Einfluß von Beschichtungen auf das Schwingungsrißkorrosionsverhalten des Chromstahls X20Cr13

Influence of coatings on the corrosion fatigue behaviour of 13% chromium steel The influence of coatings on the corrosion fatigue behaviour of 13% chromium steel has been studied. There have been selected different coating systems: Barrier coating (enamel), diffusion coatings, (aluminizing, chromizing) and anodic coating, (aluminium, zinc, tin, cadmium). The corrosion fatigue limits of coated with uncoated specimens in neutral NaCl-solution are compared. Salt-concentrations were 0,01 and 22% (? 0,38 M) NaCl at 80°C and 150°C. The tests were carried out with alternating tensions and a constant frequency of 50 Hz. Only the use of andic coatings improved the corrosion fatigue behaviour of the chromium steel.     

Selektive Korrosion an Verbindungsschweißen von Stählen

Selective corrosion at welded assemblies of steels The paper deals with the possible selective corrosion phenomena at the most important types of weld assemblies of steels, viz. those of unalloyed ferritic ship building steels, austenitic manganesechromium steals, aluminium-killed boiler steels an well as chemically resistant ferritic and austenitic chrom-nickel steels. With unalloyed ship building steels, a strong corrosion element is liable to occur between not fully descaled plates and scaleless welding material, where the latter is particularly liable to be attacked. But even where scalefree plates are welded, a local element may be set up, depending on the killing intensity and on the filler metals, between plate and welding material in such a way that, again, the welding material is liable to be dissolved first. In the case of austenitic manganese-chromium steels, exposed to sea water, intercrystalline corrosion takes place at a certain distance from the weld as a result of chrome-carbide segregation. In the case of welded assemblies of aluminium-killed steels, intercrystalline fissuration is particularly liable to occure in a more or less marked decarbonised zone at the transition. With ferritic chromium steals and austenitic chrom-nickel steels, the welds are decisively influenced by the segregation of chrome-carbides at the grain boundaries which results in a proneness to intercrystalline grain decomposition. Measures are discussed by which the segregation of chrom-carbides during welding can be avoided. Finally, mention is made of the effect of delta-ferrite on the corrosion behaviour of austenitic welding material.     

Modern steels for light automobiles (review)

The article considers the directions of work at VAZ together with metallurgists of the CIS for creating highly efficient economically-alloyed and microalloyed steels; highly ductile forged steels with improved corrosion resistance coated with zinc and with good stamping, welding, and painting capacity. Steels are created for petrol tanks with aluminum-zinc coatings instead of lead, and new heat and corrosion-resistant steels are developed for automobile exhaust gas systems.Volga Automobile Factory (VAZ). Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 22–23, October, 1994.     

Effect of SiO2:Na2O molar ratio of sodium silicate on the corrosion resistance of silicate conversion coatings

Passivation treatment by sodium silicate solution is considered as an alternative to chromium chemical conversion treatment to improve the corrosion resistance of hot-dip galvanized (HDG) steels. In this paper, a transparent silicate coating was formed on the surface of HDG steel by immersing in sodium silicate solution with SiO₂:Na₂O molar ratio in the range from 1.00 to 4.00. The parameter about the SiO₂:Na₂O molar ratio of silicate solution has been discussed using corrosion resistance and surface morphology. Tafel polarization, electrochemical impedance spectroscopy (EIS) measurements and neutral salt spray (NSS) test show that silicate coatings increase the corrosion resistance of HDG steels. From the results obtained, it is deduced that the optimum SiO₂:Na₂O molar ratio is 3.50. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD), and reflectance absorption infrared spectroscopy (RA-IR) show that there are no obvious differences of the chemical composition and structure in various silicate coatings. The silicate coatings mainly consist of zinc oxides/hydroxides, zinc silicate and SiO₂. However, atomic force microscopy (AFM) images reveal that the surface of silicate coatings with a molar ratio of 3.50 is more compact and uniform than other silicate coatings.     

Effect of boron concentration on the corrosion resistance of cast B‐bearing steel in molten zinc

The microstructures, mechanical properties and corrosion resistance in molten zinc of five kinds of cast B‐bearing steels containing X wt% B ‐ 0.8 wt% Si ‐ 1.0 wt% Mn ‐ (1.0～2.0) wt% Cr ‐ (0.3～0.5) wt% C (X = 0.50, 1.00, 1.50, 2.00, 2.50) were studied. The effects of boron concentration on microstructure and mechanical properties of cast B‐bearing steels have been investigated by optical microscopy (OM), X‐ray diffraction (XRD) analysis, hardness and impact tester. The evaluation of corrosion resistance in molten zinc of cast B‐bearing steel is calculated from the slopes of mass loss versus dipping time and surface area of sample at 480 °C. The results showed that boride volume fraction and hardness increased and the impact toughness of cast B‐bearing steel decreased with the increase in boron concentration. The corrosion rate of cast B‐bearing steels decreased and corrosion resistance in molten zinc increased with the increase in boron concentration. Moreover, the corrosion rate of cast B‐bearing steels decreased with the increase in temperature of molten zinc.     

Development of novel diffusion coatings for 9–12 % Cr ferritic‐martensitic steels

Eventhough 9–12% Cr steels are mechanically designed for power plant applications up to 650 °C, their effective use is limited by the corrosion resistance at this temperature. Therefore, the present paper addresses the development of diffusion coatings on 9% Cr ferritic‐martensitic steels. The difficulty of coating these materials with conventional diffusion processes arises from the temperature limit above which the conversion of the martensite is accelerated and the mechanical properties would be deteriorated. Aluminide coatings consisting of Fe₂Al₅ or FeAl phases were thus developed for deposition temperatures between 650 and 715 °C by the conventional pack cementation technique. As the addition of boron was expected to improve the oxidation properties of the coating, the influence of B on the aluminide coating was investigated. The precedent diffusion of Cr as an interdiffusion barrier before switching to the Al diffusion step was also investigated. As a further technique, the fluidised bed chemical vapour deposition (FBCVD) method allowed the development of Fe₂Al₅ coatings at 550 °C. Furthermore, Si or codiffusion Al‐Si coatings were developed at temperatures as low as 550 °C.     

钼酸盐后处理提高热镀锌上磷化膜耐蚀性的探讨

将磷化后的热镀锌钢板用钼酸盐后处理,以提高磷化膜的耐蚀性。用SEM、EDS、电化学极化测量和盐雾试验研究了钼酸盐后处理对磷化膜组成和耐蚀性的影响。结果表明,经钼酸盐处理后,磷化膜上磷酸锌晶体间的孔隙被钼酸盐膜填补,从而在锌层表面形成了由磷化膜和钼酸盐膜构成的连续完整致密的复合膜;复合膜的极化电阻Rp显著增大,腐蚀电流密度显著减小,耐蚀性大大增强。磷化300s、后处理50s时复合膜的耐蚀性最优,Rp比单磷化膜的增加了一个数量级。     

Elektrochemisches Verhalten und Deckschichtbildung hochlegierter Manganstähle

Electrochemical behaviour and scaling of high alloy manganese steels Passivating surface layers are considered to be one of the indispensable requirements for stress corrosion cracking of metallic materials. It is shown by potentiostatic and potentiokinetic current density-potential curves that the steel X 40 MnCrN 19 in neutral aqueous chloride solutions has a passive potential region. The passivation behaviour Of precipitation hardened samples is in agreement with the chromium depletion theory. The effect of alloying on the passivation behaviour of low carbon Mn steels is studied in 3 % NaCl solution at 20 and 100 °C Increasing proportions ε-martensite reduce the passivation of susceptibility. Increasing the Mn content has the same effect. The vital factor concerning passivation behaviour, however, is chromium content. Increasing the temperature of the corrodent results in an increased tendency to form scales of steels containing less than 8 % Cr. Long-term corrosion tests have shown, that increasing the Cr content produces a continuous transition from general localized and even pitting Corrosion. Tests made without applied current in aerated solutions have shown, that the variation in time of corrosion potentials depends from the tendency to be passivated of the materials and from the oxygen content of the solutions. In oxygen containing solutions passivable steels exhibit a pronounced corrosion in the pitting region, because with such alloys anodic dissolution current densities equal to those of the limiting diffusion current of oxygen reduction are obtained only at potentials above the pitting potential.     

Degradation behaviour of ZrO2-Ni/Al gradient coatings in molten Zn

In order to improve the corrosion resistance of metallic materials in molten zinc, ZrO₂-Ni/Al gradient coatings were sprayed on the surface of the Fe-0.35-0.44 wt.% C steel. The corrosion behaviour and corrosion mechanism of the ZrO₂-Ni/Al gradient coatings in molten zinc were studied. The ZrO₂-Ni/Al gradient coatings on the surface of steels prolonged the lifetime of samples and changed the corrosion behaviour of the samples in molten zinc. The lifetime of the ZrO₂-Ni/Al gradient coatings immersed in molten zinc at 620 °C is 28 days, which is 4 times as long as that of the general ZrO₂ coatings. The ZrO₂-Ni/Al gradient coatings were corroded in molten zinc at 620 °C, which was caused by zinc atom diffusing along the crystal boundary and pores of the ZrO₂-Ni/Al gradient coatings, and reacting with Ni/Al particle in the ZrO₂-Ni/Al gradient coatings. The corrosion mechanism of the coatings in molten zinc at 620 °C was crystal boundary corrosion, pitting corrosion and reaction corrosion.     

Suppressing type IV failure via modification of heat affected zone microstructures using high boron content in 9Cr heat resistant steel welded joints

Abstract

Creep rupture strength at 923 K and microstructural evolution of welded joints have been investigated for high boron–low nitrogen–9Cr heat resistant steels developed at the National Institute for Materials Science (Japan). Welded joints were prepared from plates containing 47–180 ppm boron using gas tungsten arc welding and Inconel type filler metal, and showed superior creep properties to those of welded joints of conventional high chromium steels such as P92 and P122. No type IV failure was observed in the boron steel welded joints. A large grained microstructure was observed in the heat affected zone heated to Ac ₃ (Ac ₃ HAZ) during welding, whereas the grains are refined at the same location in conventional steel welded joints. The simulated Ac ₃ HAZ structures of the boron steels have a creep life almost equal to that of the base metal. Large grained HAZ microstructures and stabilisation of M₂₃C₆ precipitates are probable reasons for suppression of type IV failure and improved creep resistance of the boron steel welded joints.     

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.     

Evaluation of sensitization in stainless steel 304 and 304L using nonlinear Rayleigh waves

Austenitic stainless steels have a wide range of applications in the energy industry, but the corrosion resistance of these stainless steels can be reduced by sensitization, particularly in the heat affected zones in welds. Sensitization is the formation of chromium carbide precipitates along the grain boundaries, causing the formation of a zone of chromium depletion around the grain boundary. Since chromium is the primary alloying element that makes stainless steel corrosion resistant, this chromium depleted zone is susceptible to intergranular stress corrosion cracking (IGSCC). Sensitization occurs when a stainless steel is exposed to a high temperature for an extended time period, such as during welding. The objective of this research is to determine the sensitivity of nonlinear ultrasound to the presence of sensitization by using nonlinear Rayleigh waves to quantitatively track the sensitization of 304 and 304L stainless steels as a function of holding time at 675 °C. The effect of the carbon content of the alloys (304 versus 304L) to the sensitization process and the measured nonlinearity parameter, β are investigated. Annealing of these specimens isolates the effect of just sensitization, removing the presence of cold work which can also affect the material nonlinearity. Complementary electrochemical potentiodynamic reactivation (EPR) measurements and microscopy are used to confirm the absence or presence of sensitization. The results show that the acoustic nonlinearity parameter is sensitive to the presence of chromium carbide precipitates in sensitized austenitic stainless steels.     

机械镀锌镀层钝化与耐蚀性能研究

    对机械镀锌层分别用三价铬、稀土和六价铬进行了钝化处理,利用盐雾试验和电化学测试对不同钝化膜的耐蚀性与电化学行为进行了比较研究.盐雾试验结果表明,稀土与三价铬钝化处理的效果均已超过传统的六价铬钝化,比六价铬钝化膜的耐蚀性提高了一倍以上;稀土钝化膜的耐蚀性最好,三价铬钝化膜的耐蚀性仅次于稀土钝化膜的.电化学测试表明,三价铬、稀土和六价铬钝化膜都能够不同程度地抑制腐蚀的阴极电极反应,抑制阴极反应程度最大的是稀土钝化膜,其次是三价铬钝化膜,最小的是六价铬钝化膜.三价铬与稀土钝化工艺的环保和良好的防腐效果使其具有良好的应用前景.     

Der Einfluß des Prüpotentials und der Wärmebehandlung auf das Korrosionsverhalten niob- und titanstabilisierter ferritischer Chromstähle mit rund 17% Chrom

The influence of test potential and heat treatment on the corrosion behaviour of ferritic chromium steels stabilized with niobium or titanium By means of corrosion-chemical, electrochemical, metallographical and electronmicroscopical investigations, the influence of the electrode potential and the heat treatment on the corrosion behaviour of steels of the X 8 CrTi 17 and X 8 CrNb 17 has been determined. With ferritic 17 pC chromium steels, a distinction must be made between two different types of grain boundary corrosion:

• (1) Grain boundary corrosion on steels which were quenched at high temperatures and therefore sensitized, unstabilized or understabilized, due to the segregation of chrome-rich carbides at the grain boundaries, causing a chromium reduction in their vicinity (typical inter-crystalline corrosion), and
• (2) Grain boundary corrosion on steels quenched at high temperatures but fully stabilized, due to the chemical dissolution of the type MX carbonitrides segregated at the grain boundaries during quenching (carbide corrosion).

The heat treatment conditions conducive to carbide corrosion were determined, and the correlation of this type of corrosion with the potential was ascertained by potentio-static tests in sulphuric acid and compared with the behaviour of synthetic carbides. The different corrosion behaviour of the ferritic chromium steels quenched at high temperature and stabilized with niobium and titanium, respectively, is attributed to the different chemical dissolution rates of the carbo-nitrides segregated. The findings also provide an explanation of the corrosion behaviour of sensitization-annealed, stabilized austenitic chrome-nickel steels in acid solution.     

应用熔结环氧涂装技术抗局部腐蚀

熔结环氧（SEBF）涂装技术目前已在许多行业重腐蚀环境下广泛应用,具有独特的腐蚀防护效果。针对SEBF涂层抗应力腐蚀（SCC）、疲劳腐蚀（CF）、焊接部位腐蚀及点蚀等局部腐蚀进行了测试及应用研究,结果表明,SEBF涂层可解决金属材料在腐蚀环境下局部腐蚀问题,试验及应用效果良好,其抗局部腐蚀效果明显,经济实用,特别是对异型复杂工件的防护具有其它常规防护方法无法比拟的优点。     

Electrochemical Doping of Zinc Coatings with Chromium and Nickel Coatings with Phosphorus

The electrochemical doping of coatings with metals and nonmetals is discussed. Using the examples of the electrodeposition of zinc–chromium and nickel–phosphorus coatings, it has been shown that the presence of donors of the electrodeposited coating components in the inner sphere of a heteronuclear or heteroligand complex contributes to their coreduction and the formation of an alloy. The composition, morphology, and properties of the coatings have been characterized. It has been shown that the corrosion resistance of the zinc–chromium coatings is two times higher than that of the zinc coatings. After storage, the nickel–phosphorus coatings preserve their solderability with low-temperature solders.     

Boron based complex wear-resistant coatings

Applying boron, boron-copper, and boron-nickel diffusion coatings to die steels, as well as the microhardness, microbrittleness and wear resistance of the steels with the coatings are considered. Original Russian Text ? Yu.A. Balandin, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 2, pp. 150–153.     

热镀锌层上磷酸锌转化膜的生长与耐蚀性

热镀锌钢板在pH3.0、45℃的磷酸锌溶液中磷化2～600s,用扫描电镜、能谱仪和X射线衍射仪分析磷化膜的组织形貌和成分,并探讨膜层的生长行为。结果表明:磷酸锌晶体在锌晶粒内及晶界处均可成核,开始是以接近平行的片状生长,并逐渐向多方向生长成扇骨状的晶片。随着磷酸锌晶体的成核和生长,磷化膜的覆盖率增加,但晶体之间的孔隙难以完全消除;长大的磷酸锌晶片容易折断脱落,导致磷化后期膜层的质量增量减小;磷化膜主要由Zn3(PO4)2.4H2O组成。热镀锌钢板经磷化处理后,耐蚀性显著提高,磷化膜的耐蚀性随磷化时间和膜层覆盖率的增加而提高。     

Interfacial morphology and corrosion resistance of Fe–B cast steel containing chromium and nickel in liquid zinc

The interfacial morphology and corrosion resistance of low carbon Fe–B cast steels in zinc bath at 520 °C were investigated. The results show Fe–B cast steel containing high Cr and Ni exhibits the best corrosion resistance to liquid zinc. The corrosion layers are composed of Γ-Fe₃Zn₁₀, δ-FeZn₁₀, ξ-FeZn₁₃ and η-Zn. The corrosion behaviour of Fe–B cast steels includes the following processes: the preferential leach and dissolution of Cr and Ni, the formation of Fe–Zn compounds controlled by zinc atom diffusion, and the spalling of borides without the supporting role of α-(Fe, Cr) matrix corroded by liquid zinc.     

Untersuchungen zur Rißkorrosion hochfester Baustähle in Meerwasser

Studies of stress corrosion of high-strength structural steels exposed to seawater Seawater is liable to cause stress corrosion cracking. The risk of cracking may increase as the strength of the steel rises. The report describes the results of a number of test series with welded highstrength structural steels. Long-time exposure tests were performed in natural seawater of the North Sea near Helgoland. In constant deflection tests the influence of the maximum hardness in the heat affected zone on the corrosion behaviour and the effect of chromium as an alloying element were investigated. The potential risk attributable to welded joints containing undiscovered cracks was determined by fracture mechanics tests. Proof was given that under static stress conditions, flawless welded joints on high-strength structural steels up to S890Q grade are not susceptible to hydrogen-induced stress corrosion cracking. Maximum hardness of 400 HV in the heat affected zone also do not have a negative effect on steels containing up to 1% chromium. Steels with more than 1.5% chromium are endangered if the maximum hardness exceeds values of 350 HV. A susceptibility to stress corrosion under slow strain and creep conditions can be excluded from the potential of free corrosion up to the potential of cathodic protection with zinc. High-strength tensile structural steels do not differ in this regard. Limitations on the use of high-strength structural steels in the submerged area of offshore structures are shown by the fracture mechanics tests with welded joints. The results of the tests show that under free corrosion conditions in seawater high-strength steels up to S500Q do not react more sensitively in terms of corrosion crack growth than the proven steel grade S355N. The choice of steel grade may therefore be guided by other criteria such as the fracture mechanics or fatigue characteristics and processing behaviour.