Songjie Li

Studies of Evaluation of Hydrogen Embrittlement Property of High-Strength Steels with Consideration of the Effect of Atmospheric Corrosion

Hydrogen embrittlement of high-strength steels was investigated by using slow strain rate test (SSRT) of circumferentially notched round bar specimens after hydrogen precharging. On top of that, cyclic corrosion tests (CCT) and outdoor exposure tests were conducted prior to SSRT to take into account the effect of hydrogen uptake under atmospheric corrosion for the evaluation of the susceptibility of high-strength steels. Our studies of hydrogen embrittle properties of high-strength steels with 1100 to 1500 MPa of tensile strength and a prototype ultrahigh-strength steel with 1760 MPa containing hydrogen traps using those methods are reviewed in this article. A power law relationship between notch tensile strength of hydrogen-precharged specimens and diffusible hydrogen content has been found. It has also been found that the local stress and the local hydrogen concentration are controlling factors of fracture. The results obtained by using SSRT after CCT and outdoor exposure test were in good agreement with the hydrogen embrittlement fracture property obtained by means of long-term exposure tests of bolts made of the high-strength steels.

Hydrogen embrittlement property of a 1700-MPa-class ultrahigh-strength tempered martensitic steel

Abstract The hydrogen embrittlement property of a prototype 1700-MPa-class ultrahigh-strength steel (NIMS17) containing hydrogen traps was evaluated using a slow strain rate test (SSRT) after cathodic hydrogen precharging, cyclic corrosion test (CCT) and atmospheric exposure. The hydrogen content in a fractured specimen was measured after SSRT by thermal desorption spectroscopy (TDS). The relationship between fracture stress and hydrogen content for the hydrogen-precharged specimens showed that the fracture stress of NIMS17 steel was higher, at a given hydrogen content, than that of conventional AISI 4135 steels with tensile strengths of 1300 and 1500 MPa. This suggests better resistance of NIMS17 steel to hydrogen embrittlement. However, hydrogen uptake to NIMS17 steel under CCT and atmospheric exposure decreased the fracture stress. This is because of the stronger hydrogen uptake to the steel containing hydrogen traps than to the AISI 4135 steels. Although NIMS17 steel has a higher strength level than AISI 4135 steel with a tensile strength of 1500 MPa, the decrease in fracture stress is similar between these steels.

Electrochemical hydrogen permeation tests under galvanostatic hydrogen charging conditions conventionally used for hydrogen embrittlement study

Abstract Electrochemical hydrogen permeation tests using pure Fe sheet specimens were performed under various galvanostatic hydrogen charging conditions commonly applied to tensile test specimens used for evaluation of hydrogen embrittlement property to obtain a guideline for efficient hydrogen charging method for a wide range of hydrogen content. Aqueous NaCl solutions containing varied concentrations of ammonium thiocyanate and a 0.1-m NaOH solution were used as electrolytes for relatively high and low hydrogen content, respectively. Addition of ammonium thiocyanate changes the mechanism of hydrogen evolution reaction and enhances hydrogen entry. By changing the concentration of ammonium thiocyanate and by changing cathodic current density, a wide range of hydrogen content can be covered. The hydrogen content in an AISI 4135 steel estimated from hydrogen permeation current density obtained for a pure Fe specimen was in good agreement with the hydrogen content experimentally measured by hydrogen thermal desorption analysis for the AISI 4135 steel. The hydrogen permeation current density data in various hydrogen charging conditions can be used as a reference for hydrogen charging of specimens.