Pearlitic Steel Research Articles

Theoretical study of the prestressing strand's stress by computer modeling methods

The modern construction industry widely uses reinforced concrete structures, where high-strength prestressing strands are used. Key parameters determining strength and relaxation resistance are a steel microstructure and internal stresses. The aim of the work was a computer research of a stage-by-stage formation of internal stresses during production of prestressing strands of structure 1х7(1+6), 12.5 mm diameter, 1770 MPa strength grade, made of pearlitic steel, as well as study of various modes of mechanical and thermal treatment (MTT) influence on their distribution. To study the effect of every strand manufacturing operation on internal stresses of its wires, the authors developed three models: stranding and reducing a 7-wire strand; straightening of a laid strand, stranding and MTT of a 7-wire strand. It was shown that absolute values of residual stresses and their distribution in a wire used for strands of a specified structure significantly influence performance properties of strands. The use of MTT makes it possible to control in a wide range a redistribution of residual stresses in steel resulting from drawing and strand laying processes. It was established that during drawing of up to 80% degree, compressive stresses of 1100-1200 MPa degree are generated in the central layers of wire. The residual stresses on the wire surface accounted for 450-500 MPa and were tension in nature. The tension within a range of 70 kN to 82 kN combined with a temperature range of 360-380°С contributes to a two-fold decrease in residual stresses both in the central and surface layers of wire. When increasing temperature up to 400°С and maintaining the tension, it is possible to achieve maximum balance of residual stresses. Stranding stresses, whose high values entail failure of lay length and geometry of the studied strand may be fully eliminated only at tension of 82 kN and temperature of 400°С. Otherwise, stranding stresses result in opening of strands.

Effect of pearlitic morphology with varying fineness on the cavitation erosion behavior of eutectoid rail steel

The present work discusses the effect of the pearlitic morphology with varying fineness on the cavitation erosion behavior of eutectoid rail steel. Cavitation erosion of three different types of the pearlitic steels (furnace-cooled, air-cooled, and forced-air-cooled) consisting of coarse, fine, and very fine microstructures were tested in 3.5% NaCl solution and compared with that of the as-received pearlitic rail steel. The variation in the mean depth of erosion (MDE) and mean depth erosion rate (MDER) with erosion time was analyzed. Furthermore, the cavitation erosion resistance of the as-received, the air-cooled, and the forced-air-cooled was found to be 1.03, 1.51, and 2.14 times better than the furnace-cooled pearlitic steel, respectively. It was concluded that the cavitation erosion resistance of the pearlitic steel increased with the increase in the fineness of the microstructure.

Mechanism Behind the Onset of Delamination in Wire-drawn Pearlitic Steels

Mechanism Behind the Onset of Delamination in Wire-drawn Pearlitic Steels

Cross-rolling mediated microstructure and texture evolution in severely cold-rolled and annealed ultrafine pearlite

Effect of cross-rolling on the evolution of microstructure and texture in pearlite was investigated in the present work. For this purpose, near pearlitic steel was cold-rolled to 95% reduction by unidirectional cold-rolling (UCR) and different cross-rolling routes. The UCR processed material showed a predominantly lamellar structure, while the microstructure development in selected cross-rolled materials was featured by the presence of profuse shear bands and severely bent lamellae. While the UCR processed materials showed the presence of the typical RD (//〈110〉) and ND (//〈111〉) fibers, the texture formation in different cross-rolled materials was featured by the strong presence of a {001}〈110〉 component of the RD-fiber. The presence of the prominent {001}<110 > component could be explained by the stability of this component under cross-rolling. Recrystallization resulted in progressive spheroidization of the cementite. The pinning of the high angle boundaries by the cementite particles hindered the long-range migration of boundaries, thus inhibiting typical discontinuous recrystallization but favoring a recovery dominated softening process. The recrystallization textures in different cross-rolled materials were featured by the retention of deformation texture, namely the prominent {001}<110 > component of the RD-fiber, which amply corroborated a recovery dominated mechanism. Extended annealing resulted in the onset of abnormal grain growth in selected cross-rolled materials, which appeared to affect the microtexture, while the global texture remained mostly unaffected.

Computational thermodynamics/kinetics aided design for the microstructure of pearlitic steels during cooling process

Abstract The effect of cooling rate on the microstructure of SGLX82A steel was systematically investigated by coupling of experimental characterizations and thermodynamic/ kinetic calculations. The as-received casting ingots were heated and hot-deformed using a Gleeble simulator before being subjected to continuous cooling with rates of 5, 10, 15 and 20 K s-1. The microstructure of the SGLX82A steel was analyzed by using laser scanning confocal microscopy and scanning electron microscopy. The homogeneous microstructure with different proeutectoid ferrite fraction, pearlite colony size as well as pearlite lamellar spacing was examined at varied cooling rate. The calculation of the para-equilibrium phase diagram was performed by using Thermo-Calc software, while the DICTRA module was applied to calculate the diffusion-controlled ferrite formation and pearlite growth. Based on the calculations, the deviation between equilibrium and realistic eutectoid point was well explained, and the detected small amount of proeutectoid ferrite was attributable to the short duration before pearlite transformation. For the calculated pearlite lamellar spacings, good agreement was obtained compared with the experimental determinations. In addition, the present thermodynamic/kinetic method was also valid for a Crmodified steel SWRS87B, indicating the composition, processing parameters and microstructure of pearlitic steels can be reasonably designed with the aid of the present computational techniques.

Computational thermodynamics/kinetics aided design for the microstructure of pearlitic steels during cooling process

Abstract The effect of cooling rate on the microstructure of SGLX82A steel was systematically investigated by coupling of experimental characterizations and thermodynamic/ kinetic calculations. The as-received casting ingots were heated and hot-deformed using a Gleeble simulator before being subjected to continuous cooling with rates of 5, 10, 15 and 20 K s-1. The microstructure of the SGLX82A steel was analyzed by using laser scanning confocal microscopy and scanning electron microscopy. The homogeneous microstructure with different proeutectoid ferrite fraction, pearlite colony size as well as pearlite lamellar spacing was examined at varied cooling rate. The calculation of the para-equilibrium phase diagram was performed by using Thermo-Calc software, while the DICTRA module was applied to calculate the diffusion-controlled ferrite formation and pearlite growth. Based on the calculations, the deviation between equilibrium and realistic eutectoid point was well explained, and the detected small amount of proeutectoid ferrite was attributable to the short duration before pearlite transformation. For the calculated pearlite lamellar spacings, good agreement was obtained compared with the experimental determinations. In addition, the present thermodynamic/kinetic method was also valid for a Crmodified steel SWRS87B, indicating the composition, processing parameters and microstructure of pearlitic steels can be reasonably designed with the aid of the present computational techniques.

Rolled Stock Structure Preparation for Cold Forging of Pearlite Steel Grades

Special requirements are applied to the structural-mechanical characteristics of rod bolt products manufactured by cold die forging of pearlite steel class. A very common and productive method of obtaining finished metal products with high mechanical properties is their landing on cold heading (cold-heading) machines made of rolled metal, which must have a certain quality along the entire length: a sufficient ductility, homogeneous structure and parameters of technological properties, absence of any defects. Hardware plants receive the initial blank for the manufacture of various fasteners in the form of hot-rolled steel, which is not possible to use for the landing of high-strength hardware, due to the poor quality structure and surface layer. Therefore, the calibrated rolled stock is subjected to intermediate heat treatment before driving, which should guarantee the quality of the metal products at transitions of the cold heading. Further, the driven products of strength class 8.8 and up, made of alloy steel grades, must be subjected to hardening with subsequent tempering. However, such thermal operation often leads to decarburization of the surface, cracking and warping of finished products, thus increasing labor intensity, energy consumption and, consequently, the final production cost. The paper proposes an alternative method of the rolled stock structural preparation, which includes isothermal treatment of pearlite steel grades 35X and 38X, which excludes from the technological process the recrystallization annealing and quenching with the release of finished bolt products, and which minimizes any appeared scratches, warping and decarburization on the rolled stock and the rolled product. The structure of rolled stock induced in the drawing die, and the surface hardening by reduction, and thread rolling provide the parameters of mechanical properties of M8 bolts and pins, corresponding to the strength class 9.8.

Microstructure and Crystallographic Texture Changes under Torsion Loading of Pearlitic Steel Strips

Cold-drawn pearlitic steel strips exhibit a great combination of strength and ductility and are widely used in many engineering applications. Some of these applications require further mechanical conformation for the final use. An analysis of the microstructure and the change in crystallographic texture when strips are subjected to torsion processes necessary for some applications was made in the current study. It was shown that the formation of the wavy pearlite morphology associated with the fiber texture parallel to the drawing axis could improve fatigue damage. Extreme dislocation densities and crystallographic defects induced by torsion enhanced the formation of ultrafine ferritic grains accompanied by partial cementite decomposition. The relationship between ferrite and cementite interfaces successfully simulated using the Shackleton model.

Structural Turbulence of Pearlitic Steel 09G2S at Low-Temperature Impact Toughness

Structural Turbulence of Pearlitic Steel 09G2S at Low-Temperature Impact Toughness

Effect of bainitic transformation on the microstructure and wear resistance of pearlitic rail steel

PurposeThe purpose of this study is to develop a lower bainite structure consists of a dispersion of fine carbide inside plates of bainitic ferrite from chemical composition unmodified conventional pearlitic steel under bainitic transformation and to investigate its effect on tensile properties and wear resistance.Design/methodology/approachA commercial hypereutectoid pearlitic rail steel was subjected to three different bainitic transformation treatments followed by tempering to develop a desirable microstructure with a DIL805 BÄHR dilatometer. A comprehensive microstructural study was performed by scanning electron microscopy and energy dispersive x-ray spectroscopy. Finally, the mechanical properties and wear resistance were evaluated by tensile, microhardness, and pin-on-disc tests.FindingsThe results showed that the best combination of mechanical properties and sliding wear resistance was obtained in the sample subjected to bainitic transformation at 300°C for 600 s followed by tempering at 400°C for 300 s. This sample, which contained a bainitic ferrite structure, exhibited approximately 20% higher hardness and approximately 53% less mass loss than the as-received pearlitic sample due to the mechanically induced transformation in the contact surface.Originality/valueAlthough pearlitic steel is widely used in the construction of railways, recent studies have revealed that bainitic transformation at the same rail steels exhibited higher wear resistance and fatigue strengths than conventional pearlitic rail at the same hardness values. Such a bainitic microstructure can improve the mechanical properties and wear resistance, which is a great interest in the railway industry.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2019-0282/

Effect of periodic overloads and spectrum loading on fatigue life and microstructure in a Grade 900A rail steel

Fatigue life and crack growth retardation due to spectrum loading, which are superposed on constant amplitude cycles, have been investigated in this paper. For this purpose, numerical and experimental methods are used to investigate the behavior of fatigue crack growth in the rail specimens. A 3D nonlinear boundary element model has been applied to estimate the fatigue life of the rail specimens. Then, the effect of several parameters on the fatigue life in rail specimens is investigated using the suggested 3-D boundary element model and experimental tests. In the numerical analysis, the modified Paris model has been used. The analysis and experimental tests have been performed on C(T) specimens made of a pearlitic Grade 900A steel. In the experimental tests and numerical analysis, the periodic overloads have remained constant and the effect of overload ratio (OLR) and occurrence ratios (OCR) on the fatigue life has been investigated. Finally, microstructure analysis on microstructure morphology of the region where cracks grow for specimens was performed. Comparison between experimental results and numerical data indicates that the modified Paris model and the Forman_Newman_De Koning (FNK) model is actually accurate.

Microstructure evolution of railway pearlitic wheel steels under rolling-sliding contact loading

The objective of this work is to investigate the microstructure evolution of railway pearlitic wheel materials (ER7, CL60 and C-class) under a rolling-sliding contact loading. Firstly, microstructures of CL60 wheel steel at different depths from the strain-free matrix to the top surface were systematically investigated via laser scanning confocal microscope (LSCM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Secondly, the differences in microstructures of the top layers of those three types of wheel steels were explored. At last, the correlation between microstructure evolutions and their wear and rolling contact fatigue (RCF) behaviours was discussed. These information could provide a guide in development of premium railway wheel materials and choosing wheel materials.

Improving the abrasion resistance of pearlitic steels by high-temperature hardening and cold treatment

The influence of high-temperature quenching and cold treatment on the amount of residual austenite, its stability and ability to deformation martensitic transformation, hardening and wear resistance during the abrasive wear of pearlite grade 150KhNML carbon steel is studied. It is shown that maximum wear resistance during abrasive wear is ensured by a structure consisting of metastable residual austenite and martensite. Such a microstructure is created by high-temperature hardening before testing: during operations, austenite on the working surface, as a result of abrasive particles, turns into dispersed and nanocrystalline martensite with a high level of frictional hardening. This also results in the operability of the secondary steel microstructure due to the micro-TRIP effect. An additional means for increasing abrasion resistance is cold treatment after high-temperature hardening, which provides an increase in carbon martensite cooling before testing for wear resistance and the formation of new portions of carbon martensite deformation during testing.

Effects of inclusion size and stress ratio on the very-high-cycle fatigue behavior of pearlitic steel

The effects of inclusion size and stress ratio (R) on the very-high-cycle fatigue (VHCF) behavior of pearlitic steel were experimentally assessed. TheS–Ncurve under rotating bending loading exhibited a horizontal asymptote shape and a clear fatigue limit. In contrast, the S–Ncurve under ultrasonic axial loading exhibited a continuously descending shape, and the fatigue limit disappeared at a fatigue life of 107 cycles. The fine granular area (FGA) within nanograins formed in the crack initiation region only for the samples subjected to VHCF at R = −1. All instances of interior crack initiation were caused by the MnS inclusions.

The microstructure, texture evolution and plasticity anisotropy of 30SiMn2MoVA high strength alloy steel tube processed by cold radial forging

Cold radial forging is an efficient and high-precision process for producing rotary parts such as axles and gun barrels, etc. 30SiMn2MoVA high strength alloy steel is a kind of fine pearlite steel usually used for moulds and barrels. This work focused on the effect of the cold radial forging on the microstructure, texture evolution and plasticity anisotropy of forged steel tube under different forging reductions. The results suggest that most banded structures that are parallel to the axial direction are developed by the radial forging process. The grains are elongated and refined after forging. The increase of dislocation density with the increase of deformation is the reason for grain refinement. Refined grains and high dislocation lead to high strength. Meanwhile, anisotropy was obvious and was exacerbated by the growth of the forging deformation. The circumferential strength and elongation are inferior to the axial. With the increasing of forging ratios, the α-fiber texture is well developed. The relationship between the volume fraction of texture and plastic strain was built. It can predict the volume fractions of the main texture components in the cold radial forged 30SiMn2MoVA steel tube. The Taylor factors of the main orientations were calculated. The {111}<011>(γ-fiber), {110}<110>, {111}<110>(α-fiber), {114}<110>, {112}<110> and {223}<110> texture components help to enhance the axial yield strength. Comparing the ratio of the axial average Taylor factor and the circumferential average Taylor factor with the yield strength ratio, it is found that yield strength anisotropy is not well predicted only taking into account the crystal texture. The effect of banded structures on the strength should also be considered.

Characterization of used and virgin pearlitic rail steel

Rail transport system experience complex loading conditions that alters the microstructure of wheel and rail material near the contact interface region. This paper presents microstructure and hardness study of virgin and used pearlitic rail steel. Samples are prepared from the railhead section taken from nearby Kazipet Railway Division, (South Central Railway). The microstructure and hardness variation along the depth from the surface is presented. In continuation to the author’s previous study [1], along the transverse direction, this time samples are taken in a longitudinal direction. Microstructural observations show the existence of pro-eutectoid ferrite at the grain boundaries for the sample near to the rail surface. Presence of this softer material favours micro-crack initiation causing wear debris formation and rolling contact fatigue defects. Hardness test results reveal an increase in hardness values for material points close to the surface, while base material hardness remains almost the same. Higher hardness values at the surface level are indicating the formation of a brittle material which is more susceptible to crack initiation and propagation. This experimental investigation enriches knowledge domain in the formation of rolling contact fatigue defects. This will help railway engineers to schedule proper maintenance planning and material scientists to develop superior rail material.

Effect of Tempering Temperature on Microstructure and Mechanical Properties of Bainitic Railway Wheel Steel with Thermal Damage Resistance by Alloy Design

Thermal damage is one of the principle modes of wagon railway wheels. A new bainitic railway wheel steel with high thermal damage resistance and good combination of strength, plasticity, and toughness was developed. Microstructure and mechanical properties of the new steels in a tempered condition at different temperatures were examined. Microstructures were observed using scanning electron microscope and transmission electron microscope. Mechanical properties were evaluated by tensile, hardness, and Charpy impact tests with a simultaneous comparison to pearlitic railway wheel steel. The characteristic of retain austenite and V(C,N) were measured through X-ray diffractometry and energy disperse spectroscopy. The results indicate that this new bainitic wheel steel presents a submicron-sized carbide-free bainite morphology and preferable integrated mechanical properties when tempered at 280–360 °C. Precipitation strengthening plays an important role for the high strength, since a two-time-strengthening mechanism of the yield strength led by precipitation has been found at 280–360 and 480–560 °C, respectively. Compared with a pearlitic railway wheel steel, bainitic wheel steel tempered at 320 °C has a 10% higher yield strength, five times higher impact toughness, and much better thermal damage resistance, which is a promising railway wheel material for higher speed or heavier axle-load service conditions.

Multi-axial Fatigue of Head-Hardened Pearlitic and Austenitic Manganese Railway Steels: A Comparative Study

Switches and crossings (S&Cs) in rail networks suffer from damage and deformation due to severe loading of their complex geometric shapes. This article presents a comparative study of the cyclic deformation characteristics and fatigue behavior of two typical crossing materials, namely head-hardened pearlitic steel and Hadfield manganese steel, as well as the associated microstructural changes. Both uniaxial and biaxial loadings (proportional and non-proportional) are studied. The pearlitic steel endured more cycles to failure for a given strain amplitude compared to the manganese steel. The cyclic response of manganese steel shows significant hardening whereas softening was observed for the pearlitic steel except under biaxial non-proportional loading. The microstructures developed in the two types of steels after deformation are characterized by optical (OM) and transmission electron microscopy (TEM). TEM micrographs reveal that the deformed microstructure of the pearlitic steel consists of threading dislocations and dislocation tangles in the ferrite lamellae. The microstructures in the manganese steel after the different loadings are composed of dislocation cells with dislocation tangles inside, intersected by straight stacking fault lamellae. The observed microstructures are related to the results of the mechanical test, and the suitability of the steels for use in S&Cs is discussed.

Formation of optimal structure and properties of automotive pearlite steel during cold processing

Special requirements for structural and mechanical properties are applied to core fasteners manufactured on cold-forming machines made of automotive pearlitic steel. Mill products come as an original unit to manufacture various fasteners of hot-rolled steel, which can not be used for forming hardware due to the poor quality of the structure and surface layer. Therefore, the calibration rod undergoes intermediate heat treatment before drawing. In addition, products of strength grade 8.8 and higher, obtained from alloy steels on cold-forming machines, are quenched during tempering, which often leads to decarburization, cracking and bending of finished products, which increases the labor intensity, energy intensity and, consequently, the final cost. The article suggests a method for producing rolled products from automotive pearlitic steel 35Cr and 38CrA, including an isothermal process that excludes full annealing, quenching when tempering rod-shaped products and preventing decarburization, risks and curvature. The design, caused by passing through the drawing die, strengthening the surface by reducing and rolling the thread, provides mechanical properties of bolts and studs M8 strength grade 8.8 and 9.8.

Investigation of steel corrosion in MX80 bentonite at 120°C

AbstractCorrosion experiments were performed on two metallic substrates, a ferritic–pearlitic steel (P285NH) and a ferritic one (Armco), in silicate environment during 30 days at 120°C. Corrosion products were characterized in terms of morphology (scanning electron microscope and transmission electron microscopy), composition (energydispersive X‐ray spectroscopy) and structure (µ‐Raman, selected area electron diffraction, X‐ray absorption near edge structure). Results show a nanometric inner layer made of compact and adherent nanocrystallized magnetite with, locally a thickness up to several micrometers due to the metal microstructure. An outer layer of Fe‐rich phyllosilicate, smectite and serpentine, more porous than the inner one and poorly adherent is observed around both the samples.