Ferrite Pearlite Research Articles

Corrosion failure analysis of steel tubes operating in mining installations: Metallurgical, chemical and mechanical investigations

AbstractCorrosion of steel tubes represents a major challenge for various industries, leading to significant economic and environmental impacts, such as material losses, operational interruptions and safety risks. This study focuses on the metallurgical, chemical and mechanical characterization of corroded steel tubes operating in mining installations using metallographic analysis, X-ray diffraction (XRD), SEM-EDS studies, chemical analysis and micro-hardness measurements. The results reveal the existence of a considerable extent of corrosion, of which, the main corrosion products are magnetite – 72% and goethite – 18.1 associated with corrosion. The corroded tubes measured 0.128% carbon, against 0.23% in new tubes, indicating a loss in weight and mechanical strength properties. The observed tensile strength for the new tubes was 481 MPa while the same for the corroded tubes was to a large extent lower. Furthermore, metallographic examination indicates that indeed the structure is ferrite pearlite as to the composition. This study indicates that 304 L or 316 L stainless steels may be utilized which have better corrosion-protecting coatings thus prolonging service life and reducing maintenance activities.

Understanding the Phenomenon of High Temperature Hydrogen Attack (HTHA) Responsible for Ferrito-Pearlitic Steels Damage

This article focuses on the fine characterization of steels commonly used in the petrochemical industry damaged by the phenomenon of high temperature hydrogen attack (HTHA). The study was conducted in two steps. To begin with, a damaged 0.5-Mo pearlitic steel from the petroleum refineries, submitted to HTHA for decades, was characterized in detail using multiscale electron microscopy techniques. As part of an upstream study to better understand the onset and the growth of cavities, a brand new SA516 grade 60 low carbon–manganese steel was subsequently exposed to accelerated HTHA conditions through interrupted cycles carried out in autoclaves and then examined. Numerous cavities, plausibly filled with methane, were noticed in both materials. These cavities were mostly located at ferrite–pearlite grain boundaries along carbides and at triple grain boundaries near large carbides. The 0.5-Mo pearlitic steel showed cavities reaching significant sizes, up to 1 µm, but surprisingly no cracks were observed in the depth of the pipe. The major outcome is that 3D focused ion beam–scanning electron microscopy combined with transmission electron microscopy (TEM) analyses unveiled different natures of precipitates as well as in and nearby HTHA cavities for both 0.5-Mo and low carbon–manganese steels. Inclusions, likely AlN, but also Mo- and Cu-rich precipitates were observed in cavities of the industrial steel. These results confirmed a previous study performed on a similar industrial steel that drew a possible correlation between cavities nucleation and the intersection of transgranular inclusion-enriched plane with a grain boundary or carbides in pearlite grains (Flament in Microscopy and Microanalysis 28:1602–1604, 2022).

Contribution of EBSD for the Microstructural Study of Archaeological Iron Alloy Artefacts from the Archaeological Site of Loiola (Biscay, Northern Spain)

Iron palaeometallurgy was carried out on three artefacts, classified as nails and excavated from the archaeological site of Loiola (La Arboleda, Biscay, northern Spain), to investigate Roman manufacturing techniques. Energy Dispersive Spectroscopy (EDS) coupled with Environmental Scanning Electron Microscopy (ESEM) and micro-Raman spectroscopy were used to obtain elemental composition and structural characterization of mineral phases. Metallurgical properties and crystallographic texture were studied by combining microscopic methods such as optical microscopy (OM), Electron Backscatter Diffraction realized in environmental mode (EBSD) and measurements of local Vickers microhardness. The three artefacts had different microstructures, distinguished by a large gradient of carbon content, although important segregations (inclusions) were observed in all of them. Two pearlite-rich artefacts showed a high density of structural defects (geometrically necessary dislocations and large crystallographic orientation gradients in pearlitic ferrite, curved pearlitic cementite) resulting from a high level of plastic deformation that occurred during the manufacturing process. The third artefact consisted of pure ferrite without structural defects. This one was clearly manufactured differently from the two others, so it probably had another functionality.

Effect of surface rolling process on rolling contact fatigue behavior and failure mechanism of powder metallurgy steel

The effect of surface rolling process on the surface microstructure and rolling contact fatigue of the Fe-2Cu-0.6 C powder metallurgy steel was investigated in the present investigation. Results indicated that a densified and hardened layer with a densification depth of 330 μm and a surface hardness of 330 HV0.1 was generated in the surface layer after rolling process. Ferrite grain and pearlite lamellae became typical fibrous structures on the top surface. The microstructure of pearlite was presented by two typical features. One was that the discrete cementite plates were severely curled and wavy. The other one was that the cementite plates remained parallel to each other, but were a reticular structure at a macroscopic level. The rolling contact fatigue (RCF) test showed that the RCF life of the rolled sample was superior. The L10, L50, L63.2 life increased by 182%, 105%, 92%, respectively. Surface initiated spalling was the main fatigue failure mode. Subsurface equivalent contact stress and local equivalent stress were calculated. The results showed that surface cracks were due to the repetitive tensile stress, which caused pits. Subsurface cracks nucleated and propagated in the region where the local equivalent stress was higher than the matrix yield strength, which caused spalling as connecting with surface cracks. The surface densified layer plays an important role in improving the rolling fatigue resistance of the material.

Multiscale Finite Element Analysis of Yield-point Phenomenon in Ferrite–Pearlite Duplex Steels

Multiscale Finite Element Analysis of Yield-point Phenomenon in Ferrite–Pearlite Duplex Steels

Analysis of the influence of groove welds of oxy-acetylene welding joints on tensile strength and microstructure on steel ST 37

In this study, the authors conducted a study on the analysis of the effect of oxy-acetylene welding joints on tensile strength and microstructure in the HAZ and weld metal areas on st 37 steel plates. The results of this study indicate that the average value of the highest tensile strength value is at V groove weld with the average strength of the welded joint is 4.796 kgf/mm2. While the lowest tensile stress is on the I groove weld of 4.674 kgf/mm2. Meanwhile, from the microstructure test, it can be seen that in the HAZ area each groove. Microstructure in the HAZ area shows that the double V groove weld types are fine ferrite, coarse pearlite and martensite. In type V groove weld the structures formed are ferrite, coarse pearlite and martensite. In type I groove weld the structures formed are ferrite, grain boundary ferrite and fine pearlite. Whereas in the weld metal area, and the results of the microstructure test of the weld area on the V seam, it shows a dense microstructure arrangement, the arrangement is identical to pearlite (dark color) so that the specimen is harder.

Multiscale Finite Element Analysis of Yield-point Phenomenon in Ferrite–Pearlite Duplex Steels

Multiscale Finite Element Analysis of Yield-point Phenomenon in Ferrite–Pearlite Duplex Steels

Unlocking the Mechanisms behind Austenite Formation of Cold‐Rolled Ferrite–Martensite Dual‐Phase Steels: The Role of Ferrite Recrystallization

In this study, the austenite formation behavior is investigated for the ferrite–pearlite initial microstructure, considering the influence of ferrite recrystallization and cementite distribution. Special attention is also given to the effect of recrystallization state on cementite distribution for varied heating routes. Austenite nucleation for varied recrystallization state is elucidated in terms of activation energy evaluation and post microstructural characterization, and the austenite transformation kinetics are modeled and experimentally validated. In the uncrystallized state, austenite forms on the original pearlite colonies quickly due to the short carbon diffusion path. The high activation energy leads to the exceptionally difficult nucleation at the ferrite–cementite interface inside ferrite matrix. Once recrystallization occurs partially, priority of austenite nucleation is on those ferrite boundaries (both recrystallized and unrecrystallized boundaries) decorated by cementite. With complete recrystallization, preferential nucleation sites are found to be junctions of ferrite–cementite interface on recrystallized ferrite boundaries. Austenite transformation kinetics is well predicted by considering the varied nucleation density due to different recrystallization state, showing a good agreement with experimental data. It is demonstrated directly by experimental evidence that proceeding of recrystallization postpones the austenite transformation kinetics, while getting rid of the interference of heating rate and nucleation location.

Analyzing the Failure of a Truck's Rear Axle Shaft Requires a Thorough Investigation to Pinpoint the Root Cause of the Issue

The analysis of a failed rear axle shaft from a dumper truck involved a comprehensive investigation to ascertain the underlying cause of the failure. Visual inspection, material analysis, mechanical testing, and fracture analysis were conducted to assess the condition of the axle shaft. The axle shaft exhibited signs of fatigue failure, with the fracture surface showing fatigue striations. Microstructural analysis revealed a coarse grain structure with inclusions, indicating potential material defects. Tensile testing showed that the axle shaft had lower-than-expected mechanical properties, suggesting a possible issue with material quality or heat treatment. Based on the analysis, the root cause of the failure was determined to be a combination of material defects and fatigue loading. Types of investigation like as visual examination, chemical analysis, hardness test, tensile test, fractography and ultrasonic test, and microstructure examination. Microstructure observation of the sample indicates a normal ferrite–pearlite (lower critical point) sorbite-type structure with some spheronization seen on some portions Results indicate that the failure occurred due to a sudden load on the axle shaft, specifically at its weakest point. The shear stresses on the axle shaft were insufficient to withstand the stresses caused by the sudden loading. Based on the analysis, make recommendations for corrective actions to prevent similar failures in the future. This may include design improvements, material changes, maintenance procedures, or operational changes. This may include design improvement, material changes, maintenance procedures, and operational changes. Implement the recommended corrective actions to prevent similar failures in other axle shafts or similar components.

Effect of Cooling Rate on Sulfide Stress Cracking Resistance of a Q345 Pressure Vessel Steel Subject to Hydrogen Sulfide

As an important equipment for the separation, store, and transport of the oil and natural gas in energy industry, the pressure vessels are subjected to harsh service environments of sulfide stress cracking (SSC). In this work, the effect of the cooling rate on the SSC susceptibility of a Q345 pressure vessel steel is studied. A pronounced distinction in microstructure is presented as the cooling rate is increased from ≈1 to ≈15 °C s−1. At ≈1 °C s−1, the microstructure is consisted of polygonal‐like ferrite and distinct banded pearlite. At ≈5 °C s−1, the microstructure is consisted of polygonal‐like ferrite and faintly banded pseudo‐pearlite. At ≈15 °C s−1, the microstructure is acicular ferrite with a complete elimination of banded structure. The cooling rate decides the level of the banded structure. As the cooling rate increases, the banded structure becomes relatively slight and even disappears. Strength in sort ascending is ≈1, ≈ 5, and ≈15 °C s−1. The SSC failure happens at ≈1 and ≈5 °C s−1, while does not happen at ≈15 °C s−1. The strength is not the only dominant factor responsible for the SSC failure. The SSC is preferentially generated at the banded structure. The elimination of the banded structure is necessary to improve the SSC resistance of the Q345 pressure vessel steel.

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.

Jointing Achievement and Performance Evaluation of Bogie Crossmember Ring Joint Welded via Inertia Friction Welding.

As a major load-bearing component of trains, the weld quality of the bogie beam is critical to the safety of railway operations. This study specifically investigates the inertia friction welding process of S355 bogie crosshead tubes, with the aim of improving the weld quality and achieving one-time formation of the crosshead tube and tube seat. The microstructural features and mechanical properties of S355 inertia-welded joints were also compared with the base metal. Research indicates that inertia friction welds have no visible defects, and that the microstructure of the welding seam (WS) consists of granular bainite, acicular ferrite and little pearlite. The thermo-mechanically affected zone (TMAZ) consists of granular bainite bands and ferrite + pearlite bands. The hot work strengthening mechanism of inertia friction welding results in a higher level of hardness for both WS and TMAZ. The tensile property of the welded joints can be compared to the base metal. The yield strength, tensile strength and elongation of the welded joints, respectively, reach 87.5%, 100% and 79.5% of S355. However, the impact toughness of the welds at room temperature is lower than that of the base material, particularly in the TMAZ zone. Conversely, in an environment with a temperature of -40 °C, WS's impact toughness surpasses that of the parent material.

Effects of Normalizing Temperature on Microstructure and Impact Toughness of V-N Micro-Alloyed P460NL1 Steel.

In this work, the influence of normalizing temperature on vanadium micro-alloyed P460NL1 steel is studied in terms of microstructures and impact toughness. With the normalizing temperature increased from 850 °C to 950 °C, the V(C,N) particles are dissolved. The dissolution of V(C,N) particles leads to a reduction in their ability to pin the primitive austenite grain boundaries, resulting in the coarsening of the primitive austenite grain. Simultaneously, the number of precipitated particles promoting ferrite nucleation decreased. The combination of these two effects led to the coarsening of ferrite grains in the steel samples. Of note, in the sample normalized at a temperature of 850 °C, the ferrite and pearlite crystals clearly exhibited banded structures. As the normalizing temperature increased, the ferrite-pearlite belt phase weakened. The highly distributed belt phase resulted in poor impact toughness of the steel sample normalized at 850 °C. The belt phase was improved at a normalizing temperature of 900 °C. In addition to that, the microstructure did not undergo significant coarsening at this normalizing temperature, thereby allowing it to achieve the highest toughness among all samples that were prepared for this study. The belt phase almost vanished at the normalizing temperature of 950 °C. However, microstructure coarsening occurred at this temperature, resulting in the deterioration of impact toughness.

Electrofrictional Hardening of the 40Kh and 65G Steels

This study investigated the influence of electrofrictional treatment on the structure and hardness of the surface layers of the 40Kh and 65G steels. Based on the results of scanning electron microscopy, it was determined that during the electrofrictional hardening (EFH) of 40Kh steel, a hardened surface layer, with a microhardness of 873 ± 37 HV0.1, was formed. This layer consisted of two zones: a surface-quenched zone, with a structure of fine needle-like martensite and austenite; and a heat-affected zone (transition layer), with a structure of martensite and high-dispersion pearlite (troostite), smoothly transitioning into the original ferrite–pearlite structure. After EFH, a layer with a thickness of ~150 μm containing carbides in the martensite was formed on the surface of the 65G steel, which smoothly transitions into the heat-affected zone with a structure of needle-like martensite. The microhardness of the 65G steel in its initial state was 277 ± 20 HV0.1, and after EFH, it reached 811 ± 23 HV0.1. The results of the microstructure analysis of the 40Kh and 65G steels after EFH were consistent with the results of X-ray phase analysis. It was established that the phase composition of the 40Kh and 65G steels in their initial states consisted of an α-Fe phase with a body-centered cubic (BCC) lattice, and after EFH, both steels formed strengthening phases: residual austenite (γ-Fe) and martensite (α′-Fe). During EFH, under high temperature and pressure conditions, carbon from the cast iron electrode was alloyed with iron, contributing to the formation of cementite on the surface of the 65G steel. These obtained data allowed us to conclude that electrofrictional treatment is an effective method for the surface hardening of 40Kh and 65G steels.

Impact of interlamellar spacing and non-pearlitic features on mechanical properties and cyclic damage initiation in near-eutectoid pearlitic steels

The relationship between microstructural characteristics and mechanical properties was investigated for C72 and C82 pearlitic steel rods patented at temperatures between 500 °C and 600 °C using a lead bath. Results revealed a refinement of interlamellar spacing upon reduction of patenting temperature. At the same time, the fraction of grain-boundary ferrite and Widmanstätten ferrite as common non-pearlitic regions was slightly increased, reaching a maximum of nearly 1.3 vol.-% in the case of C72 steel patented at 500 °C. Reduction of patenting temperature was associated with strengthening, as confirmed by tensile, fatigue and hardness tests. The strengthening was explained in terms of the Hall-Petch effect for ferrite due to increase in the boundary area. The Hall-Petch coefficient, obtained by taking the apparent interlamellar spacing as the mean free path of dislocations, was in the range 70–140 MPa.μm12. To some extent, these low values could be related to the low solute interstitial content of pearlitic ferrite. More importantly, the coefficients are underestimated due to the plate-shaped morphology of pearlitic ferrite, which causes the average mean free path of dislocations be longer than the apparent interlamellar spacing. Scanning electron microscopy examinations after interrupted fatigue tests indicated the preferred occurrence of intrusions and extrusions, as precursors to fatigue crack, in the non-pearlitic ferrite. The enhancement of fatigue limit at lower patenting temperatures—in spite of slight increase in the fraction of ferrite—is justified by the stress shielding effect of pearlite and necessity of crack propagation into pearlitic regions for stable crack propagation. In effect, as long as the fraction of non-pearlitic features remains low, the interlamellar spacing of pearlite serves as the most efficient strength-controlling microstructural parameter. Furthermore, due to the preferred growth of fatigue cracks parallel to lamellae and deflection at colony boundaries, the refinement of colonies at reduced patenting temperatures is an additional contribution to the fatigue strength.

The effects of heat-treatment parameters on the mechanical properties and microstructures of a low-carbon dual-phase steel

The austenite decomposition phase transformation in a low-carbon dual-phase (DP) steel is studied as a function of inter-critical annealing parameters: annealing time, annealing temperature, and cooling rate. The austenization kinetics are obtained by dilatometric analyses, water-quenched metallography, and thermodynamic calculations, and the austenite formed at different inter-critical annealing temperatures influences the subsequent formation of secondary phases during continuous cooling. Results indicate that the austenite volume fraction increases with both annealing temperature and time; although their effect on the final microstructure and mechanical properties lessens when the cooling rate decreases to the slow cooling regime below air cooling. Interestingly, the yield strength (YS) values of samples cooled at ∼1 °C/s with sand cooling, are 75∼100 MPa greater than the corresponding values at a rate of ∼6 °C/s with air-cooling. The results indicate that the yield strength is positively correlated with yield-point elongation but negatively correlated with the ultimate tensile strength. The effects of the cooling rate on the mechanical properties can be explained by the formation of Cottrell atmospheres of carbon together with the increase of the pearlite volume fraction. Based on the secondary phase components and strength evolutions, there are four possible outcomes for the different cooling rates: (I) martensite (M); (II) ferrite-martensite (FM); (III) coexistence of martensite and pearlite (MP); and (IV) ferrite-pearlite (FP). Our results reveal that the microstructure-property correlation can be illustrated schematically as a function of cooling rates and can thereby direct the heat-treatment parameters required to obtain desirable mechanical properties.

Scanning Three-Dimensional X-ray Diffraction Microscopy for Carbon Steels

Plastically deformed low-carbon steel has been analyzed by nondestructive three-dimensional orientation and strain mapping using scanning three-dimensional X-ray diffraction microscopy (S3DXRD). However, the application of S3DXRD is limited to single-phase alloys. In this study, we propose a modified S3DXRD analysis for dual-phase alloys, such as ferrite–pearlite carbon steel, which is composed of grains detectable as diffraction spots and a phase undetectable as diffraction spots. We performed validation experiments for ferrite–pearlite carbon steel with different pearlite fractions, in which the ferrite grains and the pearlite corresponded to the detectable grains and an undetectable phase, respectively. The regions of pearlite appeared more remarkably in orientation maps of the ferrite grains obtained from the carbon steel samples than that of the single-phase low-carbon steel and increased with the increase in the carbon concentration. The fractions of the detectable grains and the undetectable phase were determined with an uncertainty of 15%–20%. These results indicate that the proposed modified analysis is qualitatively valid for dual-phase alloys comprising detectable grains and an undetectable phase.

A Novel Process for Hot‐Galvanized Quenching and Partitioning Steel with Excellent Yield–Ductility Synergy by Prior Treatment

The present work is aimed at a process to obtain a hot‐galvanized quenching and partitioning (Q&P) steel with excellent yield–ductility synergy by prior treatment. For this purpose, the cold‐rolled sheets with ferrite–pearlite structure are applied to “quenching (Q),” “quenching and tempering (Q&T),” “quenching and austempering (QAT),” and “quenching and austempering followed by tempering (QAT&T)” before the continuous galvanizing line (CGL)‐compatible Q&P treatment. Compared with Q&P sample, Q + Q&P, Q&T + Q&P, QAT + Q&P, and QAT&T + Q&P samples can obtain more homogeneous filmy/lath retained austenite (RA) with an increased C concentration, which can provide the transformation‐induced plasticity (TRIP) effect and improve elongation significantly. The maximum austenite reverse transformation rates are obtained in Q&T and QAT&T samples because of the increased nucleation sites, such as grain boundaries and cementite particles. QAT&T + Q&P sample has the longest plateau region before break and obtains the attractive mechanical properties with a yield strength of 694 MPa, tensile strength of 927 MPa, total elongation of 31.3%, and product of strength and elongation above 29 GPa%.

Molecular dynamics study of hydrogen-induced cracking behavior of ferrite–pearlite gas transmission pipeline steel

Molecular dynamics study of hydrogen-induced cracking behavior of ferrite–pearlite gas transmission pipeline steel

Experimental Evaluation of Quality of TMT/QST Steel Bar by Using TM Ring Test

bstract: This steel is frequently used on our construction site. However, there are numerous issues with the quality of this steel. Recently, a test method for evaluating the calibre of tempered Martensite rings on TMT steel was developed and refined. The tempered Martensite ring gives TMT rebars their strength, while the ferrite pearlite core gives them their ductility. Because of their unique properties, we use them in earthquake-resistant systems that require both strength and ductility. We bend these components at a 135-degree angle for use in stirrups. A typical 135-degree bend stirrup is seen here. Because of its superior surface crack resistance, TMT rebar will not have a cracked surface. Steel has been employed in structural applications for many decades due to its durability. Designers advocate high strength steel bars in a contemporary concept to reduce steel consumption in reinforced cement concrete (RCC) structures. Microalloying, thermomechanical treatment, cold working, and other methods are used to manufacture them. Some designers believe that thermomechanical treatment (TMT) steel bars are more sensitive to corrosive environments. Corrosion behaviours of high strength steel bars of 500W (weldable steel bar of yield strength 500MPa) grade from two different local industries in fresh water and sea water were studied and compared to weldable low strength (yield strength 300MPa) bars from the same companies. The addition of minor amounts of alloying elements such as Cr, Ni, and Cu enhances the corrosion resistance of steel bars in all test mediums, but strength levels have no effect on the corrosion rate. There is also a link between the degree of tensile property loss and the severity of corrosion damage