Einfluß der Festigkeit unlegierter und niedriglegierter Stähle auf H-induzierte Korrosionserscheinungen bei zügiger plastischer Belastung

Influence of mechanical strength on hydrogen-induced corrosion effects on unalloyed and low-alloysteels subjected to slow strain rate tests Three steels were subjected to various heat treatments or cold working to produce 7 variants of strength. Specimens from these materials were tested in 9 aqueous solutions containing various acidic components by the constant strain rate technique under cathodic polarisation or free corrosion conditions. Hydrogen induced cracks were only observed after passing the maximum load. Hydrogen induced cracking and the decrease in the reduction of area (hydrogen embrittlement) show a good correlation with the mechanical properties of the materials. For less ductile materials the number of cracks decreased with increased embrittlement. The magnitude of hydrogen embrittlement depends on the concentration of undissociated acid in the test solution and is independent of pH value. O₂ can reduce the embrittlement. The effect of test solution composition decreases as the cathodic polarisation potential becomes more negative, because hydrogen will then be generated from H₂O. There is no correlation between the type of corrosion effects and the strength of the material, except in the case of highly sensitive high strength variants with R_m in excess of 1000 N/mm². Quenched and tempered low alloy steels, even at high strength levels, have significantly higher resistance to hydrogen embrittlement than significantly higher resistance to hydrogen embrittlement than unalloyed steels. The same is also ture for workhardened variants. For unalloyed steels, metallurgical cleanness seems to have a favourable influence. No hydrogen induced corrosion effects were observed in specimens tested at 907°C under free corrosion conditions.     

Untersuchungen zur Lötbrüchigkeit hochlegierter Stähle

A study of the liquid mentla embrittlement of high allowy steels The action of zinc on austenitic stainless CrNi steels at high temperatures may give rise to a type of intercrystalline corrosion called “soldering brittleness” (liquid metal embrittlement) which can be attributed to the formation of a low melting phase rich in nickel. These phenomena have been known for a long time in connection with other metals and alloys and have been described by several authors. As to liquid metal embrittlement of high alloy steel, however, no data have been available so far.     

Evaluation of hydrogen entry into high strength steel under atmospheric corrosion

Hydrogen entry into high strength steels by atmospheric corrosion has been investigated to evaluate their susceptibility to hydrogen embrittlement. High strength steels were corroded by dry/wet cyclic corrosion after NaCl deposition. The maximum diffusible hydrogen concentration around the surface was successfully obtained by means of thermal desorption analysis after keeping the specimens at high humidity to reproduce enhanced hydrogen entry influenced by the rust layer and to homogenize the hydrogen distribution. Despite decrease in corrosion rate, hydrogen content in specimens did not decrease. Decrease of pH in inner rust layer is responsible for the enhanced hydrogen entry into steel.     

A quantified concept of the hydrogen permeability of passivating films at a crack tip during stress corrosion cracking of structural materials

A general theoretical and methodological approach to local dissolution and hydrogen embrittlement contributions to stress corrosion cracking in various structural materials is discussed. According to this approach a quantified determination of the hydrogen embrittlement contribution to stress corrosion cracking in high-strength steels, titanium, aluminium, and zirconium, and zirconium alloys appears to be possible. On the basis of a few postulates, a quantitative concept of hydrogen permeability of the passivating film at the tip of a crack in the metal is developed; this concept allows for the first time a quantified determination of the relationship between critical hydrogen concentration and stress intensity factor in steels, titanium, and aluminium, and aluminium alloys under hydrogen embrittlement. Two new methods for studying adsorption processes at the tip of a growing crack during stress corrosion cracking are an additional outflow of this concept.     

Permeation measurements to study hydrogen uptake by steel electroplated with zinc-cobalt alloys

Hydrogen permeation measurements were performed to investigate hydrogen uptake by a steel substrate when electroplated with zinc-cobalt alloys. The influence of plating bath composition and pH were studied and the effect of absorbed hydrogen on embrittlement of high strength steel was measured in slow strain rate tests. It was shown that the majority of the hydrogen generated during electroplating was either evolved from the surface or trapped in the coating. Only a very small proportion, equivalent to 0.1-0.6% of the total charged passed, was absorbed by the steel and was responsible for causing embrittlement. The average amount of hydrogen required to cause hydrogen embrittlement failure of quenched and tempered AISI 4340 steel was 1.5 × 10⁻⁷ g H atoms cm⁻². There was a linear relationship between the rates of hydrogen uptake from the different coatings and the extent of hydrogen embrittlement produced in the high strength steel. In certain conditions, a cobalt-rich layer formed at the steel/coating interface and this layer was shown to be beneficial in restricting hydrogen uptake and embrittlement.     

Corrosion Behaviour and Mechanical Properties of Plated Zn-Alloys

Zinc represents the most effective and economic corrosion protection especially for steel base materials. Improved corrosion resistance can be achieved by alloying zinc with small amounts (around 1%) of transition metal elements like Co, Ni and Fe. ZnFe and Zn-Co alloys containing up to 1·5% of the transition metal were plated using an alkaline and acidic electrolyte respectively. Zn-Ni alloys with Ni-contents up to 14% were deposited on steel substrates using both types of electrolytes. The very homogeneous texture of the Zn-Fe-alloys proved by X-ray investigations obviously leads to the formation of a very uniform and protecting Chromate layer in the chromatizing process. Corrosion tests in the salt spray cabinet show a superior behaviour of chro- mated Zn-Fe-layers after heat treatment when compared to conventional chromated pure zinc layers and other low alloyed zinc layers. These results are confirmed by outdoor exposure tests and electrochemical investigations. As zinc-alloys are supposed to replace cadmium for fastener applications mechanical properties like hardness as well as tribological data are of importance and were investigated. Further, the hydrogen embrittlement of deposited high strength steel was also tested. On the basis of electro-chemical data a dopant-vacancy interaction model is presented for a qualitative explanation of the corrosion behaviour of plated Zinc-alloys.     

Die wirtschaftliche Verwendung von hitzebeständigen Werkstoffen in Prozeßöfen der Petrochemie

Rational utilisation high temperature materials in petrochemical furnaces While tubular furnaces in petrochemical industries were originally manufactured of cast materials, advantage is being taken now increasingly from wrought materials processed by hot deformation. These materials are characterized by a high degree of homogeneity and enable long tubular material to be obtained without transverse weld seams; in addition, they allow the use of additional specific alloying elements. In the EDC furnaces (ethylene-dichloroethylene) for the manufacture of vinyl chloride use is made of the high corrosion resistance of nickel alloys; these materials possess a remarkable resistance in chlorinated media, in particular at temperatures exceeding 600°C. Another property of importance in such conditions is the resistance to stress corrosion cracking produced by the formation of hydrogen chloride and chlorides. In the enthylene production furnaces operating at temperatures above 800°C steels are used with 32.5% Ni and 21% Cr; they resist carburazation and are creep resistant. These materials are also used for reforming furnaces and in particular for the catalyst tubes where high resistance to creep cracking is indispensable.     

Ursachen und Mechanismen der Spannungsrißkorrosion

Causes and mechanisms of stress corrosion cracking The paper provides a synopsis of the causes and mechanisms of stress corrosion cracking discussed at the present time. The discussion covers: selective metal dissolution (formation of cover layers, influence of lattice imperfections on the anodic metal dissolution, crack spreading rate, anodic hydrogen embrittlement); adsorption and brittle fracture (energy balance, atomistic and electro-chemical aspects); metallurgy (plastic deformation, alloying influence, sliding condition); fracture mechanics (crack formation and growth). Particularly important is the formation of cover layers where stress corrosion cracking depends on a certain ratio of the rate at which the cover layer is reformed and the rate at which surfaces free from cover layer are formed at the bottom of the crack. At high crack expansion rates, the adsorption-brittle fracture mechanism may play a part, as it tends to lower the cohesion at the bottom of the crack. As the crack represents an ideally sharp notch, it is possible to apply the linear elastic fracture mechanics to the crack expansion phenomena.     

Advances in Replacements for Cadmium Plating in Aerospace Applications

This paper examines some of the problems associated with the replacement of cadmium plating for the protection of aircraft components and fasteners manufactured from steel. It reviews the range of coatings which are available commercially and are currently being considered as alternatives to cadmium plating. Results of research being undertaken into the corrosion behaviour and galvanic compatibility of electrodeposited zinc alloy coatings and aluminium-magnesium alloy coatings are presented. Other aspects of coating performance are also considered including frictional properties, effects of coatings on fatigue strength, hydrogen embrittlement of steels and the repair of damaged coatings. It is concluded that although the corrosion performance of cadmium plating may be achieved with several coating systems, no one coating is likely to be acceptable as a replacement for cadmium for all aerospace applications.     

Untersuchungen über das Korrosionsverhalten von Zirkoniumlegierungen II. Verhalten bei Wasserdampfkorrosion

Investigation into the corrosion behaviour of zirconium alloys. 11. Behaviour under steam corrosion conditions An investigation into the corrosion behaviour of about 50 Zr alloys in high pressure high temperature steam (240 atm, 400°C) and hot air (4OO°C) has revealed a clear correlation between the behaviour in the two media. Alloys characterized by lower scaling susceptibility are also less susceptible to corrosion in steam, while, on the other hand, thicker scale layers tend to reduce hydrogen embrittlement. From the alloying additions studied Sn, Fe, Cr and Ni have a clearly favourable influence and W may have a similar effect. Ti has an outspoken negative influence on the behaviour in steam (spalling off of the scale) and Si, too, is deleterious because the SiO₂ being formed is soluble in steam, so that the scale layers retain their penetrability. Mo cannot be recommended either, while Nb is favourable in particular because of its grain refining effect. The favourable effect of Cu additions has been confirmed. Alloys with Fe, Cr and Ni and single types with Mo, Nb and Cu are superior to pure Zr with respect to steam resistance and are in part superior to Zircaloy 2 with respect to their mechanical strength.     

Characteristics and Verification of a Low Hydrogen Embrittling Zinc-Nickel Electroplate,Developed for Corrosion Protection of High Strength Steels

A coating process is outlined that gives low hydrogen embrittling zinc-nickel binary alloy electroplate for sacrificial corrosion protection of high strength steels, and the physical properties of the coatings produced are presented. The highly corrosion resistant zinc-nickel binary alloy coatings produced by the new process comply fully with the ASTM test requirements for control of hydrogen embrittlement. They are an alternative to the cadmium coatings currently employed for the corrosion protection of high strength steels. The results of hydrogen embrittlement tests and of structural analyses are discussed in light of the structure of the zinc-nickel coating, and of its efficiency in allowing labile hydrogen to diffuse out of the coated high strength steels.     

Comparative evaluation of environment induced cracking of conventional and advanced steam turbine blade steels. Part 1: Stress corrosion cracking

Stress corrosion tests have been conducted to assess the performance of a high strength steel, PH13-8 stainless steel, being considered for advanced steam turbine blades relative to that of a conventional blade steel, FV566. The higher strength steel had a higher threshold stress intensity factor, K_ISCC, under normal water chemistry conditions (albeit aerated) but in higher chloride solutions the K_ISCC was relatively low for both alloys with the threshold for the FV566 being slightly lower than that of the PH13-8 steel. It is proposed that hydrogen assisted cracking is the mechanism of failure for both steels. The higher threshold for the PH13-8 steel is considered to be associated with the higher alloying content of the alloy constraining hydrogen uptake as a consequence of enhanced refilming kinetics. The crack growth rate for the higher strength steel was about an order of magnitude greater than that for the FV566 steel, which is consistent with the greater sensitivity to hydrogen once the hydrogen gets into the steel. For both steels, deaeration of the solution to reflect continuous on-load conditions in service caused the growing crack to arrest.     

Investigation of the pore-formation process during the chromizing of steel 40Kh by the circulation method

During the chromium plating of carbon steels, a carbide possessing elevated hardness and wear resistance is formed on the surface. It is known that the development of diffusion porosity, which is associated with the different diffusion mobilities of the atoms, is possible in the coatings. Use of carbides as an anti-corrosion protective layer requires its continuity; this is difficult to achieve by chromium plating in accordance with applicable regimes. In the literature, there are virtually no studies in which pore formation processes are addressed as applies to carbide coatings. This paper examines diffusion processes that take place in the surface layers of steel 40Kh during long-term annealing after chromium plating by the circulation method. The composition and properties of the chromium plated layer are studied. Possible mechanisms of pore formation and recommendations for the use of diffusion carbide coatings are proposed.Translated from Metaliovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 11–14, May, 1994.     

一种用于显示中高强度钢晶粒的方法

中高强度钢随着碳含量的逐渐增加,组织愈发细小,通过直接腐蚀等传统方法得到的晶界往往比较模糊。为了能够清晰地显示中高强度钢的晶粒度,利用其具有氢脆敏感性以及氢脆易于产生沿晶断裂形貌的特点,提出了一种晶粒度检测方法。通过对 55SiCr弹簧钢和 440冷墩钢分别使用直接腐蚀、电子背散射法（EBSD）与氢致开裂断口法显示晶界,对比可以发现在中高强度钢的晶粒度检测中,氢致开裂断口法显示的晶界更为清晰,评定的结果更加准确。     

Lochkorrosion an Nichtrostenden Stählen

Pitting corrosion of stainless steels Stainless steels can get pitting corrosion in halide containing solution, which make them a big risk in industrial production. Many investigations were made in the past in order to understand processes involved in pitting corrosion, pit initiation and pit growth. Results about the influence of alloying elements, their contents, the state of the structure, the condition of the surface, the content of chloride, the temperatures, the pH-value, the velocity of flow and of the oxidizer on the chloride induced pitting corrosion of passive stainless steels are presented. Electrochemical measurements and the application of surface analytical methods (SEM, SAM, XPS) with high lateral resolution are carried out. A part of the samples received a diffusion annealing in order to obtain reproducible results. Pitting Resistance Equivalents (PRE) – Pitting Index – with different multipliers are given and discussed critical. An electrochemical method for selecting materials without susceptibility to pitting corrosion are also presented.     

低合金高强度抗应力腐蚀开裂海洋软管用钢的开发

通过合金成分设计,轧制、热处理工艺的探索,开发了低合金高强度海洋软管用钢,其屈服强度大于600 MPa且满足抗氢脆、抗氢致开裂、抗应力腐蚀开裂性能,并通过全浸腐蚀实验对该钢的海水腐蚀行为进行了研究。结果表明,采用低C、低Mn并复合添加耐蚀元素Cr、Mo和采用合理的热轧、冷轧、调质处理工艺,可获得满足抗应力腐蚀开裂性能的600 MPa级高强钢。耐蚀元素的添加使实验钢具有良好的耐海水腐蚀能力,腐蚀稳定状态下的平均年腐蚀速率为0.11 mm/a。     

Formation of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Diffusion Barrier Between Cr-Contained Stainless Steel and Cold-Sprayed Ni Coatings at High Temperature

A novel approach to prepare a coating system containing an in situ grown Cr₂O₃ diffusion barrier between a nickel top layer and 310SS was reported. Cold spraying was employed to deposit Ni(O) interlayer and top nickel coating on the Cr-contained stainless steel substrate. Ni(O) feedstock was prepared by mechanical alloying of pure nickel powders in ambient atmosphere, acting as an oxygen provider. The post-spray annealing was adopted to grow in situ Cr₂O₃ layer between the substrate and nickel coating. The results revealed that the diffusible oxygen can be introduced into nickel powders by mechanical alloying. The oxygen content increases to 3.25 wt.% with the increase of the ball milling duration to 8 h, while Ni(O) powders maintain a single phase of Ni. By annealing the sample in Ar atmosphere at 900 °C, a continuous Cr₂O₃ layer of 1-2 μm thick at the interface between 310SS and cold-sprayed Ni coating is formed. The diffusion barrier effect evaluation by thermal exposure at 750 °C shows that the Cr₂O₃ oxide layer effectively suppresses the outward diffusion of Fe and Cr in the substrate effectively.     

Hydrogen embrittlement in electroplating: avoidance using pulse plating

Abstract

During plating, hydrogen is evolved as a competing reaction and may therefore penetrate into the base material followed by a total fracture of the high strength steel component being plated. Normally, the amount of hydrogen in the component is reduced to below a critical value by a baking procedure. It is shown, however, how plating of Zn–Ni alloy or pulse plating of hard chromium on high strength steel, usually susceptible to hydrogen embrittlement, is possible without any hydrogen embrittlement and baking procedure.     

Behavior of hydrogen in high-speed steels upon treatment in a glow discharge

Themochemical treatment in a glow discharge in hydrogen-containing gaseous media is used to harden highspeed tool steels. Such treatment is accompanied by saturation of the metal by hydrogen, which leads to the appearance of hydrogen embrittlement. Transfer of hydrogen from the surface layers into the volume of the steel is accomplished by difusion fluxes. Accordingly, the investigation of diffusion processes occurring under thermochemical treatment conditions in a glow discharge is of both theoretical and practical interest.Kursk Polytechnic Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, Vol. 36, No. 9, pp. 6–8, September, 1994.     

用电化学极化方法研究缓蚀剂对高强度钢氢脆性能的影响

用电化学动电位极化的方法研究了缓蚀剂对高强度钢环境氢脆性能的影响。结果表明,根据动电位极化测试的腐蚀电位和慢电流可以预测高度钢发生蚀氢脆的倾向性。在飞机外表面清洗溶液中添加含氮有机缓蚀剂可有效地抑制松孔镀镉层的腐蚀和高强度钢的腐蚀氢脆。