Kann das Beizen von Schweißnähten austenitischer CrNi-Stähle durch andere Verfahren ersetzt werden?

Can Pickling of Weld Seams of Austenitic CrNi-Steels be Replaced by Other Methods of Surface Treatment? After heat treatment or welding stainless steels, scale resp. slag will remain on the surface so that the corrosion resistance of such passivating steels is distinctly lowered. In order to avoid this it is common practice to pickle all weld seams and their surroundings or even the whole apparatus. Pickling solutions for austenitic stainless steels are mixtures of hydrochloric acid, nitric acid, sulphuric acid and hydrofluric acid with water. For reasons of environmental protection it became desirable to use other surface treatments. This leads to the question whether or not other surface cleaning methods will work as reliable and economical as pickling securing the same corrosion resistance. In this paper the relative merits of some usual cleaning operations and their possible applications are shown, namely brushing, grinding, blasting and, for reasons of comparison, pickling. Our results showed that pickling yields the best cleaning effect and secures the best surface conditions for the formation of a good passive layer. Glass ball-blasting, properly conducted, gives the same cleaning efficiency. Welding and brushing can only be tolerated in special cases.     

304Cu抗菌不锈钢盐酸基酸洗工艺的研究

为了明确盐酸基酸洗液对含Cu抗菌不锈钢表面氧化层的酸洗行为,采用正交试验法研究以盐酸为基础,Fe~(3+)、H_2O_2和HNO_3为氧化剂的304Cu抗菌不锈钢酸洗工艺.并运用扫描电镜、透射电镜及电化学等手段分析经最佳配方酸洗后试样的表面形貌、成分及酸洗机理.结果表明:最佳酸洗工艺配方为HCl(36%~38%)120 ml/L、H_2O_2(30%)80 ml/L、FeCl_3·6H_2O 20g/L、HNO_310 ml/L,酸洗温度30℃,酸洗时间15 min.经该配方酸洗后材料表面平整度和光亮度较好,具有抗菌性能的点状ε-Cu相在基体上弥散分布.材料经酸洗去除氧化层后,仍具有足够含量的抗菌元素Cu存在.酸洗脱除氧化层过程由电荷传递过程控制,该酸洗液对不锈钢具有孔蚀诱导性,酸洗时间不宜过长.     

Beizung von BIOHOCH®-Reaktoren als Vorbehandlung für eine Beschichtung

Pickling of Steel Tanks for Use in Biological Water Purification Plants as a Pretreatment to the Application of an Organic Coating High-level tanks made from structural steel, so called BIOHOCH®-Reaktoren for biological purification of chemical waste water, had to be protected against corrosion by an organic coating. After the usual pretreatment, which means cleaning of the steel surface by sand or furnaceslag blasting, pittinglike corrosion was observed in two cases. Therefore, the required grade of surface preparation was not available. Nevertheless, to get good preconditions for a sufficient service life, both tanks with a volume of about 20 000 m³ were pickled in such a manner, that the final furnace blasting operation furnished the presumed white metal state. The problematic nature of organic coatings, which has recommended the pickling of the steel surface, is discussed. The selection, realization and controlling of this treatment are specified.     

钢板表面酸洗工艺研究

采用扫描电子显微镜（SEM）和能谱仪（EDS）观察酸洗后钢板表面的形貌和检测化学组成，借助XRD分析了欠酸洗的残留氧化物为Fe2O3，Fe3O4。通过正交试验确定最佳酸洗工艺为：酸洗浓度200g／l，酸洗温度700c，酸洗时间45s，或酸洗浓度220g／l，酸洗温度70℃，酸洗时间45s。     

Lokale Last- und Eigenspannungsverteilungen an rißbehafteten Oberflächen nach Korrosionsermüdung von vergütetem Ck 45

Distributions of Loading and Residual Stresses in Cracked Surfaces of Corrosion Fatigued Quenched and Tempered Steel Ck 45 Corrosion fatigue in the active state leads to a great number of short cracks and corrosion pits in the surface of metallic materials. This paper deals with the resulting distributions of loading and residual stresses in the case of bending fatigue. The material investigated was the quenched and tempered CBN-ground steel Ck 45. Results presented clearly indicate that stress distributions around cracks and corrosion pits are very inhomogeneous. Corrosion pits lead to a relaxation of manufacturing induced residual stresses. In the loaded state as a consequence of notch effects, maximum stresses are observed, which explains the importance of corrosion pits as crack initiation sites.     

Werkstoffanstrengung bei Wälzbeanspruchung – Einfluß von Reibung und Eigenspannungen

Material Stressing under Rolling Contact – Influence of Friction and Residual Stresses Material stressing of parts in rolling contact is in the main made up by the normal load to be transmitted, by surface friction due to slippage of the body in rolling contact and by residual stresses. The effects of varying slippage rates are described as well as the additional influence of residual stresses on magnitude, position and direction of load. By the aid of mere mechanical reflections the formation of flat and steep White Bands can be interpreted which are observed in long-lived ball bearings subjected to high stresses. The report shows that residual stresses and friction must not be neglected when describing the material stressing by rolling contact. This especially applies to residual stresses originating from rolling contact.     

Spezielle Korrosionsschutzverfahren bei Wärmetauschern

Special Methods of Anti-Corrosion Treatment in Heat Exchangers An anti-corrosion treatment must be adapted to the design of the heat exchanger and the conditions under which it is used. It is often the case, therefore, that highly specialized solutions are found. For the tubular heat exchanger, an organic coating has frequently proved suitable. The results obtained are determined by the construction, the surface characteristics of the components and paying attention to the risk of blister formation. The enamelling is problematic due to the complicated shapes involved and is still at the early stages of development. With water-cooled condensers, cleaning of the tubes while the equipment is running has proved successful. It alleviates the corrosion problem and assists the action of the inhibitors. Equipment made from materials such as titanium and austenitic CrNi steels, which are capable of being passivated, can frequently be retained in a passive state by adding air to the corrosive medium. In such cases, the excessive corrosion would normally necessitate the use of an expensive material. Where damage is caused by gaps and dead spaces it is not always possible to find a constructional remedy. A well-devised construction can subsequently be decisively influenced by manufacturing techniques relating to the structure, the state of internal stress or the surface condition.     

Einfluß der Oberflächenbeschaffenheit auf die Schwingfestigkeit von Aluminium-Druckguß

Effect of Surface Condition on Fatigue Strength of Die-Cast Aluminium Surface processing like milling or shot peening involves modifications of the surface and subsurface condition of a material that can be described by changes of the residual stresses, the hardness, and the surface roughness. Moreover, there is the possibility of introducing additional surface defects. In this paper the influence of these modifications on the fatigue behaviour of the aluminium die-casting alloy GD-AlSi8Cu3 is presented. S-N curves are determined for four surface conditions produced by milling, shot peening, and a combined treatment. The improvement of fatigue limit by shot peening is confirmed for this material. The additional effect of mean stresses is determined. Investigations of the fatigue fracture surfaces show that pores and pipes as well as surface defects induced by shot peening act as fatigue crack initiation sites.     

Zur Frage der Dauerwälzfestigkeit

The Mechanism of Contact Fatigue. This Paper reviews the mechanism of contact fatigue and the different effects of material, lubricant, surface conditions and load on this type of surface failure in bearings and gears. An analysis of the combined stresses of two cylinders clearly demonstrates that the methods applied to calculate the actual stress in the contact zone are based on idealized conditions. The consideration of the effective conditions which influence life time of machine parts under concentrated contacts — for example residual stresses, dynamically changing thermal stresses, surface roughness — has not succeeded till now.     

Beeinflussung der Korrosionsbeständigkeit von nichtmetallischen Werkstoffen durch Herstellen,Umformen und Fügen

Effects of Production, Forming and Joining on the Corrosion Resistance of Non-metallic Materials The effects of production and processing on the corrosion resistance of parts consisting of thermosetting plastics and thermoplastics are described. The resistance of parts made from glass-reinforced reactive resins can be influenced via their curing and surface quality. High internal stresses in thermoplastic parts, caused by production, forming and welding, lead to stress cracking, which may be considerably accelerated by certain ambient media. Bonded joints between fibres reinforced pipes are often weak points because they are made with fillercontaining cements that may be less resistant to corrosion than the pipe materials. Practical examples illustrate the effects of the factors described on the corrosion resistance of parts made from plastics.     

Spannungsintensitätsfaktoren für vollständig umlaufende Oberflächenumfangsrisse in Rohren bei Thermoschockbelastung

Stress Intensity Factors for Complete Circumferential Surface Cracks in Thermally Shocked Pipes In the case of an emergency cooling of a reactor thermal stresses are generated in the pipes of the primary loop, which may be described conservatively as a thermal shock problem. In this paper complete interior circumferential surface cracks loaded by these thermal stresses are considered. By means of the weight function method stress intensity factors were calculated for this loading case.     

Correlation between corrosion pits and stresses in Al alloys

Pitting corrosion is commonly observed in a wide range of aluminum alloys that are being used for aerospace applications. There is a need to study the stress environment around pits in order to predict the nucleation of cracks. The objective of this study is to investigate the correlation between pits and stresses in aluminum alloys. Corrosion experiments were carried out on aluminum 2024-T3 alloy samples and imaged through Atomic Force Microscopy (AFM) to obtain the pit profiles. An analysis procedure was developed using CAD and finite element analysis to predict stresses resulting from corrosion pits. Based on the analysis, it was observed that the stress distribution and levels on the corroded surface varied due to irregularity in the corrosion process. The results obtained indicate that the stress initially increases and reaches a plateau with increasing corrosion time. From these stresses it is possible to estimate the initiation of cracks, from which the life can be estimated for failure in the material.     

Mechanische Verträglichkeit bei Verbundwerkstoffen – Naßkorrosion

Mechanical compatibility of metallic composites . Corrosion in aqueous media. As a main condition for corrosion in aqueous media between components of a composite material, both components have to be touched by an invironmental wed atmosphere or of a fluid. If this condition is given contact corrosion can take place with any composite, independent of the mechanical compatibility of the components. Crevice corrosion is possible too if mechanical incompatibility (or extern loads) causes cracks between the components; stress corrosion cracking is possible as well. Stainless steel vires, for instance, can not reinforce the composit if attached by SCC. The other kinds of corrosion mostly dammage the matrix, which also reduces properties of the composit. Examples are given of possible kinds of corrosion for some fiber reinforced metallic composites and for metal laminates.     

Einsatzhärten mit Stickstoff für nichtrostende Wälzlager und Werkzeuge

Case hardening of stainless bearings and tools using nitrogen Case hardening of low alloy steels is widely used for bearings, tools, gear wheels etc. Carburizing of high alloy stainless steels, however, leads to the precipitation of carbides and lowers the corrosion resistance. This may be avoided by case hardening with nitrogen instead of carbon. Dissolved nitrogen increases the hardness, the corrosion resistance and the compressive residual stresses of the martensitic case. Secondary hardening during tempering allows for service temperatures up to about 350°C with only little loss of corrosion resistance. The new heat treatment, which is quite different from nitriding, may be applied e. g. to advanced bearings for aircraft or tools for processing aggressive polymers.     

磁屏表面裂纹分析

本文对磁屏外表面的轴向开裂进行了分析。结果表明，该表面开裂为应力腐蚀开裂。其原因是磁屏表面存在较大的切向拉应力，从而在酸洗过程中产生了应力腐蚀开裂。对冲压后的磁屏采用消除应力退火，随后再酸洗，未发生表面轴向开裂。     

Influence of Die Lubricants on Pickling and Conversion Treatment of High‐Pressure Die‐Cast AM30 Magnesium Alloy

The pre‐treatment of magnesium‐based components plays an important role in surface engineering technology to guarantee good adhesion of the final coating system to the magnesium substrate in order to achieve good corrosion resistance. This paper focuses on the influence of two different die lubricants—one based on mineral oil, the other on siloxane—on the pickling and conversion treatment of an AM30 alloy. The surface conditions after casting, pickling, and conversion treatment were determined by X‐ray‐induced photoelectron spectroscopy, spark erosion, optical emission spectroscopy, IR spectroscopy, and scanning electron microscopy (including EDX). The influence of the different die lubricants on the result of the pickling treatment in terms of surface morphology and composition was significant. The mineral–oil‐based lubricant was found to be removed more easily and uniformly from the surface. Only sufficient removal of the die lubricants can guarantee homogeneous and uniform formation of the conversion coating.     

Einfluß des Festwalzens auf die Oberflächen‐ und Randzoneneigenschaften der Magnesiumlegierungen AZ31 und AZ91

Influence of burnishing operations on surface‐ and subsurface properties of AZ31 and AZ91 A mechanical surface treatment on magnesium‐alloys can be used to improve surface and subsurface characteristics after the cutting process. Investigations show, that the grooves, resulting from the turning process, are planed. The hardness of the surface rises. Compared to turned and polished samples, the increased strength and the induced residual stress of burnished samples cause an increased fatigue strength under rotating bending stresses. The corrosion resistance of AZ31 is enhanced by roller burnishing.     

Rohr-Innendruck-Zeitstanduntersuchungen bei überlagerter Heißdampf-Korrosion. Ausmaß und Erscheinungsform der spannungsbedingt verstärkten Oberflächen- und Gefüge-Oxidation von Rohrmaterial der Leigierung Incoloy 800

Stress-Rupture Testing under Superimposed Steam Corrosion . Extent and Morphology of Stress-Assisted Surface and Bulk Oxidation of Incoloy Alloy 800 Thin Wall Tubing. Continuing long-time stress-rupture testing under biaxial stresses and superimposed steam corrosion of Incoloy Alloy 800 thin wall tubing, the extent and morphology of stress-assisted additional surface and bulk oxidation was evaluated by quantitative metallography. This paper describes the stress-assisted additional corrosion as function of tangential stress or corresponding rupture-life, creep strain, and creep rate. The results are presented and explained on the basis of surface and bulk penetrating oxide morphology.     

Virtuelles Werkstoff‐ und Prozessdesign funktionaler Schichten

Virtual Material‐ and Processdesign of Functional Coatings Thermally sprayed and plasma transferred arc clad coatings are often used to improve the surface properties of mechanical parts with regard to an improved wear and corrosion behavior. New coating processes and applications can be developed, if it is possible to control the coating microstructure by a defined management of the process parameters. Simulation can be used to get a detailed understanding of the process‐material interaction for a defined controlling of the process parameters with less experimental effort. This allows a systematic variation of the coating structure and to calculate the parameter set which represents the best compromise between a high deposition rate and low residual stresses in the coating. In order to model thermal spraying, the following sub‐processes are considered: gas flow, material supply, heating and accelerating of particles, particle impact on the substrate, coating formation, solidification and formation of residual stresses. The results presented in this paper will demonstrate the influence of the process parameters on particle properties and subsequently on the splat formation, the coating formation and the coating microstructure. Controlling different process parameters like material injection conditions and substrate properties, the heating, cooling and solidification behavior of the particles and the coating structure can be influenced significantly.