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

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

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

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

Influence of vanadium on the dynamic recrystallization of austenite in high carbon microalloyed steels

NRC publication: N

Empirical Modeling of the Isothermal Transformation of Pearlite in Hypereutectoid Steel

The rate controlling mechanism for pearlite growth in a hypereutectoid steel composition was examined through an analysis of the microstructural characteristics of the pearlite structure, namely interlamellar spacing, for different isothermal transformation and austenitising conditions. From a metallographic analysis of the pearlite structure as a function of the austenitisation and undercooling conditions applied to the hypereutectoid steel, the interlamellar spacing was observed to increase with increasing austenitising temperature and increasing isothermal transformation temperature. Through the application and experimental validation of a theoretical model (Zener and Hillert) for the calculation of the pearlite interlamellar spacing as a function of the undercooling, the growth rate of pearlite in the hypereutectoid steel was determined to be controlled by the volume diffusion of carbon in austenite during isothermal transformation in the temperature range of 550\u2013620\ub0C.NRC publication: Ye

Design and processing of high carbon microalloyed steels

Peer reviewed: YesNRC publication: N

Influence of silicon on the kinetics of metadynamic recrystallization in microalloyed high carbon steels

Peer reviewed: YesNRC publication: N