“…These results quantitatively underpin that the alloying elements are unevenly distributed within the microstructure after intercritical annealing. It is noteworthy that clusters of Ni and Al ions, which represent intermetallic β ‐NiAl particles in APT 3D reconstructions of PH 13‐8 Mo maraging steels, [ 35 ] were not found in the investigated tip.…”
The standard heat treatment of PH 13‐8 Mo maraging steels consists of solution annealing and subsequent aging. Herein, it is investigated how an additional intercritical annealing step prior to aging affects the microstructure, and, consequently, the mechanical properties of a PH 13‐8 Mo maraging steel. In situ techniques by means of high‐temperature electron backscatter diffraction and high‐temperature X‐ray diffraction are applied to study the microstructural changes during intercritical annealing and subsequent aging. In addition, high‐resolution investigation methods, such as transmission electron microscopy and atom probe tomography supplemented by transmission Kikuchi diffraction, are used for an in‐depth characterization of the microstructure. The results reveal that a diffusion‐controlled martensite to austenite transformation accompanied by partitioning of the substitutional atoms Cr, Ni, and Mo takes place during intercritical annealing. As a result of partitioning during intercritical annealing, an inhomogeneous distribution of Ni remains in the microstructure after the martensitic transformation. Consequently, the formation of reverted austenite is facilitated during subsequent aging due to existing Ni‐enriched zones in martensite. Since the fracture toughness is significantly enhanced compared to the standard heat treatment, it is suggested that this improvement is related to the increased phase fraction of reverted austenite.
“…These results quantitatively underpin that the alloying elements are unevenly distributed within the microstructure after intercritical annealing. It is noteworthy that clusters of Ni and Al ions, which represent intermetallic β ‐NiAl particles in APT 3D reconstructions of PH 13‐8 Mo maraging steels, [ 35 ] were not found in the investigated tip.…”
The standard heat treatment of PH 13‐8 Mo maraging steels consists of solution annealing and subsequent aging. Herein, it is investigated how an additional intercritical annealing step prior to aging affects the microstructure, and, consequently, the mechanical properties of a PH 13‐8 Mo maraging steel. In situ techniques by means of high‐temperature electron backscatter diffraction and high‐temperature X‐ray diffraction are applied to study the microstructural changes during intercritical annealing and subsequent aging. In addition, high‐resolution investigation methods, such as transmission electron microscopy and atom probe tomography supplemented by transmission Kikuchi diffraction, are used for an in‐depth characterization of the microstructure. The results reveal that a diffusion‐controlled martensite to austenite transformation accompanied by partitioning of the substitutional atoms Cr, Ni, and Mo takes place during intercritical annealing. As a result of partitioning during intercritical annealing, an inhomogeneous distribution of Ni remains in the microstructure after the martensitic transformation. Consequently, the formation of reverted austenite is facilitated during subsequent aging due to existing Ni‐enriched zones in martensite. Since the fracture toughness is significantly enhanced compared to the standard heat treatment, it is suggested that this improvement is related to the increased phase fraction of reverted austenite.
“…Fracture mechanics test is an important way of stress corrosion testing [12]. The fracture test is different from the stress corrosion cracking test, which requires the use of specimens with prefabricated cracks.…”
Cast steel parts can realize rapid prototyping effectively, which is suitable for complex structural design. However, due to the large residual stress, the problem of mechanical property degradation is more obvious. In order to solve this problem, a high temperature excitation vibration treatment scheme is proposed in this paper. By applying different excitation frequencies and impact forces, the effects of mechanical properties and stress corrosion properties are studied and verified. Based on the finite element software ANSYS, the modal shape and resonant frequency of the cast steel parts are obtained, and verified by the sweep frequency module in the excitation vibration system. According to the characteristics of modal shape, five typical detection paths are set, and stress sensors are arranged every 200 mm. In order to obtain the specific effects of excitation frequency and impact force amplitude on mechanical properties, nine parts samples were prepared on the same production line according to the matching requirements of test parameters. In addition, the main external parameters that remain unchanged during vibration excitation are set as initial 750 ℃ and vibration excitation time of 60 s, which can fully affect the effect of austenite transformation. Keeping the synchronization of test parameters in different samples, the distribution rules of residual stress under different excitation frequencies and forces are obtained and analyzed. In the aspect of mechanical properties, the microstructure, hardness, yield strength and tensile strength of the specimens subjected to vibration were compared and analyzed. In the aspect of stress corrosion performance research, stress corrosion cracking test was carried out in weak acid environment to obtain the tensile stress curve and fracture morphology of the specimen. The results show that the excitation vibration at high temperature can effectively eliminate the residual stress of cast steel parts, but the increase of excitation frequency does not correspond to the effect of residual stress elimination. When the exciting force exceeds a certain value, the stress relief effect cannot be further improved. Excitation vibration can reduce the internal hardness of cast steel parts to a certain extent, and improve the yield strength and tensile strength. At the same time, it has a positive role in promoting the improvement of stress corrosion resistance.
“…The amount of energy that metals and alloys can absorb depends on several factors such as composition, microstructure and temperature ( Fig. 1 b) [ [47] , [48] , [49] ]. Corrosion is a much less explored factor.…”
Section: Introductionmentioning
confidence: 99%
“… Fig. 1 (a) Charpy (Simple-Beam) impact test specimen, Type A [ 46 ], (b) Results from Charpy impact testing of different maraging steels, tested at 80 °C and – 30 °C [ 48 ]. …”
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