The interlamellar crystallography of pearlite in iron-carbon alloys is examined in Fe-0.8C and Fe-0.81C-12Mn steels with attention given to the Bagaryatsky, Pitsch-Petch, and Isaichev orientation relationships and their related atomic habit planes. A survey of the overall literature reveals confusion about the crystallographic uniqueness in these orientation relationships. The present article focuses on this uniqueness and on habit planes between the pearlitic ferrite and cementite, from which the crystallography of ferrous pearlite orientation relationships is proposed to emanate. Techniques to characterize and identify orientation relationships unambiguously are developed. Habit planes are shown to be consistently obtained, even during curvature, with all deviations accommodated by microscopic steps.

Ferrite: Cementite crystallography in pearlite

Fully pearlitic steels are of great importance in a number of extremely demanding structural applications, in large part because of their combination of strength and toughness. Strength and toughness are controlled by the microstructures developed in pearlitic steels, especially interlamellar spacing, pearlite colony size, and prior austenite grain size. This article reviews the effects of these microstructural features on the yield strength and toughness of fully pearlitic steels, the importance of hypereutectoid alloy compositions for increasing the strength of fully pearlitic steels.

Microstructure-property relationships in pearlitic eutectoid and hypereutectoid carbon steels

Two ultrahigh carbon steel (UHCS) alloys containing 1.5 and 1.8 wt pct carbon, respectively, were studied. These materials were processed into fully spheroidized microstructures and were then given heat treatments to form pearlite. The mechanical properties of the heat-treated materials were evaluated by tension tests at room temperature. Use of the hypereutectoid austenite-cementite to pearlite transformation enabled achievement of pearlitic microstructures with various interlamellar spacings. The yield strengths of the pearlitic steels are found to correlate with a predictive relation based on interlamellar spacing and pearlite colony size. Decreasing the pearlite interlamellar spacing increases the yield strength and the ultimate strength and decreases the tensile ductility. It is shown that solid solution alloying strongly influences the strength of pearlitic steels.

Pearlite in ultrahigh carbon steels: Heat treatments and mechanical properties

The surface and cross-section of a genuine Damascus sword was characterised by means of wide-angle X-ray scattering techniques complemented by optical and transmisssion electron microscopy. Position-resolved X-ray phase analysis revealed that, unlike ferrite and martensite, the distribution of cementite is inhomogeneous in different spatial zones parallel to the cutting edge of the blade. For the first time a quantitative X-ray phase and texture analysis was made possible by averaging all spatial zones of the surface and the cross-section of the sword and applying the Rietveld method with code TOPAS. Differences concerning texture and structure characteristics of ferrite, martensite and cementite are discussed. More evidence for the structure of cementite nanowires is supplied. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Microstructure of a genuine Damascus sabre

Comparison of the structure of ancient Damascene steel blades at nanoscale with more recent ones – all made using crucible (wootz) technology and exhibiting ultra-high carbon content – showed for the first time a common feature. Despite different microstructures, colonies of wire- and tube-like particles with diameters of 40-50 nm have been observed with the aid of high-resolution transmission electron microscopy. Crystalline Fe3C is the main phase forming those particles covered in numerous cases by a tube-like layer. These tubes were also found in an empty or partly – covered filled variant. To assess the strengthening capacity of cementite various models were compared. Dispersion strengthening seems the most efficient. Cutting edge qualities may be related to surface corrugations due to nanoparticles. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

G.A. Chadwick

Papers

The crystallography of herringbone pearlite