Loading...

Upset Resistance Welding of Duplex Stainless Steel to Martensitic Stainless Steel

Ozlati, Ashkan | 2018

537 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51257 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Movahedi, Mojtaba
  7. Abstract:
  8. Upset Resistance Welding (URW) is a solid-state joining process which can be used to join a variety of parts and profiles including railways, wheel rims and pipes used in oil and petrochemical industries. This process has three primary parameters, welding current, current passage time and mechanical pressure. Martensitic Stainless Steels (MSSs) due to high strength and wear resistance, good atmospheric corrosion resistance and relatively low price and Duplex Stainless Steels (DSSs) because of higher strength and better corrosion resistance in chlorine environments, are widely used in different industries. Dissimilar MSS/DSS joints are of great importance for piping, specially in oil and petrochemical industries. In this study, the effects of welding current (2-4 kA) and in-situ Post Weld Heat Treatment (PWHT) current (1, 1.2 kA) and time (10-99 cycles) on the microstructure and mechanical properties of MSS to DSS upset resistance welds were investigated. Results show that in lower welding currents (2-3 kA) no martensite phase was formed in the MSS, whereas in higher welding currents (3.5 and 4 kA) a small amount of martensite was present in the microstructure. In the DSS side of the samples, changes in ferrite/austenite phase balance and formation of hotspots were the most important metallurgical phenomena. Additionally, an optimal welding current was found (3.5 kA) at which tensile strength of the joint was the highest (~372 MPa). Lower and higher welding currents led to lower tensile strengths due to lack of plastic deformation and formation of hotspots, respectively. Moreover, only the optimal welding current moved the fracture location of the samples from weld interface to the MSS base material. Optimal current and time of in-situ PWHT for the sample having the highest tensile strength after welding were 1 kA and 10 cycles respectively, and caused restoration of ferrite/austenite phase balance, while reducing the tensile strength for about 5%. On the other hand, for the sample possessing the lowest tensile strength after welding, in-situ PWHT led to enhancement of tensile strength to about 2.25 times. Fracture location of the samples did not change after PWHT. In summary, PWHT for the sample with lowest tensile strength led to enhancement of tensile strength, while forming an unbalanced microstructure having about 69% ferrite phase. Whereas for the sample with highest tensile strength, PWHT caused a minor decrease in tensile strength while restoring the phase balance
  9. Keywords:
  10. Duplex Stainless Steel ; Microstructure ; Mechanical Properties ; Microhardness ; Martensitic Steels ; Upset Resistance Welding

 Digital Object List

 Bookmark

No TOC