Ferrite-pearlite Microstructure Research Articles

Grain Boundary Detection and Phase Segmentation of SEM Ferrite–Pearlite Microstructure Using SLIC and Skeletonization

In this paper, we report an efficient segmentation and grain boundary detection process using modern image processing operators like simple linear iterative clustering and skeletonization. Accurate phase segmentation is the major requirement for any phase identification and quantification operations. The proposed image processing methods have been experimented on the in-house generated 48 scanning electron microscopy (SEM) microstructures obtained from plain carbon steel samples containing 0.1, 0.22, 0.35 and 0.48 wt%C and have been subjected to both annealing and normalizing treatments. The microstructures for dataset have been captured in SEM using secondary electron mode over a wide range of magnification × 500–× 5000. The experimental results significantly validate the segmentation of ferrite and pearlite regions. Also, the grain boundary detection results appear to be plausibly effective in case of ferrite–ferrite and ferrite–pearlite boundaries. However, the grain boundary detection efficiency is found to be relatively poor in case of pearlite–pearlite boundary. The overall performance of the proposed image processing technique in context of ferrite–pearlite steel SEM images shows promising results in all circumstances of compositional range, heat treatment and magnification.

The effect of heating rate and soaking time on microstructure of an advanced high strength steel

This work focuses on the effect of soaking time on the microstructure during ultrafast heat treatment of a 50% cold rolled low carbon steel with initial ferritic-pearlitic microstructure. Dilatometry analysis was used to estimate the effect of heating rate on the phase transformation temperatures and to select an appropriate inter-critical temperature for final heat treatments. A thorough qualitative and quantitative microstructural characterization of the heat treated samples is performed using a wide range of characterization techniques. A complex multiphase, hierarchical microstructure consisting of ferritic matrix with embedded martensite and retained austenite is formed after all applied heat treatments. In turn, the ferritic matrix contains recrystallized and non-recrystallized grains. It is demonstrated that the ultrafast heating generally results in finer microstructure compared to the conventional heating independently on the soaking time. There is a significant effect of the soaking time on the volume fraction of martensite of the ultrafast heated material, while in the samples heated with conventional heating rate it remains relatively unchanged during soaking. Recrystallization, recovery and phase transformations occurring during soaking are discussed with respect to the applied heating rate.

Intercritical and subcritical spheroidization of 10B38 cold heading steel

For the production of bolts by cold forging, the hardenable steel has to be in a soft and ductile state. The Cold Heading Quality Steel is achievable by a spherodization heat treatment on the hot rolled material. The scope of this study is a boron bearing medium carbon steel which has many promising properties as bolting material. The experimentations covered two different initial conditions before the spheroidization heat treatment: hot rolled (ferrite-pearlite microstructure) and quenched (martensitic microstructure). In combination, two spheroidization procedures were considered too: subcritical and intercritical heat treatments. Intercritical heat treatment process included heating to 750 °C , holding for 2 h and then cooling to 715 °C and then holding for 12 h. In the subcritical heat treatment proess, the materialwas heated to 715 °C , holding for 12 h followed by cooling in the furnace. To assess the cold formability, a special notched tensile test was employed and the results were supported with metallographic and microhardness measurements. For both subcritical and intercritical heat treatment, higher levels of spheroidizatin were achieved with the quenched samples compared with the hot rolled condition. On the other hand the subcritical heat treatment resulted in higher levels of spheroiization. A practical equation is developed which relates the failure strain of notched tensile specimens with pearlite content and the hardness of the 10B38 steel.

Failure of a hydrogenerator reactor inlet piping by high-temperature hydrogen attack

A case of cracking in carbon steel inlet piping of a hydrogenerator reactor by high-temperature hydrogen attack that resulted in a leak after 47 years of service is examined. A transverse crack formed in the flange neck close to a non-post-weld-heat-treated butt weld, just outside the heat-affected zone (i.e. in the sub-critical region). Although the main factor in the failure was a recent increase in hydrogen partial pressure that placed the operating conditions above the pre-2016 API 941 Nelson curve for carbon steel, there were some pre-existing/dormant contributing factors, namely lack of post-weld heat treatment, bending stress on the piping, the presence of H2S in the process fluid, coarse ferrite-pearlite microstructure (i.e. the grain size effect) and some impurities in the vintage steel. An interesting observation was that the grain boundaries were decorated with a film of light-etching phase that was identified to be cementite by electron backscatter diffraction as opposed to being ferrite that could form upon internal decarburization (i.e. pearlite decomposition). An explanation is provided for the formation of cementite along the grain boundaries. Overall, the findings of this investigation attest to the usefulness and relevance of the (simplistic and imperial) Nelson curve for carbon steel, which has been questioned over the last few decades.

Effect of microstructure and temperature on the stress corrosion cracking of two microalloyed pipeline steels in H2S environment for gas transport

The stress corrosion cracking resistance of two API X65 microalloyed steels, with different microstructures has been evaluated both at room temperature and at 55 °C, by means of Linear Elastic Fracture Mechanics (LEFM) specimens known as MWOL (Modified WOL specimen), under constant displacement. The material with a ferritic–pearlitic microstructure showed crack tip dissolution, a transgranular crack growth mode and some evidence of Hydrogen Induced Cracking (HIC). At room temperature, besides crack propagation, decohesion between grain boundaries was also observed, as well as some cavitation at the front of the crack tip. The material with martensitic microstructure tested at room temperature showed a mixed transgranular-intergranular crack growth mode, without cavitation at the crack tip front. At 55 °C, the crack growth path observed was transgranular, with cracks longer than those observed at room temperature, indicating that some Hydrogen mechanisms, probably thermally activated, could be present in addition to the anodic dissolution mechanisms.

Microstructure and Texture Control in Cold Rolled High Strength Steels

Formability had been important property of metals which is attributed to the texture development during thermomechanical processing particularly during hot rolling and cold rolling. In the present paper, the high strength steels with different carbon and manganese composition have been hot rolled above and below of austenite recrystallization temperature and followed by fast cooling up to different coiling temperature to get hot bands with different texture and two phase microstructure consisting ferrite with pearlite, bainite and martensite. Subsequently, these hot bands were cold rolled with 80 percent under plain strain condition. The microstructure of cold rolled sheets samples were analyzed using scanning electron microscope and showed the cold rolled microstructure with strong pancaked of two phase which was carried from the hot rolling. Cold rolled texture in ferrite pearlite microstructure is completely replaced by new texture components from hot rolled condition without the effect of Tnr. Hot rolled texture was retained in ferrite-bainite and martensite microstructure with the effect of Tnr. Increase in alloy chemistry weakens the texture intensity in ferrite pearlite/bainite microstructure. Whereas increase in alloy chemistry strengthens the texture intensity in ferrite martensite microstructure.

Railway Vehicle Wheel Restoration by Submerged Arc Welding and Its Characterization

When a railway vehicle moves on a curved rail, sliding contact occurs between the rail head side and wheel flange, which wears the wheel flange down. The thinned flange needs to be restored above the required minimum thickness for structural safety. In this study, a new process and welding wire for restoring worn-out railway wheels by submerged arc welding was developed. To characterize the properties of the restored wheel, dilatometric analysis of phase transformation, SEM/EDX analyses, hardness measurement, and residual stress measurement using the X-ray diffraction method were performed. Finally, wear tests with full-size wheel/rail specimens were carried out. It was confirmed that the weld metal was composed of bainitic microstructures as intended, and welding defects were not observed. The wear amount of the restored wheel was greater than that of the base material, but it was less than half of the wear depth of the weld-repaired wheel with ferritic–pearlitic microstructures. The developed process seems applicable to industry.

Analysis of Mechanical and Metallurgical Properties of Friction Welded ASTM A106Gr.B Carbon Steel Pipe Joints by Varying Upset Pressures

Friction welding is one of the most common methods employed in the joining of carbon and alloy steel tubular sections. In the present work, the analysis of the effect of upset pressure on mechanical and metallurgical properties of friction welded ASTM A 106 Gr. B low carbon steel pipes has been investigated. The test joints were made using continuous drive welding machine with upset pressures of 5 MPa to 8 MPa and evaluated for microstructure, hardness, tensile strength and impact toughness. The weld joints exhibited mostly ferrite and pearlite microstructure in both fully plastically deformed zone (FPDZ), partially deformed zone (PDZ) on the either side of the weld interface and a distinct dynamically recrystallized ferrite pearlite microstructure was observed in the FPDZ at the weld centre line. Better tensile properties were observed in case of the joints made with upset pressure of 6.4 MPa. It is observed that the weld region is stronger than base metal and the hardness has increased with the increase in the upset pressure. Marginal reduction in the toughness was noted with the increase in the upset pressure.

Intercritical Heat Treatment Temperature Dependence of Mechanical Properties and Corrosion Resistance of Dual Phase Steel

Abstract This study investigated the effect of intercritical heat treatment temperature on the tensile properties, work hardening and corrosion resistance of dual phase steel. Ferrite-martensite dual phase steel with different martensite volume fractions were obtained after heat treatment at different intercritical temperatures. Microstructure, mechanical properties of steel were measured and the corrosion resistance was evaluated via polarization test. Tensile strength of the specimens increased by increasing the martensite volume fraction up to 48.2%. Further increase in martensite volume fraction led to decrease in tensile strength. Work hardening behavior analyzing showed that in DP steel with less than 50% martensite volume fraction, the work hardening took place in one stage and by increasing the martensite volume fraction two-stage work hardening behavior was observed in the Holloman analysis. The results of polarization test showed that, the corrosion resistance of dual phase steel is higher than that of plain carbon steel with ferrite-pearlite microstructure.

Micro-Alloyed Steel for Forgings

To fulfill the industrial demand of forged steels with high tensile properties and microstructural requirements coupled with reduced cost, the possibility to increase the properties of C-Mn steels by means of precipitation strengthening as achieved by micro-alloying (and without the addition of expensive elements such as Mo and Cr) has been evaluated. In order to do that, the effect of V addition has been exploited by means of metallurgical modelling followed by a laboratory ingot manufacturing. Heat treatment has been designed aimed to achieve the desired target tensile properties. Results show that ASTM A694 F70 grade requirements can bel fulfilled by 0.15% V addition and a proper heat treatment in a ferrite-pearlite microstructure, representative of a forged component. Results are discussed in comparison to those of a similar steel without V addition.

Influence of Manganese and Boron Alloying and Processing Conditions on the Microstructure and the Mechanical Properties of 0.4% Carbon Steels

The performance of three steels with 0.4% carbon content was evaluated in the warm forging condition and benchmarked against the as-hot-deformed and hardening and tempering condition. The steels include a plain carbon steel S45C, a carbon-manganese steel 40Mn5 and a carbon-manganese-boron-alloyed steel 15B41. Such lean alloyed steels are preferred by automotive companies for component manufacture. In the as-hot-rolled condition, the steel with a ferrite pearlite microstructure shows, a good strength and lowest impact toughness. In the hardened and tempered condition at 650 °C, a tempered martensite microstructure with a moderate improvement in strength and significant enhancement in impact toughness, than the hot-rolled steel, is obtained. The steel subjected to warm forging at 760 °C, shows a ferrite pearlitic microstructure with a moderate improvement in strength but with the highest impact toughness level. The microstructure evolution at the various processing conditions has been brought out and correlated with the mechanical properties. The relative merits in processing the steels at the different processing conditions show that warm forging is an effective means to achieve the highest strength toughness combination in a ferrite pearlitic matrix.

Effect of Ti(C, N) Particle on the Impact Toughness of B-Microalloyed Steel

Simultaneously improving the toughness and strength of B-microalloyed steel by adding microalloying elements (Nb, V, Ti) has been an extensively usedmethod for researchers. However, coarse Ti(C, N) particle will precipitate during solidification with inappropriate Ti content addition, resulting in poor impact toughness. The effect of the size, number density, and location of Ti(C, N) particle on the impact toughness of B-microalloyed steel with various Ti/N ratios was investigated. Coarse Ti(C, N) particles were investigated to act as the cleavage fracture initiation sites, by using scanning electron microscopy (SEM) analysis. When more coarse Ti(C, N) inclusions were located in ferrite instead of pearlite, the impact toughness of steel with ferrite–pearlite microstructure was lower. Meanwhile, when the size or the number density of Ti(C, N) inclusions was larger, the impact toughness was adversely affected. Normalizing treatment helps to improve the impact property of B-microalloyed steel, owing to the location of Ti(C, N) particles being partly changed from ferrite to pearlite. The formation mechanism of coarse Ti(C, N) particles was calculated by the thermodynamic software Factsage 7.1 and Thermo-Calc. The Ti(C, N) particles formed during the solidification of molten steel, and the N-rich Ti(C, N) phase precipitated first and, then, followed by the C-rich Ti(C, N) phase. Decreasing the Ti and N content is an effective way to inhibit the formation of coarse Ti(C, N) inclusions.

Roughness Parameters during Cavitation Exposure of Nodular Cast Iron with Ferrite-Pearlite Microstructure

The cavitation erosion resistance of EN-GJS-400-15 nodular cast iron was tested in the laboratory according to ASTM G32- 2010 standard. The erosion average penetration depth values, MDE, were correlated with the roughness parameters and the microstructure of the samples subjected to volume heat treatments consisting from stress relieving and for softening, annealing, normalization and quenching followed by tempering. The results obtained showed that the changes in the surface roughness of the samples tested at cavitation can be used to predict the resistance of the material to this wear phenomenon.

Modelling of Induction Heating of Steel Work Piece for Forging of Crankshaft

Vanadium microalloyed steel forgings provide high performance and cost effective solutions for automotive components in powertrain and chassis of modern cars and trucks. The majority of these forgings are produced from medium carbon steel with small additions of vanadium, manganese and sulphur to provide precipitation strengthening of the cooled ferrite-pearlite microstructure. This article deals with modelling of induction heating of steel billet prior to forging for automotive applications using COMSOL Multiphysics. The main aim of computer modelling was to evaluate the temperature distribution in billet since precise temperature control is required to prevent process-induced defects such as overheating or insufficient heating. Obtained numerical results for development of induction heating of steel billets have represented eventual increase of effectiveness by reducing of operation time.DOI: http://dx.doi.org/10.5755/j01.ms.24.3.18313

Fine-grained dual phase steel via intercritical annealing of cold-rolled martensite

The effect of intercritical annealing on the microstructure and mechanical properties of a low carbon steel with the chemical composition (wt%) of 0.12C–1.11Mn-0.16Si is studied. The cold rolled martensite and ferrite-pearlite microstructure are considered as the starting microstructures for producing dual phase (DP) steels. It is revealed that intercritical annealing of cold-rolled martensite is a viable technique for grain refinement of DP steels, where a microstructure consisting of ferrite grains with average grain size of less than 5 μm and fine martensite islands can be easily obtained. This DP steel exhibits much better strength-ductility balance compared with that obtained by intercritical annealing of the ferritic-pearlitic microstructure due to much finer microstructure and enhancement of work-hardening behavior in the former. The fine-grained microstructure is also obtained at higher intercritical annealing temperatures for the aim of increasing the volume fraction of martensite. Accordingly, the work-hardening response and the overall mechanical properties are enhanced.

Study of Microstructural and Mechanical Behavior of Mild Steel Wires Cold Drawn at TREFISOUD<i></i>

The aim of the present work is to study the evolution of microstructure, texture and mechanical properties during drawing of mild steel wire of type F8Z used in the manufacture of welding electrodes TREFISOUD. It was found that the as received wire has a ferritic-pearlitic microstructure corresponding to an isotopic state (without texture). This microstructure is relatively heterogeneous in the wire section. On the other hand, after strong drawing structure appears relatively homogeneous, throughout the section of the drawn wire. Also the deformation process by drawing causes the hardening of wire as a function of deformation with a reinforcing component of the fiber texture <110> // ND (majority), typical for bcc materials. Characterization methods used in this work is: Optical microscopy (OM), Scanning Electron Microscopy (SEM), the Electron Back Scattered Diffraction EBSD, Vickers microhardness and the tensile tests.

Effects of Controlled Cooling-Induced Ferrite–Pearlite Microstructure on the Cold Forgeability of XC45 Steel

The combination of hot/warm and cold forging with an intermediate controlled cooling process is a promising approach to saving costs in the manufacture of automobile parts. In this work, the effects of the ferrite–pearlite microstructure, which formed after controlled cooling, on the cold forgeability of a medium-carbon steel were investigated. Different specimens for both normal and notched tensile tests were directly heated to high temperature and then cooled down at different cooling rates, producing different ferrite volume fractions, ranging from 6.69 to 40.53%, in the ferrite–pearlite microstructure. The yield strength, ultimate tensile strength, elongation rate, percentage reduction of area, and fracture strain were measured by tensile testing. The yield strength, indicating deformation resistance, and fracture strain, indicating formability, were used to evaluate the cold forgeability. As the ferrite volume fraction increased, the cold forgeability of the dual-phase ferritic–pearlitic steel improved. A quantitatively relationship between the ferrite volume fraction and the evaluation indexes of cold forgeability for XC45 steel was obtained from the test data. To validate the mathematical relationship, different tensile specimens machined from real hot-forged workpieces were tested. There was good agreement between the predicted and measured values. Our predictions from the relationship for cold forgeability had an absolute error less than 5%, which is acceptable for industrial applications and will help to guide the design of combined forging processes.

New Steel Combinations Produced by the Damascus Technique

Multilayered forged steel plates, which combine the properties of diverse steel qualities, are referred to as Damascus steels. Since the 3rdcentury AD blades and weapons have been produced by the Damascus technique in Europe. In this work four different steel combinations were investigated. Combining Fe with carbon steel C60 resulted in a ferritic-pearlitic microstructure. By forging two heat-treatable steels C40 and C60 martensite with an inhomogeneous carbon distribution was formed. Combining Fe with an austenitic stainless steel showed ferrite and austenite with grain boundary carbides and segregation bands. The last combination of two cold working steels K110 and K600 led to a complex microstructure with martensite, retained austenite and two special types of carbides. After metallographic preparation and using of different etchants the various microstructures were characterized by light optical microscopy and confirmed by Vicker ́s microhardness measurements. Of high interest are the interfaces and the quality of the weld between the individual steel layers. In some regions oxidation and carbon diffusion were observed.

Optimization of Controlled Cooling of Forgings from Finishing Temperature with the Use of Light and Electron Microscopy

Customer requirements represent the driving force in the market, dictating the directions of development, production and processing of forged parts. Meeting these requirements is of paramount importance to forge shops as a precondition for their continuing operation and competitiveness. Consequently, optimization of manufacturing operations and their rapid response to market requirements are necessary for the forge shops to survive. However, any production stoppage for optimization results in extra costs. Forge shops thus strive to carry out optimization in as few steps as possible and within the shortest possible timeframe. A viable solution emerges in the form of material-technological modelling which involves laboratory-based optimization taking place away from the forge shop without any constraints on the production operations. This paper deals with selection of a material for a forged part to be controlled-cooled from the finishing temperature to substitute a C45-steel part treated by normalizing. One criterion was that the entire forged part should contain ferritic-pearlitic microstructure.

Evolution of Microstructure During Short-term Overheating Failure of a Boiler Water Wall Tube Made of Carbon Steel

This paper highlights the evolution of different microstructures during short-term overheating failure of a boiler water wall tube made of SA210 Grade C steel. Short-term overheating failure of the boiler tube caused fish mouth rupture with thin lips, along the longitudinal direction of the tube with extensive tube bulging. Microstructure examination revealed elongation of grains at the fracture signifying plastic deformation due to hoop stress becoming equal to the flow stress of the tube at the elevated temperature. Overheating caused degeneration of the initial ferrite–pearlite microstructure. Spheroidization and coalescence of carbides occurred in the ferrite matrix from the initial ferrite–pearlite microstructure of the boiler tube near the ruptured region. Moreover, the formation of bainite microstructure at the fracture fish mouth opening indicates heating above the eutectoid temperature (lower critical temperature) of the tube material.