Abstract
Friction stir welding (FSW) can generate large residual stresses during solid state joining of oxide dispersion strengthened steels. In this work, a plate of MA956 steel was friction stir welded at three conditions: 500 rpm/25 mm per minute (mmpm), 400 rpm/50 mmpm and 400 rpm/100 mmpm. The residual stresses across these welds were measured using both x-ray and neutron diffraction techniques. The distribution and magnitude of the residual stresses agreed well between the two techniques. Longitudinal residual stresses up to eighty percent of the yield strength were observed for the 400 rpm/100 mmpm condition. The surface residual stresses were somewhat larger on the root side of the weld than on the crown side. Increases in the relative heat input during FSW decreased the measured residual stresses in the stir zone and the thermomechanically affected zone (TMAZ). Increasing the traverse rate while holding the rotational speed fixed increased the residual stress levels. The fatigue strength of the material is predicted to decrease by at least twenty percent with cracking most likely in the TMAZ.
| Original language | English |
|---|---|
| Pages (from-to) | 313-321 |
| Number of pages | 9 |
| Journal | Materials Science and Engineering: A |
| Volume | 647 |
| DOIs | |
| State | Published - Oct 28 2015 |
Funding
This work was performed in part under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The two plates measured in this study were provided by Lawrence Livermore National Laboratories . We are grateful for technical assistance from Dr. E.S.K. Menon at NPS and Dr. M. Mahoney at MegaStir Technologies. Research conducted at ORNL's High Flux Isotope Reactor was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.
Keywords
- Friction stir welding
- Neutron diffraction
- ODS steel
- Residual stress
- X-ray diffraction