Pan American Materials Congress: Steels: Thermomechanical Processing and Properties
Sponsored by: Third Pan American Materials Congress Organizing Committee
Program Organizers: Omar Garcia-Rincon, TERNIUM Mexico SA de CV; Andre Costa E Silva, EEIMVR - Universidade Federal Fluminense
Wednesday 10:10 AM
March 1, 2017
Room: Marina E
Location: Marriott Marquis Hotel
10:10 AM Invited
New Challenges in Thermomechanical Processing: Applications in the Cold Mill: Yu Gong1; M. Hua1; J. Uusitalo2; Anthony DeArdo1; 1University of Pittsburgh; 2University of Oulu
Thermomechanical Processing has been successfully applied in the hot mill since about 1970. Its attractiveness comes from its ability to control the strength and toughness of structural grades in a efficient, continuous process, based mainly on control of microstructure. This research has shown that variations in the stored energy of the cold band going into the CGL anneal can drastically alter the final microstructure and properties of high strength dual-phase steel. This stored energy is influenced by the composition, especially microalloying, the processing of the hot band coils and by the degree of cold reduction. In this study, the changes in microstructure were characterized by OM, SEM, HRTEM and EBSD(IQ, KAM, Stored Energy and grain boundary analysis). The hardness, tensile and hole expansion properties were also determined. These experiments, results and implications will be presented and discussed.
Microstructural Evolution in Microalloyed Steels during Thermomechanical Rod Rolling: Lijia Zhao1; Robert Cryderman1; John Speer1; 1Colorado School of Mines
Steel rods are hot-rolled at high strains and strain rates with a subsequent controlled cooling process to influence the microstructure. The microstructure and mechanical properties of the hot-rolled rods are controlled to produce high-strength fasteners in the cold heading process without subsequent heat treatment. In the present study, simulations of rod rolling by torsional deformation and controlled time-temperature schedules were conducted to examine the effects of thermomechanical processing parameters and microalloying additions on the microstructure evolution and mechanical properties of low-carbon steel rods. Transformation and precipitation behaviors during the thermomechanical process were investigated and related to the increased strength in the steel rods.
Modeling Precipitation and Dissolution of Microalloying Carbonitrides in Steels Using Computational Thermodynamics- techniques, Possibilities and Present Challenges: Andre Costa E Silva1; 1EEIMVR - Universidade Federal Fluminense
Microalloying to form carbonitrides (Nb,Ti and V) is widely used in alloy design for various purposes. Understanding conditions at which these carbonitrides will precipitate or dissolve and predicting their size, volume fraction and distribution is of paramount importance. Computational thermodynamics can be a powerful tool in answering these questions, not only through direct use of equilibrium information but also by coupling it with mobilities and other properties to model the kinetics of the processes involved. In this work, an overview of the information that can be presently gained via the CALPHAD approach with different modeling tools is presented. The advantages, limitations and potential of these tools are discussed, through comparison with experimental results available in the literature. The potential of the tools within ICME is immense; furthermore the discussion indicates that, as in thermodynamic assessments, the use of these tools helps in understanding the critical information needed for modeling.
Evolution of Austenite Dislocation Density during Hot Deformation using a Physical Dynamic Recrystallization Model: Peng Zhou1; Qingxian Ma1; 1Tsinghua University
A new model to predict the dislocation density evolution of 30Cr2Ni4MoV steel during hot deformation was proposed in this study. Hot compression of 30Cr2Ni4MoV steel was carried out on Gleeble 1500 at different conditions. The dependence of yield stress, critical stress and strain of dynamic recrystallization and the saturation stress of dynamic recovery, which were identified from the strain hardening rate curves, on temperature and strain rate was determined. Two sets of dislocation density equation were derived from the experimental flow curves: I) a dislocation density relation describing the grains in which dynamic recovery took place only; and II) an average dislocation density expression pertaining to the recrystallized grains. The kinetics model of dynamic recrystallization was determined with the aid of the above relations. Finally, the dependence of the dislocation density on strain, deformation temperature and strain rate was determined and the predicted results agreed well with the experimental results.
The Research on the Relationship between Gas Movement Behaviors and Circulating Flow of the Molten Steel in RH: Jialiang Xu1; Yanping Bao1; Lihua Zhao1; Min Wang1; Lu Lin1; Yadi Li1; Xingle Fan1; 1University of Science and Technology Beijing
Circulating kinetic energy has important influences on process of rapid decarburization rate in RH. A physical model of 300 t RH in 1:6 ratio is established to study the relationship between gas behaviors and circulating kinetic energy in this paper. The studies showed that the circulating kinetic energy of liquid steel has an exponential relationship with the bubble velocity and gas volume fraction (17%~26%) However, the proportion that the circulating kinetic energy accounted for the total energy is less than 1%, when the void fraction in the up leg is lower than 22% or the bubble velocity less than 0.5m/s. Therefore, in order to avoid appearing lowest energy value and take advantage of gas-driven energy, must satisfy threes below requests. Ensuring the void fraction is greater than 22%. The vacuum chamber bubble residence time is around 0.15s. And the bubble rising velocity is not less than 0.5m/s. Satisfying the above conditions can optimize flow effect of molten steel and improve the decarbonization
Influence of a Rapid Heating on the Microstructure and Properties of Press-hardening Steel Sheets: Anatolii Andreiev1; Mirko Schaper1; Olexandr Grydin1; 1Paderborn University
The work presents results of investigation on a new heating method for production of high-strength car body elements. It’s proposed to substitute the conventional heating of blanks in gas or electric furnaces through the rapid contact heating. The blank at this process is pressed between two heated plates during few seconds and subsequently quenched in water-cooled dies to obtain high-strength properties due to the martensitic transformation. The influence of heating temperature in the range between 800 °C and 1000 °C and dwell time from 4 s to 16 s on the microstructure and mechanical properties of 1 mm thick sheet of a low alloyed manganese-boron steel was studied. Furthermore, press hardening including common heating in electric furnace at 950 °C during 360 s and quenching in water-cooled dies of the same sheet was performed to compare the resulted microstructure and mechanical properties with the rapid heated and press hardened material.