Complex Microstructural Banding of Continuously Cooled Carbide-Free Bainitic Steels

2014 ◽  
Vol 783-786 ◽  
pp. 980-985 ◽  
Author(s):  
Lucia Morales-Rivas ◽  
Hans Roelofs ◽  
Stephan Hasler ◽  
Carlos García-Mateo ◽  
Francisca García Caballero
Keyword(s):  
Volume Fraction ◽  
Electron Backscatter Diffraction ◽  
High Strength ◽  
Gradual Transition ◽  
Bainitic Steels ◽  
Segregation Of Alloying Elements ◽  
Steel Grades ◽  
Chemical Segregation ◽  
Bainitic Structure ◽  
Morphological Differences

Chemical segregation of alloying elements during solidification of steel grades leads to development of a banded microstructure, causing a degree of anisotropy that can be detrimental to the mechanical behavior under service conditions. It is well-known that the presence of strongly orientated martensite bands in carbide-free bainitic microstructures, associated to inhomogeneous Mn redistribution during solidification, leads to a remarkable deterioration in toughness in advanced high strength bainitic steels. In this study, while bands were clearly visible on light optical micrographs of continuously cooled carbide-free bainitic steels, scanning electron microscopy examination revealed only a gradual transition between matrix and bands, both with a granular bainitic structure. Electron backscatter diffraction was used to quantify the bainitic packet size and volume fraction of martensite/austenite constituent between and within the bands, after a process of optimization of the analysis settings in order to minimize the inherent difficulties linked to sub-micrometric and minority phase indexation. The quantitative microstructural results showed negligible morphological differences between bainitic structure bands and matrix, only solute segregation of Cr and Mo was detected by energy-dispersive X-ray spectroscopy within bands, which must be responsible for a stronger resistance against metallographic etching in those regions.

Development of Low Carbon Microalloyed Bainitic Steels for Structural Plate Applications

2005 ◽  
Vol 500-501 ◽  
pp. 573-580 ◽  
Author(s):  
D. Ormston ◽  
Volker Schwinn ◽  
Klaus Hulka
Keyword(s):  
High Strength ◽  
Carbon Steels ◽  
Chemical Compositions ◽  
Low Carbon ◽  
Controlled Processes ◽  
Bainitic Steels ◽  
Steel Grades ◽  
Carbon Microalloyed ◽  
Hot Rolled ◽  
Plate Steels

Steels with bainitic microstructures show the capacity to fulfil the requirements of high strength and low temperature toughness necessary for plate steels in specialised industrial constructions. The introduction of steels with higher strength allows for weight reductions of steel constructions. This paper investigates the development of hot rolled structural plate steels through laboratory hot rolling simulations of thermo-mechanically controlled processes (TMCP). Specific alloying and microalloying along with an optimised TMCP process has allowed high tensile properties to be achieved in combination with high levels of toughness. Tensile strengths of up to 900 MPa have been achieved with Charpy V-notch toughness greater than 200J at –40°C. Elements such as molybdenum, niobium and boron have been added to low carbon steels to promote the formation of fully bainitic microstructures with much lightened chemical compositions. The presented concepts allow the production of steel grades above S500 up to S690.

scholarly journals Microstructural Features of Strain-Induced Martensitic Transformation in Medium-Mn Steels with Metastable Retained Austenite/ Cechy Mikrostrukturalne Indukowanej Odkształceniem Przemiany Martenzytycznej W Stalach Sredniomanganowych Z Metastabilnym Austenitem Szczątkowym

2014 ◽  
Vol 59 (4) ◽  
pp. 1673-1678 ◽  
Author(s):  
A. Grajcar ◽  
A. Kilarski ◽  
K. Radwanski ◽  
R. Swadzba
Keyword(s):  
Electron Microscopy ◽  
Retained Austenite ◽  
Volume Fraction ◽  
Electron Backscatter Diffraction ◽  
Bainitic Ferrite ◽  
Tensile Tests ◽  
Bainitic Steels ◽  
Transmission Electron ◽  
Strain Induced Martensite ◽  
Backscatter Diffraction

Abstract The work addresses relationships between the microstructure evolution and mechanical properties of two thermomechanically processed bainitic steels containing 3 and 5% Mn. The steels contain blocky-type and interlath metastable retained austenite embeded between laths of bainitic ferrite. To monitor the transformation behaviour of retained austenite into strain-induced martensite tensile tests were interrupted at 5%, 10%, and rupture strain. The identification of retained austenite and strain-induced martensite was carried out using light microscopy (LM), scanning electron microscopy (SEM) equipped with EBSD (Electron Backscatter Diffraction) and transmission electron microscopy (TEM). The amount of retained austenite was determined by XRD. It was found that the increase of Mn addition from 3 to 5% detrimentally decreases a volume fraction of retained austenite, its carbon content, and ductility.

Research on Multi-Artificial Aging Applied to Aluminum Alloy 7150 Plate

2012 ◽  
Vol 706-709 ◽  
pp. 340-345
Author(s):  
Zhi Hui Li ◽  
Bai Qing Xiong ◽  
Yon Gan Zhang ◽  
Xin Yu Lu ◽  
Zhen Bo He ◽  
...  
Keyword(s):  
Tensile Property ◽  
Artificial Aging ◽  
Volume Fraction ◽  
Electron Backscatter Diffraction ◽  
High Strength ◽  
Microstructural Characterization ◽  
Grain Structure ◽  
Artificial Ageing ◽  
Thickness Direction ◽  
Near Surface

The AA 7150-T351, in the form of 40 mm thick plates, was subjected to single-stage aging leading to peak aged condition, and two selected multi-artificial aging treatments leading to the over aged conditions. The microstructural differences along the thickness direction of the AA 7150-T351 plate were investigated using OM and electron backscatter diffraction (EBSD) technique, and the microstructural characterization was studied at different stages of multi-artificial ageing process by transmission electron microscopy. Tensile properties and electrical conductivity measurements were used to evaluate the property homogeneity along the thickness direction of the plate under various artificial aging tempers. It was revealed that the microstructural features and tensile property are inhomogeneous in different layers along the thickness direction, and both grain structure and tensile property exhibit appreciable anisotropy at the same thickness layer. The volume fraction of recrystallized grain of T351 plate in the near surface layer is higher than that in the center layer remarkably. It is also shown that two selected multi-artificial aging tempers can provide optimal precipitates in matrix and at grain boundaries, which gives rise to a combination of high strength and stress corrosion cracking (SCC) resistance in such materials.

scholarly journals Effect of microstructure and cooling rate on the fatigue performance of TIMETAL® 575

2020 ◽  
Vol 321 ◽  
pp. 12019
Author(s):  
M. Bodie ◽  
M. Thomas ◽  
A. Ayub
Keyword(s):  
Titanium Alloys ◽  
Cooling Rate ◽  
Mechanical Performance ◽  
Volume Fraction ◽  
Electron Backscatter Diffraction ◽  
Material Selection ◽  
Weight Ratio ◽  
High Strength ◽  
Fatigue Performance ◽  
Aerospace Applications

A key design consideration for material selection in the aerospace industry is weight reduction; with excellent strength to weight ratio, high temperature resistance, and fatigue performance, titanium alloys are extensively used. New titanium alloys continue to enhance performance and broaden the range of applications. Titanium Metals Corporation (TIMET) recently developed TIMETAL® 575 (Ti575), a high strength titanium alloy with superior fatigue performance over Ti-6Al-4V, aimed at aerospace applications where these properties are imperative i.e. aerospace turbine discs and blades. [1] [2] This work intends to advance the understanding of the effect of thermal processing of Ti575, by investigating the effect of primary alpha (αp) volume fraction and cooling rate on tensile and fatigue performance in post forged heat-treated microstructures. Microstructural assessment and mechanical performance were completed and are discussed. Three cooling methods from three solution heat-treat temperatures were investigated in this work. The results from these experiments were compared using optical microscopy, electron backscatter diffraction (EBSD), room temperature tensile and high cycle fatigue (HCF) tests.

Effect of Phosphorus Contents on Texture and Grain Boundary Character for the Annealing High Strength Ti-IF Steels

2013 ◽  
Vol 652-654 ◽  
pp. 929-933 ◽  
Author(s):  
Xin Li Song ◽  
Kun Peng ◽  
P.P. Zhang ◽  
J.Y. Wu ◽  
J. Zhou ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Recrystallization Texture ◽  
Volume Fraction ◽  
Electron Backscatter Diffraction ◽  
Coincidence Site Lattice ◽  
High Strength ◽  
Fiber Texture ◽  
Grain Boundary Character ◽  
Electron Backscatter ◽  
Backscatter Diffraction

The effect of phosphorus contents on texture and grain boundaries character for the high strength Ti-IF annealed for 120sec at 810oC are researched by electron backscatter diffraction technique（EBSD）. The recrystallization texture is approximated by the γ-fiber texture whose components are {111} and {111} orientation texture. The highest volume fraction of //ND texture is almost 80% for the sample containing 0.056%P. A large amount of coincidence site lattice(CSL) grain boundaries ∑3，∑5, ∑7，∑9，∑11 and ∑13b are obtained.

scholarly journals Microstructure Transformation on Pre-Quenched and Ultrafast-Tempered High-Strength Multiphase Steels

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 396
Author(s):  
Yonggang Zhao ◽  
Zijie Xiang ◽  
Yuanbiao Tan ◽  
Xuanming Ji ◽  
Ling Zhang ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Volume Fraction ◽  
Electron Backscatter Diffraction ◽  
High Strength ◽  
Transformation Process ◽  
Isothermal Treatment ◽  
Tempered Martensite ◽  
Quenching Temperature ◽  
Multiphase Microstructure ◽  
Multiphase Steels

High-strength, multiphase steels consisting of pearlite surrounded by tempered martensite were prepared by pre-quenching and ultrafast tempering heat treatment of high-carbon pearlitic steels (0.81% C). The microstructures were analyzed by scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. With an increasing quenching temperature from 120 °C to 190 °C, the quenched martensite variants nucleated via autocatalytic nucleation along the interface. Furthermore, the tempered nodules exhibited a distinct symmetrical structure, and the tempered martensite and pearlitic colonies in the group also showed a symmetrical morphology. In addition, a reasonable model was formulated to explain the transformation process from quenching martensite to the multiphase microstructure. When the quenching temperature was set to 120 °C, followed by ultrafast heating at 200 °C/s to 600 °C and subsequent isothermal treatment for 60 s, the multiphase structure showed highest strength, and the pearlite volume fraction after tempering was the lowest. The microhardness softening mechanism for the tempered structures consisted of two stages. The first stage is related to martensitic sheets undergoing reverse transformation and the nucleation of cementite on dislocations. The second stage involves the transformation of austenite into pearlite and continued carbide coarsening in the martensitic matrix.

The stabilization of B.C.C. Cu in Cu/Nb nanolayered composites

1996 ◽  
Vol 54 ◽  
pp. 228-229
Author(s):  
H. Kung ◽  
A.J. Griffin ◽  
Y.C. Lu ◽  
K.E. Sickafus ◽  
T.E. Mitchell ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Layer Thickness ◽  
Volume Fraction ◽  
Ion Beam ◽  
High Strength ◽  
Cross Sectional ◽  
Metastable Structure ◽  
High Resolution Tem ◽  
Potential Improvement ◽  
Two Phases

Materials with compositionally modulated structures have gained much attention recently due to potential improvement in electrical, magnetic and mechanical properties. Specifically, Cu-Nb laminate systems have been extensively studied mainly due to the combination of high strength, and superior thermal and electrical conductivity that can be obtained and optimized for the different applications. The effect of layer thickness on the hardness, residual stress and electrical resistivity has been investigated. In general, increases in hardness and electrical resistivity have been observed with decreasing layer thickness. In addition, reduction in structural scale has caused the formation of a metastable structure which exhibits uniquely different properties. In this study, we report the formation of b.c.c. Cu in highly textured Cu/Nb nanolayers. A series of Cu/Nb nanolayered films, with alternating Cu and Nb layers, were prepared by dc magnetron sputtering onto Si {100} wafers. The nominal total thickness of each layered film was 1 μm. The layer thickness was varied between 1 nm and 500 nm with the volume fraction of the two phases kept constant at 50%. The deposition rates and film densities were determined through a combination of profilometry and ion beam analysis techniques. Cross-sectional transmission electron microscopy (XTEM) was used to examine the structure, phase and grain size distribution of the as-sputtered films. A JEOL 3000F high resolution TEM was used to characterize the microstructure.

scholarly journals Mechanical properties, deformation and fracture mechanisms of bimodal Cu under tensile test

2021 ◽  
Vol 60 (1) ◽  
pp. 15-24
Author(s):  
Silu Liu ◽  
Yonghao Zhao
Keyword(s):  
Yield Strength ◽  
Grain Refinement ◽  
Volume Fraction ◽  
Shear Fracture ◽  
High Strength ◽  
Tensile Specimen ◽  
Deformation Mechanisms ◽  
Fracture Mechanisms ◽  
Fracture Angle ◽  
Area Reduction

Abstract Metals with a bimodal grain size distribution have been found to have both high strength and good ductility. However, the coordinated deformation mechanisms underneath the ultrafine-grains (UFGs) and coarse grains (CGs) still remain undiscovered yet. In present work, a bimodal Cu with 80% volume fraction of recrystallized micro-grains was prepared by the annealing of equal-channel angular pressing (ECAP) processed ultrafine grained Cu at 473 K for 40 min. The bimodal Cu has an optimal strength-ductility combination (yield strength of 220 MPa and ductility of 34%), a larger shear fracture angle of 83∘ and a larger area reduction of 78% compared with the as-ECAPed UFG Cu (yield strength of 410 MPa, ductility of 16%, shear fracture angle of 70∘, area reduction of 69%). Grain refinement of recrystallized micro-grains and detwinning of annealing growth twins were observed in the fractured bimodal Cu tensile specimen. The underlying deformation mechanisms for grain refinement and detwinning were analyzed and discussed.

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