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Copper Precipitation during Repeated Thermal Cycling of Steel Weld Metal

Research Scholar

Honghong Wang, Materials Science and Engineering (China)
Xinghua Yu, Co-Researcher
S. S. Babu, Faculty Mentor

Biography

Honghong Wang was born in Shanxi province of China in 1967. She earned her bachelor's degree in welding technology from the Department of Materials Science and Engineering at Taiyuan University of Technology in 1990. After working for 12 years, she completed a master's degree in welding metallurgy from the same university in 2005, as well as a doctorate in welding metallurgy from Shanghai Jiao Tong University in 2009. She is an associate professor at Wuhan University of Science and Technology, and her research focuses on the investigation of welding metallurgy and development of advanced welding consumables.

What is the issue or problem addressed in your research?

Cu is being considered as an allying addition for high strength low alloys to increase strength by precipitation hardening, as well as, blast resistance. It is now generally accepted that the following sequence is characteristic of precipitation in this system.

α (supersaturated solid solution) → BCC copper → 9R copper → FCC ε

Research on Fe-Cu alloys has generally involved quenching followed by aging treatment at temperature in the range 400-700 ºC. Different copper precipitate microstructures lead to the different strengthening mechanisms.

As to the weld metal, mechanisms of Cu precipitation during solidification and subsequent repeated thermal cycles in the austenite and ferrite phase region, as well as, during post weld heat treatment is not known.

What methodology did you use in your research?

The selected area FIB sample preparation and local electrode atom probe tomography is used to quantify the Cu precipitate characteristics (composition, size, shape and number density). These measurements will be correlated to observed spatial differences in hardness, as well as, predicted thermal cycles in different locations. It is hypothesized that the large differences in the copper precipitate characteristics in different locations is due to subtle differences in the onset of copper precipitation during thermal cycling.

What are the purpose/rationale and implications of your research?

The aim of current study is to study the copper precipitation during repeated thermal cycle of high strength weld metal and its strength mechanism. We characterize copper precipitation sequences and calibrate the phase transformation models for welding in order to optimize the Cu bearing high strength weld metal.