The effect of heating rate on the formation and decomposition of austenite was investigated on cold-rolled low carbon steel. Experiments were performed at two heating rates, 150 °C/s and 1500 °C/s, respectively. The microstructures were characterized by means of scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Experimental evidence of nucleation of austenite in α/θ, as well as in α/α boundaries is analyzed from the thermodynamic point of view. The increase in the heating rates from 150 °C/s to 1500 °C/s has an impact on the morphology of austenite in the intercritical range. The effect of heating rate on the austenite formation mechanism is analyzed combining thermodynamic calculations and experimental data. The results provide indirect evidence of a transition in the mechanism of austenite formation, from carbon diffusion control to interface control mode. The resulting microstructure after the application of ultrafast heating rates is complex and consists of a mixture of ferrite with different morphologies, undissolved cementite, martensite, and retained austenite.

This paper presents the characterization of a secondary cone crusher concave liner made of Hadfield steel used in Chilean mining after crushing copper minerals during all service life. During use, a cone crusher concave liner suffers indentation (cold working) and abrasion; this combination provides the concave with a layer that constantly renews itself, maintaining a surface highly resistant to abrasive wear. The results presented here were obtained using optical microscopy, microhardness test, measuring abrasion using the dry sand/rubber wheel apparatus, and x-ray diffraction peaks analysis through the classic Williamson–Hall method. After analysis of results, two hardened surfaces have been found—one a product of heat treatment and the other due to deformation during use. This work proposes ways to explain them; the first one uses a thermodynamic model to calculate stacking fault energy, and the second compares the liner with cold-rolled samples.

The objective of the present study is to analyze the microstructure and mechanical properties of a twinning-induced plasticity (TWIP) steel at different temperatures. For this purpose, tensile tests were performed on a Fe-22Mn-0.65C TWIP steel in a temperature range between 25 °C and 400 °C. The microstructure after deformation was characterized via optical microscopy. It was observed that the microstructure consists of mainly deformation twins at low temperatures, whereas dislocation bands are the predominating feature at high temperatures. The analysis of mechanical data suggests a transition of the deformation mechanism from twinning at low temperatures to dislocation slip at high temperatures. The work-hardening rate and area reduction variation with temperature are discussed and correlated to the decrease of twinning contribution to the deformation mechanism. The role of other processes, such as dynamic strain aging and precipitation hardening, are discussed. A thermodynamic-based description for the dependence of yield stress with temperature was developed, suggesting two acting work-hardening mechanisms.

The microstructure of the coating during hot-dip galvanizing under industrial conditions of two structural steels, a low-silicon ASTM A36 steel and a high-silicon Q345B steel, both of commercial grade, have been characterized for industrial-relevant times. In both cases, it is noted that the formation of the Fe–Zn phases begins in the early stages in the heating step of the steel, a situation in which all the phases are in the solid state. These last observations have been taken into consideration and the microstructures of short times are analyzed, showing that the effect of silicon is present at longer times. The characterization was carried out through traditional metallographic techniques including SEM-EDS and XRD equipment. The evolution in time of the microstructure of both steels is examined, being able to observe that the mechanism by which silicon accelerates the formation of Fe–Zn phases in galvanizing is related to the presence of the liquid phase in contact with the ζ layer formed in earlier times, accumulating silicon in the ζ–liquid interphase. These results are directing the analysis towards proposing the hypothesis of a mechanism of penetration of the liquid phase through ζ–ζ boundaries by variations in the surface free energies that allow the penetration of the liquid phase according to the Gibbs Smith condition. Finally, the observations provided us with a deeper understanding of the phase evolution in the hot-dip galvanizing of high silicon steels.

The effect that the microstructure exerts on the Transformation-Induced Plasticity (TRIP) phenomenon and on the mechanical properties in a multiphase steel was studied. Samples of an initially cold-rolled ferrite–pearlite steel underwent different intercritical annealing treatments at 750 °C until equal fractions of austenite/ferrite were reached; the intercritical treatment was followed by isothermal bainitic treatments before cooling the samples to room temperature. Samples in the first treatment were heated directly to the intercritical temperature, whereas other samples were heated to either 900 °C or 1100 °C to obtain a fully homogenized, single-phase austenitic microstructure before performing the intercritical treatment. The high-temperature homogenization of austenite resulted in a decrease in its stability, so a considerable austenite fraction transformed into martensite by cooling to room temperature after the bainitic heat treatment. Most of the retained austenite transformed during the tensile tests, and, consequently, the previously homogenized steels showed the highest Ultimate Tensile Strength (UTS). In turn, the steel with a ferritic–pearlitic initial microstructure exhibited higher ductility than the other steels and texture components that favor forming processes.

The evolution of the elastic constants, $C_{33}$, $C_{44}$ and $C_{55},$ Poisson’s ratio and acoustic birefringence of a Fe-0.5 wt% C-21.5 wt% Mn twinning-induced plasticity (TWIP) steel with reduction by cold rolling and recrystallization annealing was assessed from measurements of the times of flight of ultrasonic waves propagating along the thickness of the rolled plates. As the reduction increased, changes in the elastic constants resulted in a steadily increasing orthotropy, which was clearly shown by Poisson’s ratio and acoustic birefringence. Although optical metallography and hardness measurements showed that partial or full recrystallization is attained after annealing at 600 °C and 700 °C, the ultrasonic measurements revealed that a high level of orthotropy remains.