High Carbon Pearlitic Steel Research Articles

Altering the Microstructure of Pearlitic Steel Using Pulsed Electric Current

Electropulsing treatment was applied to high carbon pearlitic steel to assess the effects of the treatment on microstructure and properties. Ferrite recrystallisation and cementite spheroidisation were induced in samples treated at pulse duration and frequency greater than 40μs and 50Hz, respectively. Ferrite grain size of electropulsed samples was refined compared to similarly annealed samples. The results are explained through a combination of heating and athermal dislocation and atomic mobility effects. With optimisation, electropulsing may offer an improved annealing processing method.

Microstructure and microhardness of pearlitic steel after laser shock processing and annealing

The microstructure evolution of the high carbon pearlitic steel after laser shock processing (LSP) with different laser pulse energy and high temperature annealing was investigated. After LSP, the cementite lamella were bent, fractured and broken into granules. Fragmentation and dissolution of the cementite lamella were enhanced by increasing the laser pulse energy. Results show that the ferrite lattice parameter increased due to carbon atom dissolution in the ferrite matrix, and the corresponding ferrite X-ray diffraction peaks shifted significantly towards the smaller diffraction angles. After annealing at 650°C for 30 min, an ultrafine duplex microstructure (ferrite+cementite) was formed on the surface. After LSP with a high energy, equiaxed ferrite grains were refined to 400 nm and the cementite lamella were fully spheroidised with the particle diameter of ∼150 nm. The corresponding grain size of ferrite and cementite under low pulse energy was 500 and 300 nm respectively. After annealing, the ferrite peaks significantly shifted towards the higher diffraction angles, and the ferrite lattice parameter decreased. The microhardness initially increases after LSP and then slightly decreases after subsequent annealing but remained higher than without LSP.

Formation of grain boundary ferrite in eutectoid and hypereutectoid pearlitic steels

Formation of grain boundary ferrite (GB-α) in high carbon pearlitic steels deteriorates ductility of steel wires. Since it is generally believed that fully pearlitic structure forms in eutectoid steels, GB-α formation in eutectoid or even hypereutectoid steels is curious. Therefore, effects of temperature and carbon content on the formation of GB-α in Fe-1mass%Mn-(0.75 and 1.05) mass%C alloys transformed isothermally at temperatures ranging from 873 K (600 °C) to 973 K (700 °C) were investigated to clarify the formation mechanism of GB-α. It was found that volume fraction of GB-α increases with decreasing transformation temperature, carbon content and prior austenite grain size. Pearlite nucleated at prior austenite grain boundary usually grows into only one of austenite grains separated by the grain boundary, and GB-α forms on the other austenite grain. Orientation analyses revealed that GB-α and pearlitic-α hold the same orientation, indicating that one α grain grows as pearlite into one of austenite grains, and as GB-α into the other austenite grain. It was shown that such morphology difference is caused by the difference in orientation relationship (OR) between ferrite and austenite such that near K–S OR and non K–S OR correspond to GB-α and pearlite, respectively. Consequently, it was proposed that suppression of cementite nucleation at ferrite/austenite boundary holding near K–S OR is a reason for the formation of GB-α in the transformation at low temperature. Furthermore, degenerated pearlite (DP) and Widmanstatten ferrite (WF) is formed as well as GB-α at lower temperature, and OR dependency of GB-α, WF, DP and pearlite were clarified.

Electrothermomechanical Processing of High Carbon Steels

Passing high density electric current through some metals has been shown to induce microstructural changes, such as grain refinement. Known as electropulsing, the process has previously been successfully applied to cold-drawn pearlitic steel wire over a very short treatment period (current density >103 A·mm-2 and pulse width <10-4s) and with low energy expenditure. Once optimised, electropulsing treatment may offer potential time-and energy-saving advantages over traditional grain refinement techniques. However, to date, very little research on the effects of electropulsing on pearlitic steel exists in the literature and is limited to steel wire. The current work was conducted to determine whether electropulsing treatment is capable of producing similar grain refinement and spheroidisation behaviour in the microstructure of cold-deformed high carbon pearlitic steel sheet (0.92wt%C). High current density electropulsing treatment was applied to pearlitic steel samples of 40 to 70% rolling reduction for 50 or 100 pulses. The electropulsing treatment did produce microstructural changes in pearlitic steel plate that was similar to that observed in pearlitic steel wire over a relatively short treatment time. These changes involved grain refinement and spheroidisation and were enhanced with increasing cold rolling reduction.

激光冲击次数对高碳珠光体钢组织和显微硬度的影响

激光冲击次数对高碳珠光体钢组织和显微硬度的影响

Relations between the micro and macro levels of plastic deformation in the drawing of high-carbon pearlitic steel

The deformation of pearlitic steel is considered at different scale levels. The pearlitic steel may be regarded as a nanocomposite consisting of ferrite and cementite plates. The stress-strain state of pearlitic steel in drawing may be analyzed at the micro level by means of Drawing 2d software (developed at AGH University of Science and Technology, Krakow, Poland). The macro-level parameters are taken into account in the analysis.

Magnetic inspection of fatigue degradation of a high-carbon pearlitic steel

The effect of high-cycle fatigue loading of U10 steel specimens with a fine-lamellar pearlite structure that were a annealed for a short time on the character of variations of the tangential component of the magnetic induction vector of specimens in a residual-magnetization state has been studied. It was found that fatigue loading up to major fatigue-crack formation leads to an increase in the tangential component of the magnetic induction vector and to nonuniformity of the magnetic induction distribution along the length of a specimen. This is due to the spheroidization of cementite plates, which occurs in U10 steel specimens under a fatigue load. Major fatigue-crack formation is accompanied by the appearance of a clearly pronounced peak in the distribution of the tangential component of the magnetic induction vector. The magnetic measurement technique that was used allows us to record both structural changes and cracks that result from the fatigue degradation of high-carbon-pearlitic steel.

Structural features of the behavior of a high-carbon pearlitic steel upon cyclic loading

The structural evolution upon high-cycle fatigue (tension with the magnitude of stress in a cycle below the macroscopic yield stress) of the hypereutectoid steel U10 (1.03 wt % C), in which pearlite of different morphology (fine-lamellar, coarse-lamellar, and partially spheroidized pearlite) was formed, has been investigated by scanning and transmission electron microscopy. Based on the fractographic analysis, features of fracture of these structural states have been considered. At a significant distance (10 mm) from the fatigue fracture, features of structural transformations caused by cyclic loading have been revealed. It has been shown that upon high-cycle fatigue in the steel U10 with structures of lamellar and partially spheroidized pearlite, substantial structural changes occur, namely, fragmentation and partial dissolution of cementite plates, and in fine pearlite, additionally, spheroidizing of cementite and polygonization of the ferritic component are observed. A dependence of the character of fracture on the type of structure formed upon fatigue loading has been established. In the steel with a nonequilibrium structure of unannealed fine pearlite, an enhanced elasticity modulus, as compared to other more stable structures (coarse-lamellar, annealed fine, and spheroidized pearlite), and a reduction in the magnitude of the elasticity modulus under the action of cyclic loading have been found. It has been established that the structural changes in fine pearlite of laboratory specimens of the steel U10 upon cyclic tension are qualitatively similar to those in a railroad wheel of the steel 65G under the service conditions.

Recrystallization and Spheroidization Behavior of High Carbon Pearlitic Steels Investigated by Means of Orientation Imaging Microscopy

The microstructural evolution and the softening behavior of hot rolled and 60% cold rolled 0.85wt% carbon pearlitic steels during spheroidization annealing have been investigated by using the textural and microstructural information contained in the Orientation Imaging Microscopy (OIM) scans. The local boundary energy map, recently suggested by the present authors, is used to monitor the changes of stored plastic strain energy distribution in ferrite during the annealing process, which shows that the spheroidization process of cementite is finished before the completion of recrystallization of the 60% cold-rolled high carbon pearlitic steel.

Deformation-induced phase transitions in a high-carbon steel

Abstract The methods of Mossbauer spectroscopy, X-ray diffraction analysis, electron microscopy, magnetostructural analysis and durometry were used to examine structural and phase transitions in a high-carbon pearlitic steel of the formula Fe–1.37mass% C (U13) during cold deformation (300 K) by compression shear in Bridgman anvils. The dissolution kinetics of a cementite having different morphologies was established. A supersaturated solid solution of carbon in BCC iron, an austenite with a high carbon concentration, and metastable e - and χ -carbides were formed during dissolution of the pearlite. Strengthening of the U13 steel depended on the formation of solid solutions of carbon in iron and precipitation of dispersed metastable carbides facilitating pinning of dislocations.

Optimization of mechanical properties of high-carbon pearlitic steels with Si and V additions

Systematic research has been undertaken on the effects of single and combined additions of vanadium and silicon on the mechanical properties of pearlitic steels being developed for wire rod production. Mechanical test results demonstrate that the alloy additions are beneficial to the mechanical properties of the steels, especially the tensile strength. Silicon strengthens pearlite mainly by solid-solution strengthening of the ferrite phase. Vanadium increases the strength of pearlite mainly by precipitation strengthening of the pearlitic ferrite. When added separately, these elements produce relatively greater strengthening at higher transformation temperatures. When added in combination the behavior is different, and substantial strength increments are produced at all transformation temperatures studied (550 °C to 650 °C). The addition of silicon and vanadium to very-high-carbon steels (>0.8 wt pct C) also suppresses the formation of a network of continuous grain-boundary cementite, so that these hypereutectoid materials have high strength coupled with adequate ductility for cold drawing. A wire-drawing trial showed that total drawing reductions in area of 90 pct could be obtained, leading to final tensile strengths of up to 2540 MPa in 3.3-mm-diameter wires.

An experimental and theoretical investigation of the response of BS11 steel to cyclic loading

This paper contains a detailed experimental investigation of the cyclic properties of a standard high-carbon pearlitic rail steel (BS11) subjected to complex uniaxial cyclic loading. The experiments were designed to be either load- or strain-controlled. It is found that the material response strongly depends on the mean value of stress or plastic strain as well as its amplitude. In a strain-controlled process, the mean stress does not reduce to zero but to a value corresponding to the plastic mean strain assuming the amplitude is kept constant. The specimen ratchets in the direction of mean stress but the cyclic ratcheting rate greatly reduces during the cyclic process and ends at a constant value. There is no sign that the ratcheting would stop, which is a new observed feature different from Bower's observation. The constitutive description proposed by the authors is found to give a good correlation to the experimental observation.

Void nucleation and growth in dual phase steel wires

Composite ferrite–lath martensite dual phase steel is an alternative to high carbon pearlitic steel for producing high strength wire and may be drawn with no intermediate patenting treatments because of its high work hardening rate and formability. This paper presents the study of the relationships between the void density in drawn wires, the drawing limit, and the initial structure. An Fe–2Si–0·1C (wt-%) dual phase steel was treated to produce three different martensite morphologies at constant volume fraction, then wire drawn. The void density varied linearly with total drawing strain in all three conditions. High magnification scanning electron microscopy revealed that voids were initiated by decohesion at ferrite/martensite interfaces and by shear cracking of martensite particles. The voids grow to form cracks parallel to the drawing direction and affect the drawing limit. The character of the martensite, either dislocated lath or twinned plate, was determined by transmission electron microscopy. The void density was least in the fibrous lath martensite structure, where the lath martensite has a high degree of initial structural coherency with the surrounding ferrite, which hindered void formation and hence delayed the drawing limit.MST/1024

Void nucleation and growth in dual phase steel wires

Composite ferrite–lath martensite dual phase steel is an alternative to high carbon pearlitic steel for producing high strength wire and may be drawn with no intermediate patenting treatments because of its high work hardening rate and formability. This paper presents the study of the relationships between the void density in drawn wires, the drawing limit, and the initial structure. An Fe–2Si–0·1C (wt-%) dual phase steel was treated to produce three different martensite morphologies at constant volume fraction, then wire drawn. The void density varied linearly with total drawing strain in all three conditions. High magnification scanning electron microscopy revealed that voids were initiated by decohesion at ferrite/martensite interfaces and by shear cracking of martensite particles. The voids grow to form cracks parallel to the drawing direction and affect the drawing limit. The character of the martensite, either dislocated lath or twinned plate, was determined by transmission electron microscopy. The void density was least in the fibrous lath martensite structure, where the lath martensite has a high degree of initial structural coherency with the surrounding ferrite, which hindered void formation and hence delayed the drawing limit.MST/1024

Temperature dependence of the magnetic coercivity of pearlite

Reversal of remanent magnetization and peaks in the temperature dependence of the coercivity which are associated with the presence of lamellar Fe 3C (pearlite) have been observed in previous magnetic studies of iron-carbon alloys. New data are presented for the temperature dependence of the coercive force for temperatures from −200 to 770°C for five steels with carbon contents from 0.08 to 1.6 wt. %. Coercivities for medium- and high-carbon pearlitic steels are strongly temperature dependent: with increasing temperature the coercivity initially decreases to a minimum value near 100°C, then increases through a maximum near the Fe 3C Curie temperature, and then decreases to zero as the temperature approaches the magnetic or crystallographic transformation temperature for the ferrite. In contrast, in steels with spheroidized carbides, maxima in coercivity are not observed and coercivity decreases continuously with increasing temperature. A computational model is presented which explicitly takes into account magnetocrystalline and magnetostatic energies for two recognized crystallographic orientations of pearlite. The temperature dependence of the coercivity of lamellar pearlite calculated for this model is in qualitative agreement with experimental observations. The model also provides a basis for understanding the reversal of remanent magnetization in pearlitic steels during heating.

Odd uses of dyes : F. Hill in Chemical Industries, Vol. 41, No. 2

Formation of grain boundary ferrite (GB-α) in high carbon pearlitic steels deteriorates ductility of steel wires. Since it is generally believed that fully pearlitic structure forms in eutectoid steels, GB-α formation in eutectoid or even hypereutectoid steels is curious. Therefore, effects of temperature and carbon content on the formation of GB-α in Fe-1mass%Mn-(0.75 and 1.05) mass%C alloys transformed isothermally at temperatures ranging from 873 K (600 °C) to 973 K (700 °C) were investigated to clarify the formation mechanism of GB-α. It was found that volume fraction of GB-α increases with decreasing transformation temperature, carbon content and prior austenite grain size. Pearlite nucleated at prior austenite grain boundary usually grows into only one of austenite grains separated by the grain boundary, and GB-α forms on the other austenite grain. Orientation analyses revealed that GB-α and pearlitic-α hold the same orientation, indicating that one α grain grows as pearlite into one of austenite grains, and as GB-α into the other austenite grain. It was shown that such morphology difference is caused by the difference in orientation relationship (OR) between ferrite and austenite such that near K–S OR and non K–S OR correspond to GB-α and pearlite, respectively. Consequently, it was proposed that suppression of cementite nucleation at ferrite/austenite boundary holding near K–S OR is a reason for the formation of GB-α in the transformation at low temperature. Furthermore, degenerated pearlite (DP) and Widmanstatten ferrite (WF) is formed as well as GB-α at lower temperature, and OR dependency of GB-α, WF, DP and pearlite were clarified.