Relationship Between Solidification Microstructure and Hot Cracking Susceptibility for Continuous Casting of Low-Carbon and High-Strength Low-Alloyed Steels: A Phase-Field Study

Abstract

Hot cracking is one of the major defects in continuous casting of steels, frequently limiting the productivity. To understand the factors leading to this defect, microstructure formation is simulated for a low-carbon and two high-strength low-alloyed steels. 2D simulation of the initial stage of solidification is performed in a moving slice of the slab using proprietary multiphasefield software and taking into account all elements which are expected to have a relevant effect on the mechanical properties and structure formation during solidification. To account for the correct thermodynamic and kinetic properties of the multicomponent alloy grades, the simulation software is online coupled to commercial thermodynamic and mobility databases. A moving-frame boundary condition allows traveling through the entire solidification history starting from the slab surface, and tracking the morphology changes during growth of the shell. From the simulation results, significant microstructure differences between the steel grades are quantitatively evaluated and correlated with their hot cracking behavior according to the Rappaz-Drezet-Gremaud (RDG) hot cracking criterion. The possible role of the microalloying elements in hot cracking, in particular of traces of Ti, is analyzed. With the assumption that TiN precipitates trigger coalescence of the primary dendrites, quantitative evaluation of the critical strain rates leads to a full agreement with the observed hot cracking behavior.

An ICME Process Chain for Diffusion Brazing of Alloy 247

“…This approach is implemented in the MICRostructue Evolution Simulation Software MICRESS® [13] and includes direct coupling to Calphad databases using efficient extrapolation algorithms [14,15] as well as other additional features which are detailed in [16,17]. This tool has been successfully used for simulations of phase transformations in a number of technical alloy systems [18][19][20][21]. The important and central role of applied microstructure simulations and their potential in ICME settings has already been demonstrated using this software tool [22].…”

Cross-Permeability of the Semisolid Region in Directional Solidification: A Combined Phase-Field and Lattice-Boltzmann Simulation Approach

“…This has been done recently by calibration against a representative high-resolution reference simulation. 21 In the present case, however, the high computational effort makes such a calibration impossible, particularly as no substantial reduction of the domain size is possible without affecting the selection of the correct stationary tip temperature. Therefore, in this work, another …”

“…A constant temperature gradient of G = 40 K/cm and cooling rate of V = 0.40 K/s were applied in all cases, ensuring a constant secondary arm spacing, 19 the average of which has been determined as 31.2 lm. TiN particles were nucleated at the beginning according to a seed-density model by using an arbitrary densityradius distribution 20,21 and were given time to grow and ripen before the primary dendrite appeared. To reach stationary growth conditions as quickly as possible, nucleation of the initial seed of fcc phase was performed exactly at the stationary tip temperature of 1618.8 K at the lower left corner of the simulation domain.…”

Experimentally-aided Simulation of Directional Solidification of Steel

“…7) The MICRESS ® code has been previously employed to address microstructural formation during solidification of steel. [8][9][10][11] There is no need to describe the MICRESS ® code in detail, but in the context of the present discussion, it is pertinent to briefly describe the underpinning principles of the code, which essentially provides a mathematical solution to the coupled phase-field and diffusion differential equations. In the phase field description each phase is described by a phase-field parameter (order parameter) which contains some physical properties of the different phases.…”