Evaluation of Hydrogen Embrittlement for High Strength Steel Sheets

Abstract

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 in the studies of high strength steel bolts. However, there are few detailed reports investigating the influence of these factors on hydrogen embrittlement of steel sheets quantitatively. In this study, the influence of plastic strain, as well as stress and diffusible hydrogen content, on hydrogen embrittlement of steel sheet was quantitatively studied to evaluate the hydrogen embrittlement susceptibility of steel sheet by using an 1180 MPa grade cold rolled dual phase steel sheet. Plastic strain was introduced by U-shape bending, and stress was applied by tightening the bent specimen with a bolt. Then, hydrogen was introduced by dipping in hydrochloric acid, and the time to fracture and the content of diffusible hydrogen entered into steel during dipping were investigated. The fracture was promoted by severe deformation near the bending limit, 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 were 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 3D map and the service conditions of the parts.

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

“…Table 1 shows studies concerning the evaluation of hydrogen embrittlement properties in UHSS sheets. 4,5,8,[12][13][14][15][16][17][18][19][20] The most widely-used evaluation method for UHSS sheets is the U-bending method. This method is used because UHSS sheets are generally applied to door impact beams and bumper reinforcements, which are mainly formed by bending.…”

“…Our research group has been evaluating the hydrogen embrittlement resistance of UHSS sheets by various methods. [4][5][6][7][8][9][10][11] This paper introduces those results, and suggests the scope of future work in this field with the aim of promoting the application of UHSS sheets.…”

“…uation of Automotive UHSS Sheets 1,4,5) First, the aim of hydrogen embrittlement evaluation of automotive UHSS sheets will be explained. The controlling factors in hydrogen embrittlement fracture of HSS bolts are stress, diffusible hydrogen content and material characteristics, for example, material strength, microstructures and applied strain.…”

“…Content on Hydrogen Embrittlement Resistance of 1 180 MPa Grade Dual Phase Steel Evaluated by Ubend Test [4][5][6] The hydrogen embrittlement resistance of 1 180 MPa grade dual phase steel (1180DP) with a thickness of 1.6 mm was evaluated. The microstructure and mechanical properties of 1180DP are shown in Fig.…”

Application of NH4SCN Aqueous Solution to Hydrogen Embrittlement Resistance Evaluation of Ultra-high Strength Steels

“…">BackgroundIt is well known that the risk of hydrogen embrittlement fracture becomes significant when ultra-high strength steels (UHSS) with tensile strength over 980 MPa are used in atmospheric corrosion environments.1,2) Recently, application of UHSS sheets to automobiles has increased as a means of reducing auto body weight.3) Although the hydrogen embrittlement resistance of UHSS sheets has been evaluated by various methods, [4][5][6][7][8][9][10][11][12] it is difficult to predict the risk of hydrogen embrittlement fracture quantitatively. In order to expand the automotive applications of UHSS sheets, precise prediction of the risk of hydrogen embrittlement fracture is important.…”