4 Joes First Job … Joe goes to work for TLA Welding Consultants Joes first assignment: Qualify a weld procedure for joining an F22 forging (2.25Cr-1Mo) to X65 pipeline steel F22 has a maximum hardness restriction X65 must maintain the minimum strength level (YS >65 ksi) #1

5 Joes First Assignment … 1 st Iteration: PWHT schedule produces acceptable hardness in the F22 HAZ, but the cross-weld tensile samples fail in the X65 base-metal. 2 nd Iteration: Joe backs off on the PWHT schedule, and the cross-weld tensile samples pass … but now the F22 HAZ is too hard! X teenth Iteration: Joe cannot find a combination of welding parameters and PWHT schedule that will produce the desired result!

6 Butter Welds Welding dissimilar hardenable steels One material must be PWHT (HAZ hardness limit) One material cannot be PWHT (strength loss) Solution: Butter weld Butter weld a layer onto the member that must be PWHT Use filler metal that (1) is not hardenable, and (2) may be PWHT without deleterious effects PWHT the butter welded component Machine butter layer to weld groove Weld second member to butter layer No PWHT necessary for closure weld

7 Butter Welds F22 X65 F22 625 F22 625 Butter Weld Machine PWHT F22 Closure Weld

8 Joes Second Assignment … Qualify a cladding procedure to deposit IN625 onto the ID of X65 pipe Joe selects a set of welding parameters and a PWHT schedule that produce acceptable results! However, Joe notices a number of peculiarities when he examines the metallurgical section from the qualification coupon. #2

9 Cladding Steel with CRA Type-II Boundaries Reference: Kou (2003) Reference: Lippold and Kotecki (2005)

10 Cladding Steel with CRA Other Issues: 1.Martensitic transition layer 2.Carbon migration HAZ softening Creep failure Reference: Lippold and Kotecki (2005)

11 Joes Third Assignment … Qualify a welding procedure for IN625 The shop is out of matching filler metal Joe selects 25.10.4L duplex SS filler metal instead The weld procedure passes the qualification tests, and is subsequently used to fabricate production parts Only months into service, welds fabricated using this weld procedure start to experience corrosion failures … #3

12 Galvanic Corrosion Chemical potential difference between dissimilar metals Galvanic couple between dissimilar metals Anode - active metal has lower potential Cathode - noble metal has higher potential Net current flow from anode to cathode Effect of dissimilar base and/or weld metals Galvanic series in seawater. Ref.: Jones (1996)

13 Solution Potential vs. Location Solution Potential, mV Anode Cathode Weld MetalHAZBase Metal (Good) (OK) (Bad) Distance

14 Joes Fourth Assignment … Characterize a diffusion bond between an aluminum alloy and stainless steel Joe finds intermetallics forming along the bondline of some of the joints Joe must now explain why intermetallics only form sometimes #4

15 Intermetallic Formation 430SS Al-alloy 436SS (Mo+Nb additions) Al-alloy

16 Joes Fifth Assignment … Design a stainless steel to structural steel joint for a high temperature water environment Significant coefficient of thermal expansion (CTE) mismatch Stresses develop at the interface on heating/cooling Cyclical heating and cooling can be especially problematic (i.e., thermal fatigue) #5

17 CTE Mismatch Courtesy of EPRI MRP-169 R.1

18 Joes Sixth Assignment … Qualify a welding procedure to join carbon steel to a copper alloy Joe selects a copper alloy as the weld consumable #6

19 Copper to Steel Joint Iron and copper are insoluble in liquid form Copper penetrates into the stainless steel HAZ More appropriate choice: Ni-200 (commercially pure Cu) High solubility for both iron and copper Courtesy of www.metallographic.comwww.metallographic.com

20 The moral of the story … After having spent a short time in industry, Joe (begrudgingly) develops a respect for the importance of metallurgy … especially with dissimilar joints. In fact, his experiences make him a pretty good metallurgist himself!

21 Questions? Morgan Gallagher Applications Engineer, Materials Group Email: mgallagher@ewi.orgmgallagher@ewi.org Phone: 614.688.5134

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