Invar alloys with both high strength and low thermal expansion are urgently needed in fields such as overhead power transmission, aero-molds, and so on. In this paper, Cr was introduced as a cost-efficient alloying element into the Fe-36Ni binary invar alloy to increase its mechanical strength. Our results confirmed that fine Cr₇C₃ precipitants, together with some Fe₃C, in the invar alloy aged at 425 °C could be obtained with a short aging time. Those precipitants then grew and aggregated at grain or sub-grain boundaries with an increase in aging time. Simultaneously, mechanical strength and coefficient of thermal expansion (CTE) parabolically varied with the increase in aging time. The sample aged at 425 °C for 7 h presented a maximum strength of 644.4 MPa, together with a minimum coefficient of thermal expansion of 3.30 × 10⁻⁶ K⁻¹ in the temperature range of 20–100 °C. This optimized result should be primarily attributed to the precipitation of the nanoscaled Cr₇C₃.

The vacuum hot-rolled SUS314/Q235 stainless steel clad plate has many drawbacks including serious interface alloy element diffusion, stainless steel cladding’s sensitization, and carbon steel substrate’s low strength. In this study, the comprehensive properties were systematically adjusted by changing the thickness of the Ni interlayer (0, 100, 200 μm) and the quenching temperature (1000~1150 °C). The results showed that the Ni interlayer can obviously hinder the diffusion of carbon element, so as to achieve the purpose of eliminating the decarburized layer and reducing the carbon content of the carburized layer. Meanwhile, the perfect metallurgical bonding between the substrate and cladding can be obtained, effectively improving the stainless steel clad plate’s tensile shear strength and comprehensive mechanical properties, and significantly reduce the brittleness of the carburized layer. As the quenching temperature increases, the grains coarsening of carbon steel and stainless steel became more and more serious, and the sensitization phenomenon and the thickness of the carburized layer are gradually decreased. The stainless steel clad plate (Ni layer thickness of 100 μm) quenched at 1050 °C had the best comprehensive mechanical properties. Herein, the interface shear strength, tensile strength and the fracture elongation reached 360.5 MPa, 867 MPa and 16.10%, respectively, achieving strengthening and toughening aim. This is attributed to the disappearance of the sensitization phenomenon, the grain refinement and the lower interface residual stress.

Wire arc additive manufacturing (WAAM) is a viable technology for manufacturing complex and medium-to-large-sized invar alloy components. However, the cyclic thermal input during the WAAM process may cause the austenite grains in the component to grow abnormally, adversely impacting the material’s mechanical properties. The addition of alloying elements such as Cr, Mo, and V can refine the microstructure of invar alloy to solve these problems. This study examines the influence of Cr, Mo, V, and N on the microstructure and mechanical properties of invar alloy produced through wire arc additive manufacturing. The elements Cr, Mo, and V can form various carbides and nitrides in invar alloys. These precipitation phases are distributed in various forms at grain boundaries and inside the grain, which can refine both the grain and the cellular substructure inside the grain. Moreover, these precipitation phases are distributed in different forms, impeding dislocation movement, thereby enhancing the strength of the invar alloy. The mean tensile strength of WAAM-fabricated high-strength invar alloy in this study attained 793 MPa, approximately 99% higher than that of ordinary invar alloy. The mechanical anisotropy of WAAM-fabricated invar alloy can be ascribed to the thermal interactions between adjacent deposition units.