The crystallography and nucleation of pearlite

Abstract

By choice of a suitable iron—manganese—carbon alloy it has been possible to study pearlite nodules growing in austenite, without the austenite transforming on cooling to room temperature. Thin foil electron microscopy has been used to examine the orientation relations between cementite, ferrite and austenite as well as morphological aspects of the transformation. It is shown that one of the classical ferrite—cementite orientation relations found in pearlite (Pitsch—Petch) arises when the pearlite colonies nucleate on ‘clean’ austenite grain boundaries. The other familiar relation (Bagaryatski) arises when the colonies nucleate on pre-existing hyper-eutectoid cementite layers at the austenite grain boundaries. Some observations are made on the mode of nucleation of the pearlite nodules.

The effect of microstructural characteristics of pearlite on the mechanical properties of hypereutectoid steel

“…Considering the compositional differences between the hypereutectoid and eutectoid steels, the value for the material constant determined in this work, k y = 8.5 MN, is in good agreement with the reported data given in Table 3. However, the application of the Hall-Petch type equation for relating the strength to the interlamellar spacing results in a negative intercept value (friction stress), which, although clearly inconsistent with the definition of the friction stress (i.e., stress for dislocation movement in the lattice), has been generally accepted for regression analyses of eutectoid steel compositions [6,26], albeit with no apparent physical mean- ing. Regardless, previous investigations have determined the friction stress value to be considerably lower than that determined in this work, 134 MPa and the theoretical expression for σ o was used to calculate a value according to the following equation [27]:…”

“…Specifically considering the microstructural development in high carbon steels, the transformation of austenite to pearlite occurs by the nucleation of alternating ferrite and cementite phases on the grain boundaries [1][2][3][4][5][6] that grow to form a lamellar structure. In this pearlitic microstructure, neighboring ferrite and cementite lamellae that have grown parallel to each other constitute, for the most part, a colony.…”

Influence of Orientation Relationship Between Ferrite and Cementite in Pearlite on Stabiblity of Cementite Plates

“…where subscripts Z and F refer to cementite and ferrite, respectively. The Pitsch OR [17] occurs when pearlite nucleates on a "pure" boundary of austenite, while Bagaryacki OR [1] appears when pearlite nucleates on pre-eutectoid cementite [5,7] (or on pre-eutectoid ferrite [19,20]). Simultaneously, the majority of results indicate that regardless a carbon content in steel and a degree of undercooling, dominating in a structure was the Pitsch OR (Pitsch [17] -carbon steels 0,25% C, 0,7% C, 1,25% C, Stackleton and Kelly [22] -low-alloy steels from 0,52% C to 0,96% C and Hadfield steel , Lupton and Warrington [9] -carbon steel 0,8% C, Ohmori [16] -steel 0,19% C, 0,0087% B.…”

Kinetics and Crystallography of Intragranular Pearlite Transformation Nucleated at (MnS+VC) Complex Precipitates in Hypereutectoid Fe-Mn-C Alloys.

“…Fe-12Mn-0.8C (hereafter V-free alloy) was chosen because pearlite transformation occurs approximately below 923 K in this alloy 22) and austenite matrix is metastable at room temperature so that as-transformed microstructure can be retained by quenching from transformation temperatures. Furthermore, this alloy contains MnS as inclusions in austenite.…”

“…For crystallography of pearlite transformation, the earlier indirect X-ray study by Smith and Mehl 21) indicated that intergranular pearlite does not have a specific orientation relationship with respect to its austenite matrix. However, Dippenaar and Honeycombe 22) provided, through transmission electron microscopy investigation, the direct experimental evidence showing that ferrite or cementite in intergranular pearlite holds the near-rational orientation relationships with one of the adjacent austenite matrix in its nucleation stage. The present authors 23) recently studied the crystallography of intergranular pearlite in Fe-12Mn-0.8C (almost identical in composition to the alloy studied by Dippenaar and Honeycombe) and Fe-12Mn-0.8C-0.3V alloys both of which austenite matrix can be retained even after quenching, by electron backscatters diffraction pattern (EBSP) analysis.…”