Die Korrosionsbeständigkeit metallischer Werkstoffe für Automobilbremsleitungen

Corrosion resistance of metallic materials in automobile brake lines A statistical evaluation of the data compiled by the Swedish Automobile Inspection Authority and covering corrosion effects in brake fluid lines enables the following recommendation to be made:

• (a) Copper-brazed steel tubes, though very common, have no sufficient corrosion resistance; the same applies to welded or seamless drawn steel tubing.
• (b) The best suited materials are phosphorus deoxidized copper and stainless steels (about X 5 CrNiMo 18 12). The lower fatigue strength of copper must be compensated by suitable design; as compared to the stainless steel, copper is advantageous from the cost side.
• (c) Copper as well as stainless steel tubing can be corroded at fittings and fastening points; these problems must be eliminated by suitable design to be decided uon in each particular case.

     

Messerlinienkorrosion von automatisch hergestellten Schweißverbindungen aus korrosionsbeständigen Stählen

Knife-line corrosion of weld connections of corrosion resistant steels, produced with automatic welding equipment The investigation of submerged arc weldings (obtained with automated equipment) and electro-slag weldings (obtained by manual methods) of a steel of CSSR production and of AISI 316 L steel have revealed, that the behaviour of both is practically identical, i.e. that both of them are not susceptible to knife-line attack (testing in standard solutions, i.e. sulfuric acid/copper sulfate and 65% nitric acid). In the case of the submerged arc weldings the damaged zone is some what narrower, but in either case the cause of attack in the adjacent region is due to overheating to a temperature close to the solidus line. An important influence must be attributed to heat treatment: after sensitizing, the weld metal, too, may become susceptible to intercrystalline corrosion, while after certain types of heat treatments even sensitizing has no deleterious effects.     

硝酸级(NAG)310L不锈钢焊接接头在含Cr~(6+)的HNO_3溶液中的耐蚀性

对硝酸级(NAG)310L不锈钢焊接接头在含氧化性离子的沸腾硝酸中进行浸泡实验及金相分析。研究表明,在不同Cr~(6+)含量的沸腾40%HNO_3中,材料的腐蚀程度主要受Cr~(6+)含量的影响。随Cr~(6+)含量的增加,母材和焊缝均出现不同程度腐蚀,但焊缝较母材腐蚀严重。Cr~(6+)含量是促进焊缝过钝化腐蚀和晶间腐蚀的主要因素。     

黄铜与304不锈钢的电阻软钎焊封装工艺

针对某热量表的温度传感器中由于尼龙成分的存在导致其构成材料黄铜和304不锈钢不能在高温下焊接的问题,采用电阻软钎焊的低温连接方法进行焊接试验,以实现密封连接效果. 结果表明,在0.3 MPa的焊接压力下,当焊接电流设定为26 kA时,以双层Sn-Pb箔片为钎料的焊件进行的试验效果良好,达到了可靠的连接,且黄铜中心尼龙成分未受到焊接温度的影响而损坏. 在扫描电镜下观察到钎料与不锈钢和黄铜均发生了表面扩散. 将焊接后的样品置于水中进行密封性试验,结果显示焊缝区域实现了可靠地连接,达到了密封防水效果.     

Zur Frage einer Korrosionsgefährdung von hartgelöteten Edelstahlfittings,insbesondere durch die sogenannte „Messerschnittkorrosion”︁

The problem of potential corrosion of brazed alloy steel fittings, in particular by the so--called “knife-line attack” Longterm tests (1 year) with brazed alloy steel fittings (13% Cr steel and AgCd or AgCuInNi solder) in tap-water enriched in sodium chloride (50, 200, 500 ppm Cl^?). The results show that there is no danger of knife-line attack attributable to the brazed joint. Attack was purely local and could be detected by microskopic observation only. The reduction of mechanical strength of the brazed joints is attributed to low filling degree of the soldered seam; in this context residual flux may have some bearing too.     

Sicherung von Schraubenverbindungen aus nichtrostenden Stählen

Securing screws of stainless steels The author emphasizes the importance of screwed connections in technology and discusses the conclusions which must be drawn from existing standards with respect to the utilization of stainless steel screws. Examples are shown to demonstrate the corrosion resistance of such connections (tests in sea water, 3% NaCl, tap water, salt spray) giving prominence to the problems resulting from the use of spring elements (crevice corrosion danger).     

Untersuchungen zum Korrosions- und Verschleißverhalten von hartstoffverstärkten „Duplexstahl“-Schutzschichten

Investigations on corrosion and wear behaviour of duplex stainless steel coatings reinforced with hardening components This paper is dealing with corrosion and wear resistance results of protective duplex stainless steel coatings (X2CrNiMoN25-10-4) made by two-powder-plasma weld surfacing with additional hardening components Cr₂C₃ and WC-WC₂. First the developing of a process technique was important which allows an exact addition of hardening components and an as low as possible dissolution of carbides. The microstructure did not show the typical ferritic-austenitic structure. The wear and corrosion resistance in sulphuric acid is very good and reveals the high quality of the protective coatings. However the corrosion resistance in synthetic sea water is considerable reduced. Low grain size and pre-heat temperatures of 100 °C have a positive influence on the corrosion resistance.     

Korrosion nichtrostender austenitischer Stähle in (kondensierender) chloridhaltiger Salpetersäure

Corrosion of austenitic stainless steels in (condensing) nitric acid containing chlorides The corrosion parameters involved in the behaviour of austenitic stainless steels and nickelbase alloys in chloride containing nitric acid are being stated. Investigation of the corrosion resistance of the austenitic stainless steel 1.4306, ESR grade for application in nitric acid, in nitric acid condensates containing small amounts of chlorides. The condensates were formed from boiling nitric acids of molarities 6 to 10 containing 15 to 45 mg chlorides/1. The calculated corrosion rates of < 1 μm/y can be considered rather small. Especially in cases of insufficient wetting of the heat exchanger surfaces, however, local roughening and pitting corrosion is to be expected, mostly under rust-colored, chloride-containing deposits. The intensity of pitting corrosion increases with increasing chloride contents of the nitric acid solutions that evaporate. The sealing surfaces consisting of steel 1.4306 and PTFE did not exhibit any crevice corrosion. Nitric acid grade ESR-1.4306 definitely does not suffice requirements as described in this paper. It is suggested to use stainless steels which exhibit an improved resistance against chlorides and, at the same time, a high resistance against nitric acid attack. The following steel grades may be considered: X 1 CrNi 25 21 (Mat. No. 1.4335), X 2 CrNiMoN 25 22 2 (Mat. No. 1.4466) and/or X 1 NiCrMoCuN 31 27 4 (Mat. No. 1.4563).     

Oberflächenbehandlungsverfahren und deren Einfluß auf die Korrosionsbeständigkeit nichtrostender Stähle

Surface treatments and their influence on the corrosion resistance of stainless steel The surface treatments pickling, grinding and glass beading were investigated on several stainless austenitic steels and one ferritic/austenitic steel. The different surface treatments were used on two different prepared types of samples:

• 1 high temperature oxidized samples
• 2 welded samples

The quality of the surface treatments has been examined by means of potentiodynamic, ferric chloride, dip and spray tests made in series. The corrosion resistance was highly depending on the used treatments. All in all the examination showed that a higher corrosion resistance was achieved by pickling than by grinding or glass beading.     

Dissimilar Joining of Zircaloy-4 to Type 304L Stainless Steel by Friction Welding Process

Zirconium- and titanium-based dissolver vessels containing highly radioactive and concentrated corrosive nitric acid solution needs to be joined to the rest of fuel reprocessing plant made of AISI type 304L stainless steel (SS), which demands high integrity and corrosion resistant dissimilar joints. Solid-state joining process of friction welding was proposed in the present work to join zircaloy-4 and type 304L SS since fusion welding processes produce brittle intermetallic precipitates at the interface which reduce the mechanical strength as well as the corrosion resistance of the joint. The present study attempts to optimize joining parameters, without and with thin Ta and Ni interlayers that can prevent brittle intermetallic formation. Tensile test, three-point bend test, and microhardness measurements were performed on the joints. Characterization techniques such as optical microscopy, scanning electron microscopy (SEM), and x-ray diffraction (XRD) were employed. A good friction weld joint of zircaloy-4 to 304L SS was achieved with the joint strength (~540 MPa) greater than that of the base of zircaloy-4, without using any interlayer. A bend ductility of 5° was only obtained without using any interlayer. However, XRD patterns indicated the presence of intermetallics in the friction-welded joints without interlayers. Corrosion test carried out on zircaloy-4 to 304L SS friction joint in boiling 11.5 M nitric acid exhibited corrosion rate of 225 μm/year after 240 h. SEM examination of the corroded joint indicated severe intergranular corrosion attack over stainless steel and preferential dissolution at the interface.     

Zum Korrosionsverhalten nichtrostender austenitischer Chrom-Nickel-(Molybdän,Kupfer)-Stähle in nahezu wasserfreier Essigsäure

Corrosion of stainless austenitic steels in almost anhydrous acetic acid As-welded samples and looped specimens from 5 differently alloyed stainless steels were tested for up to 246 days in 99,5% to 99,95% acetic acid at 118°C (boiling temperature/normal pressure) and at 150°C; the chloride content was varied between < 1 and 100 ppm. Pitting corrosion – of shallow depth, however (approx. 0,1 mm) – was already observed at surprisingly low chloride concentrations. Only the following were found to be resistant to pitting corrosion:

• – stainless steels 1.4439 and 1.4539, containing approx. 4,5% molybdenum, in 99,5% acetic with < 1 ppm chloride at 118 and 150°C,
• – stainless steels 1.4439 and 1.4539 in 99,9% acetic acid with < 1 ppm chloride at 118°C, and
• – special stainless steel X 2 CrNiMoCuN 20 18 6, containing approx. 6% molybdenum, in 99,5% acetic acid with > 3, < 10 ppm chloride at 118 and 150°C.

Looped specimens and ground as-welded samples showed no sensitivity to transcrystalline, chloride-induced stress corrosion cracking at any of the concentration ranges. High surface-removal rates can be expected if air has access to the specimens; under this condition pitting corrosion and general corrosion may overlap. Contamination of acetic acid with chlorides must be prevented under all circumstances.     

Experiences with a high-alloyed stainless steel under highly corrosive conditions

The paper emphasizes experiences from the chemical industry with a highly alloyed stainless steel, Avesta 254 SMO. A number of installations are reported where this 6 Mo austenitic stainless steel has been selected since conventional stainless steels have shown inadequate corrosion resistance. These installations are at the production of

• – aluminium fluoride
• – chlorate, sodium and potassium
• – diamines
• – synthetic fibres
• – soda and at the recovery of
• – solvents, viz. chlorinated hydrocarbons
• – sulphur dioxide

Further the paper summarizes some experiences from the fabrication point of view.     

Schwingungsrißkorrosion feuerverzinkter Schweißverbindungen im bauteilähnlichen Maßstab bei wechselnden Korrosionsbedingungen in chloridhaltigem Medium

Corrosion fatigue of hot-galvanized component-like welded joints in chloride medium at changing corrosion conditions The project was focussed on the investigation of the fatigue behaviour of welded specimens of hot-galvanized plate material of steel RSt 37-2, St 52-3 and St 70-2 as frequently used in steel constructions which were mended by thermal zinc-spraying in the fillet area and tested at changing corrosion conditions. In addition, the fatigue behaviour of welded specimens with additional PVC coating of both non-galvanized and galvanized types at changing corrosion reaction was also investigated. The established findings can be summarized as follows:

• – At constant amplitude loading, hot-galvanized precludes very markedly the drop in endurance which would occur under corrosion. By contrast, an increase of fatigue strength in the corrosive medium due to galvanizing is only conditionally discoverable at variable amplitude loading. In regard to the protection against corrosion, welding of hot-galvanized parts brings an improvement at variable amplitude loading only if a given thickness of the zinc coating depending on the material is not exceeded. Too thick coating results in the formation of pores at the subsequent welding and reduces the fatigue strength in spite of the later zinc-spraying.
• – The structural steels RSt 37-2 and St 52-3 in hot-galvanized state are better suitable for welding than the more notch- and corrosion-sensitive St 70-2.
• – Soldering brittleness could not be established as cause of the failure.
• – The application of PVC protective layers secures high rates of increase or the fatigue for the non-galvanized specimens.

     

Einfluß von Seigerungen auf das Korrosionsverhalten von austenitischem nichtrostendem Schweißgut

Influence of segregations on the corrosion behaviour of austenitic stainless weld metal Fully austenitic stainless weld metal on solidification acquires a segregation structure. The segregation takes place with the participation of the alloying elements responsible for the corrosion behaviour. Regions of low alloy content are preferentially attacked and microelements form between them and more corrosion resistant regions. The progress of corrosion is enhanced by lamellar segregation structures and is inhibited by cellular structures. The corrosion due to segregations is particularly pronounced when the resistance in one medium is a pronounced function of an alloying element prone to segregation. This is demonstrated on the example of weld metal X 2 CrNiSi 1815 having different Si contents. The effect of the base metal/weld metal macro-element is discussed. Corrosion due to segregation takes place only when the weld metal is subject to attack in the vicinity of its resistance limit.     

城市输水用Q235B+304不锈钢复合管环焊焊接工艺

不锈钢复合管内侧为具有耐腐蚀性能的不锈钢,外侧为具有一定强度的碳钢,成为新一代环保型输水管。为了研究8 mm+2 mm厚城市输水用Q235B+304不锈钢复合钢管的环焊焊接工艺,试验选用合理的焊接材料及坡口形式等,获得了复合板与复合板、复合板与碳钢板的焊接接头。通过拉伸、冲击、弯曲试验评价两种焊接接头的力学性能;通过检测接头不锈钢焊道化学成分,评估复合管焊接接头内侧不锈钢焊道的耐晶间腐蚀性能。结果表明,所采用的焊接工艺获得的接头力学性能满足技术要求且富余量较大,复合管接头不锈钢焊缝获得了A+(5%~10%)δ组织,耐晶间腐蚀性能优异。     

Die Inhibition von Kühlkreisläufen

The inhibition of cooling systems The choice of an efficient corrosion inhibitor has to take in account the type of the cooling system, the materials used as well as the specific operating conditions, for instance

• – very low or very high velocities of the cooling water
• – heat transfer
• – the inhibitor may be asked to have some lubricating properties
• – vibrations, that can cause cavitation or fatigue corrosion
• – interaction between the corrosion inhibitor and other electrochemical systems of corrosion protection (cathodic protection).

In numerous applications it is necessary to improve the inhibition by an addition of other effective substances (like dispersants, hardness stabilizers, mixture of inhibitors with selective protection properties).     

电子束焊工艺对304不锈钢焊缝的抗晶间腐蚀性能影响

采用3种不同的电子束焊接工艺焊接304不锈钢,通过显微组织观察、XRD分析、极化曲线测试、动电位再活化(EPR)试验研究了不锈钢焊缝的抗晶间腐蚀性能.结果表明:减少焊接热输入量和添加熔入性焊丝这两种方法都能减少电子束焊缝中铬的碳化物的析出,降低焊缝的敏化度,提高焊缝的抗晶间腐蚀性能;与减少焊接热输入量相比,添加熔入性焊丝对晶间腐蚀的影响更大,焊缝抗晶间腐蚀性能提高更显著.     

Qualifizierung metallischer Werkstoffe für die Eindampfung von Abwässern aus der Rauchgasentschwefelung

Qualification of metallic materials for evaporation of waste water from flue gas desulfurization plants The ecologically-minded processing of waste water from the wet scrubbing of flue gases of coal-fired power plants to produce environmentally acceptable products is carried out in a two-step evaporater operating in closed loop mode. The evaporating process leads to high concentration of chlorides in the two evaporation steps: up to about 100 g/l in the 1st step and up to about 350 g/l in the 2nd step. Therefore in case of metallic design of the evaporation equipment materials of construction with exceptional resistance to chloride induced pitting are required. The corrosion resistance of the high-alloyed stainless steel Alloy 31 (X1NiCrMoCu32-28-7 – UNS N 08031) and of the NiCrMo-alloys Alloy C-276 (NiMo16Cr15W – UNS N 10276) and Alloy 59 (NiCr23Mo16Al – UNS N 06059) including their weldments were to be tested for this application both in the laboratory and in field tests. In addition the behaviour of Alloy 59 heat exchanger tubes had to be determined in field tests under heat-transfer service conditions. The critical pitting corrosion temperatures of the 3 materials after having been GTAW welded under uniform conditions with FM 59 (ERNiCrMo–12) filler were determined in potentiostatic tests in model solutions imitating concentrated waste water products as they may occur in practice, using 5 K temperature intervals. As to be expected the critical corrosion resistance limits of the materials lie at 85 °C at chloride concentrations of 100 g/l Cl⁻ for the Alloy 31 and of 300 g/l Cl⁻ for both the Alloy 59 and the Alloy C–276 respectively. Field tests in waste water evaporation units of flue gas desulfurization plants of coal-fired power stations are carried out as immersion tests with the welded materials and as heat-exchange experiments using longitudinally welded tubes of Alloy 59 (2.4605). The immersion tests over a period of 32 months show the Alloy 31 (1.4562) to be a corrosion resistant construction material for tubes and containers in the first evaporation step, whereas the Alloy 59 (2.4605) and the Alloy C–276 (2.4819) have to be used for the second evaporation step, where the chloride contents are much higher. The Alloy 59 is to value as the most resistant material according to its lower tendency to crevice corrosion. The heat-exchange experiments over a test period of 9 months cause to expect the Alloy 59 to be a suitable construction material for heat-exchanger tubes in both evaporation steps in comparison to graphite which is more succeptible to mechanical destroying.     

Untersuchung des chemischen und elektrochemischen Verhaltens von zementmörtelausgekleideten Stahlrohren in kohlensäurehaltigen Wässern

Investigation of electrochemical element formation by crevices of different width in cement lined steel tubes The author describes an experimental setup for the investigation of the attack of water with aggressive carbonic acid on the cement lining of steel tubes. In equilibrium waters crevices in the cement are covered by protective layers; in aggressive waters, however, there is a critical crevice width (probably 2 mm), which must not be exceeded without the danger of corrosion. When dissolved calcareous constituents aer replaced by iron oxide in the mortar the resistance of the cement is increased.     

Applications and experience with a Superaustenitic 7Mo stainless steel in hostile environments

A new superaustenitic stainless steel is described in terms of chemical composition. mechanical properties and corrosion resistance. Results obtained by using this highly alloyed stainless steel, EN 1.4652, in a number of hostile environments are reported. Applications include neutral and acid chloride containing environments such as those existing in e.g. – pulp bleach plants, – ventilation systems of pharmaceutical plants, – equipment for flue gas cleaning in power plants and municipal waste incineration plants, – equipment for recovery of chlorinated hydrocarbons, – sea water piping, – nuclear power plant condenser tubes. The paper also contains laboratory corrosion test results positioning this steel in relation to other highly alloyed stainless steels and nickel base alloys, mainly in terms of its resistance to chloride induced localised corrosion.