Structure‐Property Relationship in a Micro‐laminated Low‐Density Steel for Offshore Structure

Self Cite

Herein, the start laminar cooling temperature to obtain different volume fractions of ferrite and bainite/martensite is optimized. Lower start laminar cooling temperature yields a higher volume fraction of ferrite and also decreases the transformation temperature of bainite/martensite. The yield strength of the experimental dual‐phase steel at 600 °C increases from ≈484.8 to ≈526.2 MPa by decreasing the start laminar cooling temperature from 650 to 600 °C. To understand the effect of microstructure, the dislocation density, volume fraction of precipitates, and Young's modulus at elevated temperature are statistically analyzed. A machine learning method, known as gradient boosting decision tree, is used to classify the grain boundaries. The statistical results suggest that the steel subject to lower start laminar cooling temperature shows higher Young's modulus and larger volume fraction of precipitates at elevated temperature. Furthermore, at elevated temperature, the boundary is stable and the proportion of Σ3 boundary is greater, when lower start laminar cooling temperature is adopted. Theoretical calculations results suggest that the lower transformation temperature of bainite/martensite improves the fire resistance of dual‐phase steels.

Section: Resultsmentioning

confidence: 99%

Effect of Microstructures on the Mechanical Behavior of Fire‐Resistant Dual‐Phase Steels at Elevated Temperature

Cong

Zhao

et al. 2021

Self Cite

“…The cuboid billets were subjected to a thickness of %13 mm on a pilot hot rolling mill. [16,29] Tensile test adopts the standard GB/T 228.1-2010. In detail, tensile specimens with 5 mm diameter and 25 mm gauge length were prepared along the rolling direction and tested at room temperature at an extension rate of 2.5 Â 10 À3 s À1 .…”

Section: Methodsmentioning

confidence: 99%

“…Under the action of deformation, the dual‐phase composed of δ‐ferrite and austenite is expected to be elongated and forms micro‐laminated microstructure. [ 5–17 ]…”

Section: Introductionmentioning

confidence: 99%

“…[ 28 ] In fact, we have confirmed that these two mechanisms exist at the same time in our early study. [ 16 ] The choice of these two mechanisms may be related to many factors, such as undercooling, strain, strain rate, and so on.…”

Section: Introductionmentioning

confidence: 99%

“…Under the action of deformation, the dualphase composed of δ-ferrite and austenite is expected to be elongated and forms micro-laminated microstructure. [5][6][7][8][9][10][11][12][13][14][15][16][17] Except prior δ-ferrite lamellae, through diversified alloy design, hot working process, and heat treatment process, the microstructure transformed from prior austenite can be designed as dual-phase or multiphase constituents, containing austenite, [5][6][7][8][9][10][12][13][14] α-ferrite, [5][6][7][8]12] martensite, [5][6][7][8][9][10][11][12][13] pearlite, [10] and bainite, [10] and the fraction range of each phase is also wide. Accordingly, the mechanical properties also vary among different phases.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Strain‐Associated Alpha‐Ferrite Phase Transformation in a Micro‐Laminated Low‐Density Steel

Liú

Shang

et al. 2022

Self Cite

Aluminum-alloyed low-density steels have recently received significant attention because of the advantage in strength-todensity ratio [1] and superior corrosion resistance. [2][3][4] Aluminum is a strong ferrite-forming element and expands both α-ferrite and δ-ferrite phase region. Thus, the addition of aluminum in steel can result in δ-ferrite that always exists below solidification temperature, in spite of the addition of austenitic stabilizing elements. Under the action of deformation, the dualphase composed of δ-ferrite and austenite is expected to be elongated and forms micro-laminated microstructure. [5][6][7][8][9][10][11][12][13][14][15][16][17] Except prior δ-ferrite lamellae, through diversified alloy design, hot working process, and heat treatment process, the microstructure transformed from prior austenite can be designed as dual-phase or multiphase constituents, containing austenite, [5][6][7][8][9][10][12][13][14] α-ferrite, [5][6][7][8]12] martensite, [5][6][7][8][9][10][11][12][13] pearlite, [10] and bainite, [10] and the fraction range of each phase is also wide. Accordingly, the mechanical properties also vary among different phases. Hence, micro-laminated low-density steels have a broad application prospect, with extraordinary combinations of mechanical properties. [8,[10][11][12][13] Based on the microstructure, the deformation-induced evolution of the microstructure and the fracture mechanism are also complex. In general, δ-ferrite is a brittle phase, while the complex microstructure transformed from the original austenite has superior plasticity and resistance to crack growth. [17,18] Cracks propagate preferably into δ-ferrite or at the interface l ayer along the δ-ferrite {100} planes. [15,18] The embrittlement of δ-ferrite is because of higher aluminum content. [17][18][19] With the increase of aluminum content, the reduced mobility of dislocations [19,20] and the formation of ordered structure [17][18][19] result in lower ductility and toughness. Given that the retained austenite stability is critical for fracture resistance, [17] previous studies have focused on controlling the content and stability of retained austenite.However, studies on α-ferrite phase transformation on δ-ferrite and corresponding effect on mechanical properties are rare. Li et al. [14] reported that coarse δ-ferrite is harmful to mechanical properties. The grain refinement of ferrite is simultaneously beneficial to both strength and toughness.

Effect of Cr₂O₃ Addition on Sintering Behavior of Novel Chromite‐Based Ladle Filler Sand

Li,

Kong,

Zang

2023

Developing novel filler sands has garnered significant interest in improving the ladle’s free‐opening rate and enhancing the cleanliness of high‐Mn and high‐Al steel. Laboratory studies explored the effect of adding Cr2O3 powder on the sintering behavior of chromite‐based ladle filler sands. Furthermore, interfacial phenomena were examined between the sands and high‐Mn and high‐Al steel grades, varying in Mn contents. The results demonstrate that adding Cr2O3 power played a role in inhibiting the liquid phase formation in the filler sand. With a 16% addition, the steel (Mn mass%=30) reacted with the sand, leading to the shape of a spinel phase (SP), specifically (Mn, Fe, Mg)O·(Al, Cr)2O3, which facilitated the separation of the liquid phase. The reduction of FeO to Fe by Mn, Al, and C in steel, especially Al, was hindered by adding Cr2O3, resulting in a suitable sintering degree that ultimately benefited ladle free‐opening. SiO2 is crucial for forming the liquid phase during the sintering process. The SiO2 content of the sand should be about 20% to achieve optimal sintering effects. Chromite sand for casting is not suitable for the high‐Mn and high‐Al steels. The mixed sand composition presented in the current study demonstrates potential as a suitable filler sand material for high‐Mn and high‐Al (20 ≤ Mn mass% ≤ 30) steel.This article is protected by copyright. All rights reserved.