Divorced pearlite in steels

Abstract

Steels containing large carbon concentrations are used particularly when a high hardness is required, for example, in the manufacture of components such as bearings. This, however, makes it difficult to shape or machine the alloys during the process of component manufacture unless they are first heat-treated into a softened condition. One method of achieving this economically is to generate a microstructure known as divorced pearlite, in which ferrite and cementite grow from the austenite in a non-cooperative manner, leading to a final microstructure that consists of coarse, spherical particles of cementite dispersed in a matrix of ferrite. This is in contrast to the harder lamellar pearlite which normally develops when high-carbon steels are cooled. The theoretical framework governing the transition from the divorced to the lamellar form is developed and validated experimentally.

Deviations from cooperative growth mode during eutectoid transformation: Mechanisms of polycrystalline eutectoid evolution in Fe–C steels

“…By analyzing the simulated carbon http redistribution mechanisms as the transformation proceeds from different 'k' and DT, we establish the criteria which govern the transition from cooperative to non-cooperative mode. In accordance with the earlier theories as well as the experimental studies [2,11,12], the numerical results presented in Paper 1 show that the mechanism by which an advancing a=c front evolves to form a lamellar or divorced morphology is strongly dependent on the initial interparticle spacing (k) of the preexisting cementite (h) and undercooling (DT) below the A 1 temperature. We also identify the onset of a coarsening regime and amended the criteria for the non-cooperative eutectoid transformation.…”

Deviations from cooperative growth mode during eutectoid transformation: Insights from a phase-field approach

“…The LDC transition map generated by conducting phase-field simulations for three different undercoolings (5, 7.5 and 10 K) below the eutectoid temperature and initial particle spacings predicts the morphology that is favored for a given set of initial conditions during an isothermal transformation. In a nut-shell, the most significant contribution of the work presented in the current letter is the addition of an alphabet 'C' (acronym for concurrent growth and coarsening regime which is favored at smaller spacing and lower undercooling) to the classical Lamellar-Divorced (LD) map [11,13]. Further, the present numerical findings are also in complete agreement with the existing theory for the divorced to lamellar morphological transition; lamellar morphology being more favorable at large spacings and high undercooling.…”

“…al [12] study the influence of chromium concentration on the formation of divorced pearlite in a hypereutectoid steel. Pandit and Bhadeshia [13] amend the earlier theory of lamellar to divorced eutectoid transition, by accounting for the diffusion of carbon along the transformation front.…”

Critical Assessment 13: Elimination of white etching matter in bearing steels

“…It is sometimes considered that the proeutectoid cementite is needed in the microstructure to facilitate the divorced eutectoid reaction 53,54 that helps soften the steel in preparation for manufacturing operations. However, heat treatments can be designed so that the proeutectoid cementite need not be present in the final microstructure.…”