November 2020 Volume 2

Martensite

2 µm FORGING RESEARCH AND TECHNOLOGY

FORGING RESEARCH

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3.4 Advanced Microstructural Analysis (EBSD-IQ) after Dilatometry 3.4.1 SLM4340 UniformContinuous Cooling The reheated conditions were also analyzed and the reconstructed microstructures based on EBSD measurements and on EBSD IQ for SLM 4340 are shown on Figure 19. Figure 19A shows the Inverse Pole Figure (IPF), Figure 19B, the IQ map and Figure 19C, a MatLab figure showing the IQ map in a colored scale, all for the cooling rate of 0.25C/min, Figure 19 from (d) to (f) show the same for the cooling rate of 500C/min. Figure 18: SEM pictures of ( A ) 0.25C/min, ( B ) 0.5C/min, ( C ) 1C/min, ( D ) 5C/min, ( E ) 10C/min, ( F ) 20C/min, ( G ) 50C/min, ( H ) 100C/min, ( I ) 500C/min; all samples were etched with 3% Nital. In summary, the results from the uniform continuous cooling transformation study clearly showed that the fabrication technique of the SLM steel provides a finer Austenite grain size prior to transformation, more uniform chemical composition, however, has lower hardenability than the Wrought steel. The different fabrication and processing techniques generate a strong effect on the final microstructural constituents and their volume fraction. The next section will present the results of the advanced microstructural analysis based on the EBSD-IQ technique. This approach has been used successfully in other studies. 3.4. Advanced Microstructural Analysis (EBSD-IQ) after Dilatometry 3.4.1. SLM 4340 Uniform Continuous Cooling The reheated conditions were also analyzed and the reconstructed microstructures based on EBSD measurements and on EBSD-IQ for SLM 4340 are shown on Figure 19. Figure 19A shows the Inverse Pole Figure (IPF), Figure 19B, the IQ map and Figure 19C, a MatLab figure showing the IQ map in a colored scale, all for t e cooling rate of 0.25C/min, Figure 19 from (d) to (f) show the same for the cooling rate of 500C/min.

Ferrite

Granular Bainite

Pearlite

MA \\\ \\

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Martensite

Bainite

Granular Bainite

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FORGING RESEARCH

Martensite

Martensite

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Bainite

Bainite

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17

Martensite

Martensite

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111

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Bainite FORGING RESEARCH

101

001

Figure 19: Reconstructed microstructures and EBSD-IQ for SLM 4340 cooled at (A, B and C) 0.25C/min and (D, E and F) 500C/min. The color scale in Figure 19C and Figure 19F shows the micro constituents that have lower dislocation density hence higher IQ values represented by purple and blue colors, while micro constituents with higher dislocation density and lower IQs are shown by the green and yellow colors. Figure 20 shows the EBSD-IQ phase balance for the SLM samples after cooling at 0.25C/min and 500C/min. The difference in the microstructural components supports the CCT and SEM results. Figure 19: Reconstructed microstructures and EBSD-IQ for SLM 4340 cooled at ( A , B and C ) 0.25C/min and ( D , E and F ) 500C/min. The color scale in Figure 19C and Figure 19F shows the micro-co stituents that have lower dislocation density hence higher IQ values represented by purple and blue colors, while micro-constituents with higher dislocation density and lower IQs are shown by the green and yellow colors. Figure 20 shows the EBSD-IQ phase balance for the SLM samples after cooling at 0.25C/min and 500C/min. The difference in the microstructural components supports the CCT and SEM results. Cr-C-rich Constituents – 11.9% Pearlite – 28.3% Ferrite – 59.8%

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Martensite

0 0.1 0.2 0.3 0.4 0 0.1 0.2 0.3 0.4

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Figure 18: SEM pictures of (A) 0.25C/min, (B) 0.5C/min, (C) 1C/min, (D) 5C/min, (E) 10C/min, (F) 20C/min, (G) 50C/min, (H) 100C/min, (I) 500C/ min; all samples were etched with 3%Nital. In summary, the results from the uniform continuous cooling transformation study clearly showed that the fabrication technique of the SLM steel provides a finer Austenite grain size prior to transformation, more uniform chemical composition, however, has lower hardenability than the Wrought steel. The different fabrication and processing techniques generate a strong effect on the final microstructural constituents and their volume fraction. The next section will present the results of the advanced microstructural analysis based on the EBSD-IQ technique. This approach has been used successfully in other studies. Figure 18: SEM pictures of ( A ) 0.25C/min, ( B ) 0.5C/min, ( C ) 1C/min, ( D ) 5C/min, ( E ) 10C/min, ( F ) 20C/min, ( G ) 50C/min, ( H ) 100C/min, ( I ) 500C/min; all samples were etched with 3% Nital. In summary, the results from the uniform continuous cooling transformation study clearly showed that the fabrication technique of the SLM steel provides a finer Austenite grain size prior to transformation, more uniform chemical compositio , however, has lower hardenability than the Wrought steel. The different fabrication and processing techniques generate a strong effect on the final microstructural constituents and their volume fraction. The ext section will present the results of the advanced microstructural analysis based on the EBSD-IQ technique. This approach has been used successfully in other studies. 3.4. Advanced Microstructural Analysis (EBSD-IQ) after Dilatometry 3.4.1. SLM 4340 Uniform Continuous Cooling The reheat d conditions were als analyzed and the reconstructed microstructures based on EBSD measurements and on EBSD-IQ for SLM 4340 are shown on Figure 19. Figure 19A shows the Inverse Pole Figure (IPF), Figure 19B, the IQ map and Figure 19C, a MatLab figure showing the IQ map in a colored scale, all for the cooling rate of 0.25C/min, Figure 19 from (d) to (f) show the same for the cooling rate of 500C/min.

Frequency

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Figure 20: EBSD-IQ measurements for SLM 4340 cooled at ( A ) 0.25C/min and ( B ) 500C/min.

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FIA MAGAZINE | NOVEMBER 2020 91

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