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Abstract
In this study, FSW of AISI 1080 high carbon (0·85 wt-%) steel was carried out at a temperature below its AC1 under two sets of conditions, one entailing natural cooling and the other rapid cooling with liquid CO2. The joint structures and mechanical properties obtained under both sets of conditions were investigated, whereupon it was found that defect free joints can be successfully fabricated under either. The resulting joint microstructures mainly consisted of grain refined ferrite with some globular cementite. Higher (harder) joint microhardness profiles were obtained under liquid CO2 cooling below AC1 than under natural cooling below AC1. In tensile testing, all joint fractures were observed to occur in the base metal. Also, stir zone tensile strength and toughness were found to be higher in liquid CO2 cooled samples (820 MPa and 76·7 mm N respectively) than in naturally cooled samples. Note that in both cases, the joints were formed at temperatures below AC1.
This study was financially supported by a Grant-in-Aid for Science Research from the Japan Society for the Promotion of Science and Technology; by the Global COE Program; by a Grant-in-Aid for the Cooperative Research Project of Nationwide Joint-Use Research Institutes from the Ministry of Education, Sports, Culture, Science, and Technology and the Toray Science Foundation; by an ISIJ Research Promotion Grant; by the Iketani Foundation and Collaborative Research Based on Industrial Demand; by JFE steel Corporation; and by the Industry-University cooperative research project ‘Heterogeneous structure control: towards innovative development of metallic structural materials’ by JST agency.