Proeutectoid Ferrite Research Articles

Three-Dimensional Morphology and Analysis of Widmanstätten Sideplates Ferrite

The three-dimensional (3D) morphology and crystal structure of Widmanstätten sideplate ferrite were simulated using a focused ion beam (FIB) scanning electron microscope equipped with electron backscatter diffraction (EBSD). The primary Widmanstätten sideplates nucleated and grew directly at the austenite grain boundary (GB). A certain included angle between the sideplates and the austenite GB was observed. The sideplates grew approximately parallel to the grain, and were separated by a small-angle GB. The primary Widmanstätten sideplates are best described as “∃” shaped, with a long intermediate ferrite strip. The interface with the austenite GB was smooth and flat, and the sideplate surface contained pits and holes. The secondary Widmanstätten sideplates nucleated and grew on the surface of the proeutectoid GB ferrite, with the sideplates and GB ferrite perpendicular to each other. Sideplates parallel to one another grew into the grain, and were separated by small-angle GB. The 3D morphology was distinguished by its “comb” shape. The sideplates’ tail was clustered and its front end remained sharp. The contact side of the GB ferrite was smooth and flat. The surface contained several uneven pits and defects.

Wear mechanisms and wear resistance of austempered ductile iron in reciprocal sliding contact

Austempered ductile irons (ADIs) are used in applications commonly exposed to severe contact conditions, and as a consequence wear damage frequently followed by failure of components. Hence, wear resistance of the material governs the final life time of a component. In the present work, the sliding wear resistance of two ausferritic spheroidal graphite ductile irons ADI1 and ADI2 used commonly in mining and construction equipment was investigated. ADI1 and ADI2 were heat treated to a similar strength, the volume fraction of the carbon-rich austenite in ADI1 and ADI2 was around 30% and 16%, respectively, and they both contained 10 – 13% nodular graphite. The wear tests were performed using a slider-on-flat-surface (SOFS) tribometer. Case-hardened steel plates made of a high strength steel, 22NiCrMo12–F, were used as the counterface. The wear tests were conducted under lubricated sliding contact at normal loads of 50, 100, 200 and 300 N, and at each load level sliding at 100, 200 and 300 m. The friction force between contacting surfaces was continuously monitored during sliding. The lubrication used in the present investigation was a mineral-oil-based paste commonly used in applications where high frictional heating is generated. Wear mechanisms of the tested specimens were investigated by means of optical and scanning electron microscopy and X-ray diffraction, and the wear damage was quantified using a 3D-profile optical interferometer. The main wear mechanisms, severe plastic deformation and surface delamination, were discussed concerning test conditions and material properties. The ADI1 grade with the higher volume of carbon-rich austenite displayed better resistance to sliding wear at high normal loads. The higher normal loads promoted larger deformation at and beneath the contact surface and initiated austenite transformation into hard martensite. Thus, it was concluded that the increase of wear resistance in ADI1 was due to the formation of marteniste. On the other hand, the ADI2 grade with higher silicon content showed lower wear resistance at high normal loads. This was associated with cracking of the proeutectoid ferrite presented in ADI2.

Oscillating wire arc additive manufacture of rocket motor bimetallic conical shell

This paper studies the temperature field, dynamic strain, and forming accuracy of the oscillate-WAAM conical shell in the forming process and manufactures the WAAM conical shell part. The results show that compared with the offset filling WAAM, the oscillate-WAAM conical shell shows the following characteristics: the temperature difference value between the inner and outer walls of the shell is significantly reduced, the cooling rate doubled decreased, the interlayer temperature is above 300 °C, and the average temperature gradient, the dynamic strain stability value, and deformation are reduced by about 50%. Under the same process parameters, the travel speed of oscillate-WAAM is low, which increased the heat input large and the interlayer temperature high. Meanwhile, the molten pool of oscillate-WAAM is in consistent with the width of the shell. The molten pool’s simultaneous solidifying changes the stress state of printed shell from three-dimensional to two-dimensional. All the above are conductive to stress release and reduce the strain and deformation of components. The bimetallic rocket motor shell composed of HS600 and HS950 is manufactured by oscillate-WAAM. The section roundness of the shell is 0.31 mm, and the overall forming accuracy is ± 0.625 mm. The deposited metal in HS600 part of conical shell is composed of pearlite and pro-eutectoid ferrite, while the deposited metal of HS950 is composed of pearlite, acicular ferrite, and bainite. The forming accuracy and mechanical properties of conical shell formed by oscillate-WAAM meet the requirements.

Formation mechanism for the white etching microstructure in the subsurface of the failure pearlite wheel steel

The subsurface white etching microstructure (WEM) was an important reason to cause the rolling contact fatigue (RCF) failure of wheel materials. The WEM formation mechanism in the subsurface layers of failed pearlite steel wheel was analyzed by using a scanning electron microscope, transmission electron microscope, and nanoindenter. The results showed that RCF cracks were mostly at the interface between the WEM and pearlite matrix. A large amount of the WEM was found in areas with no RCF cracks. This indicates that the WEM was formed prior to the RCF cracks. The WEM was comprised of nanostructured ferrite grains and residual cementite particles, and its hardness (approximately 920 HV) was about 3 times as high as that of the pearlite matrix. A soft area model for WEM formation is proposed based on the microstructural characteristics of two types of ferrite grains and the dissolution of cementite in pearlite resulting from continuous plastic deformation. During the wheel–rail contact, continuous plastic deformation in the subsurface under high contact stress conditions causes the successive refinement of the proeutectoid ferrite (PF) with low strength and ferrite grains in pearlite, the dissolution of cementite, and the improvement in the corrosion resistance, which cause the WEM to look white under an optical microscope. The WEM formation processes induced by alternating fatigue load were similar to that of surface nanocrystallization through surface mechanical attrition treatment. The great difference between the WEM and the pearlite matrix in the strength results in the crack propagating along their interface, therefore the nonuniform distribution of the WEM along both edges of RCF cracks was found commonly.

Microstructure and strength in ultrastrong cold-drawn medium carbon steel

Via traditional wire drawing, the medium carbon ferrite-pearlite (MCFP) steel wires can achieve the ultrahigh strength beyond 4 GPa normally for high-carbon pearlitic steel wires, but have a 30–60% lower production cost. The microstructural evolution and mechanical properties of medium carbon ferrite-pearlite steel wires have been investigated by means of scanning electron microscopy, transmission electron microscopy and tensile testing. The tensile strength of medium carbon ferrite-pearlite steel wires increases from 750 MPa up to 4120 MPa when the drawing strain increases up to ε = 6.4, which represents the highest strength reported so far – to our knowledge for a carbon steel with such low carbon content. At low and medium strains (ε ≤ 1.95), the proeutectoid ferrite forms dense dislocation walls (DDWs) via dislocation activities, including sliding, accumulation, interaction, and tangling. With the drawing strain increase, the reorientation of DDWs to the drawing direction forms the coarse proeutectoid ferrite lamellae. Finally, the proeutectoid ferrite deformed to high strains is characterized by a lamellar morphology and the average lamellar spacing of proeutectoid ferrite is about 55 nm at ε = 6.4. The interlamellar spacing of pearlite and thickness of cementite decreases with the drawing strain increases. The dislocation density in ferrite lamellae increases with the drawing strain increases, and the dislocation density in ferrite lamellae is 7.8 × 1015 m−2 at ε = 4.19. A higher dislocation density of 3.1 × 1016 m−2 can be obtained at ε = 6.4 by means of extrapolation and TEM investigations. The stress contributions of proeutectoid ferrite and pearlite to the flow stress are estimated based on quantified structural parameters. Based on the assumption that the stress contributions from different strengthening mechanisms are linearly additive and the general rule of mixtures, a good agreement between the measured and estimated flow stresses has been found in a large range of flow stress. The good application of the general rule of mixture to the medium carbon ferrite-pearlite steel wires indicates the importance of quantitative characterization of microstructural evolution and parameters with the strain.

Evaluation of the Effect of Heat Input and Cooling Rate of Rail Flash-Butt Welding using Finite Element Method Simulation

Abstract Simulations using the finite element method (FEM) were done to understand the effects of heating/cooling rates on the distribution of residual stresses. Two material parameters from rails were used while the boundary conditions remained constant: heat-affected zone size, maximum temperature and heating extraction rate. To complement the analysis, a flash-butt weld of a Premium rail was done with welding parameters adjusted to obtain a narrow HAZ, without forced cooling, to examine the microstructure formed in the critical regions in the web and the edge of the rail foot. The results showed that there was a concentration of vertical residual stresses in the web region, while the presence of horizontal compression residual stresses was mostly superficial in the rail head region. The main result from the simulation sets was that when using two simulation parameters with similar materials (rails) substantially different results were obtained. Metallographic examinations showed that there was no presence of acicular microconstituents (martensite/bainite). In the rail web, proeutectoid ferrite was observed in the central region, cementite in a previous austenitic grain boundary, in the region that reached temperatures close to AC3, and almost complete spheroidization in the region of maximum spheroidization. In contrast, in the rail foot edge region, there was a completely pearlitic microstructure, in the central region and in the zone that reached temperatures close to AC3, and a lower volume of spheroidization in the region where maximum spheroidization is typically observed, probably due to the higher cooling rate in this region.

Mechanical Properties and Precipitation Behaviors of a Low‐Mo Nb–V–Ti Complex Microalloyed Fire‐Resistant Steel with Two Kinds of Microstructure

A new type of low‐Mo Nb–V–Ti complex microalloyed fire‐resistant steel is designed. Two kinds of controlled rolling and controlled cooling processes are employed to obtain the two steels with predominantly composed of fine‐grained proeutectoid ferrite (1#) and coarse‐grained full bainite (2#), respectively. The microstructures and precipitates of the experimental steels in room temperature and 600 oC are characterized by means of the scanning electron microscope (SEM), electron backscattered diffraction (EBSD), transmission electron microscope (TEM), and physicochemical phase analysis, and the strengthening mechanisms at room temperature and elevated temperature are quantitatively calculated and analyzed. The results show that the mechanical properties of the two steels are close to each other at room temperature. However, the fire resistance of bainite steel is much better than that of ferrite steel. Nanosized M(C, N) further precipitates from bainite at elevated temperature, which improves the stability of the bainitic structure and compensates for the loss of yield strength caused by the shear modulus decreased at high temperature. The grain refinement strengthening may not play a role at 600 oC in proeutectoid ferrite steel.

EBSD Study on Proeutectoid Ferrite and Eutectoid Ferrite Refinement Mechanism of D2 Wheel Steel Under a Rolling Condition

This study used scanning electron microscopy with an electron backscatter diffraction system to study the refinement mechanism of proeutectoid ferrite (Pro-F) and eutectoid ferrite (Eut-F) in a D2 wheel steel under rolling contact conditions. The results indicate that as the shear strain increased (γ < 0.21), the dislocation density in the proeutectoid ferrite increased continuously, and the formed dislocation cells were distributed uniformly in the grains. Subsequently, the dislocation cell boundaries were changed into low-angle boundaries (LABs); these LABs gradually became high-angle boundaries (HABs), and the average grain size was refined from 8 μm to 710 nm. Under a shear strain of 0.21 ≤ γ ≤ 0.84, dislocation pile-up occurred at the ferrite side of the eutectoid ferrite–cementite interface, and the spatial misorientation between the two adjacent eutectoid ferrites increased gradually. The ferrite lamellar was divided into bamboo-like grains by the LABs, and the proeutectoid ferrite was refined gradually into equiaxed grains. When the shear strain was at 0.84 < γ < 3.314, the number of HABs inside the eutectoid ferrite lamellar increased, and they were refined into bamboo-like grains. The two kinds of ferrite grains are refined repeatly by the equiaxial grains in an “elongation-bamboo like refinement-elongation” process, which gradually reduced the size difference. As the shear strain further increased, the two ferrites were completely mixed into the same morphology, the dislocation density was reduced dramatically, and ultra-fine equiaxed grains of approximately 110 nm were formed.

An electron backscatter diffraction investigation on microstructural evolution of pearlite wheel steel near rolling contact fatigue crack tip

AbstractAfter rolling contact fatigue (RCF) failure, ultrafine grains are formed in the proeutectoid ferrite (PF) and ferrite grains near the RCF crack tip. During the RCF process, the plastic strain of the samples increases as the cycle increases. When the RCF crack is initiated, a stress field is formed at the RCF crack tip. The accumulation of plastic strain before initiation of the RCF crack is the main reason to result in grain refinement near the RCF crack tip. The stress field also contributes to the grain refinement near the RCF crack tip. The accumulation of plastic strain and the stress field at the RCF crack tip lead to the generation of a large number of dislocations in the PF and ferrite grains in the zone in front of the RCF crack tip. Then, the dislocations are gradually transformed into subboundaries. Finally, the subboundaries evolve into high‐angle grain boundaries, leading to grain refinement. The RCF cracks are mainly propagated at the interface between the grain refinement zone and the unrefined zone at the RCF crack tip. The local grain refinement zone at the RCF crack tip can accelerate the propagation of the RCF cracks.

Experimental study on the surface microstructural evolution and fatigue wear resistance of pearlite wheel steels during rolling-sliding condition

In present paper, the relationship between fatigue and wear of three kinds of pearlite wheel steel samples is investigated by using rolling wear tester under 0.2% slip ratio condition. The results show that the weight loss, the surface hardness and the thickness of plastic deformation layer of three kinds of wheel samples are increased as the increase of cycles during rolling wear process. The weight loss of the G1 wheel sample is the highest owing to the existence of a large amount of proeutectoid ferrite (PF)grains. The correlation between weight loss and fatigue is competitive. High weight loss of the G1 wheel sample can hinder the formation of fatigue wear cracks. As a result, the G1 wheel sample surface changes to smooth after wear. The low weight loss of the G2 wheel sample and the G3 wheel sample cannot hinder the production of fatigue wear cracks during wear process. At the late wear stage, the wheel sample surface produces many fatigue wear cracks, and the wear mechanism becomes fatigue wear. Fatigue wear cracks, which are the rolling contact fatigue (RCF) crack source, can accelerate the RCF failure of wheel samples.

Fatigue mechanism of medium-carbon steel welded joint: Competitive impacts of various defects

Fatigue of welded joint is a scientific issue of great significance, because welding process always causes the loss of fatigue strength up to 40–60% for welded joint of the key components, resulting in a relatively poor reliability in service. In the present work, the fatigue behavior and damage mechanism of a medium-carbon steel welded joint were systematically investigated by microstructure observation and fatigue tests. It was found that, for the medium-carbon steel welded joint, fatigue crack mainly initiated at the welding defects, e.g., welding porosity, slag inclusion and heterogeneous microstructure with a poor mechanical property (i.e., the network-block proeutectoid ferrite). The competitive impact of various defects on the fatigue damage behaviors of welded joint was discussed, i.e., the competition between the volume defects (e.g., porosity and inclusions) and the heterogeneous structure. It is revealed that the smaller surface defects are more susceptible to fatigue damage due to the low constraint of plane stress state and higher stress intensity factor at high stress amplitude, while the larger internal defects easily cause fatigue damage at low stress amplitude because the driving force for crack propagation is larger than that of the damage case from the sample surface. Generally, the fatigue lives of samples with fatigue crack initiating from the weak phase are relatively longer, about 10 times as long as those of the samples with fatigue crack starting from the sample surface. In addition, the residual fatigue crack growth life, Nf, and the initial stress intensity factor (SIF), ΔK1 at the volume defect tip exhibit a linear relation in the double logarithmic coordinate system. The present findings can provide a theoretical basis for the anti-fatigue design and fatigue life extension technology for the metallic component with welded structures.

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.

Low Cycle Fatigue Behavior and Failure Mechanism of Wire Arc Additive Manufacturing 16MND5 Bainitic Steel

In this study, the low cycle fatigue behavior and failure mechanism of WAAM 16MND5 bainitic steel, which is commonly used in the nuclear reactor, were investigated thoroughly via a series of strain-controlled and stress-controlled low cycle fatigue tests. Results show that the microstructure of WAAM 16MND5 steel is granular bainite with a certain number of banded pro-eutectoid ferrite. WAAM 16MND5 steel exhibits similar cyclic deformation behavior under different strain amplitudes, i.e., a long stage of continuous cyclic softening and rapid cyclic softening till failure. The fatigue life decreases with the increasing strain amplitude. Moreover, the persistent slip markings in ferrite grains, the interface of pro-eutectoid ferrite and large Al2O3 inclusions are the preferred locations for microcrack initiation. The crack initiated from the edge of the specimen is observed to develop into a main crack. The main crack propagates mainly in transgranular mode and can also propagate along the pro-eutectoid ferrite interface.

Strain gradient induced grain refinement far below the size limit in a low carbon hypoeutectoid steel (0.19 wt% C) via pipe inner surface grinding treatment

A low carbon hypoeutectoid steel (0.19 wt% C) with proeutectoid ferrite and pearlite dual-components was subjected to surface plastic deformation via pipe inner surface grinding (PISG) at room temperature. The deformation microstructures for each component were systematically characterized along depth, and the patterns of structural evolution toward nanometer regime as well as the governing parameters were addressed. Proeutectoid ferrite grains were refined down to 17 nm, and the pattern covering a length scale of 4–5 orders of magnitude from micron- to nanometer-scale follows: formation of cellular dislocation structure (CDS), elongated dislocation structure (EDS), ultrafine lamellar structure (UFL) and finally the nanolaminated structure (NL). The pearlite experiences the deformation and refinement, and finally the transforming the ultrafine pearlite (UFP) into nanolaminated pearlite (NLP) with the ferrite lamellae as thin as 20 nm. Refinement for both UFL (UFP) and NL (NLP) can be realized via forming novel extended boundaries within ferrite lamellae. A critical lattice curvature of ∼2.8° is required for forming such extended boundary, corresponding to a minimum strain gradient of 0.25 μm−1 for a 100 nm-thick lamella. Refinement below size limit (expressed by lamellar thickness dT in nm) is correlated with the strain gradient (χ, in μm−1) by: dT=12.5χ. Refinement contributions from strain gradient caused by PISG processing and material heterogeneity were discussed.

Effect of Ta and Ti on Modified Reduced Activation Ferritic/Martensitic Steels with a Thermo‐mechanical Control Process

Modified reduced activation ferritic/martensitic steels with different amounts of Ta and Ti are fabricated with a thermo‐mechanical control process (TMCP). TMCP greatly enhances the refinement of both the precipitates and the martensite matrix. In addition, an increase in the dislocation density is achieved. The modified steels show excellent comprehensive mechanical properties compared with traditional reduced activation ferritic/martensitic steels. In addition, under the conditions of the TMCP, the effects of Ta and Ti on the microstructure and properties are analyzed. Simply increasing the amounts of Ta and Ti does not increase the phase fraction of MX, which is quite different from that derived from equilibrium thermodynamics theory or the typical hot rolling process for traditional reduced activation ferritic/martensitic steels. Without a high enough nucleation rate for MX, the excess Ta and Ti, which are not consumed by the formation of MX, promotes the formation of proeutectoid ferrite. This decreases the impact on toughness significantly. Herein, preliminary guidance is offered for a comprehensive design with a combination of both composition and rolling processing modification for the production of reduced activation ferritic/martensitic steels.

Influence of a Nonuniform Microstructure on the Rolling Contact Fatigue Properties of ER8 Steel Wheel

To mitigate the damage caused by rolling contact fatigue (RCF) on wheels, RCF tests are conducted to obtain the RCF limit of the surface area of an ER8 wheel tread that comprised a nonuniform microstructure. The microstructure topography of the RCF area is observed with optical microscopy, a scanning electron microscopy, and a transmission electron microscopy. The hardness, elasticity, and plasticity of different areas of the nonuniform microstructure are analyzed with a nanoindentation instrument. The results show that, besides pearlite and proeutectoid ferrite (matrix), a large amount of upper bainite is present. This component, therefore, interrupts the continuity of the wheel steel matrix, leading to a nonuniform microstructure and an RCF limit of 1074 MPa, which is lower than that of a wheel worn to the limit area and that comprised a normal microstructure. Furthermore, cracks mainly initiate and propagate at the boundary of the upper bainite and matrix. Although the hardness and the elasticity of the upper bainite are higher than those of the matrix, the plasticity is lower. Furthermore, under the effect of the contact stress, the difference between their deformations leads to stress concentration at the boundary, facilitating the initiation and propagation of cracks in steel wheels and accelerating the damage due to RCF.

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.

The Role of Microstructural Constituents on Strength–Ductility–Local Formability of a Transformation‐Induced‐Plasticity‐Aided Bainitic Steel

The microstructural evolution for varied austenitizing temperature is investigated in a transformation‐induced‐plasticity (TRIP)‐aided bainitic steel. Special attention is given to the effect of microstructural constituents on mechanical properties and local formabilities (stretch flangeability and bendability). With the decreasing of austenitizing temperature, proeutectoid ferrite is formed due to the refinement of prior austenite grain size, which yields the increased amount of large blocky martensite/austenite (M/A) constituents. The existence of ferrite and the TRIP effect provided by blocky retained austenite contributes to the higher strain hardening rate in the early stage of deformation as well as the more gradual decreasing of the strain hardening rate, leading to higher uniform elongation (UEL) for decreased austenitizing temperature. Whereas, the post uniform elongation (PEL) shows the opposite trend. Both hole expansion ratio (HER) and bending ratio (BR) have a linear relationship with PEL as well as yield ratio (YR). Replacing the multiphase microstructure with uniform bainitic microstructure would increase the balance of strength and local formability, in which the role of PEL is consistent with YR.

Study on Wear Properties of J11 Wheel Steel with Nonuniform Microstructure

In actual wheel–rail systems, a nonuniform microstructure of the wheel and rail materials is a serious problem. A double-disk rolling wear test device was used to study the influence of the nonuniform microstructure on the wear properties of wheel materials in the present study. The results show that the microstructure of the sample 1 includes proeutectoid ferrite, pearlite, and upper bainite, which is a nonuniform microstructure. By contrast, the microstructure of sample 2 contains only proeutectoid ferrite and pearlite. During wear tests, with the increasing number of test cycles, the weight loss of the sample 1 is consistently larger than that of the sample 2. A similar trend is observed with respect to deformation of the plastic layer. For the sample 1, fatigue cracks mainly propagate along the interface between the upper bainite and pearlite, leading to rapid wear failure; the main wear mechanism changes from spalling to fatigue with the increasing number of cycles. For the sample 2, the main wear mechanism changes from adhesive wear to fatigue wear with increasing number of cycles.