Influence of Microstructure on Strength and Ductility in Fully Pearlitic Steels (original) (raw)
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Role of the microstructure on the mechanical properties of fully pearlitic eutectoid steels
This paper analyses how the microstructure of an eutectoid pearlitic steel affects its conventional mechanical properties (obtained by means of a standard tension test) and the associated micromechanisms of fracture. Results show how the yield strength, the ultimate tensile strength (UTS) and the ductility, increase as the continuous cooling rate rises, whereas on the other hand the strain at UTS decreases. The fracture surface exhibits more brittle features when the continuous cooling rate decreases, in such a manner that in the fracture process zone an increasing area appears where the pearlite lamellae can be detected and less regions of microvoids are observed.
Materials Science and Engineering: A, 2005
The relationship between mechanical properties and microstructural characteristics of pearlite was investigated using various heat treatments on a hypereutectoid steel. The materials were reheated between 900 and 1200 • C and these microstructures were then subjected to isothermal transformation at temperatures of 550, 580 and 620 • C. For the hypereutectoid steel, the mean value of the interlamellar spacing was observed to increase with increasing reheat and transformation temperatures. Examination of the mechanical properties of the resulting pearlitic microstructures indicated that the strength was related primarily to the interlamellar spacing by a Hall-Petch type relationship, while the ductility was dependent also on the prior-austenite grain size and pearlite colony size.
Tailoring the Processing Route to Optimize the Strength-Toughness Combination of Pearlitic Steel
Metallurgical and Materials Transactions A, 2022
The present study fine tunes the processing route of a eutectoid steel to shape an optimum strength–toughness combination through appropriate microstructural design. A fully lamellar coarse pearlite microstructure leads to poor strength and toughness. Hot deformation prior to the isothermal treatment breaks down the lamellar pearlite to a spheroidized structure. Moreover, reducing the hot deformation temperature not only refines the pearlite nodule size but also increases the spheroidized pearlite fraction, which thereby improves the toughness of the steel. However, no proportionate increase in yield strength was obtained due to insignificant change in the interlamellar spacing. Remarkable refinement in lamellar spacing and increase in the spheroidization amount was ensured when the hot deformation was carried out just below the eutectoid temperature, owing to the strain-induced pearlite transformation. The presence of a mixed microstructure of fine lamellar pearlite along with spheroidized pearlite constituents simultaneously improves both the yield strength and toughness of the steel. Optimum strength–toughness combination was attained when the hot deformation strain (just below the eutectoid temperature) was increased up to 45 pct. Subsequent increase in strain creates deformation bands and traces of strain-induced bainite in the microstructure, which again deteriorates the tensile elongation of the steel.
Strength and ductility of heavily deformed pearlitic microstructures
IOP Conference Series: Materials Science and Engineering, 2017
The fracture toughness and deformation behavior of heavily deformed pearlitic steels have been investigated. A strong anisotropy of the fracture toughness and the plastic deformation behavior with respect to the lamellar orientation is observed. The consequences of this anisotropy both for processing and application, as well as for the limits in strengthening, are discussed. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Impact of Hypo and Hyper Eutectoid Steels Microstructures in Their Properties
2015
Quantitatively a pearlitic structure is characterized by ferrite - pearlite percentage and interlamellar spacing of the pearlite.These parameters vary as a function of the transformation temperature.When the carbon content is below 0.6%, pearlite always degenerate, with low yield strength but good reduction in area. Pearlites containing more than 0.6%C always present normal cementite lamellae with high yield strength but small reduction in area. For 0.6%C steel, fragmented or continuous lamellar structures can be obtained, leading to high yield strength and reduction in area values.
Journal of Materials Engineering and Performance, 2015
The processes governing the deformation and damage of C70 pearlitic steel were investigated in nanometer and micrometer scales using electron backscatter diffraction technique and ''in-situ'' scanning electron microscope tensile testing. The ferrite behavior was identified by ''in-situ'' x-ray tensile tests. Investigations were carried out on annealed microstructure with two interlamellar spacings of Sp = 170 and Sp = 230 nm. It is shown that pearlite yielding is controlled by the deformation mechanisms occurring in ferrite. Deformation and damage mechanisms were proposed. At low strain, pearlite deforms homogeneously with low misorientation (<5°) inside the pearlite colonies and elongates the cementite plates. At high strain, pearlite deforms heterogeneously in intense localized shear bands inside the more favorably oriented pearlite colonies. Misorientation reaches values up to 15°. Cementite deforms by an offset of lamella along the shear bands. The nucleation of these shear bands occurs at strain level of E 11 = 7% for coarse pearlite and at a higher value for fine pearlite. Damage occurs by brittle fracture of the elongated cementite lamellae parallel to the tensile axis and which are developed by shear micro-cracks along the slip bands. The plastic-induced damage is thus delayed by the fine pearlite structure.
Microstructural Engineering in Eutectoid Steel: A Technological Possibility?
Metallurgical and Materials Transactions A
Eutectoid wire rods were subjected to controlled thermo-mechanical processing (TMP). Both increased cooling rate and applied stress during the austenite-to-pearlite decomposition produced significant changes in the microstructure: major increases in the pearlite's axial alignment and minor decreases in the interlamellar spacing. The pearlite alignment was correlated with changes in the ferrite crystallographic texture and the state of residual stress. Microstructural engineering, improved axial alignment of pearlite, through controlled TMP gave a fourfold increase in torsional ductility. TMP of eutectoid steel thus appears to have interesting technological possibilities.
International Journal of Fatigue, 2004
The effects of changes in load ratio, R, and test temperature on the fatigue crack growth behaviour of fully pearlitic eutectoid steel have been investigated. Separate fatigue crack growth experiments were performed at load ratios of 0.1, 0.4, and 0.7 at Ϫ125°C and compared to the behaviour at room temperature. An increase in load ratio at Ϫ125°C decreased the fatigue threshold and significantly increased the Paris Law slope. Similar effects of changes in R, but less in magnitude, were observed in tests conducted at 25°C. Fracture surfaces were examined using SEM. The significantly increased Paris Law slope exhibited in separate tests conducted at Ϫ125°C and/or higher load ratio was coincident with an increase in the amount of cleavage fracture present on the fracture surface.
Materials & Design, 2015
In this research, the effects of transformation temperature, time and cooling rate during continuous and isothermal heat treatment processes on microstructure evolutions and mechanical properties of a hot rolled plain eutectoid steel rod were investigated. Austenitizing was performed at the temperatures of 850 and 950°C for 5 min. Cooling rate was selected between 7 and 26°C/s for the continuous cooling and isothermal cooling was conducted in a salt bath furnace at the temperature range of 520 and 560°C. The results showed that the finest pearlite microstructure and a good combination of strength and ductility were achieved by isothermal heat treatment at 560°C. On the other hand, continuous cooling from 850°C at the rate of 26°C/s resulted in an adequate tensile strength (1040 MPa) and substantial increase in the ductility (elongation: 21% and reduction area: 51%).
Microstructural Evolution of a Pearlitic Steel Subjected to Thermomechanical Processing
Materials Research
The microstructural alterations suffered during the process of drawing deformation and subsequent annealing of pearlitic steel wires, were evaluated by scanning electron microscopy and atomic force microscopy. The deformed material showed the curling structure in cross section while, in the longitudinal section, the lamellae was aligned with the drawing direction. The microstructural characterization of deformed samples also allowed observing an interlamellar spacing reduction and the intermediate lamellae alignment process. After the heat treatment at 1000ºC for 5 min the microstructure was restored, however, few recrystallized grains were observed. The recovery was the dominant phenomenon, due to factors associated with curling structure that inhibited recrystallization.