Delayed Fracture Properties of 1500 MPa Bainite/Martensite Dual-phase High Strength Steel and Its Hydrogen Traps.

Gu, Jianfeng; Chang, Kaidi; Fang, Hongwei; Bai, Bin

doi:10.2355/isijinternational.42.1560

Cited by 49 publications

(22 citation statements)

References 7 publications

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“…The lath boundary is able to become a valid hydrogen trapping site 24) as well as retained austenite. So, it is considered that the hydrogen exists uniformly and hydrogen concentration at the grain boundary was decreased in the steels containing aluminum because of hydrogen trapping on refined lath boundary and in retained austenite.…”

Section: High Delayed Fracture Strength Of Tbf Steelmentioning

confidence: 99%

“…It was reported by Tsubakino et al 11) that the hydrogen which evolved at about 100°C corresponded to hydrogen trapping at grain boundaries, at carbide/matrix interfaces, on dislocations and on vacancies, and a peak of about 130°C was hydrogen evolved from retained austenite. Furthermore it was pointed out by Gu et al 24) that an increase of lath boundary area led to increase in the hydrogen trapping site in 1 500 MPa grade bainite/martensite dual-phase steels containing retained austenite. The lath microstructure of TBF steel was refined by aluminum addition, with refined lath structure (Fig.…”

Section: Effect Of Alloying Elements On Hydrogen Absorption Propertiesmentioning

confidence: 99%

See 1 more Smart Citation

Effects of Aluminum on Delayed Fracture Properties of Ultra High Strength Low Alloy TRIP-aided Steels

et al. 2008

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Section: High Delayed Fracture Strength Of Tbf Steelmentioning

confidence: 99%

Section: Effect Of Alloying Elements On Hydrogen Absorption Propertiesmentioning

confidence: 99%

Effects of Aluminum on Delayed Fracture Properties of Ultra High Strength Low Alloy TRIP-aided Steels

et al. 2008

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“…This high level of sensitivity is probably due to the final microstructure obtained as a result of very high cooling rate. After water quenching, no tempered martensite is observed and the mechanical properties are significantly high that lowers critical level of diffusible hydrogen 8) to initiate the crack. However, it is worth noting that this is only a potential risk before e-coating as according to the present research the baking treatment at 170°C associated with the e-coating process reduces the hydrogen content, in our experiment from 0.8 to 0.1 ppm, and tempers the as quenched microstructure.…”

Section: Mechanical Testsmentioning

confidence: 99%

“…Previous investigations have shown that a critical combination of factors govern the occurrence of the delayed fracture: the presence of diffusible hydrogen, 3,4) the rise of applied or residual stresses 5,6) to a sufficient level during assembling for example and other metallurgic factors such as the chemical composition or the steel. [7][8][9][10] As metallurgy and the stresses are usually driven by the process, uncontrolled hydrogen charging must be avoided to obtain safe products, especially when a coating hinders hydrogen escaping from the steel. 11,12) Thermal desorption analysis, TDA, has been largely applied for the study of the diffusible hydrogen in bare iron and steels.…”

Section: Introductionmentioning

confidence: 99%

Absorption/Desorption of Diffusible Hydrogen in Aluminized Boron Steel

Georges¹,

Sturel

Drillet

et al. 2013

ISIJ Int.

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Currently, boron steel with Al-Si coating experiences a rapid growth in the anti-intrusion applications in the car body due to its superior mechanical properties after hot stamping. However, the final microstructure can be sensitive to delayed fracture if the product is exposed to a critical combination of diffusible hydrogen content, stresses and other metallurgical factors. As the metallurgical parameters and stresses are usually defined, the proper control of the diffusible hydrogen content is the key parameter to improve the safety aspect of the product. However, this content is quite difficult to determine. In this paper, the parameters governing the absorption and desorption of diffusible hydrogen in aluminized boron steels is investigated. The present research shows that the dew point and the austenitizing holding time have a bigger influence on the diffusible hydrogen content than the austenitizing temperature. Simultaneously, four-point bending test, which is simple and representative of the stress field that may be encountered in car bodies, is used to determine the acceptable limit of the diffusible hydrogen amount. Using this test, a delayed fracture map is proposed, which can be used as a guideline to determine the safe process areas. The study reveals that fast cooling rates or the sheared edges lead to lower the critical diffusible hydrogen content. Nevertheless, under the standard industrial operating conditions, the materials remain safe. Finally, an e-coating process that is applied to the sample surface induces an efficient degassing that provides an additional safety margin.KEY WORDS: aluminizing boron steel; delayed fracture; hot stamping; diffusible hydrogen; bending test; thermal desorption analysis.

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“…Unless the concrete value of migration energy is known, accurate evaluation of the binding energy between hydrogen and dislocation have not been conducted so far. Gu et al 30) also calculated the binding energy of bainite or martensite lath boundaries as 28.1 kJ · mol…”

Section: Activation Energy For Hydrogen Desorptionmentioning

confidence: 99%

Absorption of Hydrogen in High-strength Low-alloy Steel during Tensile Deformation in Gaseous Hydrogen

Takasawa¹,

Ishigaki²,

Wada³

et al. 2010

ISIJ Int.

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Absorption of hydrogen in a high-strength nickel-chromium-molybdenum steel during tensile deformation in 0.5 MPa gaseous hydrogen was examined using a thermal desorption analysis method. The tensile strength of the specimen was varied in the range from 1 214 to 947 MPa by heat treatment. The dislocation density of the specimens was measured by X-ray diffractometry after tensile testing in a hydrogen atmosphere. The hydrogen content absorbed during tensile deformation increased with increasing tensile strain in proportional elastic range until just before yielding. The yield stress was defined as 0.2 % proof stress in this work. At the same tensile strains, the hydrogen content of lower-strength specimens was larger than that of higher-strength specimens. The dislocation density gradually decreased until just before yielding, corresponding to the proportional increase of hydrogen content to the tensile strain. This implies that the hydrogen absorption behavior during tensile deformation in gaseous hydrogen is related to the motion of mobile dislocations initially contained in the specimens. The activation energy for desorption of hydrogen absorbed during tensile deformation did not depend on the strength of the steel. This indicates that the trap sites of hydrogen atoms created through the tensile deformation were the same regardless of the strength levels.

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Delayed Fracture Properties of 1500 MPa Bainite/Martensite Dual-phase High Strength Steel and Its Hydrogen Traps.

Cited by 49 publications

References 7 publications

Effects of Aluminum on Delayed Fracture Properties of Ultra High Strength Low Alloy TRIP-aided Steels

Effects of Aluminum on Delayed Fracture Properties of Ultra High Strength Low Alloy TRIP-aided Steels

Absorption/Desorption of Diffusible Hydrogen in Aluminized Boron Steel

Absorption of Hydrogen in High-strength Low-alloy Steel during Tensile Deformation in Gaseous Hydrogen

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