Pearlitic Cementite Research Articles

Effect of Vanadium Alloying on the Precipitation Reactions during Pearlite Formation in Medium and High Carbon Steels

Vanadium microalloyed medium carbon steels are currently used in the automotive industry due to the improved tensile and impact properties that are achieved with moderate additions of vanadium. So far, from results published in the literature, the improvement in mechanical properties is attributed to the precipitation of VC within the proeutectoid ferrite that constitutes the major microstructural phase of these steels, while the pearlitic component has received relatively less attention. The purpose of the present study is to elaborate on the precipitation of vanadium carbide occurring during the isothermal pearlitic reaction in vanadium alloyed medium and high carbon steels. Since during this isothermal transformation the formation of proeutectoid ferrite precedes that of pearlite, the precipitation of VC within the proeutectoid ferrite was also studied, in order to verify existing literature results and to establish a basis of comparison with the VC precipitation occurring within the pearlitic ferrite during the subsequent pearlite formation. Three vanadium alloyed steels were used during the present research. These included two experimentally produced alloys, and a commercially available steel. The present study confirmed that, vanadium carbide interphase precipitates always exist within the pearlitic ferrite component of the lamellar and within non-lamellar pearlite. In the case of the lamellar pearlite, aligned arrays of interphase VC precipitates are present within the pearlitic ferrite, whereas in the non-lamellar pearlitic ferrite random distributions are most frequently observed. No partitioning of vanadium was observed into the adjacent pearlitic cementite regions even in cases of prolonged ageing at the high temperatures of the isothermal transformation. Morever, the experimental results show clearly that interphase VC precipitation exists not only within pearlitic ferrite but also within the proeutectoid ferrite,that forms in low carbon steels, in a form of well defined linear or curved arrays of regular shaped and uniformly sized particles.

The effect of carbon content on the hall-petch parameter in the cold drawn hypereutectoid steels

Influencing factors on the Hall-Petch parameter in the cold drawn hypereutectoid steels were investigated. The Hall-Petch parameter in the present hypereutectoid steels is independent of cooling rate and in turn, interlamella spacing but increases considerably with increasing carbon content. Analysis showed that increment ofKp with carbon content was attributed to the corresponding increment of volume fraction of pearlitic cementite with increasing carbon content.

A microscopic examination of the precipitation phenomena occuring during the isothermal pearlitic transformation in high carbon-copper nickel steels

During isothermal pearlitic transformation of high carbon austenite, the formation of proeutectoid phases precedes that of pearlite. Widmanstatten cementite is the major proeutectoid phase that forms at all temperatures. Within this constituent the precipitation of ε-Cu always occurs, together with the formation of stabilized coarse austenite entrapments. Within pearlitic cementite interphase precipitation of ε-Cu occurs at all transformation temperatures, while within pearlitic ferrite a banded interphase precipitation of ε-Cu occurs only at temperatures close to the eutectoid point. As the temperature of the isothermal pearlitic transformation is lowered the formation of non-partitioned pearlitic ferrite is possible and ε-Cu precipitation only forms within this ferrite as a result of ageing occurring during prolonged isothermal holding. It was concluded that interphase precipitation of ε-Cu always occurred on the migrating austenite/cementite interphase boundaries, but ε-Cu interphase precipitation occurred on the migrating austenite/ferrite boundaries only at temperatures close to the eutectoid point.

Microscopic characterisation of ε-Cu interphase precipitation in hypereutectoid Fe-C-Cu alloys

During isothermal pearlitic transformation in medium or high carbon copper steels the decomposition of austenite leads, apart from the formation of proeutectoid phases and pearlite, to the precipitation of the ε-Cu phase. At temperatures close to that of the eutectoid of the system interphase precipitation of ε-Cu occurs within proeutectoid ferrite (medium carbon steels), within grain boundary proeutectoid cementite (high carbon steels) and within both pearlitic ferrite and cementite. As the temperature of the isothermal pearlitic transformation is lowered the formation of copper supersaturated pearlitic ferrite occurs while within proeutectoid cementite (grain boundary or Widmanstatten) and pearlitic cementite interphase precipitation of ε-Cu continues. This study of the isothermal pearlitic transformation in the Fe-Cu-C system revealed that interphase precipitation of ε-Cu always occurs on moving cementite/austenite interphase boundaries but ε-Cu interphase precipitation only occurs on moving ferrite/austenite boundaries at temperatures close to the eutectoid temperature range of the system.

Strengthening of hot-rolled high- carbon steels by copper additions and controlled cooling

It is well-known that copper additions can produce significant improvements in strength levels through an age-hardening reaction in low- carbon steels in the quenched and tempered condition. In the present work the effect of copper additions for a number of different processing treatments, as-rolled, normalized and accelerated cooled, on the mechanical properties of high- carbon experimental steels have been studied. The morphology of copper precipitation observed in the pearlitic ferrite and cementite phases after different treatments is considered in order to assess its contribution to the mechanical properties. It is anticipated that these high- carbon copper-containing steels may be suitable for a variety of applications, for example, railway track products, or rod-stock for cold reduction to wire gauges, because of the improved strength levels.

A transmission electron microscopy study of copper precipitation in the cementite phase of hypereutectoid alloy steels

The precipitation of copper has been detected and studied in three of the main decomposition products of austenite: allotriomorphic grain-boundary cementite, pearlitic cementite, and Widmanstatten cementite plates. The investigation has been carried out on two high-alloy hypereutectoid steels containing copper contents of 1.0 and 2.5 wt pct. The main advantage of these high-alloy steels is that the parent austenite phase remains stable upon cooling to room temperature, thus preserving the parent phase and the parent/product interfaces in the microstructure for subsequent examination. Transmission electron microscopy (TEM) revealed that the copper precipitation occurs in proeutectoid allotriomorphic grain-boundary cementite in association with the transformation interface. The copper particles were dispersed in the form of rows (or sheets) within the allotriomorphs of cementite. Evidence for copper precipitate particles nucleated at structural features imaged at the growth interface was also obtained. Copper precipitation was found to occur in both the ferrite and cementite lamellae of pearlite, and again, examination of partially decomposed structures revealed copper particles nucleated at the austenite/pearlite transformation interface. In addition, copper particles were also observed at the ferrite/cementite interface of pearlite. Copper precipitation observed in Widmanstatten cementite plates revealed a precipitate-free midrib region in the plates and a higher concentration of copper particles toward the broad faces of the plate. Copper particles were also found located at coarse linear interface defects at the broad faces of the plate.

Modelling the carbide composition changes in [formula omitted]Cr [formula omitted]Mo [formula omitted]V steel during long-term tempering

The composition of pearlitic cementite in a 1 2 Cr 1 2 Mo 1 4 V steel has been extensively for long tempering times at a number of different temperatures. The chromium content of the cementite is found to increase steadily with time as the microstructure is tempered, at the expense of the iron content. Transformation of the cementite to alloy carbides occurs at long tempering times. The composition changes in the cementite have been modelled theoretically using numerical methods. There is excellent agreement between the predictions of the model and the experimental results. The dependence of composition on particle size has been studied and has been shown not to be significant because of the relatively large size and low chromium concentration of the pearlitic cementite. It is therefore possible to estimate an effective service temperature of components of 1 2 Cr 1 2 Mo 1 4 V steel in power plant for use in prediction of their remanent life.

The growth of holes in plates of cementite

Isotropic and anisotropic of circular and elliptic holes in plates of cementite of lamelar pearlite is discussed. The driving force for hole growth is obtained either from the difference in surface energy of the plates or from the inverses of the curvature of the holes. Two types of model are developed. In the first, constant thickness of the plate and, in the second, constant volume of the plate is assumed. For both models it is shown that the growth of holes is possible if the holes are of minimum size. The dependence of the size of this critical hole on the shape of the holes and on the ratio of half the distance of the holes on the plate to the thickness of the plate is discussed. Using the proposed models, experimental observations on the spheroidization of lamellar pearlite can be explained. A short discussion is given on the anisotropy of the ferrite-cementite phase boundary energy.

Fundamental study of microstructure-oriented strength assessment of a spheroidal graphite cast iron. 2nd Report. Corrosion fatigue in 3% hydrochloric acid and synthetic seawater.

Ferrite-base and pearlite-base spheroidal graphite cast irons were prepared to examine corrosion fatigue resistance in 3% hydrochloric acid and synthetic seawater. Rotating bending corrosion fatigue tests were conducted at two rates 3400 rpm and 260 rpm. From the tests in air and two corrosive environments, the following results were obtained : (1) The pearlite-base material (F) showed a fatigue strength stronger than that of the ferrite-base material (A) in the intermediate-cycle fatigue range, irrespective of environment or rotating speed. In the high-cycle fatigue range, the fatigue strengths of both materials asymptotically approached to coincide. (2) Anodic dissolution of graphite and local cathodic dissolution of cementite in pearlite played a primary role in the high-cycle corrosion fatigue process. (3) Those dissolutions described above induced a fatigue process different from that in air and resulted in diminished scatter of the S-n curves.

Near-Coincident Site Lattice Fitting of Ferrite/Cementite Orientation Relationships

AbstractA computer program was developed which takes experimental orientation analysis data from the transmission electron microscope and determines the corresponding best fit crystal orientation. This program was used to analyse the relative orientations between pearlitic ferrite and cementite in annealed and as-rolled eutectoid steel in terms of near-coincident site lattice (NCSL) solutions.The NCSL theory predicted not only the “standard” orientation relationships, i.e. Bagaryatskii and 2nd Petch, but also “non-standard” orientation relationships. Certain observed ferrite/cementite relative orientations showed significant deviations from any NCSL. The explanation of these deviations and of the non-observation of certain low-sigma solutions probably requires the consideration of inter-atomic forces, rather than only the near-coincidence of lattice points.

Effect of heating temperature on microstructure and properties of magnesium cast iron

1. Heating at temperatures below Ac1S leads to spheroidization and intensive dissociation of cementite in pearlite with formation of a structure that is mainly ferritic, which promotes some equalization of the microdistribution of silicon. 2. Heating in the intercritical range leads to formation of a special type of microstructure in the metallic matrix in which the austenite formed in ferrite is lamellar or acicular. With rapid cooling this type of structure is fixed at room temperature. Various decomposition products may be present in prior austenite sections. 3. The formation of the special microstructure in the intercritical range is accompanied by the formation of exceedingly fine silicon in the metallic matrix and thus a reduction of its embrittling effect. 4. Heat treatment in the intercritical range ensures a good combination of mechanical properties in magnesium cast iron.

Room temperature plastic deformation of pearlitic cementite

Cementite lamellae extracted from a eutectoid carbon steel wire drawn to ϵ = 0.43 show a substructure of intersecting straight bands, probably slip bands, which can be ascribed to (001), (010), (100), (011), (110) or (101) cementite traces. Only the (001) and (010) planes had been previously reported as cementite slip planes. There is extensive evidence in the literature concerning the ability of cementite to sustain plastic deformation but the important question of its potential ductility (capability to sustain any imposed strain) remains unanswered. The necessary condition for a crystal to behave ductilely, i.e. to possess five independent slip systems, would be unfulfilled if the (001) and (010) were the only available slip planes. The observation of four possible new slip planes supports the potential ductility of cementite.

The work hardening and fracture of steels containing cementite

Internal stresses have been calculated in deformed steels by tension containing spheroidal or pearlitic cementite on the basis of a continuum model by assuming that the cementite is non-deformable and the accumulated internal stresses are unrelaxed. The maximum principal stress in cementite is tensile and higher in particles with their longest axis oriented more closely along the tensile axis, whereas the minimum principal stress is compressive and its magnitude is larger in the particles aligning more normal to the tensile axis. The angular dependency of the internal stress becomes stronger as the particles become flatter. These tendencies account for the geometric features of cementite cracking and kinking observed in spheroidized and pearlitic steels. On the other hand, the work hardening of the steels results from the average internal stresses in the ferrite matrix, which are balancing the opposite stresses in the particles. These stresses increase linearly as plastic straining develops and depend insensitively on the morphology of the particles.

鉄鋼中の炭化物の電解分離による研究（第6報）低合金鋼中のセメンタイトの不均質性について

Thermo-magnetic studies on cementite isolated from low alloy steels confirmed that the compositions of cementite are frequently heterogeneous. (1) In 0.61%, 1.08%Mn steel, tempered between 500 to 650°, the cementite particles randomly contained various amounts of Mn; 1∼3%Mn at 500°,1∼5.5%Mn at 550°,1.5∼6.2%Mn at 600°,and 4∼6.3%Mn at 650°, by 1 hr tempering. It is conceivable that the heterogeneous enrichment of Mn in cementite particles intemp tempering was caused by ununiform or structure-sensitive movement of Mn atoms in ferrite matrix. Similar appearance was recognized in cementite in tempered 1.13%C, 1.42%Cr steel. (2) Cr concentration in pro-eutectoid cementite was higher than in the pearlitic cementite. But, Mn concentration in pro-eutectoid cementite was lower than in pearlitic cementite. Generalizing these results, it is deduced that A1pt-raising elements (Cr,Mo,W,V,Ti etc) dissolve in pro-eutectoid cementite more than in pearlitic cementite. On the contrary, A1pt-lowering elements (Mn,Ni etc) dissolve in pearlitic cementite more than in pro-eutectoid cementite.

Cementite morphology in pearlite

Some characteristic growth patterns of cementite in pearlite, revealed by electron microscopy, are discussed in terms of the geometry of growth and of diffusion and surface energy factors. These include 1. (a) linear discontinuities in the lamellar structure, which are shown to be one possible origin of branching, 2. (b) curved and striated lamellae, 3. (c) acicular growth of cementite. It is concluded that lamellar precipitation of cementite has its origin in anisotropy of ferrite-cementite interfacial energy.

鐵鋼中に於けるジルコニウム

Behaviours of Zirconium in steel are studied, the follwing effects are recognized: (1) Acm points of high carbon steel are depressed by addition of Zr and Al points are inva-riable by being of Zr. (2) Zr produces the secondary hardening in steel and its effects are accerelated by being togethei of silicon and chromium. (3) Zr makes the austenite grains finer. (4) Zr have ability spheroidizing the cementite in pearlite. (5) Zr makes slow the softening speed on tempering of quenched steel, e.g. Zr have ability in-creasing the retarding effect to tempering.

On the inner crystalline structure of ferrite and cementite in pearlite

In a previous paper on “The Inner Structure of the Pearlite Grain” read to the Iron and Steel Institute in 1922 the author advanced views on the stereometry of the pearlite grain. It was shown that the angle of inclination of a secant plane ω could be computed from the equation cos ω = Δ 0 /Δ ω , (1) where Δ 0 is the actual distance between two consecutive cementite or ferrite lamellæ and Δ ω is the trace of that distance on the secant plane. It follows from (1) that Δ ω = Δ 0 sec ω. (2) As the diameter d c of a cementite lamella or the diameter d f of a ferrite lamella is a constant fraction of Δ, it may be assumed that d ω = d 0 sec ω, (3) where d ω is the trace of d 0 on the secant plane.

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