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An investigation of reheat cracking in the weld heat affected zone of type 347 stainless steel

Phung-on, Isaratat
http://rave.ohiolink.edu/etdc/view?acc_num=osu1188419315

Abstract Details

2007, Doctor of Philosophy, Ohio State University, Welding Engineering.
Reheat cracking has been a persistent problem for many alloys such as the stabilized stainless steels: Types 321 and 347 and Cr-Mo-V steels as well as Ni-base superalloys termed “strain-age cracking”. Cracking occurs during PWHT at the HAZ. Many investigations have been conducted on the RHC with still no comprehensive theory to explain underlying mechanism. One proposed mechanism is the weakening of PFZ. The other is the creep-like grain boundary sliding that causes microvoid formation and coalescence. In this study, Type 347 was selected for investigation. The Gleeble™ 3800 system was employed to provide precise control of both thermal and mechanical simulation. Cylindrical samples were subjected to thermal cycles for the HAZ simulation followed by PWHT as the reheat cracking test. “Susceptibility C-curves” were plotted as a function of PWHT temperatures and time to failure 70% and 80% of yield strength at temperature. The sample shape was modified containing two flat surfaces at the center followed by HAZ simulation and the placement of micro-indentation arrays for tracing of grain boundary sliding. Then, the reheat cracking test was performed. At the 80% stress level, the cracking mechanism was identified as the PFZ weakening, while at the 70% stress as the creep-like grain boundary sliding. A DOE was employed to investigate the effects of microstructures. The microstructures were modified by heat treatment prior to the test. The grain size and cooling rate had moderate effects. The amount of MC (NbC) and its statistical interaction had significant effects. The more NbC formed prior to test, the more resistance to reheat cracking. The amount of GB carbide (M23C6) had an insignificant effect. The heat treatment schedules (during heating) had moderate effects. Cracks were intergranular path and wedge shapes with the evidence of grain boundary sliding. SEM revealed intergranular cracking with precipitates identified as Nb-rich, MC carbide. The fracture surfaces showed micro-ductility and microvoid coalescence. A SS-DTA technique determined the possible precipitation temperatures in the range of 850°C to 650°C with unconfidently reliable due its sensitivity. A simple grain boundary sliding and a finite element model were generated to explain the RHC mechanism.
John Lippold (Advisor)
215 p.
Engineering, Materials Science
Welding; Reheat Cracking; PWHT; Precipitation; PFZ; Grain boundary sliding; Creep-like; SS-DTA

Recommended Citations

Citations

  • Phung-on, I. (2007). An investigation of reheat cracking in the weld heat affected zone of type 347 stainless steel [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1188419315

    APA Style (7th edition)

  • Phung-on, Isaratat. An investigation of reheat cracking in the weld heat affected zone of type 347 stainless steel. 2007. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1188419315.

    MLA Style (8th edition)

  • Phung-on, Isaratat. "An investigation of reheat cracking in the weld heat affected zone of type 347 stainless steel." Doctoral dissertation, Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=osu1188419315

    Chicago Manual of Style (17th edition)

osu1188419315
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© 2007, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.