August 2020 Volume 2

and a cooling rate, and then produce diagrams to analyze the expected microstructure phase constitution. Some diagrams which can be derived from the software include CCT diagrams (shown in Figure 21), TTT diagrams (shown in Figure 35), and phase-temperature diagrams (shown in Figure 36).

FORGING RESEARCH

Figure 35: TTT diagram for M1 steel drom JMATPro These diagrams are extremely useful in the design of the cooling schedule, as they allow for the selection of cooling rates and holding times for optimization of the microstructure for a set of desired properties. It is well known the general property differences and disadvantages between the various phases in steel and modifying the microstructure to utilize these phases when needed is a core focus of the experiments discussed herein. These diagrams are extremely useful in the design of the cooling schedule, as they allow for the selection of cooling rates and holding times for optimization of the microstructure for a set of desired properties. It is well known the general property differences and disadvantages between the vari us phases in steel and modifying the microstructure to utilize these phases when needed is a core focus of the experiments discussed herein. 49 Figure 35: TTT diagram for M1 steel drom JMATPro

Figure 33: Constant S V curves plotted on a grain size vs reduction axis system [59]

Figure 33: Constant SV curves plotted on a grain size vs reduction axis system [59] Figure 33: Constant S V curves plotted on a grain size vs reduction axis system [59]

Figure 34: RCF operating window in V-Ti-N systems [17] Figure 34: RCF operating window in V-Ti-N systems [17]

2.4 Cooling and Transformation 2.4.1 Cooling Rates

Figure 34: RCF operating window in V-Ti-N systems [17]

Figure 36: M1 phase-temperature diagram at 5°C/s from JMATPro An example of phase changes with cooling modifications provided in the literature is presented in Table 4 below, where the author changed the cooling rate of the steel and produces microstructures varying in phase compositions and strength. [67] In this table, an introduction of granular bainite into the polygonal ferrite and pearlite microstructure, due to an increase in the cooling rate, causes a significant rise in the hardness of the steel. Note that further increases in the cooling rate resulted in a martensitic microstructure with a significantly higher hardness level. Figure 36: M1 phase-temperature diagram at 5 ° C/s from JMATPro An example of phase changes with cooling modifications provided in the literature is presented in Table 4 below, where the author changed the cooling rate of the steel and produces microstructures varying in phase compositions and strength. [67] In this table, an introduction of granular bainite into the polygonal ferrite and pearlite microstructure, due to an increase in the cooling rate, causes a significant rise in th hardness of the steel. No e that fu ther in reas s in the cooling rate resulted in a martensitic microstructure with a significantly higher hardness level.

Following high temperature conditioning of the austenite in the steel, proper cooling schedules are necessary to capitalize on the former processing. JMATPro simulation software is an excellent resource in this regard, as it allows for one to specify an initial austenite grain size and a cooling rate, and then produce diagrams to analyze the expected microstructure phase constitution. Some diagrams which can be derived from the software include CCT diagrams (shown in Figure 21), TTT diagrams (shown in Figure 35), and phase-temperature diagrams (shown in Figure 36). 48 48

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