Pearlite Interlamellar Spacing Research Articles

Interlamellar Spacing of Pearlite in a Near-eutectoid Fe–C Alloy Measured by Serial Sectioning

The interlamellar spacings of pearlite formed isothermally at 700 and 680°C in a near-eutectoid Fe–0.82mass%C alloy were measured by serial sectioning coupled with scanning electron and atomic force microscopy. The intersection angle of cememtite lamellae with the metallographic surface was determined from the variation of horizontal displacement of cementite lamellae with removal depth. The true lamellar spacing was then calculated from the apparent lamellar spacing on the surface. When the angle was small, i.e. less than ~20°, it was measured directly by atomic force microscope. The minimum and mean true lamellar spacings are in good agreement with those measured by other methods. The distribution of interlamellar spacings on the specimen surface back calculated from the spectra of true interlamellar spacing assuming the random orientation of cementite lamellae was in fair agreement with the measured one. It is likely that the distribution of true lamellar spacings is primarily due to recalescence and the minimum true spacings rather than the mean value may be relevant to the thermodynamic theory of pearlite transformation.

Reheating Austenitizing Temperature of Spring Steel 60Si2MnA for Railway

The microsturctural transformation of austenite grain, pearlite interlamellar spacing, and lamellar cementite thickness of spring steel 60Si2MnA for railway were studied in the hot-rolled and reheated states. Furthermore, the effect of microstructural characterization on its final mechanical properties was discussed. The results showed that as far as 60Si2MnA, the pearlite interlamellar spacing determined the hardness, whereas, the austenite grain determined the toughness. Compared with microstructure and mechanical properties in the hot-rolled state, after reheating treatment at 950 °C, its average grain sizes are apparently fine and the pearlite interlamellar spacing and lamellar cementite thickness coarsen to some extent, but both hardness and impact toughness increase to HRC 48 and 8. 5 J, respectively. In the course of making spring, the optimum reheating austenitizing temperature for the 60Si2MnA steel is 950 °C.

Calculation Models of Interlamellar Spacing of Pearlite in High-Speed 82B Rod

With the investigated subject of 82B rod, the interlamellar spacings of pearlite at different isothermal transformation temperatures and different cooling rates during continuous cooling transformation were measured, and the effect of the isothermal transformation temperature and cooling rate on the interlamellar spacing was analyzed quantitatively. Moreover, the relationship models between undercooling and interlamellar spacing were presented by data regression. The experimental results show that the relationship between undercooling and reciprocal interlamellar spacing remains linear when the undercooling is not very large, or else, the interlamellar spacing tends to be constant and the relationship will deviate from linearity.

Application of mathematical model for microstructure and mechanical property of hot rolled wire rods

A set of integrated mathematical models for predicting microstructures evolution during hot rolling and controlled cooling of high carbon wire rods has been developed through laboratory research work and industrial validation experiments. It consists of many sub-models such as critical strain, static and dynamic recrystallization of austenite, fraction of transformed austenite, interlamellar spacing of pearlite, microstructure–property relations. Based on the models, a simulating software is programmed which can run on PC computers. The physical metallurgy process during hot rolling and controlled cooling including the temperature distribution, the evolution of austenite grains, fraction of transformation austenite, final microstructure and mechanical properties were predicted. The predicted results are agree well with measured of the industrial tests.

A computational study of austenite formation kinetics in rapidly heated steels

Surface hardening of steels involves rapid austenitization and subsequent quenching of the surface. The resulting extent of hardening largely depends on the rate of austenitization of the surface under the applied high heating rates. In the present work the kinetics of austenite formation in Fe–C alloys during rapid, non-isothermal heating conditions, characterized by high heating rates and short austenitization periods, were studied by means of computational simulation. Austenitization of lamellar pearlite/proeutectoid ferrite microstructures was simulated by assuming two kinetically distinct stages: i) dissolution of lamellar pearlite followed by ii) dissolution of proeutectoid ferrite. The two stages were simulated by two corresponding 1-D diffusion models employed in series. Numerical solution of the resultant moving-boundary diffusion problems provide calculated results regarding the dependency of vol. fraction austenite on thermal cycle parameters and on initial microstructural features of the steel. Analysis of calculated results showed that the vol. fraction of pearlite transforming to austenite during pearlite dissolution depended on maximum temperature, dwell time and pearlite interlamellar spacing. A functional relationship between these variables, consisting of a thermodynamic and a kinetic term, was established. On the other hand, the total vol. fraction of austenite forming in the steel, after both stages of austenitization, was found to follow a typical sigmoidal kinetic behaviour.

Evaluation of Microstructure and Mechanical Properties of Metals by Non-Destructive Methods

Microstructural parameters (kinds of phases, inter-lamellar spacing of pearlite, precipitate size, number of precipitates), mechanical properties(UTS, Vickers hardness) and non-destructive parameters(ultrasonic velocity, ultrasonic attenuation coefficient, electrical resistivity, magnetic coercivity, magnetic remanence, Barkhausen noise) in various metallic materials were measured in order to investigate the mutual relationship among these parameters. The optimum non-destructive parameters were selected for particular purposes in order to evaluate the level of damage to the metallic structures, to differentiate the microstructures and to predict the mechanical properties of superalloy, low and eutectoid steel and Cu alloys non-destructively.

Analysis on the deformation and fracture behavior of carbon steel by in situ tensile test

The deformation and fracture behaviors of low-carbon steel, medium-carbon steel, and high-carbon steel were studied on internal microstructure using the scanning electron microscopy in situ tensile test. The microstructure mechanism of their deformation and fracture behavior was analyzed. The results show that the deformation and fracture behavior of low-carbon steel depends on the grain size of ferrite, the deformation and fracture behavior of medium-carbon steel depends on the size of ferrite grain and pearlite lump, and the deformation and fracture behavior of high-carbon steel depends on the size of pearlite lump and the pearlitic interlamellar spacing.

Empirical modelling of the isothermal transformation of pearlite in hypereutectoid steel

The rate controlling mechanism for pearlite growth in a hypereutectoid steel composition was examined through an analysis of the microstructural characteristics of the pearlite structure, namely interlamellar spacing, for different isothermal transformation and austenitising conditions. From a metallographic analysis of the pearlite structure as a function of the austenitisation and undercooling conditions applied to the hypereutectoid steel, the interlamellar spacing was observed to increase with increasing austenitising temperature and increasing isothermal transformation temperature. Through the application and experimental validation of a theoretical model (Zener and Hillert) for the calculation of the pearlite interlamellar spacing as a function of the undercooling, the growth rate of pearlite in the hypereutectoid steel was determined to be controlled by the volume diffusion of carbon in austenite during isothermal transformation in the temperature range of 550–620°C.

The application of stereological analysis in understanding differences in toughness of V- and Nb-microalloyed steels of similar yield strength

The present paper describes an attempt to relate small variations in toughness of V- and Nb-microalloyed steels, characterized by almost similar yield strength and ferrite–pearlite microstructures, to stereological parameters. Stereological parameters derived from two-dimensional microstructure include mean intercept length ( L ¯ α ) of ferrite, ferrite grain boundary surface area per unit volume [ S V] α, contiguity ratio ( C α) of ferrite grains, pearlite colony size, and pearlite interlamellar spacing. Stereological analysis was carried out as a function of depth from the surface using serial sectioning method. The analysis predicts that the toughness of the microalloyed steels is related to uniformity in the stereological parameters and the contiguity ratio. If the processing conditions such as cooling rate are increased, a convincingly higher toughness is obtained for Nb-containing steel in relation to V-microalloyed steels, at similar yield strength.

Microalloyed V–Nb–Ti and V steels Part 1 – Stereological study of ferrite–pearlite microstructure and its relationship to toughness

Stereological analysis was applied to quantify the ferrite–pearlite microstructure and relate it to the toughness of similar strength V–Nb–Ti and V microalloyed steels. The V–Nb–Ti and the V steel were characterised by average yield strengths of ∼ 375 and 363 MPa, respectively and an elongation of ∼20%. The relationship between the microstructure and toughness was investigated in terms of stereological parameters, namely: (a) mean intercept length of polygonal ferrite and its distribution, (b) mean intercept length of pearlite colonies and their distribution, (c) ferrite grain boundary surface area per unit volume, (d) total grain boundary surface area per unit volume, (e) contiguity ratio of ferrite grains and pearlite colonies, and (f) pearlite interlamellar spacing and its distribution. Stereological analysis of core and flange sections of beams of both steels indicated that the core and flange sections of V steel are characterised by a marginally finer ferrite grain size and narrower grain size distribution, higher contiguity ratio of ferrite grains, finer pearlite interlamellar spacing and its distribution, and more uniform distribution of pearlite colony size, in comparison with respective core and flange sections of the V–Nb–Ti steel. These characteristics influence the toughness of the investigated steels.

Neural Network Model for Isothermal Pearlite Transformation. Part I: Interlamellar Spacing

The present paper is the first of a two-part paper which deals with a neural network model to describe the isothermal pearlite formation. The isothermal austenite-to-pearlite transformation has been analyzed using a neural network technique within a Bayesian framework. In this framework, the pearlite interlamellar spacing and growth rate of pearlite can be represented as a general empirical function of variables such as Mn, Cr, Ni, Si and Mo alloying contents and temperature which are of great importance for the pearlite growth mechanisms. The method has limitations owing to its empirical character, but it has been demonstrated that it can be used in such way that the predicted trends make metallurgical sense. In this first part paper, the method has been used to examine the relative importance of the alloying elements on pearlite interlamellar spacing.

Effect of controlled rolling and cooling on the microstructure and mechanical properties of 60Si2MnA spring steel rod

The effect of controlled rolling and cooling process parameters, such as finish rolling temperature, loop-laying temperature and the cooling rate in the process from the loop layer to the coil station, on the microstructures and mechanical properties of 60Si2MnA spring steel rod were carefully investigated by thermal simulation, tensile tests and quantitative metallography. Experimental results indicate that the microstructure is mainly determined by finish rolling temperature, especially the cooling rate in the process from the loop layer to the coil station. In a given range, the more rapid the cooling rate, the thinner the interlamellar pearlite spacing, the less the proeutectoid ferrite bulk volume and the smaller the average ferritic grain size. Low finish rolling temperature is in favor of decreasing pearlite colony size. Therefore, low finish rolling temperature followed by properly accelerated cooling is suggested so as to improve its cold workability.

Characterization of Microstructures of Variously Heat Treated Hypoeutectoid and Eutectoid Steel by Magnetic Coercivity Measurement

The microstructures of variously heat treated hypoeutectoid(<TEX>$0.45\%$</TEX> carbon) and eutectoid(<TEX>$0.85\%$</TEX> carbon) steel were characterized by magnetic coercivity measurement. The effect of spheroidization of cementites on the coercivity was investigated for <TEX>$0.45\%$</TEX> carbon steel. In case of <TEX>$0.85\%$</TEX> carbon steel, microstructural parameters such as prior austenite grain size, phase and pearlite interlamellar spacing were measured along with coercivity to investigate the relationships between them. Prior austenite grain size had little effect on the measured coercivity. Coercivity was observed to be high in order of martensite, pearlite and ferrite phases. The linear decrease of coercivity with increasing pearlite interlamellar spacing was found. The effect of each microstructural factor on the coercivity and the potential of coercivity as a nondestructive evaluation parameter for assessing microstructures of steel products are discussed.

Relationship between microstructure and strength in eutectoid steels

Abstract This paper analyzes the influence of the microstructural changes undergone by eutectoid pearlitic steels during continuous cold drawing on their yield strength. To this end, samples from a real manufacturing process (wire drawing) were studied, and consideration was given to the microstructure evolution as the drawing progresses up to the final commercial product which is heavily drawn and has undergone severe straining. It is seen that the pearlite interlamellar spacing (decreasing with cold drawing) influences clearly the improvement of yield strength (increasing with cold drawing, which is the final aim of manufacturing), although a relationship of the Hall–Petch type cannot be fitted in this case, probably because cold drawing produces not only an increasing closeness of the pearlitic packing, but also a microstructural orientation in the material.

Microstructure and mechanical properties of spray-deposited ultra-high carbon steel after hot rolling

The tensile mechanical properties of as-cast ingot metal (IM), spray-formed (SF), and as-hot-rolled (HR) ultra-high carbon steels (UHCS) containing silicon were investigated in this paper. The relationship between microstructure and tensile properties was described for these steels. The carbide networks, the pearlitic interlamellar spacing, the size of carbide particles, and the volume ratio between lamellar and spheroidized structure are all microstructure factors influencing the tensile properties in UHCS.

Evaluation of microstructures of variously heat treated carbon steel by magnetic coercivity measurement

AbstractThe microstructures of variously heat treated 0.85% carbon steel were evaluated by magnetic coercivity measurement. Austenitizing, isothermal transformation, continuous cooling or spheroidization heat treatment was carried out to produce various microstructures. Microstructural parameters such as prior austenite grain size, phase and pearlite interlamellar spacing were measured along with coercivity to investigate the relationships between them. Prior austenite grain size had little effect on the measured coercivity. Coercivity was observed to be high in order of martensite, pearlite and ferrite phase. The linear decrease of coercivity with the increasing pearlite interlamellar spacing was found. Therefore, coercivity was suggested as a potential nondestructive evaluation parameter for assessing the microstructures – pearlite interlamellar spacing and kind of phase – of 0.85% carbon steel. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Evaluation of Microstructures and Mechanical Property of Variously Heat Treated 0.85% Carbon Steel by Magnetic Method

Microstructures and mechanical properties of variously heat treated 0.85% carbon steel(eutectoid steel) were evaluated by magnetic property measurements. Microstructural analysis (pearlite interstellar spacing), measurement of mechanical properties(Rockwell hardness, yield stress, fracture stress) and magnetic properties(coercivity, remanence, hysteresis loss, saturation magnetization) were performed to clarify mutual relationships among these parameters. Water quenched specimens with martensite structure showed much higher coercivity and remanence than air cooled or furnace cooled specimens with pearlite structure. The linear dependence of coercivity and remanence on pearlite interlamellar spacing as well as on Rockwell hardness, yield stress and fracture stress was observed in the pearlitic steel. Hysteresis loss and saturation magnetization showed no distinct trend with pearlite interlamellar spacing.

Magnetic Evaluation of Microstructures and Strength of Eutectoid Steel

Microstructures and strength of variously heat treated eutectoid steel were evaluated by magnetic property measurements. Isothermal transformation, continuous cooling or spheroidization heat treatment was performed to produce various microstructures. Microstructural parameters (phase, pearlite interlamellar spacing), mechanical properties (fracture strength) and magnetic parameters (coercivity, remanence, hysteresis loss, saturation magnetization) were measured to investigate the relationships among these parameters. Coercivity and remanence were observed to be high in order of martensite, pearlite and ferrite phase. The linear decrease of coercivity and remanence with the interlamellar spacing and the linear increase of those with fracture strength of pearlitic eutectoid steel were found. Coercivity and remanence were suggested as potential magnetic parameters for discriminating phases and quantitatively assessing the pearlite interlamellar spacing as well as strength of eutectoid steel.

Artificial neural network prediction of the microstructure of 60Si2MnA rod based on its controlled rolling and cooling process parameters

An artificial neural network (ANN) model was developed for prediction of the microstructure of the 60Si2MnA spring steel rod based on its controlled rolling and cooling process parameters. The ANN predicted results show that the interlamellar pearlite spacing, the ferrite content and the average ferrite grain size all decreases rapidly with the increase of the cooling rate from the rod layer to the coil collecting station, and the effect of the rod-laying temperature and the finishing temperature on the microstructure is not obvious. The ANN model can predict the microstructure whether the process parameters interact or not, so it is critical for the quality control of the 60Si2MnA rod and will be widely used in its controlled rolling and cooling process.

Effect of carbon content on the Hall-Petch parameter in cold drawn pearlitic steel wires

The effect of the carbon content on the Hall-Petch parameter has been investigated for fully pearlitic steels with the carbon range of 0.52–0.92 wt%. The increase of the carbon content in pearlitic steels enhances tensile strength and hardening rate of cold drawn pearlitic steels by the refinement of the initial interlamellar spacing and the increase of the Hall-Petch parameter. The Hall-Petch parameter is not influenced by the initial interlamellar spacing of pearlite although refining the initial interlamellar spacing increases tensile strength and hardening rate during wire drawing. However, the carbon content in cold drawn pearlitic steels significantly affects the magnitude of the Hall-Petch parameter. The magnitude of the Hall-Petch parameter, k, is expressed as a function of the volume fraction of cementite (V c, i.e. the carbon content); k = constant · V c 1/2 · (1 − V c), which shows a good agreement between experimental and calculated values.