The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Eiji Akiyama - One of the best experts on this subject based on the ideXlab platform.
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evaluation of Delayed Fracture property of high strength bolt steels
Isij International, 2012Co-Authors: Eiji AkiyamaAbstract:Experimental studies attempting to evaluate the Delayed Fracture property of high strength bolt steels by using slow strain rate tests (SSRT) of circumferentially notched round bar specimens are reviewed in this paper. The relationship between the notch tensile strength (NTS) of the hydrogen-precharged specimens and the hydrogen content was approximated by power law relationship. It has been found that the local stress and the local diffusible hydrogen concentration control the occurrence of Delayed Fracture. To take into account the effect of hydrogen uptake from the environment, the notched bar specimens were subjected to cyclic corrosion test (CCT) and outdoor exposure, and their NTSs were measured using SSRT. The susceptibility of high strength steels to Delayed Fracture estimated from the decrease of NTS was correspondent to the Fracture ratio of high strength bolts of the steels obtained by outdoor exposure tests, and was successfully evaluated with consideration of hydrogen uptake. Hydrogen entry behavior under CCT was monitored by electrochemical hydrogen permeation test, and continuous increase in hydrogen entry with growth of rust layer was observed. It is suggested that the “delay” of Delayed Fracture is the time required for the enhancement of the hydrogen entry efficiency.
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Hydrogen-induced Delayed Fracture of a Fe–22Mn–0.6C steel pre-strained at different strain rates
Scripta Materialia, 2012Co-Authors: Motomichi Koyama, Eiji Akiyama, Kaneaki TsuzakiAbstract:Hydrogen-induced Delayed Fracture under loading was investigated in a Fe–22Mn–0.6C twinning-induced plasticity steel that had been pre-deformed at various strain rates. Hydrogen-induced Delayed Fracture was suppressed by increasing the strain rate of the pre-deformation. In this study on the strain-rate effect, factors affecting the Delayed Fracture were found to be the negative strain-rate sensitivity of flow stress, stress drop caused by the relaxation phenomenon, and the increase in material strength due to strain aging.
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Constant-load Delayed Fracture test of atmospherically corroded high strength steels
Applied Surface Science, 2011Co-Authors: Eiji Akiyama, Katsuhiro Matsukado, Kaneaki TsuzakiAbstract:Abstract Constant load tests of circumferentially notched round bar specimens of high strength steels after cyclic corrosion test and outdoor exposure have been performed to demonstrate that Delayed Fracture occurs when the hydrogen content from the environment, H E , exceeds the critical hydrogen content for Delayed Fracture, H C . During the constant load tests the humidity around the specimen was increased in stepwise manner to increase hydrogen entry. After Fracture the specimen was kept at the humidity long enough to homogenize hydrogen in the specimen and to obtain more quantitative hydrogen content by thermal desorption analysis. H E of the Fractured specimens was higher than H C , and H E of the specimens not Fractured was lower than H C . This result confirms that the balance between H C and H E determines the occurrence of Delayed Fracture and that hydrogen-content-based evaluation of susceptibility to Delayed Fracture is reasonable. To certify the increase of H E with increase in humidity, electrochemical hydrogen permeation test was carried out. The hydrogen permeation current density was increased especially at 98%RH. Enhancement of hydrogen entry with increase in CCT number was also shown by the test.
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evaluation of Delayed Fracture property of outdoor exposed high strength aisi 4135 steels
Corrosion Science, 2010Co-Authors: Eiji Akiyama, Nobuyoshi Uno, Keiji Hirai, Kaneaki Tsuzaki, Boping ZhangAbstract:Abstract Delayed Fracture properties of AISI 4135 high strength steels with 1490 and 1310 MPa of tensile strength, represented as B15 and B13, respectively, have been studied by means of slow strain rate test (SSRT) of notched bar specimens after outdoor exposure at rural and coastal areas. The exposed specimens were kept at humid medium before SSRT to reproduce active hydrogen entry influenced by the rust layer and to homogenize hydrogen distribution. The influences of exposure site and exposure time on Fracture stress have been investigated. The susceptibility of B15 to Delayed Fracture was obviously higher than that of B13.
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evaluation of Delayed Fracture characteristics of high strength steel based on csrt method
Tetsu To Hagane-journal of The Iron and Steel Institute of Japan, 2008Co-Authors: Yukito Hagihara, Kenichi Takai, Chikahito Ito, Noriyuki Hisamori, Hiroshi Suzuki, Eiji AkiyamaAbstract:A conventional strain rate technique (CSRT) to evaluate the Delayed Fracture characteristics of high strength steels has been proposed. The critical “maximum stress—diffusible hydrogen concentration” at the Delayed Fracture initiation point near the notch tip is thought to be a material constant, which was originally demonstrated using the SSRT (slow strain rate technique) test method. The SSRT method takes hours to complete the test and uses a special test machine, which causes difficulty and complication. Therefore, a simple and conventional test technique, CSRT test method for Delayed Fracture was investigated. The crosshead speed is around 1 mm/min, so that the stress induced diffusion of hydrogen is negligible. The results obtained are as follows.(1) Since the stress induced hydrogen diffusion does not take place during the CSRT test, it is necessary to introduce the amount of hydrogen in the specimen, corresponding to the accumulated hydrogen at the vicinity of the notch tip region in the SSRT test. The electrochemical hydrogen charging conditions were established to introduce a wide range of hydrogen contents into the specimens.(2) A unique relationship between the maximum stress at the vicinity of the notch tip and hydrogen contents was obtained irrespective of the notch configuration using the CSRT test and FEM stress analysis. Therefore, it can be said that this relation is the material constants for Delayed Fracture.
Kaneaki Tsuzaki - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen-induced Delayed Fracture of a Fe–22Mn–0.6C steel pre-strained at different strain rates
Scripta Materialia, 2012Co-Authors: Motomichi Koyama, Eiji Akiyama, Kaneaki TsuzakiAbstract:Hydrogen-induced Delayed Fracture under loading was investigated in a Fe–22Mn–0.6C twinning-induced plasticity steel that had been pre-deformed at various strain rates. Hydrogen-induced Delayed Fracture was suppressed by increasing the strain rate of the pre-deformation. In this study on the strain-rate effect, factors affecting the Delayed Fracture were found to be the negative strain-rate sensitivity of flow stress, stress drop caused by the relaxation phenomenon, and the increase in material strength due to strain aging.
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Constant-load Delayed Fracture test of atmospherically corroded high strength steels
Applied Surface Science, 2011Co-Authors: Eiji Akiyama, Katsuhiro Matsukado, Kaneaki TsuzakiAbstract:Abstract Constant load tests of circumferentially notched round bar specimens of high strength steels after cyclic corrosion test and outdoor exposure have been performed to demonstrate that Delayed Fracture occurs when the hydrogen content from the environment, H E , exceeds the critical hydrogen content for Delayed Fracture, H C . During the constant load tests the humidity around the specimen was increased in stepwise manner to increase hydrogen entry. After Fracture the specimen was kept at the humidity long enough to homogenize hydrogen in the specimen and to obtain more quantitative hydrogen content by thermal desorption analysis. H E of the Fractured specimens was higher than H C , and H E of the specimens not Fractured was lower than H C . This result confirms that the balance between H C and H E determines the occurrence of Delayed Fracture and that hydrogen-content-based evaluation of susceptibility to Delayed Fracture is reasonable. To certify the increase of H E with increase in humidity, electrochemical hydrogen permeation test was carried out. The hydrogen permeation current density was increased especially at 98%RH. Enhancement of hydrogen entry with increase in CCT number was also shown by the test.
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evaluation of Delayed Fracture property of outdoor exposed high strength aisi 4135 steels
Corrosion Science, 2010Co-Authors: Eiji Akiyama, Nobuyoshi Uno, Keiji Hirai, Kaneaki Tsuzaki, Boping ZhangAbstract:Abstract Delayed Fracture properties of AISI 4135 high strength steels with 1490 and 1310 MPa of tensile strength, represented as B15 and B13, respectively, have been studied by means of slow strain rate test (SSRT) of notched bar specimens after outdoor exposure at rural and coastal areas. The exposed specimens were kept at humid medium before SSRT to reproduce active hydrogen entry influenced by the rust layer and to homogenize hydrogen distribution. The influences of exposure site and exposure time on Fracture stress have been investigated. The susceptibility of B15 to Delayed Fracture was obviously higher than that of B13.
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Atomic force microscopy of induction- and furnace-heating-tempered prestressed steels with different Delayed Fracture properties
Scripta Materialia, 2002Co-Authors: Masao Hayakawa, Kaneaki Tsuzaki, Saburo Matsuoka, Hitoshi Hanada, Masayasu SugisakiAbstract:Abstract Quantitative microstructure analyses by atomic force microscope and Delayed Fracture tests were performed for two types of prestressed steel with a tensile strength of 1470 MPa; an induction-heated-tempered specimen, and a furnace-heated-tempered specimen. Size distributions of cementite particles were measured to characterize the relationship between microstructures and Delayed Fracture properties.
Sunghak Lee - One of the best experts on this subject based on the ideXlab platform.
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Residual Stress Effect on the Delayed Fracture of Twinning-Induced Plasticity Steels
Metallurgical and Materials Transactions A, 2017Co-Authors: Jung Gi Kim, Jae Ik Yoon, Seung Mi Baek, Min Hong Seo, Won Tae Cho, Kwang-geun Chin, Sunghak Lee, Hyoung Seop KimAbstract:Residual stress effect of the deep drawn TWIP steel on Delayed Fracture was investigated. Microstructural features of the TWIP steels did not change after stress relief annealing, while the elastic lattice strain dropped to 0.0007. Delayed Fracture of the drawn TWIP steel occurred after 203 hours of HCl immersion testing, but did not occur in the annealed one. It is clear that residual stress after the drawing is the primary reason for the Delayed Fracture of TWIP steels.
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Effects of Annealing Treatment Prior to Cold Rolling on Delayed Fracture Properties in Ferrite-Austenite Duplex Lightweight Steels
Metallurgical and Materials Transactions A, 2016Co-Authors: Seok Su Sohn, Jung Gi Kim, Hyoung Seop Kim, Hyejin Song, Jai-hyun Kwak, Sunghak LeeAbstract:Tensile properties of recently developed automotive high-strength steels containing about 10 wt pct of Mn and Al are superior to other conventional steels, but the active commercialization has been postponed because they are often subjected to cracking during formation or to the Delayed Fracture after formation. Here, the Delayed Fracture behavior of a ferrite-austenite duplex lightweight steel whose microstructure was modified by a batch annealing treatment at 1023 K (750 °C) prior to cold rolling was examined by HCl immersion tests of cup specimens, and was compared with that of an unmodified steel. After the batch annealing, band structures were almost decomposed as strong textures of {100}〈011〉 α-fibers and {111}〈112〉 γ-fibers were considerably dissolved, while ferrite grains were refined. The steel cup specimen having this modified microstructure was not cracked when immersed in an HCl solution for 18 days, whereas the specimen having unmodified microstructure underwent the Delayed Fracture within 1 day. This time Delayed Fracture was more critically affected by difference in deformation characteristics such as martensitic transformation and deformation inhomogeneity induced from concentration of residual stress or plastic strain, rather than the difference in initial microstructures. The present work gives a promise for automotive applications requiring excellent mechanical and Delayed Fracture properties as well as reduced specific weight.
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effects of intergranular carbide precipitation on Delayed Fracture behavior in three twinning induced plasticity twip steels
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: Seokmin Hong, Kwang-geun Chin, Hyoung Seop Kim, Junghoon Lee, Byeongjoo Lee, Sungkyu Kim, Sunghak LeeAbstract:Abstract The Delayed Fracture behavior related with intergranular carbide precipitation of three TWinning Induced Plasticity (TWIP) steels was investigated. According to the microstructural analysis, nano-sized (Fe,Mn) 3 C cementites were precipitated along grain boundaries in the 0.6C–22Mn and 0.6C–18Mn steels, whereas their precipitation was hardly observed in the 0.6C–18Mn–2Al steel, which was confirmed by equilibrium phase diagrams calculated from a ThermoCalc program. When cup specimens were dipped in the boiled water, the 0.6C–22Mn, 0.6C–18Mn, and 0.6C–18Mn–2Al steel cups were cracked after 5.5, 15, and 169 h, respectively. The Delayed Fracture regions consisted of intergranular facets, and the tendency of intergranular facture decreased in the order of 0.6C–22Mn, 0.6C–18Mn, and 0.6C–18Mn–2Al steels. Thus, the Delayed Fracture behavior was closely related with the intergranular Fracture mode caused by grain boundary cementites. The addition of Al remarkably increased the resistance to Delayed Fracture because it suppressed the formation of grain boundary cementites and reduced the residual stresses in the cup specimen.
Kenichi Takai - One of the best experts on this subject based on the ideXlab platform.
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Effect of Plastic Strain and Preloading on Delayed Fracture Characteristics of High Strength Steel
Tetsu-to-Hagane, 2011Co-Authors: Yukito Hagihara, Noriyuki Hisamori, Hiroshi Suzuki, Tsuyoshi Oba, Kenichi TakaiAbstract:Plastic strain takes place at the bottom of the thread, when fastening force is applied to the high strength bolts. The effect of plastic strain on the Delayed Fracture characteristics was studied using conventional strain rate test (CSRT). For this purpose two kinds of methods were used in the experiments: one is applying uniform plastic strain to the specimen before machining notch and the other is preloading of notched round bar (NRB) specimen. The hydrogen content increased as increasing plastic strain and in contrast, the relationship between Fracture stress and hydrogen content using CSRT was independent of plastic strain, which indicates that plastic strain increases hydrogen content and results in decreasing Fracture stress based on the above-mentioned relation. On the contrary, the preloading affected the Fracture nominal stress obtained by CSRT of hydrogen precharged NRB specimen. Using finite element stress analysis, the maximum stress ahead of the notch tip for preloaded NRB specimen was obtained. The relationship between the Fracture maximum stress and hydrogen concentration becomes unique irrespective preloading. It is concluded that the relation of local maximum stress—the hydrogen concentration at the Delayed Fracture initiation site is the material constant and control Delayed Fracture.
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Probabilistic and Statistical Evaluation of Delayed Fracture Characteristics Obtained by CSRT Method
Tetsu-to-Hagane, 2009Co-Authors: Yukito Hagihara, Chikahito Ito, Daizen Kirikae, Noriyuki Hisamori, Hiroshi Suzuki, Kenichi TakaiAbstract:The Delayed Fracture characteristics of steels are expressed by the relationship between the maximum Fracture stress and the hydrogen content at the notch tip of circumferentially notched round bar specimen, where Delayed Fracture initiates. This material constant is easily obtained by CSRT (Conventional Strain Rate Technique) method. The CSRT tests with the notch tip radius of 0.1, 0.25 or 0.8 mm were carried out on the high strength steel having 1300 MPa in tensile strength. Based on the probabilistic and statistical evaluation of the CSRT test results, the specimen with the notch root radius of 0.25 mm gives stable and average results of all experiments. Moreover, this notch geometry has the comparable stress concentration factor to the bottom of the actual bolt screw and easily machined with high accuracy. From these points of view the 0.25 mm radius notch is considered to become the standard specimen geometry. The scattering of Delayed Fracture characteristics was evaluated by applying the P–S–N method of fatigue test and the P–S–H method was demonstrated.
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evaluation of Delayed Fracture characteristics of high strength steel based on csrt method
Tetsu To Hagane-journal of The Iron and Steel Institute of Japan, 2008Co-Authors: Yukito Hagihara, Kenichi Takai, Chikahito Ito, Noriyuki Hisamori, Hiroshi Suzuki, Eiji AkiyamaAbstract:A conventional strain rate technique (CSRT) to evaluate the Delayed Fracture characteristics of high strength steels has been proposed. The critical “maximum stress—diffusible hydrogen concentration” at the Delayed Fracture initiation point near the notch tip is thought to be a material constant, which was originally demonstrated using the SSRT (slow strain rate technique) test method. The SSRT method takes hours to complete the test and uses a special test machine, which causes difficulty and complication. Therefore, a simple and conventional test technique, CSRT test method for Delayed Fracture was investigated. The crosshead speed is around 1 mm/min, so that the stress induced diffusion of hydrogen is negligible. The results obtained are as follows.(1) Since the stress induced hydrogen diffusion does not take place during the CSRT test, it is necessary to introduce the amount of hydrogen in the specimen, corresponding to the accumulated hydrogen at the vicinity of the notch tip region in the SSRT test. The electrochemical hydrogen charging conditions were established to introduce a wide range of hydrogen contents into the specimens.(2) A unique relationship between the maximum stress at the vicinity of the notch tip and hydrogen contents was obtained irrespective of the notch configuration using the CSRT test and FEM stress analysis. Therefore, it can be said that this relation is the material constants for Delayed Fracture.
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Enhanced susceptibility to Delayed Fracture in pre-fatigued martensitic steel
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: M. Nagumo, S Sekiguchi, H Hayashi, Kenichi TakaiAbstract:Interaction between fatigue damage and hydrogen is the concern of the present study. The susceptibility of a high-strength martensitic steel to Delayed Fracture has been examined using as-heat-treated and pre-fatigued specimens. The pre-fatigued specimens showed a tendency to fail earlier, but annealing the pre-fatigued specimens at 200 °C recovered nearly all of the Delayed Fracture life. Production of point defects during fatigue was detected by means of hydrogen thermal desorption analysis (TDA), using hydrogen as a probe of defects. Hydrogen absorption capacity increased in fatigued specimens, but it was reduced to the level of the as-heat-treated specimens when fatigued specimens were annealed at 200 °C, implying that increased hydrogen-trapping defects, presumably vacancies, were produced during fatigue. Hydrogen TDA peak profiles showed alterations that imply agglomeration of vacancies associated with an increase in fatigue cycles. The involvement of vacancies created during fatigue in the enhanced Delayed Fracture is consistent with a model that proposes strain-induced vacancies and their agglomeration are the primary mechanism of hydrogen-related failure.
Shushi Ikeda - One of the best experts on this subject based on the ideXlab platform.
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effects of aluminum on Delayed Fracture properties of ultra high strength low alloy trip aided steels
Isij International, 2008Co-Authors: Tomohiko Hojo, Kohichi Sugimoto, Youichi Mukai, Shushi IkedaAbstract:To improve the Delayed Fracture strength of ultra high-strength low alloy TRIP-aided steels with bainitic ferrite matrix (TBF steels), the effects of aluminum content on hydrogen absorption behavior and Delayed Fracture properties of 0.2%C–0.2–1.5%Si–1.5%Mn TBF steel were investigated. When aluminum was added to the TBF steel, the diffusible hydrogen increased. It was expected that the hydrogen was charged not only in retained austenite films but also on lath boundary. Delayed Fracture strength of TBF steels containing aluminum were significantly increased, compared with conventional TBF steel. This was mainly caused by (1) suppression of the stress-assisted martensite transformation resulting from the stabilized or carbon-enriched retained austenite, (2) hydrogen trapping to refined interlath retained austenite films and lath boundary, and (3) relaxation of localized stress concentration by TRIP effect of the retained austenite.
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effects of aluminum on Delayed Fracture properties of ultra high strength low alloy trip aided steels
Tetsu To Hagane-journal of The Iron and Steel Institute of Japan, 2007Co-Authors: Tomohiko Hojo, Kohichi Sugimoto, Youichi Mukai, Shushi IkedaAbstract:To improve the Delayed Fracture strength of ultra high-strength low alloy TRIP-aided steels with bainitic ferrite matrix (TBF steels), the effects of aluminum content on hydrogen absorption behavior and Delayed Fracture properties of 0.2%C-0.5∼1.5%Si-1.5%Mn TBF steel were investigated. When aluminum was added to the TBF steel, the diffusible hydrogen increased. It was expected that the hydrogen was charged not only in retained austenite films but also on lath boundary. Delayed Fracture strength of aluminum bearing TBF steels was significantly increased, compared with conventional TBF steel. This was mainly caused by (1) suppression of the stress-assisted martensite transformation resulting from the stabilized or carbon-enriched retained austenite, (2) hydrogen trapping to refined interlath retained austenite films and lath boundary, and (3) relaxation of localized stress concentration by TRIP effect of the retained austenite.