Pitsch-Petch Orientation Relationship Research Articles

The effect of the misfit dislocation on the in-plane shear response of the ferrite/cementite interface

Abstract Although the pearlitic steel is one of the most extensively studied materials, there are still questions unanswered about the interface in the lamellar structure. In particular, to deepen the understanding of the mechanical behavior of pearlitic steel with fine lamellar structure, it is essential to reveal the structure-property relationship of the ferrite/cementite interface. In this study, we analyzed the in-plane shear deformation of the ferrite/cementite interface using atomistic simulation combined with extended atomically informed Frank-Bilby method and disregistry analyses. In the atomistic simulation, we applied in-plane shear stress along twelve different directions to the ferrite/cementite bilayer for Isaichev, Near Bagaryatsky and Near Pitsch-Petch orientation relationship, respectively. The simulation results reveal that Isaichev and Near Bagaryatsky orientations show dislocation-mediated plasticity except two directions, while Near Pitsch-Petch orientation shows mode II (in-plane shear) fracture at the ferrite/cementite interface along all directions. Based on the extended atomically informed Frank-Bilby and disregistry analysis results, we conclude that the in-plane shear behavior of the ferrite/cementite interface is governed by the magnitude of Burgers vector and core-width of misfit dislocations.

Two-phase and three-phase crystallographic relationships in white-solidified and nitrided Fe-C-Si cast iron

Crystallographic orientation relationships (ORs) among α-Fe, cementite θ-Fe3C1-z, and hexagonal close-packed iron carbide/(carbo)nitride ε-Fe3(N,C)1+x are highly important to phase transformations and microstructure evolution during heat-treating of cast irons and steels, and during nitriding of these materials. Several α/θ, ε/θ, and α/ε two-phase ORs have been controversially discussed in literature. In that regard, an α/ε/θ three-phase crystallographic relation has been hypothesized, yet hitherto hardly verified, which justifies the existence of two distinct α/θ ORs by making use of an ε intermediate in the θ formation.In this study, ORs in a white-solidified and gas-nitrided hypoeutectic Fe-3.5 wt%C-1.5 wt%Si model alloy were investigated by electron backscatter diffraction (EBSD). The specific alloy composition and nitriding conditions allow simultaneously examining α/θ, ε/θ and α/ε ORs, and particularly the α/ε/θ three-phase relationship, which can be hardly assessed simultaneously in conventionally treated cast irons and steels.Eutectic cementite and pearlite constitute the white-solidified microstructure. Eutectic cementite and pearlitic α-Fe frequently fulfill the Isaichev OR and certain ORs, which are close to the Pitsch-Petch OR. Upon nitriding, ε forms from surface-adjacent cementite, whereas α has largely been retained due to the presence of Si. About 70% of the ε grains fulfill the OR 010θ∥112¯2¯ε/100θ∥112¯3ε. The orientation of α adjacent to the newly formed ε determines which variant of that ε/θ OR is selected. Thereby, irrespective of the two main α/θ ORs, basically the same α/ε OR is established. The α-affected variant selection proves the existence of an α/ε/θ three-phase crystallographic relationship given by 031¯θ∥101¯1¯ε∥101¯α/100θ∥112¯3ε∥131α or 1¯11¯α.

Strain Transfer across the Ferrite/Cementite Interface in Carbon Steels with Coarse Lamellar Pearlite

A crystal geometry analysis was performed of strain transfer mechanisms across the ferrite/cementite interface in coarse lamellar pearlite. The possibility of strain transfer was evaluated using LRB criteria, which were developed by Lee, Robertson, and Birnbaum to describe the slip transfer mechanism across grain boundaries. Dislocation reactions at the Fe/Fe3C interface were studied according to the Pitsch–Petch orientation relationships between ferrite and cementite, which are valid for coarse lamellar pearlite. Slip planes and Burgers vectors of partial and full dislocations in cementite were proposed based on the results of atomistic simulation of stacking faults in close-packed planes of cementite. It was determined that the strain transfer across the Fe/Fe3C interface is possible only for two slip systems 1/2〈111〉{110}F and one slip system 1/2〈111〉{112}F of ferrite. The other slip systems of ferrite do not cross the interface and are involved in the hardening of the ferrite phase of pearlite.

EBSD characterization of the eutectic microstructure in hypoeutectic Fe-C and Fe-C-Si alloys

Hypoeutectic Fe-C and Fe-C-Si model alloys were produced at different solidification conditions. Copper mold casting yields low cooling rates promoting the formation of a eutectic microstructure, which is characterized by two morphologies: elongated cementite plates and a rod structure growing perpendicular to the plates, i.e. austenite rods in a cementite matrix. Electron beam surface remelting generates a mainly plate-like eutectic due to rapid solidification. The microstructures were characterized by light-optical microscopy and electron backscatter diffraction (EBSD). The latter allows for a spatially resolved investigation of the growth crystallography of the eutectic phases. Thereby, a possible existence of crystallographic orientations relationships between cementite and austenite within the plate-like eutectic was assessed experimentally. The eutectic phases were found to grow largely crystallographically independently. Moreover, ferrite and eutectic cementite within the decomposed eutectic microstructure frequently comply with the Bagaryatsky or the Pitsch-Petch orientation relationship. Complementary X-ray diffraction (XRD) analysis reveals a pronounced cementite {002} texture in the microstructure produced by mold casting. Characteristic changes in the lattice parameters indicate that as-cast cementite is non-stoichiometric.

Characterization of the misfit dislocations at the ferrite/cementite interface in pearlitic steel: An atomistic simulation study

The characteristics of the misfit dislocations at ferrite/cementite interfaces (FCIs) for various orientation relationships (ORs) have important implications for the mechanical behavior and the phase transformation of pearlitic steels; however, the detailed characteristics of these misfit dislocations have not been thoroughly elucidated to date. Using the extended atomically informed Frank–Bilby (xAIFB) method and atomistic simulation, we characterized the structures of misfit dislocations and calculated the interface energies of five ORs (Bagaryatsky, Isaichev, Pitsch–Petch, Near Bagaryatsky and Near Pitsch–Petch), respectively. Atomistic calculations of the interface energies of five ORs reveal that (1) the Isaichev OR has the lowest interface formation energy and (2) Near Bagaryatsky and Near Pitsch–Petch ORs are energetically more favorable than exact Bagaryatsky and Pitsch–Petch ORs in spite of small misorientation angle. The interface formation energy of each OR is qualitatively well explained by the structure and spacing of FCI dislocations, which demonstrate the importance of the characterization of misfit dislocations.

Crystal Plasticity Analyses of Scale Dependent Mechanical Properties of Ferrite/Cementite Lamellar Structure Model in Pearlite Steel Wire with Bagaryatsky or Pitsch-Petch Orientation Relationship

Crystal Plasticity Analyses of Scale Dependent Mechanical Properties of Ferrite/Cementite Lamellar Structure Model in Pearlite Steel Wire with Bagaryatsky or Pitsch-Petch Orientation Relationship

New insights into crystallographic correlations between ferrite and cementite in lamellar eutectoid structures, obtained by SEM–FEG/EBSD and an indirect two-trace method

Four different ferrite/cementite orientation relationships (ORs) in near-eutectoid steel are derived using SEM–FEG/EBSD (scanning electron microscopy–field emission gun/electron back-scatter diffraction) and an indirect two-trace method. They show a common feature of close-packed plane parallelism between ferrite and cementite. Their crystallographic compatibility with habit planes shows a variety of possible habit planes and excludes the existence of the exact conventional Bagaryatsky and Pitsch–Petch ORs. Each of these new ferrite/cementite ORs is correlated with a different edge-to-edge matching condition between austenite and pearlitic ferrite, and between austenite and pearlitic cementite, and possesses specific morphological features. The present results may give deep insight into the crystallography of pearlitic transformation and provide useful information for materials design through interface tailoring in steels.

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

Kinetics and crystallography of intragranular pearlite nucleated at the surface of (MnS+VC) complex precipitate were studied in hypereutectoid Fe-Mn-C steels. The incoherent MnS embedded in the austenite does not act as a strong nucleation site of pearlite unless the transformation time is prolonged. The intragranular pearlite transformation is promoted effectively by the addition of vanadium (V). EPMA analysis showed that the intragranular pearlite nucleates on the (MnS+VC) complex precipitate in the V-added alloy. As the transformation temperature decreases, the intragranular pearlite formation occurs more frequently. A single intragranular pearlite is composed of several colonies, indicating that multiple pearlite colonies nucleate on a (MnS+VC) complex precipitate for intragranular pearlite transformation. There is no specific orientation relationship (OR) between ferrite in intragranular pearlite and austenite matrix while there is a specific OR (Pitsch-Petch OR) between pearlitic ferrite and cementite in the intragranular pearlite.

The pitsch-petch orientation relationship in ferrous pearlite at small undercooling

The factors behind the occurrence of the Pitsch-Petch pearlitic orientation relationship (OR) in ferrous systems are investigated using a combination of crystallographic information obtained through electron-backscatter diffraction (EBSD) and knowledge of the three-dimensional (3-D) morphology of pearlite from serial sectioning. Both hypereutectoid and hypoeutectoid ferrous systems of various compositions providing a variety of morphologies are examined to consider the relationship between pearlite nucleation sites and ferrite-cementite interlamellar ORs. It is shown that the Pitsch-Petch OR occurs when a colony is cementite nucleated and this conclusion is valid for both sides of the eutectoid composition.

Mechanism and crystallography of ferrite precipitation from cementite in an Fe-Cr-C alloy during austenitization

Abstract The morphology of ferrite precipitates formed within cementite and the mechanism of their formation were examined by means of transmission electron microscopy in an Fe-2.6 wt% Cr-0.96 wt% C alloy after austenitizing in the range 800–950°C for various times. At the beginning of the austenitization process, the cementite particles dissolve rapidly by carbon diffusion in the austenite. The precipitation of ferrite occurs during the second stage of transformation when cementite dissolution is controlled by chromium diffusion in cementite or in the austenite matrix. The ferrite precipitates exhibit a lath-like shape elongated in the [010] cementite direction with the habit plane close to the (001) cementite. The cementite and ferrite were related to each other by two previously reported orientation relationships. In the case of the Pitsch-Petch orientation relationship, the habit plane of the ferrite lath is almost parallel to (152)f//(001)c and the ferrite-cementite interface is flat without any step...

Mechanism and crystallography of ferrite precipitation fromcementite in an Fe-Cr-Calloy during austenitization

Abstract The morphology of ferrite precipitates formed within cementite and the mechanism of their formation were examined by means of transmission electron microscopy in an Fe-2.6 wt% Cr-0.96 wt% C alloy after austenitizing in the range 800–950°C for various times. At the beginning of the austenitization process, the cementite particles dissolve rapidly by carbon diffusion in the austenite. The precipitation of ferrite occurs during the second stage of transformation when cementite dissolution is controlled by chromium diffusion in cementite or in the austenite matrix. The ferrite precipitates exhibit a lath-like shape elongated in the [010] cementite direction with the habit plane close to the (001) cementite. The cementite and ferrite were related to each other by two previously reported orientation relationships. In the case of the Pitsch-Petch orientation relationship, the habit plane of the ferrite lath is almost parallel to (152)f//(001)c and the ferrite-cementite interface is flat without any steps. The side facet of the lath is close to (2 15)f//(101)c, and the ferrite growth direction is close to [311]f//[010]c. In the case of the Bagaryatsky orientation relationship, the habit plane of the ferrite lath deviates several degrees from the broad face of (1 12)f//(001)c and structural ledges form at the ferrite-cementite interface, preserving coherency. The side facet of the lath is close to (121)f//(101)c and the ferrite growth direction is close to [111]c//[010]c. The results are discussed by assuming local equilibrium at the moving interfaces using the software THERMOCALC.

ACCURATE ORIENTATION RELATIONSHIPS BETWEEN FERRITE AND CEMENTITE IN PEARLITE

In most previous work, the interlamellar interface between pearlitic ferrite and cementite is considered to have a low energy and dislocations have been observed at the interfacial boundary, in both plain carbon steels and high manganese steels. Here, four new orientation relationships (ORs) between pearlitic ferrite and cementite have been determined using the more accurate CBKLDP technique. In eutectoid steel the pearlite obeys the New-2, New-3 and New-4 ORs; in hypoeutectoid steel only the Isaichev OR is observed; in hypereutectoid steel the New-5 OR is followed. The two widely accepted ORs, the Pitsch-Petch OR and the Bagaryatskii OR have never been observed. They probably do not exist.