Evaluation of SCC susceptibility of supermartensitic stainless steel using slow strain rate tests

Abstract

The susceptibility to chloride stress corrosion cracking (Cl-SCC) of supermartensitic stainless steel (SMSS) was evaluated at different temperatures through slow strain rate tests. In order to evaluate the Cl-SCC susceptibility the reduction in area and the time to failure ratio were considered. It is clear that all specimens tested in the chloride solution exhibited a generally high resistance to chloride SCC. However, according to the slow strain rate tests results, at lower temperature (5°C) the susceptibility to Cl-SCC increases compared to the other temperatures studied; also an increase in the corrosion rate was observed as the temperature decreased according to electrochemical impedance spectroscopy measurement. The corrosion mechanism observed on the material under dynamic stress was a combination of high activation resistivity with a diffusive process on the metallic interface given by a thin film from a protector layer of chromium oxides. This mechanism generates a high corrosion resistance and therefore good performance to chloride induced SCC.     

Comparison of the Stress Corrosion Cracking Behaviour of AISI 304 Pipes Welded by TIG and LBW

The stress corrosion cracking (SCC) behaviour of AISI 304 pipe girth welds which were welded by a single-pass laser beam welding (LBW) and a multi-pass tungsten inert gas welding (TIG),respectively,was studied by the slow strain rate tests combined with the electrochemical corrosion tests.The results show that fracture of both the TIG joint and LBW joint occurs in the heat-affected zone (HAZ).According to the electron-backscattered diffraction observation of the microstructures,comparison of potentiodynamic polarization curves and X-ray photoelectron spectroscopy analysis of corrosion products on HAZs of the two joints after the electrochemical tests,the LBW joint exhibits better SCC resistance than the TIG joint in corrosion environments,due to the synthetic effect of more Cr2O3 in corrosion products,finer grains,lower residual strain and higher δ-ferrite content in its HAZ.Although the TIG joint has better mechanical property,considering lower SCC susceptibility and higher production efficiency of the LBW joint,the LBW promisingly replaces the TIG for welding of AISI 304 pipes in the nuclear power industry.     

Stress corrosion cracking and hydrogen embrittlement susceptibility of an eutectoid steel employed in prestressed concrete

The stress corrosion and hydrogen embrittlement behavior of AISI 1080 steel employed in concrete prestressing tendons was studied with different experimental techniques. A simulated concrete pore solution, with and without contaminants such as chloride, sulfate and thiocyanate ions was used. For comparison purposes the standard 20% ammonium thiocyanate solution was also employed. Polarization curves, slow strain rate tests and fracture mechanics tests were used to evaluate the influence of parameters such as potential, temperature (between 0 and 100 °C), and tempering temperature of the steel. The results have shown that the fracture mechanism of the stress corrosion cracking process is associated with hydrogen action.     

Grain size effects on the SCC susceptibility of a nitrogen steel in hot NaCl solutions

The effect of grain size on the exhibited stress corrosion cracking (SCC) resistance of an austenitic stainless steel containing 0.97 wt.% nitrogen was investigated in this work. In order to vary the grain size, the as-received steel (AR) was heat treated (HT) at 550 and at 1100 °C for 1 h. Cert specimens of the AR and HT N-containing steels were then machined and tested in a Cortest machine using slow strain rates ranging from 7.95 × 10⁻⁶ s⁻¹ to 7.06 × 10⁻⁷ s⁻¹. The corrosion environment was hot water, as well as a 30% NaCl solution at 90 °C. In all the steel conditions, SCC was directly related to active pitting development. In all the cases, pits were found to preferentially form at Mn-Al inclusions, but were not able to grow too deep probably as a result of active repassivation reactions. It was found that the drop in the exhibited mechanical properties of the steels such as yield strength, UTS and % elongation was particularly enhanced for the coarse grained steel HT at 1100 °C. A SCC susceptibility index confirmed that this was indeed the case. Apparently, a drop in the yield strength tends to reduce the mechanical stability of the passive layer promoting its breakdown. Finally, quasi-cleavage and the lack of appreciable plastic deformation in some of the fracture surfaces indicated that the steel underwent some degree of embrittlement when exposed to these aqueous environments.     

The characteristics of hydrogen diffusion and concentration around a crack tip concerned with hydrogen embrittlement

Previously, we proposed a physical model for hydrogen diffusion and accumulation around the crack tip and performed accurate numerical analysis which takes account of the effects of both hydrogen diffusion and accumulation due to the stress gradient. Based on this analysis, the characteristics of hydrogen accumulation around the crack tip were clarified.Since the characteristics of stress corrosion cracking and corrosion fatigue are dominated by chemical anodic reaction, hydrogen embrittlement and dislocation mechanism, to perform the analysis on the competitive phenomenon by these mechanism and to relate the sensitivity of hydrogen embrittlement to the characteristics of corrosion fatigue, it is necessary to construct a exact physical law on the characteristics of hydrogen diffusion and concentration and to formulate the characteristics as a simple function such as diffusion constant, D, yield stress σ_ys, and stress intensity factor, K. The effect of stress field such as plane strain and plane stress on the hydrogen embrittlement is necessary to be clarified as the effect of specimen thickness on the hydrogen embrittlement.In this paper, based on this view point, the effect of D, σ_ys, and K on hydrogen embrittlement were investigated and formulated. A quantitative parameter which characterize hydrogen embrittlement was proposed for both cases of plane strain and plane stress conditions as the effect of specimen thickness on the hydrogen embrittlement.     

LC4高强铝合金的腐蚀性能研究

利用慢应变速率拉伸试验方法研究了LC4铝合金在空气和3．5％NaCl溶液中的应力腐蚀断裂行为；利用HB5455－90标准研究了LC4铝合金的剥蚀行为；利用HB5255－83标准研究了LC4铝合金的晶间腐蚀行为。结果表明：LC4铝合金具有应力腐蚀敏感性，应力腐蚀的断口形貌受应变速率ε的影响较大；LC4铝合金对剥蚀很敏感，对晶间腐蚀不是很敏感。     

Influence of Zn Content on Microstructures,Mechanical Properties and Stress Corrosion Behavior of AA5083 Aluminum Alloy

To enhance the stress corrosion cracking (SCC) resistance, Zn was utilized as an alloy element to add in the AA5083 aluminum alloys. The effects of Zn content on the microstructures, mechanical properties and SCC resistance were systematically evaluated. The results demonstrate that in the studied range adding Zn can significantly improve the SCC resistance of the AA5083 alloys. This is related to the relatively low amount of continuous β (Al₃Mg₂) phase along grain boundary and the formation of Zn-containing phase such as Al₅Mg₁₁Zn₄ phase. Based on the results, the optimal Zn content with respect to SCC resistance is approximately 0.50 wt.%. Further increasing Zn content results in coarse precipitates discontinuously distributed along grain boundaries.     

Effects of polarisation on mechanical properties and stress corrosion cracking susceptibility of 7050 aluminium alloy

The effects of polarisation (including cathodic and anodic polarisation) on mechanical properties and stress corrosion cracking (SCC) susceptibility (I_SCC) of 7050 aluminium alloy have been investigated by means of polarisation and slow strain rate test. The results of cathodic polarisation experiments showed that the I_SCC increased with shifting negatively the polarisation potential when the cathodic potential E_C≧?1100 mV(SCE), while it decreased with shifting negatively the polarisation potential when the cathodic potential E_CI_SCC increased severely with increasing the polarisation potential. In addition, the extents for the effect of polarisation potential on I_SCC were different among the 7050 aluminium alloy under various aging states. Polarisation was of the biggest effect on the I_SCC of under aged state, the smallest effect of over aged state and the middle effect of peak aged state. The SCC mechanism of aluminium alloy was a combination of anodic dissolution and hydrogen embrittlement, and the effects of hydrogen on SCC increased with increasing the hydrogen concentration.     

IncoMAPAl—9052合金在3.5%NaCl溶液中的应力腐蚀行为

采用双悬臂梁试样,实验研究了IncoMAP Al-9052合金在3.5％NaCl溶液中的应力腐蚀开裂(SCC)行为。结果表明该种合金的裂纹扩展机制有别于常规的铝合金。其初期阶段的裂纹扩展过程可划分为三个阶段,在每一阶段的裂纹扩展机制可能是不同的,但其裂纹扩展的主要机制为氢脆。     

Influence of dynamic straining on hydrogen embrittlement of UNS-G41300 and UNS-S31803 steels in a low H2S concentration environment

The hydrogen embrittlement of UNS-G41300 and UNS-S31803 steels in sodium thiosulphate solutions was studied. Slow strain rate and electrochemical tests were used. The influence of elastic and plastic strain on the hydrogen embrittlement process of these materials was investigated.The results showed that thiosulphate solutions efficiently simulate an aggressive environment containing low concentrations of hydrogen sulfide, being effective in promoting the embrittlement of the UNS-G41300 steel. For this tempered martensitic steel, under the test conditions, the role of a dynamic process of plastic straining on its hydrogen embrittlement was demonstrated.For the UNS-S31803 steel, a duplex (austenitic-ferritic) stainless steel, the study of the hydrogen embrittlement with the solutions used required cathodic polarization and showed that the embrittlement preferably occurs in the ferritic phase.     

7075铝合金应力腐蚀敏感性的SSRT和电化学测试研究

采用慢应变速率试验(SSRT)研究了7075铝合金的应力腐蚀行为。试验结果表明,外加阳极极化和阴极极化都能增加7075铝合金的应力腐蚀敏感性,即使在弱极化情况下也能显著增加合金的应力腐蚀敏感性。但是,外加极化对于不同热处理状态的7075铝合金,其应力腐蚀敏感性增加的程度不同。电极极化对T6状态合金的SCC敏感性的影响显著,而对RRA和T7351状态合金的影响较轻微。随着拉伸应力的增加,7075-RRA铝合金的阳极极化曲线略向正移,滞后环面积扩大,但并不显著。     

Atmospheric corrosion of zinc Part 1: Rural and urban atmospheres

Abstract

This paper summarises the results obtianed in the MICAT (Mapa Ibero-Americano de Corrosão Atmosférica (Latin American Map of Atmospheric Corrosion)) atmospheric corrosion project (an Iberoamerican project on atmospheric corrosion, involving 14 countries and 75 atmospheric test sites) for zinc specimens exposed for 1–4 years in 21 rural and urban atmospheres of the Latin American region. During the study, all of these atmospheres were characterised according to international standards. Complementary morphological and chemical studies were carried out using scanning electron microscopy coupled with energy dispersive spectrometry (SEM–EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) techniques, in order to correlate atmospheric characteristics and the properties of zinc corrosion product layers (ZCPLs). Soluble salts retained in these ZCPLs were also determined. The study has provided clear evidence about the wide range of zinc corrosion rates occurring in rural atmospheres and suggests an interpretation of this behaviour.     

Hydrogen embrittlement of duplex stainless steel under cathodic protection in acidic artificial sea water in the presence of sulphide ions

By slow strain rate technique, hydrogen embrittlement (HE) of a 2205 duplex stainless steel was studied in deaerated acidic (pH 6.5) artificial sea water, in the absence and in presence of sulphide ions (1-30 ppm). Strain rate tests (1 × 10⁻⁶ s⁻¹) were performed on specimens polarized at −0.9; −1.0 and −1.2 V_SCE at 25 ± 0.1 °C. HE was evaluated by R, the ratio between the % elongation to fracture in the aggressive solution and in air.Duplex stainless steel were subjected to HE in acidic artificial sea water at −0.9 V_SCE. HE increased at −1.0 V_SCE but it was reduced at −1.2 V_SCE. This decrease was attributed to the influence of a calcareous deposit.Sulphide ions at 1 ppm were sufficient to stimulate HE of duplex stainless steel. The higher the sulphide amount and the more negative the cathodic potential, the higher HE was. In the presence of S²⁻, the shielding effect of the calcareous deposit was not evident.     

Two distinct fracture modes of copper alloys in fluoride environments

The susceptibility of aluminum brass and aluminum bronze to stress corrosion cracking (SCC) was evaluated in fluoride environments by means of the slow strain rate technique. The effects of fluoride concentration and applied electrochemical potential on the SCC susceptibility were investigated. The SCC mechanism of aluminum brass was found to be dependent upon the de-alloying phenomenon while that of aluminum bronze on the film-rupture mechanism occurring within a certain range of applied electrochemical potentials. For aluminum brass, both the stress ratio and the time-to-fracture ratio were closely related to the logarithmic concentration of F⁻ ions. The fracture modes were ductile dimpled tearing fracture for the aluminum brass at the corrosion potential while intergranular for the aluminum bronze at various anodic potentials. The micro-galvanic effects of the constituent elements were used to estimate the anodic equilibrium potentials of the two alloys.     

氢对酸性气田低合金钢氢渗透及应力腐蚀行为的影响

采用电化学氢渗透、慢应变速率拉伸（SSRT）实验和体视显微镜、SEM观察断口形貌的方法进行探究80SS低合金油管钢在饱和CO2模拟采出水环境中，氢对氢渗透和应力腐蚀开裂行为的影响。结果表明，随着溶液H+浓度增大，酸性的增加，氢渗透参数i^∞、D和"C" _"0" ^"H" 均会增大，有助于氢原子的扩散行为；在拉应力和氢原子的协同作用下，与空拉对比，80SS低合金钢的断裂时间减少了近50%，发生了由韧性断裂到脆性断裂的变化，随着溶液氢浓度的增大，对钢材引起的力学损伤增强，应力腐蚀敏感性增大；80SS钢在含饱和CO2采出水介质中拉伸时，预充氢前后的指数Iδ由3.16增大到8.49，预充氢加大了试样的应力腐蚀开裂敏感性；在含1% HAc的饱和CO2采出水中拉伸时，预充氢前的微观形貌呈现出河流花样，出现准解理断裂特征，而预充氢后的80SS钢纤维区分布有不连续裂纹和小孔状结构，与预充氢前的相比，预充氢增加了钢的塑性性能，降低了钢材的应力腐蚀开裂敏感性。     

Hydrogen embrittlement susceptibility and permeability of two ultra-high strength steels

Slow displacement rate tensile tests were carried out in a saturated H₂S solution to investigate the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of two ultra-high strength steels (PH 13-8 Mo stainless steel and T-200 maraging steel). Hydrogen permeation properties were determined by an electrochemical permeation method. The results of permeation tests indicated that over-aged specimens showed a lower diffusivity/hydrogen flux and higher solubility than those solution-annealed. The great increase in reverted austenite (irreversible hydrogen traps) together with numerous precipitates at the expense of dislocations (reversible) in the over-aged specimen led to such a change in permeability. Ordinary tensile tests indicated that four tested specimens had roughly the same yield strength level. Hence, the hydrogen embrittlement susceptibility of the material could be related to their permeation properties. The uniform distribution of strong hydrogen traps in over-aged specimens instead of weak traps in the solution-annealed impeded the hydrogen transport toward the strained region, thus, the resistance to sulfide stress corrosion cracking was improved in over-aged specimens.     

Stress corrosion cracking of microalloyed pipeline steel in biofuels E-10 and E-85

This paper evaluates the stress corrosion cracking (SCC) effect in gasohol E-10 and E-85 of X-70 experimental Ni-microalloyed steel, with different aging treatments (4–12?h at 600°C). The tension tests show that for all treatment periods, the samples tensile strength and elongation increase, with the largest increment exhibited by the samples undergoing 4 and 6?h of aging treatment. Microstructural analysis showed that the microstructure remains unchanged, the increase in tensile strength in the steel is directly related to the precipitation kinetics. The slow strain rate test (SSRT) shows that the steel under all conditions presents no susceptibility to SCC, thus reducing the area ranging from 83% to 90%, with predominantly ductile fractures. The results of the polarisation tests showed no signs of pitting corrosion, as well as a low corrosion rate for both media under study.     

Amine corrosion and amine cracking of API 5L X52 carbon steel in the presence of hydrogen sulphide and carbon dioxide

In this research, stress corrosion cracking (SCC) and corrosion behaviour of API 5L X52 carbon steel in 25?wt-% diethanolamine solution, saturated/unsaturated with carbon dioxide and containing 0 and 200?ppm hydrogen sulphide at different temperatures were investigated using slow strain rate test, electrochemical measurement and microscopic analysis. In addition, the presence of heat stable amine salts (HSASs) in the test solution was studied using spectrophotometry and Fourier transform infra-red spectroscopy. Analysis of the results showed that the primary components to form HSASs exist in the solution. The results indicated that SCC is more likely in solutions without amine. Increase in corrosion rate of carbon steel by increase in temperature was clearly observed and concluded that the simultaneous presence of hydrogen sulphide and carbon dioxide in the solution can increase the corrosion rate of carbon steel more than having one of the gases in the solution.     

Stress corrosion cracking of A588 steel weldments in flue gas related environments

This study investigated stress corrosion cracking (SCC) of A588 steel welds as determined by U-bend immersion tests and slow strain rate tensile (SSRT) tests to evaluate the steel’s cracking susceptibility in various regions of the weldments. The immersion test results indicated that the fusion zone (FZ) had better corrosion resistance than the other regions in the weld. It was also demonstrated that the columnar grain boundaries exhibited a higher resistance to corrosion than the grain interior of the FZ. However, the coarse elongated ferrite in the FZ is susceptible to hydrogen embrittlement (HE), which results in the formation of microcracks. As a result, a severe degradation of the weld’s tensile properties in the saturated H₂S solution was observed. Scanning electron microscope (SEM) fractographs of tensile specimens reveal a cleavage fracture in the coarse-grained heat-affected zone (CGHAZ) and featherlike rupture in the FZ, both indicating a high sensitivity to HE.