Stress corrosion cracking susceptibility of sensitized type 316 stainless steel in sulphuric acid solution

The stress corrosion cracking (SCC) of a commercial austenitic stainless steel type 316 was investigated as a function of sensitizing temperature (800-1300 K) and test temperature (333-373 K) in 0.82 kmol/m³ sulphuric acid solution by using a constant load method, to compare with that already obtained in 0.82 kmol/m³ hydrochloric acid solution. The three parameters (l_ss, steady state elongation rate, t_ss, transition time, t_f, time to failure) were obtained from corrosion elongation curve and were divided into three regions of applied stress, irrespective of sensitizing temperature, which are dominated by either stress, SCC or corrosion. In the SCC-dominated region, the logarithm of l_ss was a linear function of the logarithm of t_f regardless of applied stress and test temperature for each sensitized specimens, showing that l_ss became a useful parameter for prediction of t_f, although the slope depended upon sensitizing temperature. The maximum applied stress, the minimum applied stress and the value of t_ss/t_f in the SCC-dominated region depended upon sensitizing temperature. Specifically, at a sensitizing temperature of around 950 K the maximum applied stress was smaller at a test temperature of 353 K, but larger at a test temperature of 333 K than that of the solution annealed specimens. In addition, sulphate ions were found to become more aggressive than chloride ions for the SCC susceptibility of the specimens with the most severe sensitization. On the basis of the results obtained, the effect of sensitization on SCC, the role of sulphate ions and an intergranular mechanism were discussed in comparison to the results of the sensitized specimens obtained in 0.82 kmol/m³ HCl solution.     

Hydrogen-induced cracking of pure titanium in sulphuric acid and hydrochloric acid solutions using constant load method

The hydrogen-induced cracking (HIC) of the commercial pure titanium (Ti) has been investigated as functions of applied stress and test temperature in sulphuric acid and hydrochloric acid solutions by using a constant load method. From the results obtained, HIC was hydrogen embrittlement (HE) related to the fracture of hydride. We have also found that the steady state elongation rate obtained from corrosion elongation curve becomes a relevant parameter for predicting time to failure and a criterion to assess whether HIC takes place or not. A parameter, t_sst_f⁻¹ was also found to become an indicator to assess whether HE takes place or not. Furthermore, it was deduced that HIC was qualitatively explained in terms of hydride formation and a localized deformation, which was basically based on a hydride formation-rupture event at crack tips.     

The effect of sensitizing temperature on stress corrosion cracking of type 316 austenitic stainless steel in hydrochloric acid solution

The stress corrosion cracking (SCC) of a commercial austenitic stainless steel type 316 was investigated as a function of sensitizing temperature (750-1300 K) and test temperature (333-373 K) in 0.82 kmol/m³ hydrochloric acid (HCl) solution by using a constant load method. From the applied stress dependence of three parameters (i_ss: steady state elongation rate, t_ss: time interval of SCC-dominated failure, t_f: time to failure), the relationships between applied stress and the three parameters were divided into three regions that are dominated by either stress, SCC or corrosion. In the SCC-dominated region, the logarithm of i_ss was a linear function of the logarithm of t_f irrespective of applied stress and test temperature, although its slope depended upon sensitizing temperature. This result showed that the i_ss became a useful parameter for prediction of t_f as well as the case of the solution annealed specimens. Furthermore, at the most severe sensitization with a sensitizing temperature of around 1000 K, the slope of the linear function of log i_ss vs. log t_f showed a minimum, the value of t_ss/t_f was a maximum and the fracture appearance was an intergranular mode. On the basis of the results obtained, the effect of sensitization on SCC was discussed in comparison to the results for the solution annealed type 316 and a qualitative intergranular SCC (IGSCC) mechanism was inferred.     

Stress corrosion cracking of type 304 austenitic stainless steel in sulphuric acid solution including sodium chloride and chromate

The stress corrosion cracking (SCC) of a commercial austenitic stainless steel type 304 was investigated as functions of chloride concentration, chromate concentration and test temperature under a constant applied stress condition in 0.82 kmol/m³ sulphuric acid solution by using a constant load method. From the dependence of the three parameters (, steady state elongation rate; t_ss, transition time; t_f, time to failure) obtained from corrosion elongation curve on chloride/chromate concentrations and test temperature, a parameter for predicting time to failure and critical values of chromate concentration and test temperature, below which little SCC takes place, were estimated. In addition, a transgranular SCC mechanism was qualitatively inferred and then the effect of chromate and chloride on SCC behavior was discussed.     

Stress corrosion cracking of sensitized type 316 austenitic stainless steel in hydrochloric acid solution--effect of sensitizing time

The stress corrosion cracking (SCC) of a commercial austenitic stainless steel type 316 was investigated as a function of sensitizing time (3.6 ks to 1.08 Ms at a sensitizing temperature of 923 K) and test temperature (333-373 K) in 0.82 kmol/m³ hydrochloric acid (HCl) solution by using a constant load method. From the applied stress dependence of the three parameters (, steady state elongation rate, t_ss, transition time, t_f, time to failure), the relationships between applied stress and the three parameters were divided into three regions that are dominated by either stress, SCC or corrosion. In the SCC-dominated region, the was a linear function of the logt_f regardless of applied stress and test temperature for each sensitized specimens, showing that became a useful parameter for prediction of t_f. Furthermore, the results obtained indicated that the degree of sensitization increased with increasing sensitizing time, reached a maximum at a sensitizing time of around 360 ks and then began to decrease at 1.08 Ms by Cr healing. On the basis of the results obtained, the effect of sensitizing time on SCC and the IGSCC mechanism were discussed.     

The effect of test temperature on SCC behavior of austenitic stainless steels in boiling saturated magnesium chloride solution

The stress corrosion cracking (SCC) of the austenitic stainless steels of types 304, 310 and 316 was investigated as a function of test temperature in boiling saturated magnesium chloride solution (MgCl₂) using a constant load method. Both of types 304 and 316 exhibited similar corrosion elongation curves, while the corrosion elongation curve of type 310 was different from those of types 304 and 316, in terms of the three parameters such as time to failure (t_f), steady-state elongation rate (l_ss) and transition time to time to failure ratio (t_ss/t_f) obtained from the corrosion elongation curves for these stainless steels. The relationship between the time to failure and a reciprocal of test temperature fell in two straight lines on a semi-logarithmic scale as well as the relationship between the steady-state elongation rate and a reciprocal of test temperature. These regions were considered to correspond to a SCC-dominated region and a hydrogen embrittlement (HE)-dominated region from the value of (t_ss/t_f) and the fracture appearance. The relationship between the steady state elongation rates versus time to failure on a logarithmic scale became a straight line, whereas the slopes of the line for the stainless steels were different with the different fracture mechanism such as SCC and HE. It was found that the linearity of the relationship can be used to predict the time to failure for the stainless steels in the corrosive environment. In addition, type 310 did not suffer from HE, which means that type 310 showed only SCC. This would be explained by whether or not a formation of α′-martensite takes place.     

Stress corrosion cracking and hydrogen embrittlement of sensitized austenitic stainless steels in boiling saturated magnesium chloride solutions

Stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of the sensitized stainless steels of type 304, 310 and 316 were investigated as a function of test temperature in boiling saturated magnesium chloride (MgCl₂) solutions under a constant applied stress condition. The test temperature dependence of fracture appearance and three parameters of time to failure (t_f), steady-state elongation rate (l_ss) and transition time to time to failure ratio (t_ss/t_f) suggests that type 304 suffered SCC and HE, while type 316 suffered only HE and type 310 SCC. It was also found that the test temperature dependence of three parameters for the sensitized type 304 and 310 was almost similar to that of the solution annealed stainless steels, whereas that of type 316 showed a clear difference between sensitized and solution annealed specimens. The relationships between the logarithms of the time to failure and the steady-state elongation rate became a straight line for all stainless steels. However, its slope depended upon the fracture mode; −2.0 for SCC and −1.5 for HE. This showed that the steady-state elongation rate was the parameter for predicting the time to failure for the stainless steels in the MgCl₂ solutions. The results obtained were explained in terms of martensite transformation, hydrogen entry site, sensitization, and so on.     

Metal dissolution and maximum stress during SCC process of ferritic (type 430) and austenitic (type 304 and type 316) stainless steels in acidic chloride solutions under constant applied stress

By using a constant load method and inductive coupled plasma (ICP) spectrometer, the metal dissolution and maximum stress (σ_m^air) of type 430 ferritic stainless, and type 304 and type 316 austenitic stainless steels during stress corrosion cracking (SCC) process were investigated under a constant applied stress condition in 0.82 kmol/m³ hydrochloric acid (HCl) and 0.82 kmol/m³ acidic chloride (pH 1.0) solutions. The σ_m^air of the specimens interrupted at various elongations up to failure under the same constant applied stress condition was measured at room temperature and air atmosphere by using an Instron type tensile machine. The metal dissolution behaviour of the stainless steels changed at the transition time (t_ss) in the corrosion elongation curve; that is, the dissolution rate before t_ss was larger than that after t_ss. The σ_m^air decreased gradually with increasing elongation, but showed a rapid small reduction at t_ss and then decreased with elongation with a sudden reduction around fracture. The results obtained were discussed in terms of the amount of metal ions per the number of cracks, selective dissolution, reduction in cross sectional area and so on.     

The stress corrosion cracking behavior of austenitic stainless steels in boiling magnesium chloride solutions

The change in the mechanism of stress corrosion cracking with test temperature for Type 304, 310 and 316 austenitic stainless steels was investigated in boiling saturated magnesium chloride solutions using a constant load method. Three parameters (time to failure; t_f, steady-state elongation rate; l_ss and transition time at which a linear increase in elongation starts to deviate; t_ss) obtained from the corrosion elongation curve showed clearly three regions; stress-dominated, stress corrosion cracking-dominated and corrosion-dominated regions. In the stress corrosion cracking-dominated region the fracture mode of type 304 and 316 steels was transgranular at higher temperatures of 416 and 428 K, respectively, but was intergranular at a lower temperature of 408 K. Type 310 steel showed no intergranular fracture but only transgranular fracture. The relationship between log l_ss and log t_f for three steels became good straight lines irrespective of applied stress. The slope depended upon fracture mode; −2 for transgranular mode and −1 for intergranular mode. On the basis of the results obtained, it was estimated that intergranular cracking was resulted from hydrogen embrittlement due to strain-induced formation of martensite along the grain boundaries, while transgranular cracking took place by propagating cracks nucleated at slip steps by dissolution.     

Stress corrosion cracking of Cu-30% Zn alloy in Mattsson’s solutions at pH 7.0 and 10.0 using constant load method - A proposal of SCC mechanism

The stress corrosion cracking (SCC) of a commercial Cu-30% Zn alloy has been investigated as a function of applied stress in Mattsson solutions with pH 7.0 and 10.0 at 313 K by using a constant load method. It was found that the elongation behavior at pH 10.0 showed clearly the step wise fashion, while that at pH 7.0 did slightly, almost over the whole applied stress. The steady state elongation rate obtained from corrosion elongation curve became a relevant parameter for predicting time to failure. Furthermore, from the results obtained, it is deduced that a unified SCC mechanism is qualitatively proposed to explain both of transgranular SCC (TGSCC) at pH 10.0 and intergranular SCC (IGSCC) at pH 7.0, where the unified SCC mechanism is basically based on a film rupture-formation event at crack tips.     

On the stress corrosion cracking and hydrogen embrittlement of sensitized austenitic stainless steels in boiling saturated magnesium chloride solutions: Effect of applied stress

Stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of sensitized stainless steels of types 304, 310 and 316 were investigated as a function of applied stress at different test temperatures in boiling saturated magnesium chloride (MgCl₂) solutions under a constant applied stress condition. The stress dependence of fracture appearance and three parameters of time to failure (t_f), steady-state elongation rate (l_ss) and transition time to time to failure ratio suggests that types 304 and 310 suffered SCC, while type 316 suffered only HE. It was also found that the applied stress dependence of three parameters for the sensitized types 304 and 310 was almost similar to that of the solution-annealed stainless steels, whereas that of type 316 showed a clear difference between sensitized and solution-annealed specimens. The relationships between the logarithms of the time to failure and the steady-state elongation rate became a straight line for all stainless steels. However, its slope depended upon the fracture mode: −2.0 for SCC and −1.5 for HE. This showed that the steady-state elongation rate was a good parameter for predicting the time to failure for the stainless steels in the MgCl₂ solutions. The results obtained were explained in terms of martensite transformation, hydrogen entry site, and sensitization.     

Environment-induced cracking of Al–Cu alloy (AA2017P-T3) under constant load in distilled water and sodium chloride solutions

The environment-induced cracking (EIC) of a commercial Al–Cu alloy has been investigated as functions of applied stress, chloride ion concentration and test temperature in distilled water and sodium chloride solutions by using a constant load method. The effect of chloride ion on EIC is complex. The EIC susceptibility increased, unchanged and then decreased with increasing the chloride ion concentration. However, whenever EIC takes place with and without chloride ion, the fracture appearance and the value of t_ss (transition time to deviation from linear elongation)/t_f (time to failure) are the same, and further the relationship between log t_f and log l_ss (steady state elongation rate) becomes the identical straight line irrespective of applied stress, chloride ion concentration and test temperature. The latter means that l_ss becomes a relevant parameter for predicting t_f. It has been concluded that EIC of Al–Cu alloy takes place by hydrogen embrittlement (HE) associated with the fracture of hydride, and a HE mechanism is qualitatively proposed to explain the results obtained.     

Effect of metallurgical variables on the stress corrosion crack growth behaviour of AISI type 316LN stainless steel

Mill-annealed AISI type 316LN stainless steels, received from two different sources (one indigenous (SS-2) and the other foreign (SS-1)), were tested for stress corrosion cracking (SCC) resistance in a boiling acidified environment of NaCl. SCC results indicated a remarkably lower value of plateau crack growth rate (PCGR) and higher values of K_ISCC and J_ISCC for SS-2, which was attributed to the lower effective grain boundary energy resulting from a higher amount of copper in it. Cold working reduced K_ISCC and PCGR; while thermal aging and welding decreased K_ISCC and increased PCGR vis-à-vis the annealed material.     

Influence of local stress on initiation behavior of stress corrosion cracking for sensitized 304 stainless steel

To investigate the influence of local stress on initiation behavior of stress corrosion cracking (SCC) for sensitized Type 304 stainless steel, cracking process during constant load SCC test was monitored and recorded with an in situ crack observation system. The changes in number of cracks, sum of crack length and cracked area on the specimen surface with test time were identified from the cracking images analyzed by image processing. In the SCC tests, many cracks were initiated and coalesced on the surface, and the coalescence of cracks played an important role to primary crack growth. The influence of applied stress on crack initiation was different from that on crack growth. In addition, there was a difference between influences of stress on incubation period to crack initiation and crack initiation rate. Due to these differences, a stress of 0.8S_y was thought to cause relatively many cracks compared with 0.5S_y and 1.3S_y (S_y = 200 MPa). Through quantitative estimation of distribution in local stress around a crack by finite element analysis method, it was deduced that the crack initiation is influenced not only by bulk stress applied at the end of the body, but also by local stress formed around pre-existing cracks. According to pre-existing cracks, stress enhancement accelerates the crack growth, while the stress relaxation causes the suppression of new crack initiation. Based on the experiment and analysis results, three types of growth process were suggested, which are caused by propagation itself, by new crack initiation at vicinity of the crack tip, and by coalescence of approaching cracks. Then, it was concluded that, in order to predict/simulate the cracking behavior of this SCC system, the influence of local stress on the crack initiation should be taken into account.     

Effect of the strain rate on stress corrosion crack velocities in face-centred cubic alloys. A mechanistic interpretation

Constant extension rate tests on smooth samples, with strain rate (SR) values from 10⁻⁶ s⁻¹ up to 20 s⁻¹, were used to study stress corrosion cracking (SCC) systems in face-centred cubic alloys. It was found that by increasing the SR a monotonic increase of the (crack propagation rate) takes place. It was also observed that the slope α in vs. plots had different values for different SCC morphologies. Intergranular SCC is more steeply accelerated by SR, α_IG=0.5-0.7, than transgranular SCC, α_TG=0.2-0.3. The differences found between intergranular SCC and transgranular SCC were analysed under the light of the available SCC mechanisms.     

Influence of the applied stress rate on the stress corrosion cracking of 4340 and 3.5NiCrMoV steels under conditions of cathodic hydrogen charging

Stress corrosion cracking (SCC) of as-quenched 4340 and 3.5NiCrMoV steels was studied under hydrogen charging conditions, with a cathodic current applied to the gauge length of specimens subjected to Linearly Increasing Stress Test (LIST) in 0.5 M H₂SO₄ solution containing 2 g/l arsenic trioxide (As₂O₃) at 30 °C. Applied stress rates were varied from 20.8 to 6 × 10⁻⁴ MPa s⁻¹. Both the fracture and threshold stress decreased with decreasing applied stress rate and were substantially lower than corresponding values measured in distilled water at 30 °C at the open circuit potential. The threshold stress values correspond to 0.03–0.08 σ_y for 4340 and 0.03–0.2 σ_y for the 3.5NiCrMoV steel. SCC velocities, at the same applied stress rate, were an order of magnitude greater than those in distilled water. However, the plots of the crack velocity versus applied stress rate had similar slopes, suggesting the same rate-limiting step. The fracture surface morphology was mostly intergranular, with quasi-cleavage features.     

Steric hindrance as a rate controlling step in stress corrosion cracking

The effect of steric hindrance in the stress corrosion cracking (SCC) of Ag-15Pd (a/o) in AgI forming solutions was studied at room temperature. The solutions used were 1 M KI at a potential higher than that of AgI formation, and iodine dissolved in different n-alcohols. It was found that Ag-15Pd (a/o) is susceptible to intergranular stress corrosion cracking in those solutions. The SCC susceptibility measured as percentage of elongation to rupture and crack propagation rate is related to the size of the active species. While in KI aqueous solutions, as well as in iodine saturated benzene or iodine saturated toluene, the rate controlling step (RCS) was the reaction at the tip of the crack, in alcoholic-iodine solutions, the diffusion rate of the iodine containing molecules became the RCS.     

Passivity breakdown and stress corrosion cracking of α-brass in sodium nitrite solutions

The stress corrosion cracking (SCC) susceptibility of pure copper and four α-brasses of different zinc alloy concentration in NaNO₂ 1 M solution, at various pH values, was studied by means of potentiodynamic polarisation curves and constant potential slow strain rate experiments. The results confirmed that passivity rupture was a necessary condition for SCC of α-brass and copper in nitrite solutions. Susceptibility to SCC was observed only when the potential was equal to or higher than a certain critical value at which passivity breakdown was triggered by the slow dynamic straining of the metal. Cracks were found only in those metal areas where passivity rupture had taken place.     

Stress corrosion cracking study of microalloyed pipeline steels in dilute NaHCO3 solutions

Studies were carried out to evaluate the stress corrosion cracking (SCC) behavior of a X-70 microalloyed pipeline steel, with different microstructures by using the slow strain rate testing (SSRT) technique at 50 °C, in NaHCO₃ solutions. Both anodic and cathodic potentials were applied. Additionally, experiments using the SSRT technique but with pre-charged hydrogen samples and potentiodynamic polarization curves at different sweep rates were also carried out to elucidate hydrogen effects. The results showed that the different microstructures in conjunction with the anodic applied potentials shift the cracking susceptibility of the steel. In diluted NaHCO₃ solutions cathodic potentials close to their rest potential values decreased the SCC susceptibility regardless the microstructure, whereas higher cathodic potentials promote SCC in all steel conditions. Certain microstructures are more susceptible to present anodic dissolution corrosion mechanism. Meanwhile concentrated solution did not promotes brittle fracture.     

A newly synthesized glycine derivative to control uniform and pitting corrosion processes of Al induced by SCN anions - Chemical, electrochemical and morphological studies

A newly synthesized glycine derivative (termed GlyD), 2-(4-(dimethylamino)benzylamino)acetic acid hydrochloride, was used to inhibit uniform and pitting corrosion processes of Al in 0.50 M KSCN solutions (pH 6.8) at 25 °C. For uniform corrosion inhibition study, Tafel extrapolation, linear polarization resistance and impedance methods were used, complemented with SEM examinations. An independent method of chemical analysis, namely ICP-AES (inductively coupled plasma atomic emission spectrometry) was also used to test validity of corrosion rate measured by Tafel extrapolation method. GlyD inhibited uniform corrosion, even at low concentrations, reaching a value of inhibition efficiency up to 97% at a concentration of 5 × 10⁻³ M. Results obtained from the different corrosion evaluation techniques were in good agreement. This new synthesized glycine derivative was also used to control pit nucleation and growth on the pitted Al surface based on cyclic polarization, potentiostatic and galvanostatic measurements. The pitting potential (E_pit) and the repassivation potential (E_rp) increased by the addition of GlyD. Thus GlyD suppressed pit nucleation and propagation. Nucleation of pit was found to take place after an incubation time (t_i). The rate of pit nucleation and growth decreased with increase in inhibitor concentration. Morphology of pitting was also studied as a function of the applied anodic potential and solution temperature. Cross-sectional view of pitted surface revealed the formation of large distorted hemispherical and narrow deep pits. GlyD was much better than Gly in controlling uniform and pitting corrosion processes of Al in these solutions.