Pearlite

About: Pearlite is a research topic. Over the lifetime, 6028 publications have been published within this topic receiving 65695 citations.

Void initiation and microstructural changes during wire drawing of pearlitic steels

Abstract: Microstructural changes and void initiation in fully pearlitic steels during cold wire drawing were investigated by performing tensile tests and microstructural examination with scanning electron microscopy. In this investigation, the primary focus was on cementite lamellae aligned transversely to the drawing axis in pearlite colonies. Unlike the cementite lamellae aligned along the drawing axis that are deformed uniformly and thinned to a fibrous shape, those aligned transversely to the drawing axis are severely bent, curled and even fractured with increasing drawing strain. At high strain, a formation of globular cementite particles that are attributed to the densification of cementite was observed in colonies of lamellae aligned transversely to the drawing axis. In addition, it was found that voids were initiated in the vicinity of relatively large globular cementite particles due to the concentration of enhanced stress. The mechanisms of a formation of globular cementite particles and a void formation are discussed in conjunction with the deformation behavior of cementite lamellae during the drawing.

Modeling of the liquid/solid and the eutectoid phase transformations in spheroidal graphite cast iron

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.

Strengthening mechanisms in vanadium microalloyed steels intended for long products

Abstract: The present work has concentrated on the roles of vanadium, nitrogen and carbon in controlling the microstructures and strength of steels designed for hot rolled long products. Effects of cooling rate and additional microalloying with titanium have also been included. The degree of precipitation strengthening of ferrite at a given vanadium content depends on the available quantities of carbon and nitrogen. The nitrogen content of the ferrite is approximately the same as that of the austenite from which it forms, i.e. the total nitrogen content in steel. It was confirmed that nitrogen is a very reliable alloying element, increasing the yield strength of V-microalloyed steels by some 5 MPa for every 0.001% N, essentially independent of processing conditions. Carbon content, on the other hand, has usually been considered not relevant to precipitation strengthening when the precipitation occurs in ferrite because of the very small carbon content in solution in ferrite at equilibrium. We demonstrate that the effective carbon for precipitation in ferrite may be much greater than this during the period of phase transformation, which in turn has a great effect on precipitation strengthening. Such behaviour is explained on the basis that the activity of carbon in ferrite is abnormally high in the presence of under-cooled austenite and before cementite nucleation so that profuse nucleation of vanadium carbonitride is encouraged. This new mechanism for precipitation is particularly significant for medium carbon steels typically used for hot rolled bars and sections. The total carbon content of the steel also contributes to the yield strength by increasing the volume fraction of pearlite. It is shown that the contribution from pearlite is stronger than generally recognised.