In the current investigation, a comparison between two type 4130 low-alloy steel powders produced by both gas and water atomization, and later processed by Laser-powder bed fusion was carried out. Samples fabricated from the water atomized powder showed relative density levels exceeding 99%, slightly lower than those achieved with the gas atomized powder. Both steels exhibited similar metallurgical features after solidification, showing a microstructure that is mainly composed of partially tempered martensite, bainite, and retained austenite. Additionally, micro-segregation of alloying elements was detected in the as-built microstructure, which contribute to a local increase in microhardness. The excess of oxygen found in the water atomized powder tended to combine with silicon and form nano-sized SiO2 inclusions. During the laser processing, the complex heating and cooling effects generated by adjacent laser tracks and by overlapping layers led to an in-situ tempering of the fresh martensite. Accordingly, the hardness values of steels in as-built condition were equivalent to those of conventionally quenched samples tempered at 350 °C and 450 °C, for gas atomized and water atomized steels, respectively. Finally, a comparison in terms of mechanical properties of the investigated steels showed that the powder atomization process resulted in limited changes in steel performance.

Effect of water atomization on properties of type 4130 steel processed by L-PBF

Abdelwahed M.;Casati R.;Vedani M.
2021-01-01

Abstract

In the current investigation, a comparison between two type 4130 low-alloy steel powders produced by both gas and water atomization, and later processed by Laser-powder bed fusion was carried out. Samples fabricated from the water atomized powder showed relative density levels exceeding 99%, slightly lower than those achieved with the gas atomized powder. Both steels exhibited similar metallurgical features after solidification, showing a microstructure that is mainly composed of partially tempered martensite, bainite, and retained austenite. Additionally, micro-segregation of alloying elements was detected in the as-built microstructure, which contribute to a local increase in microhardness. The excess of oxygen found in the water atomized powder tended to combine with silicon and form nano-sized SiO2 inclusions. During the laser processing, the complex heating and cooling effects generated by adjacent laser tracks and by overlapping layers led to an in-situ tempering of the fresh martensite. Accordingly, the hardness values of steels in as-built condition were equivalent to those of conventionally quenched samples tempered at 350 °C and 450 °C, for gas atomized and water atomized steels, respectively. Finally, a comparison in terms of mechanical properties of the investigated steels showed that the powder atomization process resulted in limited changes in steel performance.
2021
EBSD
Laser Powder Bed Fusion
Low-Alloy Steel
Mechanical behavior
Micro-segregation
Water Atomized Powder
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/1203701
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