Microstructural refinement mechanism and its effect on toughness in the nugget zone of high-strength pipeline steel by friction stir welding

Duan, R.H.; Xie, Guobo; Xue, P.; Ma, Z.Y.; Luo, Zongan; Wang, C.; Misra, R.D.K.; Wang, G.D.

doi:10.1016/j.jmst.2021.04.008

Cited by 27 publications

(11 citation statements)

References 36 publications

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“…The stress concentration points such as the MA/ferrite interface can easily become the priority positions for the initiation of microcracks [ 15 ]. According to the Griffith theory, the premise of crack nucleation is that the elastic strain energy released is higher than the surface energy of the crack [ 30 , 31 ].

where σ c is the cracking stress, E is Young’s modulus, γ p is the effective surface energy, ν is Poisson’s ratio and D is the length of the crack.…”

Section: Discussionmentioning

confidence: 99%

Inter-Critically Reheated CGHAZ of Ultra-High-Strength Martensitic Steel with Different Cooling Rates

Liu

Zhou

et al. 2023

Materials

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The mechanical properties of steel’s inter-critically reheated coarse-grained heat-affected zone (ICR CGHAZ) directly affects the service life of machinery equipment. The hardness and toughness of ICR CGHAZ can be optimized simultaneously through tailoring microstructure where cooling rate plays a key role. In this work, the samples with different cooling rates was prepared using thermal simulation. The granite bainite (GB), bainite ferrite (BF) and MA were formed at a 1 °C/s (CR1) cooling rate, while BF and MA were formed at 10 °C/s (CR2) and 30 °C/s (CR3) cooling rates. With the increase of cooling rate, the effective grain size decreased and the number of hard phases increased, resulting in monotonic increase of hardness(260HV3, 298HV3 and 323HV3). CR1 had sparsely distributed coarse slender MA and CR3 possessed tail-head connected MA along PAGBs, which was detrimental to toughness. Therefore, CR2 possessed the best toughness(25J). The microstructural evolution mechanism of ICR CGHAZ with different cooling rates is investigated, corresponding hardening and toughening mechanisms are discussed.

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where σ c is the cracking stress, E is Young’s modulus, γ p is the effective surface energy, ν is Poisson’s ratio and D is the length of the crack.…”

Section: Discussionmentioning

confidence: 99%

Inter-Critically Reheated CGHAZ of Ultra-High-Strength Martensitic Steel with Different Cooling Rates

Liu

Zhou

et al. 2023

Materials

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“…4c that the microstructure of RS-TZ is the mixture of granular bainite and ferrite containing a small amount of lath bainite. It is because that the temperature of HAZ during FSW is commonly in the range of A c1 -A c3 and difficult to be higher than A c3 of the steel, and the cooling rate reaches 260 °C/s or higher, which results in the partially austenitic transformation and a significant grain refinement in HAZ [12].…”

Section: Microstructuresmentioning

confidence: 99%

“…The average grain size of SZ (18.30 μm) is nearly 3.7 times larger than BM. It can be found in literatures that to high-strength bainitic pipeline steel, the welding peak temperature of SZ exceeds the A c3 temperature and might be increased from 912 to 1026 °C with increasing the tool rotational speed from 400 to 700 r/min [12]. During FSW, dynamic recrystallization of austenite was performed due to the hot plastic deformation, and growth of prior austenite and bainite transformation occurred in the post-welding cooling process [5].…”

Section: Microstructuresmentioning

confidence: 99%

“…And martensite with high dislocation density in the M-A constituents shell will deteriorate the impact toughness, and austenite in the core is beneficial to the impact toughness [10,11]. The coarser M-A constituents exhibit lower brittle fracture stress, resulting in the microcracks initiate more readily between the blocky M-A constituents and the matrix and propagated easily across the blocky M-A constituents [12]. The detrimental effect of coarse M-A constituent is also related to higher local stress concentrations than the finer M-A constituent.…”

Section: Introductionmentioning

confidence: 99%

“…The elevated peak temperature and slow cooling rate could promote the partitioning and diffusion of carbon and the growth of ferrite grain, thereby forming the massive M-A constituents in the SZ. While at a relative low temperature and fast cooling rate, a more dispersed distribution of M-A constituents usually occurs from insufficient time for carbon diffusion [12,16]. However, the microstructural evolution of SZ during FSW is very complex, and it is still very hard to estimate and control the M-A constituents precisely by controlling the welding parameters.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Prediction of M–A Constituents and Impact Toughness in Stir Zone of X80 Pipeline Steel Friction Stir Welds

Wang

et al. 2022

Acta Metall. Sin. (Engl. Lett.)

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This study explored a strategy for predicting the proportion of martensite-austenite (M-A) constituents and impact toughness of stir zone (SZ) on X80 pipeline steel joints welded by friction stir welding (FSW). It is found that the welding forces, including the traverse force (F x ), the lateral force (F y ) and the plunge force (F z ), are the key variables related to the change of welding parameters and influence remarkably the characteristics of M-A constituents and impact toughness of SZ. The impact toughness of SZ is commonly lower than that of the base material due to the formation of lath bainite and coarsening of austenite. The characteristics of M-A constituents in SZ are sensitive to the variation of welding parameters and respond well to the change of welding forces. The proportion of small island M-A constituents increases with the decrease in rotational speed and the increase in F z . The increase in the amount of island M-A constituents is beneficial to improve the impact toughness of SZ. Based on the above findings, a machine learning (ML) model for predicting the M-A constituents and impact toughness is constructed using the force features as the input data set. The force data-driven ML model can predict the M-A constituents and impact toughness precisely and exhibits higher accuracy than ML built with welding parameters. It is believed that the high accuracy is achieved because the force features include more details of FSW process, such as the heat generation, material flow, plastic deformation, and so on, which govern the microstructural evolution of SZ during FSW.

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Microstructure evolution of weld root in dissimilar weld metal in S690QL high-strength steel under multiple welding thermal cycles

Zhang

Liu³

et al. 2023

J Mater Sci

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Microstructural refinement mechanism and its effect on toughness in the nugget zone of high-strength pipeline steel by friction stir welding

Cited by 27 publications

References 36 publications

Inter-Critically Reheated CGHAZ of Ultra-High-Strength Martensitic Steel with Different Cooling Rates

Inter-Critically Reheated CGHAZ of Ultra-High-Strength Martensitic Steel with Different Cooling Rates

Prediction of M–A Constituents and Impact Toughness in Stir Zone of X80 Pipeline Steel Friction Stir Welds

Microstructure evolution of weld root in dissimilar weld metal in S690QL high-strength steel under multiple welding thermal cycles

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