The Influence of Deformation on Microstructure Evolution of Low Alloy TRIP Steel

Low alloy transformation-induced plasticity aided (TRIP) steels have attracted much interest over the last years. TRIP steels were initially developed for automotive applications as they offer an excellent combination of strength and ductility at reasonable costs. These excellent mechanical properties mainly arise from a complex multiphase microstructure of a ferrite matrix and a dispersion of multiphase grains of bainite, martensite and metastable retained austenite. The relevant influence of microstructure on physical and mechanical properties makes metallographic study essential for an appropriate understanding and improvement of the mechanical behavior. An accurate microstructural characterization and quantification of the amount of the different constituents is indispensable to know how the stresses and strains are distributed within the different microstructural constituents. Among the different characterization methods commonly used electron backscatter diffraction (EBSD) appears to be the unique technique able to observe retained austenite grains often no larger than 1 μm. The present work shows the evolution of retained austenite while straining. Microstructural and textural evolution after different strains was examined by optical microscopy OM, EBSD and XRD techniques on TRIP800 steel. EBSD technique appears as a powerful tool for characterizing the complex multiphase steel microstructure and provides an accurate evaluation of the local crystallographic texture. It allows to measure orientation gradients within individual grains of each different phase. The distinction between some phases is observed.

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Microstructural Characterization of Hydrogen Induced Cracking in TRIP Steels by EBSD

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.922.412 ◽

2014 ◽

Vol 922 ◽

pp. 412-417 ◽

Cited By ~ 1

Author(s):

A. Laureys ◽

Tom Depover ◽

Roumen H. Petrov ◽

Kim Verbeken

Keyword(s):

Retained Austenite ◽

Electron Backscatter Diffraction ◽

Mechanical Load ◽

High Strength ◽

Microstructural Characterization ◽

Trip Steels ◽

Multiphase Microstructure ◽

Hydrogen Induced Cracking ◽

Backscatter Diffraction

The present work evaluates hydrogen induced cracking in a high strength TRIP steel with a complex multiphase microstructure, containing ferrite, bainite, retained austenite, and some martensite. Each structural constituent demonstrates a different behavior in the presence of hydrogen and when deformed, the retained austenite transforms to martensite. The goal of this work is to understand the response of the hydrogen saturated multiphase structure to a mechanical load. A tensile test on notched samples combined with in-situ electrochemical hydrogen charging was carried out. The test was interrupted at certain specific points, before the macroscopic failure of the material. Hydrogen induced crack initiation and propagation were examined by studying several intermediate elongations. The microstructure of the samples was characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The EBSD measurements allowed both microstructural and crystallographic characterization of the hydrogen induced crack surroundings. A correlation was found between the occurrence of martensite, which is known to be very susceptible to hydrogen embrittlement, and the initiation of hydrogen induced cracks. These cracks were located at the surface in specific high stressed regions. Finite element simulations indicated that these regions were induced due to the presence of the notch.

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Effect of Retained Austenite and Non-Metallic Inclusions on the Mechanical Properties of Resistance Spot Welding Nuggets of Low-Alloy TRIP Steels

Metals ◽

10.3390/met9101064 ◽

2019 ◽

Vol 9 (10) ◽

pp. 1064 ◽

Cited By ~ 2

Author(s):

Víctor H. Vargas Cortés ◽

Gerardo Altamirano Guerrero ◽

Ignacio Mejía Granados ◽

Víctor H. Baltazar Hernández ◽

Cuauhtémoc Maldonado Zepeda

Keyword(s):

Mechanical Properties ◽

Tensile Test ◽

Retained Austenite ◽

High Strength ◽

Microstructural Characterization ◽

Spot Welds ◽

Trip Steels ◽

Resistance Spot ◽

Lap Shear ◽

Metallic Inclusions

The combination of high strength and formability of transformation induced plasticity (TRIP) steels is interesting for the automotive industry. However, the poor weldability limits its industrial application. This paper shows the results of six low-alloy TRIP steels with different chemical composition which were studied in order to correlate retained austenite (RA) and non-metallic inclusions (NMI) with their resistance spot welded zones to their joints’ final mechanical properties. RA volume fractions were quantified by X-ray microdiffraction (µSXRD) while the magnetic saturation technique was used to quantify NMI contents. Microstructural characterization and NMI of the base metals and spot welds were assessed using scanning electron microscopy (SEM). Weld nuggets macrostructures were identified using optical microscopy (OM). The lap-shear tensile test was used to determine the final mechanical properties of the welded joints. It was found that NMI content in the fusion zone (FZ) was higher than those in the base metal and heat affected zone (HAZ). Whereas, traces of RA were found in the HAZ of highly alloyed TRIP steels. Lap-shear tensile test results showed that mechanical properties of spot welds were affected by NMI contents, but in a major way by the decomposition of RA in the FZ and HAZ.

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Microstructural Characterization of Dual and Multiphase Steels Applied to Automotive Industry

Materials Science Forum ◽

10.4028/www.scientific.net/msf.775-776.146 ◽

2014 ◽

Vol 775-776 ◽

pp. 146-150 ◽

Cited By ~ 1

Author(s):

Cristina Sayuri Fukugauchi ◽

Antonio dos Reis Faria Neto ◽

Rosinei Batista Ribeiro ◽

Marcelo dos Santos Pereira

Keyword(s):

Mechanical Properties ◽

Microstructural Characterization ◽

Tensile Tests ◽

Ferrite Matrix ◽

Microstructure Characterization ◽

Second Phase ◽

Dual Phase ◽

Dual Phase Steels ◽

Trip Steels

TRIP (Transformation Induced Plasticity) and DP (Dual-Phase) steels are written in a new series of steels which present excellent mechanical properties. As for microstructure aspect, TRIP steels consist on a ferrite matrix with a second phase dispersion of other constituents, such as bainite, martensite and retained austenite, while dual-phase steels consist on martensite dispersion in a ferrite matrix. In order to identify the different microconstituents present in these materials, microstructure characterization techniques by optical microscopy (using different etchants: LePera, Heat-Tinting and Nital) and scanning electron microscopy were carried out. This being so, microstructures were correlated with mechanical properties of materials, determined by means of tensile tests. It is concluded that steels assisted by TRIP effect have a strength and elongation relation higher than the dual-phase one. With microstructure characterization, it was observed phases present in these materials microstructure.

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Microstructural Characterization of Thermo-Mechanical Treated TRIP Steels

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.344.71 ◽

2007 ◽

Vol 344 ◽

pp. 71-78 ◽

Cited By ~ 1

Author(s):

A. Barcellona ◽

L. Cannizzaro ◽

D. Palmeri

Keyword(s):

Retained Austenite ◽

Microstructural Analysis ◽

Microstructural Characterization ◽

Ferrite Matrix ◽

Total Elongation ◽

Environmental Preservation ◽

Sheet Steels ◽

Trip Steels ◽

Increasing Demand ◽

Deformation Step

The increasing demand for the reduction of automobiles CO2 emissions for environmental preservation leads the automotive industries towards the mechanical components weight reduction. Sheet steels with multiphase microstructures exhibit favourable combinations of strength and ductility. The so called TRIP steels have a metastable microstructure that consists of a continuous ferrite matrix containing a dispersion of hard second phases martensite and bainite. These steels also contain retained austenite, at room temperature, that represents the source of the TRansformation Induced Plasticity effect. When the material is subjected to deformation step, the retained austenite transforms itself into martensite; the produced martensite delays the onset of necking resulting in a product with high total elongation, excellent formability and high crash energy absorption. In the present research the steel TRIP 800 zinc coated has been subjected to different thermo–mechanical treatments in order to evaluate the relation between microstructure of material and TRIP effects. Whit this aim the microstructural analysis has been performed and the evaluation of content of different phases has been made by means of the image analysis techniques. The relation among the strain level, the content of different phases, the thermal treatments and the work hardening properties of materials have been valued. Furthermore, it has been also highlighted the dependence of the bake hardening properties of material on the different thermo-mechanical treatments.

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Microstructural Characterization and Mechanical Properties of Direct Quenched and Partitioned High-Aluminum and High-Silicon Steels

Metals ◽

10.3390/met9020256 ◽

2019 ◽

Vol 9 (2) ◽

pp. 256 ◽

Cited By ~ 8

Author(s):

Pekka Kantanen ◽

Mahesh Somani ◽

Antti Kaijalainen ◽

Oskari Haiko ◽

David Porter ◽

...

Keyword(s):

Mechanical Properties ◽

Retained Austenite ◽

Electron Backscatter Diffraction ◽

Lath Martensite ◽

Microstructural Characterization ◽

Weight Percent ◽

Impact Testing ◽

Direct Quenching ◽

Hot Rolled ◽

Backscatter Diffraction

A new experimental steel containing in weight percent 0.3C-2.0Mn-0.5Si-1.0Al-2.2Cr and 0.3C-1.9Mn-1.0Si-1.0Cr was hot rolled in a laboratory rolling mill and directly quenched within the martensite start and finish temperature range. It was then partitioned without reheating during slow furnace cooling to achieve tensile yield strengths over 1100 MPa with good combinations of strength, ductility and impact toughness. Gleeble thermomechanical simulations led to the selection of the partitioning at the temperatures 175 and 225 °C, which produced the desired microstructures of lath martensite with finely divided retained austenite in fractions of 6.5% and 10% respectively. The microstructures were analyzed using light and scanning electron microscopy in combination with electron backscatter diffraction and X-ray diffraction analysis. The mechanical properties were characterized extensively using hardness, tensile and Charpy V impact testing. In tensile testing a transformation induced plasticity mechanism was shown to operate with the less stable, carbon-poorer retained austenite, which transformed to martensite during straining. The auspicious results in respect to microstructures and mechanical properties indicate that there are possibilities for developing tough ductile structural steels through thermomechanical rolling followed by the direct quenching and partitioning route.

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Effect of Different Coiling Temperature on Mechanical Properties in Hot Rolled TRIP Steel

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.239-242.1092 ◽

2011 ◽

Vol 239-242 ◽

pp. 1092-1095

Author(s):

Xu Tao Gao ◽

Ai Min Zhao ◽

Zheng Zhi Zhao ◽

Ming Ming Zhang ◽

Di Tang

Keyword(s):

Mechanical Properties ◽

Retained Austenite ◽

X Ray Diffraction ◽

Coiling Temperature ◽

Experimental Steel ◽

Transformation Induced Plasticity ◽

X Ray ◽

Trip Steels ◽

Hot Rolled ◽

Scanning Electron

By means of optical microscopy(OM), scanning electron microscopy(SEM),X-ray diffraction(XRD),And tensile test, Mechanical Properties of hot rolled transformation -induced plasticity (TRIP) steels which were prepared through three different coiling temperature was investigated. Result reveals that the formability index of the experimental steel descends when the coiling temperature becomes low. Different coiling temperature has greater impact on retained austenite. Amount and carbon content of retained austenite in the experimental steel get less with lower coiling temperature.

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Influence of Prior Martensite on Bainite Transformation, Microstructures, and Mechanical Properties in Ultra-Fine Bainitic Steel

Materials ◽

10.3390/ma12030527 ◽

2019 ◽

Vol 12 (3) ◽

pp. 527 ◽

Cited By ~ 10

Author(s):

Hui Guo ◽

Xianying Feng ◽

Aimin Zhao ◽

Qiang Li ◽

Jun Ma

Keyword(s):

Mechanical Properties ◽

Retained Austenite ◽

Bainitic Ferrite ◽

Growth Direction ◽

Bainitic Transformation ◽

Bainitic Steel ◽

Bainite Transformation ◽

Multiphase Microstructure ◽

Microstructures And Mechanical Properties ◽

The Impact

A multiphase microstructure comprising of different volume fractions of prior martensite and ultra-fine bainite (bainitic ferrite and retained austenite) was obtained by quenching to certain temperatures, followed by isothermal bainitic transformation. The effect of the prior martensite transformation on the bainitic transformation behavior, microstructures, and mechanical properties were discussed. The results showed that the prior martensite accelerated the subsequent low-temperature bainite transformation, and the incubation period and completion time of the bainite reaction were significantly shortened. This phenomenon was attributed to the enhanced nucleation ratio caused by the introduced strain in austenite, due to the formation of prior martensite and a carbon partitioning between the prior martensite and retained austenite. Moreover, the prior martensite could influence the crystal growth direction of bainite ferrite, refine bainitic ferrite plates, and reduce the dimension of blocky retained austenite, all of which were responsible for improving the mechanical properties of the ultra-fine bainitic steel. When the content of the prior martensite reached 15%, the investigated steels had the best performance, which were 1800 MPa and 21% for the tensile strength and elongation, respectively. Unfortunately, the increased content of the prior martensite could lead to a worsening of the impact toughness.

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Characteristics of retained austenite in TRIP steels with bainitic ferrite matrix

Journal of Wuhan University of Technology-Mater Sci Ed ◽

10.1007/s11595-011-0379-x ◽

2011 ◽

Vol 26 (6) ◽

pp. 1148-1151 ◽

Cited By ~ 4

Author(s):

Mingya Zhang ◽

Fuxian Zhu ◽

Zhengtao Duan ◽

Shicheng Ma

Keyword(s):

Retained Austenite ◽

Bainitic Ferrite ◽

Ferrite Matrix ◽

Trip Steels

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Correlation Between Microstructure and Mechanical Properties in an Inconel 718 Deposit Produced Via Electron Beam Freeform Fabrication

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4028509 ◽

2014 ◽

Vol 136 (6) ◽

Cited By ~ 28

Author(s):

Wesley A. Tayon ◽

Ravi N. Shenoy ◽

MacKenzie R. Redding ◽

R. Keith Bird ◽

Robert A. Hafley

Keyword(s):

Mechanical Properties ◽

Electron Beam ◽

Crystallographic Texture ◽

Inconel 718 ◽

Electron Backscatter Diffraction ◽

Microstructural Characterization ◽

Freeform Fabrication ◽

Aerospace Applications ◽

Evolution Of Microstructure ◽

Texture Characterization

Electron beam freeform fabrication (EBF3), a metallic layer-additive manufacturing process, uses a high-power electron beam in conjunction with a metal feed wire to create a molten pool on a substrate, which on solidification produces a component of the desired configuration made of sequentially deposited layers. During the build-up of each solidified layer, the substrate is translated with respect to the electron beam and the feed wire. EBF3 products are similar to conventional cast products with regard to the as-deposited (AD) microstructure and typical mechanical properties. Inconel 718 (IN 718), a high-temperature superalloy with attractive mechanical and oxidation properties well suited for aerospace applications, is typically used in the wrought form. The present study examines the evolution of microstructure, crystallographic texture, and mechanical properties of a block of IN 718 fabricated via the EBF3 process. Specimens extracted out of this block, both in the AD and in a subsequently heat treated (HT) condition, were subjected to (1) microstructural characterization using scanning electron microscopy (SEM); (2) in-plane elastic modulus, tensile strength, and microhardness evaluations; and (3) crystallographic texture characterization using electron backscatter diffraction (EBSD). Salient conclusions stemming from this study are: (1) mechanical properties of the EBF3-processed IN 718 block are strongly affected by texture as evidenced by their dependence on orientation relative to the EBF3 fabrication direction, with the AD EBF3 properties generally being significantly reduced compared to wrought IN 718; (2) significant improvement in both strength and modulus of the EBF3 product to levels nearly equal to those for wrought IN 718 may be achieved through heat treatment.

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