In the relentless pursuit of stronger, more durable materials, a team of researchers from Nanjing University of Science and Technology has made a significant breakthrough that could revolutionize the energy sector. Led by Dr. Duan Mengwei from the School of Materials Science and Engineering, the team has uncovered new insights into the behavior of 18Ni350 maraging steel (M350) when fabricated using wire arc additive manufacturing (WAAM) and subjected to direct aging heat treatment. Their findings, published in the journal “Materials Engineering” (Cailiao gongcheng), open doors to enhanced material properties and could pave the way for more robust components in critical energy infrastructure.
Maraging steels are renowned for their exceptional strength and toughness, making them ideal for high-stress applications in the energy sector. However, the traditional manufacturing processes often fall short in achieving the desired microstructural control. This is where WAAM comes into play, offering a more precise and efficient method for fabricating complex components.
The research team delved into the effects of different aging conditions on the microstructure and mechanical properties of M350. They discovered that the solidification microstructure of M350 fabricated by WAAM consists of columnar and cellular dendrites, with notable segregation of elements like nickel, molybdenum, and titanium in the interdendritic regions. “During the direct aging process, we observed a reverse transformation in these regions,” explained Dr. Duan. “The martensite phase converted to austenite, and the size and quantity of reversed austenite increased with higher aging temperatures and longer aging times.”
This transformation is crucial because it directly impacts the material’s mechanical properties. The team found that the microhardness, yield strength (YS), and ultimate tensile strength (UTS) of M350 initially increased and then decreased with aging. The optimal conditions were identified at 530°C for 3 hours, yielding a peak microhardness of 534 HV, a YS of 1600 MPa, and a UTS of 1658 MPa. Remarkably, the material maintained an elongation after fracture above 13%, indicating excellent ductility.
However, the story doesn’t end with enhanced strength. The researchers also noted mechanical anisotropy in the M350 fabricated by WAAM, with the anisotropy difference peaking under the optimal aging conditions. This means that the material’s properties vary depending on the direction of applied stress, a factor that must be carefully considered in engineering applications.
So, what does this mean for the energy sector? The ability to precisely control the microstructure and mechanical properties of maraging steels through WAAM and direct aging could lead to the development of more reliable and durable components for energy infrastructure. From pipelines and pressure vessels to turbine blades and nuclear reactors, the potential applications are vast. “This research provides a solid foundation for optimizing the performance of maraging steels in high-stress environments,” said Dr. Duan. “It’s a step forward in ensuring the safety and efficiency of energy systems.”
As the energy sector continues to evolve, the demand for advanced materials that can withstand extreme conditions will only grow. This research, published in Materials Engineering, offers a glimpse into the future of material science, where precision manufacturing and heat treatment techniques converge to create materials that push the boundaries of what’s possible. The findings by Dr. Duan and the team at Nanjing University of Science and Technology are a testament to the power of innovation and the relentless pursuit of excellence in the field of materials engineering.