Wire-arc directed energy deposition of oxide-modified H13 steel: Microstructural characterization and mechanical properties

Abstract

The preparation of H13 steel using wire-arc directed energy deposition has broad application prospects; however, the high hardenability of H13 steel makes it prone to forming cold cracks during deposition, thus limiting its further applications. Fortunately, the oxide metallurgy technology holds promise in addressing this issue. Specifically, nano oxides have the capability to refine the grain and facilitate the formation of intracrystalline ferrite, ultimately resulting in an improvement in steel's toughness and subsequently mitigating its propensity towards cold cracking. In this study, H13 steel wires, incorporating Al-Si-Ti composite oxides, were used to deposit part (W-O-H13) with excellent performance and no cold cracks. Owing to the special thermal cycling during wire-arc directed energy deposition, a periodic build unit was formed that could be roughly divided into three zones, namely, fine grain, columnar grain, and heat-affected zones. The microstructure of the parts contained lath martensite, high-alloy martensite, and ferrite. After arc exposure, the oxide formed a complex core-shell structure, with vanadium carbide (VC) encapsulating the amorphous oxide core. Moreover, the oxide particles refine the grain structure and induce the formation of ferrite, thereby enhancing the toughness of the part and further improving its strength and wear resistance. The low mismatch between the VC thin layer wrapping the oxide and ferrite was a crucial factor in the conductive ferrite phase transformation. Additionally, the elemental segregation caused by the rapid cooling rate ultimately led to the formation of high-alloy martensite having a maximum hardness of 5.32 GPa. The results reveal that the average tensile strength of W-O-H13 steel in the X, Y, and Z directions is improved by 21.0 %, 20.3 %, and 14.3 % respectively, compared to the parts fabricated solely from H13 steel wire without the addition of oxide (W-H13). Additionally, the impact toughness of W-O-H13 steel surpasses W-H13 steel in all three directions, achieving an average of 33, 27, and 28 J/cm2 respectively in the X, Y, and Z axes. In comparison to W-H13, the impact toughness of W-O-H13 has witnessed a substantial increase ranging from 10 % to 30 %. Furthermore, the wear resistance of W-O-H13 steel significantly surpasses that of W-H13 steel, particularly under high-temperature wear conditions. Specifically, the average wear volume of W-O-H13 steel at temperatures ranging from 400 to 600 °C is merely 0.163 and 0.224 mm³, representing only 30 % and 40 % of the wear volume exhibited by W-H13 steel under the same wear conditions.