Investigation of Mechanical Tests for Hydrogen Embrittlement in Automotive PHS Steels

Hydrogen was doped in austenitic stainless steel (ASS) 316L tensile samples produced by the laser-powder bed fusion (L-PBF) technique. For this aim, an electrochemical method was conducted under a high current density of 100 mA/cm2 for three days to examine its sustainability under extreme hydrogen environments at ambient temperatures. The chemical composition of the starting powders contained a high amount of Ni, approximately 12.9 wt.%, as a strong austenite stabilizer. The tensile tests disclosed that hydrogen charging caused a minor reduction in the elongation to failure (approximately 3.5% on average) and ultimate tensile strength (UTS; approximately 2.1% on average) of the samples, using a low strain rate of 1.2 × 10−4 s−1. It was also found that an increase in the strain rate from 1.2 × 10−4 s−1 to 4.8 × 10−4 s−1 led to a reduction of approximately 3.6% on average for the elongation to failure and 1.7% on average for UTS in the pre-charged samples. No trace of martensite was detected in the X-ray diffraction (XRD) analysis of the fractured samples thanks to the high Ni content, which caused a minor reduction in UTS × uniform elongation (UE) (GPa%) after the H charging. Considerable surface tearing was observed for the pre-charged sample after the tensile deformation. Additionally, some cracks were observed to be independent of the melt pool boundaries, indicating that such boundaries cannot necessarily act as a suitable area for the crack propagation.

Section: Methodsmentioning

confidence: 96%

Effect of Hydrogen on the Tensile Behavior of Austenitic Stainless Steels 316L Produced by Laser-Powder Bed Fusion

Khaleghifar¹,

Razeghi²,

Heidarzadeh

et al. 2021

“…In this study, the average content of each element in the steels was used. The four-point bending cathode charging technique [5,8,14] was adopted to evaluate the hydrogen embrittlement properties of the steels using rectangular specimens of 65 mm in length, 10 mm in width, and 1.2 mm in thickness, with hydrogen charging in a 0.5 mol H 2 SO 4 (FUJIFILM Wako Pure Chemical Co. Ltd., Sulfuric Acid, Japan) + 0.01 mol NH 4 SCN (FUJIFILM Wako Pure Chemical Co. Ltd., Ammonium Thiocyanate, Japan) solution at 25 • C at a current density of 100 A/m 2 . Hydrogen embrittlement properties were evaluated by delayed fracture strength (DFS), which is the maximum bending stress that does not cause failure of the specimen for 5 h.…”

Section: Methodsmentioning

confidence: 99%

Effects of Alloying Elements Addition on Delayed Fracture Properties of Ultra High-Strength TRIP-Aided Martensitic Steels

Hojo

Kobayashi

Sugimoto

et al. 2019

To develop ultra high-strength cold stamping steels for automobile frame parts, the effects of alloying elements on hydrogen embrittlement properties of ultra high-strength low alloy transformation induced plasticity (TRIP)-aided steels with a martensite matrix (TM steels) were investigated using the four-point bending test and conventional strain rate tensile test (CSRT). Hydrogen embrittlement properties of the TM steels were improved by the alloying addition. Particularly, 1.0 mass% chromium added TM steel indicated excellent hydrogen embrittlement resistance. This effect was attributed to (1) the decrease in the diffusible hydrogen concentration at the uniform and fine prior austenite grain and packet, block, and lath boundaries; (2) the suppression of hydrogen trapping at martensite matrix/cementite interfaces owing to the suppression of precipitation of cementite at the coarse martensite lath matrix; and (3) the suppression of the hydrogen diffusion to the crack initiation sites owing to the high stability of retained austenite because of the existence of retained austenite in a large amount of the martensite–austenite constituent (M–A) phase in the TM steels containing 1.0 mass% chromium.

“…(Hc crit ) [21]. An analytical representation of the critical hydrogen concentration can be described with an 'atan' function in form of Equation ( 1):…”

Section: Constant Extention Rate Test (Cert)mentioning

confidence: 99%

“…This is a difficult task to perform because many variables considering that factors like chemistry, microstructure, metallurgical defects, operating temperatures, and stress states simultaneously affect the sensitivity of steel to hydrogen. It is widely reported in literature [20][21][22][23][24] that the degradation of mechanical properties of steels in the presence of hydrogen occurs only when hydrogen reaches a certain critical concentration in the steel. Hence the critical hydrogen concentration (H crit ) was proposed as a parameter to evaluate the hydrogen embrittlement property of high-strength steels [23,24].…”

Section: Introductionmentioning

confidence: 99%

Determination of Critical Hydrogen Concentration and Its Effect on Mechanical Performance of 2200 MPa and 600 HBW Martensitic Ultra-High-Strength Steel

Fangnon

Yagodzinskyy

Malictki

et al. 2021

The influence of hydrogen on the mechanical performance of a hot-rolled martensitic steel was studied by means of constant extension rate test (CERT) and constant load test (CLT) followed with thermal desorption spectroscopy measurements. The steel shows a reduction in tensile strength up to 25% of ultimate tensile strength (UTS) at critical hydrogen concentrations determined to be about 1.1 wt.ppm and 50% of UTS at hydrogen concentrations of 2 wt.ppm. No further strength degradation was observed up to hydrogen concentrations of 4.8 wt.ppm. It was observed that the interplay between local hydrogen concentrations and local stress states, accompanied with the presence of total average hydrogen reducing the general plasticity of the specimen are responsible for the observed strength degradation of the steel at the critical concentrations of hydrogen. Under CLT, the steel does not show sensitivity to hydrogen at applied loads below 50% of UTS under continuous electrochemical hydrogen charging up to 85 h. Hydrogen enhanced creep rates during constant load increased linearly with increasing hydrogen concentration in the steel.