Ferrite Precipitation Research Articles

Study on Characterization of Phase Transition in Continuous Cooling of Carbon Steel Using In Situ Thermovoltage Measurement

In this paper, a self-designed and enhanced thermovoltage measuring device was built to capture thermovoltage curves of 45 steel during continuous cooling. The phase zones of the thermovoltage curve were interpreted based on the Engel–Brewer electron theory and Fe-Fe3C phase diagram. The results show that the curve was stratified into three homogeneous phase zones and two-phase transition zones as follows: Zone Ι: single-phase austenite (A) zone; Zone III: austenite and ferrite (A+F) homogeneous phase zone; Zone V: ferrite and pearlite (P+F) homogeneous phase zone; Zone II: austenite to ferrite (A-F) phase transition zone; and Zone IV: austenite to pearlite (A-P) phase transition zone. Notably, the deflection point marked the transition temperature, which indicates that the thermovoltage curve can quantitatively characterize phase formation and transformation, as well as the phase transformation process. Furthermore, the sample was quenched at the measured ferrite phase transition temperature. Microstructure observations, electron probe microanalyzer (EPMA) and microhardness measurements corroborated our findings. Specifically, our experiments reveal ferrite precipitation first from the cold end at the phase transition temperature, leading to increased carbon content in adjacent austenite. The results of this study achieved the in situ characterization of bulk transformations during the materials heat treatment process, which expands the author’s research work conducted previously.

Study on Microstructure and Properties of Cold Metal Transfer and Pulse Hybrid Welded Super Duplex Stainless Steel

The investigation focuses on the microstructure, impact toughness, and pitting corrosion resistance of cold metal transfer and pulse hybrid welded joints of unified numbering system (UNS) S32750 duplex stainless steel. The results show that the filler pass exhibits the highest austenite ratio (47.9%), whereas the heat‐affected zone (HAZ) shows the lowest (32.3%). Notably, secondary austenite (γ2) is present in both the backing pass and HAZ, but conspicuously absent in the filler pass, indicating that reheating from subsequent weld pass is a prerequisite for the precipitation of γ2. Additionally, chromium nitride (Cr2N) also precipitates in the HAZ and backing pass. Comparative analysis with the weld metal (WM) and base metal (BM) indicates that the HAZ displays lower impact toughness, primarily attributing to imbalanced phase ratio, coarse ferrite grains and the brittle Cr2N. Owing to the lower austenite content and Cr2N precipitation in the backing pass, its toughness (122.6 J cm−2) is found to be inferior to that of the filler pass (130.1 J cm−2). Furthermore, the HAZ with a lower critical pitting temperature compared to the WM (79.1 °C) and BM (87 °C), and exhibits the worst pitting corrosion resistance due to the abundant precipitation of secondary phases and excessive ferrite with low pitting resistance equivalent number.

Mechanism of Crack Propagation during Hot‐Rolling Process of a Medium‐Carbon 40Cr Alloy Steel

In this work, the mechanism of crack propagation during hot‐rolling process of a typical medium‐carbon 40Cr alloy steel is investigated by cracks characterization, thermodynamic calculation, and confocal laser scanning microscopy (CLSM). The depth of cracks is about 2.5 mm and its length along with rolling direction can even reach 2000–3000 mm. Thermodynamic calculations show that the oxide phases including MnSiO3 and MnCr2O4 can generate when the oxygen content is 0.3–1.0 wt%, suggesting that low oxygen is beneficial to the selective oxidation of Si, Mn, and Cr elements from the medium‐carbon low alloy. Furthermore, in situ experiment by CLSM indicates that the submicron Cr–Mn–Si–O particles can refine austenite grains. In addition, the contents of chain proeutectoid ferrite in the steel containing Cr–Mn–Si oxides increase by 6.3% and 12.0% at the lower cooling rates of 5 and 10 °C min−1, respectively, comparing with that of no‐oxide particles steel. The submicron Cr–Mn–Si–O particles can refine austenite grains, which induces the precipitation of chain proeutectoid ferrite. Thus, the serious surface cracks propagate along the chain proeutectoid ferrite with the submicron Cr–Mn–Si–O particles during the hot‐rolling process.

Ferrite precipitation in quaternary Fe–C–X1–X2 systems using high-throughput approaches

This study investigates the effect of composition on ferrite growth kinetics in quaternary Fe–C–X1–X2 systems (X: Ni, Cr, Mo) using a high-throughput methodology. This study provides the largest dataset to date on ferrite growth kinetics in multi-component steels, offering novel insight into the behavior of these complex systems. To this end, high-energy X-ray diffraction is utilized to gather kinetic data in situ along composition gradients, leading to the measurement of phase transformation kinetics maps in compositional space. The obtained data is compared to predictions from various models describing ferrite growth kinetics in low-alloy steels. The modified "three-jump" solute drag model is shown to describe best the ferrite growth kinetics in these quaternary systems, without the need for additional calibration or fitting parameters. The success of this model is attributed to its consideration of individual solute interactions with the interface and inter-elemental interactions. The findings of this study provide valuable insight for robust modeling of phase transformations and microstructural evolution in multi-component steels, a critical tool in accelerating alloy optimization and in enhancing process control.

Influence of Cooling Rate on Solidification Process Ce-High Mo Austenite Stainless Steel: Nucleation, Growth, and Microstructure Evolution

Experiments were carried out to determine the effect of cooling rate on the nucleation, growth and microstructure evolution during the solidification process in Ce containing S31254 high Mo austenite stainless steel (HMASS). In situ observations and in situ quenching tests indicate that the Ce effects in this steel are to refine the equiaxed grain and change in the secondary phase from σ to δ, but are mainly suitable for the medium and low cooling rate. The high cooling rate is highly beneficial for austenite nucleation and significantly influence the primary austenite grain growth behavior. The growth velocity for austenite grain is increased with the increase in cooling rate. The morphology of the primary austenite would change from a crescent shape to rod shape with the cooling rate increased from 50 °C/min to 100 °C/min. Rod-shaped grains with high nucleation densities would make primary grains easy to be combined together, which would reduce the ability of the refined grain. Furthermore, a high cooling rate could slightly improve the solute redistribution, while it significantly deteriorated the micro-segregation of Mo in a solidified structure. The main reason is that high cooling rate could worsen the kinetic condition of ferrite precipitation and postpone the precipitation reaction at the end of the solidification process.

Influence of Free Ferrite on the Mechanical Properties of High Strength Intercritical Austempered Ductile Iron

The first stage of this study investigates the precipitation of free ferrite from the austenite on fully austenitized ductile iron. Several sets of samples of low alloy ductile iron are fully austenitized and then cooled down to different temperatures and different times within the intercritical austenite-ferrite-graphite phase field. Based on these results, heat treatment cycles aimed at obtaining microstructures composed of free ferrite and ausferrite are carried out. Tensile, impact and toughness tests are performed to characterize the mechanical properties. The results show that, related to the high strength austempered ductile iron grades, the best combinations of properties were obtained from the mixed structures composed of 5% free ferrite and 95% ausferrite, resulting from the austempering at 280°C. These amounts of free ferrite allow obtaining an increase of the elongation (about 50%) and impact toughness (about 10%) while the tensile strength and fracture toughness decrease by about 1.5 and 15% respectively.

Effect of Cooling Rate on the Grain Morphology and Element Segregation Behavior of Fe-Mn-Al-C Low-Density Steel during Solidification

Mold with diameter sizes of 140 mm, 80 mm, 40 mm and 15 mm were designed to obtain the ingot of Fe-30Mn-10Al-1.1C low-density steel under different cooling rates. The influence of cooling rate on the grain morphology and elemental segregation behavior during the steel solidification process was analyzed by methods including inductively coupled plasma, scanning electron microscope and energy dispersive spectroscopy. The solidification sequence of the low-density steel was calculated by JMatPro 7.0 thermodynamic software. The results show that the microstructure of the steel is mainly austenite and contains a small amount of ferrite. The solidification order in the steel is: L → α, L → γ and α → γ, L → γ + MC. As the cooling rate increases from 1.69 °C/s to 10.28 °C/s, the ferrite phase precipitation increases by 16.7%, and the grain size decreases significantly, and in particular, the austenitic grain size decreases by 26%. With the increase in cooling rate, the microscopic segregation value of aluminum decreases approximately to 1. Additionally, the microscopic segregation of manganese showed a trend of increasing first and then decreasing. Microscopic segregation of Al and Mn can be improved significantly by increasing the cooling rate.

Microstructure, mechanical properties and corrosion behavior of 65Mn tape-steel via electromagnetic induction heating

The heat treatment of electromagnetic induction heating (EMIH) was employed on 65Mn tape-steel. Microstructure evolution of 65Mn tape-steel was systematically characterized by scanning electron microscope and electron backscatter diffraction. Then the mechanical properties of microhardness, tensile, and corrosion resistance tests were examined. After EMIH treatment, the network-like of cementite was broken. The ferrite precipitates are melted into a large number of small particles, which were attached to the matrix. The microhardness of 65Mn tape-steel treated with EMIH is lower than that of the as-received. The average microhardness values decrease gradually with the increase of duration times during the EMIH treatment. After the treatment, the ultimate tensile strength (UTS) and tensile yield strength (TYS) reduce to about 700 MPa and 600 MPa, respectively. Meanwhile, the values of the UTS and TYS can’t be affected by a further increase of alternating current (AC) values. The elongation (EL) increases with duration time increasing from 1 s to 3 s. However, the EL declines to 1.3% and 0.5% after EMIH is treated with oil/water cooling, respectively. At an electric current value of 210 A, the sample demonstrates better corrosion resistance than the other samples.

Hot Ductility Analysis and Flow Stress Prediction of (C-Mn-S-Al-Nb-V-Ti) Micro-alloyed Steel

The objective of this work is to study the hot ductility of (C-Mn-S-Al-Nb-V-Ti) micro-alloy steel of industrial production whose initial structural state is rolling stock. To simulate the thermomechanical treatments imposed we have deformed by pulling our samples after subjecting them to a solution treatment at 1200 °C and a precipitation treatment cycle before deformation. Hot deformations were carried out at temperatures from 700 °C and 1150 °C and deformation rates ranging between 10-2 s-1 and 5.10-4 s-1. The results show a decrease in hot ductility. Minimum values of hot ductility are determined at 800°C, and another decrease in hot ductility was observed at 900°C. Ferrite precipitation is observed at austenitic grain boundaries in the intercritical temperature range, causing intergranular embrittlement. Precipitation makes the hot ductility curve wider and deeper around 900°C. Hot ductility losses can explain by the presence of precipitates in the austenitic region and the presence of the two-phase structure in the intercritical region. Finally, based on experimental stress-deformation data, artificial neuron network (ANN) methods were used to predict flow stress of (C-Mn-S-Al-Nb-V-Ti) micro-alloy steel. This model is more effective in predicting flow stress and results can also be used in the mathematical simulation of hot metal formation processes.

The treatment of electroplating wastewater using an integrated approach of interior microelectrolysis and Fenton combined with recycle ferrite

Heavy metal ions in chelated forms have aroused great concerns because of their high solubility, poor biodegradation and extreme stability. In this research, an efficient strategy, interior microelectrolysis-Fenton-recycle ferrite (IM-Fenton-RF), was developed to treat simulated electroplating wastewater containing chelated copper at room temperature. The decomplexation of chelated copper was carried out by both interior microelectrolysis and Fenton reactions. IM process can not only partly degrade the complexes of chelated copper via the microelectrolysis reaction but also it produces Fe2+ ions for the Fenton reaction. After decomplexation, the IM-Fenton effluent directly flowed into the RF reactor for copper ions removal. Under optimum reaction conditions (reflux ratio = 0.37, Fe2+ concentration = 9.20 g/L at pH 10.18), 99.9% copper was removed by the IM-Fenton-RF system. The produced IM-Fenton-RF sludge is based on ferrite precipitate and has several advantages over metal hydroxides sludge. Ferrite sludge is stable owing to the stability of ferrite's crystal structure, while the toxicity characteristic leaching procedure (TCLP) test meets relevant standards. The sedimentation rate and volume of ferrite sludge were 3.86 times faster and 11.0 times lower than those of metal hydroxides sludge. Furthermore, the yielding sludge of ferrite can be recovered and utilized for the synthesis of Fe–C metallic species, the main compound of IM packing for interior microelectrolysis reaction. All these results show that a combination of IM-Fenton and RF is an effective approach to treat wastewater containing chelated copper, showing great potential for industrial applications.

Elucidation of void defects by soft reduction in medium carbon steel via EBSD and X-ray computed tomography

In this work, void formation in medium carbon ferrite-pearlite steel is investigated with soft reduction (SR) technology as regards its initiation sites and governing factors: prior austenite grain size, grain boundary ferrite (GB-α) precipitation, pearlite block size and sub-grain boundaries misorientation. The small and tightly packed pearlite colonies attached with GB-α and irregular broken cementite lamellae provide an easier path for void initiation at prior austenite grain boundary (PAGB) and pearlite colony boundary respectively. 3-dimensional void morphology and void size including porosities with different SR parameters were characterized via X-ray computed tomography (XCT). The total number of voids, their sizes, and shape complexity are increased by increasing reduction amount, and serious void defects are evident without the implementation of SR technology. The size of shrinkage void increases with increasing reduction amount, which is twice without implementation of SR technology as compared with the high reduction amount of 6 mm. The total number of voids and their sizes was less along with porosities at minimum reduction amounts of 2 mm and 4 mm, which are small enough to compensate the solidification shrinkage voids.

3D-FEM Simulation of Hot Rolling Process and Characterization of the Resultant Microstructure of a Light-Weight Mn Steel

Computational simulation has become more important in the design of thermomechanical processing since it allows the optimization of associated parameters such as temperature, stresses, strains and phase transformations. This work presents the results of the three-dimensional Finite Element Method (FEM) simulation of the hot rolling process of a medium Mn steel using DEFORM-3D software. Temperature and effective strain distribution in the surface and center of the sheet were analyzed for different rolling passes; also the change in damage factor was evaluated. According to the hot rolling simulation results, experimental hot rolling parameters were established in order to obtain the desired microstructure avoiding the presence of ferrite precipitation during the process. The microstructural characterization of the hot rolled steel was carried out using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the phases present in the steel after hot rolling are austenite and α′-martensite. Additionally, to understand the mechanical behavior, tensile tests were performed and concluded that this new steel can be catalogued in the third automotive generation.

Treatment of waste gas from electronic dismantling workshop

At present, due to China’s electronic waste treatment technology is not mature enough. In the market, a large number of electronic wastes into the household dismantling workshop and through simple, inefficient, extensive way to recycle. After the extraction of valuable resources, the remaining toxic and harmful substances are discharged at will, resulting in a high level of toxic and harmful pollutants in the air of the region. The deposition of harmful and harmful pollutants in the air also further leads to the deterioration of the local soil, water and other ecological environment, threatening the health and survival of local residents. The paper takes the exhaust gas from electronic waste dismantling process based on family workshop of Guiyu town as the experimental object. Water absorption and activated carbon adsorption were applied to treat exhaust gas. And the ferreite precipitation was used to treat the recirculated wastewater after spray system. The experiment results indicate that the lead cadmium, tin and its compounds and benzene series could be removed above 95% after water absorption and active carbon adsorption. The lead, cadmium and copper in recirculated wastewater respectively could be removed 96.69%, 79.76% and 90.82% after ferrite precipitation process.

Study on toughening mechanism of Ti on weld metal of high strength steel

The effect of Ti element on acicular ferrite microstructure of high strength steel weld was studied by scanning electron microscope(SEM), Transmission electron microscopy(TEM) and EDX spectrum analysis. The results show that Ti element content in a certain range can promote the precipitation of acicular ferrite in high strength steel weld metal. The increase of Ti content in the weld makes the Ti-rich inclusions increase, which is conducive to the formation of acicular ferrite. Charpy impact test results show that with the increase of Ti content, the impact toughness of weld metal increases first and then decreases. The tensile test results show that the tensile strength of weld metal increases and the elongation decreases with the increase of Ti content. There are high density dislocations and M-A components in acicular ferrite. M-A elements hinder the crack growth and improve the impact toughness of weld metal. When the Ti content is 0.253%, the impact energy of the weld metal is 155 J at-60 °C, and the impact toughness is the best.

The role of grain boundary ferrite evolution and thermal aging on creep cavitation of type 316H austenitic stainless steel

Abstract To understand the interaction between microstructural evolution and creep cavitation during stress relaxation at an elevated temperature, an ex-service AISI type 316H stainless steel sample containing both weld metal and heat affected zone (HAZ) from an advanced gas-cooled reactor was studied. Multiple techniques that include secondary electron microscopy, electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and plasma focused ion beam tomograph were used for microstructure and creep cavities characterisation. Although no creep cavities were observed in the weld metal, the HAZ was extensively creep cavitated. At randomly oriented grain boundaries, creep cavities are present and closely linked with M23C6 and ferrite precipitates formed during thermal aging. Less precipitation (e.g. absence of ferrite) and less creep cavitation were observed at Σ3 coincidence site lattice boundaries. During in-service aging, at random grain boundaries, M23C6 formation and growth cause the local elemental depletion of γ stabilisers and promote a phase transformation from austenite to ferrite. The crystallographic relationship between ferrite and austenite were also studied by EBSD and TEM. Ferrite precipitates formed during aging often grow into the austenite grain not expected by traditional nucleation and growth theory, likely due to physical constraints by the existing carbides at the grain boundaries. The formation and growth of creep cavities is closely associated with the M23C6 and ferrite formed on grain boundaries. This study highlights the importance of considering the effect of thermal aging in accelerating creep cavitation.

Effect of soft reduction technique on microstructure and toughness of medium carbon steel

This paper investigated the effect of soft reduction technique on microstructure evaluation and toughness of medium carbon steel. The scanning electron microscope (SEM) was used in conjunction with fracture test to identify the comparative microstructure-toughness relationship, while the morphology of grain boundary ferrite (GBF) and widsmanstatten ferrite (WF) was analyzed by electron backscatter diffraction (EBSD) at different soft reduction amounts. It was observed that the area ratio of grain boundary ferrite phases (GBF + WF) decreases with increasing the reduction amount. Both ferrite phases nucleated at the austenite grain boundary and grow into their neighbouring grain due to the different orientation relationship. At high reduction amounts the GBF holds non K-S orientation with prior austenite grain into which it grows, caused by the presence of high energy interface between the GBF and martensite matrix. This criterion restricts the formation of GBF along the prior austenite grain boundary (PAGB) and resulting in its discontinuous growth into the adjacent austenite grain. The continuous grain boundary ferrite precipitation is more detrimental as compared to the discontinuous precipitation. Furthermore, film-like retained austenite was aligned along the growth direction of widsmanstatten ferrite plates with its increased volume fraction at high reduction amounts, which manifested the improved fracture toughness.

Electron microscopy study of carbides precipitated during destabilization and tempering heat treatments of 25 wt.%Cr-0.7 wt.%Mo high chromium cast irons

The effect of a 0.7 wt.%Mo addition on the microstructure and hardness of a heat treated 25 wt.%Cr–2.4 wt.%C cast iron has been studied via comparison with a Mo free reference 25 wt.%Cr–2.4 wt.%C iron. Destabilization led to precipitation of M7C3 and M23C6 secondary carbides in the reference iron, whereas M23C6 secondary carbide was found in the iron with 0.7 wt.%Mo. Tempering resulted in additional secondary carbide precipitation and formation of ferrite. Secondary hardening was found in the iron with 0.7 wt.%Mo. For the destabilized + tempered condition the macro-hardness of the iron with 0.7 wt.%Mo addition was higher than the reference iron due to a finer and denser distribution of secondary-carbides.

Influence of microstructural evolution and localized delta ferrite number on high-cycle fatigue crack opening and propagation rate

In this research, percentages of nickel as austenizer and chromium as ferritizer, in the molten metal pool of SS304L weldments are varied to analyze the effect on the produced delta ferrites morphology and volume. The resulting localized precipitation of delta ferrite and its effect on the fatigue crack propagation rate of the material are examined in this work. The estimation of localized delta ferrite number for a particular weld zone is assessed through the development of a MATLAB code for image processing. It is observed that a reduction in the percentage of nickel in filler alloy yields randomly scattered granular ferrites in the fusion zone and equiaxed grain growing in the heat-affected zone with the development of blocky ferrites on the grain boundaries, whereas increased percentage of chromium in the filler causes the precipitation of dendritic clusters and vermicular ferrites in fusion zone and heat-affected zone of weldments, respectively. The effect of ferrite numbers and their morphology on the crack opening displacements and the corresponding fatigue crack propagation rate in different weld zones are analyzed. It is observed that the ferrite number ranging between 15 and 19 provides optimum fatigue strength for SS 304L. Paris curves are plotted from the test data, which shows that the weldment attained with filler alloy having Cr 26.60% and Ni 10.92% depicts the highest fatigue life compared to other studied weldments.

The removal of Cu(II)–EDTA chelates using green rust adsorption combined with ferrite formation process

Classical adsorbents such as activated carbon are inefficient to remove Cu(II)-EDTA in solution. Moreover, the heavy metals in the generated sludge can easily be dissolved back into solution. In this research, a novel strategy developed by coupling green rust adsorption and ferrite formation technology was proposed for Cu(II)-EDTA chelate removal. At the adsorption stage, green rust sulfate (GRME(SO42−)) showed a high adsorption efficiency of chelated copper, with a capacity of 126.41 mg g−1, compared to other classical adsorbents. During the ferrite formation stage, GRME(SO42−)-based precipitate with high moisture content and slow settling rate could be transformed into ferrite-based precipitate with low moisture content and rapid settling rate. The volume and moisture content of ferrite were 2.20 and 1.45 times lower than those of GRME(SO42−) and the sedimentation velocity of ferrite was also 1.23 times higher than that of GRME(SO42−), which strongly demonstrated the necessity of the ferrite formation process. Toxicity characteristic leaching procedure (TCLP) test results showed that the metallic copper of GRME(SO42−) sludge could be more easily dissolved back into solution than that of ferrite precipitate under weak-acid conditions, indicating the stability of ferrite. In addition, after the ferrite process, the generated sludge exhibited soft magnetism and could be quickly separated within few seconds using an external magnetic field. All these results showed that the combined green rust adsorption with ferrite formation method was an efficient, recyclable and eco-friendly method for the treatment of wastewater containing Cu(II)-EDTA.

Study of Features of Phase Precipitation Formation, Structural State, and Properties of Ferritic Class Microalloyed Low-Carbon Steels

Features of the formation of the structural state, phase precipitates, and properties for rolled product of complex V–Nb–Ti–Mo microalloyed lowcarbon steels of the ferritic class of six different compositions melted in the laboratory are studied. It is established that with low temperatures for strip winding on a coil formation of interphase and ferritic precipitates, making a considerable contribution to strength properties, is considerably limited. Steel cooling rate after rolling, equal to 20°C/sec, is insufficient for obtaining a structure of entirely block (acicular) ferrite (AF), which has better strength properties. A reduction in this leads to lowering of the AF fraction with an insignificant effect for temperature at the end of rolling. According to the results studying rolled products produced using higher values of Twi = 650°C and a cooling rate of 25°C/sec, the possibility of simultaneous formation of an AF structure and a system of nanoscale interphase and ferrite precipitates is demonstrated making it possible to increase steel strength and other service properties considerably.