Effect of hydrogen charging on the mechanical properties of advanced high strength steels (original) (raw)
Related papers
Fracture criterion for hydrogen embrittlement of high strength steel
Materials Science and Technology, 2006
The notch tensile strength of a boron bearing steel at 1305 MPa has been investigated by means of slow strain rate tests after electrochemical hydrogen charging. Results show that the notch tensile strength of the steel decreased with increasing diffusible hydrogen content and the decrease in the notch tensile strength was more pronounced for specimens at a higher stress concentration factor. Finite element analysis results show that the dependence of the notch tensile strength on stress concentration factor cannot be accounted for by the local peak stress and local peak hydrogen concentration; however, the equivalent plastic strain at the notch root at an applied stress equal to the notch tensile strength was independent of stress concentration factor. The equivalent plastic strain at the notch root can be used as a fracture criterion for hydrogen embrittlement of the steel.
2012
The paper describes effect of hydrogen on mechanical properties and fracture characteristics of two variants of the TRIP 800 steels; C-Mn-Si variant and C-Mn-Si-Al variant. TRIP steels are very promising materials thanks to their combination of a very good strength and toughness. However, these steels can be embrittled by hydrogen during technological operations related to hot dip galvanizing. That is why the knowledge of effects of hydrogen on the properties and fracture characteristics of the TRIP steels is of particular importance. In the presented study, effects of hydrogen were studied by tensile tests at simultaneous electrolytical hydrogen charging. Special cells were used for this kind of testing. Electrolytical hydrogen charging was performed in diluted solutions of sulfuric acid. In some cases, potassium thiocyanate was added to the solution to promote hydrogen absorption. Hydrogen provoked embrittlement in both steel variants and changed their micromechanism of failure. T...
Effect of hydrogen on the fracture behavior of high strength steel during slow strain rate test
Corrosion Science, 2007
The effect of hydrogen on the fracture behavior of the quenched and tempered AISI 4135 steel at 1450 MPa has been investigated by means of slow strain rate tests on smooth and circumferentiallynotched round-bar specimens. Hydrogen was introduced into specimens by electrochemical charging and its content was measured by thermal desorption spectrometry (TDS) analysis. Results showed that the steel had high hydrogen embrittlement susceptibility. For both smooth and notched specimens, the fracture mode was changed from microvoid coalescence (MVC) to brittle intergranular (IG) fracture after the introduction of a small amount of diffusible hydrogen. Fracture initiated in the vicinity of the notch root for notched specimens, while it started from around the center in smooth specimens. The fracture stress decreased with increasing diffusible hydrogen content, and the decreasing trend was more prominent for specimens with a higher stress concentration factor. Taking into account the stress-driven hydrogen diffusion and accumulation in the vicinity of the notch root, the local diffusible hydrogen concentration and local fracture stress in notched specimens have been calculated. According to numerical results, the relationship between the local fracture stress and local diffusible hydrogen concentration was independent of stress concentration factor, which could account for the effect of hydrogen on the fracture stress of the steel.
Fracture toughness of hydrogen charged as-quenched ultra-high-strength steels at low temperatures
Materials Science and Engineering: A, 2017
The effect of hydrogen on the fracture and impact toughness of ultra-high-strength steels at sub-zero temperatures in the transition temperature region has been investigated with arctic applications in mind. Two types of as-quenched microstructure were studied, i.e. autotempered martensite and a mixture of martensite and bainite, both having yield strengths close to 1000 MPa. These were charged with hydrogen using passive cathodic protection and then tested in both the charged and uncharged condition at sub-zero temperatures. Hydrogen contents were measured with meltextraction. Fractography, kernel average misorientation measurements and cohesive zone modelling were used to analyse the results considering the degree and the active mechanisms of hydrogen embrittlement. It is shown that hydrogen embrittlement is present at sub-zero temperatures, causing an increase in fracture toughness reference temperature T 0 and a small decrease in deformation capability. The relationship between the T 0 and the impact toughness transition temperature T 28J , which, in the case of ultra-high-strength steel, deviates from that observed for lower strength steels, is proposed to be affected by the hydrogen content.
A fracture criterion for the notch strength of high strength steels in the presence of hydrogen
Journal of the Mechanics and Physics of Solids, 2014
High strength steels can suffer from a loss of ductility when exposed to hydrogen, and this may lead to sudden failure. The hydrogen is either accommodated in the lattice or is trapped at defects, such as dislocations, grain boundaries and carbides. The challenge is to identify the effect of hydrogen located at different sites upon the drop in tensile strength of a high strength steel. For this purpose, literature data on the failure stress of notched and un-notched steel bars are re-analysed; the bars were tested over a wide range of strain rates and hydrogen concentrations. The local stress state at failure has been determined by the finite element (FE) method, and the concentration of both lattice and trapped hydrogen is predicted using Oriani's theory along with the stress-driven diffusion equation. The experimental data are rationalised in terms of a postulated failure locus of peak maximum principal stress versus lattice hydrogen concentration. This failure locus is treated as a unique material property for the given steel and heat treatment condition. We conclude that the presence of lattice hydrogen increases the susceptibility to hydrogen embrittlement whereas trapped hydrogen has only a negligible effect. It is also found that the observed failure strength of hydrogen charged un-notched bars is less than the peak local stress within the notched geometries. Weakest link statistics are used to account for this stressed volume effect.
Effect of hydrogen on the properties and fracture characteristics of TRIP 800 steels
Corrosion Science, 2011
The paper describes effect of hydrogen on the properties and fracture characteristics of two variants of TRIP 800 C–Mn–Si steels. The effect of hydrogen was studied by means of tensile tests on specimens previously charged by hydrogen. Hydrogen provoked embrittlement in both variants but only for very high hydrogen content. Hydrogen embrittlement manifested itself mainly by a loss of plasticity.
Effect of hydrogen and stress concentration on the notch tensile strength of AISI 4135 steel
Materials Science and Engineering: A, 2005
The quantitative relationship between notch tensile strength and diffusible hydrogen content has been investigated for the AISI 4135 steel at 1320 MPa. The notch tensile strength was obtained by means of a slow strain rate test on circumferentially notched round bar specimens with stress concentration factors of 2.1, 3.3 and 4.9 after hydrogen charging, and the diffusible hydrogen content was then measured by thermal desorption spectrometry analysis. The diffusible hydrogen has been found to decrease the notch tensile strength in a power law manner, and the decrease is more prominent at a higher stress concentration factor. The finite element analysis results of stress and hydrogen distributions in the vicinity of the notch root have shown that the local fracture stress decreases with increasing local hydrogen concentration as the diffusible hydrogen content or stress concentration factor increases, resulting in the decrease in the notch tensile strength.
The Effect of Hydrogen on Failure of Complex Phase Steel under Different Multiaxial Stress States
Metals
The demand for advanced high-strength steel (AHSS) in the automotive industry has increased over the last few years. Nevertheless, it is known that AHSSs are susceptible to hydrogen embrittlement. Therefore, the influence of hydrogen on the localization and damage behavior of a CP1000 steel sheet was investigated in this work. The sheet metal was electrochemically charged to a hydrogen content of about 3 ppm (by weight). Tensile tests were performed at different nominal strain rates between 0.00004 s−1 and 0.01 s−1 to investigate the effects of strain rates on their susceptibility to hydrogen embrittlement. Nakajima tests were utilized to investigate the hydrogen effects on the steel’s formability under different stress states. Three different Nakajima specimen geometries were employed to represent a uniaxial stress state, a nearly plane strain stress state, and an equibiaxial stress state. Further, forming limits were evaluated with the standardized section line method. Hydrogen em...
Hydrogen Damage in Multiphase Steels after Electrochemical Charging
The harmful consequences of the exposure of steel to a hydrogen containing environment was first discussed by Johnson . He showed that hydrogen caused a decrease in ductility leading to hydrogen embrittlement. High strength steels turn out to be even more sensitive to this phenomenon. Nowadays, the use of high strength steels in hydrogen rich environments becomes increasingly important in industry. Therefore, before using these steels in this type of environment, a detailed study of their interaction with hydrogen is a prerequisite to be able to predict the potential damage, i.e. hydrogen blisters, hydrogen embrittlement and hydrogen induced cracking, which might occur during use. Blisters appear in many materials in the absence of external stress when the hydrogen concentration is above a certain threshold. The main goal of this work was to study this phenomenon for different types of steels and electrolytes. Most mechanisms trying to explain blister formation suggest that hydrogen atoms combine into hydrogen gas molecules at the interfaces such as those between second phase particles and the metal matrix, producing locally high hydrogen pressure inducing microcracks. The propagation and connection of the microcracks causes formation of the blisters and cracks .
Identification of the damage in high strength steels after electrochemical hydrogen charging
2010
Multiphase steels are quite sensitive to hydrogen embrittlement. Laboratory tests to evaluate this often use electrochemical charging to introduce hydrogen into the sample, but damage purely caused by hydrogen charging has to be avoided. A ferrite-bainite steel was charged using various conditions to identify when surface blisters occurred. Samples were also checked for internal damage by electron microscopy. This study was repeated for three other multiphase steels and pure iron. An HSLA steel was found to be more resistant whereas pure iron was quite susceptible to internal hydrogen damage. For all industrial steels, cracks concentrated in the middle of the sample were attributed to inclusions and segregations, inherent to production.