Evolution of crystal structure of Cu precipitates in a low carbon steel

Han, Gang; Xie, Z.J.; Li, Z.Y.; Bao, Lixia; Chen, Shang; Misra, R.D.K.

doi:10.1016/j.matdes.2017.08.054

Cited by 89 publications

(20 citation statements)

References 49 publications

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“…The nano-precipitates of the advanced nanostructured steels are metastable and maintain a very high coherency with the BCC steel matrix [7]. For instance, the Cu-rich nano-precipitates are ultrafine (<4 nm in diameter) and have the BCC structure during the initial stage of nucleation [5,10,85]. As the aging proceeds, they grow larger (>4 nm) and transform martensitically [86,87] into the semi-coherent 9R structure before turning into the incoherent FCC structure (>37 nm) [85,88,89].…”

Section: Nanoscale Cu and Nial Precipitations In Nanostructured Steelsmentioning

confidence: 99%

Low-carbon advanced nanostructured steels: Microstructure, mechanical properties, and applications

Kong

Jiao

et al. 2021

Sci. China Mater.

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Low-carbon advanced nanostructured steels have been developed for various structural engineering applications, including bridges, automobiles, and other strength-critical applications such as the reactor pressure vessels in nuclear power stations. The mechanical performances and applications of these steels are strongly dependent on their microstructural features. By controlling the size, number density, distribution, and types of precipitates, it is possible to produce nanostructured steels with a tensile strength reaching as high as 2 GPa while keeping a decent tensile elongation above 10% and a reduction of area as high as 40%. Besides, through a careful control of strength contributions from multiple strengthening mechanisms, the nanostructured steels with superior strengths and low-temperature impact toughness can be obtained by avoiding the temper embrittlement regime. With appropriate Mn additions, these nanostructured steels can achieve a triple enhancement in ductility (total tensile elongation, TE of~30%) at no expense of strengths (yield strength, YS of~1100 to 1300 MPa, ultimate tensile strength, UTS of~1300 to 1400 MPa). More importantly, these steels demonstrate good fabricability and weldability. In this paper, the microstructure-property relationships of these advanced nanostructured steels are comprehensively reviewed. In addition, the current limitations and future development of these nanostructured steels are carefully discussed and outlined.

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Section: Nanoscale Cu and Nial Precipitations In Nanostructured Steelsmentioning

confidence: 99%

Low-carbon advanced nanostructured steels: Microstructure, mechanical properties, and applications

Kong

Jiao

et al. 2021

Sci. China Mater.

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“…Firstly, we discuss the main reason for phenomenon (1). The strength of Cu-added steel generally depends on the dispersed state of Cu precipitation resulting from heat treatment [2,14], and the precipitated state is dependent on the L treatment temperature [15]. When the steel is heated to about 723 K to 823 K, the strength increases by age hardening, but the strength decreases in an overaging treatment at temperatures over 823 K. Additionally, L treatment is a heat treatment in the two phases (α and γ).…”

Section: Mechanism Of Improvement Of Mechanical Properties By L Treatmentioning

confidence: 99%

“…Therefore, for the A707 modified steel, the Cu precipitation state is very important to obtain the strength. On the other hand, it has been reported that the precipitation behavior of Cu-bearing steel differs depending on each stage of the refining heat treatment, especially intercritical quenching or tempering [15]. So, it is extremely important to evaluate the mechanical properties of the material whose L treatment conditions are changed and also show the optimum treatment conditions in A707 modified steel as well in order to apply for offshore structures.…”

Section: Introductionmentioning

confidence: 99%

Effect of Intercritical Quenching Temperature of Cu-Containing Low Alloy Steel of Long Part Forging for Offshore Applications

2019

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In our previous study, intercritical quenching from the dual-phase region of ferrite and austenite regions, which is called lamellarizing (L) treatment, brought a clear improvement of balance between the strength and toughness of Cu-containing low alloy steel based on American Society for Testing and Materials (ASTM) A707 5L grade. Moreover, the results imply that the reverse transformation behavior during L treatment is very important in order to optimize the L treatment temperature. Hence, the purpose of this paper is to clarify the mechanism by which L treatment improves the mechanical properties in terms of reverse transformation behavior. Additionally, offshore structures require good weldability, because the structures generally have a lot of weld joints. Therefore, weldability was also investigated in this study. The investigation revealed that coarse Cu precipitates are observed in the not-transformed α phase, so the strength tendency in relation to the L treatment temperature is relevant to the area ratio of the not-transformed α phase and the transformed γ phase during L treatment. From the in situ electron back scatter diffraction (EBSD) results, it is believed to be possible to enhance the mechanical properties of Cu-containing low alloy steel by controlling the area ratio of the reverse-transformed gamma phase and selecting the appropriate L treatment temperature. Furthermore, the long part forging of Cu-containing low alloy steel has a good weldability, since the maximum hardness of the heat-affected zone (HAZ) is less than 300 HV, and the HAZ of steel has a good crack tip opening displacement (CTOD) property with less than 2.3 kJ/mm of heat input of GTAW.

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“…Therefore, understanding the Cu precipitation mechanism is crucial for improving the mechanical properties of Cu-bearing steels. The evolutions of precipitation morphologies [ 5 , 6 ], precipitation strengthening [ 7 , 8 ], crystal structure [ 9 , 10 , 11 ] and chemical composition [ 12 , 13 , 14 , 15 ] of Cu particles have been extensively studied. The early stage of Cu precipitation is characterized by coherent body-centered cubic (bcc) particles with small size (<5 nm).…”

Section: Introductionmentioning

confidence: 99%

Age Hardening Characteristics of an Ultra-Low Carbon Cu Bearing Steel

Sun

2020

Materials

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We studied the influence of aging temperature on microstructure and mechanical properties in an ultra-low carbon Cu bearing steel in the present study. During the aging process, a continuous recovery of matrix associated with formation and growth of Cu precipitates could be observed during aging processes, exerting significant effects on the mechanical properties of the steel. At aging temperature below 600 °C, the mechanical properties were dominated by the precipitation strengthening effect, leading to excessive matrix strengthening and poor low-temperature toughness. Conversely, steel aged at temperatures above 650 °C exhibited an extraordinary improvement in toughness at the expense of strength, which can be attributed to the synergistic effects of softening matrix, coarsened Cu precipitates and formation of reverted austenite. After aging at 650 °C, reverted austenite formed at the lath boundaries. Increasing the aging temperature to 700 °C lowered the thermal stability of reverted austenite, consequently, the reverted austenite was partially transformed to fresh martensite. After aging at 650 °C for 0.5 h, the mechanical properties were optimized as follows—yield strength = 854 MPa, tensile strength = 990 MPa, elongation = 19.8% and Charpy impact energy = 132 J at −80 °C.

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Evolution of crystal structure of Cu precipitates in a low carbon steel

Cited by 89 publications

References 49 publications

Low-carbon advanced nanostructured steels: Microstructure, mechanical properties, and applications

Low-carbon advanced nanostructured steels: Microstructure, mechanical properties, and applications

Effect of Intercritical Quenching Temperature of Cu-Containing Low Alloy Steel of Long Part Forging for Offshore Applications

Age Hardening Characteristics of an Ultra-Low Carbon Cu Bearing Steel

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