Loading...

Study on the Phase Transformation and Mechanical Behavior of Duplex Stainless Steel Resistance Spot Welds

Arabi, Hassan | 2016

613 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49300 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pouranvari, Majid; Movahedi, Mojtaba
  7. Abstract:
  8. Use of materials with both high strength and good formability in car structure is a serious approach in the automotive industry to reduce weight as well as maintain the security of occupants. Stainless steels such as duplex steels are one of the most attractive candidates. Thus, metallurgical and mechanical behavior during resistance spot is important. The aim of this work is to study the microstructure-property relationships in resistance spot welding of duplex stainless steel. Austenite-ferrite phase balance and weld nugget size are two key factors determining the mechanical properties of these steels. High cooling rate of resistance spot welding can have a significant impact on the austenite-ferrite phase balance and also on deposition of carbide / nitride. In this study, after studying the effects of welding current (as the most important parameter affecting the heat-input of weld) on Macrostructure characteristics, microstructure and weld-phase reactions, it has been attempted to recover the austenite-ferrite phase balance by applying a heat treatment cycle immediately after welding. To check the phase balance changes by changing heat input, an experimental approach using microscopic images and common equations were used to predict the microstructure. Accordingly, it was observed that in resistance spot welding of duplex stainless steels, phase balance were changed. A decrease after an increase in austenite content were observed by increasing weld current. Also peak load, peak energy and failure mode of tensile-shear test were used to describe the mechanical behavior of the weldment. It was observed that by increasing the welding current, strength and energy absorption increases. In low welding currents, interfacial mode and in high welding current pullout mode of failure were observed. By applying insitu post weld heat treatment after welding for 90 cyc and the 5 kA, austenite content increased by about 5% to about 30% and austenite-ferrite phase balance improved. Furthermore, comparison of tensile-shear test results of conventional steels in the automotive industry, indicates the potential of duplex stainless steels for use in the steel industry
  9. Keywords:
  10. Resistance Spot Welding ; Metallography ; Phase Equilibrium ; Phase Transformation ; Tensile Strength Test ; Duplex Stainless Steel ; Past-Weld Heat Treatment

 Digital Object List

 Bookmark

No TOC