Zum Elektrodenverhalten des Zinks und des Eisens in Calciumhydroxidlösung und in Mörtel

The electrode behaviour of zinc and iron in calcium hydroxide solutions and in mortar The behaviour of zinc (fine zinc and metallurgical zinc) and of unalloyed steel in a saturated calcium hydroxide solution and in mortar has been the subject of electrode-kinetic investigations. The observations showed that the behaviour of fine zinc, metallurgical zinc and galvanized steel is more or less identical, and that even the mortar coating has little effect on the electrode behaviour. It is found that

• (a) zinc is passivated by a zinc oxide layer;
• (b) the potential of a short-circuit cell consisting passive zinc and iron becomes so negative that hydrogen is developed at the iron at an appreciable rate;
• (c) the passivity Of the zinc in a solution containing chloride is removed at a much higher chloride concentration than that of steel.

In the case of a galvanized electrode with an electrolytically dissolved layer of pure zinc, the current/potential characteristic was similar to that of the passive iron.     

Failure mechanisms of high strength steels in bicarbonate solutions under anodic polarization

High strength steels used in prestressing concrete structures are not exempt from the effects induced by corrosion on the normal concrete reinforcement. Carbonation of surrounding concrete or mortar is not unlikely for prestressing tendons and strands. Moreover, these steels undergo to brittle fracture as a consequence of stress corrosion cracking phenomena. To evaluate if concrete carbonation can promote this kind of failure, constant load tests in bicarbonate aqueous solutions under anodic polarization were carried out on high strength steel wires. Microscopic examination pointed out that the wires exhibited a brittle fracture mode, while its natural feature is ductile, as indicated by air testing. Failure mechanism was evaluated by a fracture mechanic approach. Cracks initiation was attributed to an anodic dissolution mechanism, while its propagation, interpreted by means of the surface mobility theory, was related to interaction between hydrogen atoms and magnetite at a crack tip.     

Hydrogen induced stress corrosion cracking in low and high strength ferritic steels of different phosphorus content in acid media

Hydrogen induced stress corrosion cracking (HSCC) resistance and mode of fracture in various low and high strength steels (yield strength 120 to 960 MPa) and containing different levels of phosphorus content were studied using constant extension rate test method in various acid media viz. sulphuric acid solutions under cathodic polarisation, hydrogen sulphide saturated solutions of sodium chloride + acetic acid (NACE solution) and synthetic sea water (BP solution). In case of low strength steels (yield strength 120–265 MPa), the HSCC susceptibility in sulphuric acid increased with phosphorus content and became very high irrespective of phosphorus content in hydrogen sulphide saturated solutions. The susceptibility was directly related to different hydrogen activities measured in these solutions. No significant dependence of HSCC susceptibility on the phosphorus segregation as high as 20 atom % at the grain boundaries was found and the fracture mode was always transgranular. In contrast, a similar segregation of phosphorus in high strength steels (yield strength 875–960 MPa) caused a reduction in HSCC resistance and changed the fracture mode to intergranular.     

氢在钢的硫化物应力腐蚀破裂中的作用

本文研究了12MnMoVNbTi低合金钢在饱和H_3S溶液中的极化和应力腐蚀行为,并与电解充氢条件下的应力破裂行为进行了对比。证明钢中Mo、Nb含量的变化与热处理条件的不同对其一般腐蚀行为影响很小,但能显著改变其抗应力腐蚀性能,12MnMoVNbTi钢在H_2S介质中的应力腐蚀破裂行为与它们在充氢条件下的应力破裂行为非常类似,显示其应力腐蚀破裂的实质是氢脆。充氢条件下应力弛豫和恒载荷拉伸试验结果表明,氢有引起钢的软化和硬化的双重作用。由于氢的进入所产生的软化作用使钢在屈服强度以下发生塑性变形,但随后的硬化过程又使变形速度逐步减慢。这种由氢的作用引起的在较低应力下发生的塑性变形过程并不直接导致断裂,但塑性变形行为和氢应力破裂行为之间的关系表明,这种变形过程中的位错运动能够帮助氢的移动和向塑变区及裂纹尖端集中,促进氢脆断裂。     

Wasserstoffinduzierte Spannungsrißkorrosion an unverzinkten und verzinkten Baustählen

Hydrogen induced stress corrosion cracking of non galvanized and galvanized construction steels The processes of atmospheric corrosion and corrosion in collected water which may lead to hydrogen induced stress corrosion cracking of high-strength reinforcing steels in casing tubes before injection with concrete are discussed. Hydrogen uptake during corrosion occurs in weakly acid solutions as well as in neutral or alkaline aqueous solutions. The hydrogen uptake by proton discharge in acid solutions decreases with increasing pH of the electrolyte. Hydrogen can also be absorbed in neutral to weakly alkaline solutions if steels are plastically deformed and water reacts with the fresh iron surface. In alkaline solutions, hydrogen uptake is possible if, at the generally passivated steel surface, localized corrosion (pitting or crevice corrosion), local galvanic cells and a sufficient decrease in the pH of the pit electrolyte occurs. In the case of galvanized steels with damaged zinc layers, hydrogen uptake may result from the cathodic polarization of the free steel surface by zinc dissolution. The absorbed hydrogen interacts with the microstructure of the steels and weakens the bonds between the iron atoms. The influence of the microstructure of high-strength steels on the fracture behaviour is discussed on the basic of the so-called decohesion theory.     

A hydrogen embrittlement mechanism for sensitized types 304, 316 and 310 austenitic stainless steels in boiling saturated magnesium chloride solutions

We have already proposed a mechanism for intergranular hydrogen embrittlement (IG-HE) for solution annealed austenitic stainless steels (types 304, 316 and 310) in HCl solutions and in boiling saturated magnesium chloride solutions. The proposed IG-HE mechanism was based on martensite transformation, hydrogen-enhanced local plasticity (HELP), grain boundary sliding (GBS). Recently, it was reported that the fracture susceptibility and fracture mode for sensitized steels in boiling saturated magnesium chloride solution under an open-circuit condition were significantly different from those observed for solution annealed steels. In the present paper, the hydrogen embrittlement behavior of sensitized types 304, 316 and 310 in boiling saturated magnesium chloride solutions was explained in more details in terms of an inhibiting effect of chloride ions, martensite transformation, Cr depletion, HELP, the degree of corrosiveness through the comparison with those for the solution annealed steels. Furthermore, a transgranular HE (TG-HE) cracking mode that was not observed for the solution annealed steels was discussed as well as IG-HE. Then a TG-HE mechanism for sensitized austenitic stainless steels was proposed, while the IG-HE mechanism for solution annealed austenitic stainless steels which was discussed in details was applied to IG-HE of sensitized austenitic stainless steels. It was also pointed out that the occurrence of both TG-HE and IG-HE was explained with an identical concept.     

Vermeidung der Wasserstoffversprödung vergüteter Stähle bei galvanotechnischen Prozessen durch thermische Legierungsbildung

Avoidance of hydrogen embrittlement of high strength steels during electroplating processes by thermal alloying Low alloyed high strength steels are often electroplated by metal layers protecting against corrosion. For ultra high strength, quenched and tempered steels with yield strengths > 1000 Nmm^?2 embrittlement by hydrogen being envolved during the electrochemical pretreatment as well as metal deposition has to be avoided. More over the corrosion protecting layers should form a diffusion barrier for hydrogen which can be formed during corrosion processes under special circumstances. In this paper two problem solutions including thermal alloying processes will be discussed. Plating the steel substrate with a nickel layer subsequently annealed at a temperature above 800°C in an inert gas atmosphere an austenitic iron-nickel-alloy at the boundary is formed, being a high efficient diffusion barrier for hydrogen. Further zinc plating is improving the corrosion resistance avoiding at the same time pitting corrosion problems. Plating the steel substrate with a copper and a following nickel layer on top and annealing it at the temperature of 800°C a highly corrosion resistant copper-nickel-alloy is formed showing excellent barrier behaviour for hydrogen diffusion. In both cases hydrogen being formed during the plating process itself and penetrating into the base metal does not lead to embrittlement as it is effusing during the annealing procedure.     

Kinetik der wasserstoffinduzierten Spannungsrißkorrosion—Tell 1: Wesentliche Einflußgrößen des Bruchvorgangs im Hinblick auf hochfeste Stähle

Kinetics of H-Induced Stress Corrosion Cracking - Part 1: Important Features of Cracking with Regard to High Strength Steels Some essential features of H-induced brittle cracking are outlined with regard to high strength steels. A literature survey shows that the electrochemical conditions at crack tips are self-controlling and can hardly be affected from outside. The increased H-solubility in strained lattice regions causes an interaction of interstitially absorbed hydrogen with stress fields. Highly strained lattice regions like crack tips and notches exert an attractive action on interstitially absorbed hydrogen which increases with increasing strength level of the steel. Theories of H-induced cracking of high strength steels and the kinetics of fracture are examined briefly. An estimate of the substantial forces acting during decohesion induced crack processes reveals the significance of the material strength for the kinetics of crack growth. Analogies to the H-induced crack growth characteristics of high strength aluminum and titanium alloys are pointed out. The common features of cracking lead to the supposition that decohesion processes may play an important role for H-induced cracking of titanium alloys, too.     

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.     

碳钢及环氧清漆在不同溶液中的半导体导电行为

采用电位-电容法结合Mott-Schottky分析技术研究了自腐蚀电位条件下20号碳钢及涂层体系在酸、碱和盐溶液中的半导体导电行为。结果表明,在不同的腐蚀溶液中,随着时间和扫描电位的增加,20号钢空间电荷层电容(Capacitance of space charge layer,Csc)变化规律不同。20号碳钢在5%硫酸溶液和5%硫酸钠溶液中呈现p型半导体导电特征,而在5%氢氧化钠溶液中,20号钢表面形成了两个空间电荷层结构,呈n型半导体特征。环氧清漆在不同电解质溶液中也表现出半导体导电特征,出现由绝缘态向半导体态转变的现象。     

Reduction in area and appearance of hydrogen-assisted fracture surfaces of cathodically charged differnt Low-alloy sulphur containing steels

The present work is concerned with the role of sulphidic inclusions in hydrogen-assisted cracking of low-alloy steels with different sulphur contents. The steels were previously cathodically charged in sulphuric acid solution. Evaluating the susceptibility to hydrogen-assisted cracking in terms of the reduction in area values, the high sulphur steel is less susceptible than the low sulphur steel. The fracture surface of the low sulphur steel appears rather brittle, with local quasi-cleavage fractures around large intergranular fracture facets. In contrast, the fracture surface of the high sulphur steel is characterized predominantly by the microvoid coalescence mode, with a great number of manganese sulphide inclusions. The difference between the two sulphur steels is based upon the concept that the interfaces between sulphidic inclusions and matrix act as trapping sites for hydrogen and thus hydrogen is uniformly distributed over the sulphidic inclusions.     

Mechanisms of tensile improvement in caliber-rolled high-carbon steel

The microstructural evolution and tensile characteristics of caliber-rolled plain carbon steels were quantitatively investigated and compared with those of the as-received plain carbon steels. The caliber-rolled steels exhibited a similar microstructure consisting of an ultrafine-grained ferritic matrix and dispersed fine cementite particles. In contrast to the general trend of caliber-rolling processes showing significant reductions in elongation while retaining a high strength, the present caliber-rolled high-carbon steel exhibited simultaneously improved strength and elongation. This distinctive tensile enhancement of the caliber-rolled high-carbon steel was attributed to the increased strain hardening rate caused by the high fraction of submicron cementite particles and to the transition of the fracture mode from a brittle state to a ductile state.     

Die Langzeit-Korrosionsgeschwindigkeit des passiven Eisens in anaeroben alkalischen Lösungen

The long-term corrosion rate of passive iron in anaerobic alcaline solutions Gas generation is an important issue in safety assessments of low and intermediate level radioactive repositories. In this connection the hydrogen production from corrosion of passive iron in saturated calcium hydroxide, in dilute alkali hydroxide and cement porewater solutions has been determined. The measurements were performed manometrically using fusion sealed glass cells, the measurement periods being between 275 and 560 days. In 0.1 M and 0.04 M alkali hydroxide solutions the initial hydrogen generation rate was 12 mmol/m²yr corresponding to a linear corrosion rate of 64 nm/yr. The reaction rate decreases with time. The smallest value obtained after 330 days is 0.3 mmol/m²yr corresponding to 1.5 nm/yr. The influence on iron of the saturated calcium hydroxide solution and the calcic porewater solutions differs from that of the alkali hydroxide solutions. At pH 12.5 the hydrogen generation rate remains practically constant up to breaking off the experiment, the value being about 1 mmol/m²yr corresponding to 5 nm/yr.     

20号碳钢在不同溶液中的半导体导电行为

    采用电位—电容法结合Mott-Schottky分析技术研究了自腐蚀电位条件下20号碳钢在酸、碱和盐溶液中的半导体导电行为.结果表明,在腐蚀性介质作用下,随着时间和扫描电位的增加,20号钢空间电荷层电容（Capacitance of space charge layer-Csc）变化规律不同.20号碳钢在5‰硫酸溶液和5%硫酸钠溶液中呈现p型半导体导电特征,而在5%氢氧化钠溶液中,20号钢表面形成了两个空间电荷层结构,呈n型半导体特征.     

Untersuchungen zum Korrosionsmechanismus von unlegiertem Stahl in sauerstofffreien Kohlensäurelösungen. Teil I. Kinetik der Wasserstoffabscheidung

Investigations into the corrosion mechanism of unalloyed steel in oxygen-free carbonic acid solutions. Part I – Kinetics of hydrogen evolution Polarisation measurements with rotating disc electrodes showed that the corrosion of mild steel in ogygen-free carbon dioxide solutions is not limited by transport processes but is controlled by cathodic activation polarisation. The reason, why oxygen-free carbon dioxide solutions are more corrosive than diluted solutions of mineral acids at the same pH, is explained by the findings that the cathodic reaction is controled by the reduction of both hydrogen ion and adsorbed undissociated carbonic acid, thus stimulating the Volmer-reaction. Electrochemical hydrogen permeation measurements showed that in carbon dioxide solutions the uptake of hydrogen in mild steel is approximately twice as high as in comparable sulfuric acid solutions. Considering the results of comparing experiments with carbon monoxide the possibility of hydrogen embrittlement of mild steel in condensates under high partial pressure of carbon dioxide must be taken into account.     

Wasserstoff-induzierte Spannungsrißkorrosion von Stählen durch dynamisch-plastische Beanspruchung in Promotor-freien Elektrolytlösungen

Hydrogen induced stress corrosion cracking of steels subjected to dynamic loading involving plastic deformation in promotor free electrolytic solutions Plain carbon steels and low alloy steels suffer internal cracking and a relatively high embrittlement when they are subjected to dynamic loading involving plastic deformation in any type of electrolytic solution where there is a simultaneous cathodic hydrogen evolution. These conditions can be encountered in service in the case of cathodic polarisation and free corrosion in acids if the mechanical stresses lead to plastic deformation, e.g. at notches. There is an upper limit to the potential range in which internal cracking occurs. This limit is independent of the yield strength (300 to 500 N mm^?2) of the materials tested and lies at U_H = ?0.5 V in oxygen free salt waters. It is more negative in oxygen bearing electrolytic solutions or in alkalaine media. Materials containing hard transformation products such as martensite and bainite are more susceptible to cracking in the regions of these hard transformation products. There is only a small decrease in susceptibility with increasing temperature. Ultra high strength, quenched and tempered steels with yield strengths > 1000 N mm^?2 undergo hydrogen induced stress corrosion cracking even when they are subjected to static loading in the elastic region. The critical potential is very negative and shifts to less negative values with increasing strength of the material. Stainless steels with stable austenitic microstructure are resistant to this type of corrosion. However, if the mechanical deformation can lead to the formation of martensite surface cracking and brittle fractures occur. The hydrogen induced damage decreases with increasing temperature.     

预置间隙对铝/钢CMT接头强度与失效模式的影响

采用CMT熔钎焊方法,对汽车用镀锌低碳钢板与6061铝合金焊接接头的强度与破坏模式进行了研究.采用不同规格的塞尺控制铝/钢搭接接头的预置间隙,以改变铝/钢异种材料熔钎焊接头的熔合面积.结果表明,通过预置间隙的方法可以有效增大熔合线长度,从而提高焊缝接头的拉剪强度.在间隙为0.5 mm时失效模式发生变化,主要原因是焊趾处铝/钢界面层中的锌元素增大了界面层的脆性.     

X80 管线钢在酸性环境下的氢致开裂行为研究

目的研究X80管线钢在我国典型酸性环境(鹰潭土壤模拟溶液)下的氢致开裂行为。方法采用电化学动电位扫描技术、慢应变速率拉伸实验和扫描电镜技术,分析氢在X80管线钢中的渗透行为、材料的放氢行为、电化学充氢对材料拉伸性能的影响以及材料断口的形貌。结果通过氢渗透实验测得,在室温下,氢在X80管线钢中的的氢扩散通量J∞=7.31×10-11mol/(cm2·s),有效扩散系数Deff=5.36×10-8cm2/s,可扩散氢浓度C0=7.64×10-5mol/cm3。钢中的氧化铝类非金属夹杂及表面点蚀坑促进了氢致裂纹的萌生,充氢后试样发生穿晶断裂。随着充氢时间的增加,断口由韧性断裂转变为脆性断裂,氢致开裂敏感性增高。结论 X80管线钢在我国典型酸性环境下(鹰潭土壤模拟溶液)具有较高的氢致开裂敏感性。     

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.     

Assessment of test methods for evaluation stress corrosion cracking susceptibility of prestressing steels

Prestressing steels can be exposed in prestressed concrete structures in construction stage (ungrouted duct) to environmental conditions causing formation and growth of hydrogen induced cracks with brittle fracture of the steel. The risk of this hydrogen induced stress corrosion cracking can be minimized by appropriate treatment, but there is a requirement for construction to approve only prestressing steel having no enhanced susceptibility to stress corrosion cracking. The paper describes the historical development of the different test methods proposed in the past and gives an overview on the general requirements for a suitable test method to assess the hydrogen‐induced stress corrosion susceptibility of prestressing steels. Since 1982, based on investigations on construction sites and transfer of the results into laboratory tests, a test method is available enabling realistic estimation of suitable application possibilities of prestressing steels. This so called DIBt‐test is approved to distinguish between prestressing steels susceptible to hydrogen induced stress corrosion cracking and those suitable and therefore approvable steels at practical environmental conditions. Furthermore the test enables estimation of corrosion risk for newly developed prestressing steels with higher strength.