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Showing papers on "Pearlite published in 1992"


Journal ArticleDOI
TL;DR: In this paper, the interlamellar crystallography of pearlite in iron-carbon alloys is examined in Fe-0.8C and Fe- 0.81C-12Mn steels with attention given to the Bagaryatsky, Pitsch-Petch, and Isaichev orientation relationships and their related atomic habit planes.
Abstract: The interlamellar crystallography of pearlite in iron-carbon alloys is examined in Fe-0.8C and Fe-0.81C-12Mn steels with attention given to the Bagaryatsky, Pitsch-Petch, and Isaichev orientation relationships and their related atomic habit planes. A survey of the overall literature reveals confusion about the crystallographic uniqueness in these orientation relationships. The present article focuses on this uniqueness and on habit planes between the pearlitic ferrite and cementite, from which the crystallography of ferrous pearlite orientation relationships is proposed to emanate. Techniques to characterize and identify orientation relationships unambiguously are developed. Habit planes are shown to be consistently obtained, even during curvature, with all deviations accommodated by microscopic steps.

138 citations


Journal ArticleDOI
TL;DR: A set of integrated mathematical models for simulating hot rolling and controlled cooling of wire rods and bars has been developed through extensive laboratory research work and validation against carefully monitored results from industrial mills.
Abstract: A set of integrated mathematical models for simulating hot rolling and controlled cooling of wire rods and bars has been developed through extensive laboratory research work and validation against carefully monitored results from industrial mills.Experimental tests have been carried out on C-Mn and eutectoid steels selected as representative of the various applications of wire rods and bars.Static and dynamic recrystallization of austenite, fraction of transformed austenite, final microstructures and mechanical properties are all calculated by modelling physical phenomena and using quantitative relationships between the microstructural and kinetic parameters and the process variables, i.e. strain, strain rate, temperature and time.The models have been applied to predict the microstructure evolution during hot rolling and to investigate the effect of working conditions and recrystallization mechanisms on the formation of heterogeneous austenitic microstructures.The effects of the cooling pattern on the temperature profile and the austenite phase transformation have also been studied to prevent: coarse pearlite and martensite formation at the centre of wire rods which have cores enriched in C and Mn; surface hardening of bars when water tube cooling systems are used to control the temperature at the cooling beds.The models provide an important insight into the process that is beneficial to enhance the quality of long products.

129 citations


Journal ArticleDOI
TL;DR: The microstructure and distribution of alloying elements in a hot rolled, low alloy plate steel containing (wt-%) 0·15%C, 0·26%Si, l·49%Mn, and 0·03%Al were examined using light microscopy and electron probe microanalysis as mentioned in this paper.
Abstract: The microstructure and distribution of alloying elements in a hot rolled, low alloy plate steel containing (wt-%) 0·15%C, 0·26%Si, l·49%Mn, and 0·03%Al were examined using light microscopy and electron probe microanalysis. Microstructural banding was caused by microchemical banding of manganese, where alternate bands of proeutectoid ferrite and pearlite were located in solute lean and solute rich regions, respectively. Bands were well defined for a cooling rate of 0·1 K s−1, but banding was much less intense after cooling at 1 K s−1. At a cooling rate of 0·1 K s−1 and for austenite grains smaller than the microchemical band spacing, austenite decomposition occurred via the formation of ‘slabs’ of proeutectoid ferrite in manganese lean regions resulting in the growth of ferrite grains across austenite grain boundaries. Abnormally large austenite grains result in the formation of large, irregularly etching pearlite nodules which traversed several bands. In specimens cooled at 1 K s−1, ferrite/pearli...

125 citations


Journal ArticleDOI
14 Aug 1992-Wear
TL;DR: In this article, the rolling-sliding dry-wear behavior of a series of bainitic steels and a pearlitic rail steel has been investigated over a wide range of contact stress and creepage conditions.

101 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of work-hardening of austenite on the nucleation and growth rates of various phases are discussed and a mathematical model of transformation kinetics from workhardened Austenite is also presented.
Abstract: To make quantitative prediction of microstructure in HSLA steels produced by isothermal or continuous cooling transformation, transformation kinetics of various phases were modeled thermodynamically. Five kinds of phases, i.e. polygonal ferrite, Widmanstatten ferrite, pearlite, bainite and martensite, and 10 alloying elements were taken into account. A program was developed on the basis of this model. Out line of the involved transformation kinetics are presented in this paper. The effects of work-hardening of austenite on the nucleation and growth rates of various phases are discussed and a mathematical model of transformation kinetics from work-hardened austenite is also presented.

92 citations


Journal ArticleDOI
TL;DR: In this article, an approach to predict mechanical properties of hot-rolled multi-phase steels referring to the stress-strain curves is proposed, which is based on regression analysis about the relationships between properties and chemical compositions and processing factors.
Abstract: An approach to predict mechanical properties of hot-rolled multi-phase steels referring to the stress-strain curves is proposed. Different from a conventional approach of regression analysis about the relationships between properties and chemical compositions and processing factors, a proposed one is based on the analysis and application of stress-strain curve: several commonly used mechanical properties such as yield strength, tensile strength, uniform elongation, total elongation, work-hardening exponent (n) and Vickers hardness, are derived systematically from the stress-strain curve of a multi-phase steel, which is calculated by using concentration factor, i.e., strain partition ratio and stress-strain curves of constituent phases. Stress-strain curves of individual component structures such as ferrite, pearlite, bainite, and martensite are expressed by Swift's equation. Physical background of the concentration factor is discussed by examining theoretical models of deformation for two-phase materials. Evaluation of plastic relaxation related to microstructural topology might be the most difficult point of this approach and some trials are presented.

71 citations


Journal ArticleDOI
TL;DR: In this article, a model of phase transformations in spheroidal graphite cast iron has been developed to quantitatively describe the microstructural evolution during solidification and the subsequent solid-state phase transformations (eutectoid reaction) during continuous cooling and to predict some of the micro-structural characteristics of final phases formed in SG iron castings.
Abstract: A model of phase transformations in spheroidal graphite (SG) cast iron has been developed to quantitatively describe the microstructural evolution during solidification and the subsequent solid-state phase transformations (eutectoid reaction) during continuous cooling and to predict some of the microstructural characteristics of final phases formed in SG iron castings. Such characteristics include phase fractions, phase spacings, and grain dimensions. In the model, the nucleation and growth of primary dendrites and eutectics were described based on existing theories, whereas the mathematical formulation for the eutectoid reaction,i.e., the formation of pearlite and ferrite from the as-cast austenite, was developed based on theories as well as physical evidence obtained from the experimental work. The Johnson-Mehl equation and the Avrami equation were used to calculate the fraction of transformed phases under continuous cooling conditions. The role of the grain impingement factor used in these two equations and the significance of the additivity principle in treating nonisothermal transformations were briefly discussed. The latent heat method was used for the numerical treatment of the release of latent heat during phase transformations. A two-dimensional finite element code which can be used in either Cartesian or cylindrical coordinates (ALCAST-2D) was used to solve the time-dependent temperature distribution throughout the metal/mold system. Numerical predictions were validated against experimental results, and good agreement was obtained.

68 citations


Journal ArticleDOI
TL;DR: In this article, the effects of the chemical composition, the finish-rolling temperature, and the cooling rate on the amount of martensite/austenite constituent formation in the as-rolled alloy steels were evaluated.
Abstract: To understand the controlled-rolled granular bainite structure, a series of high-strength low-alloy steels was specially designed and investigated. The effects of the chemical composition, the finish-rolling temperature, and the cooling rate on the amount of martensite/austenite (M/A) constituent formation in the as-rolled alloy steels were evaluated. It was found that for steels containing the same addition of Nb (0.045 wt.%), the granular bainite transformation was retarded with an increased carbon content ranging from 0.021 to 0.056 wt.%. As the carbon content was raised, more niobium combined with carbon to form carbide, and the austenite therefore became niobium-depleted. This effect significantly influenced the granular bainite transformation for the steels studied. It is also shown that the effects of Mn and Mo on the formation of second phases are different from that of carbon. These alloying elements tend to promote the M/A constituent and depress pearlite formation. As to the effect of rolling temperature, it is shown that as the finish-rolling temperature is lowered, the larger strain accumulated in austenite enhances polygonal ferrite formation along the previous austenite grain boundaries, and reduces the amount of M/A constituent. Furthermore, based on a thermodynamic analysis, it is indicated that the granular bainite transformation terminates as the carbon content of austenite reaches the TO curve. The critical carbon content increases with the decrease of the granular bainite transformation temperature. It was also found that the amount of M/A constituent formation decreases with the increase in cooling rate. This result is not consistent with that reported by Shiga et al., Tetsu-to-Hagane, 68 (1982) A227 and Bufalini et al., Accelerated cooling of steel,

49 citations


Journal ArticleDOI
15 Jul 1992-Wear
TL;DR: In this paper, a chromium-molybdenum premium rail steel was isothermally heat treated to produce microstructures of pearlite, upper bainite, upper and lower bainites, and lower and upper carbon bainitic steels.

45 citations


Book
01 Jan 1992
TL;DR: In this paper, the formation of Austenite from a structure of spheroidized carbides in ferrite and martensite is discussed, as well as the role of impurities in affecting grain growth.
Abstract: Introduction. The process of crystallization and chemical segregation. The formation of a crystal from a liquid. As-cast grain shape and size. Gross chemical segregation in ingots. Dendritic segregation [Coring]. The dendritic structure and chemical segregation of cast steel ingots. Dendritic structure in steel ingots. Gross chemical segregation in steel ingots. Dendritic segregation. Calculation of austenitizing temperature and time for chemical homogenization. Removing gross segregation. Removing dendritic segregation. Effect of homogenization on removing dendritic segregation. Banding in steels. Review of the grain growth process. The role of impurities in affecting grain growth. The effect of solutes. The effect of insoluble particles. Particle coarsening. Grain growth in austenite. Grain growth in pure iron. Grain growth in steels. Austenitization of steels. The formation of austentite in pure iron. The formation of austenite in steels. The formation of austenite from pearlite. The growth rate of austenite forming in pearlite. The nucleation of austenite in pearlite. The initial austenite grain size. The homogenization of austenite. The formation of austenite from structures of primary ferrite and pearlite and of primary iron carbide and pearlite. The formation of austenite from a structure of spheroidized carbides in ferrite. The formation of austenite from martensite. Examination of some models for carbide dissolution in austenite. Summarizing comments. Heating to the austenite region. Heat transfer relations. Some heating rate data. Closing comments. Austenitizing treatments to remove chemical segregation, either gross or dendritic, developed during solidification. Austenitizing as the first step in heat treatment. A comment on references. Index.

41 citations


Journal ArticleDOI
TL;DR: In this paper, a computer simulation model of microstructural evolution on the basis of chemical thermodynamics and classical nucleation and growth theory has been developed to evaluate the influence of steel chemistry and thermomechanical condition on the transformed microstructure of 0.10C-1.5Mn-0.35Nb steel.
Abstract: The computer simulation model of microstructural evolution on the basis of chemical thermodynamics and classical nucleation and growth theory has been developed. The metallurgical phenomena in thermomechanical treatment of steel, such as austenite grain growth, recrystallization and growth, carbonitride precipitation and austenite to ferrite phase transformation can be predicted by the model. The influences of steel chemistry and thermomechanical condition on the transformed microstructure of 0.10C-1.5Mn-0.35Nb steel (high C-high Mn steel) and 0.06C-1.25Mn-0.035Nb steel (low C-low Mn steel) are evaluated by computer simulation. With the increase of C and/or Mn concentrations, the volume fraction of second phase increases and the ferrite grain size is refined C-high Mn steel, the transformed microstructure consists of ferrite and pearlite phases at lower cooling rates and/or larger effective austenite interfacial area per unit volume, SV. The volume fraction of second phase increases with the increase of cooling rate and/or the decrease of SV value. The second phase of the steel at higher cooling rates is bainite. The transformed microstructure of low C-low Mn steel consists of ferrite and bainite phases. The influences of the rolling condition and the cooling rate on the transformed microstructure are smaller in low C-low Mn steel. However, the transformed microstructures is apparently influenced by the start temperature of accelerated cooling.

Journal ArticleDOI
TL;DR: In this article, the spheroidization of cementite at subcritical and intercritical temperatures was studied quantitatively by evaluation of a shape factor for the cementite particles, and it was found that the degree of spherodeization, as determined by the values of the shape factor, was markedly accelerated by treatments consisting in either (1) subcritical annealing after cold deformation or (2) intercritical anealing followed by subcritical reformation, while some differences were found among the microstructures resulting from the above treatments, which were related to
Abstract: The spheroidization of cementite at subcritical and intercritical temperatures was studied quantitatively by evaluation of a shape factor for the cementite particles. It was found that the degree of spheroidization, as determined by the values of the shape factor, was markedly accelerated by treatments consisting in either (1) subcritical annealing after cold deformation or (2) intercritical annealing followed by subcritical annealing. Nevertheless, some differences were found among the microstructures resulting from the above treatments, which were related to the mechanisms of cementite formation in each of them. Also, the kinetics of austenitization during intercritical annealing was found to be accelerated by previous deformation, and the analysis of the formation of austenite at intercritical temperatures in terms of an Avrami equation was consistent with an "effective" saturation of ferrite-pearlite boundaries with austenite nuclei, followed by a planar mode of growth into the pearlite nodules.

Journal ArticleDOI
TL;DR: In this paper, the stress response of the individual phases in a 1080 steel was measured by means of X-ray diffraction, and the microstresses formed by differential plastic deformation of the matrix and inclusions accurately model the spheroidite.
Abstract: By means of X-ray diffraction, the stress response of the individual phases in a 1080 steel were measured. Specimens with pearlitic, spheroidal, and tempered martensitic microstructures were subjected to low-cycle fatigue and the stress-strain hysteresis loops were separated into components for the carbide and matrix phases. Calculations of the microstresses formed by differential plastic deformation of the matrix and inclusions accurately model the spheroidite. Measured microstresses in the pearlite are smaller than the predicted values, probably due to yielding of the cementite and limitations on modeling the morphology. Work-hardening rates associated with the microstresses also qualitatively agree with the measurements. The tempered martensite cyclically softens with fatigue loading. The increased plastic strain range in the tempered martensite with cyclic softening is accompanied by an increase in the microstresses. These microstresses are significantly larger than predicted.

Journal ArticleDOI
TL;DR: In this paper, a brief rationalisation of the isothermal decomposition kinetics of supercooled austenite in steels is made and a temperature-composition-product (TCP) diagram is constructed for Fe-C alloys (plain carbon steels).
Abstract: A brief rationalisation is made of the isothermal decomposition kinetics of supercooled austenite in steels. From the experimental evidence of the past several decades, it is concluded that each type of isothermal decomposition product, i.e. grain boundary allotriomorphs, Widmanstatten ferrite (and cementite), pearlite, upper bainite, lower bainite, lath martensite, and twinned martensite, has its own independent C-curve in time–temperature–transformation (TTT) diagrams. Special emphasis is placed on the isothermal transformation kinetics of martensite. It is demonstrated that martensite transformation follows C-curve kinetics in isothermal conditions; this is a general rule and holds for all steels. The reason why most experimental TTT diagrams fail to display separate C-curves for different products is briefly explained. A temperature–composition–product (TCP) diagram is constructed for Fe–C alloys (plain carbon steels) to depict the general pattern of the decomposition process and to display th...

Journal ArticleDOI
TL;DR: In this paper, a 500 W CW CO2 laser was used to surface melt a pearlite grey cast iron at travel speeds 0.5-100 cm s−1. Detailed structural analysis of the laser modified layer was performed by optical and scanning electron microscopy (SEM).
Abstract: Pearlitic grey cast iron was surface melted using a 500 W CW CO2 laser at travel speeds 0.5–100 cm s−1. Detailed structural analysis of the laser modified layer was performed by optical and scanning electron microscopy (SEM), and microhardness depth profiles were measured. Temperature distribution was calculated from a three dimensional moving point source model, taking only the heat transfer into account. From the structural details observed in the austenitized zone some conclusions on the mechanism and kinetics of the pearlite austenite transformation at high heating rates were drawn. The melted zone consisted of primary austenite and ledeburite. At lower scanning speeds the structure was dendritic, at higher scanning speeds transition to dendritic-cellular structure was observed. From the secondary dendrite arm spacings the cooling rate during solidification was estimated as a function of the depth. Some discrepancies were found between our measurements and the literature data as well as predictions by the simple model neglecting convection in the melt.

Journal Article
TL;DR: In this paper, a brief rationalisation of continuous cooling transformations in steels is presented based on some generally neglected but sound experimental evidence, and it is demonstrated that twinned martensite can be formed in pure iron and dilute iron alloys at sufficiently high cooling rates.
Abstract: A brief rationalisation is presented of continuous cooling transformations in steels. Based on some generally neglected but sound experimental evidence, it is demonstrated that twinned martensite can be formed in pure iron and dilute iron alloys at sufficiently high cooling rates. It is further clarified that lath martensite and twinned martensite can be formed simutlaneously is one steel, with separate M s temperatures and at different cooling rates. The conditions for the formation of the various types of cooling transformation product, i.e. grain boundary ferrite, pearlite, massive ferrite, bainite (or bainite ferrite), lath martensite, and twinned martensite, are rationalised in terms of the transformation start temperature (i.e. M a , B s , M s , etc) and the critical cooling rate

Journal ArticleDOI
TL;DR: In this article, a 1% manganese alloyed ductile iron was used in the successive-stage, High-Low Austempering temperature process (HLAT Process) in different time combinations of high and low temperature austempering to improve the toughness of high-manganese ductile cast iron.
Abstract: In the austempering of ductile cast iron, it is necessary to alloy the metal to prevent pearlite transformation. The addition of alloying elements delays the pearlite transformation and at the same time, causes a similar delay in the beginning of the stage I reaction. In general, alloying addition levels greater than a specified amount are not desirable in the conventional austempering process due to the decrease in toughness and ductility. In this experiment, 1% manganese alloyed ductile iron was used in the successive-stage, High-Low Austempering Temperature Process (HLAT Process) in different time combinations of high and low temperature austempering to improve the toughness of high manganese ductile cast iron. The impact strength provided by the HLAT Process is a function of high temperature austempering time as well as low temperature austempering time. The impact strength at the best process combination is much higher than conventional high manganese ADI and well comparable to low alloy aust...

Journal ArticleDOI
TL;DR: The residual stresses in both the ferrite and cementite phases of fatigued 1080 steel specimens with pearlite, spheroidite and tempered martensite microstructures were measured using X-ray diffraction as mentioned in this paper.
Abstract: The residual stresses in both the ferrite and cementite phases of fatigued 1080 steel specimens with pearlite, spheroidite and tempered martensite microstructures were measured using X-ray diffraction giving both the macrostresses and microstresses. Specimens with no initial stresses showed little changes with fatigue. Specimens with initial macrostresses and microstresses showed fading of the stresses, the fading being slowest for the strongest microstructure. Hydrostatic microstresses are present after heat treatment owing to the differential thermal properties of the cementite and ferrite.

Journal ArticleDOI
TL;DR: In this article, the effect of chemical composition on the sintering mechanisms and microstructure of Fe-C-P alloys was studied by metallographic and thermal analysis and by secondary ion mass spectroscopy.
Abstract: The effect of chemical composition on the sintering mechanisms and microstructure of Fe-C-P alloys was studied by metallographic and thermal analysis and by secondary ion mass spectroscopy. Pore morphology was found to tend to spheroidisation with an increase in the phosphorus and, more particularly, in the carbon content. In addition, phosphorus was found to be heterogeneously distributed in ferrite and in pearlite. These results are explained by proposing a sintering mechanism, based on two main processes. The first leads to the formation of phosphorus rich ferrite through the reaction between phosphides and low carbon austenite. The second produces transient liquid through a eutectic reaction between phosphides and carbon rich austenite

Journal ArticleDOI
TL;DR: In this article, a mathematical model for the prediction of microstructural evolution and mechanical properties of steel plates is integrated with the process models that calculate the strain and temperature distribution through thickness at multiple points in the plate during the rolling and the cooling steps for the adoption to a commercial production line.
Abstract: The mathematical model for the prediction of microstructural evolution and mechanical properties shown in the previous report is integrated with the process models those calculate the strain and temperature distribution through thickness at multiple points in the plate during the rolling and the cooling steps for the adoption to a commercial production line. The experiments that cover the wide range of the chemical compositions and the manufacturing conditions of steel plates were conducted and the obtained results such as microstructures and mechanical properties of the plates were compared with the calculated results of the present integrated model. The main points of the present report are summarized as follows:(1) For the observation of austenite (γ) grain size during the interpass time of the rolling, the Thermal-Sampler that could cut off and quench a small specimen within 10 sec after the previous rolling pass was equipped in the commercial rolling line. The γ grain size calculated by using the present model almost agreed with the observed ones.(2) In the case of the air-cooled plates after the rolling whose microstructures were mainly ferrite (α) and pearlite, the calculated microstructures such as α grain size, the volume fraction and the microhardness of each phase showed good agreement with the observed ones. As a result, the calculated mechanical properties agreed well with the observed ones.(3) In the case of the acceleratedly cooled plates after the rolling whose tensile strength was above 600 MPa and major microstructure was bainite, the accuracy of the calculated results of microstructures and mechanical properties were inferior a little to the cases of the air-cooled plates. Even in the plates whose tensile strength was above 600 MPa, the calculated results were confirmed to be practically adoptable for the plates whose major microstructure consists of ferrite.


Patent
12 Jun 1992
TL;DR: In this article, a steel comprising 0.1 to 1.5% of C and 0.25 to 2.0% of Mn is heated to 900° to 1250° C, and the heated steel is hot-rolled at a temperature in the range of from Ar3 to (Ar3 +200)° C. with a total reduction of area of 30% or more.
Abstract: A steel comprising 0.1 to 1.5% of C and 0.25 to 2.0% of Mn is heated to 900° to 1250° C., and the heated steel is hot-rolled at a temperature in the range of from Ar3 to (Ar3 +200)° C. or Arcm to (Arcm+200)° C. with a total reduction of area of 30% or more. The hot-rolled material is cooled to complete a ferrite/pearlite transformation or a pro-eutectoid cementite/pearlite transformation. The transformed material is subjected to finish hot rolling at a temperature in the range of from (Ac1 -400) to Ac1 ° C. with a total reduction ratio of 10 to 70%. If necessary, the material after the finish hot rolling is cooled to 300° C. at an average cooling rate of 1° C./sec or less. A spheroidization annealing of the steel bar wire rod produced according to the process of the present invention enables a good spheroidized texture to be formed.

Journal ArticleDOI
TL;DR: In this article, complex copper bearing sulphide phases have been observed for the first time in controlled rolled niobium bearing high strength low alloy steels and their electron microscopy studies were carried out on these copper bearing sulfides.
Abstract: Complex copper bearing sulphide phases have been observed for the first time in controlled rolled niobium bearing high strength low alloy steels. Analytical electron microscopy studies were carried out on these copper bearing sulphides. The observations show that, in many cases, these particles have duplex sizes and are multiphase. The smaller particles have diameters from 0·2 to 0·7 μm with round or ellipsoidal disclike morphology, mainly present close to and/or within the pearlite banding where the segregation of the alloying elements is severe; they tend to be associated with other precipitates such as manganese sulphide, and titanium carbonitrides in the steels having titanium additions. The larger particles (>1 μm) occur occasionally, and are often associated with spinel MgO.Al2O3 and/or A12O3, Ti(C,N), MnS, and silica. These particles have complex chemical compositions with a ratio of (Cu + Mn)/S ranging from 0·77 to 1·42; their electron diffraction patterns lead to lattice parameters which ...

Patent
02 Apr 1992
TL;DR: In this paper, the authors proposed a method of producing a spheroidal graphite cast iron article containing at least one pearlite stabilizing element selected from the group consisting of Mn, Cu, Sn, Sb and Pb and having a double layer structure which comprises a surface layer portion and an inner portion.
Abstract: A method of producing a spheroidal graphite cast iron article containing at least one pearlite stabilizing element selected from the group consisting of Mn, Cu, Sn, Sb and Pb and having a double layer structure which comprises a surface layer portion and an inner portion. The surface layer portion has a matrix 60% or more of which is ferrite phase and a thickness of at least 0.5 mm. The inner portion has a matrix substantially comprising pearlite phase. The method comprises: (1) heat-treating a starting spheroidal graphite cast iron at a temperature which transforms a whole part of a matrix of the starting spheroidal graphite cast iron substantially to austenite phase; (2) slowly cooling the austenitized spheroidal graphite cast iron at a cooling rate (5° to 20° C./min) which allows in a subsequent step the surface layer portion to be ferritized before the inner portion starts to be pearlitized; (3) holding the cooled spheroidal graphite cast iron at a temperature (710° to 770° C.) which allows the surface layer portion to be first ferritized and subsequently allows the inner portion to be pearlitized while preventing the ferrite phase of the surface layer portion from being transformed to another; and (4) cooling the spheroidal graphite cast iron thus transformed immediately after completion of the pearlitization of the inner portion.

Journal ArticleDOI
TL;DR: In this paper, the first stage in the formation of the nonbanded form of nodular bainite is often the precipitation of cementite rods, or laths, in austenite at the α:γ interfaces of proeutectoid ferrite secondary sideplates formed earlier.
Abstract: Carbide precipitation during the eutectoid decomposition of austenite has been studied in an Fe-0.12 pct C-3.28 pct Ni alloy by transmission electron microscopy (TEM) supplemented by optical microscopy. Nodular bainite which forms during the latter stages of austenite decomposition at 550 °C exhibits two types of carbide arrangement: (a) banded interphase boundary carbides with particle diameters of about 20 to 90 nm and mean band spacings between 180 and 390 nm and (b) more randomly distributed (“nonbanded”) elongated particles exhibiting a wide range of lengths between 33 and 2500 nm, thicknesses of approximately 11 to 50 nm, and mean intercarbide spacings of approximately 140 to 275 nm. Electron diffraction analysis indicated that in both cases, the carbides are cementite, obeying the Pitsch orientation relationship with respect to the bainitic ferrite. The intercarbide spacings of both morphologies are significantly larger than those previously reported for similar microstructures in steels containing alloy carbides other than cementite (e.g., VC, TiC). Both curved and straight cementite bands were observed; in the latter case, the average plane of the interphase boundary precipitate sheets was near {110}α//{011}c consistent with cementite precipitation on low-energy {110}α//{111}γ ledge terrace planes (where α,β, andc refer to ferrite, austenite, and cementite, respectively). The results also suggest that the first stage in the formation of the nonbanded form of nodular bainite is often the precipitation of cementite rods, or laths, in austenite at the α:γ interfaces of proeutectoid ferrite secondary sideplates formed earlier. Although these cementite rods frequently resemble the “fibrous” microstructures observed by previous investigators in carbide-forming alloy steels, they are typically much shorter than fibrous alloy carbides. The bainitic microstructures observed here are analyzed in terms of a previously developed model centered about the roles of the relative nucleation and growth rates of the product phases in controlling the evolution of eutectoid microstructures.

Journal ArticleDOI
TL;DR: In the last century, a tremendous amount of research has been performed on every aspect of cast iron during the last decade as mentioned in this paper, with many different structures mingled together and it is difficult to distinguish the primary aus- tenite from the eutectic austenite.

Journal ArticleDOI
TL;DR: In this paper, the effect of a small prestrain on the fatigue strength of a carbon steel was investigated and compared with that of annealed and strain-aged specimens, and it was inferred that dislocations are unpinned by the small pre-strain and this causes fatigue slip to occur more readily, but the fatigue behaviour following slip initiation is not affected because the spheroidal cementite particles act as obstacles to further slip deformation and Stage I crack propagation.
Abstract: In order to clarify the effect of a small prestrain on the fatigue strength of a carbon steel, the fatigue behaviour of plain specimens of a eutectoid steel with spheroidal pearlite, previously subjected to a tensile prestrain, is investigated and compared with that of annealed and strain-aged specimens. It is found that a small prestrain of a few percent does not decrease the fatigue limit nor the crack initiation or propagation lives. Fatigue slip initiation, however, is accelerated by the small prestrain. It is also observed that cyclic strain ageing does not occur. From these results, it is inferred that dislocations are unpinned by the small prestrain and this causes fatigue slip to occur more readily, but the fatigue behaviour following slip initiation is not affected because the spheroidal cementite particles act as obstacles to further slip deformation and Stage I crack propagation.

Journal ArticleDOI
TL;DR: In this paper, the influence of continuous controlled rolling of a high strength low alloy steel on its microstructure and mechanical properties has been investigated, and it is shown that a small austenite size prior to rolling, followed by continuous rolling confined in the non-recrystallization region of Austenite leads to a fine ferrite grain size and a fine pearlite.

Patent
10 Jun 1992
TL;DR: In this article, a casting alloy for the production of cast pearlite nodular cast iron is presented, which contains Mg 5-9 wt, Ca 3.5-5.0 wt., Ba 1.0-3.5 wt.
Abstract: The present invention refers to a casting alloy, esp. nodulizer for production of cast pearlite nodular cast iron. The said nodulizer contains Mg 5-9 wt%, Ca 3.5-5.0 wt%, Ba 1.0-3.5 wt, Si 35-50 wt%, Sb 0.5-4.0 wt, and balanced Fe. The nodulizer thus made is a lump alloy, available size in two variants: 3-25 mm and 25-100 mm.

Journal ArticleDOI
TL;DR: In this article, the principles of laser transformation hardening were investigated using a low alloy special steel having a microstructure of pearlite and proeutectoid ferrite.
Abstract: The principles of laser transformation hardening were investigated using a low alloy special steel having a microstructure of pearlite and proeutectoid ferrite. Temperature fields and phase transformations were modelled. Particular attention was paid to increases of the Ac1 and Ac3 transformation temperatures owing to the rapid thermal cycles produced by laser heating. Dissolution of proeutectoid ferrite is shown to control the formation of a homogeneous hardened case. Experimental data are in good agreement with the predictions of the model. A diagram was constructed which describes the case geometry and microstructure in terms of the process variables and is an aid to optimising practical processing parameters. The models are flexible and may be used for laser transformation hardening of other ferrous alloys having inhomogeneous microstructures.MST/1606