# Effect of Interlayer Temperature-Controlled Thermal Cycling on the Microstructure and Mechanical Properties of Wire Arc Directed Energy Deposition H13 Steel

## TL;DR

This study examines how controlling interlayer temperatures during wire arc directed energy deposition affects the microstructure and strength of H13 steel.

## Contribution

The study introduces a systematic investigation of thermal cycling effects on microstructural evolution and mechanical properties in WA-DED H13 steel.

## Key findings

- At 200 °C interlayer temperature, coarse martensite with low dislocation density and large precipitates resulted in 1103 MPa tensile strength and 14.6% elongation.
- Increasing interlayer temperature to 400 °C produced finer martensite and higher dislocation density, boosting tensile strength to 1549 MPa but reducing elongation to 8.3%.
- At 600 °C, precipitate coarsening reduced tensile strength to 1434 MPa but slightly improved elongation to 8.6%.

## Abstract

Wire arc directed energy deposition (WA-DED) is a cost-effective technique for fabricating large metallic components. However, the inherent layer-by-layer deposition process leads to substantial heat accumulation, which significantly influences the resulting microstructure and mechanical properties. In this study, the effects of thermal cycling histories, at different interlayer temperatures, on the microstructural evolution and mechanical behavior of WA-DED fabricated H13 steel thin walls were systematically investigated, using an experimentally calibrated transient thermal model combined with experimental validation. Microstructural analysis revealed that at an interlayer temperature of 200 °C, the deposited material primarily consisted of coarse martensite with a low dislocation density and relatively large precipitates at a moderate volume fraction, resulting in an ultimate tensile strength of 1103 ± 28 MPa and an elongation of 14.6%. Increasing the interlayer temperature to 400 °C facilitated the formation of finer martensite with a higher dislocation density and smaller precipitates of slightly increased volume fraction. These microstructural refinements enhanced the tensile strength to 1549 ± 43 MPa, albeit at the expense of ductility, reducing elongation to 8.3%. When the interlayer temperature was further raised to 600 °C, fine martensite and a moderate dislocation density were retained; however, precipitate coarsening and a reduced volume fraction led to a decline in tensile strength to 1434 ± 33 MPa, accompanied by a slight recovery in elongation to 8.6%. Quantitative analysis based on classical strengthening models confirmed that dislocation strengthening is the dominant mechanism governing the variation in mechanical properties with changing interlayer temperature.