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Prior austenite grain size as a function of temperature of solution annealing: 820 0 C (a); 860 0 C (b); 1000 0 C (c); 1050 0 C (d); 1100 0 C (e). The graph (f) correlates the grain size and the temperature of the solution annealing.
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Maraging steels are a class of ultra high strength steels of special importance due to their extremely high mechanical strength and good toughness. In this work, the effects of the solution annealing temperature on the mechanical properties of the maraging 300 steels were evaluated, in order to maximize the toughness without considerable detriment...
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... volumetric fraction predicted for austenite was 0.999. The austenite grain grows sharply from 1000°C ( Figure 3). The austenite grain size ranges from 6.4 to 46.0 μm between the temperatures of 820 and 1050°C, but it jumps to 111.8 μm at 1100°C, in agreement with the historical studies of Rack 22 and Maxwell et al. 26 . ...
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Citations
... Correlation between fracture toughness and yield stress for Fe-based alloys that were fabricated using AM or conventional process techniques [8,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]; the conventionally processed materials include various steel grades such as stainless steel, maraging steels, or low alloy steels, and the results from the current study are shown as stars. (The limited number of data points below 1 GPa strength is due to a lack of size-independent fracture toughness data available in the literature. ...
The fracture behavior of a duplex stainless steel processed by laser powder bed fusion (LPBF) from mixed 25Cr + 5 wt.% Ni powders (i.e., 25Cr-5Ni) was compared to 25Cr that was processed without Ni but additionally heat-treated (i.e., 25Cr-HT) to give similar phase fractions of austenite and ferrite but with different micro and mesostructures. The 25Cr-5Ni alloy exhibited high yield strength (828–958 MPa) and good fracture toughness (122–167 MPa√m) while requiring no post heat-treatment after LPBF fabrication. In contrast, the 25Cr-HT alloy gave somewhat lower strength and higher fracture toughness in a classic strength-toughness trade-off due to the elimination of the high dislocation density from the LPBF process. While powder mixing induces somewhat more anisotropic properties due to a coarser mesostructure phase distribution, the results demonstrate an approach to develop LPBF processed duplex stainless steels that don't require costly post heat treatments.
... For simplicity, K JIc values will hereafter be denoted as K Ic . Fig. 1a shows fracture toughness versus yield strength plots for Al- [16,17,[21][22][23][24][25], Fe- [15,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42], and Ti-based alloys [14,[43][44][45][46][47][48][49] that were processed either conventionally (open symbols) or via an AM technique (closed symbols). While there is some correlation between the two properties for all three groups of materials, they spread more widely for the AM alloys than for those conventionally processed. ...
... Correlation between (a) fracture toughness and yield strength, as well as (b) fracture toughness and elongation to failure for Al-, Fe-, and Ti-alloys that were either AM-processed (solid symbols) or conventionally fabricated (open symbols). Data for Al-alloys was taken from [16,17,[21][22][23][24][25], for Fe-based materials from [15,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42], and for Ti-alloys from [14,[43][44][45][46][47][48][49]; only literature satisfying the data curation process was used to plot the graphs. morphology of the melt pool boundaries. ...
... In (c), separate fits and coefficients of determination, R 2 , are shown for the different AM processes (PBF-LB and wire-arc DED) using both ε f (open symbols) and ε pl u (closed symbols); inset in (c) shows the difference in ε f and ε pl u for PBF-LB processed maraging steels that have undergone different heat treatments: solutionized + aged (STA), directly aged (DA), or thermal cycling (TCA). Data was taken from[15,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]. ...
Yield strength and fracture toughness are key properties of structural materials used by designers for engineering applications, whereas secondary properties like ductility are not generally used in quantitative design calculations. However, since ductility is usually measured along with strength in the same tensile test, it is often used as an indication of the fracture toughness even though these properties are usually not directly proportional. As a result, many researchers initially, and only, screen new materials and processing routes for good combinations of strength and ductility rather than evaluating fracture toughness independently. This can result in poorly informed decisions being made early in the development stages for structural applications where materials with combinations of high strength and good fracture toughness are required. In this article, we evaluate the correlation between fracture toughness and ductility of Al-, Fe-, and Ti-based alloys that were processed using conventional methods as well as by additive manufacturing (AM) routes. We highlight that the correlation between fracture toughness and ductility is very weak, which in the case of AM materials is attributed to their often-metastable microstructures, their layer-by layer mesostructures, and their anisotropic failure characteristics that lead to pronounced variability in the fracture toughness data for materials with similar ductility. Our findings suggest that an independent assessment of fracture toughness alongside the tensile properties (strength and ductility) is required to correctly optimize the AM processing of structural materials and provide engineers with the properties required for the design of parts and components for structural and safety-critical applications.
... These results regarding grain size are consistent with findings reported by other researchers [66,67]. Lima et al. [68] observed that the growth rate of prior austenite grain size is relatively slow between 1133 and 1273 K and increases significantly above 1423 K, with grain size values ranging from approximately 8 µm at 1133 K to 164 µm for the 300-grade maraging steel solution-annealed at 1423 K. Additionally, Lima et al. noted that martensitic plates are more equiaxed up to 1133 K and transform into martensitic blocks at a solution annealing temperature of 1237 K, characterized either by the same orientation or blocks separated by high-angle boundaries [69]. The Vickers hardness values for the samples STed at 1123 and 1373 K are identical in this study, both measuring 561 HV. Figure 6 shows a schematic of the in situ observation equipment, including a digital microscope (VHX-2000, Keyence Corp.). ...
... These results regarding grain size are consistent with findings reported by other researchers [66,67]. Lima et al. [68] observed that the growth rate of prior austenite grain size is relatively slow between 1133 and 1273 K and increases significantly above 1423 K, with grain size values ranging from approximately 8 µm at 1133 K to 164 µm for the 300-grade maraging steel solution-annealed at 1423 K. Additionally, Lima et al. noted that martensitic plates are more equiaxed up to 1133 K and transform into martensitic blocks at a solution annealing temperature of 1237 K, characterized either by the same orientation or blocks separated by high-angle boundaries [69]. The Vickers hardness values for the samples STed at 1123 and 1373 K are identical in this study, both measuring 561 HV. Figure 7 presents the micrographs of the lath martensite in each sample, etched with 5% nital. ...
... These results regarding grain size are consistent with findings reported by other researchers [66,67]. Lima et al. [68] observed that the growth rate of prior austenite grain size is relatively slow between 1133 and 1273 K and increases significantly above 1423 K, with grain size values ranging from approximately 8 µm at 1133 K to 164 µm for the 300-grade maraging steel solution-annealed at 1423 K. Additionally, Lima et al. noted that martensitic plates are more equiaxed up to 1133 K and transform into martensitic blocks at a solution annealing temperature of 1237 K, characterized either by the same orientation or blocks separated by high-angle boundaries [69]. The Vickers hardness values for the samples STed at 1123 and 1373 K are identical in this study, both measuring 561 HV. ...
In welded maraging steels, mechanical properties, particularly ductility and toughness, are often compromised in the heat-affected zone (HAZ). This study focuses on 300-grade maraging steel bars, solution annealed at 1123 K for 1.5 h (5.4 ks) and welded using gas tungsten arc welding, followed by a post-weld heat treatment at 753 K for 13.33 h (48 ks). In situ observations during three-point bending tests on HAZ samples featuring coarsened prior austenite grain sizes were conducted to examine damage behavior and the crack path near the crack tip. The main crack initiated at the peak applied load during the bending test and, upon further loading, exhibited significant deflection and extension accompanied by numerous microcracks and localized crack branching. Distinctive damage features, such as transgranular cracking across block regions, intense intergranular cracking along packet boundaries with a pronounced shear component, and crowding of microcracks ahead of the crack tip, were observed in the HAZ sample during the in situ test. The interaction between the main crack tip and microcracks and its influence on the local crack propagation driving force was discussed using fracture mechanics. Experimental results, including tensile fracture surface observations and in situ images, along with analysis of the stress anti-shielding effect by microcracks, suggest that the HAZ sample exhibits embrittlement fracture behavior with lower ductility and toughness compared to the base metal sample.
... The Bimetal specimen shows a fracture toughness of 71 ± 2 MPa m 1/2 at a similar surface hardness level of MAR-60HRC (Fig. 8a). It can be clearly observed that the K app values are systematically higher than the K IC for the wrought samples, which can be attributed both to the microstructure of AM samples as well as the effect of the blunt notch on the stress field at notch tip for the Fig. 8 Apparent fracture toughness values for the samples versus surface hardness (blue points), as well as K IC for wrought 18Ni300 [59,60] and 13Ni400 [19,48] (gray points), and b Kapp versus hardness under the notch for L-DED specimens samples in the current study. The higher toughness of bimetal compared with MAR-60HRC can be attributed to the influence of concentration and hardness gradient near the interface. ...
Maraging steels are a class of low-carbon ultra-high-strength martensitic steels. Due to their excellent weldability, these steels have been widely applied for laser-based additive manufacturing (AM). MAR-60HRC is a newly developed maraging grade for AM with a nominal chemical composition of 13.0Ni-15.0Co-10.0Mo-0.2Ti, Fe bal. (wt%), capable of achieving hardness levels of ~ 740 HV. Alternatively, 18Ni300 is a commercialized maraging steel with an excellent combination of strength and toughness at the peak aged hardness (i.e., ~ 590 HV). This work aims to investigate the properties and microstructure of MAR-60HRC fabricated by Laser Directed Energy Deposition (L-DED). Further, the manufacturability of bimetallic parts comprising a tough 18Ni300 core and a hard MAR-60HRC on the surface was evaluated. After proper aging, the multi-layered material showed a surface hardness of ~ 720 HV1 and apparent fracture toughness of 71 MPa m 1/2 , higher than that of MAR-60HRC (i.e., 60 MPa m 1/2 ), and lower than 18Ni300 (i.e., 90 MPa m 1/2 ). The excellent combination of surface hardness and fracture toughness was discussed, considering the crack arrest at the interface and the flawless interface between the two steels.
Graphical Abstract
... Special heat treatment adjustments are sometimes applied to improve the mechanical properties of maraging steels, especially to address the strength-toughness trade-off. For example, the research of Xavier et al., on the solution annealing effect explored the best annealing temperature to increase the fracture toughness with the lowest tensile strength loss [68]. In the study, 18Ni (300) bars were made by vacuum induction melting/vacuum arc refining, hot forged, and solution annealed at 860 • C. ...
... Since strength-toughness is a trade-off, there are some methods that could improve the fracture toughness by losing strength to a certain degree. For example, Xavier et al. [68] combined 1000 • C solution annealing with 480 • C aging increases the fracture toughness with a slight drop in the strength in 18Ni (300) (No. 4 in Table 8). If a properly adjusted chemical composition could be combined with the right optimized heat treatments, Fe-Ni-Co maraging steels are among the best candidates. ...
Using two fencing swords manufactured in Europe and China, we investigated the typical materials used for fencing blades and compared the experimental results with the nominal compositions of a variety of steels. We found that spring steels and maraging steels were the primary metals used in fencing blades. The review then provides an overview of the chemical compositions, heat treatment processes, microstructures and associated mechanical properties of these materials. By combining the requirements for the safety of athletes, mechanical behaviors of different steels, and production costs for industry, we introduced possible directions for the heat treatments and processing methods that have the potential to enhance performance and overcome the limitations of previous materials. In addition, an ultra-strong steel, Fe-9.95Mn-0.44C-1.87Al-0.67V which could be a promising new candidate in this area, was recommended. Finally, we suggested that successful cooperation between manufacturers and researchers is necessary to reach the various requirements of fencing blades to meet the growing popularity of fencing in China.
High-pressure-torsion (HPT) processing introduces a large density of dislocations that form sub-grain boundaries within the refined nano-scale structure, leading to changes in precipitate morphology compared to hot-rolled maraging steels. The impact of such nanostructuring on the deformation and fracture micro-mechanisms is being reported for the first time usingin situcharacterization techniques along with transmission electron microscopy and atom probe tomography analysis, in this study. Digital image correlation has been used to quantify the full field strain maps in regions of severe strain localization as well as to determine the fracture toughness through critical crack tip opening displacements. It is seen that the phenomenon of planar slip leads to strain softening under uniaxial deformation and to crack branching under a triaxial stress state in hot rolled maraging steels. On the other hand, nano-structuring after HPT processing creates a large number of high angle grain boundaries as dislocation barriers, leading to strain hardening under uniaxial tension and nearly straight crack path with catastrophic fracture under triaxial stress state. Upon overaging, the hot-rolled sample shows signature of transformation induced plasticity under uniaxial tension, which is absent in the HPT processed overaged samples, owing to the finer reverted austenite grains containing higher Ni concentration in the latter. In the overaged fracture test samples of both the hot-rolled and HPT conditions, crack tips show a signature of strain induced transformation of the reverted austenite to martensite, due to the accompanying severe strain gradients. This leads to a higher fracture toughness even while achieving high strengths in the overaged conditions of the nanocrystalline HPT overaged samples. The results presented here will aid in design of suitable heat treatment or microstructure engineering of interface dominated nano-scale maraging steels with improved damage tolerance.
