Parameters for the Evaluation of Hydrogen Embrittlement of High Strength Steel

Takagi, Shusaku; Inoue, Tatsuo; Hara, Toru; Hayakawa, Masayuki; Tsuzaki, Kaneaki; Takahashi, Toshihiko

doi:10.2355/tetsutohagane1955.86.10_689

Cited by 67 publications

(24 citation statements)

References 12 publications

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“…The Constant Loading Test (CLT), 22,23) Slow Strain Rate Technique (SSRT) 24) and Conventional Strain Rate Test (CSRT), [25][26][27] which are major evaluation methods in the field of UHSS bolts, have been minor methods in the field of UHSS sheets. Presumably, these methods are not widely used with UHSS sheets because only uniaxial deformation test can be conducted by those methods and it is more difficult to predict the risk of hydrogen embrittlement fracture in actual parts with considering the influence of forming modes.…”

Section: Methods Of Evaluating Hydrogen Embrittlement Resistance Of Amentioning

confidence: 99%

Hydrogen Embrittlement Resistance Evaluation of Ultra High Strength Steel Sheets for Automobiles

Takagi¹,

Toji²,

Yoshino³

et al. 2012

ISIJ Int.

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When ultra high strength steel (UHSS) sheets with tensile strength over 980 MPa are applied in automobiles, there is a risk that a type of hydrogen embrittlement fracture called delayed fracture may occur while a vehicle is in use. This paper summarizes the effects of stress, strain, diffusible hydrogen content and the forming mode on the hydrogen embrittlement resistance of UHSS sheets for automotive applications. In this study, 1 180 MPa grade ferrite-martensite dual phase steel was used. This material was evaluated by the U-bending and drawn cup methods. It was concluded that high strain, high stress and high diffusible hydrogen content reduced hydrogen embrittlement resistance.In addition, an improved immersion-type hydrogen charging method using an ammonium thiocyanate (NH4SCN) aqueous solution was introduced in this paper. The NH4SCN solution enables control of the diffusible hydrogen content from low to high concentrations using the NH4SCN concentration, and dissolution of the specimens during immersion in NH4SCN was minimal, making it possible to maintain substantially the same surface condition as before immersion.KEY WORDS: delayed fracture; equivalent strain; equivalent stress; diffusible hydrogen; U-bending; drawn cup; ammonium thiocyanate; immersion-type hydrogen charging method.

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Section: Methods Of Evaluating Hydrogen Embrittlement Resistance Of Amentioning

confidence: 99%

Hydrogen Embrittlement Resistance Evaluation of Ultra High Strength Steel Sheets for Automobiles

Takagi¹,

Toji²,

Yoshino³

et al. 2012

ISIJ Int.

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“…Mechanical properties of the steel used. [16][17][18][19][20] иииииииииииииииииииииииииииииииииииииии( 2 )…”

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Evaluation of Hydrogen Embrittlement for High Strength Steel Sheets

Toji¹,

Takagi²,

Yoshino³

et al. 2009

Tetsu-to-Hagane

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Synopsis :The risk of delayed fracture should be evaluated when applying ultra high strength steel sheets to automotive parts. Steel sheets for automobiles are usually formed into various parts by cold working. Therefore, plastic strain introduced by the cold working must be considered as a factor affecting the hydrogen embrittlement in addition to the applied stress and the content of diffusible hydrogen entered into steels, which are considered as factors affecting the hydrogen embrittlement of high strength steel bolts. In this study, the influence of plastic strain, as well as stress and diffusible hydrogen content, on hydrogen embrittlement of steel sheets was quantitatively studied by using an 1180 MPa grade cold rolled steel sheet. Plastic strain was introduced by U-shape bending. Stress was applied by tightening the bent specimen with a bolt. Then, hydrogen was introduced by immersing in hydrochloric acid. The time to fracture and the content of diffusible hydrogen entered into steel were investigated. The fracture was promoted by severe deformation, and it seemed to be caused by the presence of micro cracks and/or micro voids. The hydrogen cracking conditions region of the steel sheet was mapped in the three-dimensional space with the axes of applied strain, applied stress and diffusible hydrogen content. It was considered that the evaluation of the risk of delayed fracture of automotive parts made of the steel sheet under service environment was possible by a comparison of the hydrogen cracking conditions and the service conditions of the parts on the 3D space.

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“…H (t＝∞, 2) is the equilibrium value at 2nd step loading. 10) . The distributions of the s p are almost same in fracture process zone where the maximum principal stress exceeds 0.8 s p (peak).…”

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confidence: 99%

“…Fig. 11 Effect of the distribution of the maximum principal stress (s p ) on H D t curves 10) . The H D t curves are same under the same distribution of the s p .…”

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Determination Method of Weibull Shape Parameter for Evaluation of the Hydrogen Embrittlement Susceptibility of High Strength Steel

Takagi

Inoue

Tsuzaki

et al. 2001

J. Japan Inst. Metals and Materials

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An experimental method to obtain the shape parameter m in the Weibull stress for evaluation of hydrogen embrittlement (HE) was examined in a commercial JIS SCM440 steel with the tensile strength of 1403 MPa. The stepwise HE tests were performed by using circumferentially notched round bar specimens with the stress concentration factor of 4.9 after hydrogen pre charging and homogenization treatments. The applied stress of the first step loading was set at 702 MPa and the stress increment from the second step was 14 MPa. The holding time was over 12 h for the first step and over 2 h for each step from the second step. It was conformed by acoustic emission measurement that the first cracking and final fracture occurred in the same step. The diffusible hydrogen content was measured by thermal desorption analysis immediately after fracture. The distribution of stress and hydrogen content near notch root was calculated by FE analysis. By this procedure, it was able to obtain the distribution of critical Weibull stress under the condition that the local diffusible hydrogen content in fracture process zone was constant. The shape parameter m was determined to be 46 for the present steel. In the discussion part, it was confirmed that the evaluation of the HE susceptibility based on the local approach is appropriate and it was pointed out that the hydrogen content distribution in the fracture process zone must be taken into account for evaluating the HE.

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Parameters for the Evaluation of Hydrogen Embrittlement of High Strength Steel

Cited by 67 publications

References 12 publications

Hydrogen Embrittlement Resistance Evaluation of Ultra High Strength Steel Sheets for Automobiles

Hydrogen Embrittlement Resistance Evaluation of Ultra High Strength Steel Sheets for Automobiles

Evaluation of Hydrogen Embrittlement for High Strength Steel Sheets

Determination Method of Weibull Shape Parameter for Evaluation of the Hydrogen Embrittlement Susceptibility of High Strength Steel

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