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Kohichi Sugimoto - One of the best experts on this subject based on the ideXlab platform.

  • fracture strength and toughness of ultra high strength trip aided steels
    Materials Science and Technology, 2009
    Co-Authors: Kohichi Sugimoto
    Abstract:

    The performance of hydrogen embrittlement, fatigue properties and impact toughness of ultra high strength transformation induced plasticity aided steels with bainitic Ferrite Matrix (TBF steels) has been discussed. Some characteristics and deformation transformation mechanism of the retained austenite has also been discussed. It has been observed that mechanical stability and volume fraction of the interlath retained austenite phase in the TBF steels play an important role in increasing delayed fracture strength, fatigue limit and impact toughness.

  • ductility of 0 1 0 6c 1 5si 1 5mn ultra high strength trip aided sheet steels with bainitic Ferrite Matrix
    Isij International, 2004
    Co-Authors: Kohichi Sugimoto, Michitaka Tsunezawa, Tomohiko Hojo, Shushi Ikeda
    Abstract:

    The effects of heat treatment and forming conditions on retained austenite characteristics and ductility of 0.1-0.6C-1.5Si-1.5Mn, mass%, ultra high-strength TRIP-aided sheet steels with bainitic Ferrite Matrix were investigated. These steels possessed large total elongations of about 20-25 % in a tensile strength ranging from 700 to 1 300 MPa when austempered at temperatures above martensite-start temperature (M S ). The total elongations were enhanced by warm forming at two temperatures, T P 1 and T P 2 . The first peak forming temperatures T P 1 s were between 0°C and 75°C and were nearly constant regardless of carbon content of the steels. This was associated with the strain-induced martensite transformation of a large amount of metastable retained austenite which suppressed a rapid fall of strain-hardening rate in an early strain range to resultantly increase the uniform and total elongations. On the other hand, the second peak forming temperatures T P 2 s were between 200 and 300°C and further large total elongations beyond 30% were achieved in high carbon steels (0.4% C and 0.6% C steels) with tensile strength of 1 300-1 500 MPa. The large improvement was controlled by both the strain-induced bainite transformation and dynamic strain aging.

  • ductility and formability of newly developed high strength low alloy trip aided sheet steels with annealed martensite Matrix
    Isij International, 2002
    Co-Authors: Kohichi Sugimoto, Shunichi Hashimoto, Akinobu Kanda, Ryo Kikuchi, Takahiro Kashima, Shushi Ikeda
    Abstract:

    Formable high-strength low-alloy TRIP-aided sheet steels with annealed martensite Matrix or "TRIP-aided annealed martensitic steel" were developed for automotive applications. The steels possessed a large amount of plate-like retained austenite along annealed martensite lath boundary, whose stability against the strain-induced transformation was higher than that of the conventional "TRIP-aided dual-phase steel" with polygonal Ferrite Matrix. In a tensile strength range between 600 and 1000 MPa, the TRIP-aided annealed martensite steels exhibited a superior large elongation and reduction of area. In addition, they possessed the same excellent stretch-flangeability and bendability as "TRIP-aided bainitic steel" with bainitic Ferrite Matrix. These properties were discussed by Matrix structure, a strength ratio of second phase to Matrix, retained austenite stability, internal stress and so on.

  • x ray residual stress and strain induced transformation of retained austenite in trip aided dual phase steels
    Transactions of the Japan Society of Mechanical Engineers. A, 1995
    Co-Authors: Kohichi Sugimoto, Mitsuyuki Kobayashi, Hidehiro Matsushima, Shunichi Hashimoto
    Abstract:

    The effects of strain-induced transformation (SIT) on X-ray residual stress of retained austenite islands in TRIP-aided dual-phase steels were examined under uniaxial tension, and were discussed using a micromechanics theory. If the retained austenite particles are stable against the SIT and strain hardening, high tensile residual stress of 100 to 200 MPa occurs in the particles. The stress corresponds to that estimated from the micromechanics theory. In such a case, the retained austenite particles effectively increase the internal stress of the Ferrite Matrix similar to bainite and martensite particles. When the retained austenite particles easily transform to martensite during straining, the residual stress is decreased by plastic relaxation resulting from expansion and shear strains on transformation, although the strain-induced martensite increases the flow stress of the steels.

Chengsi Zheng - One of the best experts on this subject based on the ideXlab platform.

  • effect of microstructure on mechanical behavior for eutectoid steel with ultrafine or fine grained Ferrite cementite structure
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017
    Co-Authors: Chengsi Zheng
    Abstract:

    A eutectoid steel with various ultrafine- or fine-grained Ferrite Matrix (α)+cementite particle (θ) structures was fabricated to explore the effects of the microstructural features on the mechanical behavior of hard particle-strengthened two-phase alloys. The effect of microstructure on the parameters of an analytical model and the mechanical behavior for the eutectoid steel with ultrafine- or fine-grained α+θ structure were analyzed basing on statistical data and physical metallurgy. The results showed that the rate of dislocation-storage caused by Ferrite grain boundaries and cementite particles is approximately a microstructural constant and is proportional to the dislocation mean free path. The larger Ferrite grains and the larger volume fraction of intragranular cementite particles are beneficial to obtaining a lower rate of dynamic recovery when ultrafine- or fine-grained α+θ structures with an equal dislocation mean free path, and the uniform elongation increases with the decrease in the rate of dynamic recovery. Moreover, the ultimate strength is closely related to the effective dislocation mean free path including both roles of the storage and the recovery of dislocations. It is feasible to design a microstructure consisting of ultrafine- or fine-grained Ferrite Matrix and tiny cementite particles mainly within grain interior to possess an enhanced strength-plasticity synergy for the eutectoid steel.

  • relationship between microstructure and yield strength for plain carbon steel with ultrafine or fine Ferrite cementite structure
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014
    Co-Authors: Chengsi Zheng, Wangyue Yang, Zuqing Sun
    Abstract:

    Abstract Plain carbon steels with different ultrafine or fine-grained Ferrite Matrix (α)+cementite particle (θ) structures were formed through thermo-mechanical processes. Scanning electron microscopy was used to analyze the initial microstructural parameters, and the dislocation morphology was analyzed by transmission electron microscopy. A relationship between the microstructural parameters and yield strength was established for plain carbon steel with an ultrafine or fine (α+θ) structure. The results indicated that the yield strength of plain carbon steel with an ultrafine or fine (α+θ) structure had a direct relationship with the grain size of the Ferrite Matrix and the size, volume fraction and location of cementite particles, and the enhancement in yield strength caused by the cementite particles was improved with the increase in carbon content or the particle-refinement.

  • microstructure evolution and mechanical properties of eutectoid steel with ultrafine or fine Ferrite cementite structure
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014
    Co-Authors: Chengsi Zheng, Wangyue Yang, Zuqing Sun
    Abstract:

    Abstract Eutectoid steel with the ultrafine or fine-grained Ferrite (α)+cementite (θ) particles structure was formed by hot deformation of undercooled austenite at 0.1 s−1 or 5 s−1 at 650 °C using a Gleeble 1500 hot simulator and subsequent annealing. The microstructural evolution of fine (α+θ) structure was investigated by means of a scanning electronic microscope, electron backscattered diffraction and transmission electron microscope, and the mechanical properties of fine (α+θ) steel were analyzed in comparison with that of ultrafine (α+θ) steel. The results show that only dynamic transformation of undercooled austenite into proeutectoid Ferrite occurs during hot deformation at 650 °C at 5 s−1. During water quenching, lamellar pearlite with small colony sizes is formed and the average size of pearlite colonies decreases with increasing the strain. By subsequent annealing at 650 °C for 30 min, the spheroidization of lamellar pearlite takes place, resulting in the formation of fine (α+θ) structure consisting of Ferrite Matrix with the average size of about 4.9 μm and fine cementite particles mainly within Ferrite grains. In comparison with ultrafine (α+θ) steel consisting of Ferrite Matrix with the average size of about 1.8 μm and relatively large cementite particles mostly located at grain boundaries, the yield strength, tensile strength, uniform elongation, total elongation and work-hardening capability of fine (α+θ) steel improve markedly.

Zuqing Sun - One of the best experts on this subject based on the ideXlab platform.

  • relationship between microstructure and yield strength for plain carbon steel with ultrafine or fine Ferrite cementite structure
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014
    Co-Authors: Chengsi Zheng, Wangyue Yang, Zuqing Sun
    Abstract:

    Abstract Plain carbon steels with different ultrafine or fine-grained Ferrite Matrix (α)+cementite particle (θ) structures were formed through thermo-mechanical processes. Scanning electron microscopy was used to analyze the initial microstructural parameters, and the dislocation morphology was analyzed by transmission electron microscopy. A relationship between the microstructural parameters and yield strength was established for plain carbon steel with an ultrafine or fine (α+θ) structure. The results indicated that the yield strength of plain carbon steel with an ultrafine or fine (α+θ) structure had a direct relationship with the grain size of the Ferrite Matrix and the size, volume fraction and location of cementite particles, and the enhancement in yield strength caused by the cementite particles was improved with the increase in carbon content or the particle-refinement.

  • microstructure evolution and mechanical properties of eutectoid steel with ultrafine or fine Ferrite cementite structure
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2014
    Co-Authors: Chengsi Zheng, Wangyue Yang, Zuqing Sun
    Abstract:

    Abstract Eutectoid steel with the ultrafine or fine-grained Ferrite (α)+cementite (θ) particles structure was formed by hot deformation of undercooled austenite at 0.1 s−1 or 5 s−1 at 650 °C using a Gleeble 1500 hot simulator and subsequent annealing. The microstructural evolution of fine (α+θ) structure was investigated by means of a scanning electronic microscope, electron backscattered diffraction and transmission electron microscope, and the mechanical properties of fine (α+θ) steel were analyzed in comparison with that of ultrafine (α+θ) steel. The results show that only dynamic transformation of undercooled austenite into proeutectoid Ferrite occurs during hot deformation at 650 °C at 5 s−1. During water quenching, lamellar pearlite with small colony sizes is formed and the average size of pearlite colonies decreases with increasing the strain. By subsequent annealing at 650 °C for 30 min, the spheroidization of lamellar pearlite takes place, resulting in the formation of fine (α+θ) structure consisting of Ferrite Matrix with the average size of about 4.9 μm and fine cementite particles mainly within Ferrite grains. In comparison with ultrafine (α+θ) steel consisting of Ferrite Matrix with the average size of about 1.8 μm and relatively large cementite particles mostly located at grain boundaries, the yield strength, tensile strength, uniform elongation, total elongation and work-hardening capability of fine (α+θ) steel improve markedly.

Jerren Yang - One of the best experts on this subject based on the ideXlab platform.

  • Microstructural variation in fatigued interphase arrayed nano-precipitated Ti-microalloyed steel
    'Elsevier BV', 2021
    Co-Authors: Chieh-ning Yen, Jerren Yang, Liu-wen Chang, Chen-an Hsu, Horng-yi Chang, Shing-hoa Wang, Hsueh-ren Chen
    Abstract:

    In the present study, arrayed nano-precipitated TiC in a Ferrite Matrix was obtained through thermal treatment. The size and shape of the arrayed interphase nano-precipitates were unaffected by fatigue deformation in this Ti-microalloyed steel. In addition, arrayed arrangement of the interphase nano-precipitates was not disrupted by fatigue and still remained only at low cycle numbers, which corresponded to the shortest fatigue life. The interphase nano-precipitated steel was strengthened through a bowing mechanism through which unpinning occurred, dislocation loops were formed, and the microhardness of Ferrite was increased. The development of an incipient cell structure in the Ferrite Matrix was caused by wavy dislocation. After the onset of fatigue, the grain was preferentially rotated toward the {101}α orientation. Higher strain amplitude or lower strain rate led to a more favorable degree of misorientation in the low-angle grain boundaries

  • microstructural characterization and strengthening behavior of nanometer sized carbides in ti mo microalloyed steels during continuous cooling process
    Materials Characterization, 2016
    Co-Authors: Chih-yuan Chen, Jerren Yang, Chien Chon Chen, Shihfan Chen
    Abstract:

    Abstract Nanometer-sized carbides that precipitated in a Ti–Mo bearing steel after interrupted continuous cooling in a temperature range of 620–700 °C with or without hot deformation were investigated by field-emission-gun transmission electron microscopy. The nanometer-sized carbides were identified as randomly homogeneous precipitation carbides and interphase precipitation carbides coexisting in the Ferrite Matrix. It is found that this dual precipitation morphology of carbides in the steel leads to the non-uniform mechanical properties of individual Ferrite grains. Vickers hardness data mainly revealed that, in the specimens cooled at a rate of 0.5 °C/s without hot deformation, the range of Vickers hardness distribution was 230–340 HV 0.1 when cooling was interrupted at 680 °C, and 220–360 HV 0.1 when cooling was interrupted at 650 °C. For the specimens cooled at a rate of 0.5 °C/s with hot deformation, the range of Vickers hardness distribution was 290–360 HV 0.1 when cooling was interrupted at 680 °C, and 280–340 HV 0.1 when cooling was interrupted at 650 °C. Therefore, a narrower range of hardness distribution occurred in the specimens that underwent hot deformation and were then cooled with a lower interrupted cooling temperature. The uniform precipitation status in each Ferrite grain can lead to Ferrite grains with a narrower Vickers hardness distribution. On the other hand, interrupted cooling produced a maximum Vickers hardness of 320–330 HV 0.1 for the hot deformed specimens and 290–310 HV 0.1 for the non-deformed specimens with cooling interrupted in the temperature range of 660–670 °C. The maximum Vickers hardness obtained in such a temperature range can be ascribed to the full precipitation of the microalloying elements in the supersaturated Ferrite Matrix with a tiny size (~ 4–7 nm).

  • orientation relationship transition of nanometre sized interphase precipitated tic carbides in ti bearing steel
    Materials Science and Technology, 2010
    Co-Authors: Hungwei Yen, Chingyuan Huang, Chungli Chen, Tuchih Wang, Jerren Yang
    Abstract:

    AbstractThe objective of the present study was to investigate the crystallography and morphology of TiC particles in a titanium containing high strength low alloy (HSLA) steel that form during isothermal transformation at a temperature in the (α + γ) phase field. The orientation relationships (ORs) were identified from selected area diffraction patterns (SADPs) and from moire fringes in high resolution transmission electron microscopy (HRTEM) lattice images. It was found that in the initial stages of the isothermal transformation, fine plate-like TiC particles develop and that these exhibit the Baker–Nutting (BN) OR with respect to the Ferrite Matrix. In the later stages of the transformation, however, coarser plate-like carbides are observed, and these adopt approximately the Nishiyama–Wassermann (NW) OR with respect to the Ferrite Matrix. The evidence indicates that OR transition is brought about simply by aging for a longer time at the transformation temperature, and also manifests a rotation of the pr...

  • microstructural characterization of simulated heat affected zone in a nitrogen containing 2205 duplex stainless steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002
    Co-Authors: T H Chen, Jerren Yang
    Abstract:

    Abstract In order to investigate the microstructural evolution in a nitrogen-bearing 2205 duplex stainless steels (DSS) during welding, a simulated weld thermal cycle with 5 kJ cm−1 heat input followed by exposure at 700 °C for different time intervals was performed. The microstructure of high-temperature heat affected zone (HTHAZ) developed with the thermal experience was characterized via optical metallography and transmission electron microscopy (TEM). The duplex structure with equivalent phase components was drastically destroyed by the rapid thermal cycle. In the simulated HTHAZ structure, three different morphologies of newly formed austenite were observed in the coarse-grained δ-Ferrite Matrix; i.e. allotriomorphic austenite, Widmanstaten autenite and intragranularly nucleated autenite. During the exposure at 700 °C, the intragranularly nucleated austenite got coarse and the Widmanstaten austenite grew progressively. TEM revealed that several variants of rod-like Cr2N were precipitated selectively at intragranular and intergranular sites. From the analyses of diffraction patterns of TEM, Kurdjumov–Sachs orientation relationship was found to describe the interface between intragranularly nucleated autenite and δ-Ferrite, while Pitch–Schrader orientation relationship to describe the disposition between hexagonal Cr2N precipitates and δ-Ferrite Matrix.

Guodong Wang - One of the best experts on this subject based on the ideXlab platform.

  • precipitation behavior and mechanical properties of a hot rolled ti bearing dual phase steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016
    Co-Authors: Guo Yuan, R D K Misra, Jian Kang, Guodong Wang
    Abstract:

    Abstract We have studied here the microstructure, precipitate evolution and mechanical properties in a Fe-Mn-Cr-Ti dual phase steel processed by thermo-mechanical control processing. When the deformed austenite was treated in the temperature range of 640–760 °C, the microstructure consisted of Ferrite and 7–80% martensite. Both random and interphase precipitation of nanoscale TiC particles occurred in the Ferrite Matrix. With decrease in temperature, the average size of precipitates was reduced from 5.4 nm to 2.2 nm, and the morphology of interphase precipitation was altered from curved to planar because of the change in the mechanism of TiC interphase precipitation. Hot rolling inhibited interphase precipitation but promoted precipitation on dislocations. Given that the Ferrite Matrix was significantly strengthened by nanoscale TiC particles, the hardness difference between the Ferrite Matrix and martensite was significantly decreased, and the strength of hot rolled Ti-bearing dual phase steels was less dependent on the martensite content compared to the conventional dual phase steels. The strength of hot rolled Ti-bearing dual phase steels was derived from a number of strengthening mechanisms, namely phase transformation, precipitation and grain refinement strengthening.

  • the impact of thermo mechanical controlled processing on structure property relationship and strain hardening behavior in dual phase steels
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016
    Co-Authors: Chengning Li, R D K Misra, Guo Yuan, Jian Kang, Fengqin Ji, Guodong Wang
    Abstract:

    Abstract We elucidate here the impact of thermo-mechanical controlled processing (TMCP) in governing nucleation of second phase in Nb-Ti microalloyed dual-phase steels. A wide range of mechanical properties were obtained through change in the microstructure, depending on the TMCP cooling schedule. Polygonal Ferrite Matrix with martensite as the second phase exhibited highest initial strain hardening rate, lowest yield strength, and highest tensile strength as compared to the situation when bainite or bainite-martensite was the second phase. The Crussard–Jaoul (C-J) strain hardening behavior of granular bainite and granular bainite-martensite as the second phase exhibited one-stage characterized by linear and parabolic behavior, respectively. On the other hand, two stages were observed in steel containing martensite as the second phase, viz., linear stage I and parabolic stage II.

  • controlled cooling process and mechanical property of 590mpa grade structural steel with low yield ratio
    Advanced Materials Research, 2011
    Co-Authors: Jian Kang, Guo Yuan, Zhao Dong Wang, Guodong Wang
    Abstract:

    To develop 590MPa grade low yield ratio steel for high-rise buildings, the new generation TMCP based on ultra fast cooling (UFC) technology was proposed. Then effects of UFC final temperature on microstructure and mechanical properties were investigated. The results show that the control of composite phases is important to obtain high strength, low yield ratio and high work hardening exponent. When UFC final temperature is 521°C, 22.5% (volume fraction) M-A phases are distributed in bainite Ferrite Matrix, and the excellent overall properties can be obtained, i.e., the yield strength is 570MPa, tensile strength 760MPa, yield ratio 0.75 and percentage elongation 22% with the Charpy impact energy 284J at -40°C. All these indexes can meet the requirements of relevant standards.