Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels
Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to delayed cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC) phases ferrite and α’-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No delayed cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α’-martensite increases the hydrogen-induced cracking susceptibility.
The Hydrogen Induced Mechanical Degradation of Duplex Stainless Steel
This study considers the interaction between duplex stainless steel type 2205 and electrochemically charged hydrogen. Duplex stainless steels combine the mechanical properties of ferrite with the corrosion resistance of austenite and are widely used in many industrial applications. However, they are susceptible to hydrogen embrittlement. In this work, the steel microstructure is first characterized by scanning and transmission electron microscopy, X‐ray diffraction, and electron backscatter diffraction. Subsequently, melt extraction is done to determine the amount of hydrogen charged into the material, while in situ hydrogen charged tensile tests are combined with a fractography analysis to evaluate the effect of hydrogen on the mechanical behavior. The material displays a rather significant ductility loss of about 26% as a result of the applied hydrogen charging. Melt extraction identifies the increased hydrogen content in the steel microstructure (up to 50 wppm). Moreover, the hydrogen embrittled regions correspond well to the hydrogen diffusion penetration depth from the edges onwards. These cleavage brittle areas are observed up to the theoretical hydrogen diffusion distance, demonstrating the hydrogen embrittlement effect.
Interaction of hydrogen with external stress fields
Abstract Measurements of the chemical potential of hydrogen at room temperature as a function of external tensile stress and torsional stress are presented for crystalline Pd, deformed Pd and amorphous PdSi alloys. The partial molar volume of hydrogen has also been measured for deformed Pd. As in amorphous PdSi alloys a volume contraction has been observed from 0 to 40 ppm H Pd with a partial molar volume of about −0.5 cm3/mole H. Above 40 ppm the partial molar volume increases from 0.9 to 1.4 cm3/mol H with increasing concentration. In the case of tension the change of the chemical potential is shown to be proportional to the applied stress and the partial molar volume of hydrogen. No change of the chemical potential occurred by applying torsional stress.