Pearlite Microstructure Research Articles

Evaluation of optimum condition to improve the microstructure in hot-rolled medium carbon steel by elimination of coarse pearlite patches

The present study is aimed to eliminate the undesirable microstructure in the real working condition of the steel unit. In this work, the microstructure of hot-rolled medium carbon steel (grade 45C8) is studied for application in the automotive industry. The effect of the temperature and rolling rate on the microstructure has been thoroughly investigated by analyzing the microstructure containing ferrite and pearlite phases after each trial run of hot-rolled steel. The desired microstructure of fine ferrite and pearlite is very much essential in hot-rolled medium carbon steel for better strength and uniform properties of the material. The formation of coarse pearlite is undesirable, which may lead to breakage during drawing and hardness variation in the hot-rolled steel. Therefore, this study is focused to find the optimum condition for achieving the microstructure containing uniform distribution of fine pearlite and ferrite without the presence of blocky pearlite patches.

Fatigue failure of ball joint heads connected to the weight holder mechanism in railway applications

The premature causes of failure of ball joint heads attached to the weight bearing bar used on high speed trains, which were continuously under traction, have been studied, with an average load of 47.5 kN plus a cyclical load of ± 7.5 kN. Ball joint heads made of C45 (AISI 1045) carbon steel show a pearlite microstructure (80–90 %) with ferrite surrounding the prior-austenite grain boundaries. Two different external elliptical-shaped fatigue cracks of 14.5 mm and 7.7 mm nucleated in opposite positions on the cylindrical surface of the threaded shank prior to catastrophic cleavage failure. The Griffith equation applied in this study gave a value of 37 MPa for the fracture stress (σf) produced by the largest crack, which multiplied by the section of the thread is equivalent to a load of 37 kN, similar to the applied service load. In addition, the critical stress intensity factor (KIc) calculation yielded a value of 8.8 MPa m1/2, this lower KIc value was determined to be responsible for the large fatigue crack produced and the cleavage fracture causing the C45 carbon steel bolt joint failure. The pearlite/ferrite microstructure contributed to crack growth, since this type of microstructure in high carbon steels has lower strength and lower toughness than a tempered martensite microstructure. Using Paris equation, the cycles to failure were 1.5 × 105, which in service lifetime was an approximated 6 × 106 km for the piece to finally fail.

Formation mechanism of pearlite during thermal cycling in U75V steel rail repaired by laser directed energy deposition

Laser additive manufacturing is used to repair the damaged area of the rail, which is prone to martensite microstructure in the cladding layers, and it seriously affects the mechanical properties and threatens the safety of rail service. Therefore, in order to avoid the formation of martensite microstructure in the cladding layers, U75V steel rail cladding layer process experiment with different layers was carried out and the pearlite microstructure was successfully prepared by considering self-tempering characteristics. Moreover, combined with the finite element method to research the phase transformation behavior of U75V steel rail affected by thermal history, the mechanism of pearlite transformation in the process of laser directed energy deposition (LDED) repairing steel rail was studied. The results indicate that the cooling rate of the solid phase transformation stage is approximately 100–101 °C/s. Two indispensable conditions for pearlite formation in U75V steel repaired by LDED were revealed: the laser thermal accumulation must enable the cladding layers to maintain the valley temperature above the martensite start temperature and the cooling rate of the cladding layers in the solid phase transformation must be lower than the critical cooling rate of pearlite transformation. Based on this theory, pearlite microstructure can be obtained efficiently by means of preheating pretreatment and Co element doped alloying and optimizing the process parameters. Preheating pretreatment is beneficial to increase basic temperature, and Co-doped alloying can change continuous cooling transformation curve of U75V steel rail.

Tekerlek Ray Etkileşimi, Perlitik ve Beynitik Çeliklerin Yorulma Hasar Direnci Üzerine Bir Sonlu Elemanlar Analizi

Bu çalışmada ülkemizde ve dünyada demiryolu hatlarında işletme şartlarında çoğunlukla kullanımda olan perlitik mikroyapıdaki çelikler ve perlitik çeliklere alternatif olarak sunulan, gelişmiş mekanik özelliklere sahip olan beynitik mikroyapıdaki çelikler ele alınmıştır. Geniş bir literatür özetiyle konvansiyonel ray sınıfları ve gelişmiş ray sınıfları, kimyasal kompozisyonları ve temel mekanik özellikleri dikkate alınarak değerlendirilmiştir. Ayrıca dünyada farklı bölge ve ülkelerde geliştirilen beynitik ray çelikleri incelenmiştir. Daha sonra tekerlek ray etkileşimi, sürtünme şartları ve temas yüzeyleri dikkate alınarak, geliştirilen sonlu elemanlar modelinde rayın yorulma hasar direnci analiz edilmiştir. Sonuç olarak analiz edilen beynitik mikroyapıdaki çeliğin yorulma hasar direncinin perlitik mikroyapıya göre üstün olduğu ve 386,69 MPa yük altında on milyon çevrime dayanabildiği anlaşılmıştır.

3D Growth of Intragranular Pearlite in an Aged 100Mn13 Steel

The morphology and microstructure of intragranular pearlite in 100Mn13 high‐carbon, high‐manganese steel aged at 600 °C are observed by a scanning electron microscope (SEM) and transmission electron microscope (TEM) and analyzed, and growth models describing the morphology and growth process in 3D space are proposed. The results show that pearlite could nucleate directly in the austenite grain and present a 3D morphology after deep etching, and ferrite and cementite in pearlite keep the orientation relationship (OR) with austenite, , , , and . Also, the overall continuous ledges at the lamellar ferrite surface and end surround the whole ferrite lamellae, corresponding to a fringe structure and a curved frontier interface in 2D space, which shows a terraced morphology in 3D space. The different structures of the α/γ interface in 3D directions result in different growth rates of ferrite lamellae, that is, edgewise grows fastest along the direction of due to the incoherent interface composed of with a 28% mismatch, and sidewise grows slowest along the direction of due to the coherent interface composed of with a 1.9% mismatch.

Under-stoichiometric cementite in decomposing binary Fe-C pearlite exposed to rolling contact fatigue

In this study, we investigate the fundamentals of deformation-driven cementite decomposition during rolling contact fatigue in a binary Fe-0.74C (wt.%) steel with pearlitic microstructure. To reveal the involved nano-scale mechanisms, we apply transmission electron microscopy and atom probe tomography, as well as the combination of both techniques on the same probe volume for correlative structural and chemical analysis. After ~32,500 individual ball contacts under a nominal Hertzian contact stress of ~1,250 MPa, cementite lamellae are consistently depleted in carbon (C) down to ~20 at.%, which is a reduction of 20% in comparison to the original stoichiometric composition of 25 at.% before deformation. By electron diffraction on atom probe tip volumes, we show that this under-stoichiometric cementite still maintains its crystal structure. The potential effect of temperature increase during rolling contact fatigue on cementite decomposition is addressed by carrying out annealing experiments at 150°C and 250°C for 30 minutes after rolling contact fatigue. Our results show that slip transmission across cementite lamellae is primarily responsible for the observed C-depletion in cementite. We quantitatively discuss slip transmission from ferrite to cementite using slip trace analysis and correlate the amount of slip activity with the observed C-depletion. In this way, we explain the formation of under-stoichiometric cementite by combined slip transmission and solute drag by dislocations, where C is transported out of cementite by dislocation gliding through cementite lamellae. Only afterward, cementite decomposition in terms of phase dissolution is suggested to occur by the dislocation-shuffle mechanism.

Pengaruh Variasi Jenis Katalisator Dan Holding Time Pada Proses Pack Carburizing Terhadap Perubahan Komposisi Karbon Dan Nilai Kekerasan Baja Karbon Rendah (Low Carbon Steel) St 37

In this study, a pack carburizing process was carried out on low carbon steel using activated carbon, coconut shell charcoal and various catalysts in the form of ale-ale shells, eggshells, and beef bones. The method used is heating at an austenite temperature of 900 oC with a variation of holding time of 30, 60, and 90 minutes, then quenching using water, followed by hardness testing with the Vickers method and composition testing. The general result is that the three types of catalysts can accelerate the diffusion-reaction so that the carbon addition process occurs and the longer holding time can provide an opportunity for the carbon formed to transform from the pearlite microstructure to the austenite microstructure, and when quenching it forms the Martensite microstructure. Of the three types of catalysts that produced the highest hardness was an ale-ale shell, from the initial hardness 119 HV to 464 HV.

Influence of components and 20GL steel microstructure hardness on impact toughness of car castings

Microstructural analysis of low-alloy 20GL steel showed the need to improve heat treatment (normalization) in terms of impact on grain quantity, size and hardness, average grain area and properties, in particular impact toughness of wagon castings «Side frame» and «Truck bolster». Relationships between the 20GL low-alloy steel microstructure parameters and toughness at negative temperature have been established. The method of optical microscopy was used to carry out metallographic and statistical analyzes of the ferrite (F) and pearlite (P) microstructure of 20GL steel samples of car castings for «Side frame» and «Truck bolster» according to GOST 5639-82 using the Vestra Image System program. Graphical dependences are constructed between the number and average area of grains on the section, the number of F and average area of grains on the section, and the impact toughness of 20GL samples of open-hearth and electric arc melting steel. For open-hearth melts with the same values of the amount and average area of grain on the section, the amount of F and the average area of grain on the section, the impact toughness can be both KCV – 60 ≤ 2.0 and KCV – 60 > 2.0∙102 kJ/m2. Analysis of electric arc melts showed that low values of the average area of ferrite grains do not increase the impact toughness of KCV – 60> 2.0∙102 kJ/m2. The problem of obtaining satisfactory results of impact toughness KCV – 60 > 2.0∙102 kJ/m2, associated with heat treatment in 20GL steel samples, was established.

Continuous cooling transformation behaviour of 30CrMo steel simulated by CSP process

ABSTRACT The continuous cooling transformation (CCT) diagram of 30CrMo steel simulated by compact strip production process was constructed. And the effect of austenite deformation on the CCT behaviour was investigated. The results showed that the microstructure gradually transformed from proeutectoid ferrite and pearlite to bainite and martensite with the increase of cooling rate, accompanying a refined microstructure and an increasing hardness. When the cooling rate was lower than 0.1°C s−1, the desired microstructure of ferrite and pearlite could be obtained. And the austenite deformation strongly promoted the formation of proeutectoid ferrite, which led to a decreasing hardness of deformed steel. When the cooling rate was larger than 10°C s−1, the fully martensite microstructure was obtained. And the austenite deformation inhibited martensite transformation, resulting in a decrease of the martensite transformation starting (M s) temperature from 391°C to 368°C.

Three-dimensional multi-phase-field simulation of eutectoid alloy based on OpenCL parallel

Seeking high-performance computing methods to solve the problem of a large amount of calculation, low calculation efficiency, and small simulation scale on the traditional single central processing unit (CPU) platform is of great value to the simulation study of micro-structure. In this study, based on the three-dimensional multi-phase-field model of KKSO coupling phase-field and solute field, the open computing language (OpenCL) + graphics processing unit (GPU) heterogeneous parallel computing technology is used to simulate the eutectoid growth of Fe-C alloy and the end growth process of pearlite under pure diffusion. The effects of initial supercooling and different diffusion coefficients on the growth morphology of lamellar pearlite were investigated. The results show that ferrite and cementite are perpendicular to the front of the solid-solid interface and are coupled and coordinated to grow, and there is no leading phase under the initial supercooling degree of 20 K. With the continuous increase of the initial supercooling degree (19 K–22 K), the morphology changes of the eutectoid layer are as follows: cementite stops growing → slice amplitude increases → regular symmetric growth → oblique growth → layer merge. With the increase of the diffusion coefficient from 3×10−13 m2·s−1 to 15×10−13 m2·s−1, the growth rate of the microstructure of the lamellar pearlite increases linearly, and there is no obvious change in the frontal appearance of the pearlite.

The Effect of Heat Treatment on the Performance of Antiwear Steel Coatings Deposited on AISI 1015 Steel Substrates

The critical components of mining equipment generally work in relative motion and in an abrasive environment. Under these circumstances, wear by friction represents the largest portion of the cost associated with failure and maintenance of sliding bearings. Thus, antiwear coatings are extensively applied aimed at returning such equipment to its initial condition. Tamping machines are a typical type of equipment working in this condition and the focus of the present research work, whose goal is to investigate the performance of conjugates made of an MnSi low-alloy steel coating deposited on an AISI 1015 low-carbon steel substrate and subjected to three distinct heat treatment routes (normalizing and deep and surface hardening). Coating deposition was performed using gas metal arc welding. The performance assessment is based on microhardness and residual stress distributions, friction coefficient, wear mechanisms, and wear rate. The results indicate that ferritic and pearlitic microstructures were obtained after normalizing, whereas deep and surface hardening produced lath martensite. Consequently, the value of surface microhardness of the coating was 176 HV after normalizing, 356 HV after deep hardening, and 466 HV after surface hardening. Normalizing induced shallower compressive residual stresses of lower intensity, whereas surface hardening induced compressive residual stresses of higher intensity to reach deeper beneath the coating surface. More refined grains (martensite laths) were associated with higher microhardness values and compressive residual stresses of higher intensity, thus suggesting that this condition leads to higher wear resistance. The normalized conjugate presented the lowest friction coefficient and the highest wear rate, and the hardened coatings presented similar behaviors with regard to wear resistance.

Wear Resistance of Medium Carbon Steel with Different Microstructures.

In this research, the tribological properties of different microstructures of medium carbon steel produced by either an austempered process or quenched-tempered process are investigated. The as-received samples with annealed microstructure (spherodized) are austempered to obtain a bainite microstructure or quenched-tempered to obtain a tempered martensite microstructure. The tribological performance of these microstructures was studied using a ball-on-disk UMT3 tribometer. The results indicated that both bainite microstructures and tempered-martensite microstructures produced better wear resistance than pearlite microstructures. At the same hardness level, the austempered disk specimens have less cracking due to higher fracture toughness compared to quenched and tempered steel. For the disks, tempered martensite microstructures produced more plastic deformation compared with bainite microstructures. Mild abrasive wear was observed on the harder disks, however, smearing wear was observed on the softer disks. Adhered debris particles were observed on the balls.

Characterization of Mechanical Properties, Macroscopic Deformation Behavior, and Microstructure of Functionally Graded 22MnB5 Steel

The focus of this study is on the characterization of the local plastic deformation and failure of functionally graded 22MnB5 plates after hot stamping using an in situ approach. Various forming strategies at elevated temperatures are performed using differentially tempered forming tools to locally tailor the microstructure. By controlling the cooling rate, graded as well as martensitic and ferritic–pearlitic microstructures are obtained. Experimental analysis includes evaluation of the material‐ and geometry‐dependent local strain evolution by tensile tests coupled with digital image correlation conducted on two different sample geometries, tapered and nontapered. Experimental results reveal a much more complex deformation behavior for the functionally graded than for homogenous samples. As expected, the distribution of plastic strain of the graded sample is depending on the mixture of its constituting microstructures; however, different types of localized failure after necking are found. Obviously, failure evolution also depends on the sample geometry. Failure patterns observed include shear bands, crossed bands, or homogenous localization of strain, i.e., traditional necking. Eventually, in the case of the nontapered geometry, a lower level of local plastic strain with multiple necking sites is observed. Based on findings presented, detailed process‐microstructure‐property‐damage relationships are established.

Effect of the galvanization process on the fatigue life of high strength steel compression springs

Abstract In this study, a compression spring fatigue problem arising from the galvanization process was investigated. Fatigue, crack initiation and growth of galvanized and non-galvanized springs manufactured from fully pearlitic high strength steel wires were investigated. According to the results, the galvanized compression springs exhibited a low fatigue life due to hydrogen embrittlement. Hydrogen embrittlement induced crack initiations formed under the galvanizing layer and adversely affect fatigue life. It was observed that local embrittlement on the outer surface of the spring wire causes crack initiations and disperses through the pearlitic interlamellar microstructure. Compared to non-galvanized and shot-peened specimens with the same surface roughness, compression springs, galvanized compression springs exhibited a 25 % reaction force loss at 50 000 cycles.

Targeted adjustment of residual stresses in hot-formed components by means of process design based on finite element simulation

The aim of this work is to generate an advantageous compressive residual stress distribution in the surface area of hot-formed components by intelligent process control with tailored cooling. Adapted cooling is achieved by partial or temporal instationary exposure of the specimens to a water–air spray. In this way, macroscopic effects such as local plastification caused by inhomogeneous strains due to thermal and transformation-induced loads can be controlled in order to finally customise the surface-near residual stress distribution. Applications for hot-formed components often require special microstructural properties, which guarantee a certain hardness or ductility. For this reason, the scientific challenge of this work is to generate different residual stress distributions on components surfaces, while the geometric as well as microstructural properties of AISI 52100 alloy stay the same. The changes in the residual stresses should therefore not result from the mentioned changed component properties, but solely from the targeted process control. Within the scope of preliminary experimental studies, tensile residual stresses in a martensitic microstructure were determined on reference components, which had undergone a simple cooling in water (from the forming heat), or low compressive stresses in pearlitic microstructures were determined after simple cooling in atmospheric air. Numerical studies are used to design two tailored cooling strategies capable of generating compressive stresses in the same components. The developed processes with tailored cooling are experimentally realised, and their properties are compared to those of components manufactured involving simple cooling. Based on the numerical and experimental analyses, this work demonstrates that it is possible to influence and even invert the sign of the residual stresses within a component by controlling the macroscopic effects mentioned above.

Cleavage Stress Producing Notch-Induced Anisotropic Fracture and Crack Path Deflection in Cold Drawn Pearlitic Steel

The fracture performance of axisymmetric notched samples taken from pearlitic steels with different levels of cold-drawing is studied. To this end, a real manufacture chain was stopped in the course of the process (on-site in the factory), and samples of all intermediate stages were extracted from the initial hot-rolled bar (not cold-drawn at all) to the final commercial product (prestressing steel wire). Thus, the drawing intensity or straining level (represented by the yield strength) is treated as the key variable to elucidate the consequences of manufacturing on the posterior fracture issues. On the basis of a materials science approach, the clearly anisotropic fracture behavior of heavily drawn steels (exhibiting deflection in the fracture surface) is rationalized on the basis of the markedly oriented pearlitic microstructure of the cold-drawn steel that influences the operative micromechanism of fracture. In addition, a finite element analysis of the stress distribution at the fracture instant allows the computation of the cleavage annular stress required to produce anisotropic fracture behavior and thus crack path deflection associated with mixed-mode cracking. Results show that such a stress is the variable governing initiation and propagation of anisotropic fracture by cleavage (a specially oriented and enlarged cleavage fracture) appearing along the wire axis direction in the case of sharply-notched samples of heavily drawn pearlitic steels.

Analysis of microstructure and wear resistance of NM400 thick plate

The hardness distribution and microstructure morphology of NM400 low alloy wear resistant steel plate with thickness of 50mm and 60mm were tested and analyzed, and the sliding wear performance of typical measuring points was also analyzed. The results show that the depth of the NM400 (50mm) hardening layer is about 35mm, accounting for about 70% of the plate thickness. The depth of the NM400 (60mm) hardening layer is about 22mm, accounting for about 37% of the plate thickness. With the position of the measuring point gradually away from the surface of the steel plate, the martensite content in the microstructure of NM400 (50mm) and NM400 (60mm) gradually decreased, and the contents of pearlite, bainite and other microstructure gradually increased. The hardness of NM400 (50mm) gradually decreased from 410HV to 335HV, and the hardness of NM400 (60mm) gradually decreased from 410HV to 305HV. The micro-wear morphologies of NM400 (50mm) and NM400 (60mm) at each measuring point are mainly furrow and contact fatigue spalling, and the wear types are mainly abrasive wear and contact fatigue wear. The furrow depth and the number of furrows on the worn surface of the sample at the corresponding measuring point position gradually increased as the measuring point position moved away from the steel plate surface, and the spalling area and the depth of the spalling pit gradually increased. The wear type gradually changed from particle wear to contact fatigue wear.

Peritectoid carbide transformation based on ε-carbide Fe2C in Fe-C system alloys. Part 2. Metallographic studies

Original metallographic studies of annealed medium carbon steel (steel 45, steel 40X and steel 35XGA) are carried out in order to reveal leakages in pearlite of these steels of low-temperature carbide transformation of peritectoid type, in which solid solutions of ferrite and cement form a solid solution of wide area of homogeneity based on ε-carbide Fe2C. Most of the inclusions of pearlite cement 45 steel are almost entirely covered with a light grey “foam” shell of nanoglobular crystals ε-сarbide Fe2C. In the process of crystallization of ε-сarbide Fe2C on the cement plates of pearlite steel 45 three morphological types of structure of ε-сarbide Fe2C can be distinguished: “foam” globular shell, granular “outgrowths” and wrapping of particles of decomposed and partially dissolved cement plates. Chromium, which is a part of steel 40X, abruptly inhibits peritectoid transformation. On many cement plates pearlite surface is smooth. In areas where the concentration of chromium is low, the process of formation of ε-сarbide Fe2C is active, with the formation of individual sites with light gray “foam” shell of nanoglobular crystals ε-сarbide Fe2C. It can be expected that in high-alloy chrome steels, the peritectic transformation can be completely blocked through the stabilization of chrome cement or its transformation into thermodynamically stable high chrome carbides. In 30ХГСA steel a sharp intensification of the process of peritectoid transformation of solid solutions of ferrite and cement which are part of pearlite is fixed. The reason for acceleration of the disintegration process of pearlite cement into individual fragments and intensification of release of ε-сarbide Fe2C in the form of column-shaped crystals between the plates of pearlite cement is silicon and manganese, which are part of steel 30ХГСА. As a result of the acceleration of martensite decomposition, the morphology of the released crystals of ε-сarbide Fe2C has changed from “foam” nanocrystals of ε-сarbide Fe2C, typical for steel 45 and steel 40X, to granular. There was also intensive fragmentation or disintegration of cement plates with the appearance of plane-parallel boundaries between the fragments and the formation of large longitudinal flat inclusions of ε-сarbide Fe2C above 100 nm, whose axis is mainly perpendicular to the axis of the cement plate. On the basis of the performed experiments it is possible to consider as proved the presence of low-temperature carbide peritectoid phase transformation in the Fe-C alloy system as a result of interaction of solid solutions of ferrite and cement at 3820C with formation of solid solution on the basis of ε-сarbide Fe2C with wide area of homogeneity. The influence of the chemical composition of steel on the peritectoid transformation between ferrite and cement slurries opens up additional possibilities for regulating the microstructure of pearlite, such as the degree of dispersion of pearlite, which has a determining influence on a number of performance characteristics of steel, such as wear resistance, yield strength and others.

Enhancement of the AISI 5140 Cold Heading Wire Steel Spheroidization by Adequate Control of the Initial As-Rolled Microstructure

The effect of the initial microstructure and soft annealing temperature on cementite spheroidization and microstructure softening is studied on an AISI 5140 hot-rolled wire. In coarse pearlite microstructure (λ: 0.27 μm), the cementite spheroidization progresses slowly under subcritical treatment, and the microstructure does not achieve the minimum G2/L2 IFI rating defined in the ASTM F2282 to be used in cold forming operations under any of the annealing treatment studies. Fine pearlite (λ: 0.10 μm) and upper bainite microstructures are more prone to spheroidization, and the minimum G2/L2 IFI rating is achieved under subcritical annealing at 720 °C for 6 h. Independent of the initial microstructure, even in the case of martensite, low hardness values within 165–195 HV are attained after imposing a 10 h long treatment at 720 °C. Annealing treatments conducted at 660 °C and 600 °C on pearlitic microstructures give rise to very poor softening. The G2/L2 rating is not achieved in any of the treatments applied at these two temperatures in this study. In pearlitic microstructures, the spheroidization progresses according to a fault migration mechanism, enhanced by the presence of defects such as lamella terminations, holes, and kinks. In the upper bainite, the row-like disposition of the cementite along the ferrite lath interface provides necks where dissolution and consequent lamellae break-up take place quickly under annealing.

Tempered Bainite and Martensite Embrittlement in Microalloyed Steel for Forged Railroad Wheel to Heavy Haul Application

Abstract This research shows two new microalloyed steels with niobium (Nb) for railroad wheels (Nb1 and Nb2) applied on heavy haul transportation (load over 30 tons/axle). The steels have mixed microstructure composed of pearlite and bainite (finished wheel rim section), and another one composed of martensite with bainite (black wheel section removed on machining) obtained by continuous cooling quenching heat treatment followed by tempering. The bainitic and martensitic microstructure are sensitive to the temper embrittlement phenomenon; therefore, knowing the embrittlement temperature range of these steels is mandatory in order to avoid such an event in the tempering process. Charpy specimens were extracted from the rim of railroad wheels, austenitized (860 oC), quenched in water for four minutes, and tempered at different temperatures to obtain the embrittlement curve. Three materials were compared: AAR (Association of American Railroads) Class C steel with pearlitic microstructure (not sensitive to embrittlement), Nb1, and Nb2 microalloyed steels with martensitic, bainitic, and pearlitic microstructures. The microalloyed steels have niobium (Nb), molybdenum (Mo), and silicon (Si) addition. The effect of Si content and the microstructure (analyzed by Scanning Electronic Microscope (SEM)), regarding the embrittlement phenomenon, was also studied. The microstructure of Nb2 steel was analyzed by with Transmission Electronic Microscope (TEM) for improving its characterization.