Pearlite

About: Pearlite is a research topic. Over the lifetime, 6028 publications have been published within this topic receiving 65695 citations.

Strain-hardening due to Dispersed Cementite for Low Carbon Ultrafine-grained Steels

Abstract: Strain(work)-hardening in tensile tests was examined for low carbon steels with various ferrite grain sizes ranged from 0.4 to 16 μm. The steels had microstructures composed of ferrite grains and dispersed cementite particles. They were fabricated through warm caliber bar-rollings with an accumulative area reduction of 93%. Strain-hardening rate at a given strain increased with an increase in volume fraction of cementite particles. The balance of yield strength and uniform elongation for ultrafine-grained structures could be improved by the dispersion of cementite particles. Effects of the cementite dispersion and the ferrite grain size on the strain-hardening rate can be roughly explained by the work-hardening model with GN-dislocation density. Strain-hardening design using dispersed cementites was proved to be effective in controlling ductility of the ultrafine-grained steels.

Bainite viewed three different ways

Abstract: The present status of the three principal definitions of bainite currently in use is reviewed. On the surface relief definition, bainite consists of precipitate plates, producing an invariant plane strain (IPS) surface relief effect, which form by shear,i.e., martensitically, at temperatures usually aboveMs andMd. The generalized microstructural definition describes bainite as the product of the diffusional, noncooperative, compctitive ledgewise growth of two precipitate phases formed during eutectoid decomposition, with the minority phase appearing in nonlamellar form. This alternative mode of eutectoid decomposition is thus fundamentally different from the diffusional, cooperative, shared growth ledges mechanism for the formation of pearlite developed by Hackney and Shiflet. The overall reaction kinetics definition of bainite views this transformation as being confined to a temperature range well below that of the eutectoid temperature and being increasingly incomplete as its upper limiting temperature, the kineticBs, is approached. Recent research has shown, however, that even in steels (the only alloys in which this set of phenomena has been reported), incomplete transformation is not generally operative. Revisions in and additions to the phenomenology of bainite defined in this manner have been recently made. Extensive conflicts among the three definitions are readily demonstrated. Arguments are developed in favor of preference for the generalized microstructural definition, reassessment of the overall reaction kinetics definition, and discarding of the surface relief definition.

Microstructure and high strength–toughness combination of a new 700 MPa Nb-microalloyed pipeline steel

Abstract: A new ultrahigh strength niobium-microalloyed pipeline steel of yield strength ∼700 MPa has been processed. The Charpy impact toughness at 0 °C was 27 J and tensile elongation was 16%. The ultrahigh strength is derived from the cumulative combination of fine grain size, solid solution strengthening with additional interstitial hardening, precipitation hardening from carbides, dislocation hardening, and mixed microstructure. The microstructure was characterized by polygonal ferrite, upper bainite, degenerated pearlite, and martensite–austenite (MA) constituents. The microstructure of weld and heat-affected zone (HAZ) was similar to the base metal such that the hardness is retained in the weld region implying insignificant softening in the weld zone. Niobium and titanium precipitates of different morphology and size range evolved during thermomechanical processing and include rectangular (∼500 nm), irregular (∼240–500 nm), cuboidal/spherical (∼125–300 nm), and very fine (

Effect of microstructural banding in steel

Abstract: Tensile and notch-impact properties in wrought steel containing 0.25 pct C and 1.5 pct Mn, with and without elongated inclusions and processed so as to be severely banded or virtually free of microstructural banding, are compared. A short-time, high-temperature normalizing treatment removed the banded condition. Both banding and elongated inclusions cause anisotropy in tensile ductility and impact energy. Elimination of banding is effective in reducing anisotropy in clean steel, but results in only modest improvement in steel containing numerous elongated inclusions. Eliminating microstructural banding alters austenite transformation to only a small extent but improves subsequent machining and cold forming by replacing martensite concentrated in bands with randomly dispersed small volumes of martensite in steel incompletely transformed to ferrite and pearlite or to bainite.