# Functionally Graded AISI 316L and AISI H13 Manufactured by L-DED for Die and Mould Applications
## 3 Results  
In this section, the results obtained in the experimental testing are presented and discussed. When analysing the central cross-section of the sample from a macroscopic perspective, severe cracking, mostly on the right side of the section, was observed (Figure 5). In addition, several lack-of-fusion defects were also identified. Apparently, this cracking phenomenon was not related to the formation of carbides, as the hardness was not found to be particularly high in the cracked areas. On the contrary, it was attributed to the formation of the brittle sigma phase, which is common in stainless steels. According to [PERSON] et al., subsequent heating and cooling cycles in L-DED may promote the growth of the sigma phase, leading to cracking of the component [32]. In addition, it has been reported in the literature that FGMs which grade from metals or alloys with different crystal structures (as it is in this case) present a higher tendency for the generation of macrocracks [3]. Additionally, graded corrosion resistance was not observed when etching the sample, in contrast with previous works when functionally graded Stellite-6 and tungsten carbide metal matrix composite samples were manufactured, and some sort of linear corrosion  
Figure 4: Dimensions of the manufactured samples: (**a**) functionally graded material (FGM) sample during the L-DED process, (**b**) schematic illustration of the fabricated FGM sample with dimensions, and (**c**) fabricated FGM sample with dimensions. Figure 5: Macro metallographic inspection of the deposited FGM sample. resistance was obtained. Lower layers were just slightly etched, whereas the intermediate layers were further etched and the upper layers were more prominently etched [33]. In the present case, the lower and intermediate layer were just slightly etched while the upper three layers, which correspond to 100% unmixed AISI H13, showed a strong reaction to the etching procedure. This is due to the fact that corrosion resistance was not linear for the chromium content range present in the sample, e.g., from 5.12% in the AISI H13 to 18.50% in the AISI 316L, as depicted in Figure 6 (note the logarithmic scale). On the other hand, the microstructure of the sample also evolved along the FGM. Initially, three layers of AISI 316L were deposited, which are constituted by 90% austenite and 10% ferrite. Then, the ferrite content decreased gradually until the sixth layer, which should be constituted by austenite. Finally, the last three layers were composed of AISI H13, which corresponded to martensite and austenite. These theoretical microstructural constituents were estimated based on the Schaeffler diagram, shown in Figure 7 [34], and validated with the microscope images shown in Figure 8. For that purpose, nickel and chromium equivalents were calculated, according to the following formulae [35]:  
\[C_{eq}=Cr+2\cdot Si+1.5\cdot Mo+5\cdot V, \tag{1}\]  
\[Ni_{ea}=Ni+0.5\cdot Mn+30\cdot C. \tag{2}\]  
Figure 6: Corrosion resistance of each layer as a function of chromium content of the alloy. Figure 7: Schaeffler diagram for microstructural constituent estimation [36]. Finally, as far as the hardness of the sample is concerned, a nonlinear hardness increase has been observed from the first layers and up to the last three layers, showing typical cladded AISI H13 hardness values. In Figure 9, the hardness values measured along the building direction of the FGM are shown, and at the same time compared with the maximum attainable hardness of the steels calculated from the carbon content according to [37; 38]. It can be observed that the upper layers, corresponding to the unmixed tool steel, reached the maximum attainable hardness values owing to the formation of martensite and the characteristic precipitation of the carbides that constitute AISI H13. However, in the graded intermediate layers, the hardness decreased abruptly rather than in a gradual manner, as could be expected based on carbon content of the added material.