Study on Equilibrium and Non-equilibrium Solidification of Boron-Containing High-Speed Tool Steel: Effect of Cooling Rate and Microstructure Investigation

This work intends to understand the microstructure evolution of new and enhanced boron-containing high-speed tool steel. The solidification reactions of investigated steels are discussed under equilibrium and non-equilibrium conditions. The Thermo-Calc program was utilized to predict the microstructure characteristics of studied high-speed tool steel in equilibrium conditions. On the other hand, the Schiel-Gulliver simulation model was applied to explore the influence of the cooling rate on the microstructure of the examined steel produced under non-equilibrium conditions. The effect of boron addition and production conditions (equilibrium and non-equilibrium) on microstructure evolution and their effect on hardness and wear resistance were discussed. The results demonstrate that both variations of boron contents and production conditions affect the solidification reaction sequences and the volume fraction of different phases and their types. The microstructure of the boron-containing steel is well homogenous distributed, dense, and higher ferrite volume fractions change with boron contents. The boron-containing steel is characterized by resistance to wear, about 117 and 230% of standard AISIM2 tool steel in equilibrium and non-equilibrium production conditions, respectively. The Expected Life Cycle Cost Analysis of the innovative boron-containing AISIM2 high speed tool steel is summarized as the following: The total production cost per part is reduced by 10-20% due to the double working lifetime of the innovative boron-containing AISIM2 high speed tool steel. Double-cutting feed cuts cost by a further 10-15%, so the total reduced production cost per produced material is 20-40%. Tool replacing, which causes production stops and is often due to broken tools, is reduced to 30%.