Characterization and Morphological Analysis of Pearlite in an Eutectoid Steel
نویسندگان
چکیده
Pearlite is a lamellar product of eutectoid decomposition, which may form in steels and non-ferrous alloys during transformations under isothermal or continuous-cooling (1,2). A pearlite nodule is composed of multiple colonies; each colony has parallel lamellae, which are orientated differently with respect to lamellae in adjacent colonies. This also exhibits a wide range of interlamellar spacings in different colonies because of the intersection of pearlite colonies at different angles with the polishing plane. The interlamellar spacing is reflected by the diffusion kinetics at the transformation front and is a sensitive parameter which, in a particular steel, is larger as the transformation temperature increases (3). Mehl and co-workers (3) demonstrated that the spacing decreased as the degree of undercooling, ∆T, below the eutectoid temperature, increased. Zener (4) provided the first theoretical analysis of these observations, which allows to calculate the interlamellar spacing of pearlite as a function of undercooling. Pearlite transformation in steels is reconstructive and known to show a constant growth rate (5). The growth rate of pearlite is believed to be controlled by either volume diffusion of carbon (4,6) or by boundary diffusion of substitutional alloying elements (7). In the present work, three different morphologies of pearlite were formed isothermally at three temperatures in an eutectoid steel finding out, as Mehl et al. and Zener reported (3,4), that the pearlite is finer as the formation temperature decreases. Moreover, the interlamellar spacings were calculated using the theoretical method proposed by Zener and Hillert (4,6,7). Experimental results suggest that the growth of pearlite is controlled mainly by volume diffusion of carbon in austenite in the temperature range studied in this steel.
منابع مشابه
Effects of Tungsten on the Pearlite Reaction in a Eutectoid Steel
The effect of an addition of 0.37 Wt % Won the overall transformation rate of the austenitepearlite reaction in a eutectoid steel is examined. Pearlite growth rates and interlamerllar spacing are measured as a function of transformation temperatures. Tungesten raises the Ael temperature, for most transformation temperatures, decreases the overall reaction rate, the growth rate and the interlame...
متن کاملInfluence of Pearlite Morphology and Heating Rate on the Kinetics of Continuously Heated Austenite Formation in a Eutectoid Steel
A model that describes pearlite-to-austenite transformation during continuous heating in a eutectoid steel has been developed. The influence of structure parameters, such as interlamellar spacing and edge length of pearlite colonies, and heating rate on the austenite formation kinetics has been experimentally studied and considered in the modeling. It has been found that the kinetics of austeni...
متن کاملMicrostructures of Pearlite and Martensite Transformed from Ultrafine-Grained Austenite Fabricated through Cyclic Heat Treatment in Medium Carbon Steels
This study investigated the microstructures of pearlite and martensite transformed from ultrafine-grained austenite in 0.45C steel and Vadded 0.45C steel. The mean prior austenite grain sizes were refined to be 4.5 μm in the 0.45C specimen and 2.4 μm in the V-added 0.45C specimen through cyclic heat treatment of austenitizing and water quenching, i.e., repetition of martensite § austenite trans...
متن کاملPOSCO Lectures: The Bainite Reaction
Examination of a time–temperature–transformation (TTT) diagram for an eutectoid carbon steel (Fig. 1), bearing in mind the fact that the pearlite reaction is essentially a high temperature one occurring between 550C and 720C and that the formation of the martensite is a low-temperature reaction, reveals that there is a wide range of temperature ∼250–550C within which neither of these phases for...
متن کاملModelling of Kinetics and Dilatometric Behavior of Non-isothermal Pearlite-to-austenite Transformation in an Eutectoid Steel
Austenitization is an inevitable occurrence during the heat treatment of steels. Despite this consideration, less attention has been paid so far to the study of the formation of austenite as compared with the vast amount of research on its decomposition. That is because the steel properties depend basically on the transformation processes following austenitization. However, the initial austenit...
متن کامل