Ferrous friction stir weld physical simulation
Author: Norton, Seth Jason
Degree: Doctor of Philosophy, Ohio State University, Welding Engineering, 2006.
Advisor: John C. Lippold

Abstract
   
Friction stir welding an application which has the potential to make full thickness welds in a single pass, while eliminating fume, reducing distortion, and eliminating solidification defects. Interest in the process by industries which rely on iron and its alloys for structural material is increasing. While friction stir welding has been shown to be feasible with iron alloys, the understanding of friction stir welding process effects on these materials is in its infancy. Friction stir weld material tracer experiments utilizing stainless steel markers were conducted with plates of ingot iron and HSLA-65. The markers showed that material is moved in a curved path around the tool and deposited behind the tool. Material near the surface is moved a greater distance as it is acted upon by the tool shoulder. A friction stir weld was made on a plate of HSLA-65 with Inconel sheathed thermocouples embedded in the tool path. Heating rates calculated from the slope of the acquired temperature data show that the peak heating rate occurs at temperatures between 350ºC and 500ºC. An increase in the heating rate occurring at elevated temperature was associated with the transformation from ferrite to austenite.

Peak temperatures on the top of the plate exceeded 1200ºC and peak temperatures acquired on the bottom exceeded 1000ºC. Hot torsion tests with non-uniform temperature profiles were conducted on both ingot iron and HSLA-65 samples. An annular sample geometry with internal and external gas quench achieved cooling rates in the hot torsion samples similar to those observed in friction stir welding. Localization of strain in the intercritical temperature region was determined to be caused by differences in the activation energy for deformation for ferrite and austenite. Adiabatic heating due to shear strain was shown to be related to the Zener-Holloman parameter. Microstructures created in both the ingot iron and HSLA-65 were very similar to those observed in friction stir welds made in the same material. Here's the link to the .pdf;

http://search.ohiolink.edu/etd/send-pdf.cgi/Norton%20Seth%20Jason.pdf?osu1143252009

Enjoy the reading... I know I will!!! :) :) ;)

Respectfully,
Henry