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R D K Misra - One of the best experts on this subject based on the ideXlab platform.

  • influence of intercritical tempering temperature on Impact Toughness of a quenched and tempered medium mn steel intercritical tempering versus traditional tempering
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2018
    Co-Authors: C Sun, Shilong Liu, R D K Misra
    Abstract:

    Abstract The influence of intercritical tempering temperature on Impact Toughness of quenched and tempered 0.05C-5.42Mn medium-Mn steel was studied and compared with traditional tempering. The experimental steel had high hardenability because of high Mn-content. Lath-like α'-martensite without retained austenite was obtained over a wide range of quenching rate of 0.5–30 °C/s, and the quenched steel showed high strength but low Impact Toughness. On intercritical tempering at 625 °C and 665 °C, the Impact Toughness was enhanced, as compared to traditional tempering at 570 °C. The reversed austenite enriched with Mn and C formed between the martensite laths was the underlying reason for the increased absorbed crack propagation energy, and the ductile-brittle transition temperature (DBTT) was reduced because of increased stability of reversed austenite. Compared to the steel tempered at 625 °C, the steel tempered at 665 °C contained more reversed austenite, but the reversed austenite was less stable because of reduced enrichment of Mn and C. The enrichment or depletion of Mn and C in austenite and martensite was thermodynamically studied by DICTRA. In striking contrast to the steels tempered between 625 and 665 °C, twinned martensite was formed in the steel tempered at high temperature of 700 °C, and the steel exhibited Impact Toughness lower than the quenched steel.

  • the microstructural evolution and Impact Toughness of nugget zone in friction stir welded x100 pipeline steel
    Journal of Alloys and Compounds, 2016
    Co-Authors: Guodong Wang, R D K Misra
    Abstract:

    Abstract The X100 pipeline steel was successfully friction stir welded at rotation speed of 600 rpm and welding speed of 50 mm/min using W-Re stirring tool. Microstructural analysis and Charpy v-notch Impact-tests of the welds were carried out in nugget zone (NZ). In this case, the NZ exhibits inhomogeneous microstructure. Fine granular bainite was observed on the advanced side (AS) of the NZ as a result of mechanical stabilization effect, whereas the coarse lath-bainite with few granular bainite was observed on the retreating side (RS), which resulted from coarse prior austenite grains due to the lower cooling rate. Furthermore, a transition region containing intersecting bainite laths appeared between the two zones above. Generally, it was found that boron, which dissolved into the nugget zone during FSW, contributed the formation of classical lath-bainite in hard zone when FSWing pipeline steel using the PCBN stirring tool. The Charpy v-notch Impact-tests results show that the whole NZ achieved good Impact Toughness and the poor Impact Toughness microstructure was successfully avoided in our study.

Hanqian Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Impact Toughness scattering of bainitic steel in the ductile brittle transition temperature region
    Journal of Wuhan University of Technology-materials Science Edition, 2016
    Co-Authors: Kun Shi, Jiangbiao Chen, Hong Hou, Lingti Kong, Hanqian Zhang
    Abstract:

    The Impact Toughness scattering in the ductile-brittle transition temperature (DBTT) region was experimentally examined on mixed and homogeneous grains of low alloy high strength bainitic steel under dynamic loading conditions. The results revealed that the mixed grain microstructure had larger Impact Toughness scattering than the homogeneous one, and the Impact Toughness scattering was mainly caused by the scattering in the cleavage fracture stress σf. The value of σf is related to the size of the microcrack formed in the bainitic packet. When a bainitic packet-sized microcrack propagates from one bainitic packet into the adjacent packet, cleavage fracture occurs. The cleavage fracture is controlled by the few coarse packets in the microstructures, and the σf scattering is influenced by the varied distances/relative locations between these coarse packets, and homogenizing the distribution of fine bainitic packet sizes is an effective way to reduce the Impact Toughness scattering in the DBTT region.

  • effect of bainitic packet size distribution on Impact Toughness and its scattering in the ductile brittle transition temperature region of q t mn ni mo bainitic steels
    Steel Research International, 2016
    Co-Authors: Kun Shi, Jiangbiao Chen, Hong Hou, Lingti Kong, Hanqian Zhang
    Abstract:

    The Impact Toughness of Q&T Mn-Ni-Mo bainitic steel in the ductile–brittle transition temperature (DBTT) region was measured. The fracture micromechanism associated with the microstructural features was studied, by statistically analyzing the grain sizes of various structures. The results reveal that the cleavage fracture behavior is controlled by bainitic packets. There exists a critical bainitic packet size. When a microcrack formed in the bainitic packet with a size exceeding the critical size propagates into adjacent packets, brittle cleavage fracture occurs. The probability of finding the bainitic packets larger than the critical size dominates the Impact Toughness and its scattering. It is suggested that refining the bainitic packets and homogenizing their sizes is an effective method of improving the Impact Toughness and reducing its scattering in the DBTT region.

  • effect of aging on the Impact Toughness of 25cr 20ni nb n steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010
    Co-Authors: Bicao Peng, Hongxiang Zhang, Jie Hong, Jiaqiang Gao, Qijiang Wang, Hanqian Zhang
    Abstract:

    Abstract The Impact Toughness evolution of 25Cr–20Ni–Nb–N stainless steel during aging for different time at 973 K has been systematically investigated. It is found that the Impact Toughness of 25Cr–20Ni–Nb–N stainless steel declines sharply in the early stage of the aging (about 500 h). Thereafter, the Impact Toughness decreases slowly with the increase in aging time. The hardness on grain boundaries and within grains is analyzed by micro-indentation. The results of micro-indentation show that the hardness in grains during aging is higher than that on grain boundaries due to the precipitation of M23C6 and the decrease of the Impact Toughness of 25Cr–20Ni–Nb–N can be attributed to the reduction of the bonding interface strength when M23C6 precipitated on grain boundaries.

Fuping Yuan - One of the best experts on this subject based on the ideXlab platform.

  • high Impact Toughness of crconi medium entropy alloy at liquid helium temperature
    Scripta Materialia, 2019
    Co-Authors: Muxin Yang, Lingling Zhou, Chang Wang, Ping Jiang, Fuping Yuan
    Abstract:

    Abstract We show that face-centered-cubic CrCoNi medium-entropy alloy sustains a Charpy V-notch Impact Toughness (AK) as high as 340 J at 4 K. Deformation twinning (DT) is rendered exceptionally profuse by this alloy's low stacking fault energy, combined with liquid-helium temperature and high strain rates that both incur high stresses to favor DT across a large plastic zone. This efficiently dissipates imposed mechanical energy, accumulates defects to sustain high strain hardening, and restrains strain localization events from evolving into major shear bands. Martensitic transformation to hexagonal phase is insignificant. CrCoNi is therefore a strong competitor to the best existing cryogenic alloys.

Hongwei Liu - One of the best experts on this subject based on the ideXlab platform.

  • effect of matrix carbon content and lath martensite microstructures on the tempered precipitates and Impact Toughness of a medium carbon low alloy steel
    Journal of materials research and technology, 2020
    Co-Authors: Chen Sun, Hanghang Liu, Yanfei Cao, Hongwei Liu
    Abstract:

    Abstract Different austenitizing temperatures were used to obtain medium-carbon low-alloy (MCLA) steels with different initial states of tempering, including lath martensite microstructures and matrix carbon contents. The effects of these factors on the tempered carbides and Impact Toughness of the MCLA steels were investigated via optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the matrix carbon content and lath martensite substructure sizes could be effectively controlled by the austenitizing temperature. The morphologies of the tempered carbides precipitated at the boundaries were controlled by both the matrix carbon content and the lath martensite substructure sizes. Higher matrix carbon content and boundary densities increased the nucleation rate and promoted the formation of spherical carbides. The spheroidization of carbides was conducive to improving the Impact Toughness. However, the decrease in the density of high-angle grain boundaries and the appearance of long strip-shaped carbides drastically reduced the Impact Toughness.

Fucheng Zhang - One of the best experts on this subject based on the ideXlab platform.