Effects of Zr, Ti, and Al Additions on Nonmetallic Inclusions and Impact Toughness of Cast Low-Alloy Steel
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A microalloying of the low-carbon and low-alloy cast steel was conducted with Zr, Ti, and Al that were added to the steel in four combinations. After heat treatment, the samples were tested for impact toughness at room temperature using the Charpy method. The highest values of impact toughness were obtained in the group treated with Zr, while Zr-Ti and Zr-Ti-Al groups showed moderate toughness values; the lowest values were observed in the Zr-Al group. Difference among the treatment groups was observed in the fracture mechanisms, morphology, and area distribution of the inclusions. High toughness values achieved in the trials treated with zirconium corresponded with smooth ductile fracture. The metal treated with a combination of zirconium and titanium had a relatively small area occupied by inclusions, but its toughness was also moderate. Lowest impact toughness values corresponded with the larger area occupied by the inclusions in the trials treated with aluminum. Also, a connection between the solubility product [Al][N] and impact toughness was established. The study also provides a qualitative description and quantitative analysis of the nonmetallic inclusions formation as a result of microalloying treatment. The precipitation sequence of the inclusions was described based on the thermochemical calculations for the nonmetallic compounds discovered in the experimental steel. A description of the size distribution, morphology, and composition was conducted for the oxides, nitrides, sulfides, and multiphase particles.
Keywordsaluminum complex deoxidation impact toughness microalloyed steel nonmetallic inclusions titanium zirconium
The authors acknowledge funding from Caterpillar Inc. and thank the company for providing assistance in preparation and testing of the experimental material. The authors thank Jim Barlow and Gary Raab, both with Caterpillar Inc., for their valuable comments and suggestions on the paper. The authors thank the University of Northern Iowa Metal Casting Center for providing their facilities and materials for the experimental work. The authors would like to acknowledge Professor Timothy Kidd, Department of Physics, University of Northern Iowa, for his support in the SEM analysis.
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