scholarly journals Addressing Retained Austenite Stability in Advanced High Strength Steels

2013 ◽  
Vol 738-739 ◽  
pp. 212-216 ◽  
Author(s):  
Elena V. Pereloma ◽  
Azdiar A. Gazder ◽  
Ilana B. Timokhina
Keyword(s):  
Retained Austenite ◽  
Mechanical Stability ◽  
Volume Fraction ◽  
High Strength Steels ◽  
High Strength ◽  
Processing Parameters ◽  
Advanced High Strength Steels ◽  
Austenite Stability ◽  
Retained Austenite Stability ◽  
Size And Morphology

Advances in the development of new high strength steels have resulted in microstructures containing significant volume fractions of retained austenite. The transformation of retained austenite to martensite upon straining contributes towards improving the ductility. However, in order to gain from the above beneficial effect, the volume fraction, size, morphology and distribution of the retained austenite need to be controlled. In this regard, it is well known that carbon concentration in the retained austenite is responsible for its chemical stability, whereas its size and morphology determines its mechanical stability. Thus, to achieve the required mechanical properties, control of the processing parameters affecting the microstructure development is essential.

Quenching and Partitioning of Ni-Added High Strength Steels

2007 ◽  
Vol 539-543 ◽  
pp. 4476-4481 ◽  
Author(s):  
F.C. Rizzo ◽  
A.R. Martins ◽  
John G. Speer ◽  
David K. Matlock ◽  
A. Clarke ◽  
...  
Keyword(s):  
Retained Austenite ◽  
High Strength Steels ◽  
High Strength ◽  
Processing Parameters ◽  
Carbide Formation ◽  
X Ray Diffraction ◽  
Quenching And Partitioning ◽  
Steel Microstructure ◽  
Advanced High Strength Steels ◽  
Treatment Procedures

High strength steels containing significant fractions of retained austenite have been developed in recent years, and are the subject of growing commercial interest when associated with the TRIP phenomenon during deformation. A new process concept “quenching and partitioning” (Q&P) has been proposed by CSM/USA, and the results show the potential to create a new kind of steel microstructure with controlled amounts of retained austenite, enriched by carbon partitioning. Four steels containing C, Si, Mn, Ni, Cr and Mo, were designed with variation in the Ni and C content, aiming to decrease Bs temperature and to suppress carbide formation during the partitioning treatment. Several heat-treatment procedures were performed in specimens previously machined for tensile testing, while x-ray diffraction was used to determine the fraction of retained austenite. The tensile test results showed that except for the high C high Ni alloy, most of the processing conditions resulted in strengths superior to those of advanced high strength steels (AHSS), although it is importantly recognized that higher alloy additions were used in this study, in comparison with conventional AHSS grades.. A variety of strength and ductility combinations were observed, confirming the potential of the Q&P process and illustrating the strong influence of the final microstructure on the mechanical properties. Experimental results for samples partitioned at 400 °C indicate that higher ultimate tensile strength is associated with higher fraction of retained austenite for multiple heat treatments of each alloy investigated. The amount of retained austenite obtained was generally lower than that predicted by the model. Further studies are in progress to understand the influence of alloying and processing parameters (time/temperature) on the partitioning of carbon and precipitation of transition carbides.

scholarly journals The Effect of Mn and Si on the Properties of Advanced High Strength Steels Processed by Quenching and Partitioning

2010 ◽  
Vol 654-656 ◽  
pp. 94-97 ◽  
Author(s):  
Bohuslav Mašek ◽  
Hana Jirková ◽  
Daniela Hauserova ◽  
Ludmila Kučerová ◽  
Danuše Klauberová
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
Volume Fraction ◽  
High Strength Steels ◽  
High Strength ◽  
Microstructural Development ◽  
X Ray Diffraction ◽  
Quenching And Partitioning ◽  
Advanced High Strength Steels ◽  
High Ultimate Strength

The concepts new types of materials are, for economic reasons, focused mainly on low alloyed steels with a good combination of strength and ductility. Suitable heat and thermo-mechanical treatments play an important role for the utilization of these materials. Different alloying strategies are used to influence phase transformations. The quenching and partitioning process (Q-P Process) is one of the heat treatment methods which can result in a high ultimate strength as well as a good ductility. However, these good properties can be obtained only if a sufficient amount of retained austenite is stabilized. The influence of different contents of manganese, silicon and chromium on microstructural development and mechanical properties were experimentally tested. Alloying elements were used to stabilize the retained austenite in the final microstructure and also to strengthen the solid solution. Ultimate strengths of over 2000MPa with ductility over 10% were reached after the optimization of the Q-P Process. The microstructures were analyzed using several microscopic methods; mechanical properties were determined by a tensile test and the volume fraction of the retained austenite was established by X-ray diffraction phase analysis.

Effects of Retained Austenite Conditions on the Ductility of the Advanced High Strength Steels

2021 ◽  
Vol 1016 ◽  
pp. 984-989
Author(s):  
Toshio Murakami
Keyword(s):  
Carbon Content ◽  
Retained Austenite ◽  
High Strain ◽  
Volume Fraction ◽  
High Strength Steels ◽  
Strain Range ◽  
High Strength ◽  
High Carbon ◽  
High Carbon Content ◽  
Advanced High Strength Steels

It was investigated that the effects of retained austenite (γR) conditions on ductility of advanced high strength steels for automotives. 0.4mass% C steels were heattreated in various austemper conditions to control the retained austenite conditions. In the result of the evaluation of mechanical properties of these steels, it was confirmed there were steels which indicated different elongation even if they had almost same volume fraction and carbon content of retained austenite. In order to clarify the reason, the conditions of retained austenite and work hardening behavior were investigated in detail. It was indicated that the existence of high carbon content region in a part of retained austenite promoted the deformation induced martensitic transformation in the high strain range and improved the elongation of AHSS.

scholarly journals Heat Treatment Design for a QP Steel: Effect of Partitioning Temperature

Metals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1136
Author(s):  
Marcel Carpio ◽  
Jessica Calvo ◽  
Omar García ◽  
Juan Pablo Pedraza ◽  
José María Cabrera
Keyword(s):  
Retained Austenite ◽  
High Strength Steels ◽  
High Strength ◽  
Tensile Tests ◽  
Quenching Temperature ◽  
Advanced High Strength Steels ◽  
New Family ◽  
Automotive Parts ◽  
Fresh Martensite ◽  
Industry Needs

Designing a new family of advanced high-strength steels (AHSSs) to develop automotive parts that cover early industry needs is the aim of many investigations. One of the candidates in the 3rd family of AHSS are the quenching and partitioning (QP) steels. These steels display an excellent relationship between strength and formability, making them able to fulfill the requirements of safety, while reducing automobile weight to enhance the performance during service. The main attribute of QP steels is the TRIP effect that retained austenite possesses, which allows a significant energy absorption during deformation. The present study is focused on evaluating some process parameters, especially the partitioning temperature, in the microstructures and mechanical properties attained during a QP process. An experimental steel (0.2C-3.5Mn-1.5Si (wt%)) was selected and heated according to the theoretical optimum quenching temperature. For this purpose, heat treatments in a quenching dilatometry and further microstructural and mechanical characterization were carried out by SEM, XRD, EBSD, and hardness and tensile tests, respectively. The samples showed a significant increment in the retained austenite at an increasing partitioning temperature, but with strong penalization on the final ductility due to the large amount of fresh martensite obtained as well.

scholarly journals Carbon Redistribution and Microstructural Evolution Study during Two-Stage Quenching and Partitioning Process of High-Strength Steels by Modeling

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2302 ◽  
Author(s):  
Yilin Wang ◽  
Huicheng Geng ◽  
Bin Zhu ◽  
Zijian Wang ◽  
Yisheng Zhang
Keyword(s):  
Retained Austenite ◽  
Volume Fraction ◽  
High Strength Steels ◽  
High Strength ◽  
Simulation Method ◽  
Low Carbon ◽  
Two Stage ◽  
Quenching And Partitioning ◽  
Carbon Redistribution ◽  
Carbon Martensite

The application of the quenching and partitioning (Q-P) process on advanced high-strength steels improves part ductility significantly with little decrease in strength. Moreover, the mechanical properties of high-strength steels can be further enhanced by the stepping-quenching-partitioning (S-Q-P) process. In this study, a two-stage quenching and partitioning (two-stage Q-P) process originating from the S-Q-P process of an advanced high-strength steel 30CrMnSi2Nb was analyzed by the simulation method, which consisted of two quenching processes and two partitioning processes. The carbon redistribution, interface migration, and phase transition during the two-stage Q-P process were investigated with different temperatures and partitioning times. The final microstructure of the material formed after the two-stage Q-P process was studied, as well as the volume fraction of the retained austenite. The simulation results indicate that a special microstructure can be obtained by appropriate parameters of the two-stage Q-P process. A mixed microstructure, characterized by alternating distribution of low carbon martensite laths, small-sized low-carbon martensite plates, retained austenite and high-carbon martensite plates, can be obtained. In addition, a peak value of the volume fraction of the stable retained austenite after the final quenching is obtained with proper partitioning time.

scholarly journals Effect of Quenching and Partitioning Temperatures in the Q-P Process on the Properties of AHSS with Various Amounts of Manganese and Silicon

2012 ◽  
Vol 706-709 ◽  
pp. 2734-2739 ◽  
Author(s):  
Hana Jirková ◽  
Ludmila Kučerová ◽  
Bohuslav Mašek
Keyword(s):  
Tensile Strength ◽  
Retained Austenite ◽  
Isothermal Holding ◽  
Bainitic Ferrite ◽  
High Strength Steels ◽  
High Strength ◽  
Experimental Program ◽  
Quenching Temperature ◽  
Quenching And Partitioning ◽  
Advanced High Strength Steels

The use of the combined influence of retained austenite and bainitic ferrite to improve strength and ductility has been known for many years from the treatment of multiphase steels. Recently, the very fine films of retained austenite along the martensitic laths have also become the centre of attention. This treatment is called the Q-P process (quenching and partitioning). In this experimental program the quenching temperature and the isothermal holding temperature for diffusion carbon distribution for three advanced high strength steels with carbon content of 0.43 % was examined. The alloying strategies have a different content of manganese and silicon, which leads to various martensite start and finish temperatures. The model treatment was carried out using a thermomechanical simulator. Tested regimes resulted in a tensile strength of over 2000MPa with a ductility of above 14 %. The increase of the partitioning temperature influenced the intensity of martensite tempering and caused the decrease of tensile strength by 400MPa down to 1600MPa and at the same time more than 10 % growth of ductility occurred, increasing it to more than 20%.

Influence of the Processing Variables on the Microstructure Evolution of a Bainitic Carbide-Free Steel

2016 ◽  
Vol 879 ◽  
pp. 867-872 ◽  
Author(s):  
M.C. Taboada ◽  
I. Gutiérrez ◽  
D. Jorge-Badiola ◽  
S.M.C. van Bohemen ◽  
F. Hisker ◽  
...  
Keyword(s):  
Retained Austenite ◽  
High Strength Steels ◽  
High Strength ◽  
High Volume ◽  
X Ray Diffraction ◽  
Tempered Martensite ◽  
Trip Steels ◽  
Volume Fractions ◽  
Advanced High Strength Steels ◽  
Processing Variables

New trends focused on achieving higher performance steels has led to a so-called 3rd Generation Advanced High Strength Steels (AHSS), in which the typical polygonal ferrite found in TRIP steels as a matrix phase is replaced by harder phases as Carbide-Free Bainite (CFB) and/or (tempered) martensite. Besides, large volume fractions of retained austenite (R.A.) with adequate stability are aimed for to improve the formability of the steels. Si containing steels are regarded as the most suitable to retard cementite formation and consequently reach high volume fractions of RA. In this work, CFB annealing schedules were applied to dilatometer samples of Fe-0.22C-2.0Mn-1.3Si. The overaging temperature TB was varied between 390 oC and 480 oC, and other processing variables investigated were the austenitizing temperature Taus, and the overaging holding time tB. The annealed samples analyzed with LOM, FEG-SEM, EBSD and X-ray diffraction techniques show that markedly different complex microstructures made up of bainite, ferrite, MA phase and retained austenite (R.A) are accomplished depending on the specific thermal cycle. These results are described in detail and discussed in relation to the dilatometry measurements.

scholarly journals Substructure Development and Damage Initiation in a Carbide-Free Bainitic Steel upon Tensile Test

Metals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 1261
Author(s):  
Mari Carmen Taboada ◽  
Amaia Iza-Mendia ◽  
Isabel Gutiérrez ◽  
Denis Jorge-Badiola
Keyword(s):  
Retained Austenite ◽  
High Strength Steels ◽  
High Strength ◽  
Tensile Tests ◽  
Formation Mechanisms ◽  
Tempered Martensite ◽  
Damage Initiation ◽  
Advanced High Strength Steels ◽  
Significant Strength ◽  
The Stability

Carbide-free bainitic (CFB) steels belong to the family of advanced high strength steels (AHSS) that are struggling to become part of the third-generation steels to be marketed for the automotive industry. The combined effects of the bainitic matrix and the retained austenite confers a significant strength with a remarkable ductility to these steels. However, CFB steels usually show much more complex microstructures that also contain MA (Martensite–Austenite) phase and auto-tempered martensite (ATM). These phases may compromise the ductility of CFB steels. The present work analyzes the substructure evolution during tensile tests in the necking zone, and deepens into the void and crack formation mechanisms and their relationship with the local microstructure. The combination of FEG-SEM imaging, EBSD, and X-ray diffraction has been necessary to characterize the substructure development and damage initiation. The bainite matrix has shown great ductility through the generation of high angle grain boundaries and/or large orientation gradients around voids, which are usually found close to the bainite and MA/auto-tempered martensite interfaces or fragmenting the MA phase. Special attention has been paid to the stability of the retained austenite (RA) during the test, which may eventually be transformed into martensite (Transformation Induced Plasticity, or TRIP effect).

scholarly journals Enhancing the Mechanical Properties of a Hot Rolled High-Strength Steel Produced by Ultra-Fast Cooling and Q&P Process

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 958 ◽  
Author(s):  
Teng Wu ◽  
Run Wu ◽  
Bin Liu ◽  
Wen Liang ◽  
Deqing Ke
Keyword(s):  
Retained Austenite ◽  
High Strength Steels ◽  
High Strength ◽  
Controlled Rolling ◽  
Grain Structure ◽  
Ultra Fast Cooling ◽  
Advanced High Strength Steels ◽  
Fast Cooling ◽  
Austenite Grains ◽  
Hot Rolled

The quenching and partitioning (Q&P) process of advanced high strength steels results in a significant enhancement in their strength and ductility. The development of controlled rolling and cooling technology provides an efficient tool for microstructural design in steels. This approach allows to control phase transformations in order to generate the desired microstructure in steel and, thus, to achieve the required properties. To refine grain structure in a Fe-Si-Mn-Nb steel and to generate the microstructure consisting of martensitic matrix with embedded retained austenite grains, hot rolling and pressing combined with ultrafast cooling and Q&P process is employed. The slender martensite in hot rolled Q&P steel improves the strength of test steel and the flake retained austenite improves the plasticity and work hardening ability through the Transformation Induced Plasticity (TRIP) effect.

Modeling of Twinning Based Plasticity Phenomenon in Austenite Dominated Steels Under Combined Loading

2014 ◽  
Author(s):  
Rashid Khan ◽  
Tasneem Pervez ◽  
Omar S. Al-Abri ◽  
Majid Al-Maharbi
Keyword(s):  
Finite Element ◽  
Volume Fraction ◽  
Micromechanical Model ◽  
High Strength Steels ◽  
High Strength ◽  
Combined Loading ◽  
Plastic Behavior ◽  
Successful Implementation ◽  
Advanced High Strength Steels ◽  
Finite Element Software

Advanced high strength steels cover a vast range of applications more specifically in aerospace and oil industry where large deformation of a material is desired in order to attain a specified shape and geometry of the product. The main reason behind their successful implementation is having an optimum combination of strength and formability. Austenite based twinning induced plasticity steel lies in the second generation and has excellent strength-cum-formability combination among the group of advanced high strength steels. The stress assisted phase transformation from austenite to martensite, which is known as twinning, found to be principal reason behind an enhancement of these properties. This work is aimed to investigate an elastic-plastic behavior of an austenite dominated steel, which undergoes slip and mechanical twinning modes of deformation. Initially, a micromechanical model of twining induced plasticity phenomenon is developed using crystal plasticity theory. Then, the developed model is numerically implemented into finite element software ABAQUS through a user-defined material sub-routine. Finally, finite element simulations are done for single and poly-crystal austenite subjected to combined load. This replicates the complex loading condition which exists in material forming processes like pipe expansion, extrusion, rolling. The variation in stress-strain response, magnitude of shear strain, and volume fraction of twinned martensite are plotted and analyzed.

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