Nanoscale precipitation and ultrafine retained austenite induced high strength-ductility combination in a newly designed low carbon Cu-bearing medium-Mn steel

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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Investigation on Microstructure and Martensitic Transformation Mechanism for the Warm-Stamped Third-Generation Automotive Medium-Mn Steel

Journal of Engineering Materials and Technology ◽

10.1115/1.4037017 ◽

2017 ◽

Vol 139 (4) ◽

Cited By ~ 4

Author(s):

Xiaodong Li ◽

Ying Chang ◽

Cunyu Wang ◽

Shuo Han ◽

Daxin Ren ◽

...

Keyword(s):

Martensitic Transformation ◽

Strain Rate ◽

Compressive Load ◽

High Strength ◽

Third Generation ◽

Transformation Mechanism ◽

Loading Method ◽

Strain And Strain Rate ◽

Medium Mn Steel ◽

Mn Steel

With the development of the automotive industry, the application of the high-strength steel (HSS) becomes an effective way to improve the lightweight and safety. In this paper, the third-generation automotive medium-Mn steel (TAMM steel) is studied. The warm-stamped TAMM steel holds the complete and fine-grained martensitic microstructure without decarbonization layer, which contributes to high and well-balanced mechanical properties. Furthermore, the martensitic transformation mechanism of the TAMM steel is investigated by the dilatation tests. The results indicate that the effects of the loading method on the Ms temperature under different loads are different. The Ms temperature is hardly influenced under the tensile loads and low compressive load. However, it is slightly decreased under the high compressive load. Moreover, the effects of the strain and strain rate on the Ms temperature are insignificant and can be neglected. As a result, this research proves that the martensitic transformation of the TAMM steel is rarely influenced by the process parameters, such as stamping temperature, loading method, load, strain, and strain rate. The actual stamping process can be designed and controlled accurately referring to the continuous cooling transformation (CCT) curves to realize the required properties and improve the formability of the automotive part.

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Microstructural evolution and strain hardening behavior of a novel two-stage warm rolled ultra-high strength medium Mn steel with heterogeneous structures

International Journal of Plasticity ◽

10.1016/j.ijplas.2022.103212 ◽

2022 ◽

pp. 103212

Author(s):

Yuming Zou ◽

Hua Ding ◽

Yu Zhang ◽

Zhengyou Tang

Keyword(s):

Strain Hardening ◽

Microstructural Evolution ◽

High Strength ◽

Two Stage ◽

Hardening Behavior ◽

Medium Mn Steel ◽

Heterogeneous Structures ◽

Strain Hardening Behavior ◽

Mn Steel ◽

Strength Medium

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Manganese controlled transformation and twinning of the nanoscale austenite in low-carbon-medium-Mn steel

Materials Science and Engineering A ◽

10.1016/j.msea.2021.142162 ◽

2021 ◽

pp. 142162

Author(s):

W.Y. Xue ◽

H.F. Zhang ◽

Y.F. Shen ◽

N. Jia

Keyword(s):

Low Carbon ◽

Medium Mn Steel ◽

Mn Steel

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Quantitative Description of External Force Induced Phase Transformation in Silicon–Manganese (Si–Mn) Transformation Induced Plasticity (TRIP) Steels

Materials ◽

10.3390/ma12223781 ◽

2019 ◽

Vol 12 (22) ◽

pp. 3781

Author(s):

Zhongping He ◽

Huachu Liu ◽

Zhenyu Zhu ◽

Weisen Zheng ◽

Yanlin He ◽

...

Keyword(s):

Phase Transformation ◽

Carbon Steel ◽

Trip Steel ◽

Retained Austenite ◽

Low Carbon Steel ◽

High Strength ◽

High Plasticity ◽

Low Carbon ◽

Transformation Induced Plasticity ◽

Trip Steels

Transformation Induced Plasticity (TRIP) steels with silicon–manganese (Si–Mn) as the main element have attracted a lot of attention and great interest from steel companies due to their low price, high strength, and high plasticity. Retained austenite is of primary importance as the source of high strength and high plasticity in Si–Mn TRIP steels. In this work, the cold rolled sheets of Si–Mn low carbon steel were treated with TRIP and Dual Phase (DP) treatment respectively. Then, the microstructure and composition of the Si–Mn low carbon steel were observed and tested. The static tensile test of TRIP steel and DP steel was carried out by a CMT5305 electronic universal testing machine. The self-built true stress–strain curve model of TRIP steel was verified. The simulation results were in good agreement with the experimental results. In addition, the phase transformation energy of retained austenite and the work borne by austenite in the sample during static stretching were calculated. The work done by austenite was 14.5 J, which was negligible compared with the total work of 217.8 J. The phase transformation energy absorption of retained austenite in the sample was 9.12 J. The role of retained austenite in TRIP steel is the absorption of excess energy at the key place where the fracture will occur, thereby increasing the elongation, so that the ferrite and bainite in the TRIP steel can absorb energy for a longer time and withstand more energy.

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A New Approach Using EBSD to Quantitatively Distinguish Complex Transformation Products Along the HAZ in X80 Linepipe Steel

Volume 3: Materials and Joining; Risk and Reliability ◽

10.1115/ipc2014-33668 ◽

2014 ◽

Cited By ~ 4

Author(s):

Jennifer M. Reichert ◽

Matthias Militzer ◽

Warren J. Poole ◽

Laurie Collins

Keyword(s):

Orientation Relationship ◽

Transformation Temperature ◽

Retained Austenite ◽

Electron Backscatter Diffraction ◽

High Strength ◽

Transformation Products ◽

Carbon Steels ◽

Low Carbon ◽

Structure Property ◽

Linepipe Steel

State-of-the-art linepipe steels are microalloyed low-carbon steels that combine high strength and fracture toughness with good weldability. During welding of pipe sections the heat affected zone (HAZ) experiences rapid thermal cycles resulting in a graded microstructure that can be significantly different from that of the base metal. In particular a variety of bainitic microstructures can form in the HAZ. Depending on the type of bainite mechanical properties may be improved or may lead to poor fracture resistance and be detrimental to the overall HAZ performance. Optical microscopy is not sufficient to differentiate bainitic morphologies which vary with the transformation temperature. The investigated X80 linepipe steel also contains retained austenite at room temperature. Based on the retained austenite it is possible to characterize the orientation relationship (OR) between austenite and the transformation products. It is found that bainite shows an orientation relationship near Kurdjumov-Sachs with the prior austenite. Variant selection is related to the driving force for the bainite reaction and hence depends on the transformation temperature. In the current study Electron BackScatter Diffraction (EBSD) mapping is used to characterize transformation products based on their orientation relationship. This approach offers a quantitative way to determine volume fractions of different types of bainite in complex HAZ microstructures which is necessary to establish structure-property relationships of the HAZ.

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