Untersuchung des SwRK-Verhaltens des martensitaushärtenden Stahls X 5 CrNiCuNb 17 4 PH im Vergleich zum weichmartensitischen Stahl X 4 CrNiMo 16 5 1 ESU in chloridhaltigen wäßrigen Medien. Teil 1: Korrosionsuntersuchungen und SpRK-Untersuchungen zur Optimierung der Wärmebehandlung bezüglich der SpRK-Beständigkeit

Investigations of the corrosion fatigue behaviour at a super pure martensitic stainless steel (X 5 CrNiCuNb 17 4 PH) in comparison to the soft martensitic stainless steel X 4 CrNiMo 16 5 1 ESR in chloride containing aqueous media — Part 1: Corrosion investigations and stress corrosion tests to optimize the heat treatment according to the stress corrosion resistance The aim of this investigation was to improve the reliability of operation and the economy of corrosion fatigue stresses of structural elements, especially at elevated temperatures, by optimizing the material. This investigation is of great interest both to the industry and to related fields. It concerns the influence of a higher degree of purity achieved by the secondary metallurgical aftertreatment of soft martensitic steel X4CrNiMo 16 5 1 ESR (ESR-electroslag remelting) in comparison to the corrosion fatigue behaviour of the precipitation hardening steel X5CrNiCuNb 17 4 PH, which was specially heat-treated with respect to stress corrosion cracking resistance. The stress corrosion was investigated for all heat-treatments of the 17-4 PH in 22% NaCl(pH3) solution. The precipitation hardening steel was most resistant to stress corrosion in concentrated NaCl-solution after a three-stage heat-treatment. There was no improvement of corrosion fatigue resistance after metallurgical aftertreatment of soft martensitic steel compared to the untreated material. This is due to the instable passive behaviour of the material which led to crack initiation, especially during the 150°C experiments, at chloride-induced places of pitting. The investigation of the electrochemical corrosion behaviour of both materials showed that the pH-value hardly influences corrosion restistance. An increase of the salt content leads to higher pitting induction. At temperatures of 80°C in a saturated NaCl-solution the material showed no corrosion resistance. In potentiokinetic investigations, a direct transition from the active area to the pitting potential was observed. In accordance with both the corrosion fatigue and the stress corrosion cracking investigations, it was found that pitting at the martensite precipitator starts primarily around Cu-containing or oxidic inclusions.     

Untersuchung des SwRK-Verhaltens des hochreinen martensitaushärtenden Stahles X5CrNiCuNb 17 4 PH im Vergleich zum weichmartensitischen Stahl X4CrNiMo 16 5 1 ESU in chloridhaltigen wäßrigen Medien. Teil 2: SwRK-Untersuchungen und Rißeinleitungsmechanismen

Investigations of the corrosion fatigue behaviour at a super pure martensitic stainless steel X5CrNiCuNb 17 4 PH in comparison to the soft martensitic stainless steel X4CrNiMo 16 5 1 ESR in chloride containing aqueous media — Part 2: Corrosion fatigue tests and crack initiation mechanisms The following report concerns the study of the corrosion fatigue behaviour of the soft martensitic steel X4CrNiMo 16 5 1 ESR and the precipitation hardened X5CrNiCuNb 17 4 PH in sodium solution in the temperature range between 20° and 150 °C and the determination of their general corrosion properties and the mechanism of crack propagation. Their corrosion fatigue limits were compared with each other. A comparision was also made between an electro-slag-remelted soft martensitic steel and a charge without an ESR aftertreatment. Microfractographical fracture and crack path investigation were carried out for interpretation of the experimental results. It was observed that in both super pure steels (soft martensitic and precipitation hardened) the oxidic inclusions are not responsible for the crack intiation, as it was found in the non ESR treated steels. In the 17-4 PH steel copper containing inclusions in the crack initiation areas were observed. In concentrated sodium solution pitting corrosion was found at both steels.     

Corrosion‐technical properties of high‐strength stainless steels for the application in prestressed concrete structures

Experience with prestressed concrete over about half a century has indicated that the corrosion resistance of conventional prestressing steel does not always satisfy, especially the prestressing steels are susceptible to chloride attack (de‐icing salts) and hydrogen (hydrogen‐induced stress corrosion cracking). On the other hand corrosion agents, such as chloride, condensation water, can penetrate in the concrete and arrive at the surface of steels. Hence, corrosion damage of prestressing steels can happen and, in the extreme cases, the prestressed concrete structure collapsed resulting from the failure of the tendon. In this paper, consideration is made to use high‐strength stainless steels as prestressing tendon with bond in concrete. The high‐strength stainless steels of qualities 1.4301 (X5CrNi18‐10), 1.4401 (X5CrNiMo17‐12‐2), 1.4436 (X3CrNiMo17‐13‐3) and 1.4439 (X3CrNiMoN17‐13‐5) with sequence of increasing austenite stability were investigated. For application in prestressing tendon with bond in concrete the cold‐drawn high‐strength stainless steel of quality 1.4401 is an optimal proposition regarding its satisfactory resistance against pitting corrosion and stress corrosion cracking (SCC) in structure‐related corrosive conditions. The lower alloyed steel 1.4301 has an insufficient resistance against the chloride‐induced corrosion because of the lack of molybdenum and the content of deformation martensite due to the strong cold‐drawing of its unstable austenitic structure.     

Study of the pitting corrosion of superduplex stainless steel and X-65 carbon steel during erosion–corrosion by cyclic polarisation technique

Erosion-enhanced corrosion behaviour of X-65 carbon steel and UNS S32750 superduplex stainless steel was investigated by electrochemical cyclic polarisation. The tests were performed using a jet slurry device coupled with a potentio-galvanostat at various jet velocities of 4, 6.5 and 9?m?s^?1 and impingement angles of 30 and 90? in a 3.5?wt-% NaCl water containing 6?wt-% silica sand particles. The results showed that increasing the jet velocity and impingement angle increased the corrosion rate of both alloys. Negative hysteresis and greater E_rp than OCP were observed for superduplex stainless steel in all erosion–corrosion conditions that indicated the pitting resistance of the alloy. However, the low resistance of carbon steel against pitting during erosion–corrosion was demonstrated by positive hysteresis in the cyclic polarisation curves as well as SEM images of the eroded surfaces.     

Kurzzeituntersuchungen zur Auswahl von rostbeständigen Cr-Stählen mit verbessertem Widerstand gegen Schwingungsrißkorrosion

Short-time investigations into the selection of stainless chromium steels with improved corrosion fatigue resistance Using the steel X 20 Cr 13 various short-time test methods have been tested for evaluating the corrosion fatigue susceptibility in concentrated air-saturated sodium chloride solution. In addition the steels X 15 CrNi17, X 35 CrMo 17, X 5 CrNiMoCuNb 14 5, X 4 CrNiCuNb 16 4, X 2 CrNiMoN 22 5 3, X 5 CrNiMoCu 25 5, X 8 CrNiMo 27 5 and X 1 CrNiMoNb 28 4 2 have been studied at room temperature of 80° C using crack propagation, constant straining and pitting corrosion methods. The two last mentioned steels are superiour under the test conditions.     

调整处理对17-4PH不锈钢耐海水腐蚀性能的影响

运用化学浸泡、极化曲线、循环极化曲线、电化学阻抗谱等方法研究了固溶后直接时效状态和调整＋时效状态的17—4PH不锈钢在人工海水中的耐蚀性能，并对显微组织作了观察和分析。结果表明，17—4PH不锈钢过调整处理后再进行时效处理，自腐蚀电位和点蚀电位升高而年腐蚀率下降，耐海水腐蚀性能全面优于直接时效态试样。其原因是17-4PH不锈钢经过调整处理后进行时效可避免贫铬区的形成，并使马氏体组织呈细小化特征，材料的组织均匀性提高。     

Influence of Sulfur Content on the Corrosion Resistance of 17-4PH Stainless Steel

According to specification standards, the basic chemical composition of steel 17-4PH for special and critical applications is 15-17% Cr, 3.0-5.0% Ni, 3.0-5.0% Cu, 0.07% C (max) and 0.15-0.45% (Nb + Ta) (wt.%). The maximum sulfur content is 0.030%. However, as it will be shown in this work, this maximum limit for sulfur is too high for services where high corrosion resistance is necessary. Two samples of 17-4PH steel with similar base compositions, but quite different sulfur contents (0.027% and 0.001%S), were compared with respect to pitting corrosion and sensitization. Both materials were heat treated according to commercial treatments A, H900, H1100, H1150 and H1150D (ASTM A-1082). Two corrosion tests were applied to compare the steels. The first one was the double-loop electrochemical potentiodynamic reactivation (DL-EPR) test in 0.25 M H₂SO₄ + 0.01 KSCN solution, which is used to measure the degree of sensitization. The second test was the anodic polarization in 3.5%NaCl solution, commonly used to evaluate the pitting corrosion resistance. Detailed microstructural characterization by magnetic measurements, light optical and scanning electron microscopy was performed. As main conclusion, despite that both steels have chemical compositions in accordance with the standards, the steel with higher sulfur was much more susceptible to pitting and sensitization.     

Effect of aqueous LiBr solutions on the corrosion resistance and galvanic corrosion of an austenitic stainless steel in its welded and non-welded condition

The corrosion resistance and galvanic behaviour of a highly alloyed austenitic stainless steel (UNS N08031) and a nickel-base alloy (UNS N06059) in its welded (GTAW) and non-welded condition were analysed in LiBr solutions by means of electrochemical measurements. Samples microstructure was studied by SEM and EDX analysis. The alloys considered showed passive behaviour and they were able to repassivate after the breakdown of the passive film. The pitting resistance of the materials increased as the LiBr concentration decreased. With regard to galvanic corrosion, the welded metal was always the anodic element of the UNS N08031-welded metal pair.     

Influence of the microstructure on the corrosion behaviour of low-carbon martensitic stainless steel after tempering treatment

The microstructure of grade X4CrNiMo16.5.1 stainless steel was studied at different scales. The chemical composition of the native passive film formed on the different phases was then determined at the microscale. The degree of homogeneity of the native passive film is discussed. Subsequently, the susceptibility to pitting corrosion of X4CrNiMo16.5.1 was quantified using the electrochemical microcell technique. The nature of precursor sites and the morphology of pits were investigated by combining scanning electron microscopy with Electron BackScatter Diffraction and potentiostatic pulse tests. The role of the microstructure and the cold-worked layer generated by polishing in pitting is discussed.     

Influence of microstructure on the corrosion resistance of hyperduplex stainless steel

Hyperduplex UNS S32707 is a newly developed austenitic–ferritic stainless steel. The steel contains about 27%Cr, 7%Ni, 4.5%Mo, and 0.4%N, which results in a pitting resistance equivalent factor (PRE) equal to 49. In this study, the pitting corrosion resistance of this new grade of stainless steel was investigated by varying the microstructure using different thermal processes. The critical pitting temperature measurement and cyclic polarization tests confirm the high corrosion resistance of the hyperduplex steel in the solution treated condition. However, deleterious phases form easily during thermal processing and cause a drastic decrease in the corrosion resistance.     

Elektrochemische Methode zur Prüfung des Korrosionsverhaltens austenitischer CrNiMo-Stähle im Schweißnahtbereich

Electrochemical method for testing of the corrosion behaviour of austenitic CrNiMo-stainless steel weldments Austenitic CrNiMo stainless steel welds can be more susceptible to pitting and crevice corrosion than the base material owing to segregation and precipitation in the heat affected zone, in the high temperature zone and in the welded zone. Suitable test methods are needed to optimize welding technology. Comparison of potential curves (DIN 50919), comparison of critical pitting corrosion temperatures in FeCl₃- or other model solutions, visual estimation after longterm corrosion tests with or without electrochemical load are discussed. A small measurement cell heated from the rear with circulating and temperature controlled electrolyte is shown. With its help separate areas of a weld can be electrochemically investigated. Welds of the materials X 2 CrNiMoN 17 12 2 (1.4406), X 2 CrNiMoN 17 13 5 (1.4439) and X 1 NiCrMoCu 31 27 4 (1.4563) are tested in acidic NaCl solutions in the range of 25 to 75°C. Critical pitting corrosion potentials are obtained for base materials, heat affected zone and weld material. An influence of the welding energy is probable, but cannot be proved in this case without statistical certainty.     

Influence of Postbuild Microstructure on the Electrochemical Behavior of Additively Manufactured 17-4 PH Stainless Steel

The additive manufacturing build process produces a segregated microstructure with significant variations in composition and phases that are uncommon in traditional wrought materials. As such, the relationship between the postbuild microstructure and the corrosion resistance is not well understood. Stainless steel alloy 17-4 precipitation hardened (SS17-4PH) is an industrially relevant alloy for applications requiring high strength and good corrosion resistance. A series of potentiodynamic scans conducted in a deaerated 0.5-mol/L NaCl solution evaluated the influence of these microstructural differences on the pitting behavior of SS17-4. The pitting potentials were found to be higher in the samples of additively processed material than in the samples of the alloy in wrought form. This indicates that the additively processed material is more resistant to localized corrosion and pitting in this environment than is the wrought alloy. The results also suggest that after homogenization, the additively produced SS17-4 could be more resistant to pitting than the wrought SS17-4 is in an actual service environment.     

Eigenschaftsprofil des neuentwickelten Stahls X2 CrNiMnMoN 23 1764

Properties of the newly developed steel X 2 CrNiMnMoN 23 17 6 4 A well balanced alloying composition allows to produce the high alloyed stainless steel X 2 CrNiMnMoN 23 17 6 4 containing more than 0.4% nitrogen by conventional processes. Features of this material are a stable fully austenitic microstructure, 0.2% yield strength higher than 420 N/mm², excellent corrosion resistance and good working and welding properties. The critical pitting temperature evaluated in ferric chloride solution according to ASTM G 48–76 standard is higher than 85 deg C and it is only lightly lowered when tested in the as welded condition. By these properties Remanit 4565 S may bridge the gap between high-alloyed stainless steels and non-ferrous materials for applications in the chemical process industries.     

Einfluß von Passivierungs- und Kohlenstoffschichten auf austenitischen CrNiMo-Stählen auf die Beständigkeit gegen Lochfraß und Spannungsrißkorrosion

Effects of passivation and carbon films on austenitic CrNiMo steels on their piting and stress corrosion resistance The influence of passive film and combinations of a passivation and a carbon layer on the resistance to pitting and SCC of austenitic CrNiMo steels has been investigated in physiological sodium chloride solution (Tyrode solution) at pH 6.9 to 7.4 at 37 ± 1°C. The passive film was obtained after electrolytic polishing in H₃PO₄ + H₂SO₄ + C₆H₅NHCOCH₃ + oxalic acid + corrosion inhibitor CS by treatment with 40% nitric acid the carbon film was obtained by CVD. Impurities in the steel (non-metallic inclusions) and the different metallic phases were investigated and the chemical composition of the passive film was determined by quantitative analysis. The resistance to pitting of the steel with and without passive film was determined potentiodynamically in Tyrode's solution at 37 ± 1°C. The resistance to SCC was determined in Tyrode's solution at 37 ± 1°C, in neutral glycerole and in boiling magnesium chloride solution at 154 ± 1°C and evaluated in terms of K_σ and K_τ. The corrosion damage was investigated by optical and scanning electron microscopy. The investigations have revealed that the different surface conditions considerably improve the pitting and SCC resistance of the steels in the media used in this work, so that they make possible the use of these materials as surgical implants.     

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.     

Herstellung und Eigenschaften stickstofflegierter,korrosionsbeständiger Stähle und Sonderstähle mit niedrigen Kohlenstoffgehalten

Production and properties of nitrogen alloyed, corrosion resistant steels and special steels with low carbon contents Alloying with nitrogen has favourable influence in particular on the mechanical properties of CrNiMo steels (X 2 CrNiMoN 17 12, materials No. 1.4406, X 2 CrNiMoN 17 13 5, materials No. 1.4439 und X 2 CrNiMoN 22 5, materials No. W.-Nr. 1.4462). This comes to bear when ambient temperature and low temperature strength and toughness are concerned. With respect to the corrosion behaviour the data concerning the effect of nitrogen are contradictory. It has become clear that nitrogen improves pitting corrosion resistance; this applies, however, only to pit initiation but not to pit growth. Stress corrosion cracking is not delayed by nitrogen but different results have been obtained with different media: while the duplex steel X 2 CrNiMoN 22 5 is attacked considerably faster than the corresponding nitrogen-free steel in 42% boiling magnesium chloride solution the time-to-failure of both steels are comparable in 30% boiling MgCl₂-solution. The nitrogen alloyed steels can be welded by all known welding procedures, provided fully austenitic welding rods are used.     

Theoretical description of the practical possibility of stress corrosion cracking from crevice corrosion sites

Stress corrosion cracking (SCC) from crevice corrosion sites had been found in an experimental work at polarization potential of + 200 mV_SCE. In that work, an occluded U‐bend specimen of Type 316L (UNS S31603) stainless steel was used. The testing was done in sodium chloride (NaCl) solution. Based on that work, the practical possibility of SCC from the occluded U‐bend specimen was described theoretically. It was shown that it would also be possible for SCC to occur in practice (i.e. at practical corrosion potential), but the crevice needs to be tighter. Meanwhile, it would take a longer time for obvious SCC to emerge. For a practical crevice usually formed by placing a crevice former on a large uniform metal surface, the crevice geometry may have little effect on SCC although the crevice can sustain an acidified solution more easily than pitting. The possibility of SCC should mainly depend on the corrosion system itself, i.e. material and environment.     

石油测井仪器表面材料点蚀原因分析

高Cr合金能够有效的抑制CO2腐蚀,但是在实际中,有些测井仪器在深井测井后表面材料出现点蚀现象,严重的有穿孔现象。点蚀现象主要是因为Cl-深挖造成,Cr(OH)3能够有效的抑制Cl-富集,能够有效的缓解点蚀现象,17-4PH钢出现点蚀现象的原因可能是FeCO3依然能够通过阴离子使其到达金属表面,从而腐蚀基体。穿孔可能是因为腐蚀产物膜脱落使得该区域形成大阴极小阳极的腐蚀环境而造成的。     

Pitting and crevice corrosion of superaustenitic stainless steels

Superaustenites are mainly used in offshore applications, oil production and chemical industry. Most important types of localised corrosion of these steels are pitting and crevice corrosion. Investigated materials were N08028, S31254 and three modified alloys. Chromium content of investigated alloys varied between 20 and 27%, molybdenum between 3.2 and 6.0%, nitrogen between 0.1 and 0.36% and copper between 0 and 1.1%. For means of comparison stainless steel AISI 316L has been included in the study. Pitting and crevice corrosion of these highly corrosion resistant steels has been investigated by use of standardized tests. Critical pitting temperature and critical crevice temperatures were determined according to ASTM G 48, Methods C and D, respectively. Electrochemical measurements for determination of pitting potentials were done according to ASTM G 61 as well as for determination of critical pitting temperatures according to ASTM G 150. Results are presented as function of MARC (Measure of alloying for resistance to corrosion) defined by Speidel since linear correlation coefficients were higher when compared to conventional PREN. Results obtained by different testing methods must not be compared directly. Every test however is sensitive to microstructural defects like precipitations and segregations that decrease corrosion resistance. The higher alloyed a material is, the higher is its tendency to form microstructural defects, and the more difficult is it to reach its theoretical corrosion resistance at given chemical composition.     

Stress-corrosion cracking susceptibility of various product forms of aluminum alloy 2519

Aluminum alloy 2519 is the main structural alloy for the Advanced Amphibious Assault Vehicle (AAAV). A potential drawback to the use of 2519, particularly for an amphibious vehicle, is its susceptibility to corrosion. General corrosion, which is largely in the form of pitting, may reduce the effective life of the system, while stress-corrosion cracking (SCC) of any high strength aluminum alloy can lead to catastrophic failure. Therefore, an evaluation of the SCC susceptibility of various 2519 product forms was performed. Plate, extrusions, ring roll forgings, and weldments all exhibited excellent SCC resistance as measured by a series of standard ASTM tests. Multi-axis hand forgings were the only product forms that exhibited SCC susceptibility, and this susceptibility was remedied via the use of a specifically designed heat treatment. While all product forms passed the prescribed SCC tests, each exhibited a significant reduction in strength after simultaneous exposure to both stress and the saline corrosion environment. Such behavior was not apparent when the exposure was limited to the corrosion media alone. That is, while resistant to SCC, the load-bearing capacities of all products tested are somewhat degraded during concurrent exposure to stress and corrosive media by a mechanism that includes pitting. This article will discuss the effort that was conducted by the National Center for Excellence in Metalworking Technology (NCEMT) to evaluate the SCC susceptibility of 2519 in various product forms and tempers.