Metal Dusting Resistance of Alloy 602 CA (marketing department of Shanghai HY Industry Co., Ltd)

Metal powdering, also known as catastrophic carburization, is an unusual form of high-temperature corrosion commonly seen in the petrochemical and energy industries, especially in production processes such as coal conversion and heat treatment. Metal powdering generally occurs in environments between 400°C and 800°C, with low oxygen levels and high levels of hydrogen and carbon monoxide gases. Metal powdering results in the breakdown of iron- and nickel-based alloys to form dust and powder consisting of carbides, metal particles and graphite.

Alloy 602 CA, the material of the alloy in this paper, has excellent resistance to metal powdering.

Alloy 602 CA (N06025) is a new type of high-strength high-temperature material specially developed for industrial furnace construction and petrochemical industry. It shows excellent mechanical properties under high temperature environment, as well as first-class oxidation resistance and carbonization resistance, and the primary carbide precipitation ensures its creep rupture strength.

In addition, Alloy 602 CA has excellent resistance to metal powdering, so it is widely used in related processes in the petrochemical industry, and is also used to produce prefabricated parts in iron ore direct reduction plants.

Material properties of Alloy 602 CA

Alloy 602 CA is a high temperature material with excellent creep and oxidation resistance in environments up to 1200°C.
Alloy 602 CA products are delivered in a solution annealed state with an oxidized or descaled surface.

* The high temperature mechanical properties of Alloy 602 CA are as follows:

Corrosion resistance of Alloy 602 CA

Alloy 602 CA has excellent oxidation resistance, which is better than Alloy 601 in the application range below 1200°C. Even under extreme conditions such as cyclic heating and cooling, Alloy 602 CA maintains high oxidation resistance thanks to a dense, spalling-resistant alumina layer.

High temperature oxidation tests show that the material exhibits minimal mass loss under repeated extreme conditions compared to other high temperature materials. Due to its chromium and aluminum content, 602 CA maintains good corrosion resistance to oxidizing sulfur-containing gases at high temperatures. The carburization resistance of 602 CA is better than that of 601, and it also has obvious advantages in metal powdering resistance.

1. Antioxidant
Elements with a greater thermodynamic affinity for oxygen tend to form passive barriers in the alloy, thus providing the alloy with the required corrosion resistance. Cr, Al and Si are the three main passivation barrier forming elements.

Chromium trioxide (Cr203) can only be protected up to 950°C because volatile chromium oxide (Cr03) is formed at this temperature. The alumina sublayer has high thermodynamic stability even at a very low oxygen partial pressure, thereby improving the oxidation resistance of the 602CA alloy in the cycle test, and the rare earth elements further reduce the protective alumina sublayer. Cracks, cracks and peels.

The table above provides the cyclic oxidation test results. It can be seen from the table that the 602CA alloy has excellent oxidation resistance compared with many other iron-based, nickel-based and cobalt-based alloys. The metallographic examination of the 602CA alloy shows that there is no selective inner layer in a continuous alumina sublayer. oxidation, while alloy 601 exhibits internal oxidation. The higher thermodynamic stability and lower decomposition pressure (5 orders of magnitude higher) of alumina are the main reasons for the formation of the protective alumina layer.

2. Anti-carbonization/anti-metal dusting

In addition to the attack of oxygen, superalloys are often attacked by carbon. Degradation of metal systems in carbonized environments may occur in two ways, usually carbonization and metal dusting (also known as catastrophic carbonization). Due to the very low solubility of carbon in nickel, some materials with high nickel content are therefore considered to be beneficial against carburization. Alloys of high chromium, aluminum and silicon form a protective oxide layer that prevents the intrusion of carbonaceous corrosion and thereby improves carburization resistance.

However, if the material is alternately exposed to carbonizing and oxidizing environments, the precipitated carbides will convert to oxides releasing carbon monoxide which widens the grain boundaries, thus creating a loose oxide layer that accelerates the degradation of the material .

A recent study was conducted on the pulverization behavior of 9 kinds of nickel-based alloys and 4 kinds of Fe-Ni-Cr-based alloys. The test was carried out at 650°C in a carbonized H2-CO-H2O atmosphere with carbon activity >1. The results show that 602CA alloy is one of the materials with the best resistance to metal dusting.

Machinability/weldability of Alloy 602 CA

Welding of Alloy 602 CA follows the same rules as other highly alloyed nickel-based materials, where cleanliness is very important and critical.

The heat input should be kept low, and the interlayer temperature should not exceed 150°C, preferably not exceeding 120°C. TAW welding process and matching electrode materials are recommended. For CMAW (shielded metal arc welding), matching electrodes are available (UTP6225A1). Submerged arc welding with a CTAW top layer is also adequate and does not require preheating. The shielding gas for the GTAW process is Ar+2%N2, which is important to prevent any cracking during the welding process. The protective gas of the CMAW process is Ar gas containing He, N2 and carbon dioxide.

application of Alloy 602 CA

Alloy 602 CA has a wide range of applications in thermal engineering and high temperature processing in the chemical industry, in power plants and in the automotive industry.

Typical applications are:

• Heat treatment industry: Furnace bars, bell furnaces, bright annealing furnaces, muffle furnaces, accessories, and conveyor hooks for enamel furnaces, transmission rollers and conveyor belts for ceramic kilns, pins for refractory materials, furnace tubes for bright annealing lines , and other furnace accessories.

• Satin fired furnace: Rotary kiln for burning and producing high-purity alumina, burning chromite ore to produce chromium steel, and recycling expensive nickel catalysts from the petrochemical industry.

• Chemical/petrochemical industry; production of hydrogen with a new steam reformer and production of phenols from benzene with a new, inexpensive process.

• Automobile: Catalyst support systems, ignition plugs, automotive exhaust system components, glow plugs for diesel engines.

•  Nuclear reactor cleanup.

• Steel production: direct reduction process for the production of sponge iron.

Summarize

A damage known as “metal dusting” is often found in the direct reduction process of iron ore and in the petrochemical industry, as well as in the synthesis of hydrocarbons, methanol and ammonia. Metal powdering is a kind of corrosion, manifested as “pit”, at the temperature of 500 ℃ to 800 ℃, in the atmosphere of carbon as the medium, the metal is rapidly lost.

The research of HY in the test cycle of 10000 hours shows that compared with the previous materials, such as 601 alloy and 600 alloy, the new alloy 602CA does not show metal dusting, and under the appropriate test conditions, after 10000 hours, it shows good oxidation resistance sex. This is one of the reasons why in 1996 it was decided to use this material for 50mm thick preforms in the COREX direct reduction process.

Shanghai HY Industry Co., Ltd has international first-class material production equipment such as high temperature alloy isothermal forging production line, CONSARC vacuum melting furnace, VAR vacuum arc remelting furnace etc., with strong professional ability and highly responsible management team. We are a member of China Application of nuclear energy materials, Member of the International Council of the Aeronautical Sciences. Years of experience in Corrosion Resistant Alloy & Superalloy. When you have superalloy material inquiry, please contact us without hesitation. Shanghai HY Industry Co., Ltd is Corrosion & fatigue nickel alloy professional manufacturer,We will provide you with sincere and thoughtful service.

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