Vergleichende Untersuchungen des SwRK-Verhaltens verschiedener Dampfturbinenschaufelstähle

Comparative investigations into the corrosion fatigue behaviour of different steam-turbine-blade steels Corrosion fatigue tests in NaCl-solution in the temperature range from ambient temperature to 150°C revealed a decrease of the corrosion fatigue strength of the steels X20Cr13 with 1% resp. 2.5% Mo, X4CrNiMo 16 5 1 and X2CrNiMoN 22 5 with increasing temperature; a minimum of the corrosion fatigue strength is reached at 150°C. At temperatures of about 80°C it was found an optimum corrosion fatigue behaviour of the Mo-alloyed steel X20CrMo13 2.5 in comparison with the other investigated steels. It was observed that crack initiation of the ferritic, Mo-alloyed steel is caused by Cl-induced pitting, of the soft martensitic steel by oxide inclusions and of the duplex steel by non metallic, brittle inclusions and/or by grain boundarys of the ferritic/austenitic microstructure. Crack initiation caused by pre-deformation at slip bands was observed on the duplex steel. All materials investigated failed at elevated temperatures. At temperatures higher than 80°C an optimum corrosion fatigue behaviour was not found.     

Selektive Korrosion von Duplexstahl. Teil 2: Lokale Korrosionserscheinungen an Duplexstahl X2CrNiMoN22‐5‐3 unter Einwirkung von Chloriden und mechanisches Verhalten in Abhängigkeit vom Gefügezustand

Selective corrosion of duplex stainless steel. Part 2: Localized corrosion manifestations under exposure of chlorides on duplex stainless steel X2CrNiMoN22‐5‐3 and mechanical behavior in dependence of the microstructure In completion to part 1 of this paper this part deals with interrelations between localized corrosion manifestations, mechanical properties and the microstructure of duplex stainless steel X2CrNiMoN22‐5‐3. The pit formation on duplex stainless steels is substantially determined by the distribution of the alloying elements within single phases and by defects in the oxide layer. The positive properties of molybdenum become ineffective at thicker oxide layers due to the fact, that molybdate, which is responsible for inhibition of pitting, can not be formed. Depletion areas caused by precipitations are preferential attack places for corrosion. The influence of chlorides for duplex stainless steels in rolled and welded conditions is characterized by a logarithmic dependence.     

Temperatur- und Konzentrationsabhängigkeit der Korrosion nichtrostender austenitischer und ferritischer Werkstoffe in 20- bis 75%iger Salpetersäure

Corrosion resistance of austenitic and ferritic stainless alloys in 20 to 75% nitric acid as a function of temperature and concentration A series of stainless austenitic and ferritic materials was exposed for 100 days to boiling nitric acid which contained no corrosion products; the corrosion rates and depths of the grain boundary attack were observed. Provided the structure is precipitation-free, the following are suitable for long-term exposure; the austenitic steels X 2 CrNi 1912, X1 CrNi 25 21, X1 CrNiMoN 25 222 and X1 NiCrMoCu31274, the practically Mo-free and Cu-free development steel X1 NiCr31 27, and the highly Mo-alloyed variant X1 NiCrMoCu 31275. In the case of alloy NiCr21 Mo it is advisable to limit the concentration and/or the temperature of the nitric acid. The “superferrite” X1CrNiMoNb2842, the Japanese steel X1 CrNiNb 30 2 and the austenitic steels X2 CrNiMoN 1713 3 and X1 CrNiMoN 25 22 2 in the version with high nickel content are unsuitable. Thus, as an alloying element, molybdenum does not always impair the resistance of stainless steels to nitric acid. The decisive factor affecting the corrosion rates is the chromium content of the material. The temperature-dependent function of the corrosion in azeotropic nitric acid conforms to Arrhenius relations. The concentration-dependent function of the corrosion in 20 to 75 (80)% nitric acid can be described by a hyperbolic equation. An exception is formed by X1 CrNiSi 1815; here the corrosion rate increases with the concentration of the acid until the azeotropic point is reached; then, owing to the formation of a surface film, it falls until the acid becomes highly concentrated.     

Untersuchungen über den Einfluß des Gefügezustandes auf das Korrosionsverhalten hochlegierter,rost- und säurebeständiger Stähle in reiner sowie in chloridhaltiger Schwefelsäure

Corrosion Properties of High Alloyed Stainless Steels in Pure as well as in Chloride Containing Sulfuric Acid The corrosion behaviour of the high alloyed stainless steels material no. 1.4439 (X3CrNiMoN17135), 1.4539 (X2NiCrMoCu25205), 1.4503(X3NiCrMoCuTi2723) as well as the reference materials AlSI 316 L and alloy 825 was tested in diluted sulfuric acid (5, 10, 20 and 50%) at 50, 100 and 150°C. The test solutions additionally contained impurities as chlorides and cupric ions. On the material side the effect of various microstructures was checked as well: material as received (commercial production), solution annealed under laboratory conditions, cold deformed and for two selected steels electroslag remelted. Corrosion testing methods are: the immersion test will sheet coupons and the measurement of the weightloss; electrochemical testing, i.e. Current potential-and free corrosion potential-time-curves. No pitting corrosion is observed in the presence of chloride ions. In some cases the general corrosion rate is lowered if chloride ions are present. This beneficial effect of chloride ions, however, is observed only at low chloride concentrations (500 ppm). Annealing under laboratory conditions as well as electroslag remelting does not generally improve the corrosion resistance. A negative effect by cold deformation is only observed for standard stainless steel AlSI 316. Cupric ions added to the 20% sulfuric acid solution improve the corrosion resistance of all steels investigated to that extent, that they can be used in practice up to 100°C provided that the concentration of cupric ions in the solution is sufficiently high (2000 ppm). Electrochemical test results indicate that the positive effect of cupric ions is due to the shift of the free corrosion potential into the potential range of stable passivity. Copper alloyed stainless steels show the highest 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.     

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.     

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).     

Hochlegierte korrosionsbeständige Stähle für Chemie‐, Energie‐ und Meerestechnik – Rückblick und Ausblick

High‐alloyed corrosion resistant steels for the chemical process industry, power engineering and marine technology – past and future Today's most common high‐alloyed corrosion resistant steels are in their majority characterised by very low contents of carbon and sulphur and, in many cases, by substantial amounts of nitrogen as an alloying constituent. Their broad use in the chemical process industry, power generation and marine technology has become possible when new metallurgical processes for steel making had been introduced in the 1960s. The time before had seen mainly stabilised grades, being highly alloyed with copper in many cases, which have disappeared to a large extent in our days. The superferritic grades (ferritic steels with ≥ 25% chromium) had been the materials of great expectations in the 1970s, but have found a very limited application only in the chemical industry since then, e.g. for the handling of hot concentrated sulphuric acid, due to the high risks of low ductility cracking of these materials at greater wall thickness. These risks can be managed better if the highly alloyed ferritic phase is present in a finely dispersed compound with an austenitic phase where the ferritic part is adding its advantages, higher strength and resistance to stress corrosion cracking, to the duplex compound. This can result in low weight and corresponding cost saving. The application of the corrosion resistant duplex grades will expand further as much as users will better learn the special requirements of manufacturing of these materials and to take advantage of their unique properties. However, the most important alloy developments since the 1960s have been seen in the field of the austenitic stainless steels being highly alloyed with chromium, molybdenum and nitrogen. Especially the austenitic 6% Mo grades as e.g. X1NiCrMoCuN25‐20‐7 – alloy 926 (1.4529) have found many applications in chemical process industry, power generation and marine technology. Higher alloyed grades as e.g. X1NiCrMoCu32‐28‐7 – alloy 31 (1.4562) are excelling in extraordinary resistance to corrosion by acids and pitting attack. In addition today's upper limits of alloying austenitic corrosion resistant grades have been explored with grade X1CrNiMoCu33‐32‐1 – alloy 33 (1.4591) for chromium additions up to about 33% and with grade X1NiCrSi24‐9‐7 – alloy 700 Si (1.4390) for additions of silicon up to about 7%, providing a high corrosion resistance mainly in oxidising acids. When considering the prospects of further development of the corrosion resistant duplex grades the ferritic phase within these materials is both offering chances and setting limits. The high‐alloyed austenitic corrosion resistant steels have a potential being unexplored so far in the alloy range where molybdenum and nitrogen are becoming more prominent compared to the chromium content.     

Der Einfluß des Titangehaltes auf die Aktivkorrosion ferritischer Cr-Stähle und austenitischer Cr-Ni-Stähle in Schwefelsäure

The influence of the Titanium content on the active corrosion of ferritic Cr steels and austenitic Cr-Ni steels in sulphuric acids Non-stabilized and Ti-stabilized steels of types X8Cr17, X8Crti17, X5CrNi189, X10CrNiTi189 and X5CrNiMoTi25 25 are compared with each other in respect of their behaviour in the potential range of active corrosion in sulphuric acid. With ferritic 17 per cent. chromium steels, no Ti influence was detected. With more highly alloyed austenitic Cr-Ni or Cr-Ni-Mo steels, the titanium had the effect of narrowing down the potential range of active corrosion and reducing the corrosion rate which facilitates the passivation capacity of the steels. These phenomena are particularly marked with the steel known as X5CrNiMoTi25 25. With this steel, the corrosion rate in the active-passive transition range with titanium contents from 0.41 to 0.66 per cent. and about 0.66 per cent. C ist increased in the sensitivized state. Within a narrow potential range of about 200 mV, intercrystalline corrosion is encountered which decreases with increasing Ti content and is completely prevented if the C content is reduced below 0.03 per cent. The potential range of the inter-crystalline corrosion is more negative than the test potential of the Strauss test normally used for testing the grain disintegration resistance.     

Überblick über die Entwicklung und Eigenschaften stickstofflegierter austenitischer Stähle für den chemischen Apparatebau

A review of the devolopment and the properties of nitrogen containing austenitic steels for chemical apparatus construction Addition of nitrogen results in increased strength austenitic steels and in increased austenite stability, so that the formation of undesirable phases is suppressed or at least delayed. This feature eliminates in particular the Structural stability problems encountered during welding. The increase of mechanical strength involves qualitatively all the properties related to strength, including fatigue strength and corrosion fatigue strength; it should be noted that this improvement has not been achieved at the expense of ductility, so that the steels are suitable for low temperature application as well. For these reasons it is recommended to include nitrogen alloyed steels in standardization projects.     

Plasma-Auftragschweißen mit CrNiMoN-legierten Duplex-Werkstoffen

Plasma arc surfacing with CrNiMoN-alloyed duplex stainless steels This paper presents results of researching the Plasma-Hot-Wire-Surface-Welding process with duplex stainless steels X2CrNiMoN22-5-3 and X2CrNiMoN25-7-4. This includes the determination of the microstructure as well as the mechanic-technological and corrosion properties of the layers. The welding parameters have been optimized first in order to produce claddings of a thickness between 2–3 mm. Primary, the welding process influence regarding the degree of dilution on the ferrite-austenitecontent has been investigated. The rate of cooling t_12/8 and t_8/5 have been evaluated during duplex claddings of one and two layer. The results correspond to rate of cooling of PHA-weldings with duplex stainless steels without any dispersion. These results were confirmed by metallographic investigations of one and two layer duplex claddings. Layer analysis shows the homogeneity of the layer composition. Bending tests with normal and side bending samples of one and two layer revealed the excellent bonding between substrate and cladding. In the chemical corrosion experiments the claddings show approximately the similar pitting behaviour as the by rolling manufactured reference material. The surface quality of the X2CrNiMoN22-5-3 claddings is significant to the pitting behaviour. One and two layer claddings of X2CrNiMoN25-7-4 shows, independent of their initial conditions, the same pitting resistance as the reference material. It has been proved by SEP 1877 and EPR (electrochemical potentiodynamic reactivation) tests, that PHA-claddings are resistant against intercrystalline corrosion.     

Hochkorrosionsbeständige Sonderstähle für Rauchgas-Entschwefelungsanlagen

Highly corrosion resistant special steels for flue gas desulfurisation plants Highly corrosion resistant stainless steel grades have been proved under the severe corrosion conditions existing in flue gas desulfurisation scrubbers (FGD). Besides general corrosion pitting, crevice corrosion and eventually stress corrosion cracking can occur. Thus highly alloyed special steels must be used. Steel grades with a minimum content of 2.75% Mo are essential. At higher chloride levels and decreasing pH-values higher alloyed stainless steels containing up to 6% Mo are necessary. Some of these special steels are described in view to their composition and mechanical properties; their corrosion behavior has been tested under laboratory and field conditions. The use of nitrogen alloyed grades has been shown of remarkable advantage. Nitrogen additions enhance the mechanical properties and structure stability. Furthermore the precipitation of deleterious intermetallic compounds during heat treatment will be delayed by nitrogen additions, thus e.g. multi layer weldings can be carried out with higher security in view to corrosion resistance and mechanical properties. Materials selection for the different scrubber systems will be illustrated by examples. Up to now experiences about stainless steel components in FGD plants are taken into consideration. Welding with distinctly higher alloyed filler metal at the medium-touched side has been well proved in view to adequate corrosion properties.     

Korrosionsuntersuchungen an ausgewählten metallischen Werkstoffen im System Essigsäure/Esigsäureanhydrid

Corrosion tests of selected metallic materials in the system acetic acid/acetic anhydride The corrosion behaviour of the ferritic austenitic stainless steels X2 CrNiMoN 22 5 (UNS S31803) and X2 CrNiMoN 25 7 4 (UNS S32750), the nickel base alloy NiMo16Cr16Ti (alloy C-4) and the titanium grades Ti2 (Grade 2) and Ti2Pd (Grade 7) was investigated by immersion tests in boiling mixtures of acetic acid and acetic anhydride in the presence of air. All materials tested were corrosion resistant in acetic acid and acetic anhydride but were corroded rapidly by the mixtures with a corrosion loss up to 1 mm/a, except the nickel base alloy (alloy C-4). It was corrosion resistant in all solutions with a corrosion loss not exceeding 0.01 mm/a. Electrochemical tests show that all materials tested exhibit stable passivity in glacial acetic acid and active corrosion in the presence of 10% acetic anhydride.     

Entwicklung,Verarbeitung und Einsatz des stickstofflegierten,hochmolybdänhaltigen Stahles X 3 CrNiMoN 17 13 5

Development, processing and use of nitrogen alloyed high molybdenum steel X3CrNiMoN 17 13 5 Addition of 0,15% Ni to the steel X5-CrNiMo 17 13 delays the precipitation of intermetallic phases and chromium carbides. The nitrogen containing steel can be welded up to a plate thickness of 30 mm without precipitation; hot cracking has not been observed either. The weld metal corresponds to the base material with respect to ductility and corrosion resistance. It is resistant to pitting, crevice corrosion and stress corrosion cracking, in particular in mixed acids. Successful applications include textile industry (bleaching equipment, heating equipment), shipbuilding (driving shafts, exhaust gas coolers, waste gas condenser tubing), water desalination equipment, nuclear industry (evaporator for radioactive waste water, processing of radioactive waste in fluoride containing nitric acid), chemical industry (pressure container material, heat exchangers for brackish water).     

Die Ermittlung der Beständigkeit gegen Spannungsrißkorrosion (SpRK) von hochlegierten Sonderstählen in chloridhaltigen wäßrigen Medien

Determination of resistance to stress corrosion cracking (SCC) of high-alloy special steels in chloride-containing aqueous media The 18 Cr 10 Ni(Mo) based stainless steels have been continually improved by raising the Cr, Ni and Mo contents. The behavior of these high-alloy steels towards SCC was determined in test media generally used in practice since the question of the resistance to stress corrosion cracking (SCC) had still remained unanswered to a large extent. SCC tests on U-bend samples in boiling 62% CaCl₂ solution showed a good differentiation depending on the Ni and Mo contents. With increasing Ni content, the susceptibility of special high-alloy steels to SCC is shifted towards longer service lives, alloys containing ≧ 42% by weight of Ni being resistant. High-Mo special alloy steels are more resistant to SCC than low-Mo special alloy steels. These results could be confirmed by tests carried out on circular cross section samples in boiling 62% CaCl₂ solution under constant load and potentiostatic control. The free corrosion potentials recorded for 25% Ni special alloy steel and Ni-based alloys are within the potentiostatically determined range of insusceptibility to SCC. The high-Mo special alloy steel X 2 NiCrMoCu 25 20 6 (1.4529) shows the same critical SCC potential on the anodic side as the Ni alloy NiCr21 Mo (2.4858). Superferrit X 1 CrNiMoNb 28 4 2 (1.4575) and austenitic ferritic steel X 2 CrNiMoN 22 5 (1.4462) showed that the SCC behavior was unsatisfactory in both tests as in the case of steel X 10 CrNiMoTi 18 10 (1.4571). Tests in boiling 4 m NaCl showed no SCC, not even under the aggrevated test conditions in the test set-up. The great influence of the oxygen content was demonstrated in tests carried out in the autoclave with defined oxygen and chloride concentrations. The resistance of the steels to SCC decreases under air-saturated conditions (8 … 10 ppm O₂) whereas the chloride concentration (200 and 2000 ppm Cl^?) does not exercise an important influence. U-bend samples should be given preference to Erichsen samples for SCC tests. SCC break characteristics could be determined metallographically and by scanning electron microscope.     

Zur Korrosionsprüfung von Schweißverbindungen hochlegierter CrNiMo-Stähle und NiCrMo-Legierungen

On the corrosion testing of weldments of high alloyed CrNiMo-stainless steels and NiCrMo-alloys Weluments of high-alloyed CrNiMo stainless steels and Nicro alloys can he more susceptible to localized corrosion than the solution annealed basic material owing to segregations and precipitations in the heat affected zone, the high temperature zone and/or in the weld. To investigate these differences the FeCl₃-test (10% FeCl₃ · 6aq), the test “green death” (11.5% H₂SO₄, 1.2% HCl, 1% CuCl₂, 1% FeCl₃) as well as chronopotentiostatic tests in artificial sea water or in 3% NaCl-solution are used. In particular for testing the highest alloyed materials a CaCl₂ test was developed (4.5M CaCl₂, chronopotentiostatic test in duration of 8 to 10 hours at + 200 mV (SCE)), which can be carried out to a temperature of 115°C at atmospheric pressure. The aggressivity increases in the range FeCl₃-test, “green death”-test, CaCl₂-test. Matching and graduated over-alloyed weldments (TIG, heat input of 7 and 15.5 kJ/cm) of materials 1.4529, 1.4562, 2.4856, 2.4819 (german materials No.) are comparingly examined in various tests, of materials 1.4406, 1.4539, 1.4439 and 1.4563 (german materials No.) only matching weldments in the FeCl₃-test. In strongly oxidizing media only a highly over-alloyed performed weldment (filler material 2.4607, german material No.) produces the best corrosion behaviour, measured as the critical temperatures of localized corrosion. Measurements of critical current densities of passivation can be used for investigations of corrosion behaviour of weldments, too. Critical current densities of passivation are showing a tendency to inverse proportion to the critical temperatures of localized corrosion. Suitable electrolytes are among others 0.2M H₂SO₄ + 1M NaCl + 10^?3% KSCN, N₂-bubbled, 25 to 60°C and xM H₂SO₄ + 4M NaCl + 10^?3% KSCN (x = 0.05 to 1), 25°C, in contact with air. An influence of heat input at the welding is indicated in the test of localized corrosion, but it is only small. It is sometimes more clearly shown at measurements of passivation.     

Untersuchungen zum Korrosionsverhalten nichtrostender Stähle in Phosphorsäure in Abhängigkeit von dem Chlorid- und Fluoridgehalt und einer Wärmebehandlung beim Schweißen

Investigations into the corrosion behaviour of stainless steels in phosphoric acid in dependence on the chloride and fluoride contents and a heat-treatment during welding In the present investigation the corrosion behaviour of recently developed high-alloyed austenitic (X 2 NiCrMoCU 25 20) and austenitic-ferritic (X 2 CrNiMoCuN 25 5) steel has been tested towards phosphoric acid, the composition and concentration of which was adjusted to correspond to crude phosphoric acid with varying contents of Cl^?, F^?, Fe³⁺, and SO₃. Current density-voltage curves were recorded on steel test-specimens at room temperature, 45°C, and 80°C. In addition, test-pieces of both steels, after annealing treatment between 800°C and 500°C, as well as welded specimens of similar type were examined for the effect of heat input and consequent structural alterations on the corrosion behaviour. Both steels exhibit good corrosion resistance towards pure phosphoric acid. Cl^? and F^? ion impurities render the acid more aggressive. Austenitie-ferritic steel reacts more sensitively than austenitic steel towards heat input, resulting in deterioration in corrosion resistance. This may be attributed to the precipitation of inter-metallic phases in the ferritic structure.     

Untersuchungen über den Einfluß der Wärmebehandlung auf die Korrosion titanstabilisierter ferritischer Chromstähle in siedender konzentrierter Salpetersäure

Investigations into the influence of the thermal treatment on the corrosion of titanium-stabilized ferritic chromium steels in boiling concentrated nitric acid Titanium-stabilized ferritic chromium steels with about 17% Cr are, after quenching from high temperature, susceptible to grain boundary corrosion in boiling nitric acid; this corrosion is attributable to the chemical dissolution of the titanium carbonitrides coherently segregated at the grain boundaries. This carbide corrosion can be reduced by heat treatment within the temperature range around 850°C. In this process, the segregated carbo-nitrides are formed-in (in-formation annealing). The influence of quenching (0.5–5 hours, 900–1200°C/W[L]) and subsequent in-formation annealing (1–30 hours, 850°C/W) on the corrosion rate in boiling 65% nitric acid has been investigated in detailed on two steels of types X 8 Cr Ti 17 and X 8 Cr Mo Ti 17. In addition, the corrosion behaviour of titanium-stabilized and unstabilized ferritic chromium steels with about 17 pC chromium have been compared with each other.     

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.     

Interkristalline Korrosion ferritischer Chromstähle mit rd. 17 Gew.-% Chrom nach Glühen im Temperaturbereich um 500 °C

Intergranular corrosion of ferritic 17% chromium stainless steels after heat-treatment in the 500 °C temperature range After stabilizing heat-treatment at 750°C, the non-stabilized, ferritic 17% chromium stainless steel Mat.-Nr. 1.4016 (X8Cr17) still contains a sufficient high concentration of carbon dissolved in solid solution, that after heat-treatment in the 500 °C temperature range carbides rich in chromium of the M₂₃C₆-type are precipitated, causing a relatively weak pronounced susceptibility of the steel to intergranular attack. The susceptibility to this type of attack can be detected by testing specimens in the sulfuric acid-copper sulfate-test with increased concentration of sulfuric acid as compared with the DIN standard 50914, followed by metallografic examination of the specimens. The susceptibility to intergranular corrosion of the material investigated occurring after heat-treatment in the low temperature range, which until now is unknown, is described in terms of a Rollason-diagram as it is commonly used for austenitic chromium-nickel stainless steels. As it is to be expected, the stabilized 17% chromium steels Mat. No. 1.4510 (X8CrTi17), 1.4511 (X8CrNb17) and 1.4523 (X8CrMoTi17) are resistant to intergranular corrosion after heat-treatment at low temperatures.