Pearlite with its lamellae oriented mainly parallel to the longitudinal direction was prepared by Bolling's method of transformation in a steep temperature gradient. The Fe-0.7 pct Mn-0.9 pct C pearlite was drawn into wire and also into strip in dies designed to minimize macroscopically nonuniform deformation. Cross sections of the drawn wires and strip were examined by conventional and high-voltage transmission electron microscopy and were analyzed by quantitative metallography for a) average interlamellar spacing, b) distribution of interlamellar spacings, and c) orientation relationship between the cementite lamellae and the slip systems in the ferrite. The strength of pearlite is proportional to the reciprocal square root of the average interlamellar spacing, and the proportionality constant analogous to the Hall-Petch constant (k) is related to the strength of the cementite lamellae. If the stress for the propagation of slip through the cementite is assumed constant, a Hall-Petch type of equation can be derived for the strengthening of the pearlite against slip in the ferrite by piled-up groups of dislocations. Evidence for the plastic deformability of cementite is presented; sufficiently thin cementite plates were fully plastic. The exponential strain hardening of drawn pearlitic wires and of rolled pearlite is explained in terms of locally inhomogenous deformation revealed by the lack of fragmentation of the lamellae.

Deformation of pearlite

An experimental program was carried out to clarify the structure-property relationships in fully-pearlitic steels of moderately high strength levels, and to identify the critical microstructural features that control the deformation and fracture processes. Specifically, the yield strength was shown to be controlled primarily by the interlamellar pearlite spacing, which itself was a function of the isothermal transformation temperature and to a limited degree the prior-austenite grain size. Charpy tests on standard and fatigue precracked samples revealed that variations in the impact energy and dynamic fracture toughness were dependent primarily on the prior-austenite grain size, increasing with decreasing grain size, and to a lesser extent with decreasing pearlite colony size. These trends were substantiated by a statistical analysis of the data, that identified the relative contribution of each of the dependent variables on the value of the independent variable of interest. The results were examined in terms of the deformation behavior being controlled by the interaction of slip dislocations with the ferrite- cementite interface, and the fracture behavior being controlled by a structural subunit of constant ferrite orientation. Preliminary data suggests that the size of such units are controlled by, but are not identical to, the prior-austenite grain size. Possible origins of this fracture unit are considered.

The role of microstructure on the strength and toughness of fully pearlitic steels

The available experimental data and hypotheses concerning cementite decomposition during the cold work of pearlitic steels are reviewed. The results of studies performed using thermomagnetic analysis, Mossbauer spectroscopy, internal friction and APFIM are used to discuss the mechanism governing cementite decomposition. The following features of this phenomenon seem to be important: (i) the fraction of the decomposed cementite increases with the refining of the initial pearlitic structure, i.e. with the increase of the ferrite–cementite interfacial area; (ii) the decomposition effect saturates as strain increases; (iii) carbon–dislocation interaction in ferrite and MeC bonding in cementite have a strong influence on cementite decomposition. The conclusion is made that cementite decomposition is controlled by the transfer of carbon atoms from cementite to dislocations accumulated near the interface during deformation. This is because the binding enthalpy between carbon atoms and dislocations in ferrite exceeds the solution heat of cementite. Some relevant effects of cementite decomposition in practice are discussed.

Decomposition of cementite in pearlitic steel due to plastic deformation

Dynamic studies of the tensile deformation and fracture of pearlite

Dynamic studies of the tensile deformation and fracture of pearlite using high-resolution 200-KV sem

/pdf/flow-stress-and-work-hardening-of-pearlitic-steel-3jg40ujddi.pdf

Flow Stress and Work-Hardening of Pearlitic Steel

Microstructures Dominating the Ductility of Eutectoid Pearlitic Steels

https://www.jstage.jst.go.jp/article/jinstmet1952/42/7/42_7_716/_pdf

Crystallographic Features and Formation Processes of Pearlite Block

PURPOSE:To easily manufacture a wire rod suitable for a deformed wire for a submarine cable by welding wire rods formed by the hot rolling of steel ingots having a specified and by heat treating the weld zone of the resulting long-sized wire rod under specified conditions to form a fine ferrite-pearlite structure. CONSTITUTION:Steel ingots having a composition consisting of, by weight, 0.30-0.65% C, >=1.0% Si, 0.3-1.5% Mn, =0.75% Ceq [Ceq=C+1/5(Mn+Cr)] are hot rolled to form wire rods. The wire rods are welded and the weld zone of the resulting long-sized wire rod is heated, held at a temp. in the austenite range and cooled at 3-20 deg.C/sec cooling rate to form a ferrite-pearlite structure. Thus, a wire rod for a long-sized high tension steel wire having superior weldability and cold workability is obtd.

Toshihiko Takahashi

Papers

Flow Stress and Work-Hardening of Pearlitic Steel

Microstructures Dominating the Ductility of Eutectoid Pearlitic Steels

Crystallographic Features and Formation Processes of Pearlite Block

Manufacture of wire rod for long-sized high tension steel wire