Search Results (85)

65 Mn is a high-quality carbon structural steel that exhibits excellent mechanical properties and machinability. It finds broad applications in machinery manufacturing, agricultural tools, and mining equipment, and is commonly used for producing mechanical parts, springs, and cutting tools. Fe901 is an iron-based alloy that exhibits excellent hardness, structural stability, and wear resistance. It is widely used in surface engineering applications, especially laser cladding, due to its ability to form dense and crack-free metallurgical coatings. To enhance the surface hardness and wear resistance of 65 Mn steel, this study employs a laser melting process to deposit a multi-layer Fe901 alloy coating. The phase composition, microstructure, microhardness, and wear resistance of the coatings are investigated using X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), Vickers hardness testing, and friction-wear testing. The results show that the coatings are dense and uniform, without visible defects. The main phases in the coating include solid solution, carbides, and α-phase. The microstructure comprises dendritic, columnar, and equiaxed crystals. The microhardness of the cladding layer increases significantly, with the multilayer coating reaching 3.59 times the hardness of the 65 Mn substrate. The coatings exhibit stable and relatively low friction coefficients ranging from 0.38 to 0.58. Under identical testing conditions, the wear resistance of the coating surpasses that of the substrate, and the multilayer coating shows better wear performance than the single-layer one. Full article

This research focuses on Fe-18Mn-10Al-1C-5Ni lightweight steel and deeply explores the influences of three different cooling methods, namely, water quenching (WQ), air cooling (AQ), and furnace cooling (FQ), on the precipitation behavior of the B2 phases and κ-carbides in the lightweight steel. The intrinsic relationship among the precipitated phases, mechanical properties, and fracture behavior is revealed. Compared with the WQ sample, the size of the intragranular B2 phase in the AQ sample did not change significantly (an increment of 9 nm), but nano-sized κ-carbides appeared at the grain boundaries and inside the grains. The yield strength and tensile strength of the AQ sample significantly increased to 1232 MPa and 1347 MPa, respectively, while an elongation of 17.4% was still maintained, which benefitted from the synergistic effect of the grain boundary B2, intragranular B2, and nano-sized κ-carbides. When the cooling rate of the heat treatment was further reduced, the size of the intragranular B2 phase in the FQ sample increased slightly (332 nm), and the κ-carbides at the grain boundaries became obviously coarsened (170 nm), resulting in a severe reduction in the elongation (2.3%) because, during the tensile deformation process, the coarsened κ-carbides at the grain boundaries promoted the nucleation of voids and microcracks. The present work provides new insights into the cooling heat treatment process of lightweight steel. Full article

With the global shift in energy structure and the advancement of the “double carbon” strategy, methanol has gained attention as a clean low-carbon fuel in the engine sector. However, the corrosion–wear coupling failure caused by acidic byproducts, such as methanoic acid and formaldehyde, generated during combustion severely limits the durability of methanol engines. In this study, we employed a systematic approach combining the construction of a corrosion liquid concentration gradient experiment with a full-load and full-speed bench test to elucidate the synergistic corrosion–wear mechanism of core friction pairs (cylinder liner, piston, and piston ring) in methanol-fueled engines. The experiment employed corrosion-resistant gray cast iron (CRGCI), high chromium cast iron (HCCI), and nodular cast iron (NCI) cylinder liners, along with F38MnVS steel and ZL109 aluminum alloy pistons. Piston rings with DLC, PVD, and CKS coatings were also tested. Corrosion kinetic analysis was conducted in a formaldehyde/methanoic acid gradient corrosion solution, with a concentration range of 0.5–2.5% for formaldehyde and 0.01–0.10% for methanoic acid, simulating the combustion products of methanol. The results showed that the corrosion depth of CRGCI was the lowest in low-concentration corrosion solutions, measuring 0.042 and 0.055 μm. The presence of microalloyed Cr/Sn/Cu within its pearlite matrix, along with the directional distribution of flake graphite, effectively inhibited the micro-cell effect. In high-concentration corrosion solutions (#3), HCCI reduced the corrosion depth by 60.7%, resulting in a measurement of 0.232 μm, attributed to the dynamic reconstruction of the Cr₂O₃-Fe₂O₃ composite passive film. Conversely, galvanic action between spherical graphite and the surrounding matrix caused significant corrosion in NCI, with a depth reaching 1.241 μm. The DLC piston coating obstructed the permeation pathway of formate ions due to its amorphous carbon structure. In corrosion solution #3, the recorded weight loss was 0.982 mg, which accounted for only 11.7% of the weight loss observed with the CKS piston coating. Following a 1500 h bench test, the combination of the HCCI cylinder liner and DLC-coated piston ring significantly reduced the wear depth. The average wear amounts at the top and bottom dead centers were 5.537 and 1.337 μm, respectively, representing a reduction of 67.7% compared with CRGCI, where the wear amounts were 17.152 and 4.244 μm. This research confirmed that the HCCI ferrite–Cr carbide matrix eliminated electrochemical heterogeneity, while the DLC piston coating inhibited abrasive wear. Together, these components reduced the wear amount at the top dead center on the push side by 80.1%. Furthermore, mismatches between the thermal expansion coefficients of the F38MnVS steel piston (12–14 × 10⁻⁶/°C) and gray cast iron (11 × 10⁻⁶/°C) resulted in a tolerance exceeding 0.105 mm in the cylinder fitting gap after 3500 h of testing. Notably, the combination of a HCCI matrix and DLC coating successfully maintained the gap within the required range of 50–95 μm. Full article

This study elucidated the effect of Ti–Mo microalloying on the hydrogen embrittlement (HE) resistance and fracture behavior of warm-rolled Fe-5.6Mn-0.16C-1Al (wt%) steel. After intercritical annealing, both steels, i.e., without and with Ti–Mo microalloying, showed ultrafine ferrite (α) and austenite (γ_R) duplex microstructure. The addition of Ti–Mo to 5.6Mn steel reduces the volume fraction of γ_R, facilitating the formation of (Ti, Mo)C carbides in α phase and further refining the final microstructure. The product of ultimate tensile strength (UTS) and total elongation (TEL) of 5.6MnTiMo can be as high as 35 GPa·% with an ultra-high yield strength of above 1.2 GPa. Furthermore, the addition of Ti–Mo also had a significant effect on the resistance to HE of medium Mn steels. Firstly, the limited (Ti, Mo)C carbides precipitated in γ_R could act as irreversibly trap sites to capture a considerable amount of H, effectively increasing the C_H (Diffusible Hydrogen Content). Additionally, 5.6MnTiMo displayed higher γ_R stability, resulting in a reduced susceptibility to HE. The H-assisted microcracks mainly formed inside γ(α′) and extended along γ(α′) grain boundaries, leading to intergranular cracking and premature fracture. Full article

Low-cost and low-alloy dual-phase (DP) steel with a tensile strength (TS) above 1000 MPa and high ductility is in great demand in the automobile industry. An approach to using a medium-carbon and fibrous DP structure for developing such new DP steel has been proposed. The microstructure and mechanical performance of fibrous DP steel obtained via partial reversion from martensite in Fe-C-Mn-Si low-alloy steel have been investigated. The TS of the as-quenched DP steel is above 1300 MPa, while the total elongation is less than 6%. The total elongation was increased to above 13%, with an acceptable loss in TS by performing additional tempering. The fibrous tempered-martensite/ferrite DP steel exhibits an excellent balance of strength and ductility, surpassing the current low-alloy DP steels with the same strength grade. Plate-like or quasi-spherical fine carbides were precipitated, and the relatively high-density dislocations were maintained due to the delay of lath recovery by the enrichment of Mn and C in martensite (austenite before quenching), contributing to the tempering softening resistance. In addition, nanotwins and a very small amount of retained austenite were present due to the martensite chemistry. High-density dislocations, fine carbide precipitation, and partially twinned structures strengthened the tempered martensite while maintaining relatively high ductility. Quantitative strengthening models and calculations were not included in the present work, which is an interesting topic and will be studied in the future. Full article

The development of new materials with low weight for the transport industry is required for the saving of natural resources and protection of the environment from carbon dioxide pollution. The microstructure and mechanical properties of the Fe-30Mn-10Al-3.3Si-1C steel in as-cast, quenched, aged, and hot-deformed states were investigated. Austenite, ferrite, and κ-carbides are present in the steel in an as-cast state. Hot deformation of steels was made using the thermal and mechanical simulation system Gleeble-3800 at temperatures of 900–1050 °C and strain rates of 0.1–10 s⁻¹. Mechanical properties in as-cast, annealed, aged, and hot-deformed states were determined by Vickers hardness and compression tests. A constitutive model of the hot deformation behavior of Fe-30Mn-10Al-3.3Si-1C steel with high accuracy (R² = 0.995) was constructed. The finite element analysis of the deformation behavior of the steel under the plane-strain scheme was performed. Compression tests at room temperature have shown an increase in strength and ductility after hot deformation. The strain hardening of ferrite and austenite grain refinement during dynamic recrystallization are the main reasons for the growth of steel’s plasticity and strength. A specific strength of the investigated material is in the range from 202,000 to 233,000 m²/s² which is higher than high-strength steels previously developed and used in the automotive industry. Full article

In this study, the microstructure, mechanical properties, wear resistance, and wear-hardening mechanism of Fe-28Mn-8.5Al-1.0C lightweight wear-resistant steel after heat treatment at different aging temperatures were examined. The results show that the nano-scale κ-carbides precipitated in the grains after aging treatment increased the strength and hardness of the material through the strengthening effect of the second phase. The yield strength of the material is 697 MPa, the tensile strength is 905 MPa, and the hardness is up to 294 HB after aging at 500 °C for 5 h. However, the large-sized κ-carbides precipitating continuously at the grain boundary are unfavorable to the plasticity and toughness of the material. Compared with the aging treatment at 300 °C for 5 h, the elongation and low-temperature impact energy decreased by 12.0% and 47.1%, respectively. Except for the dominant wear mechanism being plastic deformation after heat treatment at 500 °C for 5 h with a 4J impact energy, the predominant wear mechanisms for different impact energies under all other heat treatment conditions are micro-cutting. The increase in aging temperature increases the number and volume of κ-carbide precipitation, which leads to enhanced second-phase strengthening and dislocation strengthening, and the wear resistance of the material is improved. The hardening mechanism of the material after wear at different impact energy levels under aging treatment conditions is a cross-distributed dislocation wall and high-density dislocation entanglement. The increase in aging temperature reduces the spacing of the dislocation wall, increases the area and density of dislocation entanglement, and enhances the work-hardening effect. Full article

Ultra-low-carbon, high-strength steels have gained significant attention due to their exceptional mechanical properties. To enhance the performance of the steel, understanding the precipitation behavior of strengthening precipitates is crucial. In this study, the precipitation behavior of ultra-low-carbon high-strength steel strengthened by nanoscale copper (Cu)-rich precipitates (CRPs) and carbonitride (CN) atomic clusters was characterized using atom-probe tomography after tempering at 400, 450, 600, and 650 °C for 2 h. The results revealed that the nanoscale copper CRPs and the CN atomic clusters were the main strengthening precipitates. The CRPs, enriched only in Cu, were observed at 400 °C. Segregation of nickel (Ni) and manganese (Mn) to the CRPs occurred at 450 °C, and the number densities of CRPs achieved the maximum value, leading to the highest strengthening effects. The size of the CRPs increased with increasing temperature; however, the size of the clusters of the carbide-forming atoms remained at almost ~1.6 nm. At 650 °C, the concentration of Cu, Ni, and Mn atoms in the CRPs was about 85.4, 4.5, and 4 at.%, respectively; however, that of Fe decreased significantly. In the lath boundaries, the size of 10% C and 0.4% C iso-surfaces was relatively larger than that in the matrix. In a reverted austenite region at 600 °C, the concentration of Ni in the reverted austenite, CRPs, and matrix was about 15, 2.5, and 2.5 at.%, respectively. Full article

High-performance lightweight materials are urgently needed because of energy savings and emission reduction. Here, we design a new steel with a low density of 6.41 g/cm³, which is a 20% weight reduction compared to the conventional steel. The mechanical properties and microstructures of the steels prepared with different routes are systematically explored by utilizing uniaxial tensile testing and transmission electron microscopy. The steel processed by cold rolling and recrystallization annealing at 950 °C for 15 min shows an ultra-high yield strength of 1241 ± 10 MPa, while retaining a good ductility of 38 ± 1%. The high yield strength is mainly related to the synergistic precipitation strengthening introduced by nanoscale B2 and κ′-carbides. It is encouraging to notice that the yield strength increased without scarifying ductility, compared to the ST steel. The key reason is that the high strain hardening rate is activated by combined factors, including the blockage of numerous twins and nanoscale B2 to the dislocation movements, and dynamic slip band refinement. This study is instructive for concurrently enhancing the strength and ductility of austenitic lightweight steels with fully recrystallized grains and dual nano-precipitates. Full article

W-Mo-V high-speed steel (HSS) is a high-alloy high-carbon steel with a high content of carbon, tungsten, chromium, molybdenum, and vanadium components. This type of high-speed steel has excellent red hardness, wear resistance, and corrosion resistance. In this study, the alloying element ratios were adjusted based on commercial HSS powders. The resulting chemical composition (wt.%) is C 1.9%, W 5.5%, Mo 5.0%, V 5.5%, Cr 4.5%, Si 0.7%, Mn 0.55%, Nb 0.5%, B 0.2%, N 0.06%, and the rest is Fe. This design is distinguished by the inclusion of a high content of molybdenum, vanadium, and trace boron in high-speed steel. When compared to traditional tungsten-based high-speed steel rolls, the addition of these three types of elements effectively improves the wear resistance and red hardness of high-speed steel, thereby increasing the service life of high-speed steel mill-roll covers. JMatPro (version 7.0) simulation software was used to create the composition of W-Mo-V HSS. The phase composition diagrams at various temperatures were examined, as well as the contents of distinct phases within the organization at various temperatures. The influence of austenite content on the martensitic transformation temperature at different temperatures was estimated. The heat treatment parameters for W-Mo-V HSS were optimized. By studying the phase equilibrium of W-Mo-V high-speed steel at different temperatures and drawing CCT diagrams, the starting temperature for the transformation of pearlite to austenite (A_c1 = 796.91 °C) and the ending temperature for the complete dissolution of secondary carbides into austenite (A_ccm = 819.49 °C) during heating was determined. The changes in carbide content and grain size of W-Mo-V high-speed steel at different tempering temperatures were calculated using JMatPro software. Combined with analysis of A_c1 and A_ccm temperature points, it was found that the optimal annealing temperatures were 817–827 °C, quenching temperatures were 1150–1160 °C, and tempering temperatures were 550–610 °C. The scanning electron microscopy (SEM) examination of the samples obtained with the aforementioned heat treatment parameters revealed that the martensitic substrate and vanadium carbide grains were finely and evenly scattered, consistent with the simulation results. This suggests that the simulation is a useful reference for guiding actual production. Full article

The reinforcement of cast Cantor’s-type high-entropy alloys by MC carbides and their effect on the hot oxidation behavior were investigated. Three equimolar CoNiFeMnCr alloys without or with carbon and with either hafnium or tantalum were elaborated. Their as-cast microstructures were specified. Oxidation tests were carried out in air at 1100 °C. Flexural creep tests were performed at 1100 °C at 10 MPa. The carbide-free CoNiFeMnCr alloy was single-phased. The version with Hf and C added and the one with Ta and C added contained interdendritic eutectic script HfC and TaC carbides, respectively. After oxidation for 50 h at 1100 °C, all alloys were covered by a (Cr,Mn)₂O₃ scale with various proportions of Cr and Mn. HfO₂ or CrTaO₄ also formed. Oxidation resulted in a deep depletion in Cr and in Mn in the subsurface. Oxidation is much faster for the three alloys by comparison with chromia-forming alloys. Their bad oxidation behavior is obviously due to Mn and protection by coating is to be considered. The creep deformation of the carbide-free CoNiFeMnCr alloy was very fast. The creep resistance of the two versions reinforced by either HfC or TaC deformed much slower. The addition of these MC carbides led to a deformation rate divided by five to ten times. Now, creep behavior comparisons with commercial alloys are to be conducted. They will be performed soon. Full article

In this study, a novel lightweight Fe-Mn-Al-C steel composition and thermomechanical processing route was developed to produce a fully austenitic microstructure with a uniform intragranular dispersion of B2-NiAl precipitation in order to overcome the significant challenge of strengthening hot-rolled Fe-Mn-Al-C steels while retaining toughness. The new composition and processing methods allow for the processing of ultrahigh-strength Fe-Mn-Al-C steel containing nickel as thicker gauge plate for a multitude of new automotive and structural applications where lightweighting is critical. The composition investigated in this study was a fully austenitic Fe-21Mn-9Al-1C-8Ni wt% steel. Two hot rolling methods were investigated: the first procedure involved lower temperature rolling cycles to precipitate B2-NiAl during hot rolling and reheating. The second method involved higher temperature rolling to precipitate B2-NiAl after thermomechanical processing during a short isothermal treatment. The lower temperature rolling produced plate with an ultimate tensile strength of 1120 MPa and a Charpy V-Notch (CVN) toughness of 24 J at −40 °C. After the high temperature rolling procedure, precipitation of B2-NiAl through a subsequent precipitation hardening step resulted in reduced B2-NiAl size and improved the ultimate tensile strength above 1300 MPa. The two novel processing routes of a single composition can be performed with current manufacturing capabilities to produce hot rolled plate strengthened by B2-NiAl precipitation to various hardness (ranging from 33 to 41 HRC) and strength levels (ranging from 1100 to 1320 MPa ultimate tensile strength) while retaining 22–27% elongation. Full article

The research presented in this paper is part of a larger project concerning high-manganese alloys with different chemical compositions (mainly in manganese content from 21 to 31 wt.%). The presented examination results concern the analysis of the microstructure and textures in high-manganese X85MnAl29-9 steel, an age-hardenable steel, during aging at 550 °C for various times. X85MnAl29-9 steel was first hot rolled and subsequently cold rolled up to a 30% reduction. The samples were aged after deformation at 550 °C for various times in an argon atmosphere and cooled in air. The studies include X-ray phase analysis, texture measurement and observation of the microstructure by light microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), as well as microhardness measurement. Research using scanning and transmission electron microscopy identified carbides in the analyzed samples. The results indicate that, when aging takes place, precipitation of κ′-carbide in an austenitic matrix and carbide κ at grain boundaries occurs. The appearance of satellites on diffraction patterns suggests that (Fe, Mn)₃AlC nano-carbides are formed within the austenite matrix by a spinodal decomposition mechanism after the alloy is subjected to long-term aging, which is a key element for structure analysis in the design of safety systems. The use of shorter aging times (up to 24 h) leads to an increase in hardness caused by the precipitation of small κ′-carbide particles in the matrix. However, long aging times (100 h) lead to an increase in the precipitation of the carbide phase (κ and κ′), i.e., the steel becomes overage, which results in a decrease in hardness. Full article

In this study, low Mn content Fe-Mn-Si-based shape memory alloys [Fe-(17-2x) Mn-6Si-xNi-yCr-0.3C (x = 0, 1, 2, 3, 4; y = 0, 1, 3, 5)] were prepared via vacuum arc remelting. The alloys were hot-rolled and solid-solution-treated at 1150 °C for 1 h followed by aging at elevated temperatures. The effects of Cr and Ni addition on the shape memory performance and corrosion resistance of the alloys in 3.5 wt% NaCl solutions were investigated using bending test and potentiodynamic polarization, respectively. It was revealed that the recoverable strain of the alloys remains larger than 2% when 1Ni is replaced with 2Mn and Cr is added. However, it becomes less than 2% in 11Mn and 9Mn alloys because of the easy formation of the α’ martensite. The shape memory effect of alloys is highly improved due to the precipitation of fine carbides in the grains by the addition of Cr and after aging treatment at elevated temperatures (≧700 °C). The highest shape recovery ratios of 88.3% for 17Mn0Ni3Cr, 94.0% for 15Mn1Ni3Cr, 94.4% for 13Mn2Ni5Cr, 88.1% for 11Mn3Ni5Cr, and 86.8% for 9Mn4Ni7Cr, respectively, were achieved after 800 °C aging treatment. The strip-like second phase (carbides) forms at the grain boundaries in the Cr-free alloys after 600 °C aging treatment. There are lots of fine carbides (M23C6 and M7C3) precipitated in the interior of the grains at the aging treatments ≧ 700 °C. However, M7C3 is eliminated at 900 °C aging treatment. The corrosion resistance results showed that the corrosion resistance of the alloys is improved by adding Cr. The maximum corrosion potentials (−0.474 V) have been observed for 13Mn2Ni5Cr, and similar mechanisms have been analyzed in all series of alloys. Full article

The mechanical properties and electrochemical stability of high-entropy alloys are substantially affected by their composition distribution and crystal structure. However, the details concerning the conditions of milling and sintering for sintered alloys have rarely been reported. In this work, a series of CrMnFeCoNi alloys were fabricated by ball milling and spark plasm sintering for different periods. Their crystal structure, density, hardness, and corrosion resistance were investigated. As a result, a partial alloying of Cr, Mn, Fe, Co, and Ni was achieved by ball milling. However, Cr-rich particles, including Mn, were formed in the milled powders. The sintered alloys inherited the Cr-rich particles to form Cr-rich zones. The formation and change of chromium carbide were also confirmed in sintered alloys. Extended milling or sintering to 12 h achieved high hardness and corrosion resistance for the sintered alloys. The Cr-rich zones showed high hardness and Kelvin potential, which affect both the hardness and the corrosion resistance. Full article