Austenitic stainless steel is widely utilized in modern manufacturing due to its excellent corrosion resistance and ease of processing. However, it exhibits relatively low deformation resistance and poor hardness as well as wear resistance. Inconel 718, an alloy with superior mechanical properties and excellent corrosion resistance, is employed in laser directional energy deposition (LDED) to enable additive manufacturing of dissimilar metals. To improve the connection process and quality of the two materials as well as expand the application of LDED for joining Inconel 718 alloy with 304 stainless steel, it is essential to investigate the influence of the laser deposition thermal cycle on the microstructure evolution of Inconel 718/304 connectors. This study also seeks to clarify the changes in mechanical properties resulting from the microstructure evolution.

304 stainless steel was selected as the substrate, and Inconel 718 alloy powder (particle size: 53?150 μm) was used as the cladding deposition material. The laser heat source was generated using an IPG-YLS-6000 fiber laser (maximum power: 6 kW, wavelength: 1070 nm, spot diameter: 3 mm), with a volume fraction of 99.99% argon as the shielding gas. A reciprocating layer-by-layer deposition process model was constructed using the KUKA industrial robot KRL programming system. The thermal cycle temperature of the deposited parts was dynamically monitored using an infrared pyrometer. Specimens were prepared via wire cutting, and their microstructure, composition, microhardness, and tensile property were analyzed using a scanning electron microscope, X-ray diffractometer, microhardness tester, and universal testing machine to explore the effects of thermal cycling temperature on the mechanical properties of the components.

Inconel 718/304 connectors were successfully fabricated using LDED technology, and their microstructure and mechanical properties were analyzed. The results revealed the following:

(1) Due to the heat accumulation effect, heat dissipation in the deposited part is reduced, leading to increased temperatures, decreased cooling rates, and gradual coarsening of Inconel 718 dendrites from the bottom to the top. Under the combined influence of the temperature gradient (G) and solidification rate (R), dendrites predominantly appear as columnar and cellular crystals.

(2) The Inconel 718/304 macro interface is clearly defined. Delta high-temperature ferrite precipitates on the austenite crystal surface in the interface remelting zone, and M₂₃C₆ secondary hard phase disperses in the heat-affected zone. The microhardness of each zone is as follows: Inconel 718 deposition layer > heat-affected zone > base metal. The average microhardness values of the above-mentioned areas are 283, 238, and 220 HV0.1, respectively.

(3) Due to precipitation carbide dispersion strengthening, the average yield strength of Inconel 718/304 parts is higher than that of hot-rolled 304 stainless steel parts, reaching 376.0 MPa. The tensile strengths of the two parts are similar, at 720.0 MPa and 716.7 MPa, respectively. The overall elongation of the Inconel 718/304 parts is 53.9%, and their fracture mode exhibits mixed characteristics.

The short-time laser deposition process effectively facilitates the connection of Inconel 718/304 dissimilar metals. By precipitating a small amount of M₂₃C₆ hard-strengthening phase, the tensile properties and microhardness of the connectors are significantly improved compared to 304 stainless steel components.