Hydrogen Embrittlement of Automotive Advanced High-Strength Steels

Abstract

Advanced High Strength Steels (AHSS) have a better combination between strength and ductility than conventional HSS and higher crash resistances are obtained in concomitance with weight reduction of car structural components. These steels have been developed in last decades and their use is rapidly increasing. Notwithstanding, some their important features have to be still understood and studied in order to completely characterize their service behavior. In particular, the high mechanical resistance of AHSS makes hydrogen related problems a great concern for this steel grades. This paper investigates the hydrogen embrittlement (HE) of four AHSS steels. The behavior of one TRIP, two martensitic with different strength levels and one hot stamping steels have been studied using Slow Strain Rate Tensile (SSRT) tests on electrochemically hydrogenated notched samples. The embrittlement susceptibility of these AHSS steels has been correlated mainly to their strength level and to their microstructural features. Finally, the hydrogen critical concentrations for HE, established by SSRT tests, have been compared to Hydrogen contents absorbed during the painting process of Body In White (BIW) structure, experimentally determined during a real cycle in an industrial plant.

Corrosion resistance of high-Mn austenitic steels for the automotive industry

“…Due to the slow diffusion rate of hydrogen in austenite, it is hardly to enrich it homogeneously to a hydrogen content causing embrittlement. However, it was shown (Lovicu et al, 2010) that the hydrogen concentration in surface regions of the high-Mn steel is much higher than in the centre zone. It can lead to the intragranular fracture in these regions because of strain-induced or hydrogen-induced martensitic transformation and finally to reduction of strength and ductility.…”

“…If hydrogen content reaches the critical value, it can induce a reduction of strength and ductile properties. A critical concentration of hydrogen is various for different steels (Lovicu et al, 2010;Sojka et al, 2010). Hydrogen embrittlement is usually investigated by performing slow strain rate tensile tests on hydrogenerated samples.…”

Resistance of Hydrogen Embrittlement on Hot-sheared Surface during Die-quench Process

“…In addition to the cost-effectiveness problem, shearing of high strength materials like quenched steels risks hydrogen embrittlement cracking. [4][5][6] Actually, cold-sheared surface of a quenched steel sheet is cracked under the conditions of higher diffusible hydrogen density and residual tensile stress than their criteria. 7,8) To solve the above tasks, hot-shearing has been developed in recent years.…”

Determination of the fatigue fracture characteristics of steel MS1700 under corrosion conditions

“…Applying a tensile stress to steel in a hydrogen atmosphere can lead to brittle fracture. High-strength steels have been proved to be vulnerable to hydrogen embrittlement (Hirth, 1980;Depover et al, 2014;Nagumo et al, 2003), particularly, those containing high levels of martensite in their microstructure (Depover et al, 2014.;Lovicu et al, 2012;Rehrl et al, 2014). This has been attributed, amongst others, to their natural lack of ductility, the embrittlement caused by the strain-induced phase transformation from retained austenite to martensite (Wang et al, 2014;Solheim et al, 2013) and the high diffusivity of hydrogen in the martensite lattice.…”

“…A major problem with MS-AHSS is its susceptibility to hydrogen embrittlement (HE), which is slowing down the development of these materials (Lovicu et al, 2012). The presence of small amounts of hydrogen in steel can influence negatively the mechanical properties of the steel.…”