Effect of microstructure on fatigue behavior of advanced high strength steels produced by quenching and partitioning and the role of retained austenite

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%.

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Quenching and Partitioning of Ni-Added High Strength Steels

Materials Science Forum ◽

10.4028/www.scientific.net/msf.539-543.4476 ◽

2007 ◽

Vol 539-543 ◽

pp. 4476-4481 ◽

Cited By ~ 12

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.

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Effect of Quenching and Partitioning Heat Treatment on the Fatigue Behavior of 42SiCr Steel

Metals ◽

10.3390/met11111699 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1699

Author(s):

Marco Thomä ◽

Guntram Wagner

Keyword(s):

Electron Microscopy ◽

Mechanical Properties ◽

Heat Treatment ◽

Material Properties ◽

Retained Austenite ◽

Fatigue Behavior ◽

High Strength Steels ◽

High Strength ◽

Advanced High Strength Steels ◽

Scanning Electron

The manufacturing of advanced high-strength steels with enhanced ductility is a persistent aim of research. The ability of a material to absorb high loads while showing a high deformation behavior is a major task for many industrial fields like the mobility sector. Therefore, the material properties of advanced high-strength steels are one of the most important impact factors on the resulting cyclic fatigue behavior. To adjust advanced material properties, resulting in high tensile strengths as well as an enhanced ductility, the heat treatment process of quenching and partitioning (QP) was developed. The quenching takes place in a field between martensite start and martensite finish temperature and the subsequent partitioning is executed at slightly elevated temperatures. Regarding the sparsely investigated field of fatigue research on quenched and partitioned steels, the present work investigates the influence of a QP heat treatment on the resulting microstructure by light and scanning electron microscopy as well as on the mechanical properties such as tensile strength and resistance against fatigue regarding two different heat treatment conditions (QP1, QP2) in comparison to the cold-rolled base material of 42SiCr steel. Therefore, the microscopic analysis proved the presence of a characteristic quenched and partitioned microstructure consisting of a martensitic matrix and partial areas of retained austenite, whereas carbides were also present. Differences in the amount of retained austenite could be observed by using X-ray diffraction (XRD) for the different QP routes, which influence the mechanical properties resulting in higher tensile strength of about 2000 MPa for QP1 compared to about 1600 MPa for QP2. Furthermore, the transition for the fatigue limit was approximated by using stepwise load increase tests (LIT) and afterwards verified by constant amplitude tests (CAT) in accordance with the staircase method, whereas the QP 1 condition reached the highest fatigue strength of 900 MPa. Subsequent light and scanning electron microscopy of selected fractured surfaces and runouts showed a different behavior regarding the size of the fatigue fracture area and also differences in the microstructure of these runouts.

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Temperature Dependence of the Static and Dynamic Behaviour in a Quenching and Partitioning Processed Low-Si Steel

Metals ◽

10.3390/met10040509 ◽

2020 ◽

Vol 10 (4) ◽

pp. 509 ◽

Cited By ~ 1

Author(s):

Florian Vercruysse ◽

Carola Celada-Casero ◽

Bernd M. Linke ◽

Patricia Verleysen ◽

Roumen H. Petrov

Keyword(s):

Mechanical Properties ◽

Retained Austenite ◽

High Strength Steels ◽

High Strength ◽

Dynamic Strain ◽

Strain Rates ◽

Trip Effect ◽

Quenching And Partitioning ◽

Advanced High Strength Steels ◽

Wide Range

Because of their excellent combination of strength and ductility, quenching and partitioning (Q & P) steels have a great chance of being added to the third generation of advanced high strength steels. The large ductility of Q & P steels arises from the presence of 10% to 15% of retained austenite which postpones necking due to the transformation induced plasticity (TRIP) effect. Moreover, Q & P steels show promising forming properties with favourable Lankford coefficients, while their planar anisotropy is low due to a weak texture. The stability of the metastable austenite is the key to obtain tailored properties for these steels. To become part of the newest generation of advanced high strength steels, Q & P steels have to preserve their mechanical properties at dynamic strain rates and over a wide range of temperatures. Therefore, in the present study, a low-Si Q & P steel was tested at temperatures from −40 °C to 80 °C and strain rates from 0.001 s−1 to 500 s−1. Results show that the mechanical properties are well-preserved at the lowest temperatures. Indeed, at −40 °C and room temperature, no significant loss of the deformation capacity is observed even at dynamic strain rates. This is attributed to the presence of a large fraction of austenite that is so (thermally) stable that it does not transform in the absence of deformation. In addition, the high stability of the austenite decreases the elongation at high test temperatures (80 °C). The additional adiabatic heating in the dynamic tests causes the largest reduction of the uniform strain for the samples tested at 80 °C. Quantification of the retained austenite fraction in the samples after testing confirmed that, at the highest temperature and strain rate, the TRIP effect is suppressed.

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

Materials Science Forum ◽

10.4028/www.scientific.net/msf.654-656.94 ◽

2010 ◽

Vol 654-656 ◽

pp. 94-97 ◽

Cited By ~ 14

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.

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

Metals ◽

10.3390/met11071136 ◽

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.

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

Materials ◽

10.3390/ma11112302 ◽

2018 ◽

Vol 11 (11) ◽

pp. 2302 ◽

Cited By ~ 2

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.

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Application of Quenching-Partitioning-Tempering Process in Hot Rolled Plate Fabrication

Materials Science Forum ◽

10.4028/www.scientific.net/msf.654-656.82 ◽

2010 ◽

Vol 654-656 ◽

pp. 82-85 ◽

Cited By ~ 3

Author(s):

Shu Zhou ◽

Ying Wang ◽

Nai Lu Chen ◽

Yong Hua Rong ◽

Jian Feng Gu

Keyword(s):

Mechanical Properties ◽

Retained Austenite ◽

High Strength Steels ◽

High Strength ◽

Significant Fraction ◽

Rolled Plate ◽

Quenching And Partitioning ◽

Good Ductility ◽

Hot Rolled ◽

Rolled Plates

The quenching-partitioning-tempering (Q-P-T) process, based on the quenching and partitioning (Q&P) treatment, has been proposed for producing high strength steels containing significant fraction of film-like retained austenite and controlled amount of fine martensite laths. In this study, a set of Q-P-T processes for C-Mn-Si-Ni-Nb hot rolled plates are designed and realized. The steels with Q-P-T processes present a combination of high strength and relatively good ductility. The origin of such mechanical properties is revealed by microstructure characterization.

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

Materials Science Forum ◽

10.4028/www.scientific.net/msf.879.867 ◽

2016 ◽

Vol 879 ◽

pp. 867-872 ◽

Cited By ~ 1

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.

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

Metals ◽

10.3390/met9121261 ◽

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).

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