Ferrite Matrix Research Articles

Microstructural and Hall–Petch Analysis of Additively Manufactured Ferritic Alloy Using 2507 Duplex Stainless Steel Powder

The powder bed fusion–laser beam (PBF-LB) process, a method of additive manufacturing (AM), was used to print duplex stainless steel (DSS) using commercial-grade 2507 powders. While conventionally processed DSS has a two-phase microstructure consisting of 50% austenite and 50% ferrite, the PBF-LB-printed 2507 alloy was nearly 100% ferrite. Optimal processing conditions that minimized porosity were determined to be 290 W laser power and 1000 mm/s scan speed, and grain size, texture, and phases were characterized as a function of laser power and scan speed. Grain size increased with increasing laser power but decreased with increasing scan speed. A <100> texture diminished with increasing scan speed from 1000 mm/s to 1400 mm/s. No austenite phase was detected. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) characterization revealed nanoscale chromium nitride precipitates in the ferritic matrix (incoherent hexagonal close-packed (HCP) precipitates at grain boundaries and coherent body-centered cubic (BCC) precipitates within the grains) and a high density of tangled dislocations. Tensile tests of as-printed alloys showed a yield strength of 570 MPa, an ultimate tensile strength of 756 MPa, and an elongation to failure of 10%. The tensile properties were analyzed based on the observed microstructure considering grain size, nanoscale precipitates, and the high density of dislocations.

Evolution from clusters to precipitates in niobium-micro-alloyed ferritic steel: A combined in situ scanning transmission electron microscopy and atomistic study

Nano-sized carbides are essential for strengthening steel. In this study, we examined the evolution of metal carbide (M-C) clusters (M = Ti and Nb) into MC precipitates within a ferrite matrix through a reverse Bain transformation at the atomic level using the first-principles method. Through in situ transmission electron microscopy, the evolution of the Nb-C cluster into an NbC precipitate was observed for the first time. The Nb-C cluster was confirmed to maintain coherence with a limited carbon content, assuming a disc-shaped form that grew in a specific direction owing to misfit strain upon reaching a critical size. Interface dislocations were also formed. The NbC precipitate formation was subsequently completed through additional carbon diffusion. The findings of this study indicate that MC precipitation in a ferrite matrix can be attained through coherent cluster evolution with a specific carbon content.

Microstructure evolution and tribo-oxidation induced by friction and wear of cast iron brake discs

Braking discs play an important role for the safety of vehicles whereas severe frictional contacts in repeated braking operations result in thermal and tribological failures. This paper reports comprehensive surface and subsurface analyses of a used grey cast iron braking disc to investigate its failure mechanisms as well as related microstructure evolution. Thermal cracking, spalling wear and tribo-oxidation have been found to contribute to the wear failure. The flake-type graphite of the grey cast iron triggered propagation and internal oxidation of the metallic matrix. In a depth of 3 mm beneath the rubbing surface, extensive microstructure evolution occurred by severe plastic deformation of the ferritic matrix, nodularisation and partial dissolution of the lamellar carbides, and internal oxidation. The microstructure evolution resulted in decreased surface hardness to HV0.3 247 as compared to HV0.3 284 of the bulk cast iron.

Influence of Cooling Rate and Alloying by “Cr, V, and Ni” on Microstructure and High-Temperature Wear Behavior of SiMo Ductile Iron

AbstractSiMo ductile irons, typical heat-resistant materials, are subjected to varied wear environments during operation in high-temperature applications. SiMo ductile iron castings of different thicknesses were cast in investment and greensand molds, achieving a wide range of cooling rates. The present work aims to investigate the effect of the cooling rate and alloying elements (Cr, V, and Ni) on the microstructure and the abrasive wear behavior of these grades of SiMo ductile iron at high-temperature 700 °C under different loads. Thermodynamic calculations were used to propose the phase diagrams, critical transformation temperatures, and phase volume fractions in all SiMo alloys by using the Thermo-Calc software then verified by and Differential Scanning Calorimetry (DSC). The microstructure of unalloyed SiMo ductile cast iron consists of graphite nodules and carbides embedded in the precipitates at the grain boundary regions in a ferrite matrix. The alloyed SiMo microstructure contains nodular graphite and the carbides promoted by the alloying elements (Cr and V). The alloyed SiMo alloys exhibit higher wear resistance than unalloyed ones. These wear results support that the microstructure plays a chief role in wear loss. The combination of M6C, VC, and M7C3 carbides embedded in a ferrite-pearlite matrix (alloyed SiMo) seems to be more resistant to wear than the ferritic matrix with lamellar pearlite and eutectic M6C carbides (unalloyed SiMo).

Role of Cerium on the Intricacies of Deformed State and Softening Mechanisms of Low‐Carbon Steels

The present study investigates the softening kinetics of two cerium (Ce)‐modified steels after 60% cold rolling and annealing at 600 °C for 2–16 h. Cold rolling accumulates substantial strain in the ferritic matrix of low Ce (LCe) steel (0.03 wt% Ce) compared to high Ce (HCe) steel (0.6 wt% Ce). The acicular ferrite and Fe3C partition the imposed strain preferentially inside the ferrite matrix of LCe sample. Contrarily, a homogenous strain distribution in HCe sample is promoted by soft Ce2O3 particles embedded in ferrite. Both the steels achieve partial recovery and recrystallization even after 16 h of annealing. LCe steel experiences a softening fraction of ≈28 vol% after 16 h, inferior to HCe steel (≈34 vol%). During initial stage of annealing, nucleation of strain‐free grains are observed in LCe sample due to availability of grain and interphase boundaries. Subsequently, recrystallization kinetics get delayed because of the pinning effect exerted by fine CeO2 and Fe3C particles. In HCe samples, the early stage of ferrite nucleation is hindered by the segregation of Ce at grain boundaries. However, at a later stage, the recrystallization kinetics are accelerated owing to the ineffective pinning of dislocations and boundaries by coarse Ce2Fe17 and Ce2C3 particles.

Investigations on dry sliding wear and friction behaviour of alloy steel obtained by powder metallurgy

The present work investigates the dry sliding wear and friction behaviour of an alloy steel developed through powder metallurgy. Prealloyed Atomet 4601 powder was thoroughly mixed with elemental powders of 0.35 C, 0.25 Mn, 0.1 Si and 0.9 Cr (in wt. %) to create this alloy steel, whose composition closely matches EN24 (AISI 4340) wrought steel. The dry sliding friction and wear test experiments were performed in a pin-on-disc tribometer. For the various cases considered in friction and wear tests, the wear rate is lowest (0.32 × 10–3 mm3/m) at 15 N and 1.77 m/s and highest (1.02 × 10–3 mm3/m) under severe conditions of 32.5 N and 2.83 m/s. The coefficient of friction is highest (0.673) at 15 N and 0.71 m/s and lowest (0.1311) at 32.5 N and 2.83 m/s. Subsequently, regression models are developed based on experimental results and the interaction effect of load and speed on the response parameters are plotted using MATLAB. An R2 value of 0.98 indicates a strong correlation between the response and the input variables. X-ray diffraction (XRD) and optical and scanning electron microscope (SEM) analyses of the most worn specimens revealed carbides and oxides in the ferrite grain matrix, with adhesive, abrasive and oxidative wear being the primary mechanisms observed.

Influence of Spheroidized Cementite on Ferritic Matrix Boundary Characteristics and Mechanical Behavior in Commercial Carbon Steels

Influence of Spheroidized Cementite on Ferritic Matrix Boundary Characteristics and Mechanical Behavior in Commercial Carbon Steels

Influence of δ ferrite on impact toughness of M50NiL bearing steel

M50NiL bearing steel is widely used in the aerospace field because of its excellent properties. δ ferrite would affect the impact toughness of steel, but there is little research on it in M50NiL bearing steel. In this study, the effect of the δ-ferrite content on the impact toughness of M50NiL bearing steel and the corresponding mechanism were investigated through microstructure characterization and mechanical property testing. The results indicated that the impact toughness of the steel at room temperature, as well as the energy needed for crack initiation and crack propagation, improved with δ-ferrite content reduction. This suggests that the presence of δ ferrite in M50NiL steel is detrimental to its impact toughness and that reducing the δ-ferrite content can suppress crack initiation and crack propagation, significantly improving the impact toughness. The adverse effect of δ ferrite on impact toughness is mainly attributed to the fact that δ ferrite is prone to crack initiation and cannot effectively prevent crack propagation due to its low strength and shear resistance. Additionally, the difference in microstructure and strength between the δ ferrite and martensite matrix may weaken the interface, which is conducive to crack initiation and rapid propagation.

Improved resistance to hydrogen embrittlement in the nugget zone of friction stir welded medium Mn steel via post-welding annealing

In this work, medium-Mn steel was friction stir welded and then intercritically annealed. Hydrogen diffusion and hydrogen embrittlement (HE) behavior in the nugget zone (NZ) were investigated. The as-welded NZ exhibited the highest HE index (HEI) of 79.2%, and hydrogen‑induced cracks propagated along the grain boundary, probably depending on grain boundary decohesion caused by H segregation. However, this condition was improved by post-welding annealing since fine lath reversed austenite, acting as a strong hydrogen trap, was introduced into the ferritic matrix, inhibiting the segregation of H to grain boundaries. Ultimately, the lowest HEI of 10.7% was obtained in the as-annealed NZ.

Single-pulse MIG welded Perform 700 steel joints with various welding parameters

In this work, Perform 700 steel sheets with 5-mm thickness were welded with single pulse MIG welding method with different welding currents and welding speeds. The welded specimens were subjected to tensile tests, hardness measurements and microstructural observations. According to the results, the heat input has an important role in tensile strength of the joint. The maximum tensile strength was obtained as 594.75 MPa at 140A welding current and 450 mm/min welding speed. The tensile specimens were always separated between fusion zone and heat affected zone. The heat affected zones have exhibited tempered martensitic structure. The tempering effect have increased the sizes of the martensitic structure; therefore, the hardness was considerably increased. However, the fusion zone, which was consisted of bainitic structure inside the ferrite matrix, was exhibited soft and ductile behavior. The boundary of soft fusion zone and hard heat affected zone formed the weakest point through the joint.

EFFECT OF STEEL’S THERMAL CONDITION ON THE TRANSFORMATION TEMPERATURES OF TWO HOT-WORK TOOL STEELS WITH INCREASED THERMAL CONDUCTIVITY

The aim of our study was to investigate how different thermal conditions affect the transformation temperatures of two hot-work steels with high thermal conductivity. We focused on two conditions: soft annealing, and quenching and tempering. Soft annealing results in a ferritic steel matrix with spherical carbides, while quenching and tempering result in a fully hardened and tempered martensitic matrix with secondary and tempering carbides. We analysed samples using a simultaneous thermal analysis (STA) and differential scanning calorimetry (DSC) to determine the transformation temperatures. Controlled heating and cooling allowed us to observe the energy changes associated with the phase transformations. The equilibrium temperatures were calculated using the CALPHAD method. Our study investigated the influence of thermal conditions on different transformation temperatures, including solidus/liquidus temperatures, austenite solid transformation temperatures (A1 and A3), austenite solidification temperatures and bainite and/or martensite transformation temperatures. A DSC analysis was used to quantitatively measure the transformation temperatures and energy absorption during the endothermic processes (austenite solid transformation and melting) and to study the energy release during the exothermic processes (solidification and transformation). The results showed that soft annealing reduced the solidification interval and the solidus temperature, while energy absorption increased during melting. Conversely, quenching and tempering reduced the austenite solid transformation temperatures and energy release during solidification, including δ-ferrite solidification.

Research on the influence mechanism of titanium on corrosion resistance of ferritic stainless steel in aluminum solution

The immersion corrosion test of ferritic stainless steel with different titanium content was carried out in molten aluminum at 750 °C. Scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were used to observe the microstructure and basic morphology of ferritic stainless steel with different titanium content, and the corrosion cross-section morphology after corrosion was observed. The types and contents of carbides in steel were analyzed by electrolytic extraction device and X-ray diffractometer (XRD), and the influence mechanism of Ti element on the corrosion resistance of experimental steel was studied. The test results show that the corrosion resistance of the test steel is significantly improved by adding 0.8%Ti. At this time, the microstructure of the test steel is ferrite matrix and carbides dispersed in the grain, including TiC, TiN and Cr23C6. Carbide dispersed in the grain and Fe–Ti intermetallic compound formed at the intersection of two intermetallic compound layers (IMC1 and IMC2) during the corrosion of molten aluminum simultaneously hindered the diffusion of Al atoms and improved the corrosion resistance of the tested steel.

Correction: Tumarkin et al. Composite Metamaterial: Ferrite Matrix with Ferroelectric Inclusions. Coatings 2023, 13, 117

The authors were not aware of errors made in the proofreading phase, and, hence, wish to make the following corrections to this paper [...]

Assessment of structure-property relationships at the micrometer length scale in dual phase steels by electron microscopy and nanoindentation

This work presents a correlative investigation using nanoindentation and electron microscopy to characterize Advanced High Strength Steels (AHSS) that consist of a ferrite matrix along with a strengthening secondary phase/constituent such as pearlite, bainite and martensite. DP600 grade steel was hot rolled above the austenite non-recrystallization temperature (TnR) followed by coiling at different transformation temperatures to obtain ferrite-pearlite, ferrite-bainite and ferrite-martensite microstructures with identical nominal carbon content. Unlike the macroscale mechanical testing on dual phase steels which provides a composite response, in this work the variation in local mechanical properties as a function of processing was captured by high speed nanoindentation mapping at the length scale of the microstructure. Excellent agreement between the microstructure and hardness was observed for different dual phase microstructures (ferrite-pearlite (FP), ferrite-bainite (FB) and ferrite-martensite (FM)). High speed nanoindentation mapping data was deconvoluted using a clustering algorithm to obtain the hardness of the constituents. The hardness of ferrite in FP, FB and FM samples was found to be 3.26 GPa, 3.33 GPa and 4 GPa, respectively and the corresponding second phase / constituent was found to be 4.6 GPa, 4.43 GPa and 4.93 GPa, respectively. In spite of having identical nominal composition, the three different dual phase microstructures show differences in area fraction and hardness of ferrite and also the secondary constituents. These experimental observations are reconciled based on processing conditions and the length scale of the microstructure.

Effect of Cr on the phase transformation and interphase nanoprecipitation behaviours of high-strength microalloyed steels

In this work, the microstructures and mechanical properties of interphase precipitation strengthening microalloyed steels were investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy, atom probe tomography and tensile tests. Microstructural analysis shows that the studied steels coiled at 620 °C possess a microstructure consisting of a single-phase polygonal ferrite matrix and disc-liked interphase-precipitated carbides. Tensile test results show that with the addition of Cr, the yield strength increased from 644 MPa to 728 MPa and 748 MPa for 0Cr, 0.1Cr and 0.2Cr steels, respectively, without a substantial decrease of ductility. Thermodynamics analysis indicates that the addition of Cr increases the driving force of γ → α transformation, which was responsible for grain refinement and decrease of sheet spacing of nanoprecipitates. The strengthening contributions from solid solution, dislocations, grain boundaries and interphase precipitation were calculated, and the results indicate that the decrease of interphase-precipitated carbides sheet spacing and the refinement of grain size were responsible for the strength enhancement of Cr microalloyed steel.

Grain refinement, strain hardening and fracture in thermomechanically processed ultra-strong microalloyed steel

The current research in microalloyed steel has witnessed a continuous improvement in strength-ductility combination. The intention is to reduce the gauge thickness of automotive body sheets without compromising formability, thereby enhancing fuel efficiency. In this light, the present work has devised a novel thermomechanical controlled processing (TMCP) for a low-carbon automotive-grade (Nb+V)-stabilized microalloyed steel. The microstructural modification by TMCP has resulted in an excellent combination of yield strength (782 MPa), ultimate tensile strength (1059 MPa) and ductility (21%). The critical factor translating the investigated alloy towards advanced high strength steel is the ferrite grain refinement by dynamic recrystallization (DRX) and deformation-induced ferrite transformation (DIFT). The DRX predominated during TMCP at the intercritical temperature domain of 800–700 °C, imparting the average recrystallized grain size of 2 ± 0.8 µm. In contrast, the DIFT starts well above the upper intercritical temperature regime (i.e., around 810 °C), but it contributes less to the ferrite grain refinement. The thermodynamic reason has been analyzed keeping in view the changes in grain boundary energy and dislocation energy. The plastic deformation additionally leads to precipitation of cubic (Nb, V)-rich carbides in ferrite. The incoherency, coarse precipitate size (70–80 nm), and a poor phase fraction (⁓0.5%) are the key factors that the strengthening mechanism is governed by ferrite grain refinement majorly, followed by dislocation and solid solution strengthening. The segregation of Mn, Nb and S leads to MnS-type inclusion formation, which acts as potential sites for crack initiation due to plasticity mismatch with ferrite matrix during the tensile deformation.

Pre-strain and hydrogen charging effect on the plastic and fracture behavior of quenching and partitioning (Q&P) steel

This study investigates the fracture behavior of plastically deformed quenching and partitioning (Q&P) steel under hydrogen conditions. The experimental results from slow strain rate tensile (SSRT) tests reveal a considerable decrease in elongation with increase of hydrogen traps induced by pre-strains. The effect of pre-strain on hydrogen susceptibility is analyzed through fractography and microstructure measurements. The relative reduction of area decreased from 0.389 at 0 % pre-strain to 0.181 at 12 % pre-strain with hydrogen. For hydrogen-free case, fracture surfaces show typical ductile fracture with shallow dimples by micro-void coalescence induced by phase transformation. For hydrogen-charged specimens, the fractography indicates quasi-cleavage and transgranular fracture at specimen center and brittle-like fracture can be analyzed by the hydrogen-enhanced decohesion. Additionally, the brittle fracture area is enlarged with pre-strain. The mixed fracture between the edge and center of cross-section can be explained using finite element modeling, which calculates the distributions of dislocation density and flux, hydrostatic stress during SSRT at different pre-strains. As an effect of pre-strain in the hydrogen-charged Q&P steel, micro-cracks initiate at transformed martensite with low level of pre-strain, whereas their propagation is blunted at ferrite interface. For specimens with pre-strains exceeding 8 %, the cracks initiate predominantly at the martensite, which propagate through deformed ferrite matrix with high dislocations and trapped hydrogens. Our findings shed light on a new metallurgical design for improving the resistance to hydrogen embrittlement in Q&P steel when pre-strain, hydrogen transport, and phase transformation are properly controlled.

Unusual plate-type iron-carbonitrides development in nitrocarburized Fe-4 at.% V alloy

The influence of substitutionally dissolved V in ferritic Fe-4 at.% V alloy, on the structure and morphology of iron-carbonitrides ε-Fe3(N, C)1+x and γ'-Fe4(N, C)1-y was investigated upon salt bath nitrocarburizing. An unusual plate-type morphology of γʹ and ε carbonitrides development was evidenced during nitrocarburizing of Fe-V alloy as against to the usual layer-type growth of γʹ and ε nitrides reported for nitrided Fe-V alloys. The ε phase developed first along ferrite matrix grain boundaries, followed by its formation as plates on the plates of γʹ within the grains of ferrite matrix and finally as a layer at the surface. In contrast to ε, γʹ has developed only as plates within the ferrite matrix grains either with Kurdjumov-Sachs or Pitsch orientation relationship. Initially the inwardly diffusing N gets consumed for the development of VN precipitates in the ferrite matrix while C gets enriched at the ferrite-matrix grain boundaries leading to the development of ε carbonitride. Once all the V precipitates as VN, the development of γʹ occurs as plates within the grains and upon further increase in the N content lead to the development of ε within grains. This demonstrates that as a consequence of drastically different solubility and diffusivity of C and N in ferrite, ε and γʹ phases can lead complex microstructural evolution upon nitrocarburizing of Iron-based alloys.

Comparison of structural, optical, electrical and magnetic properties between Ni0.5Co0.5Gd0.005Tb0.005Fe1.99O4 and Ni0.5Co0.5Gd0.0033Tb0.0033Dy0.0033Fe1.99O4

In this work, rare-earth (RE) ions, specifically Gd, Tb, and Dy, were simultaneously doped into a nickel cobalt ferrite (Ni0.5Co0.5Fe2O4) matrix to compare the enhancement of its electrical, magnetic, and optical properties depending on the number of distinct RE-ions in the matrix. Two compositions having distinct number of RE-ions that is NCR1 (Gd0.005 and Tb0.005) and NCR2 (Gd0.0033, Tb0.0033, and Dy0.0033) at Fe-site of the matrix, were prepared using the sol-gel technique. Both compositions exhibited the spinel phase according to the studies X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. Microstructure observed from micrographs revealed that NCR2 had a relatively porous structure and larger grain size compared to NCR1. This suggests that the different doping compositions can influence the microstructure of the material, which can impact its properties. An increase in the Curie temperature (the temperature at which a material loses its ferromagnetic properties) was noted for NCR2, indicating improved magnetic behavior. An improvement in magnetostriction behavior for NCR2 implies that it can be used in applications where precise control of shape or mechanical properties in a magnetic field is required. The enhanced properties in NCR2 were attributed to the multicity of impurity doping (Gd, Tb, Dy), which led to structural changes within the material.

Influence of hydrogen on Kurdjumov-Sachs interfacial structure of M23C6/ferritic matrix at high temperatures

Secondary phase thermal stability and strengthening are strongly influenced by the interface structure between the secondary phase and the matrix. The influence of hydrogen on the interfacial structure of (Fe,Cr)23C6 carbides in ferritic matrix at high temperatures is systematically studied. The incoherent interface between (Fe,Cr)23C6 and ferrite matrix acts as a hydrogen trap region at high temperatures. Moreover, the hydrogen at high temperatures does not change the morphological features of (Fe,Cr)23C6 in the ferritic matrix. (Fe,Cr)23C6 obeys the Kurdjumov-Sachs orientation relationship with the ferritic matrix. Hydrogen at high temperatures decreases the mismatch between (Fe,Cr)23C6 and ferrite matrix interface from 7.65 % to 4.63 %. Furthermore, the (Fe,Cr)23C6 interface induced by hydrogen at high temperatures acts as a dislocation emission source. The decrease in interfacial misfit caused by hydrogen at high temperatures is the reason for (Fe,Cr)23C6 to maintain thermal stability and act as a dislocation emission source under a high-temperature hydrogen atmosphere.