Electropulse-induced microstructural evolution in a ferritic–pearlitic 0.14% C steel

The present work reports the experimental observation of electropulse-induced microstructural evolution in a ferritic–pearlitic steel at ambient temperature. Electropulsing initially causes the fragmentation of lamellar structure. Further treatment leads to the formation of new cementite plates aligned with the current direction. This is attributed to the reduction of the system free energy. The hardness of the material decreased with an increase in the number of electric current pulses. Electrical resistivity is thought to be responsible for the observed phenomenon

Measurement of pearlite interlamellar spacing in hypereutectoid steels

In hypereutectoid steels, determination of interlamellar spacing is essential to microstructural characterization, since both static and dynamic properties have been related to the pearlitic structure. Generally, quantitative analysis of the size of a pearlite colony and its interlamellar spacing is performed using optical and electron microscopy techniques. In this work, laser scanning confocal and field emission scanning electron microscopes were used to examine interlamellar spacing in isothermally transformed hypereutectoid steels to benefit from increased resolving power and statistical significance capabilities as compared to light optical and transmission electron microscopes, respectively.NRC publication: Ye

The Effect of Microstructural Characteristics of Pearlite on the Mechanical Properties of Hypereutectoid Steels

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 \ub0C and these microstructures were then subjected to isothermal transformation at temperatures of 550, 580 and 620 \ub0C. 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\u2013Petch type relationship, while the ductility was dependent also on the prior-austenite grain size and pearlite colony size.NRC publication: Ye

3-D Image Analysis of Multiphase Materials using Laser Scanning Confocal Microscopy

For the measurement of the characteristics of lamellar structures, such as pearlite (Fe 3 C and ferrite) in steel and Widmanst\ue4tten alpha-beta in titanium alloys, the application of laser scanning confocal microscopy (LSCM) enables three-dimensional imaging with a resolution capability that allows quantification of the interlamellar spacing and lamellae thickness with statistical confidence. In particular, z-axis (height) or topographic profiling using LSCM permits accurate measurement of the lamellae spacing and thickness due to the possibility for selecting colony regions in the lamellar structure that are perpendicular to the observation plane. Hence, the application of LSCM for materials characterization has the advantage of permitting relatively simple, effective and efficient analytical output as compared to field emi ssion scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) techniques. However, although LSCM is an established characterization method in biological sciences, this technique is recent to the materials science field in North America.NRC publication: Ye

Continuous Cooling Transformation Temperature and Microstructures of Microalloyed Hypereutectoid Steels

The transformation behavior under continuous cooling conditions was investigated for four hypereutectoid steels of 1% carbon with different microalloying additions of vanadium and silicon. Continuous cooling compression testing of the hypereutectoid steels was employed to study the influence of processing conditions (re-heat temperature), microstructure (prior-austenite grain size) and chemical composition (vanadium and silicon) on the critical transformation temperature (Ar3). Overall, for the hypereutectoid steel compositions examined, the transformation temperatures were determined to be relatively stable, with a variation of roughly 15\ub0C when the reheat temperature was changed from 1000 to 1200\ub0C. The addition of microalloying elements such as vanadium and silicon was determined to increase the austenite-to-pearlite transformation start temperature of the hypereutectoid steels by about 10\u201330\ub0C. These changes in the transformation behavior observed with decreasing re-heating temperature and microalloying additions were related to microstructural changes in the hypereutectoid steels, such as prior-austenite grain size refinement, carbide precipitation and grain boundary cementite fragmentation.NRC publication: Ye

Dynamic recrystallization of austenite in microalloyed high carbon steels

Hypereutectoid steels of 1% carbon, alloyed with high silicon and microalloying levels of vanadium were subjected to dynamic recrystallization. It was found that an increase in carbon and vanadium content leads to smaller grain size. To characterize the dynamic recrystallization behavior of these steels, compression tests were performed over the temperature range 900\u20131050 \ub0C using strain rates of 0.01, 0.1 and 1 s 121. Equations were generated that can be used to predict the critical strain for dynamic recrystallization. Of interest is the finding that there is an activation energy for deformation specifically associated with dynamic recrystallization (i.e. peak strain). This activation energy associated with the peak strain is lower than that associated with the steady state stress. This is contrary to Sellar's original observation that the peak strain is a function of the activation energy for deformation according to the Zener\u2013Hollomon relationship.NRC publication: Ye

Metadynamic and Static Recrystallization of Hypereutectoid Steel

The metadynamic and static recrystallization behavior in hypereutectoid steel containing 1% carbon was determined by hot compression testing. Compression tests were performed using double hit schedules at temperatures between 900 to 1050\ub0C, strain rates of 0.01 to 1 s 121 and recrystallization times of 0.1 to 500 s. The characteristics of static and metadynamic recrystallization are distinctly different. Results show that the metadynamic kinetics was twice as fast as the static kinetics. These data were used to generate equations to predict the kinetics of static and metadynamic recrystallization, as well as the evolution of grain size, after recrystallization.NRC publication: Ye

Critical Condition for Dynamic Recrystallization for High Carbon Steels

A softening mechanism for dynamic recrystallisation has been determined through analysis of the continuous compression flow curves of both hypoeutectoid and hypereutectoid steels, 0\ub77 and 0\ub79% carbon respectively, in the range 900 \u2013 1050\ub0C for strain rates 0\ub701 to 1 s 121. The critical stress and strain for the initiation of dynamic recrystallisation were determined from the inflection points in plots of strain hardening rate against flow stress.NRC publication: Ye

FEG-SEM investigation of vanadium carbide precipitation in microalloyed hypereutectoid steel

NRC publication: Ye