Effect of Titanium and Niobium on Modifying the Microstructure of Cast K100 Tool Steel

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Process metallurgy and materials processing science, 2014-12, Vol.45 (6), p.2304-2314
• Main Authors: Mirzaee, Masoud, Momeni, Amir, Keshmiri, Hamid, Razavinejad, Reza
• Format: Article
• Language: English
• Subjects: Applied sciences; Casting; Characterization and Evaluation of Materials; Chemistry and Materials Science; Exact sciences and technology; Grain size; Ingot casting; Ingots; Materials Science; Metallic Materials; Metals. Metallurgy; Microstructure; Nanotechnology; Niobium; Production of metals; Segregations; Steel; Structural Materials; Surfaces and Interfaces; Thin Films; Titanium; Tool steels
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-014-0150-8

The effects of Ti and Nb on the microstructure of cast K100 tool steel were studied by optical and scanning electron microscopes. The amounts of Ti as 0.3, 0.7, and 1 wt pct and Nb as 0.2 and 1 wt pct were added to the studied steel. The addition of 0.3 wt pct Ti did not result in a considerable change in the size of carbides and prior austenite grain size. However, microstructure of K100 with 0.7 and 1 wt pct Ti was considerably modified (about 55 pct) and a uniform grain size was obtained at different positions (bottom, middle, and top) of the ingot. With addition of 0.2 and 1 wt pct Nb, microstructure was modified and a more uniform grain size was obtained all over the ingot. The average modification of microstructure in the bottom, middle, and top of the ingot was about 22 pct. Both Ti and Nb could effectively decrease the segregation of Cr and C from the bottom (high cooling rate positions) to the top of the ingots (low cooling rate positions). The homogeneity of chemical composition increased with increasing Nb or Ti. In alloy with 0.7 to 1 wt pct Ti, the average size of prior austenite grains was finer than alloys with 0.2 to 1 wt pct Nb. Therefore, Ti was found more capable than Nb in the modification of microstructure and decreasing the segregation of Cr and C in cast K100 tool steel.