Nickel-iron-chromium alloys, corrosion

Inconel, a nickel-iron-chromium alloy, is normally used in manufacturing the RTD sheath because of its inherent corrosion resistance. When placed in a liquid or gas medium, the Inconel sheath quickly reaches the temperature of the medium. The change in temperature will cause the platinum wire to heat or cool, resulting in a proportional change in resistance. 

Raymond, E. L., Mechanism of Sensitisation and Stabilisation of Incoloy Nickel-Iron-Chromium Alloy 82S , Corrosion, 24, 180 (l%8)... 

At moderate temperatures, the general corrosion resistance of alloy 800 is similar to that of other austenitic nickel-iron-chromium alloys. However, as the temperature increases, alloy 800 continues to exhibit good corrosion resistance, whereas other austenitic alloys are unsatisfactory for the service. 

HUNTINGTON alloy HA-330 A nickel-iron chromium alloy with good high-temperature strength and corrosion resistance. Provides good resistance to oxidation and carburization. 35.5 44.0 18.5 A NR X A G-E G-E A A A G-E... 

Description and corrosion resistance. Alloy 800 is a nickel-iron-chromium alloy with good strength and excellent resistance to oxidation and carburization in high-temperature atmospheres. It also resists corrosion by many aqueous environments. 

Description and corrosion resistance. Incoloy 825 is a nickel-iron-chromium alloy with additions of molybdenum and copper. It has excellent resistance to both reducing and oxidizing acids, stress-corrosion cracking, and localized attack such as pitting and crevice corrosion. The alloy is especially resistant to sulfuric and phosphoric acids. 

The composition of this alloy (54% nickel, 15% molybdenum, 15% chromium, 5% tungsten and 5% iron) is less susceptible to intergranular corrosion at welds. The presence of chromium in this alloy gives it better resistance to oxidizing conditions than the nickel/molybdenum alloy, particularly for durability in wet chlorine and concentrated hypochlorite solutions, and has many applications in chlorination processes. In cases in which hydrochloric and sulfuric acid solutions contain oxidizing agents such as ferric and cupric ions, it is better to use the nickel/molybdenum/ chromium alloy than the nickel/molybdenum alloy. 

Intergranular and transgranular cracking often occur simultaneously in the same alloy. Such transitions in crack modes are observed in alloys with high amounts of nickel, iron chromium and brasses. In corrosion under tension, ruptures are fragile and are sometimes characterized by the presence of cleavages, notably in the case of hydrogen embrittlement.16... 

Iron-nickel alloys tend to be of lower corrosion resistance than iron-chromium alloys except towards attack by hot concentrated alkalis. Iron-chromium-nickel alloys are superior to either of the above and are resistant to alkaline and neutral aqueous solutions, atmospheric and seawater attack. Hot non-oxidising acids will cause corrosion, the rate depending on concentration and temperature. 

Nickel has a very small effect on the anodic polarization behavior of iron, and hence, iron-nickel alloys are of minor significance as corrosion-resistant alloys. However, the addition of nickel to iron-chromium alloys (AISI 200 series) permits conversion of the latter as ferritic alloys to austenitic iron-chromium-nickel alloys (AISI 300 series). In... 

E6.2. Predict whether or not galvanic corrosion will cause the following alloys to be subjected to leaching (i) carbon and carbon steel alloys in an oxidizing atmosphere, (ii) steel rivets in aluminum drain gutters, (iii) copper-nickel alloy in refinery condenser tubes, (iii) graphite fiber-reinforced aluminum composites, (iv) brass in water, (v) iron-chromium alloys, and (vi) carbon steel pipe in contact with the weld to stainless steel pipe. 

Interest in passivity started with the studies of Faraday [1] and Schonbein [2] over 150 years ago. The lack of metallic corrosion in the case of iron immersed in certain solutions was attributed to either the presence of an oxide film or an electronic change in the metal. This basic argument has persisted in various forms to this day, although the majority of scientific evidence suggests protection by a three-dimensional oxide film. Much has been published on passivity and its breakdown over the last 50 years. This chapter does not attempt to cover all the literature but concentrates on work over the past 10-15 years, emphasizing the passivity of iron, nickel, iron-chromium, and iron-nickel alloys in aqueous environments. Examples are given fi om the authors and other selected laboratories. 

Nickel-iron-chromium (for example, aUoy 800) and nickel-chromium-iron (alloy 600) may become sensitized by precipitation of chromium carbides and subject to intergranular corrosion... 

Anodic polarization of active/passive metals - alloys of nickel, iron, chromium, titanium, and stainless steel in weak-to-extiemely corrosive environments, where economy in consumption of protective currents is required. 

Nickel—Iron. A large amount of nickel is used in alloy and stainless steels and in cast irons. Nickel is added to ferritic alloy steels to increase the hardenabihty and to modify ferrite and cementite properties and morphologies, and thus to improve the strength, toughness, and ductihty of the steel. In austenitic stainless steels, the nickel content is 7—35 wt %. Its primary roles are to stabilize the ductile austenite stmcture and to provide, in conjunction with chromium, good corrosion resistance. Nickel is added to cast irons to improve strength and toughness. 

The metal parts of the injection molder, ie, the liner, torpedo, and nozzle, that contact the hot molten resin must be of the noncatalytic type to prevent accelerated decomposition of the polymer. In addition, they must be resistant to corrosion by HCl. Iron, copper, and zinc are catalytic to the decomposition and caimot be used, even as components of alloys. Magnesium is noncatalytic but is subject to corrosive attack, as is chromium when used as plating. Nickel alloys such as Duranickel, HasteUoy B, and HasteUoy C are recommended as constmction materials for injection-molding metal parts. These and pure nickel are noncatalytic and corrosion-resistant however, pure nickel is rather soft and is not recommended. 

Copper is primarily alloyed to increase strength, however, electrical and thermal conductivities, corrosion resistance, formabiUty, and color are also strongly affected by alloying. Elements typically added to copper are 2inc, tin, nickel, iron, aluminum, siUcon, chromium, and beryUium. 

The resistance of a metal to erosion-corrosion is based principally on the tenacity of the coating of corrosion products it forms in the environment to which it is exposed. Zinc (brasses), aluminum (aluminum brass), and nickel (cupronickel) alloyed with copper increase the coating s tenacity. An addition of V2 to 1)4% iron to cupronickel can greatly increase its erosion-corrosion resistance for the same reason. Similarly, chromium added to iron-base alloys and molybdenum added to austenitic stainless steels will increase resistance to erosion-corrosion. 

Because the composition of this alloy (47% nickel, 22% chromium, 7% molybdenum and 17% iron) has a higher iron content it cannot withstand such aggressive corrosion conditions as nickel/molybdenum and nickel/... 

---