Crystallography, Morphology, and Martensite Transformation of Prior Austenite in Intercritically Annealed High-Aluminum Steel

Auto-tempering is a feature of the technologically important as-quenched low-carbon martensitic steels. The focus of this paper is on the morphology of the martensite and the orientation of the last forming untempered regions in relation to the earlier formed auto-tempered martensite in both small and large austenite grains. A low-carbon martensitic steel plate was austenitized for 24 h and quenched to room temperature. The resulting microstructure was characterized using electron microscopy and electron back scattered diffraction (EBSD) imaging. It was found that all the untempered regions in the martensitic microstructure were oriented with the plane normals {100} close to the thickness, or normal, direction of the plates. Variant analysis revealed that the untempered regions and the auto-tempered regions are part of the same packet.

Section: Methodsmentioning

confidence: 99%

Observations on the Relationship between Crystal Orientation and the Level of Auto-Tempering in an As-Quenched Martensitic Steel

Babu

Nyyssönen

Jaskari

et al. 2019

“…The martensitic EBSD maps were processed to reconstruct prior-austenite maps. MATLAB (R2017b, The Mathworks Inc., Natick, MA, USA) with MTEX toolbox was used, following the procedure proposed by Nyyssönnen, et al [16,17]. This procedure starts by determining the experimental Orientation Relationship (OR) between martensite and its parent austenite.…”

Section: Introductionmentioning

confidence: 99%

Impact of Precipitate Morphology on the Dissolution and Grain-Coarsening Behavior of a Ti-Nb Microalloyed Linepipe Steel

Solís-Bravo

Merwin²,

García

2020

The relationship between precipitate morphology and dissolution on grain coarsening behavior was studied in two Ti-Nb microalloyed Linepipe (LP) Steels. The developed understanding highlights the importance of the complex relationship between precipitate constitutive make-up, dissolution mechanism and grain boundary (GB) pinning force. Equilibrium-based empirical solubility products were used to calculate precipitate volume fractions and compared to experimental measurements. Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD) and Electron Probe Micro-Analysis (EPMA) were conducted on bulk samples. Transmission Electron Microscopy (TEM)-based techniques were used on C-replica extractions and thin-foils. A retardation in the grain-coarsening temperature compared to the predicted coarsening temperature based on equilibrium calculations was noticed. In addition, a consistent NbC epitaxial formation over pre-existing TiN was observed. The resulting reduction in total precipitate/matrix interface area and the low energy of the TiN/NbC interface are pointed to as responsible mechanisms for the retardation in the kinetics of precipitates’ dissolution. This dissolution retardation mechanism suggests that a lower Nb content might be effective in controlling the grain coarsening behavior of austenite.

“…Figure 12 shows representative results of the EBSD measurements as band contrast maps overlaid with austenite grains (shown in random coloring). Prior austenite and packet boundaries were determined using a previously developed iterative reconstruction algorithm [8,27] and are shown in red (packet boundaries) and black (prior austenite grain (PAG) boundaries and ferrite boundaries).…”

Section: Qandp Experiments Steel Cmentioning

confidence: 99%

“…Intercritical annealing opens up some interesting possibilities for controlling the condition of the austenite at the conclusion of annealing. The grain size and the relative fraction of the intercritical austenite can be controlled to a large extent by suitably varying the annealing parameters [1,8,9]. The growth of the austenite phase in low-and medium-carbon steels has been observed in various research works to be controlled essentially by the diffusion of carbon across the interphase boundary.…”

Section: Introductionmentioning

confidence: 99%

“…Q&P-aided dual-phase microstructures were also produced for a Fe-0.2C-2.0Mn-1.5Si (wt %) steel after intercritical annealing by Wang et al [18]. These calculations do not take into account prior austenite grain size, which has been observed to have a significant effect on the martensite transformation of intercritically annealed steel in a previous study [8]. Essentially, the prior austenite grain size potentially remains very small during intercritical annealing, further reducing the Ms temperature.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Quenching and Partitioning of Multiphase Aluminum-Added Steels

Nyyssönen

Oja

Jussila

et al. 2019

The quenching and partitioning response following intercritical annealing was investigated for three lean TRIP-type high-Al steel compositions. Depending on the intercritical austenite fraction following annealing, the steels assumed either a ferrite/martensite/retained austenite microstructure or a multiphase structure with ferritic, bainitic and martensitic constituents along with retained austenite. The amount of retained austenite was found to correlate with the initial quench temperature and, depending on the intercritical annealing condition prior to initial quenching, with the uniform and ultimate elongations measured in tensile testing.