Evaluation of the influence of hydrogen on some commercial DP, Q&P and TWIP advanced high-strength steels during automobile service

Abstract

The hydrogen influence was evaluated (A) for laboratory conditions with hydrogen concentrations larger than in service, and (B) at substantial loading rates to simulate a crash. Hydrogen in the studied laboratory conditions caused minimal influence for 980DP and 1200DP, and some influence for 980DP-650YS, 980DP-700YS, 980QP and 950TW. Simulated crash situations caused some influence for 980DP, 980QP and 950TW; their properties quickly reverted after the end of hydrogen charging. Two new mechanisms are proposed: (i) hydrogen enhanced macroscopic plasticity (HEMP) decreasing the yield stress, and (ii) hydrogen assisted micro-fracture (HAM) decreasing ductility at fracture at the ultimate tensile strength.

The role of the microstructure on the influence of hydrogen on some advanced high-strength steels

“…However, these AHSS may be influenced by hydrogen [5], which may cause decreased mechanical strength and decreased ductility [6][7][8][9][10]. Our previous research [11,12] showed that the influence of hydrogen on some commercial DP, Q&P and TWIP steels was manifested by (i) a somewhat decreased yield strength (by 1% to 20%), (ii) a reduced ductility caused by hydrogen assisted fracture processes occurring after the onset of necking at the ultimate tensile strength of the steel. Furthermore, the magnitude of the hydrogen influence increased with increasing strength, decreasing applied stress rate, and increasing hydrogen fugacity.…”

“…Furthermore, inclusions have been also shown to decrease the hydrogen embrittlement (HE) resistance of steels [9,15,16]. This literature indicates that it is useful to analyse the role of microstructure on the influence of hydrogen on the commercial DP, Q&P and TWIP steels studied in our prior research [11,12,[17][18][19].…”

UQ eSpace

“…Hydrogen caused a reduction in the UTS but fracture only occurred once the applied stress had reached the UTS [11]. This indicates that some mechanisms that promote subcritical cracks, often associated with hydrogen embrittlement, are not directly applicable [11,15]. ii.…”

“…ii. Hydrogen assisted micro-fracture (HAM): Hydrogen causes a change in microfracture mode from a ductile to brittle fracture that is initiated at the specimen surface during the final fast fracture [15].…”

“…For tests conducted at E Zinc and E Corr , specimens required charging and prestressing as discussed below.The voltage was measured across the gauge section of the specimen due to a supplied 3A current for the potential drop technique (Section 3.4). Upon failure of the test specimen, the mass displacement ruler was used to determine the ultimate tensile stress using Equation 4 obtained from previous LIST research[15]. Distance to fracture (m), = Cross-sectional Area (m 3 )…”