奥氏体不锈钢的形变与阳极溶解的相互作用

研究了形变对奥氏体不锈钢在酸性氯离子溶液中阳极溶解的加速作用以及阳极溶解对力学行为的影响。形变使腐蚀电流密度显著增加,使阳极和阴极反应加速。阳极电流不但使恒载荷下的不锈钢蠕变速度增加,而且使屈服强度下降。形变的热激活理论分析表明蠕变速率的对数和阳极电流的对数成线性关系,屈服强度的倒数和阳极电流的对数成线性关系,这和实验结果符合得很好。     

The correlation between mechanical and electrochemical parameters of stress corrosion cracking of austenitic stainless steels

Extension measurements of exposed specimens of austenitic stainless steels in hot magnesium chloride solutions are interpreted with the potential-time curves. For austenitic stainless steels, it is very difficult to determine the yield point; it is necessary to study the stress-elongation curves at different elongation rates and to known the creep behaviour of the steels. In dead load stress corrosion tests the elongation-time curves allow the incubation time of stress corrosion cracks to be distinguished from the propagation time. The propagation time is more important than incubation time for the classification of the susceptibility of austenitic stainless steels to stress corrosion cracking, because the incubation time is more dependent on experimental procedure than is the propagation time. The stainless steel classification obtained was compared with a new test in which a load is applied and immediately taken off; after a rapid fall the potential-time behaviour provides information about the crack velocity.     

Effect of nickel alloying on crevice corrosion resistance of stainless steels

The crevice corrosion behaviour of stainless steels containing 25 mass% Cr, 3 mass% Mo and various amounts of Ni was investigated in natural seawater. The results showed that ferritic steels containing nickel were more resistant to corrosion than both ferritic steels without nickel and austenitic steels. The superiority of the Ni bearing ferritic steel over the other steels was in close agreement with the depassivation pH of those steels in acidic chloride solutions. The results showed that the addition of Ni to ferritic steel was effective in decreasing the depassivation pH and the dissolution rate in acidic chloride solutions at crevices.     

奥氏体304不锈钢在活化态下的应力腐蚀与马氏体相变

用ＳＳＲＴ和电化学方法研究了３０４不锈钢在酸性氯化物溶液中的应力腐蚀与形变诱发马氏体的关系．结果表明形变诱发马氏体相不仅有利于应力腐蚀裂纹的形核而且它的选择性溶解构成了裂纹扩展的活性通道．文中讨论了裂纹沿马氏体相扩展的机制．     

Effect of stress on electrochemical characteristics of pre-cracked ultrahigh strength stainless steel in acid sodium sulphate solution

The electrochemical behaviors of ultrahigh strength stainless steel Cr12Ni5MoCo14 at crack tip under applied stress were studied by micro-electrochemical measurements as well as finite element analysis. The non-uniform distribution of the stress and strain induces a higher electrochemical activity at crack tip and promotes the anodic dissolution rate. The corrosion rate increases with increasing applied stress. In the elastic stress range, the effect of the applied stress on the electrochemical behaviors of Cr12Ni4Mo2Co14 steel is small. In the plastic stress range, the plastic deformation has a dramatic effect on the mechanical–electrochemical interaction and enhances the anodic activity.     

Creep and stress corrosion cracking of austenitic stainless steel in boiling 35% magnesium chloride solution

The stress-corrosion crack initiation and propagation in two austenitic stainless steel wires was studied using a 35 wt.%MgCl₂ solution at constant electrode potential. The results of stress corrosion tests were compared with those of creep tests in 35%MgCl₂ and in n-octane at 125°C. Both the SCC rate vs applied stress curve and the primary creep rate vs applied stress curve were found to exhibit a maximum followed by a minimum. This behaviour was probably associated with the mechanism of the plastic deformation of austenitic stainless steels, the competition between film failure and film repair and the effects of surface films on plasticity.     

Effect of selective dissolution on fatigue crack initiation in 2205 duplex stainless steel

The effect of selective dissolution on fatigue crack initiation of 2205 duplex stainless steel (DSS) was investigated in this study. In mixed sulfuric and hydrochloric acid aqueous solution, there existed two distinctly separated anodic peaks in the active-to-passive transition region of the polarization curve. Either ferritic or austenitic phase was selectively dissolved at each characteristic anodic peak potential. Under sinusoidal cyclic loading condition, however, selective dissolution did not assist fatigue crack initiation instead resulting in the elimination of stress concentration site in the selectively dissolving phase. As a consequence, under selective dissolution condition, fatigue crack initiated in the phase while its dissolution rate was lower with respect to the other constituent phase in the duplex stainless steel. The microstructural evolution of the corrosion fatigue crack initiation in 2205 DSS in the mixed sulfuric and hydrochloric acid solution is highlighted in this investigation.     

A correlation between phosphorous impurity in stainless steel and a second anodic current maximum in H2SO4

Phosphorous as a minor element (0.03%) in AISI 304 austenitic stainless steel greatly affects the polarization and corrosion behavior in sulfuric acid solution. The presence of P in stainless steel created a second current maximum in the anodic polarization curve and the current increased with increasing aging in the solution. An adhesive corrosion surface layer, rich with phosphate, formed on the surface of a P-containing steel during active dissolution. The layer lowered the cathodic Tafel slope at low current densities, and is likely, due to a change in hydrogen evolution mechanism. Phosphorous increases the H-adsorbed (and/or absorbed) atoms on the surface, leading to the appearance of a second anodic current peak that is interpreted as re-oxidation of hydrogen atoms. Also, P shifted the corrosion potential to the noble side, decreased effectively the active anodic dissolution, and lowered the corrosion rate.     

Effects of dissolved hydrogen and elastic and plastic deformation on active dissolution of pipeline steel in anaerobic groundwater of near-neutral pH

The mechano-electrochemical effects of deformation and hydrogen on active dissolution of pipeline steel in near-neutral pH groundwater are described. Thermodynamic analysis shows that the free energy increment due to elastic deformation is insufficient to alter active dissolution rate remarkably. The synergistic effect of stress field and dissolved hydrogen on active dissolution (corrosion) is negligible. The effect of plastic deformation on corrosion relies heavily on the heterogeneity of dislocation structures formed in the deformation. The plastic deformation cannot significantly change the corrosion rate at the open circuit potential. There is good agreement between these theoretical predictions and experimental observations, indicating that the stress corrosion cracking of pipeline steel in the anaerobic groundwater of near-neutral pH is unlikely to be related to the hydrogen-facilitated anodic dissolution mechanism.     

Creep and stres corrosion cracking of austenitic stainless steel in boiling 35% magnesium chloride solution

The stress-corrosion crack initiation and propagation in two austenitic stainless steel wires was studied using a 35 wt.%MgCl₂ solution at constant electrode potential. The results of stress corrosion tests were compared with those of creep tests in 35%MgCl₂ and in n-octane at 125°C. Both the SCC rate vs applied stress curve and the primary creep rate vs applied stress curve were found to exhibit a maximum followed by a minimum. This behaviour was probably associated with the mechanism of the plastic deformation of austenitic stainless steels, the competition between film failure and film repair and the effects of surface films on plasticity.     

1Cr18Mn14N双相不锈钢在腐蚀介质中的抗空蚀性能

利用磁致伸缩空蚀实验机研究了1Cr18Mn14N双相不锈钢在3%NaCl和05 mol/L HCl溶液中的空蚀行为.结果表明：在3%NaCl溶液中，低硬度的Cr18Mn14N双相不锈钢的抗空蚀性能优于高硬度的水轮机常规用材0Cr13Ni5Mo.1Cr18Mn14N双相不锈钢的空蚀破坏首先在铁素体相发生，铁素体相的失效方式为脆性失效，而奥氏体相是延性失效.奥氏体相区由滑移和孪生引起的塑性变形耗散了空泡溃灭产生的冲击能量，从而提高1Cr18Mn14N双相不锈钢的抗空蚀性能.在05 mol/L HCl溶液中，1Cr18Mn14N的抗空蚀性能不如0Cr13Ni5Mo，结果与3%NaCl溶液中的正好相反，这是由于阳极溶解和氢共同作用的结果.     

Study of the influence of welding parameters on the stress corrosion resistance of AISI 304 steel

Austenitic stainless steel has been welded to coat pressure vessels in petrochemical plants. The material is highly susceptible to stress corrosion in chloride environments, which can damage the weld and lead to the rupture of the component. In this work we did the evaluation of the influence of welding parameters on the stress corrosion resistance of AISI 304 steel exposed to a magnesium chloride solution. AISI 304 sheets were manually welded using three different coated electrodes (AWS E309-16, E308L-16, E316L-16) and two heat inputs (5.0 and 9.0 kJ/cm). The welded samples were analysed by tensile strength tests, optical microscopy and corrosion tests carried out according to ASTM G36-73 guidelines. The results showed that the AWS E309-16 electrodes produced the best results due to the microstructure of the resulting weld metal. The presence of a network of ferrite particles in an austenitic matrix acts as a barrier to crack propagation, thus enhancing the resistance to stress corrosion of the material. This effect is associated to the morphology and distribution of the phase rather than its contents. Welding in a direction parallel to the stress axis using a relatively high heat input improved the stress corrosion of the material even further. The HAZ (Heat Affected Zone) of AISI 304 steel was highly susceptible to stress corrosion in chloride solution. The presence of carbide precipitates in the austenite grain boundary deteriorated the corrosion resistance of the steel, as they promoted anodic dissolution and the development of stress corrosion cracks.     

Stress corrosion cracking of type aisi 304 stainless steel at room temperature; influence of chloride content and acidity

The influence of chloride concentration and acidity on the occurrence of stress corrosion cracking (s.c.c.) of type AISI 304 austenitic stainless steel at room temperature has been studied. The results obtained show that s.c.c. in acidic chloride solutions can occur in a wide range of acidity as a function of the total chloride content. Cracking occurs in the active potential range.     

The enrichment of hydrogen and chloride ions in the crevice corrosion of steels

The changes in concentration of hydrogen and chloride ions during corrosion in an artificial crevice on steel were observed from potential changes of Pd-H and Ag/AgCl micro-electrodes inserted in the crevice. Increasing the bulk chloride ion concentration accelerated the rate of pH change and resulted in more acidic conditions in the crevice. Such pH changes were delayed by the addition of inhibitor such as dialkylamines. Though the free chloride ion concentration did not change appreciably, the total concentration of free and complex ions in the crevice increased with continuous dissolution of the steel. Increasing the hydrogen and total chloride ion concentration in the crevice accelerated the anodic dissolution of steels within the crevice.     

1Cr13不锈钢的应力腐蚀开裂和应力腐蚀的缓蚀剂

研究了在酸性氯毁子溶液中抑制1Cr13不锈钢应力腐蚀开裂的缓蚀剂,研究表明这种不锈钢的应力腐蚀开裂受氢脆机理所控制,抑制应力腐蚀开裂的缓蚀剂均抑制了阴极过程,这是与奥氏体不锈钢的结果不同的,对于奥氏体不锈钢抑制应力腐蚀开裂的缓蚀剂均抑制了阳极过程     

Transkristalline Spannungsrißkorrosion an austenitischen Manganstählen in chlorionenhaltigen Angriffsmedien

Transcrystalline stress corrosion cracking of austenitic manganese steels in corrodent containing chloride ions Experimental investigation with steels (0,5% C, 20% Mn, 0.2—2.7% Cr) in the shape of U-bent specimens in seawater (RT and boiling) under loads between 30 and 45 kp/mm². The electrochemical behaviour of chromium-free types (i.e. below 0.5% Cr) at RT is identical to that of ferritic shipbuilding steels (equal break-through potential, then uniform attack). Addition of N, Ni, Co and Cu have little influence on the potential behavior. In boiling sea-water, however, transcrystalline corrosion takes place, accelerated by high tensional loads and anodic polarization, and slowed down by cathodic polarization. Additions, in particular of Co and Ni, reduce specimen life, perhaps by reducing yield strength. At higher Cr contents (1.7–2.8%) susceptibility to intercrystalline corrosion begins to supersede susceptibility to transcrystalline cracking. On the basis of ideas concerning the active-passive behavior under the influence of gliding phenomena the author shows analogies to the stress corrosion behaviour of austenitic stainless steels.     

Corrosion of stainless steels in acid solutions with organic sulfur-containing compounds

The influence of the organic sulfur-containing compounds on the corrosion of ferrite and austenitic stainless steels in sulfuric acid was studied. The results showed that the anodic dissolution and self-corrosion of stainless steels were remarkably accelerated in solutions with a low amount of the organic sulfur-containing compounds (0.02 mmol/dm³). With an increase of the organic sulfur-containing compound concentration, more and more the organic sulfur-containing compound molecules adsorbed on the electrode surface and segregated the metal surface from the solution, which caused the decrease of the anodic dissolution and hydrogen evolution current of stainless steels. The anodic polarization behaviors of stainless steels were also changed with the various types of the organic sulfur-containing compounds and stainless steels.     

Spannungsrißkorrosion nichtrostender austenitischer Chrom-Nickel-Stähle bei Raumtemperatur

Stress corrosion cracking of austenitic chromium-nickel stainless steels at ambient temperature For the chloride-induced SCC with transgranular crack path in austenitic 18Cr10Ni stainless steel, a critical temperature between 45 and 50°C exists. This critical temperature, however, is valid only for the passive state of the steel in nearly neutral, chloride-containing aqueous environments. In the active state, SCC with transgranular crack mode can occur at temperatures down to ambient temperature. The active state is caused by highly acidic, high-chloride containing aqueous corrosive media. Adherent aqueous films with these properties can grow on the surface of structural components inside swimming-pools when the water is disinfected by addition of chlorine. Under these conditions, failure of austenitic CrNi and CrNiMo stainless steels by SCC with transgranular crack path at ambient temperature is possible and actually occurred. SCC with preferentially intergranular crack path can also occur at ambient temperature when austenitic stainless steels with a sensitized microstructure are used. Under these conditions, the corrosion attack is caused by non-specific aggressive environments, e.g., adherent aqueous films not containing chloride ions. The crack mode, intergranular or mixed, depends on the stress level.     

An electrochemical impedance study on atmospheric corrosion of steels in a cyclic wet-dry condition

The corrosion rates of steels with different nickel contents (0, 2.5, 10 and 20 wt%) were monitored by the AC impedance method under a cyclic wet-dry condition, which was conducted by exposure to alternate conditions of 1 h immersion in a 0.05 M NaCl solution and 7 h drying at 60% RH and 25 °C. The corrosion rates of the ordinary carbon steel and the 2.5% Ni containing steel were greatly accelerated by the wet-dry cycles, while those of steels containing at least 5% Ni were only slightly affected. AC impedance tests indicated that the addition of 5% Ni greatly reduced the corrosion rates of the steel exposed to the cyclic wet-dry environments containing chloride ions, in good agreement with one year exposure tests in the atmospheric marine environments. Within the wet-dry cycle for the carbon steel, a gradual increase in the corrosion rate and a shift of the corrosion potential to negative values were observed at the initial stage of the drying period. These indicated that the anodic metal dissolution rate was accelerated by a slight increase in the chloride ion concentration. At the intermediate stage of drying, the corrosion rate rapidly increased and the corrosion potential remained constant. This can be attributed to the acceleration of both the anodic metal dissolution process and the cathodic oxygen reduction process which is usually controlled by the rates of O₂ transport through the thin electrolyte film. At the final stage, just before the surface dried out, the corrosion rate rapidly decreased, shifting the corrosion potential to the noble direction. At this stage, the anodic process was greatly inhibited. The corrosion testing system employed in this study is very useful for the rapid evaluation of the corrosion performance of metals in atmospheric marine environments and for mechanistic study.     

Corrosion behaviour of Lotus-type porous high nitrogen nickel-free stainless steels

Corrosion behaviour of three austenitic Lotus-type porous high nitrogen Ni-free stainless steels exposed to an acidic chloride solution has been investigated by electrochemical tests and weight loss measurements. Polarization resistance indicates that the corrosion rate of Lotus-type porous high nitrogen Ni-free stainless steels is an order of magnitude lower than that of Lotus-type porous 316L stainless steel in acidic environment. The localised corrosion resistance of the investigated high nitrogen Ni-free stainless steels, measured as pitting potential, E_b, also resulted to be higher than that of type 316L stainless steel. The influences of porous structure, surface finish and nitrogen addition on the corrosion behaviour were discussed.