Ferritic-pearlitic Steel Research Articles

Effect of Zr addition on MnS inclusion characteristics and mechanical properties in medium carbon ferrite-pearlite steel

In this paper, the influence of decreasing Zr content (0.0110 wt%, 0.0044 wt%) on the microstructure, MnS inclusion characteristics, and mechanical properties of medium carbon ferrite-pearlite steel was studied. The results show that the volume fraction of intragranular ferrite (IGF) in steel increases with a reduction in Zr content. The ductility of the steel is reduced by 1.83%, the impact toughness is increased by 2.5 times, and the yield strength is almost unchanged. Compound MnS inclusions are the main inclusions that induce IGF formation. The proportion of heterogeneous nucleation of MnS inclusions using oxides as nucleation sites is increased, which is the main reason for the increase in the volume fraction of IGF. Furthermore, MnS inclusions change from type Ⅲ to type Ⅰ and Ⅱ, and their distribution is gradually uniform. Thermodynamic analysis reveals that the underlying cause for the morphological transformation of MnS inclusions is the rapid surge in the supersaturation of S element in molten steel. The presence of liquid-phase low-melting inclusions (MnS–Al2O3) promotes the formation of type Ⅰ MnS inclusions. The volume fraction and the dimension perpendicular to the fracture surface of the MnS inclusions are increased by at least 33% and 111%, while their aspect ratio is reduced by a maximum of up to 19%. The change in the volume fraction of MnS inclusions is the primary factor contributing to the decrease of tensile plasticity. The toughness of steel is mainly affected by the aspect ratio and the dimension perpendicular to the fracture surface of MnS inclusions.

Improving the quality of processing articles made of low-alloy ferrite-pearlite steels using concentrated laser emission

Improving the quality of processing articles made of low-alloy ferrite-pearlite steels using concentrated laser emission

A probabilistic model to predict specimen geometry effects on fracture toughness in ferritic–pearlitic steels

This work describes a probabilistic framework for cleavage fracture of ferritic–pearlitic steels incorporating experimental measurements of microcrack distribution associated with the cracking of the pearlitic microstructure. A central objective of this study is to explore and further extend application of a probabilistic framework incorporating the statistics of microcracks to predict specimen geometry effects on the fracture toughness distribution for a typical ferritic–pearlitic structural steel. Fracture toughness values for an ASTM A572 Grade 50 structural steel derived from fracture tests using conventional SE(B) specimens with varying thickness and a/W-ratios provide the cleavage fracture resistance data needed to assess specimen geometry effects on the probability distribution of Jc-values. The present exploratory study successfully predicts the measured statistical distribution of cleavage fracture toughness in shallow crack specimens and provides further support of the proposed probabilistic model as a more advanced and effective engineering-level procedure in fracture assessment methodologies.

The formation mechanism of fracture surface separations and their effects on the toughness for ferrite-pearlite steels

The formation mechanism of fracture surface separations for ferrite-pearlite steels is investigated by combining experimental testing and numerical simulation, and the effects of fracture surface separations on the toughness are discussed. The fracture surface of Charpy impact samples for both the as-rolled and the normalized ferrite-pearlite steel were compared. The fracture surface separations occur in the as-rolled plate above the ductile-brittle transition temperature instead of the normalized plate. The fracture surface separations are triggered by transverse tensile stress, which is supported by band-shaped pearlite with poor deformability. It is demonstrated that the formation of fracture surface separations is not only dependent on band-shaped pearlite and temperature but also on the stress state. The normal stress S11 in the X-direction is the largest, and the normal stress S33 distribution concentrates on the plate center, which can explain the location of the fracture surface separations. In contrast to the dispersed distribution of the normal stress S33 for the as-rolled plate, the large normal stress in the normalized plate is in a linear arrangement, resulting in a layered crack. The effects of fracture surface separations on the materials toughness are highly dependent on the number, length, depth and location of the separations.

Effect of Ti and S Content on the Properties and Machinability of Low-Carbon Ferritic–Pearlitic Steel

This research was focused on the effect of Ti and S content on the formation of non-metallic inclusions and their influence on the mechanical properties and machinability of low-carbon ferritic–pearlitic steels. An analysis and classification of the non-metallic inclusions were carried out. The tensile strength and impact toughness were determined from samples taken in the rolling direction. Machinability investigations were carried out on a CNC turning machine and by analyzing the surface roughness. TiO-TiN inclusions are present in steels with an increased Ti content. In these steels, the hardness, tensile strength, and cutting forces increase with a higher proportion of Ti. In the second group of steels with increased contents of S, Al, and Ca, MnS and CaO-Al2O3-MnS non-metallic inclusions are formed. As the S content increases, the tensile strength and cutting forces decrease, while the impact toughness increases. In steels with added Ti, the machining is more difficult, but a finer surface is achieved after turning, while a higher S content results in an increased fraction of softer sulfide inclusions, which reduce the cutting forces but also result in a reduced surface quality.

The effect of microstructure on the initial corrosion behavior of low carbon steel in simulated coal solution

Abstract The service life of weathering steels in wagon body was determined by their corrosion resistance directly. This study investigated the influence of microstructure on the initial corrosion behavior of low carbon steels, systematically. The initial corrosion behavior of ferritic-bainitic (F+B) steel, bainitic (B) steel and ferritic-pearlitic (F+P) steel are thoroughly analyzed using coal leach solution immersion test, macroscopic and microcircuit electrochemical methods. The results revealed that F+B steel exhibited the highest corrosion resistance, with the potential of M-A islands surpassing that of ferrite. The initial corrosion initiates from the dissolution of the ferrite matrix, followed by detachment of the M-A islands. The potential of M-A islands is higher than that of bainitic ferrite lath, and the corrosion originates from ferrite dissolution in B steel. Moreover, F+P steel exhibited the largest potential difference between pearlitic and ferrite, leading to initiation of corrosion from the pearlitic corrosion of internal ferrite. Additionally, the multiphase characteristics of P in F+P steel exacerbates their corrosion susceptibility. Overall, the influence of microstructure on the initial corrosion behavior of low carbon steels can be attributed to the potential difference between different phases. Ferrite is the preferentially dissolved phase due to its negative potential difference.

Investigations on the hydrogen embrittlement tendency of K55 for underground storage applications using hollow probe specimens

The susceptibility of ferritic pearlitic steel K55 to hydrogen embrittlement in high pressure gas atmospheres was investigated using slow strain rate tests with hollow probe specimens. Therefore, the specimens were charged with an internal hydrogen pressure of up to 20 MPa according to planned conditions for underground gas storages. The results show a significant decrease in ductility caused by hydrogen embrittlement yielding a loss in fracture strain of 46 % at 10 MPa and 63 % at 20 MPa hydrogen partial pressure compared to a specimen tested in nitrogen atmosphere. Furthermore, observations on the cross-sections of the tested specimens reveal that pearlite acts as obstacle for hydrogen enhanced crack growth.

Fracture characterization of structural steel S690Q by using mini-CT specimens

Mini-CT specimens are an interesting alternative when characterising the fracture behaviour of structural materials and there are issues with regard to, for example, the amount of available material, the irradiation level (in nuclear materials) or material inhomogeneities. Furthermore, in ferritic-pearlitic steels, the characterisation of the fracture behaviour within the ductile-to-brittle transition zone (DBTZ) is of particular interest, given that the material may behave very different, in terms of fracture toughness, when operating at different but relatively close temperatures within this zone. In many occasions, the definition of the DBTZ behaviour is performed through the Master Curve (MC) methodology and, thus, by testing standardised fracture specimens (e.g., CT, SENB) and determining the material Reference Temperature (T0). The use of mini-CT specimens to define T0 has been validated in a wide range of steels used in nuclear industry, but its application to structural steels has been scarce. Thus, this work gathers the fracture characterisation results (T0) obtained in structural steel S690Q, comparing them to those obtained by using conventional standardized SENB specimens. It is shown that, for this particular structural steel, the use of miniaturized specimens provides a T0 value (-89.3°C) which is comparable to the value obtained from conventional larger specimens (-110°C).

On the applicability of carbon steels K55 and L80 for underground hydrogen storage

To evaluate the possibility of hydrogen storage in depleted gas reservoirs, natural gas storage facilities, aquifers and salt caverns, the applicability of ferritic pearlitic K55 and tempered martensitic L80, both very frequently used as casings and tubings, has been investigated. Materials were investigated by means of high-pressure, high-temperature autoclave tests and analyses of the hydrogen uptake. The autoclave tests were performed on tensile specimens loaded with a spring at 90 % of the specified minimum yield strength, additionally the samples were analysed to determine the hydrogen uptake. Different gas compositions were considered (pure hydrogen, with or without the presence of CO2/H2S) under a hydrogen partial pressure of 120 bar. The tests were conducted in dry or wet environments. From the results, it can be seen that the hydrogen uptake is low even under the most severe conditions. However, from the mechanical test conducted in this study, it appears that the ferritic pearlitic K55 steel seems to be a suitable pipe material for underground hydrogen storage, and the higher strength steel L80 steel can be used only in non-sour environments (no significant amount of H2S in the reservoir, which is a priori the case of underground storages).

Regularities of Structure Formation of Composite Materials Based on Ferrite-Pearlite Steel and Aluminum-Manganese Bronze by Wire-Feed Electron Beam Additive Manufacturing

Regularities of Structure Formation of Composite Materials Based on Ferrite-Pearlite Steel and Aluminum-Manganese Bronze by Wire-Feed Electron Beam Additive Manufacturing

Structure Formation of Composite Material Based on Ferrite-Pearlite Steel and Aluminum Bronze Produced by Wire-Feed Electron Beam Additive Manufacturing

Structure Formation of Composite Material Based on Ferrite-Pearlite Steel and Aluminum Bronze Produced by Wire-Feed Electron Beam Additive Manufacturing

Microstructure and Crystallographic Texture of a Ferritic–Pearlitic Steel Subjected to Fatigue Fracture

Microstructure and Crystallographic Texture of a Ferritic–Pearlitic Steel Subjected to Fatigue Fracture

Multi-instrumental approach to domain walls and their movement in ferromagnetic steels – Origin of Barkhausen noise studied by microscopy techniques

Two steels, ferrite and ferrite-pearlite were thoroughly characterized by a multi-instrumental microscopy techniques to get detailed information about their microstructure and magnetic structure. Microstructural features act as pinning sites for the motion of magnetic domain walls (DWs) leading to changes in the magnetization of the sample. This phenomenon is the basis for industrially relevant non-destructive Barkhausen noise (BN) technique. With magnetic force microscopy (MFM), using bulk samples, and Lorentz microscopy, using thin films, we noticed that bulk and thin samples have similar domain structure still giving different BN signal amplitudes. We could explain an in-plane DW movement under out-of-plane applied magnetic field using anisotropy energetics. In-situ transmission electron microscopy (TEM) in Lorentz mode was used to visualize the motion of DWs and their interactions with different pinning sites. To help the interpretation of DW motions, alignment and denoising processes were tailored for in-situ TEM studies. Multi-instrumental and multidimensional structural analysis enabled us to visualize and verify many theoretical hypotheses related to the origin of BN signal in ferrite and ferrite-pearlite steels.

Influence of Local Electropolishing Conditions on Ferritic–Pearlitic Steel on X-Ray Diffraction Residual Stress Profiling

Layer removal with electropolishing is a well-established method when measuring residual stress profiles with lab-XRD. This is done to measure the depth impact from processes such as shot peening, heat treatment, or machining. Electropolishing is used to minimize the influence on the inherent residual stresses of the material during layer removal, performed successively in incremental steps to specific depths followed by measurement. Great control of the material removal is critical for the measured stresses at each depth. Therefore, the selection of size of the measurement spot and electropolishing parameters is essential. The main objective in this work is to investigate how different electrolytes and electropolishing equipment affect the resulting surface roughness, geometry, microstructure, and consequently the measured residual stress. A second objective has been to establish a methodology of assessing the acquired electropolished depth. The aim has been to get a better understanding of the influence of the layer removal method on the accuracy of the acquired depth. Evaluation has been done by electropolishing one ground and one shot peened sample of a low-alloy carbon steel, grade 1.1730, with different methods. The results showed a difference in stresses depending on the electrolyte used where the perchloric acid had better ability to retain the stresses compared to the saturated salt. Electropolishing with saturated salt is fast and results in evenly distributed material removal but has high surface roughness, which is due to a difference in electropolishing of the two phases, ferrite, and pearlite. Perchloric acid electropolishing is slower but generates a smooth surface as both ferrite and pearlite have the same material removal rates but may cause an increased material removal for the center of the electropolished area. In this work, it is suggested to use perchloric acid electropolishing for the final layer removal step.

Fracture Load Prediction of Non-Linear Structural Steels through Calibration of the ASED Criterion

In this work, the application of the Average Strain Energy Density (ASED) criterion for the estimation of failure loads in materials with nonlinear behavior containing U-shaped notches is presented. The ASED criterion was originally defined to predict failure in the presence of notches in materials with linear-elastic behavior. However, most structural materials (e.g., ferritic-pearlitic steels) can develop non-linear behavior (e.g., elastoplastic). In this sense, this work proposes to extend the use of the ASED criterion to materials that exhibit plasticity by a thorough calibration of their characteristic parameters, and the subsequent extrapolation of the liner-elastic formulation of the ASED criterion to non-linear situations. To validate this methodology, a wide range of structural steels (S275JR, S355J2, S460M, and S690Q) were used operating in the ductile-to-brittle transition range, with six different notch radii (0 mm, 0.15 mm, 0.25 mm, 0.50 mm, 1.0 mm, and 2.0 mm). The results obtained demonstrate that the proposed calibration of the ASED criterion allows for accurate predictions of failure loads. Therefore, it is shown that, for the notch radii analyzed in this work and for testing temperatures within the material ductile-to-brittle transition range, it is possible to extrapolate the ASED criterion to obtain estimates of failure loads in materials with U-shaped notches that exhibit ductile behavior.

The microstructure and corrosion behavior of Cr-containing ferrite-pearlite steels in an acidic environment

PurposeThe poor corrosion resistance of the ferrite-pearlite steel limits its application in marine engineering because of the enhanced galvanic effect caused by continuously accumulated cementite. Cr as one principal alloying element is commonly used to improve the corrosion resistance of steels. This paper aims to study the effect of Cr on corrosion behaviors of ferrite-pearlite steels in an acidic environment.Design/methodology/approachThe tested steels were immersed in a simulated solution of 10 Wt.% NaCl with pH 0.85 for 72 h to evaluate the corrosion rate. After the immersion test, the corrosion morphologies and products were tested by scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction. Meanwhile, an electrochemical workstation was used to study the electrochemical behaviors of samples.FindingsAt the initial corrosion stage, the corrosion rate increased in the sequence of Cr0, Cr0.5 and Cr1 steels, which was because of the competitive effect between the area ratio and the driving force caused by alloyed Cr. However, Cr1 steel exhibited the best corrosion resistance after a 72-h immersion test. This was because the alloyed Cr promoted the formation of protective Fe2O3 and FeCr2O4, which suppressed the preferential dissolution of ferrite and, thus, reduced the accumulation rate of carbides, resulting in the weakened galvanic corrosion.Originality/valueThis paper reports the role that Cr plays in the galvanic corrosion of ferrite-pearlite steels, which is important for the engineering application of ferrite-pearlite steels in marine environment.

Hydrogen resistance and trapping behaviour of a cold-drawn ferritic–pearlitic steel wire

Abstract The present work investigates the resistance of a progressively cold-drawn carbon steel wire against hydrogen embrittlement. In this study, analytical and numerical methods are used to determine the critical hydrogen content, the critical hydrogen ratio and the embrittlement indices of the different material conditions. The wire with the highest degree of cold deformation shows the highest critical hydrogen content and improved resistance against hydrogen embrittlement. At higher degrees of deformation, the material shows stronger hydrogen trapping, which improves in combination with a change in the lamellar spacing and orientation of the pearlite the resistance to hydrogen embrittlement.

Influence of pre-deformation on fatigue life of high strength steels by means of micromagnetic Barkhausen noise

Abstract The micromagnetic Barkhausen noise as a nondestructive testing method was employed in this work to analyze the fatigue behavior of high-strength steels by subjecting them to multi-stage load increase fatigue tests. The micromagnetic Barkhausen noise energy (MBNEnergy) was measured during fatigue tests and coupled with digital image correlation to evaluate the effect of static and cyclic stress as well as local surface strain on MBNEnergy. The test samples were prepared from the forged bainite 18MnCrMoV6 and two ferrite-pearlite 38MnVS6 and 46MnVS5 steels. A part of the specimens was pre-strained before cyclic loading to analyze the effect of pre-deformation on cyclic strength considering measured MBNEnergy. A significant increase in MBNEnergy was observed by increasing the cyclic load on 18MnCrMoV6 specimens with bainite phases while this increase of MBNEnergy was not significant or was not changed for ferrite-pearlite steels 38MnVS6 and 46MnVS5.

Engineering Method for Calculating the Limiting Amplitudes of Stress Cycles for Structural Steels

In large-sized metal structures, various stress concentrators are often present, which affects the operation of the material. These are intermittent bonds, holes, welded joints, material defects, etc. As a result of overloads under the action of an external cyclic load on structures in the area of stress raisers, the cycle asymmetry, the level of maximum stresses and deformations increase. In this case, the determination of the limit values of the stress cycles can be performed using a diagram of the limit stress amplitudes. The paper presents an engineering method for calculating the limiting stress amplitudes and constructing Hay’s diagrams. It is based on the use of mathematical models of classical linear and structural-mechanical fracture mechanics. Analytically and by calculation, the validity of the method is shown, which consists in determining the endurance limits and limiting stress amplitudes under high-cycle loading in a wide range of variation of the cycle asymmetry coefficient for ferrite-pearlite steels with a yield strength of up to 400 MPa. Thus, a generalized calculation method has been developed for determining the endurance limits for high values of cycle asymmetry and cycle stresses. The error of the method is estimated in the area of low-cycle load. The influence of constant and average load in a cycle on the endurance limit has been investigated both for high-cycle and low-cycle loading. The proposed approach allows to construct Smith and Hay’s fatigue diagrams for the tensile region, taking into account the structural characteristics of the material and the error allowed for engineering calculations.

Estimating the Yield Point from the Structural Parameters of Ferrite–Pearlite Steels

Estimating the Yield Point from the Structural Parameters of Ferrite–Pearlite Steels