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Article

Mitigating the Anisotropy of the Microstructure and Mechanical Properties of L-PBF-Fabricated H13 Steel via Rare Earth Ce Addition

by
Xiaodan Fan
1,†,
Yuhua Deng
1,†,
Yingkang Wei
1,*,
Yaojia Ren
1,
Sitong Chen
1,
Yongwei Lv
2,
Jilei Zhu
1 and
Shifeng Liu
1,*
1
School of Metallurgical Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China
2
Shaanxi Science and Technology Holding Institute, Xi’an 710016, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Materials 2026, 19(4), 755; https://doi.org/10.3390/ma19040755
Submission received: 3 December 2025 / Revised: 22 January 2026 / Accepted: 11 February 2026 / Published: 15 February 2026
(This article belongs to the Special Issue 3D Printing Technology Using Metal Materials and Its Applications)
Browse Figures
Versions Notes

Abstract

H13 tool steel is widely used in the hot work die industry owing to its excellent mechanical properties. However, the inherent anisotropy of its microstructural and mechanical properties during additive manufacturing (AM) via laser powder bed fusion (L-PBF) hinders its broader application. In the current study, Ce-containing and as-built samples were prepared in both vertical and horizontal directions, and their microstructures and tensile properties were investigated. Notably, the grain size of the vertical samples is approximately 2.7 μm, which is 19.2% smaller than that of the horizontal samples in L-PBF H13 steel. In addition, the retained austenite (RA) content in the vertical samples reaches as high as 19.7%, whereas in the horizontal samples, it is only 0.4%. After the addition of Ce, the columnar grains of the building direction (BD) samples transform into equiaxed grains. The RA content of the scanning direction (SD) samples and BD samples is 6.3% and 5.7%, respectively. The tensile test results further demonstrate that Ce-containing BD samples exhibit a tensile strength of 2025.3 MPa and an elongation of 17.3%, with the elongation difference between the two directions being only 0.2%. The addition of Ce reduces microstructural anisotropy, resulting in a significant decrease in the mechanical property anisotropy of the formed parts.

1. Introduction

H13 steel is widely used in the field of hot work die steel due to its high strength and thermal fatigue resistance [1,2]. Modern hot work dies feature complex designs with built-in water cooling channels [3,4]. Traditional subtractive manufacturing methods face difficulties in directly forming such dies, requiring numerous post-processing steps that waste substantial human and material resources and increase costs [5,6]. L-PBF is a technology that melts continuous powder materials via laser, enabling the fabrication of precision structures and near-net-shape samples, thus occupying a dominant position in the formation of complex structures [7,8,9]. Compared with traditional subtractive manufacturing methods, it offers advantages such as personalized forming, high forming efficiency, and simple post-processing [10,11]. Therefore, producing hot dies with complex structures via L-PBF technology is currently an emerging research direction.
Many previous studies have been conducted on H13 steel fabricated via L-PBF. Li et al. [12] obtained H13 samples with a tensile strength of 1997 MPa and an elongation of 2.31% for vertical specimens under an energy input of 167 J/mm3. Lee et al. [13] achieved formed parts with a relative density of 99.8% at a laser power of 90 W and a scanning speed of 200 mm/s, where the vertical samples exhibited a tensile strength of up to 1704 MPa. Liu et al. [14] obtained samples with a relative density of 98.2% at a volumetric energy density of 86.7 J/mm3, and the horizontally built parts achieved the highest tensile strength of 1576 MPa. In these studies, L-PBF-fabricated H13 steel consistently exhibited significant mechanical property anisotropy, but the mechanism underlying this anisotropy has not been thoroughly investigated. Most previous scholars have suggested that the L-PBF process is a rapid non-equilibrium solidification process characterized by a high temperature gradient, leading to the formation of columnar grains parallel to the building direction, thereby inducing anisotropy in microstructure and properties [15,16]. Liu et al. [17] studied the microstructural anisotropy of L-PBF-fabricated 316 L stainless steel, and the results indicate that the interaction between sub-grain structures and deformation twins during plastic deformation of vertical samples results in the formation of small-sized three-dimensional pinning structures, enhancing the strength of parts built in this direction. Qu et al. [18] investigated the effect of forming angle (0° and 90°) on the microstructure of 15-5PH stainless steel; samples formed at 90° experienced more thermal cycles, resulting in an austenite content of up to 16.8% and an elongation of 23.9%. Huang et al. [19] studied the influence of microstructure on the mechanical property anisotropy of an L-PBF-fabricated Invar 36 Fe-Ni alloy, revealing that the intrinsic strength affected by the Taylor factor contributes the most to the Invar 36 alloy. Grain boundary strengthening has the greatest contribution to samples fabricated at 0°, while dislocation strengthening dominates samples fabricated at 45° and 90°. Factors such as the dislocation density, content of low-angle and high-angle grain boundaries, and Taylor factor of L-PBF-fabricated parts in different forming directions also affect the anisotropy [20]. Additionally, the size and morphology of grains in parts built along different directions exert an influence on their mechanical properties. Some scholars have proposed that sub-grain structures can effectively pin dislocations and are important contributors to the strength of formed parts [21]. Differences in sub-grain structures among parts built in different directions also become factors contributing to anisotropy. Therefore, clarifying the mechanism of microstructure and mechanical property anisotropy in L-PBF-fabricated H13 steel is particularly crucial for its development in industrial applications. These contrasting findings highlight the need for a deeper understanding of whether anisotropy arises primarily from the volume fraction of RA, its morphology, or its grain structure. Identifying the root causes of anisotropy is essential for developing strategies to mitigate anisotropy, thereby enhancing mold durability and performance.
Li et al. [22] added B4C nanoparticles, which not only refined the grains but also transformed the epitaxially grown columnar grains in the formed parts into near-equiaxed grains. The same conclusion was reached for L-PBF-fabricated Al-Li alloys: the addition of nano TiC facilitates the columnar-to-equiaxed structure transformation [23]. Additionally, in L-PBF 316 L steel, the added nano TiC particles act as heterogeneous nucleation sites to promote grain refinement, thereby alleviating the tendency of epitaxial grain growth [24]. These methods reduce the content of columnar grains and increase the content of equiaxed grains in the formed parts by increasing the number of heterogeneous nucleation sites and exerting a grain boundary pinning effect. Liu et al. [25] transformed columnar grains into equiaxed grains in PH13-8Mo stainless steel by adding the rare earth element Ce. This is because Ce combines with impurity elements in PH13-8Mo stainless steel, and the formed Ce-containing non-metallic inclusions promote heterogeneous nucleation and pin dislocations.
In summary, this study aims to explore the effects of Ce on the microstructure and mechanical properties of L-PBF H13 steel. The Ce-containing and Ce-free steels were prepared via the L-PBF process. The factors affecting the microstructure and mechanical property anisotropy of L-PBF-fabricated H13 steel are multifaceted, such as the grain size, microstructure, phase content, and so on. This study adopts multiple methods to investigate the influence of the microstructure of the formed parts on the anisotropy of their mechanical properties under the same process parameters and clarifies the causes of microstructural differences. This work lays a foundation and provides theoretical guidance for the regulation of the microstructure and properties of L-PBF-fabricated H13 steel. In sum, this study aims to clarify the formation mechanism of the anisotropic microstructure and mechanical properties of L-PBF-processed H13 steel.

2. Materials and Methods

2.1. Raw Materials and Sample Prepare

Gas-atomized H13 steel powder with a particle size ranging from 15 to 53 μm was used as raw material, which was supplied by Jiangsu Vilory Advanced Materials Technology Co., Ltd (Xuzhou, Chian). The Ce-containing sample was prepared by adding 0.047% Ce based on the composition of H13 steel (named H13-47Ce). The Ce content in this study was determined with references to prior research in casting [26,27,28], where an addition of 0.037% was found to yield favorable properties [28]. To compensate for the loss of active Ce due to its strong affinity with oxygen during melting [29], the addition level was increased to 0.047% to ensure the target composition in the final alloy. The chemical composition of the raw materials with the standard specifications is listed in Table 1. The powder morphology and particle size distribution are presented in Figure 1a. The feedstocks were dried at 80 °C for 4 h to avoid moisture before the L-PBF experiment.
L-PBF experiments were conducted under an argon atmosphere (oxygen content < 50 ppm) using commercial equipment AMC-M150B (Guangzhou Shinengine AM Technology Co., Ltd., Guangzhou, China). The L-PBF device has a maximum laser power of 500 W (IPG YLR-500-WC single-mode continuous fiber laser, wavelength in 1067 nm), a minimum spot size of 100 μm, and a maximum processing area of φ100 mm × 100 mm. The platform’s (304 stainless steel) preheating temperature was set to 80 °C. The L-PBF process parameters were set at a laser power of 270 W, a scanning speed of 900 mm/s, a hatch distance of 80 μm, a layer thickness of 40 μm, and a strip scan strategy with a scanning rotation angle of 90°, as shown in Figure 1c. These parameters were optimized to achieve parts with a relative density of 99.9% [1]. Afterwards, a batch of crack-free and dense (porosity < 0.1%) block specimens in Figure 1b were printed. During the L-PBF process, an alternating scan strategy with a relative hatch angle of 90°, as shown in Figure 1c. The tensile test and geometry of the tensile specimen shown in Figure 1d were designed according to the ISO 6892-1:2019 standard [30].

2.2. Microstructural Characterization

As-built samples were mounted, ground, and polished following standard metallographic procedures. The polished samples were etched with 4 vol% Nital for 10–20 s. The microstructure was observed by scanning electron microscopy (SEM, Gemini 300, Zeiss, Germany). Further microstructural investigations were performed via electron backscattered diffraction (EBSD, Gemini 300, Zeiss, Germany) and transmission electron microscopy (TEM, Talos F200X, USA). The samples for the EBSD investigation analysis were first electrolytically polished at 22 V for 2.5 min to eliminate the surface stress induced by mechanical polishing, followed by ion polishing (Gatan PECS II 685, Pleasanton, CA, USA) at 4 keV with a tilt angle of ±4° for 5 min to obtain a clean and stress-free surface for observation. The step size and scan area of the EBSD samples were 0.2 μm and 40 × 40 μm2, respectively. AztecCrystal 2.1 software was used to analyze the EBSD data. The samples for the TEM investigation were machined into discs. All tensile specimens were machined via electrical discharge machining (EDM) and tested on a Zwick/Roell testing machine (ZwickRoell Testing Technology, Ulm, Germany) at a crosshead speed of 1 mm/min. To elucidate the influence of microstructure on tensile anisotropy, both horizontally and vertically as-built samples were subjected to tensile testing. Given the pronounced brittleness of as-built samples in the horizontal orientation, heat-treated samples were exclusively tested in the horizontal direction. Three replicate tests were conducted for each experimental condition to ensure the reliability of test results. Subsequent to tensile testing, the fractured specimens were collected for optical microscopy (OM) and scanning electron microscopy (SEM) observations to systematically characterize the fracture behavior and fracture morphology.

3. Results

3.1. Phase Analysis

Figure 2 presents the XRD patterns of the BD and SD sections of the L-PBF H13 steel samples. The results indicate that the formed part is primarily composed of martensite (α-Fe) and retained austenite (γ-Fe). Notably, the BD section of the as-built H13 steel sample exhibits a retained austenite (RA) diffraction peak at 43.5°, which is absent in the SD section; in contrast, the SD section displays a more prominent RA peak at 52.8°. There are two main reasons for the higher retained austenite content in the BD section [31]: (1) the BD section has high residual stress, which induces stress-induced martensitic transformation; and (2) the BD section features a relatively high solidification rate, leading the retained austenite to completed solidification before undergoing martensitic transformation. It can be observed that the position of each peak in the SD section shifts leftward by 0.5–0.8° relative to that in the BD section, indicating that the residual stress on the SD section is higher than that in the BD section. Notably, after adding Ce, there was no significant difference in the XRD results between the BD and SD sections of the formed part. The XRD results demonstrate that Ce addition results in essentially identical contents of RA and martensite in the fabricated parts and eliminates microstructural anisotropy among different sections.

3.2. Microstructure Analysis

Figure 3 presents metallographic images of the formed part after etching. As shown in Figure 3a,c, the SD section of the formed part has the atypical “fish-scale” molten pool morphology of L-PBF, with minor porosity defects visible. Dendritic structures penetrating the molten pools are observed in Figure 3a,c, while fine sub-grain structures are present in the overlapping regions of the molten pool. Gas pores are one of the most common defects in laser additive manufacturing and are related to powder characteristics and process instability. In previous studies, L-PBF H13 steel was shown to be a crack-sensitive steel. During the fabrication process, if the magnitude of residual stress exceeds the yield strength of the formed part, crack defects are highly likely to initiate and propagate at grain boundaries [31]. However, no obvious crack defects were observed in our study, indicating that the yield strength of the formed part is insufficient to induce crack nucleation and propagation.
According to the macroscopic metallographic images, no significant changes in the typical L-PBF microstructure are observed with the addition of Ce. This indicates that Ce does not impair the characteristics of grain growth characteristics along the heat flow direction or the effect of the heat source on thermal cycling of the formed regions during the L-PBF process. Therefore, the modifications of the structure and properties of the formed parts due to Ce are reflected mainly in changes in the microstructure, such as its type and size.
Figure 4 presents the SEM micrographs of the BD and SD sections of the formed parts. Obvious characteristic mixed structures of cellular crystals and dendrites are observed in all the images shown in Figure 4a–d. Distinct cellular crystal structures are visible in the high-magnification images in Figure 4b,d, where obvious lath martensite and fine precipitated phases are detected. The cellular crystal size of the formed parts in both directions is less than 2 µm, a unique solidification microstructure induced by the ultra-high cooling rate (106–108 K/s) characteristic of L-PBF technology [1]. However, the lath martensite in the SD section is more prominent in the samples without Ce addition, which is consistent with the XRD results in Figure 2. After Ce addition, there is no significant change in the content of lath martensite in the BD and SD sections of the formed parts under SEM observation. These SEM results further illustrate that the Ce element promotes the transformation of RA to martensite. Therefore, by modifying the solidification kinetics itself, Ce establishes both thermodynamic and kinetic favorable conditions for the formation of a dense, crack-free deposited microstructure.
Additionally, there are significant differences in the lath martensite content between the BD and SD sections of the H13 samples. The SD section exhibits more prominent lath martensite compared to the BD section. In contrast, no significant variation in lath martensite content is detected between the BD and SD sections of the H13-47Ce samples, and the lath martensite in these samples is finer in morphology. The stability of RA is closely dependent on its carbon content. The austenite with lower stability is easily transformed into martensite during the cooling process after the L-PBF process, whereas the austenite with higher stability is retained in the final microstructure.

3.3. EBSD Analysis

Figure 5 presents the EBSD images of the BD and SD sections of the formed parts. The inverse pole figure (IPF) results for different sections of all samples indicate that there are no obvious preferred grain orientations in either direction. For the Ce-free samples, the BD section contains 19.9% RA, while the SD section has only 0.4% RA. This is consistent with the previous XRD and SEM result. However, after Ce addition, the difference in RA content between the BD and SD samples decreases to 0.5%. The BD section maintains an average grain size approximately 10% smaller. Furthermore, the distinct columnar grains observed in the BD section of the H13 samples are transformed into equiaxed grains following Ce addition. In our previous study, the BD section exhibited a higher solidification rate, resulting in finer grains in the formed parts. During the laser powder bed additive process, the continuous thermal input from the laser beam causes the accumulation of heat, and the subsequent thermal-affected zone formed by the laser results in a combined effect similar to heat treatment, causing the formed part to generate RA.
Notably, the surface layers of the L-PBF-fabricated samples do not undergo thermal cycling and therefore typically consist of high-hardness martensite. In contrast, the core regions generally contain RA induced by the inherent in situ heat treatment during L-PBF processing. Additionally, the residual stress in the SD section is greater than that in the BD section.

3.4. TEM Analysis

Figure 6 presents the TEM images of the formed parts. Low-magnification TEM images of both Ce-free and Ce-containing samples reveal prominent dislocation tangles, which are induced by the significant residual stress generated under the ultra-rapid cooling rate of the L-PBF process. Additionally, distinct lath martensitic structures are observed in both samples via high-magnification TEM. Notably, the maximum size of lath martensite in the Ce-free samples is 173.9 nm. This is consistent with the grain refinement effect induced by Ce addition. The BD section exhibits a higher solidification rate than the SD section, making it more conducive to the formation of fine lath martensite during processing. During L-PBF, the alloy undergoes a typical cooling rate of approximately 108 K/s and a temperature gradient of 106–107 K/m [31]. During solidification, the cooling rate within the parent phase exceeds the critical martensite cooling rate, thereby promoting martensite formation. Furthermore, the grain boundaries of the fine parent phase constrain the growth of martensite, resulting in fine martensite laths becoming the dominant microstructural constituent.
Although martensitic structures offer high strength, their intrinsic brittleness compromises the ductility of L-PBF-fabricated H13 steel. Additionally, the as-built samples exhibit an extremely high dislocation density, leading to numerous substructures that are barely discernible in Figure 6b. Given that the martensite lath width is closely correlated with the cooling rate, the formation of layered fine martensite laths is attributed to the complex thermal cycling experienced during L-PBF processing, which proceeds through the sequential stages of melting–solidification–remelting–solidification–quenching–tempering. The prevalence of nano-sized martensite laths indicates that the preheating-induced self-tempering effect during the L-PBF process is considerably weaker than that achieved via conventional high-temperature tempering treatments.
Figure 7 presents the TEM-EDS images of the formed parts. In the Ce-free formed parts, distinct SiO2-based non-metallic inclusions and V-rich carbides epitaxially growing along these SiO2 inclusions are observed. With the addition of Ce, the non-metallic inclusions in the formed parts are transformed into Ce-Si-O composite inclusions, around which the same type of V-rich carbides epitaxially grow. These non-metallic inclusions serve as grain nucleation sites while pinning dislocations and grain boundaries, thereby contributing to grain refinement and strength improvement. The carbides may play two key roles in this work: (i) Forming a shell to retard oxide coarsening during the L-PBF thermal cycle. VC maintains a semi-coherent interface, which provides a relatively lower interfacial energy compared to shell-free oxides. This shell may also hinder oxide growth by suppressing the trans-interface diffusion of oxide-forming elements (e.g., Si, Ce, O). (ii) This shell will increase the oxygen density in the surrounding area to promote the formation of Ce-Si-O and Si inclusions, thereby increasing the amount of silicon available for forming the oxide core, and consequently increasing the quantity and density of the nanoclusters. Furthermore, the formation of the VC shell can also prevent Ce-Si-O and SiO2 inclusions from being reduced by Si or Ce, thereby effectively stabilizing the oxides [32]. These modified inclusions can suppress the epitaxial growth of columnar grains, promote the formation of equiaxed grains, refine the grain structure, and balance the RA content across different sections, ultimately reducing the anisotropy of the formed parts and improving their mechanical properties. The precipitated phases formed after Ce addition serve two key functions in the formed parts [33]: (1) pinning phase boundaries; and (2) facilitating heterogeneous nucleation. The combined effect of these two functions results in the formation of a fine-grained microstructure in the formed parts.

3.5. Mechanical Properties

Figure 8 presents the tensile test results of the formed parts fabricated in different directions. For the Ce-free samples, the tensile strength and elongation of the vertical samples are 1893.9 ± 27 MPa and 7.2 ± 0.2%, respectively, whereas those of the horizontal samples are 1758.1 ± 222 MPa and 6.1 ± 0.3%, respectively. After the addition of Ce, the tensile strength and elongation of the BD formed parts reach 1962.2 ± 32 MPa and 17.3 ± 0.3%, respectively, while those of the SD sample formed parts are 2025.3 ± 29 MPa and 17.9 ± 0.3%, respectively. The Ce-free samples exhibit significant anisotropy in both tensile strength and elongation. In contrast, the anisotropy of the mechanical properties of the formed parts is markedly reduced after Ce addition. Specifically, the differences in tensile strength and elongation between the two directions are 7% and 22% for the Ce-free samples, respectively, whereas those for the Ce-containing samples are only 3.2% and 0.2%, respectively.
Previous studies have indicated that the elongation anisotropy of the formed parts is primarily attributed to columnar grains growing along the BD direction. For the Ce-free samples, the grain morphologies exhibit significant differences the BD and SD sections: The BD section features a higher proportion of columnar grains. Nevertheless, after Ce addition, the columnar grains in the BD direction of the formed parts undergo a distinct transformation to equiaxed grains, which substantially reduce the elongation anisotropy between the BD and SD directions. In addition, the discrepancy in RA content between the BD and SD samples contributes to the mechanical property anisotropy. Austenite possesses an FCC crystal structure with multiple slip systems and low slip resistance, which is conducive to improving the plasticity of the formed parts. After Ce addition, the difference in RA content between the BD and SD sections is minimized, resulting in negligible variation in elongation between the BD and SD samples.
It should be noted that this work constitutes the first step in tailoring the composition of L-PBF-processed H13 steel to mitigate anisotropic properties. While the characterization logically focused on key orientation-sensitive mechanical responses, the full assessment of its performance under diverse service conditions (e.g., impact, fatigue) remains an essential goal for subsequent research.

3.6. Fracture Analysis

Figure 9 presents the fracture morphologies of the formed parts in different directions. For the Ce-free samples, the fracture morphology of the BD sample exhibited fewer dimple structures compared to the SD sample. In contrast, with the addition of Ce, distinct dimple structures are observed in both the BD and SD samples, indicating that the plasticity of the formed parts is significantly enhanced after Ce treatment. The BD and SD samples display typical cup–cone fracture morphologies. Magnified observations of the fibrous regions exhibit a quasi-cleavage fracture mode, which is characterized by prominent features including cleavage facets, dimples, tearing ridges, and microcracks. Notably, brittle cleavage regions are interspersed alternately with ductile dimples across the fracture surface. Of particular relevance, the dimensions of these alternating cleavage planes are comparable to those of martensitic laths, thereby supporting the inference that the cleavage plane represents an intrinsic hallmark fracture feature of martensite. Furthermore, the H13-47Ce samples exhibit more well-developed and uniformly distributed dimples in comparison with their Ce-free counterparts, a morphological trait that correlates well with the marked enhancement in elongation observed for the Ce-doped samples. Additionally, the addition of Ce promotes the formation of fine precipitates, which likely contributes to the observed dimple morphologies and improved mechanical properties.
Hence, the key mechanism underlying the attenuated transformation-induced plasticity (TRIP) effect is that RA with a size less than 0.2 μm constitutes a large proportion of the Ce-containing steel. Additionally, Ce addition elevates the carbon content within the RA phase of BD-oriented specimens. The higher carbon content in the RA raises the chemical driving force required for martensitic transformation, thereby delaying the TRIP effect. Nevertheless, RA with high stability ensures the continuous and stable occurrence of martensitic transformation, which delays local stress concentration and fracture, ultimately improving the ductility of Ce-containing steel up to 17.3%.
The high strength of the vertical samples is attributed to the combined effects of fine lath martensite, refined grains, and a high RA content. This hierarchical fine microstructure results from rapid melting and solidification, as well as multiple quenching and tempering cycles induced by the complex thermal cycles of L-PBF. Owing to the inherent brittleness of the fine martensite laths formed by L-PBF, the elongation of the pristine samples is relatively low. However, during tensile testing of the vertical component, the dendritic structure prone to brittle fracture is avoided, resulting in an improved elongation of the formed part. However, Ce addition can simultaneously optimize the strength and ductility of the H13 steel, which provides a foundation for improving the mechanical properties of H13 steels and even other metallic materials. In this study, we demonstrate that Ce addition can influence the coherent interface of Ce2O3 by altering the interface stress concentration. In particular, Ce adsorbs impurity elements such as O to form Ce-containing inclusions, which segregate at grain boundaries (GBs) and hence retard boundary migration. In addition, Ce inclusions, which have high melting points, have lower wettability with mold steel, promoting the transformation of the inclusions into nearly spherical shapes. While generally beneficial, the rare earth element Ce can promote the aggregation of inclusions, forming detrimental Ce-Si-O composite inclusions that may negatively impact fatigue performance. In future research, we will devote ourselves to investigating the influence of non-metallic inclusions on mechanical properties. Overall, the enhancement in tensile performance of the Ce-modified samples originates from the combined effects of (1) fine grain strengthening via grain refinement; (2) second-phase strengthening from finely dispersed Ce2O3 particles; and (3) a decrease in the interface stress due to a reduced lattice misfit between Ce2O3 and the Fe matrix, the primary contribution.

4. Conclusions

In summary, this work presents the potential of using the rare earth element Ce to mitigate the anisotropy of the microstructure and mechanical in L-PBF mold steels. The microstructural evolution of mold steel with Ce during the L-PBF process is characterized and discussed. The main conclusions are as follows:
  • The RA content varies in different directions of the L-PBF formed parts: it is approximately 19.9% in the BD section and 0.4% in the SD section, which is one of the main reasons for the anisotropy of the formed parts. After the addition of Ce, the RA content is 6.3% in the BD sample and 5.7% in the SD sample.
  • The non-metallic Ce-Si-O composite inclusions formed by Ce provide heterogeneous nucleation sites and pin grain boundaries during the L-PBF process. This refines the grains and promotes the transformation of the grains from columnar to equiaxed. Ultimately, the grain size of the formed parts is reduced by approximately 23%, and the lath martensite size is reduced by approximately 13.1%.
  • After the addition of Ce in the L-PBF process, the anisotropy of the mechanical properties of the formed parts is reduced. The tensile strength and elongation of the formed part in the BD samples are 2025.3 MPa and 17.9%, respectively, whereas those in the SD samples are 1962.2 MPa and 17.3%, with a difference in elongation of only 0.2%.

Author Contributions

Methodology, X.F., Y.D., Y.R., Y.L., J.Z., and S.L.; formal analysis, Y.W.; investigation, X.F., Y.W., Y.R., S.C., and Y.L.; resources, Y.D.; writing—original draft, X.F.; writing—review and editing, Y.D., Y.W., and Y.R.; funding acquisition, S.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (52434009 and 52304357), Shaanxi Outstanding Youth Science Foundation (2024JC-JCQN-52), Young Elite Scientist Sponsorship Program by CAST (YESS20240807), Shaanxi Provincial Science and Technology Plan Project (2024QCY-KXJ-109), Xi’an Science and Technology Bureau project (2022JH-GXQY-0010), Key Research and Development Project of Shaanxi Province (Grant No. 2024GX-YBXM-211), and Xi’an Science and Technology Program Project (Grant No. 24GXFW0040).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

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Materials 19 00755 g001
Figure 1. Schematic of L-PBF-fabricated H13/H13-47Ce tool steel samples and tensile specimens: (a) powder morphology; (b) macroscopic morphology of sample; (c) forming strategy; (d) dimensions of formed part.
Figure 1. Schematic of L-PBF-fabricated H13/H13-47Ce tool steel samples and tensile specimens: (a) powder morphology; (b) macroscopic morphology of sample; (c) forming strategy; (d) dimensions of formed part.
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Materials 19 00755 g002
Figure 2. X-ray diffraction patterns of H13 and H13-47Ce samples with different building direction.
Figure 2. X-ray diffraction patterns of H13 and H13-47Ce samples with different building direction.
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Materials 19 00755 g003
Figure 3. OM images: (a) H13 section micrograph; (b) H13 SD section micrograph; (c) H13-47Ce BD section micrograph; (d) H13-47Ce SD section micrograph.
Figure 3. OM images: (a) H13 section micrograph; (b) H13 SD section micrograph; (c) H13-47Ce BD section micrograph; (d) H13-47Ce SD section micrograph.
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Figure 4. SEM images: (a) SD section low-magnification image; (b) SD section low-magnification image; (c) BD section high-magnification image; (d) BD section high-magnification image.
Figure 4. SEM images: (a) SD section low-magnification image; (b) SD section low-magnification image; (c) BD section high-magnification image; (d) BD section high-magnification image.
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Materials 19 00755 g005
Figure 5. EBSD results of the BD section and SD section of the formed parts: (a) an inverse IPF map of the BD section of the H1 formed part; (b) a phase fraction map of the BD section of the H13 formed part; (c) an IPF map of the SD section of the H13 formed part; (d) a phase fraction map of the SD section of the H13 formed part; (e) an IPF map of the BD section of the H13-47Ce formed part; (f) a phase fraction map of the BD section of the H13-47Ce formed part; (g) an IPF map of the SD section of the H13-47Ce formed part; (h) a phase fraction map of the SD section of the H13-47Ce formed part.
Figure 5. EBSD results of the BD section and SD section of the formed parts: (a) an inverse IPF map of the BD section of the H1 formed part; (b) a phase fraction map of the BD section of the H13 formed part; (c) an IPF map of the SD section of the H13 formed part; (d) a phase fraction map of the SD section of the H13 formed part; (e) an IPF map of the BD section of the H13-47Ce formed part; (f) a phase fraction map of the BD section of the H13-47Ce formed part; (g) an IPF map of the SD section of the H13-47Ce formed part; (h) a phase fraction map of the SD section of the H13-47Ce formed part.
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Figure 6. TEM images: (a) H13 sample; (b) H13-47Ce sample.
Figure 6. TEM images: (a) H13 sample; (b) H13-47Ce sample.
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Figure 7. TEM-EDS images of the formed parts: (a) without Ce addition; (b) with Ce addition.
Figure 7. TEM-EDS images of the formed parts: (a) without Ce addition; (b) with Ce addition.
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Figure 8. Stress–strain curve of H13 and H13-47Ce samples with different building direction.
Figure 8. Stress–strain curve of H13 and H13-47Ce samples with different building direction.
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Figure 9. TEM-EDS images of formed parts: (a) fracture morphology of H13 BD sample; (b) fracture morphology of H13 BD sample; (c) fracture morphology of H13-47Ce BD sample; (d) fracture morphology of H13-47Ce SD sample.
Figure 9. TEM-EDS images of formed parts: (a) fracture morphology of H13 BD sample; (b) fracture morphology of H13 BD sample; (c) fracture morphology of H13-47Ce BD sample; (d) fracture morphology of H13-47Ce SD sample.
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Table 1. Chemical composition of H13 steel powder (wt.%).
Table 1. Chemical composition of H13 steel powder (wt.%).
FeCrMoMnVSiCO
H13 steel powderBal.5.111.420.490.980.860.390.0302
ASTMBal.4.75–5.501.10–1.750.2–0.50.8–1.20.8–1.10.32–0.450.0332
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MDPI and ACS Style

Fan, X.; Deng, Y.; Wei, Y.; Ren, Y.; Chen, S.; Lv, Y.; Zhu, J.; Liu, S. Mitigating the Anisotropy of the Microstructure and Mechanical Properties of L-PBF-Fabricated H13 Steel via Rare Earth Ce Addition. Materials 2026, 19, 755. https://doi.org/10.3390/ma19040755

AMA Style

Fan X, Deng Y, Wei Y, Ren Y, Chen S, Lv Y, Zhu J, Liu S. Mitigating the Anisotropy of the Microstructure and Mechanical Properties of L-PBF-Fabricated H13 Steel via Rare Earth Ce Addition. Materials. 2026; 19(4):755. https://doi.org/10.3390/ma19040755

Chicago/Turabian Style

Fan, Xiaodan, Yuhua Deng, Yingkang Wei, Yaojia Ren, Sitong Chen, Yongwei Lv, Jilei Zhu, and Shifeng Liu. 2026. "Mitigating the Anisotropy of the Microstructure and Mechanical Properties of L-PBF-Fabricated H13 Steel via Rare Earth Ce Addition" Materials 19, no. 4: 755. https://doi.org/10.3390/ma19040755

APA Style

Fan, X., Deng, Y., Wei, Y., Ren, Y., Chen, S., Lv, Y., Zhu, J., & Liu, S. (2026). Mitigating the Anisotropy of the Microstructure and Mechanical Properties of L-PBF-Fabricated H13 Steel via Rare Earth Ce Addition. Materials, 19(4), 755. https://doi.org/10.3390/ma19040755

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