| ZHENG Bu-yun,CHEN Xin,LEI Jian-bo,WANG Tian-qi.Effect of Heat Treatment on Microstructure and Mechanical Properties of 18Ni300 Maraging Steel Prepared by Laser Melting Deposition[J],52(3):388-398 |
| Effect of Heat Treatment on Microstructure and Mechanical Properties of 18Ni300 Maraging Steel Prepared by Laser Melting Deposition |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.03.037 |
| KeyWord:laser melting deposition maraging steel microstructure heat treatment mechanical property |
| Author | Institution |
| ZHENG Bu-yun |
School of Mechanical Engineering,Tianjin , China |
| CHEN Xin |
School of Mechanical Engineering,Tianjin , China |
| LEI Jian-bo |
Institute of Laser Technology, Tiangong University, Tianjin , China |
| WANG Tian-qi |
School of Mechanical Engineering,Tianjin , China |
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| Abstract: |
| The maraging steel (18Ni300) is a typical high-strength steel with excellent weldability, good mechanical properties, and strong adaptability to complex working conditions. One of its most obvious advantages is that its heat treatment process is simple and it is less prone to deform after aging treatment. Therefore, the addition of excellent strengthening process will further broaden its application, making it an important material in marine transportation, aerospace, machinery manufacturing and other fields. The work aims to improve the mechanical properties of maraging steel in practical application and study the effects of different heat treatment methods on the preparation of 18Ni300 alloy by laser additive manufacturing. As an additive manufacturing technology with high degree of freedom and high molding efficiency, laser melting deposition was selected as the molding method in this work. Multi-channel multilayer 18Ni300 alloy samples were prepared by coaxial powder feeding. The optimum process parameters were determined after optimization. The heat treatment tests were carried out in a vacuum tube furnace with a heating rate of 3 ℃/min, and the samples were subjected to solution treatment (840 ℃/1 h ) and solution treatment (840 ℃/1 h ) + aging treatment (490 ℃/6 h). The mechanical property was analyzed by INSTRON 5982 material mechanics testing machine. The phase and microstructure were analyzed by D/MAX-2500 X-ray diffractometer (XRD) and ZEISS Sigma 300 scanning electron microscope (SEM) and supporting X-ray diffraction instruction (EDS). The effects of different heat treatment methods on mechanical properties were analyzed through tensile fracture morphology, performance characterization and element segregation behavior under different treatment methods. After solution treatment, the size of dendrites did not change significantly, but the molten pool boundary disappeared. During the high-temperature heat preservation process, the impurity phase and alloying elements were fully dissolved in austenite, and a uniform martensite structure was formed after cooling. The tensile strength changed from 662.1 MPa to 611.5 MPa, with a decrease of 7.64%, and the elongation changed from 12.328% to 13.832%, with an increase of 12.20%. After the solution treatment + aging treatment, the dendrite morphology basically disappeared, the distribution of each element was uniform, and the Ni3Mo and Ni3Ti as second phase particles were dispersed in the matrix. The tensile strength reached 1 404.6 MPa, with an increase of 112.14%, and the elongation was 7.80%, with a decrease of 36.72%. Submicron second phase particles were observed in the fracture, which were spherical or granular and distributed among the dendrites. The as-built 18Ni300 alloy is mainly composed of martensite and a small amount of austenite, with good density and low strength but good plasticity in tensile properties. After solution treatment, the phases are all composed of martensite, the distribution of elements is uniform, the tensile strength is slightly decreased, and the plasticity is improved. The combination of solution treatment + aging treatment has a dispersion strengthening effect on the alloy, so the tensile strength is greatly improved, and the plasticity is significantly weakened. The fracture mechanism of the samples before and after heat treatment belongs to ductile fracture, and the second phase dispersion strengthening is the main reason for the improvement of mechanical properties of the alloy after heat treatment. |
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