John Bohling is a master’s candidate in the Materials Science and Engineering program (metallurgy concentration) working with the Materials Joining Group (MJG) under the direction of Dr. Carl Lundin. Prior to receiving his B.S. degree in Materials Science and Engineering from the University of Tennessee in December 2010, Mr. Bohling worked in the MJG for several semesters as an undergraduate research assistant, culminating in an undergraduate thesis with Dr. Lundin entitled “Development of Optimum Welding Procedures for In Situ Weld Replacement for Main-Steam Piping.”
While working in the MJG, Mr. Bohling has assisted with several undergraduate classes taught by Dr. Lundin, including Welding Metallurgy, Materials Processing, and the two-semester MSE senior course sequence Materials Selection in Design (required for obtaining a minor in MSE) and Materials Selection (the MSE Capstone course). Mr. Bohling’s duties have included course organization and planning, proctoring and grading exams and reports, setting up laboratory sessions, and assisting the students with their group projects in areas including the planning of experiments, sample preparation, and microstructure analysis. In 2013, he received the MSE Departmental Student Award for Excellence in Service in recognition of his efforts.
Mr. Bohling’s research in the Materials Joining Group has centered on the investigation of cracking issues in a 20Cr-32Ni-1Nb heat-resistant austenitic Annual Report 19
stainless steel casting alloy (ASTM A351 Grade CT15C). This alloy is used for large-section (2-3” wall thickness) gas transfer line components in hydrogen reformers, operating at temperatures up to 1600 °F. Weldability problems with this alloy have been reported during repair welding of service-exposed material, principally as the occurrence of cracking in the base metal heat-affected zone (HAZ). Weld deposit cracking in previously trouble-free weldments after extended time in service has also been reported. Investigation of the cracking mechanism using material provided by an industry sponsor is ongoing. Microstructural evaluation of the as-received material has been performed, and the hot cracking susceptibility of the as-received material has also been evaluated using hot ductility testing. This test method utilizes the MJG’s Gleeble 1500D, a high temperature/high strain rate thermal-mechanical simulator capable of reproducing the time-temperature profile of a welding thermal cycle. Current research is focused on completing microstructural characterization of the hot ductility samples to investigate the metallurgical basis for the observed trends in the hot ductility behavior. Mr. Bohling gave a presentation on his CT15C research at the April 2015 meeting of the Welding Research Council High Alloys Committee held in Knoxville, TN, and hosted by the MJG. Mr. Bohling passed his Ph.D. qualifying exams in the summer of 2014. He plans to defend for his master’s degree later in the summer of 2016, after which he intends to continue research on 20Cr 32Ni 1Nb for his Ph.D. degree.