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Strong & Tough Steel Welds

Strong & Tough Steel Welds. M. Murugananth, H. K. D. H. Bhadeshia E. Keehan, H. O. Andr₫n L. Karlsson. 10 m m. Transition. Stress. Cleavage. Flow stress. Temperature. Fe-0.05C-2Mn-3Ni wt% Yield strength 850 MPa Charpy toughness 60 J at -60 o C.

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Strong & Tough Steel Welds

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  1. Strong & Tough Steel Welds M. Murugananth, H. K. D. H. Bhadeshia E. Keehan, H. O. Andr₫n L. Karlsson

  2. 10 mm Transition Stress Cleavage Flow stress Temperature

  3. Fe-0.05C-2Mn-3Ni wt% Yield strength 850 MPa Charpy toughness 60 J at -60 oC General perception: nickel improves cleavage resistance of ferrite Weld A: Fe -0.03C-2Mn-7Ni Weld B: Fe -0.03C-2Mn-9Ni

  4. A = 790 MPa B = 840 MPa A B

  5. Weld A: Fe -0.03C-2Mn-7Ni Weld B: Fe -0.03C-2Mn-9Ni Conclusion: Nickel has not improved toughness Different approach needed !

  6. Neural network created Charpy 3300 experimental data 22 variables chemical composition, heat treatment, welding conditions test temperature UTS

  7. Weld A: Fe -0.03C-2Mn-7Ni Weld B: Fe -0.03C-2Mn-9Ni Weld C: Fe -0.03C-0.6Mn-7Ni

  8. How to find the reason ? -Study temperature dependence of strength. -Retained austenite measurements. -Hardness testing. -Measure transformation temperatures.

  9. Temperature Dependence Study Idea was to compare toughness at same strength But... Trends remain same. Also not able to compare toughness at same strength

  10. Retained Austenite Not a significant change in volume % to explain large difference in toughness.

  11. Vickers Hardness Measurement Aoffset offset distance 5 mm from weld centerline Observation Large scatter in hardness values along depth of the weld C but not in weld A. Why large scatter ?

  12. Reason for scatter in hardness.. Dilatometric measurements revealed the difference in Ac1, as expected. Low Mn = High Ac1 High Mn = Low Ac1 Though, difference in Ac1is less, it is enough to cause a change in temper effects of reheated zones in a multi-pass weld.

  13. Mechanism of Toughness Improvement Lower Ac1 means reaustenitising and transforming back to fresh hard martensite. Higher Ac1 means tempering of already formed martensite. Tempering of substrate layers gives a combination of soft and hard final microstructure than a uniformly hard final microstructure.

  14. Hm=Va' Ha' + Vo Ho Assessment of Microstructure

  15. Future Work and Anticipation • Tempering kinetics of welds A and C may differ. Would be investigated. • Charpy sample spans many layers of the weld. Hence, homogenisation weld C should change the toughness.

  16. Conclusion • Nickel does not necessarily improve toughness under all circumstances • A well trained neural network model can predict any complex relationship. • Transformation temperature, Ac1, has a marked effect on toughness of multipass welds.

  17. http://www.msm.cam.ac.uk/phase-trans/ Murugananth M

  18. http://www.msm.cam.ac.uk/phase-trans/ Murugananth M

  19. http://www.msm.cam.ac.uk/phase-trans/ Murugananth M

  20. http://www.msm.cam.ac.uk/phase-trans/ Murugananth M

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