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<p>In the present work, maraging steel 300 parts are fabricated through the laser-powder bed fusion (L-PBF) process. In the <i>as-built</i> condition, the solidification microstructure and mechanical properties (tensile properties and microhardness) are studied. The <i>as-built</i> specimens are thereafter post-heat-treated by the solution treatment + aging (STA) schedule. The specimens are first solution-annealed (840&#xa0;°C/ 2&#xa0;h + oil cool). Then, the solution-treated specimens are aged at 490&#xa0;°C with varied holding durations (2, 4, 6 and 9&#xa0;h) followed by oil quenching. The resultant microstructure and mechanical properties obtained for the STA-treated specimens are compared to that of the <i>as-built</i> counterparts. The <i>as-built</i> solidification microstructure exhibits a typical heterostructure (when viewed onto the transverse plane, i.e., the build plane) consisting of fine columnar dendritic and cellular lattice structures. The dendritic cell/ grain boundaries are enriched with segregated element(s) especially, Ni which causes austenite retention upon fast cooling during the L-PBF process. The solution treatment is attempted herein to dissolve those segregated alloying elements (micro-segregation) and thereby to prepare an appropriate homogeneous solid solution matrix, which can be hardened through subsequent aging treatment. When compared with the <i>as-built</i> state, the STA treatment causes improved tensile strength and microhardness. However, STA treatment inversely affects ductility. Depending on the aging duration, the volumetric percentage of reverted austenite (within the martensitic matrix) tends to vary. The proportion of reverted austenite within the STAed specimens affects tensile properties as well as microhardness. An increase in the aging duration provides sufficient time for austenite reversal as well as the growth in the precipitate size. Therefore, as the aging duration increases, a declining trend in the strength and microhardness value is observed. Based on the present experiment, the aging duration of 4&#xa0;h is found beneficial to obtain the peak tensile strength (UTS ~ 1968&#xa0;MPa), which is ~ 58% increased than the <i>as-built</i> condition. In addition, 4-h aging duration caused ~ 53% improved microhardness value. Potentiodynamic polarization tests reveal a higher corrosion rate of the STAed specimen and thereby a lower corrosion resistance in comparison with the <i>as-built</i> counterpart.</p>

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Effect of Solution-Aging Treatment on Microstructure, Mechanical Properties, and Corrosion Resistance of Laser Powder Bed Fusion-Fabricated Maraging Steel 300 Part: Importance of the Aging Duration

  • 期刊论文

  • 发表日期：

    2025年9月8日

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  • Sudipta Swain,
  • Sameer Anand,
  • Saurav Datta,
  • Swapan Kumar Karak,
  • Tarapada Roy

摘要

In the present work, maraging steel 300 parts are fabricated through the laser-powder bed fusion (L-PBF) process. In the as-built condition, the solidification microstructure and mechanical properties (tensile properties and microhardness) are studied. The as-built specimens are thereafter post-heat-treated by the solution treatment + aging (STA) schedule. The specimens are first solution-annealed (840 °C/ 2 h + oil cool). Then, the solution-treated specimens are aged at 490 °C with varied holding durations (2, 4, 6 and 9 h) followed by oil quenching. The resultant microstructure and mechanical properties obtained for the STA-treated specimens are compared to that of the as-built counterparts. The as-built solidification microstructure exhibits a typical heterostructure (when viewed onto the transverse plane, i.e., the build plane) consisting of fine columnar dendritic and cellular lattice structures. The dendritic cell/ grain boundaries are enriched with segregated element(s) especially, Ni which causes austenite retention upon fast cooling during the L-PBF process. The solution treatment is attempted herein to dissolve those segregated alloying elements (micro-segregation) and thereby to prepare an appropriate homogeneous solid solution matrix, which can be hardened through subsequent aging treatment. When compared with the as-built state, the STA treatment causes improved tensile strength and microhardness. However, STA treatment inversely affects ductility. Depending on the aging duration, the volumetric percentage of reverted austenite (within the martensitic matrix) tends to vary. The proportion of reverted austenite within the STAed specimens affects tensile properties as well as microhardness. An increase in the aging duration provides sufficient time for austenite reversal as well as the growth in the precipitate size. Therefore, as the aging duration increases, a declining trend in the strength and microhardness value is observed. Based on the present experiment, the aging duration of 4 h is found beneficial to obtain the peak tensile strength (UTS ~ 1968 MPa), which is ~ 58% increased than the as-built condition. In addition, 4-h aging duration caused ~ 53% improved microhardness value. Potentiodynamic polarization tests reveal a higher corrosion rate of the STAed specimen and thereby a lower corrosion resistance in comparison with the as-built counterpart.