Search Results (27)

A novel stainless steel with high Mn and Mo content (much higher than traditional stainless steel), designated CH241SS, was developed as a potential replacement for Cr-Mo-V alloy steel in the cold forging applications of precision industry. Through carbon reduction in an environmentally friendly manner and a two-stage heat treatment process, the hardness of as-cast CH241 was tailored from HRC 37 to HRC 29, thereby meeting the industrial specifications of cold-forged steel (≤HRC 30). X-ray diffraction analysis of the as-cast microstructure revealed the presence of a small amount of ferrite, martensite, austenite, and alloy carbides. After heat treatment, CH241 exhibited a dual-phase microstructure consisting of ferrite and martensite with dispersed Cr(Ni-Mo) alloy carbides. The CH241 alloy demonstrated excellent high-temperature stability. No noticeable softening occurred after 72 h for the second-stage heat treatment. Based on the mechanical and room-temperature tensile fatigue properties of CH241-F (forging material) and CH241-ST (soft-tough heat treatment), it was demonstrated that the CH241 stainless steel was superior to the traditional stainless steel 4xx in terms of strength and fatigue life. Therefore, CH241 stainless steel can be introduced into cold forging and can be used in precision fatigue application. The relevant data include composition design and heat treatment properties. This study is an important milestone in assisting the upgrading of the vehicle and aerospace industries. Full article

Low-alloy CrNiMo cast steels are often used in the caterpillar boards of excavators in mining engineering machinery due to their good mechanical properties and low cost. Three CrNiMo cast steels with different carbon contents (0.20%, 0.29%, and 0.35% by weight) were developed in this work. The mechanical properties of ingots of these cast steels can be optimized by heat-treated quenching and tempering (QT) and surface induction hardening (QTIH). The wear behavior of QT and QTIH specimens was evaluated under dynamic load and ring block conditions. The results show that the QT specimens exhibit a good mechanical performance and wear resistance. Compared to the QT specimens, the wear resistance can be further improved by QTIH treatment. The wear weight loss of QTIH specimens decreased by 42.7% and 73.2% under dynamic load and ring block wear tests, respectively. Additionally, the strength increased while plasticity and toughness decreased with increasing carbon content. Notably, when the carbon content is 0.29%, the CrNiMo cast steel exhibits an excellent combination of strength, ductility, and wear resistance. Full article

The article addresses stress formation in the structural 3D-printed elements of a high-pressure die casting die mould used for production of aluminum castings. The 3D-printed elements with conformal cooling are manufactured of 18Ni300 powder. Initial numerical calculations were performed on a test die mould made of standard steel X40CrMoV5 to determine temperature distribution and stress state, providing a baseline for comparing 3D-printed 18Ni300 parts. A database for 18Ni300 material was developed, including optimal heat treatment parameters: aged at 560 °C for 8 h. The resulting tensile strength of approximately ~1600 MPa, yield strength 1550 MPa, and elongation 6–7%, with properties temperature-dependent from 20 °C to 600 °C. Results show that conformal cooling increases stress gradients, highlighting the demands on fatigue strength at elevated temperatures. The study revealed that the heat treatment significantly influences the final properties, with tensile strengths of 1400–2000 MPa and elongation from 1 to 8%. While the heat treatment has a greater impact on the mechanical properties than the printing parameters, optimizing the printing settings remains crucial for ensuring density and quality in the die moulds under cyclic loads. Full article

ZG25MnCrNiMo steel samples were prepared by squeeze casting under pressure ranging from 0 to 150 MPa. The effects of pressure on the microstructure, low-temperature toughness, hardness, and impact wear performance of the prepared steels were experimentally investigated. The experimental results indicated that the samples fabricated under pressure exhibited finer grains and a significant ferrite content compared to those produced without pressure. Furthermore, the secondary dendrite arm spacing of the sample produced at 150 MPa decreased by 45.3%, and the ferrite content increased by 39.1% in comparison to the unpressurized sample. The low-temperature impact toughness of the steel at −40 °C initially increased and then decreased as the pressure varied from 0 MPa to 150 MPa. And the toughness achieved an optimal value at a pressure of 30 MPa, which was 65.4% greater than that of gravity casting (0 MPa), while the hardness decreased by only 6.17%. With a further increase in pressure, the impact work decreased linearly while the hardness increased slightly. Impact fracture analysis revealed that the fracture of the steel produced without pressure exhibited a quasi-cleavage morphology. The samples prepared by squeeze casting under 30 MPa still exhibited a large number of fine dimples even at −40 °C, indicative of ductile fracture. In addition, the impact wear performance of the steels displayed a trend of initially decreasing and subsequently increasing across the pressure range of 0–150 MPa. The wear resistance of samples prepared without pressure and at 30 MPa was superior to that at 60 MPa, and the wear resistance deteriorated when the pressure increased to 60 MPa, after which it exhibited an upward trend as the pressure continued to rise. The wear mechanisms of the samples predominantly consisted of impact wear, adhesive wear, and minimal abrasive wear, along with notable occurrences of plastic removal, furrows, and spalling. Full article

This study aimed to enhance the friction and wear characteristics of materials for wind turbine sliding-bearing bushes operating under low-speed and heavy-load conditions. To this end, a high-entropy CoCrFeNiMo alloy coating was applied to the surface of 9Cr18 bearing steel, and Ni-Cr-Mo-Si alloy coating was applied to MTCrMoCu30 wear-resistant cast iron using laser cladding. The effects of varying loads on the friction and wear properties of these coatings were investigated, and the friction and wear properties were compared. Furthermore, the overall priority indices for both groups of bearing bush coatings were assessed. The findings indicated that the friction coefficient, wear quality, and wear rate of CoCrFeNiMo high-entropy alloy coating initially decreased and then increased with the increase in applied load, dominated by abrasive wear. By contrast, the friction coefficient of the Ni-Cr-Mo-Si alloy coating increased, and wear quality and wear rate initially increased and then decreased, indicating the coexistence of adhesive wear and abrasive wear. Therefore, Ni-Cr-Mo-Si alloy coating exhibited a high overall priority index and favorable friction and wear properties. Full article

Duplex steel and cast steels have a wide range of applications in many industrial sectors, for example, oil extraction, printing, petrochemical industry, energy—exhaust gases desulphurization systems, seawater desalination plants, and the shipbuilding industry. The machine elements can be produced with different techniques, which determine the operational properties. A material with the same chemical composition made as a casting will have worse mechanical properties than, for example, a forged element. This depends on the microstructure, its fragmentation and its morphology. However, the costs of casting are lower than, for example, forging, and, in addition, not all shapes obtainable in the casting process can be made using metal–plastic working methods. This article presents research results concerning the influence of the burnishing process on the properties of the duplex cast steel surface layer. The purpose of the research was to verify the impact of static pressure roller burnishing (SPRB) parameters on the wear of the surface layer of duplex cast steel. The subject of the research was cast steel in the GX2CrNiMoN22-5-3 grade—according to PN-EN 10283:2019—that was burnished using 15 variants of technological parameters. Then, the samples were subjected to surface wear tests using the INSTRON 8874 device. On the basis of the observed wear appearances, the acting wear mechanisms are defined and evaluated according their contribution to the wear behavior. Detailed information about the wear phenomena will help industries to minimize their maintenance losses related to surface wear. The possibility of shaping surface properties by mechanical burnishing is part of the current direction of surface engineering development. This technology, combined with a high-potential material such as duplex cast steel, makes it possible to increase wear resistance. Full article

This paper presents a numerical simulation of the steel grade transition from the ladle nozzle to the solidification end of the bloom. The simulation is based on models encompassing fluid flow, solidification, heat transfer, an electromagnetic field, and solute transport. To validate the accuracy of the steel grade transition model, transition blooms of high-carbon steel are sampled. Subsequently, the model is applied to investigating the steel grade transition between medium-carbon steel and low-carbon steel. The findings indicate that the regions exhibiting significant differences between their molten steel flow velocity and bloom casting speed in the strand model are primarily concentrated within 1 m below the meniscus. Additionally, the mushy zone in the strand model possesses a substantial volume. Solute elements continuously permeate the liquid phase from the solid phase through the mushy zone. Consequently, the distribution of solute elements in the transition bloom is primarily influenced by the molten steel flow in the tundish and macro-segregation in the casting process. The segregation degree of each solute element varies among grades with different carbon contents. In the austenite phase, the segregation degree of each element follows the order C > Si > Mo > Mn > Cr > Ni, while in the ferrite phase, the segregation degree is ordered as C > Si = Mn. Considering macro-segregation, the transition bloom partition model proves to be more stringent than the original partition method. This results in longer transition blooms when a significant difference exists between the new and old grades. For example, in Scheme 1, the original plan transition bloom length is 8.88 m, whereas the new plan transition bloom length is 10.88 m. Similarly, in Scheme 2, the original plan transition bloom length is 34.64 m, and the new plan transition bloom length is 35.16 m. Conversely, shorter partition intervals occur when there is an overlap in the composition of the new and old grades. In Scheme 3, the original plan partition interval for the new and old grades is 4.08 m, while the new plan partition interval is reduced to 0.94 m. Full article

This study aims at investigating the feasibility of depositing quality coatings from various high-entropy intermetallic compounds (HEICs) using detonation spraying (DS). Four different HEIC coatings, namely (NbTaVCrTi)Al₃, (NbTaVNiFe)Al₃, (NbTaVZrHf)Al₃, and (FeNiCoCrMn)(MoCr), were prepared by DS on low alloy steel substrates. The HEIC powders were first prepared by arc melting followed by ball milling and then used as reinforcement particles to deposit HEIC coatings. Elemental segregation was observed for all the as-cast samples. Powders with average particle sizes of about ~25 µm for (NbTaVCrTi)Al₃, ~22 µm for (NbTaVNiFe)Al₃, ~34 µm for (NbTaVZrHf)Al₃, and ~18 µm for (FeNiCoCrMn)(MoCr) were obtained. (NbTaVCrTi)Al₃, (NbTaVNiFe)Al₃, and (NbTaVZrHf)Al₃ HEICs exhibited a nearly single D0₂₂ (TaAl₃ type) structure, while (FeNiCoCrMn)(MoCr) exhibited a single D8_b (FeCr type) structure. Dense coatings consisted of a lamellar microstructure and sound bonding with the substrate, and low porosity was obtained for all the samples. Crystal structures of the HEIC samples were highly retained during DS, whereas all the samples underwent some degree of oxidation. Microhardness values of 745 HV for (NbTaVCrTi)Al₃, 753 HV for (NbTaVNiFe)Al₃, and 862 HV for (NbTaVZrHf)Al₃ were obtained, which are significantly higher than the microhardness of the substrate (~140 HV). Among all the samples, (FeNiCoCrMn)(MoCr) exhibited the highest microhardness values of about 1047 HV. Full article

High-molybdenum-vanadium high-speed steel is a new type of high-hardenability tool steel with excellent wear resistance, castability, and high-temperature red hardness. This paper proposes a composition design of high-molybdenum-vanadium high-speed steel for rolls, and its specific chemical composition is as follows (wt.%): C2%, Mo7.0%, V7.0%, Si0.3%, Mn0.3%, Ni0.4%, Cr3.0%, and the rest of the iron. This design is characterized by the increase in molybdenum and vanadium in high-speed steel to replace traditional high-speed steel rolls with the tungsten element in order to reduce the heavy elements’ tungsten-specific gravity segregation caused by centrifugal casting so that the roll performance is uniform and the stability of use is improved. JMatPro (version 7.0) simulation software is used for the composition design of high-molybdenum-vanadium high-speed steel. The phase composition diagram is analyzed under different temperatures. The content of different phases of the organization in different temperatures is also studied. The martensitic transformation temperature and different tempering temperatures with the different types of compounds and grain sizes are calculated. The process parameters of heat treatment of high-molybdenum-vanadium high-speed steel are optimized. The selection of carbon content and the temperature of M50 are calculated and optimized, and the results show that the range of pouring temperatures, quenching temperatures, annealing temperatures, and tempering temperatures are 1360~1410 °C, 1190~1200 °C, 818~838 °C, and 550~600 °C, respectively. Scanning electron microscope (SEM) analysis of the samples obtained by using the above heat treatment parameters is consistent with the simulation results, which indicates that the simulation has important reference significance for guiding the actual production. Full article

This research was devoted to unveiling the strain rate sensitivity (SRS) of G18NiCrMo3-6 cast steel in tension/compression asymmetry. For that purpose, detailed mechanical characterization tests were conducted providing a process window covering quasi-static and medium strain rate regimes (0.001, 0.1, 10 [s⁻¹]) in tension and compression states. Through this experimental effort, the SRS of the material could be extracted by a function of strain and the strain rate which enabled us to create a mathematical expression to easily be implemented as a state variable for constitutive material modeling. Finally, a pressure- and rate-dependent constitutive material model on the basis of the Cocks’89 yield locus definition was created using a subroutine (UMAT) file and the material parameters were verified with respect to the experimental data. The UMAT file also takes into account the tension/compression asymmetry in yielding to handle the effect of the porous media plasticity concept. The predictions of the proposed material model are in line with the experimental outputs. Full article

Cast austenitic chromium-nickel steel is commonly used for the manufacture of machine parts and components, which are exposed to the attack of corrosive media and abrasive wear during operation. The most commonly used grades include GX2CrNi18-9 and X10CrNi18-8 as well as GX2CrNiMo17-12-2 and X6CrNiMoNb17-12-2. To improve the abrasion resistance of cast chromium-nickel steel, primary niobium carbides were produced in the metallurgical process by increasing the carbon content and adding Fe-Nb. The microstructure of the obtained test castings consisted of an austenitic matrix and primary niobium carbides evenly distributed in this matrix. The measured hardness of the samples after heat treatment ranged from 215 to 240 HV and was higher by about 60 units than the hardness of the reference cast GX10CrNi18-9 steel, which had a hardness of about 180 HV. Compared to the reference cast steel, the abrasive wear resistance of the tested cast chromium-nickel steel (measured in Miller test) with contents of 4.4 and 5.4 wt% Nb increased only slightly, i.e., by 5% for the lower niobium content and 11% for the higher niobium content. Compared to ordinary cast GX10CrNi18-9 steel, the addition of 9.2 wt% Nb reduced the abrasive wear by almost 2.5 times. Full article

In this paper, the influence of small additions of Cr, Mo, Cu, Ni, B, Ca, Zr, and Ce on the hot ductility of advanced high-strength steels (AHSS) has been reviewed. Most of these small additions have a positive effect in improving hot ductility on straightening during continuous casting operations and should be considered when problems with cracking in continuous casting are encountered. In many of these cases, the reason for these generally small but important improvements in hot ductility is not known with certainty, but the segregation of these elements to the austenite grain boundaries, strengthening the bonding, is often suggested. Full article

Changes in the microstructure and selected mechanical properties of two-phase ferritic-austenitic cast steel containing 24% Cr-5% Ni-2.5% Mo-2.5% Cu after isothermal holding at 750 °C and 900 °C are presented. The choice of the two temperatures of isothermal holding was dictated by the precipitation of brittle phases within a range of 600 °C–950 °C, while the holding time depended on the casting cooling time in the mould. Changes in the microstructure were studied by the SEM-EDS and XRD techniques. As a result of the decomposition of the eutectoid ferrite, a σ phase that was rich in Cr, Mo, and Ni and a secondary γ₂ austenite with Widmannstätten morphology were formed. Compared to the austenite, the chemical composition of the secondary γ₂ austenite showed depletion of Cr and Mo. In the ferrite, the presence of Cr₂N nitrides was also detected. After a holding time of 3 h at 900 °C, these phases increased the hardness of the tested cast steel to approximately 275 HV₁₀. At the same time, the UTS value was recorded to decrease with the increasing temperature based on the tensile test results. At 750 °C, the value of UTS was 250 MPa for 1 h of holding and 345 MPa for 3 h of holding. These values decreased after increasing the temperature to 900 °C and amounted to 139 for 1 h holding and 127 MPa for 3 h holding. It was also found that the elongation values at 750 °C ranged from 7–10%, while they amounted to 35–37% at 900 °C. A fracture analysis of the tested cast steel showed that in the prevailing part, the fractures were made of ductile nature with an arrangement of dimples that is typical for this type of fracture. Non-metallic inclusions that are typical for cast steel (i.e., oxides and nitrides) were also found in the area of the fractures. Full article

Additive manufacturing processes such as selective laser melting are rapidly gaining a foothold in safety-relevant areas of application such as powerplants or nuclear facilities. Special requirements apply to these applications. A certain material behavior must be guaranteed and the material must be approved for these applications. One of the biggest challenges here is the transfer of these already approved materials from conventional manufacturing processes to additive manufacturing. Ferritic steels that have been processed conventionally by forging, welding, casting, and bending are widely used in safety-relevant applications such as reactor pressure vessels, steam generators, valves, and piping. However, the use of ferritic steels for AM has been relatively little explored. In search of new materials for the SLM process, it is assumed that materials with good weldability are also additively processible. Therefore, the processability with SLM, the process behavior, and the achievable material properties of the weldable ferritic material 22NiMoCr3-7, which is currently used in nuclear facilities, are investigated. The material properties achieved in the SLM are compared with the conventionally forged material as it is used in state-of-the-art pressure water reactors. This study shows that the ferritic-bainitic steel 22NiMoCr3-7 is suitable for processing with SLM. Suitable process parameters were found with which density values > 99% were achieved. For the comparison of the two materials in this study, the microstructure, hardness values, and tensile strength were compared. By means of a specially adapted heat treatment method, the material properties of the printed material could be approximated to those of the original block material. In particular, the cooling medium/cooling method was adapted and the cooling rate reduced. The targeted ferritic-bainitic microstructure was achieved by this heat treatment. The main difference found between the two materials relates to the grain sizes present. For the forged material, the grain size distribution varies between very fine and slightly coarse grains. The grain size distribution in the printed material is more uniform and the grains are smaller overall. In general, it was difficult and only minimal possible to induce grain growth. As a result, the hardness values of the printed material are also slightly higher. The tensile strength could be approximated to that of the reference material up to 60 MPa. The approximation of the mechanical-technological properties is therefore deemed to be adequate. Full article

In this work, gas tungsten arc welding (GTAW) was used to repair ZG06Cr13Ni4Mo martensitic stainless steel. Repair welding occurred either once or twice. The changes in the microstructure and properties of the repair welded joints were characterized by optical microscope (OM), scanning electron microscope (SEM), electron backscattering diffraction (EBSD), tensile and impact tests. The effects of reversed austenite in repair welded joints on microstructure and mechanical properties were studied. The results show that the microstructure of the welded joint after repair welding consists of a large amount of martensite (M) and a small amount of reversed austenite (A), and the reversed austenite is distributed at the boundary of martensite lath in fine strips. With the increase in the number of welding repairs, the content of reversed austenite in the welded joint increases. The microstructure in the repair welded joints is gradually refined, the microstructure in the once and twice repaired joints is 45.2% and 65.1% finer than that in the casting base metal, respectively. The reversed austenite presented in the repair welded joints decreases the tensile strength by 4.8% and 6.7%, increases the yield strength by 21.3% and 26.4%, and increases the elongation by 25% and 56%, respectively, compared with the casting base metal. In addition, the reversed austenite mainly nucleates and grows at the boundary of lath martensite. The refinement of the martensite structure was due to the generation of reversed austenite and the refinement of original austenite grain by the welding thermal cycle. After repair welding, the reverse austenite appeared in the repair welded joints and the tensile strength decreased slightly, but the plastic toughness was significantly improved, which was conducive to the subsequent service process. Full article