Deformation Microstructure and Tensile Strength of Cold Rolled Pearlitic Steel Sheets

Abstract

The deformation microstructure produced by heavy cold rolling (from 70 % to 95 % reduction) of pearlitic structure with various amounts of rolling and the tensile strength of the cold rolled sheets were studied in the plain carbon steels with various carbon contents (0.6, 0.76, and 1.0 mass%C). The deformation microstructure was classified into the following three types; 1) Irregularly Bent Lamella (IBL): lamellae originally inclined with large angles to the rolling plane and irregularly bent after deformation, 2) Coarse Lamella with Shear band (CLS) : the rhomboidal blocks of weakly deformed lamellae bounded by shear band, 3) Fine Lamella (FL): heavily deformed lamellae aligned parallel to the rolling direction with fine interlamellar spacings. As rolling reduction increases, the proportion of FL increases.The tensile strength of cold rolled specimens increases with rolling reduction. Work hardening with respect to true strain by cold rolling is similar to that obtained by wire drawing. After 92 % cold rolling of 1.0 mass%C steel, the tensile strength over 2 500 MPa was achieved.

Ultra-fine (.ALPHA.+.THETA.) Duplex Structure Formed by Cold Rolling and Annealing of Pearlite

“…The arrangement of lamellae is not uniform in cold-rolled pearlite. As was previously reported, 6) the cold-rolled pearlite structure can be classified into three types shown in the corresponding schematic illustrations; (A) irregularly bent lamellae (IBL) where alignment of q lamellae changes severely by deformation without fragmentation; (B) coarse lamellae with shear band (CLS) which consists of the area with coarse interlamellar spacing and shear bands inclined at about 30 degrees to RD; (C) fine lamellae (FL) where a and q lamellae are almost parallel to RD with fine interlamellar spacing. Figure 3 shows the variation of deformed structure with the rolling reduction.…”

“…[3][4][5] The present authors studied the microstructure and mechanical property of cold-rolled pearlite. 6) Whereas similar changes in microstructure and property by cold rolling of pearlite as in cold drawing were observed, it was found that the cold-rolled structure of pearlite was surprisingly inhomogeneous. When heavily cold-rolled pearlite is annealed, the ultra-fine grained duplex structure with ferrite (a) and cementite (q) grain sizes less than 1 mm was easily obtained.…”

“…This is presumably due to the lamellar morphology of q even though it was fragmented or changed partly to nano-sized crystals after severe plastic deformation. [3][4][5][6] A superior strength-ductility balance was also obtained in the pearlite cold-rolled and annealed at a lower temperature for a shorter period, which maintain the near-lamellar q morphology. 8) By increasing the annealing period at 973 K, strength decreases and ductility i.e., total elongation increases despite of decrease in work hardening seen in Fig.…”

Microstructure in adiabatic shear bands in a pearlitic ultrahigh carbon steel

“…For example the tensile strength of severely cold-rolled pearlitic UHCSs is 2500 MPa. 42 This is equivalent to a nano-hardness of 6.3 Gpa. 43 The result indicates that adiabatic shear, involving a temperature rise during deformation, is a requirement for ultrahigh strength.…”

Effect of Mn and Si Addition on Microstructure and Tensile Properties of Cold-rolled and Annealed Pearlite in Eutectoid Fe-C Alloys

“…1) Pearlite, which consists of ferrite (a ) and lamellar cementite (q ), is one of the most important structures in steels. For the pearlitic structures, both reduction of interlamellar spacing of pearlite (ISP) and thinning of lamellar q occur through heavy cold rolling, 2,3) and the spheroidization of a lamellae can be quite accelerated during subsequent annealing, 4) leading to the formation of (a +q ) microduplex structures. [5][6][7] The refinement of q particles, which should result in the refinement of a grain size by pinning effects, is very important for strengthening the alloy with the (a +q ) microduplex structure.…”