TiC Precipitation Research Articles

Tailoring the microstructure and mechanical properties of wire arc additively manufactured Ti6Al4V alloy by in-situ microalloying with modified nanocarbon

Carbon alloying is a validated strategy for enhancing the mechanical properties of titanium alloys prepared by wire arc additive manufacturing (WAAM). However, achieving uniform carbon distribution, particularly nanocarbon, in the melt pool via the brushing method is challenging, which limits the improvement of mechanical properties. In this paper, nanocarbon was modified by nitric acid hydrothermal treatment and added into the Ti64 melt pool during the WAAM. The distribution of modified nanocarbon in the melt pool was characterized, and the microstructure and mechanical properties of the nanocarbon-alloyed titanium alloy deposits were studied. The findings revealed that the surface of modified nanocarbon generated oxygen-containing functional groups, which enhanced its dispersion in the melt pool. The addition of 0.1–0.3 wt% modified nanocarbon induced no pores in the deposits compared to unmodified ones. The tensile strength of the deposited alloys was continually enhanced with increasing modified nanocarbon content, while the elongation had a peak value. The Ti64 with 0.1 wt% nanocarbon exhibited a balanced comprehensive performance with an ultimate tensile strength (UTS) of 981 MPa coupled with an elongation of 8 %. The achievement of the balanced mechanical performances was attributed to the refinement of α-Ti and solid solution strengthening of nanocarbon. When 0.3 wt% nanocarbon was added, the UTS increased to 1012 MPa but the elongation sharply decreased to 4.5 % due to the precipitation of TiC.

Investigating the Role of TiC Precipitation in Dynamic Recrystallization Behavior of a Novel Ship Steel

This study examines the single‐pass thermal compression behavior of Ti‐bearing ship plate steel across a temperature range of 850–1150 °C and strain rates from 0.01 to 7 s−1, employing the Gleeble‐2000D thermomechanical simulator. It delves into the evolution of TiC precipitation and dynamic recrystallization (DRX), along with the austenite decomposition transformation during hot compression and subsequent cooling. Active dynamic recrystallization commences at deformation temperatures above 1050 °C, facilitated by the diminished pinning pressure of TiC carbides. This leads to the development of fine DRX austenite grains, influenced by an increase in strain rates and a decrease in temperature. Simultaneously, the fraction of TiC dispersions decreases as the deformation temperature increases, yet they maintain a consistent size of 5–10 nm. The refined particle size is attributed to their low interfacial energy with the austenite matrix, determined by the first principle to be 0.21 J m−2. Due to the severe deformation and numerous dispersions, specimens subjected to a thermal deformation regime at 850 °C and a strain rate of 7 s−1 present a peak in hardness, reaching a maximum of 324 HV. The Ti microalloying approach offers pivotal insights into improving the rollability and mechanical characteristics of ship plate steel.

Study on the evolution of multistage and multiscale Ti-bearing precipitation and microstructure in ultrahigh-strength titanium microalloyed weathering steels

In this study, 900 MPa ultrahigh-strength weathering steels were successfully developed through thermomechanical controlled processing (TMCP). Advanced microstructure characterization, combined with precipitation thermodynamics and kinetics models, elucidated the evolution of Ti-bearing precipitation and microstructure. The results showed that coiling temperature (CT) significantly impacts phase fractions, grain boundary density, and misorientation angles, while both CT and finishing rolling temperature (FRT) influence grain sizes in acicular ferrite (AF) and granular bainite. The lower coiling temperature resulted in a higher dislocation density of the test steel, which provided more nucleation sites for AF and TiC, favoring a higher number of TiC particles and a higher proportion of AF. Above 1050 °C, the addition of nitrogen changed the shape of the precipitation kinetics curve, reduced the nucleation energy barrier of TiC, decreased the critical nucleation size, and improved the nucleation rate. Meanwhile, the addition of nitrogen accelerated the precipitation transformation of TiC, which promoted the formation of Ti(C, N). Furthermore, increasing the deformation stored energy (DSE) further accelerated the precipitation of Ti(C, N) and significantly increased the nucleation rate. The formation mechanism of large-size Ti(C, N) and the transformation mechanism of Ti(C, N) to TiC are revealed by precipitation thermodynamics and kinetics. The completion time of TiC precipitation on dislocations is shorter than that on grain boundaries, which results in the TiC on dislocations being prone to coarsening during prolonged coiling. These findings provide crucial insights for optimizing the industrial production of ultrahigh-strength titanium microalloyed weathering steels.

Enhanced tribocorrosion performance of laser-deposited Fe2CoNiCrAlTiCx high-entropy alloy coatings via in-situ graphitization in aqueous medium

The role of carbon in improving the tribocorrosion performance of Fe2CoNiCrAlTiCx high-entropy alloy (HEA) coatings prepared by laser melting deposition was comparatively studied in aqueous medium. The results showed that the initial increase of carbon enhanced the hardness and corrosion resistance, while an excessive amount leaded to a decrease due to the precipitation of TiC and the formation of FCC-phase matrix. The aqueous medium could relieve the wear rate, especially in corrosive NaCl solution. The negative synergistic effect between corrosion and wear in carbon-contained HEA coatings could be attributed to the self-lubrication of graphite-like carbon derived from in-situ graphitization.

Microstructure, phase evolution and mechanical properties of nickel-silicon carbide reinforced Ti6Al4V alloy processed by pulsed electric current sintering

In this work, fully densified Ni–SiC reinforced Ti6Al4V matrix composites were consolidated by pulsed electric current sintering (PECS) technique. The microstructural evolution and mechanical properties of the developed composites with varying SiC contents were investigated. The microstructural study revealed in-situ precipitation of TiC, Ti5Si3 and Ti3SiC2 strengthening phases within the composites. The α colony size in the composites was notably reduced compared to the fabricated SiC-deficient samples due to the addition of SiC additive into the Ti6Al4V alloy matrix. The in-situ precipitated phases enhanced the mechanical properties of the composites. Composite reinforced with 10 wt% SiC (TNi10SiC) displayed the highest hardness value of 609.8 ± 50.9 HV0.5 among the sintered samples, translating to an increment of about 88 % compared to the unreinforced sample T. Among the sintered samples, the highest flexural strength of 2094.32 ± 97.67 MPa was obtained for the TNi5SiC composite, after which the flexural strength deteriorates with increasing SiC content as witnessed in TNi10SiC composite with the least flexural strength of 863.67 ± 71.57 MPa due to agglomeration of the reinforcement phases within the composite. Samples reinforced with 0 wt% SiC experienced a ductile fracture, and the composites containing 2.5 wt% - 5 wt% SiC content witnessed intergranular and interlamellar fractures. However, at higher SiC content, reinforcement pull-out and debonding of the agglomerated reinforcement phases predominates, and composites fail by brittle fracture.

Remelting of In Situ Fe‐xTiC Metal Matrix Composites by the Sessile Drop Method: Characteristic Temperatures and Microstructural Analysis

The remelting of Fe‐xTiC metal matrix composites (MMCs) is studied using the sessile drop method. This is to determine the conditions needed for the complete dissolution of TiC precipitates in the Fe‐based melt. Samples with different amounts of TiC (2, 3.5, and 5 wt%) are analyzed in a hot‐stage microscope (HSM), capturing the softening and melting temperatures. A Cr‐alloyed steel is selected as a matrix. Consequently, the presence of TiC elevates the melting initiation temperature above the melting point of pure iron (e.g., 1659 ± 10 °C for Fe‐5TiC). Furthermore, samples with higher TiC amounts exhibit higher melting initiation temperatures. This trend is confirmed by differential scanning calorimetry measurements, conducted on the representative Fe‐xTiC samples. Microstructural examinations of the solidified (HSM) samples identify two distinct TiC precipitate morphologies: primary blocky/cubic and secondary eutectic plate like. For instance, the Fe‐5TiC sample contains numerous blocky/cubic precipitates (7.5 ± 3.1 μm) clustered at the upper cross‐ section, while secondary plate‐like precipitates (20.4 ± 11.8 μm) are uniformly distributed in eutectic assemblies with the matrix. This study provides meaningful insights for optimizing the production of as‐cast and as‐atomized Fe‐TiC MMCs, particularly in selecting reinforcement levels and homogenization temperatures for complete TiC dissolution.

Research on the strengthening mechanism of Nb–Ti microalloyed ultra low carbon IF steel

Interstitial free (IF) steels are characterized by their interstitial free ferritic matrix due to addition of micro-alloying elements that draw carbon and nitrogen out of matrix to form carbonitrides. The IF steels typically have excellent deep drawing ability, certain mechanical strength, and high plastic deformation performance. In this paper, the microstructure evolution and carbides precipitation behavior during the hot rolling, cold rolling and annealing processes have been studied using both experimental and thermodynamic and kinetic modeling approaches. The strengthening mechanism of Nb–Ti microalloyed IF steel has been investigated. The results of the thermodynamic simulation indicates that the addition of Nb into Ti bearing IF steel promotes recrystallization at 900 °C, leading to fine recrystallized grains. Due to the recrystallization of austenite during the final rolling process, Nb–Ti microalloyed hot rolled plates exhibit finer grain size, fewer substructures, and lower dislocation density compared to the hot rolled plates containing only Ti. Building upon the initial fine and uniform structure, Nb–Ti microalloyed steel maintains a refined structure after undergoing cold rolling and annealing. The study of the carbides precipitation behavior suggests that TiN precipitates at high temperature above 1100 °C, while a substantial amount of (Nb,Ti)C and TiC precipitate at about 900 °C in Nb–Ti and Ti bearing steels, respectively. There is no significantly difference between the amount of carbides in steels hot deformed at 900 °C and in the hot rolled plates, indicating that the carbides mainly precipitate during the hot rolling process. There are negligible carbides precipitated during the coiling process at 600 °C. In Nb–Ti containing steel, Nb and Ti in solid solution are significantly reduced due to the large amount precipitation of (Nb,Ti)C during the final rolling process. The reduction of solid solution Nb effectively promotes the recrystallization of austenite. Therefore, the grains of hot-rolled, cold-rolled, and annealed strips are refined. In addition, there are more small size carbides in Nb–Ti bearing steel than that in Ti bearing steel. Therefore, the higher strength of Nb–Ti steel is mainly from the strengthening effect of grain refinement and carbides precipitation.

Hydrogen trapping and embrittlement of titanium- and vanadium carbide-containing steels after high-temperature hydrogen charging

This work studies the effect of TiC and VC precipitate sizes on hydrogen trapping and embrittlement. Two experimental ferritic HSLA steels containing either TiC or VC carbides for precipitation strengthening are annealed in nitrogen and hydrogen gas. This results in a hydrogen uptake of up to 0.91 and 0.44 wppm in the TiC and VC steels, respectively. TEM and TDS analysis indicate that semi-coherent TiC particles trap hydrogen in misfit dislocations with an activation energy of 43 kJ/mol. Coherent VC particles are suggested to trap hydrogen in interface carbon vacancies, with an energy between 53 and 72 kJ/mol. Carbon vacancies are the likely trapping site in incoherent precipitates, where SIMS imaging confirms that incoherent TiC precipitates trap preferentially near the interface, whereas incoherent VC precipitates trap throughout their bulk. Neither alloy is embrittled in SSRT tests after hydrogen absorption, which shows that these precipitates can be used as both a hydrogen sink and a strengthening mechanism in steels.Graphical abstract

Melting and solidification dynamics during laser melting of reaction-based metal matrix composites uncovered by in-situ synchrotron X-ray diffraction

Laser additive manufacturing (AM) of reaction-based metal matrix composites (MMCs) involves highly complex and non-equilibrium material transformation behavior, including melting, dissolution, precipitation, and solidification. Yet, the dynamics and interplay of these phase transformation processes remain poorly understood, posing substantial challenges in identifying the microstructure formation mechanism, and predicting and controlling the microstructure in the printed parts. Here we performed the in-situ X-ray diffraction experiment to characterize the phase evolution dynamics of the 316L + 10 vol.%TiC system during laser melting, which provides direct and quantitative insights of the complex phase reaction and evolution dynamics under rapid heating and cooling conditions relevant to additive manufacturing of reaction-based MMCs. Further in-depth thermodynamic and kinetic calculations revealed that most of the phase evolution behavior observed in the in-situ X-ray diffraction experiment cannot be solely explained by widely used equilibrium thermodynamic models, and diffusion-controlled nonequilibrium dissolution and precipitation kinetics must be considered to elucidate the complex phase evolution behavior, including incomplete TiC dissolution, and three-step TiC precipitation. The three distinct types of precipitates generate unique hierarchical TiC micro- and nanostructures, which enhances the yield strength from 513 MPa to 877 MPa by 71 %, tensile strength from 628 MPa to 1054 MPa by 68 %, and Young's modulus from 193 GPa to 221 GPa by 14 %. The findings of our research provide the knowledge foundation for the design of unique microstructures and advanced MMC materials through laser AM.

Wetting and pressureless infiltration of Cu-xTi/SiC system at 1373 K

In order to clarify more clearly the action mechanism of Ti at the interface between Cu–Ti alloy and SiC during wetting, the monocrystal, polycrystalline, and porous α-SiC substrates were selected for study by modified sessile drop method under high vacuum at 1373 K. The results show that there is no significant difference in wettability and spreading dynamics between monocrystal and polycrystalline α-SiC substrates. The critical titanium concentration causing wettability transformation is between 5 wt% and 7.5 wt%. The transformation of wettability mainly depends on the precipitation of continuous Ti3SiC2 layer with metalloid properties. Multilayer precipitation layers were observed in the interface structure, corresponding to three spreading stages: rapid spreading stage, which may be caused by TiC precipitation; At the stage of spreading stagnation, the corresponding interface failed to produce enough TiC; Slowly spreading to the equilibrium stage corresponds to the precipitation of Ti3SiC2. Cu-xTi on porous-SiC substrate failed to achieve complete pressureless infiltration during wetting, mainly because the volume of SiC and TiC consumed by the reaction is much smaller than the volume of the precipitated phase Ti3SiC2, which closed the pores and hindered the infiltration process. The results can provide theoretical basis for regulating the wettability, optimizing the interface structure between titanium-containing active alloys and carbide ceramics.

Revealing the precipitation kinetics of multi-stage and multi-scale Ti-bearing precipitation in a 460 MPa grade HSLA steel

The multi-stage and multi-scale Ti-bearing precipitates, containing TiN, Ti(C, N), Ti4C2S2 and TiC, were systematically examined through experimental observations and our modified precipitation kinetic analyses. The result showed that cubic TiN (several microns) mainly precipitated in molten steel. After continuous casting, Ti(C, N) and Ti4C2S2 primarily precipitated in austenite, spanning 100–1000 nm in size. Upon subjected to severe rough rolling deformation, further precipitation of Ti(C, N) and Ti4C2S2 (tens of nanometers) appeared, accompanying with austenite recrystallization. During finishing rolling, recrystallized austenite grains were subdivided into multiple microbands, leading to an accumulation of deformation stored energy (DSE). The strain-induced precipitation (SIP) of spherical TiC particles (10–20 nm) distributed along microband walls, prior austenite grain boundaries, and even within the microbands. Subsequently, sequential matrix transformations, specifically ferrite (γ → α) and pearlite (γ → α + θ), were initiated during coiling. High-density TiC interphase precipitation occurred during the γ → α transformation, while a more dispersed, low-density TiC precipitation was observed after the γ → α + θ transformation. Kinetic analyses revealed that the nose temperature for Ti(C, N) precipitation in austenite was a minimum of 200 °C higher than that of Ti4C2S2. The DSE accelerated the TiC SIP with higher nose temperature in austenite during hot rolling. Moreover, kinetic analyses also implied that the migrating γ/α interface promoted faster TiC nucleation and growth relative to dislocation nucleation, and the relative precipitation time shortened more than 20 orders of magnitude. Furthermore, both the γ/α interface migrating velocity and the interface carbon content exhibited weak influence on the kinetics of interphase precipitation. However, the pearlite formation reduced the driving force of TiC precipitation, resulting in the TiC dispersed precipitation rather than TiC interphase precipitation.

The Effect of Niobium on <i>In Situ</i> Synthesis of Titanium Carbide in Composite Hardfacings

Niobium (Nb) and titanium (Ti) react with carbon to form high-melting-point and high-hardness MC-type carbides. This study explores the in-situ synthesis of mixed NbC-TiC carbides during plasma transferred arc welding of a steel-based hardfacing. Feedstock powders consisted of stainless steel AISI 316L, TiO2, and graphite with and without 5 wt.% Nb addition. Feedstock powders were ball milled for 72 hours, then mixed with paraffine and pre-placed on the S235 steel. The cladding current was 125 A, and the plasma torch travel velocity was 1 mm/s and 0.7 mm/s. The effect of Nb on TiC generation was examined using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS). Vickers hardness was also measured at the surface of hardfacings. Results show that previously formed NbC grains acted as nucleation sites for TiC precipitation. Increased torch velocity has resulted in improving distribution and decreasing agglomeration of carbon phases. Hardness tests showed that Nb and Ti increased the hardness resistance of the substrate steel.

Unveiling the effects of Ti microalloying and thermomechanical processing on recrystallization behavior and mechanical properties of type 316 stainless steel

For the titanium-stabilized austenitic stainless steels, the interaction of precipitation due to the addition of Ti and the recrystallization process is an important aspect of grain refinement, which needs more systematic investigations. Accordingly, in the present work, the effects of Ti microalloying and thermomechanical processing on the recrystallization behavior and mechanical properties of type 316 stainless steel were investigated. It was revealed that the strain-induced α′-martensitic transformation in these metastable alloys is sensitive to the presence of Ti and C in solid solution or their presence as TiC carbides in the aged condition, as well as the temperature of rolling and reduction in thickness. During annealing, the reversion of deformation-induced α′-martensite to austenite and primary recrystallization resulted in the formation of fine-grained equiaxed microstructures, where the precipitation of TiC and sigma-phase was found to be important in the retardation of recrystallization and grain growth (by Zener pinning mechanism) as well as refining the grain size. Annealing the cold rolled 316Ti stainless steel at 800 °C led to a fine grain size of ∼2.5 μm with the precipitation of sigma-phase; while annealing at 900 °C resulted in a coarser grain size of 4 μm but without the presence of the unfavorable sigma-phase. The yield stress of 476 MPa, ultimate tensile strength of 805 MPa, and total elongation of 68 % were obtained for the latter, revealing the merits of Ti addition and thermomechanical processing for the improvement of mechanical properties.

Tribological properties and sulfuric acid corrosion resistance of laser clad CoCrFeNi high entropy alloy coatings with different types of TiC reinforcement

CoCrFeNi, directly added TiC (D-TiC) and in-situ synthesized TiC (I-TiC) reinforced CoCrFeNi high entropy alloy coatings (HEACs) were prepared on the surface of 316 stainless steel (SS) by laser cladding (LC). The HEACs all achieved a dense and uniform structure, the TiC distributed at the grain boundaries (GBs) reduced the dilution rate of the HEACs, and the I-TiC composite coating realised a fine and diffuse distribution of the reinforcing phase compared to the D-TiC HEAC. The introduction of TiC dramatically refined the grain size of HEA system and inhibited the formation of high angle grain boundaries (HAGBs), with the average grain size decreasing from 23.6 µm in the TiC-free HEAC to 12.3 µm in D-TiC HEAC and 9.3 µm in I-TiC HEAC, and the proportion of low angle grain boundaries (LAGBs) of D-TiC and I-TiC composite coatings was even as high as 64.8% and 70.4%. As a result, the density of geometrically necessary dislocations (ρGND) in TiC-containing coatings also increased greatly, and ρGND in CoCrFeNi, D-TiC and I-TiC HEACs were 0.55 × 1015, 1.08 × 1015 and 1.27 × 1015 m−2, respectively. The highest average microhardness values of 420.2 ± 6 HV0.2 was achieved with I-TiC HEAC, which relied on TiC precipitation in a nucleation-growth mode. In electrochemical corrosion tests, the introduction of TiC also provided additional channels for ion diffusion. The ordered and dense passivation film of the I-TiC composite coating impeded sulfuric acid attack effectively, with an Icorr value of only 2.28 × 10−2 ± 0.8 μA/cm2, which was less than that of the substrate as well as the other two HEACs. In both dry sliding friction and wear and corrosive wear experiments, abrasive wear was the dominant wear pattern of I-TiC HEAC due to the increase in local stresses caused by the "point-to-point" contact between the TiC particles and the friction pair. Thanks to the diffuse and homogeneous distribution of the TiC reinforcing phase, I-TiC HEAC exhibited the best tribological performance in both dry sliding friction and wear or corrosive wear experiments with specific wear rates as low as 0.05 mm3/Nm in air and 0.06 mm3/Nm in sulfuric acid.

Laser welding of SiCp/2024Al composites with novel TiB2/2024Al composite filler

The effect of TiB2/2024Al filler on the microstructure and mechanical properties of SiCp/2024Al joint was investigated in this paper. The results indicated that needle-like Al4C3 phase with a content of 18.9% was the dominant precipitate in the weld zone (WZ) of direct welded (DWed) joint, which weakened the tensile strength (109.3 MPa) of DWed joint. The introduction of TiB2/2024Al filler changed the microstructure of WZ. In the molten pool, TiC precipitate was precipitated preferentially due to the higher chemical affinity of Ti and C atoms and lower Gibbs free energy of TiC formation. The dispersed TiC blocks presented strong fine grain strengthening and precipitation strengthening effects. Compared with DWed joint, the strength of SiCp/2024Al joint with TiB2/2024Al filler increased to 268 MPa, approximately 72.9% of that of base metal (BM).

Study on microstructure and properties of laser-clad Fe-based (Ti, V)C composite coatings

An in-situ autogenous ceramic phase reinforced laser cladding containing vanadium (V) and titanium (Ti) has been developed for improving the surface properties of rolls in the field of iron and steel metallurgy. In this study, the effect of the V and Ti content on the microstructure, hardness, shear property, and wear behavior in high temperatures of the laser cladding was evaluated. The results showed that with the increase of the V and Ti content, TiC and VC precipitated with a growing volume in the grain and grain boundaries, and their shapes gradually changed from circle to polygon. In addition, the grain size was smaller and smaller while the microhardness was higher and higher. The precipitation of TiC and VC ceramic phase has a bad effect on the shear properties of the cladding layer due to the weak bonding strength between large-size carbide and matrix. The cladding layer with 5 % content of V and Ti showed better wear-resisting properties which are >21 times and twice higher than that without V and Ti at room temperature and 600 °C, respectively. Indicating that the size of the ceramic phase has the most important effect on the wear property because the ceramic particles with larger sizes were easy to dislodge and cause scratches to the specimen.

Assessment of improved tribocorrosion in novel in-situ Ti and β Ti–40Nb alloy matrix composites produced with NbC addition during arc-melting for biomedical applications

Nontoxic and nonallergenic β-type Ti–Nb alloys are considered attractive metallic materials for long-term bone implant applications. However, metallic implants present poor wear resistance, and the degradation process can be intensified with the friction occurring in corrosive body fluids, such as joint prostheses. The present study aimed to improve the tribological behavior of Ti–Nb alloys by adding hard reinforcement. The applied strategy is based on in-situ conditions, in which the reinforcing phase can be synthesized during the fabrication of the composite. Thus, a strong interfacial bond can be achieved due to the high chemical compatibility between the matrix and the reinforcement. Therefore, two different in-situ composites were developed by adding NbC powder to Ti and β Ti–40Nb alloy during the arc-melting process. As-cast samples of Ti and β Ti–40Nb alloy without NbC were used as the control groups. Structural characterization was performed, along with corrosion and tribocorrosion tests in a phosphate-buffered solution at body temperature. Results demonstrated that in-situ reactions occurred during the arc-melting process and promoted the precipitation of TiC as the reinforcing phase surrounded by α Ti phase (when NbC was added to Ti), and by β Ti–Nb phase (when NbC was added to Ti–40Nb). Finally, both produced composites showed improved tribocorrosion behaviors with wear volumes less than half of that recorded by the unreinforced Ti and β Ti–40Nb alloy. Thus, this study presents promising alternatives for wear-resistant biomedical applications.

Production of a Non-Stoichiometric Nb-Ti HSLA Steel by Thermomechanical Processing on a Steckel Mill

Obtaining high levels of mechanical properties in steels is directly linked to the use of special mechanical forming processes and the addition of alloying elements during their manufacture. This work presents a study of a hot-rolled steel strip produced to achieve a yield strength above 600 MPa, using a niobium microalloyed HSLA steel with non-stoichiometric titanium (titanium/nitrogen ratio above 3.42), and rolled on a Steckel mill. A major challenge imposed by rolling on a Steckel mill is that the process is reversible, resulting in long interpass times, which facilitates recrystallization and grain growth kinetics. Rolling parameters whose aim was to obtain the maximum degree of microstructural refinement were determined by considering microstructural evolution simulations performed in MicroSim-SM® software and studying the alloy through physical simulations to obtain critical temperatures and determine the CCT diagram. Four ranges of coiling temperatures (525–550 °C/550–600 °C/600–650 ° C/650–700 °C) were applied to evaluate their impact on microstructure, precipitation hardening, and mechanical properties, with the results showing a very refined microstructure, with the highest yield strength observed at coiling temperatures of 600–650 °C. This scenario is explained by the maximum precipitation of titanium carbide observed at this temperature, leading to a greater contribution of precipitation hardening provided by the presence of a large volume of small-sized precipitates. This paper shows that the combination of optimized industrial parameters based on metallurgical mechanisms and advanced modeling techniques opens up new possibilities for a robust production of high-strength steels using a Steckel mill. The microstructural base for a stable production of high-strength hot-rolled products relies on a consistent grain size refinement provided mainly by the effect of Nb together with appropriate rolling parameters, and the fine precipitation of TiC during cooling provides the additional increase to reach the requested yield strength values.

Three-Body Abrasive Wear-Resistance Characteristics of a 27Cr-Based 3V-3Mo-3W-3Co Multicomponent White Cast Iron with Different Ti Additions

A multicomponent white cast iron containing 5 wt.% each of Cr, V, Mo, W, and Co (MWCI) is known to have excellent wear-resistance properties due to the precipitation of some very hard carbides, such as MC, M2C, and M7C3. However, it seems possible to improve the wear resistance of MWCI by increasing the carbide volume fraction (CVF). Thus, 27 wt.% Cr based on 3 wt.% each of V, W, Mo, and Co was simultaneously added into the white cast iron. To avoid the tendency of carbides to crack due to high M7C3 precipitation levels, titanium (0–2 wt.% Ti) was also added. A rubber wheel abrasive machine test according to the ASTM G65 standard with two different abrasive particle sizes (average: 75 and 300 μm) was used to evaluate the wear characteristics of the alloy. The results show that the wear resistance of these new alloys (0Ti, 1Ti, and 2Ti) is lower than that of MWCI in small silica sand, owing to the lower hardness. However, a different condition is present in large silica sand, for which the abrasive wear resistance of MWCI is lower than that of the 0Ti and 1Ti specimens. In addition, TiC precipitation effectively refined the size of M7C3 carbides and reduced their cracking tendency. Thus, the wear resistance of 1Ti is comparable to that of 0Ti, although it has a lower hardness factor. However, the wear resistance of the alloy significantly decreased following the addition of Ti by more than 1 wt.% due to the lower hardness and CVF. Therefore, it can be said that the abrasive wear characteristics of the alloy are not only affected by the hardness, but also by the micro-structural constituents (type, size, and volume fraction of carbides) and silica sand size.

A strategy combining machine learning and physical metallurgical principles to predict mechanical properties for hot rolled Ti micro-alloyed steels

Determining the exact relationships between rolling parameters and mechanical properties is important to predict and even control the mechanical properties of hot rolled Ti micro-alloyed steel products. In this paper, two data dimension reduction strategies, respectively guided by physical metallurgical (PM) principles and data-driven (DD) strategy were proposed to preprocess the high dimensional steel composition and rolling parameters, and a comprehensive set of machine learning (ML) models was developed to predict yield strength (YS) and elongation (EL) combined with the reconstructed inputs. The artificial neural network (ANN) with the inputs including dislocation density, fractions, and sizes of ferrite and TiC precipitate transferred by PM principle outperformed that with the inputs extracted low variance feature elimination (LVFE) and autoencoder (AE) algorithms. Based on the proposed model, the effects of alloying elements, rolling temperatures, and microstructures on mechanical properties were comprehensively analyzed. Also, the variations of microstructures and mechanical properties over the strip length were discussed, which were consistent with the measured results. • PM-guided dimension reduction was proposed to transfer rolling parameters to microstructures. • The dimension reduction guided by PM performed better than that guided by DD methods with LVFE and AE. • The predicted effects of process and microstructures on YS and EL were consistent with experiments. • The predicted variations of YS and EL over strip length were consistent with measured results.