Experimental process design of martensitic steel in wire and arc additive manufacturing based on heat input regulation

Wire and arc additive manufacturing (WAAM) is an important technology for fabricating large-scale metallic components, but its forming quality and mechanical properties are highly sensitive to process parameters. Students in experimental courses on material forming often struggle to understand how heat input affects molten pool behavior, solidification structure, defect formation, and final performance. For oxide dispersion-strengthened (ODS) steel, controlling heat input is particularly important because the distribution of Y₂O₃ particles, carbide precipitation, segregation behavior, and defect formation all influence strengthening efficiency. Therefore, this study presents a comprehensive experimental teaching scheme focusing on the effect of heat input on the formability, microstructure, and mechanical properties of WAAM-formed ODS steel. The objective is to help students understand the necessity of process optimization in additive manufacturing and establish the relationship between process parameters, microstructural evolution, and mechanical performance.

ODS steel specimens were fabricated using a WAAM system under different heat input conditions. Several heat input levels were established by adjusting the forming parameters, allowing students to compare forming behavior and material responses under different thermal cycles. The experiment included three main parts. First, the macroscopic morphology and forming quality of the specimens were observed, including deposition stability, layer appearance, surface morphology, and the presence of possible forming defects. Second, microstructural characterization was conducted to analyze dendritic morphology, interdendritic solute segregation, carbide precipitation, Y₂O₃ particle distribution, and shrinkage porosity. Third, microhardness testing was performed to evaluate variations in mechanical properties under different heat input conditions. By combining forming observation, microstructure analysis, and hardness measurements, students were guided to analyze how heat input affects molten pool size, cooling rate, element diffusion, particle evolution, and defect formation.

Heat input had a pronounced influence on the forming quality and microstructural evolution of ODS steel. With increasing heat input, the molten pool’s thermal effect was enhanced, element diffusion became more complete, and interdendritic solute segregation was gradually alleviated. The number of carbides first increased and then decreased with increasing heat input. At moderate heat levels, carbide precipitation was promoted, contributing to dispersion strengthening, whereas excessive heat input caused carbide coarsening, dissolution, or redistribution, thereby reducing its strengthening contribution. The Y₂O₃ particles also changed markedly with heat input, appearing as agglomerated clusters at relatively low heat input. As heat input increased, these clusters gradually decomposed, the particles became refined, and their distribution became more uniform, improving microstructural stability. Nevertheless, high heat input also aggravated solidification defects. The size of shrinkage pores increased continuously from about 1–5 μm at Q3 to more than 10 μm at Q5. This indicates that although higher heat input can reduce segregation and refine oxide particles, it may also enlarge the molten pool and increase pore growth. The microhardness first increased and then decreased with increasing heat input, reaching a maximum value of 743 HV at Q4. This peak hardness was mainly attributed to the synergistic effects of dislocation proliferation, carbide dispersion strengthening, and the uniform distribution of refined Y₂O₃ particles. When the heat input became excessive, increased shrinkage porosity and weakened precipitation strengthening led to a reduction in hardness.

Heat input is a key factor controlling the formability, microstructure, and mechanical properties of WAAM-formed ODS steel. Moderate heat input can improve microstructural uniformity, promote oxide particle refinement, enhance carbide strengthening, and increase microhardness. However, excessive heat input may intensify shrinkage porosity and reduce overall performance. Optimizing heat input should therefore balance forming quality, segregation control, precipitate refinement, and defect suppression. From a teaching perspective, this experiment is systematic and practical. It helps students understand the process–structure–property relationships in additive manufacturing and improves their ability to design process parameters, analyze microstructures, interpret experimental data, and solve engineering problems. Thus, the proposed scheme holds considerable teaching value and can be adopted in experimental courses related to material forming and additive manufacturing.