A paper published in IOP Conference Series: Materials Science and Engineering investigates various fundamental concepts that are at play during the solidification of continuously cast steel billets at different cooling rates. The simulations in the paper, Continuous Casting of High Carbon Steel: How Does Hard Cooling Influence Solidification, Micro and Macro Segregation?, were performed with the Thermo-Calc software package to investigate solidification as well as micro and macro segregation of steel billets from continuous casting. Thermo-Calc, together with the TCFE database, was used to calculate different steel properties and perform Scheil solidification simulations to compare simplified C80D steels with no carbon diffusion and fast carbon diffusion. The calculated steel properties were then used in the solidification simulation in CHILL (developed by the SMS Group). With information from the CHILL simulations, the diffusion equations were solved using the Diffusion module (DICTRA) together with the free mobility database MFEDEMO. Thermo-Calc was also used to calculate the driving forces for diffusion with the free database FEDEMO.Continue reading
Computational thermodynamics is a rapidly developing field at the forefront of materials design. But did you know that the field is already over 40 years old? This year at the TMS Annual Meeting in San Antonio, Texas, John Ågren, one of the original developers of Thermo-Calc, gave a presentation on the history of computational thermodynamics at the Royal Institute of Technology (KTH) in Stockholm, Sweden, one of the earliest schools to teach computational thermodynamics. In his fun and fascinating presentation, he discusses how the education of computational thermodynamics started, which issues arose and how they were solved.
It all started in the late 1970s when the Materials Science and Engineering (MSE) department at KTH got a minicomputer which was used in both research and education. But in the early days they came across some unexpected issues. It appeared that most students disliked computers and couldn’t do much coding themselves, which resulted in teachers spending a lot of time debugging codes. Besides that, there were also technical issues. About 30 students were working on the same computer at the same time, which made the response times very long. These difficulties made it hard for the students to understand the point of the computational exercises. As an attempt to solve these problems, teachers prepared codes for the students and handed out some written material about the underlying physics. Despite this, most time was spent on making correct inputs, which made the students not likely to understand the role of computers in materials science.Continue reading
Cobalt-base alloys are important for high temperature applications due to their possibility to form duplex fcc + hcp structures and their low stacking fault energy. However, there is an interest in substituting cobalt for economical, ethical and health reasons.
Both the thermodynamic and kinetic calculations in this publication were performed with Thermo-Calc software and the Diffusion module (DICTRA) together with the thermodynamic database TCHEA and the kinetic database MOBNI. Thermo-Calc was used to predict the phase fractions of fcc and hcp which were compared with experimental results. In the article, it is stated that the calculated thermodynamic values correlate relatively well with the experimental values. The authors concluded that designing duplex fcc + hcp Co-based alloys with computational tools is feasible.Continue reading
In the paper Alloy Composition and Critical Temperatures in Type 410 Steel Welds, Thermo-Calc was used to evaluate the effect of alloy composition on critical temperatures (A1 and A3) in Type 410 steels.
Type 410 steels are typically welded by using consumables with matching composition. However, this type of steel has shown to have poor weldability which is related to formation of hard and brittle martensite in the weld zone, hydrogen-included cracking or retention of δ-ferrite which affects the toughness. One theory that explains the inconsistent toughness is that the wide composition ranges of the base metal results in wide variations of the A1-temperature. In the paper, this theory was investigated with the design of experiment (DoE) approach using Thermo-Calc to perform thermodynamic simulations. Thermo-Calc together with the TCFE8 database was used to predict A1 and A3 temperatures for various compositions.Continue reading
In a paper out of Ohio State University, the mechanism of δ-ferrite retention in the coarse-grained heat-affected zone is studied.
The efficiency of fossil-fired and nuclear power plants has caused raised operating temperatures, which requires use of creep-resistant stainless steels in the hottest regions of the plant. Grade 91 steels are used in the lower-temperature heat recovery steam generators. To be able to join the high- and low-temperature sections, dissimilar metal welds (DMWs) are necessary. The problem with using DMWs is that it often results in extensive carbon diffusion near the fusion boundary which creates brittle and large carbides that make the welds weaker.
Creep strength-enhanced ferritic (CSEF) steels are today welded with Ni-based filler metals to reduce the carbon diffusion between the dissimilar steels, which reduces the formation of hard and soft zones that negatively affects the creep strength. However, the high concentration of carbide forming elements in Ni-based alloys still creates a driving force for carbon diffusion toward the filler metal.Continue reading