Ni-Fe-Cr-Mo-Cu alloys

Ni-Fe-Cr-Mo-Cu alloy is an important part of iron-nickel based corrosion resistant alloy. It is a series of alloys formed by adding a proper amount of copper to the 1Ni-Fe-Cr-Mo alloy. After adding Cu, the corrosion resistance of the alloy in the reducing acid is improved, especially in the hot sulfuric acid. Corrosion resistance. Usually such alloys contain a relatively high amount of Cr and an appropriate amount of Mo. Therefore, they all have good resistance to oxidation of medium. It also has good resistance to stress corrosion, pitting and crevice corrosion. Compared with the commonly used Ni-Cr-Mo-Cu casting corrosion resistant alloy, the corrosion resistance in some media is comparable or superior to that of the alloy, and the partial Ni in the Ni-Cr-Mo-Cu alloy is replaced by Fe. And elements such as Cu make it cheaper. The comprehensive advantage of price and performance is an important reason why Ni-Fe-Cr-Mo-Cu alloy has become a brand of Fe-Ni based corrosion resistant alloy and has a wide range of uses. The development of various chemical processing industries has placed urgent demands on inexpensive and corrosion-resistant structural materials. This demand is the driving force for the development of Ni-Fe-Cr-Mo-Cu iron-nickel-based corrosion-resistant alloys. In the 20th century research and development of Ni-Fe-Cr-Mo-Cu corrosion resistant alloys, it is not difficult to find that there are two highlights in the development of such alloys. First, in the early 1960s (1964), China confirmed in the laboratory and on-site corrosion tests that Ni-Fe-Cr containing 25% Cr in a highly corrosive acidic solution containing F- and Cl- at high temperature. The corrosion resistance of the -Mo-Cu alloy is sharply improved. The discovery and confirmation of the amount of Cr at this inflection point lays the foundation for the subsequent corrosion resistance alloy with a Cr content of 25% or more, for example, iron-nickel-based new No. 2 alloy (China) ), Sanicro-28 (Sweden), Hastelloy G-30 (USA), etc. The second is to introduce nitrogen into the iron-nickel-based corrosion-resistant alloy. It is well known that in stainless steel, the good effect of N has been achieved and has been successfully applied in austenitic stainless steel and duplex non-pound steel. In 1990, Thyssen Krupp VDM of Germany introduced the alloying of N to the iron-nickel-based corrosion-resistant alloy and introduced Nicrofer3127 hMo-alloy 31. In 1995, the alloy 33 was successfully developed. These two points can be considered to have a breakthrough value in the history of such alloys.

Effect of Copper on Corrosion Resistance of Ni-Fe-Cr-Mo-Cu Alloy In terms of uniform corrosion, the addition of Cu significantly improves the corrosion resistance of Ni-Fe-Cr-Mo-Cu alloy in reducing media. The optimum Cu content is related to the acid concentration and temperature. At 65 ° C, adding 1% Cu in 50% H2S04, the corrosion rate of Fe-38Ni-20Cr-2Mo alloy is reduced from 0.4mm.a of low Cu (0.2%) alloy to 0.1mm / a, continue The optimum copper content in the 80% H2S04 and the boiling 50% H2S04 is 2% and 2.5% at 65 ° C. In boiling 10% H2S04, the addition of Cu is detrimental to the corrosion resistance of Fe-28Ni-20Cr-2Mo alloy. However, for the high Mo alloy of Ni-22Cr-20Fe-6.5Mo, the addition of 2% Cu has a favorable effect on the corrosion resistance of the alloy in various concentrations of boiling H2S04 and H3P04. From the electrochemical point of view, the addition of Cu significantly improved the electrochemical behavior of the alloy in a reducing medium. In boiling 10% H2s04, the Cu-containing alloy has the lowest critical current density, and its ICP value is 354 UA/CM2, without The Cu alloy has an ICP value of 1860 UA/CM2. The lowest ICP value of the Cu-containing alloy makes it easy to passivate and gives the alloy the best corrosion resistance in reducing H2S04 media. In contrast, in an oxidizing medium, the addition of Cu adversely affects the corrosion resistance of the alloy. The copper content in the Fe-Ni based corrosion-resistant alloy generally varies from 1% to 4% under the premise of satisfying both the corrosion resistance of the alloy and the hot workability of the alloy.

Table 12-1 Effect of Cu on Corrosion Resistance of Ni-Fe-Cr-Mo Alloy

Note: Corrosion data is the average of 5 24h tests.

Effect of Chromium on Corrosion Resistance of Ni-Fe-Mo-Cu Alloy
Corrosion test results of chromium content in liquid phase and gas of Fe-35Ni-(2~3)Mo-(3~4) Cu alloy in Cl- and F–containing wet solutions. In two different media, under the condition that the Fe-Ni based alloy has suitable Mo and Cu ratio, Cr has a good influence on the corrosion resistance of the alloy. Corrosion resistance is significantly improved as the chromium content of the alloy increases. When the chromium content of Cr reaches 25%, the corrosion rate drops sharply and a significant inflection point appears. In the liquid phase, the corrosion rate is 0.08 g/m2·h, and the corrosion resistance is improved by nearly 20 times compared with the mass fraction of 20% Cr alloy; in the gas phase, the same law is observed, and only the corrosion rate is different. Laboratory simulations of wet-process phosphoric acid and tests in field practical media have also indicated that chromium content in alloys is a key factor in determining the corrosion resistance of such materials.
In summary, in the Ni-Fe-Mo-Cu alloy, in order to obtain satisfactory corrosion resistance, the complex content of Cr should be above 20%. In some acidic media containing F ̄, Cl ̄ , only when Cr>=25%, the best resistance to uniform corrosion, pitting corrosion, crevice corrosion and stress corrosion resistance can be obtained. From the electrochemical point of view, the high chromium content not only makes the alloy easy to passivate, reduces the blunt current density and thus the dissolution rate, but also gives the alloy re-passivation ability to repair the damaged passivation film, which is high & alloy The basic reason for good overall corrosion resistance.

Typical materials for Ni-Fe-Cr-Mo-Cu: N08031 (alloy 31), N08535, N08825, N08221, N08028, N08026, N08024