A multiscale mean field model for elastic properties of hypereutectoid pearlitic steels with different microstructures

Multiscale modeling of macroscopic elastic properties of pearlitic hypereutectoid steel using the Eshelby matrix–inclusion approach is possible. The model works through successive homogenization steps, based on the elastic properties of cementite and ferrite. Globular pearlite is homogenized using α Mori–Tanaka approach. Lamellar pearlite and pearlite colonies with fragmented proeutectoid cementite are homogenized by α classical self-consistent scheme. In the case of pearlite colonies surrounded by α continuous cementite film, α generalized self-consistent scheme is used. The influence of microstructural parameters such as the pearlite colony size or the thickness of the proeutectoid cementite on Young’s and shear moduli and on coefficients of the stiffness tensor is simulated. Proof of concept is obtained by comparison between predicted elastic behavior and experimental results from the literature.

Microstructure and Mechanical Properties of 3-Wire Electroslag Welded (ESW) High-Speed Pearlitic Rail Steel Joint

The present paper aims at utilizing the 3-wire electroslag welding (ESW) to join high-speed pearlitic rail steels where microstructure and mechanical properties were investigated. The welded joint has produced an improved fracture force of 1396KN. WM was consisted of ferrite and pearlite having hardness of 27HRC, tensile strength of 748MPa and toughness of 12J, successively. HAZ was composed of pro-eutectoid ferrite and pearlite, where austenite grain size and pearlite colony size were reduced by moving away from the fusion line. In HAZ, near to the fusion line, the austenite grain size was 143±19μm, pearlite colony size was 52±9μm and pearlite interlamellar spacing was 90±27nm, which has produced hardness of 43.5HRC, tensile strength of 1228MPa, and toughness of 8J, successively. The entire investigation concludes that 3-wire ESW is an optimum and viable method, which has provided fine pearlite microstructure along with improved hardness and tensile strength.

Quantitative Characterisation of Pearlite Morphology in Hot-Rolled Carbon Steel

During the hot rolling of carbon steel, austenite phase transforms into a pearlitic morphology, which essentially is a matrix of ferrite lamellae (α-Fe) and cementite (Fe3C). This transformation occurs at the cooling bed after an equalisation temperature of around 600 °C. Pearlitic steels find their use in ropes for bridges and elevators, rails, and tyre cords among others. Characterisation of microstructure has not been broadly applied to pearlitic steels because of their complex microstructures. Therefore, the characterisation of this morphology becomes inevitable, in order to identify potential weaknesses in the matrix. In this study, hot-rolled reinforcement bars (rebars) produced from recycled steel and direct reduced iron (DRI), were used for microstructural examination using standard metallurgical procedures. Although the optical microscope (OM) and scanning electron microscope (SEM) were used to obtain qualitative microstructure, they could not characterise the pearlite morphology quantitatively because of their three-dimensional (3D) limitation. Hence, the image analyser - Gwyddion Software, was used to quantify the pearlite morphology of these Y16 rebars. The results indicate that the pearlite colony is characterised by 3D single interpenetrating crystals of ferrite and cementite running parallel to each other due to their common growth during the transformation process of austenite. It was further observed that, the dimensional properties of the phases in the morphology in terms of their width and Interlamellar spacing (S), including the roughness of the pearlite colony can vary significantly. These results could be used to enhance the processing methodology of the industrial production processes.

Study on the Nucleation and Growth of Pearlite Colony and Impact Toughness of Eutectoid Steel

The relationship between microstructure parameters and mechanical properties was studied in this paper. The steel was heat-treated at different austenitizing temperatures to acquire varying microstructure. The results showed that austenite grain size increases with austenitizing temperature, while the pearlite colony size was relatively constant. The strength followed a Hall–Petch relationship with the austenite grain size, but the austenite grain size has nothing to do with the impact toughness. The control unit for determining the impact toughness of pearlitic steel is the pearlite colony size using a comparison method. Further studies have found that, in the hypoeutectoid steel and hypereutectoid steel, the pearlite colony size changes with the austenitizing temperature. However, when the eutectoid steel with a carbon content of 0.81% undergoes the isothermal transformation, the number of grain boundary precipitates is very few. There are many nucleation sites at the grain boundary. The pearlite colonies randomly nucleate at the grain boundaries and grow into the interior of the grains. Simultaneously, new pearlite colonies nucleate by the side of the existing pearlite colony. The intragranular pearlite colonies are also randomly nucleated. These nucleation sites increase the chance of the growing pearlite colonies colliding with each other, eventually resulting in a constant pearlite colony size.

Stability of a Lamellar Structure – Effect of the True Interlamellar Spacing on the Durability of a Pearlite Colony / Stabilność Struktury Płytkowej – Wpływ Rzeczywistej Odległości Międzypłytkowej Na Trwałość Kolonii Perlitu

A lamellar microstructure is, beside a granular and dispersive one, the most frequently observed microstructure in the case of metal alloys. The most well-known lamellar microstructure is pearlite, a product of a eutectoidal transformation in the Fe-Fe3C system. The lamellar morphology of pearlite - cementite and ferrite lamellae placed interchangeably within one structural unit described as a colony - is dominant. The durability of the lamellar morphology is much diversified: in the microstructure of spheroidizingly annealed samples, one can observe areas in which the cementite is thoroughly spheroidized, next to very well-preserved cementite lamellae or even whole colonies of lamellar pearlite. The mentioned situation is observed even after long annealing times. The causes of such behaviour can vary. The subject of the previous work of the authors was the effect of the orientation between the ferrite and the cementite on the stability of the lamellar morphology. This work constitutes a continuation of the mentioned paper and it concerns the effect of the true interlamellar spacing on the stability of the lamellar morphology of cementite.

Effect of Microstructure on Mechanical Properties of High Carbon Steel Wire Rod

In this study, the effect of pearlite microstructure on mechanical properties has been analyzed.The high carbon steel wire rods were treated by traditional salt-bath isothermal heat treatment and a new process, respectively. The microstructures and mechanical properties of the wire rods were tested with SEM and Instron 8501. The results shown that with the decrease of the isothermal holding temperature, the pearlite interlamellar spacing and pearlite colony size decreased and the mechanical properties of the wire rod increased. Especially the interlamellar spacing and pearlite colony size were decreased by new heat treatment observably. With the new treatment, the reductions of area increase.