Ni-Cr-Mo-Cu corrosion resistant alloy

The nickel-chromium-molybdenum-copper corrosion-resistant alloy was developed by adding Cu to the nickel-chromium-molybdenum alloy, mainly to improve its corrosion resistance in non-oxidizing acids, especially in phosphoric acid and sulfuric acid. Since the alloy contains both a high amount of Cr and Mo and Cu, the alloy is resistant to corrosion by a reducing acid other than hydrochloric acid or hydrofluoric acid and an oxidizing plus reducing mixed acid. The chemical composition of the commonly used nickel-chromium-molybdenum-copper corrosion-resistant alloy is listed in Table 9-1.

Table 9-1 Chemical composition of common nickel-chromium-molybdenum-copper corrosion-resistant alloy

Effects on the Corrosion Resistance of Nickel-Chromium-Molybdenum Alloys Although many copper-containing nickel-chromium-molybdenum corrosion-resistant alloys have been developed, there are not many literatures on the effects of Cu on the corrosion properties of nickel-chromium-molybdenum alloys. To Cr-Ni-Mo stainless steel and Fe-Ni-Cr-Mo (Ni mass fraction about 35%) iron-nickel based corrosion-resistant alloy, adding 1%~3% Cu, which is resistant to sulfuric acid, phosphoric acid, etc. The role is beneficial. Table 9-2 lists the effect of 2% Cu on the corrosion resistance of Ni-Fe-Cr-Mo alloy with a Ni content of about 45%. Figure 9-1 and Figure 9-2 show the results obtained by studying the corrosion behavior of Cu (mass fraction 1%~10%) on 75Ni-15Cr-2Mo-lTi alloy in dilute hydrochloric acid and high temperature HF gas. Obviously, the mass fraction of 1% ~ 3% Cu is beneficial to the alloy’s resistance to dilute HC1 acid, while Cu has no significant effect on the alloy’s resistance to HF gas corrosion. Among boiling HF acids, Cu has a significant benefit to the corrosion resistance of Ni-Cr-Mo alloys.

Table 9-2 Effect of Cu on Corrosion Resistance of Ni-Fe-Cr-Mo Corrosion Resistant Alloy

9.2 Microstructure, Properties and Applications of Several Nickel-Chromium-Molybdenum-Copper Corrosion Resistant Alloys
In order to meet the corrosion resistance of H2SO4, H3PO4 and HNO3 and H2SO4, H3PO4 or their mixed acid, nickel-chromium-molybdenum-copper alloy 021Ni60Mo4.5Cu6.5W2 was developed as early as 1915. On the basis of this alloy, some nickel-chromium-molybdenum-copper corrosion-resistant alloys have appeared in the past decades. The latest development of Ni-Cr-Mo-Cu alloys in the late 20th century is introduced in Chapter 8. ), the main alloys with wider application are shown in Table 9-1. 0Cr28Ni55Mo8. 5Cu5. 5 alloy is produced to solve the 98% thermal H2S04 corrosion. In order to improve the corrosion resistance of OCr28Ni55M08.5Cu5.5 alloy, the 0Cr28Ni50Mo8.5Cu5.5Si4B alloy which is added with Si and B can achieve this by aging heat treatment. Of the several grades listed in Table 9-1, the OCr21Ni68M05Cii3 alloy is the only deformed alloy. Due to the high content of Cr and Mo, it is difficult to achieve thermal deformation by thermal processing, so it is often used as a casting.
9. 2.1 Chemical composition and structure of several alloys
The four nickel-chromium-molybdenum-copper alloys listed in Table 9-1 are the earliest developed and relatively widely used alloys. The solid solution treatment state of these alloys is generally a single-phase austenite structure, but the 0Cr50Ni28MO8.5Cu5.5Si4B alloy has a complex Si content, both in solid solution state and in aging state, due to the high content of Si and B. The precipitated phase of B precipitated. The presence of these phases hardens the 0Cr50Ni28Mo8.5CU5.5Si4B alloy and improves its wear resistance and abrasion resistance.
9. 2.2 Mechanical properties
Table 9-3 shows the room temperature mechanical properties of several Ni-Cr-Mo-Cu corrosion resistant alloys.

Table 9-3 Mechanical properties of several nickel-chromium-molybdenum-copper alloys at room temperature

9.2.3 Corrosion resistance in various media 9. 2. 3. 1 Seawater
In seawater, the four Ni-Cr-Mo-Cu corrosion-resistant alloys given in Table 9-1 generally have good seawater corrosion resistance, and the flow rate of seawater has no significant effect on them. For example, = low flow rate, alloy surface fouling or microbial adhesion, the alloy still has some pitting resistance. The experiment shows that the corrosion rate of 0Cr22Ni56Mo6.5Cu6.5 alloy is 0.0075mm/a, and that of 0Cr21Ni68Mo5Cu3 alloy is 0.0000mmmm/a, and no corrosion occurs in both alloys.

9.2.3.2 Sulfuric acid
In sulfuric acid, the rare earth 504 is essentially reductive in the absence of air and oxidant; at >80% (room temperature), 40% more (boiling) and about 60% (60~95弋). Under the conditions of constant concentration and temperature, the essence of H2S04 is oxidative. The Ni-Cr-Mo-Cu alloys described in this section have nearly the same corrosion resistance in the reducing H2S04; and the difference in H2S04 resistance between them is mainly in hot and concentrated sulfuric acid. The temperature is higher than 65 ft and the concentration is 70%~85% H2S04, which is the most corrosive to corrosion resistant alloy. Thus, alloys resistant to this concentration of $H2S04 are rare. However, the concentration is higher, and the corrosive property is weakened because the ionization tendency of the acid is lowered. High Ni-Cr-Mo-Cu corrosion resistant alloy, due to its chemical composition, can not only withstand different temperatures and concentrations of H2S04, but also can be used under oxidation, reduction and alternating conditions.
Figures 9-3 and 9-4 show the experimental results of several Ni-Cr-Mo-Cu alloys in H2S04. It can be seen from Fig. 9-4 that 0Cr22Ni56Mo6. 5Cu6. 5 alloy is resistant to all concentrations of H2S04 below 601; except for 65%~85% H2SO4, this alloy can be used to resist corrosion of other concentrations of 1″1#04 at about 90T; in boiling H2SO4 This alloy is limited to use at <40% concentration. The Cr content and Mo content in the alloy are correspondingly increased, which extends the range of use of the alloy, and has satisfactory corrosion resistance in all concentrations of sulfuric acid of <80$, remarkable Better than IlliimiG alloy (Fig. 9-5, Fig. 9-6), which compensates for the insufficient corrosion resistance of the Illium G alloy at 65% ~ 85% H2SO4.

The isocorrosion of three cast Ni-Cr-Mo-Cu corrosion resistant alloys in H2S04 is shown in Figures 9-7 to 9-9. With the increase of Cr and Mo content in the alloy, the use temperature and the concentration range of the alloy in H2S04 are expanded. However, the addition of Si only increases the use temperature in the concentration of >65% H2SO4 at a concentration of <65% H2SO4. Corrosion resistance decreases in the middle (Figure 9-10). In 100 ° C H 2 SO 4 , with 0.51 mm / a as a criterion, the use boundary of the three alloys is shown in Figure 9-11. The corrosion resistance of the three alloys in 96% to 98% H2S04 is shown in Figure 9-12. Illium B alloy has the best corrosion resistance, however, in this medium, high Si stainless steel and alloy 33 have better performance and are not competitive.

9.2.3.3 Hydrofluoric acid
Among hydrofluoric acid, the nickel-chromium-molybdenum-copper corrosion-resistant alloy is resistant to corrosion of many non-airless anhydrous hydrofluoric acids below 60 qui. However, once the temperature is higher or the acid is filled with air, the corrosion rate of these alloys increases significantly. Table 9-4 lists the test results for the 0Cr21Ni68Mo5Cu3 deformed alloy. Obviously, the filling of the air has a significant effect of accelerating corrosion, and the corrosion rate of the sample partially immersed when the person is fully immersed is also significantly improved. Some tests have also shown that grades with high chromium content and high molybdenum content in nickel-chromium-molybdenum-copper alloys have better resistance to hydrofluoric acid corrosion.

Table 9-4 Corrosion resistance of deformed 0Cr21Ni68Mo5Cu3 alloy in HF acid

Tests in HF + H2SO4 mixed acid (25% ~ 35% H2S04 + 4% ~ 8% HF acid, 50 ~ 80 °C show that several nickel-chromium-molybdenum-copper alloys have quite good corrosion resistance, see Table 9- 5.

Table 9-5 Corrosion resistance of several nickel-chromium-molybdenum-copper alloys in H2SO4 mixed acid

Hydrofluorosilicic acid is generally less corrosive than hydrofluoric acid. The foregoing nickel-chromium-molybdenum-copper alloys are resistant to corrosion by such acids. Table 9-6 is some experimental results.

Table 9-6 Test results of Ni-Cr-Mo-Cu alloy in hydrofluorosilicic acid

9.2.3.4 Hydrochloric acid
In hydrochloric acid, since the metal chloride has a high solubility in the solution and the chloride ion has a large concentration, increasing the concentration, temperature, flow rate, and air volume of the hydrochloric acid accelerates the corrosion of the alloy. Nickel-chromium-molybdenum-copper alloy can only be used in hydrochloric acid which is near room temperature and is not filled with air, except for dilute hydrochloric acid (≤ 2%). For example, 0Cr22Ni56Mo6.5Cu6.5 alloy is limited to mass fraction ≤ 15%, used in room temperature hydrochloric acid, and some test results are listed in Table 9-7.

Table 9-7 Corrosion test results of 0Cr22Ni56Mo6.5Cu6.5 alloy in hydrochloric acid

9.2.3.5 in phosphoric acid
Among the phosphoric acid, the test results of 0Cr22Ni56Mo6.5Cu6.5 alloy are shown in Table 9-8. From the results in the table, it is known that the corrosion resistance of the alloy is about 50% and about 80% H3PO4h at the boiling temperature under the conditions tested. In the actual wet production of phosphoric acid, there are a certain number of sulfuric acid, hydrofluoric acid and hydrofluorosilicic acid and metal salts in the industrial acid, and the medium is oxidizing in nature. The corrosive nature of such media often depends on its F-content. The F-content varies with the source of the phosphate rock. If the phosphate rock contains enough silicon and reacts with free HF acid to form hydrofluorosilicic acid, the corrosiveness of the medium is reduced. Table 9-9 lists the test results when a small amount (0.8%) of HF acid is added to 55% H3PO4. Obviously, the nickel-chromium-molybdenum-copper alloy with high chromium content and Mo and Cu composite has the best corrosion resistance. Table 9-10 shows the results of corrosion tests performed on two nickel-chromium-molybdenum-copper alloys under wet H3PO4 production conditions. It can be seen from the table that under the same test conditions, when the chromium content is high (for example, 0Cr28Ni55Mo8.5CU5.5 alloy), it has better corrosion resistance.

Table 9-8 Corrosion resistance of 0Cr22Ni56Mo6. 5Cu6. 5 alloy cast in H3PO4

Table 9-9 Comparison of Corrosion Resistance of Some Common Alloys in 55% H3PO4 + 0.8% HF Medium

Table 9-10 Corrosion test results of two Ni-Cr-Mo-Cu alloys in the production process of wet H3P04

9.2.3.6 Sulfite
In sulfurous acid, the nickel-chromium-molybdenum-copper alloy is resistant to moisture 302 and corrosion of most concentrations and temperatures of sulfurous acid. In the corrosion resistance of relatively pure sulfurous acid, the Cu-containing alloy is not superior to the alloy containing no Cu but the same content of Cr and Mo. Of course, when a certain amount of H2S04 is present in the sulfurous acid to form a mixed acid, the Cu-containing alloy is much better than the Cu alloy, and its corrosion resistance is much better.
Nitric acid
9.2.3.7 In nitric acid, these nickel-chromium-molybdenum-copper alloys have a high resistance to HNO3 corrosion due to their high chromium content in the disk. For example, 0Cr22Ni56Mo6. 5Cu6. 5 alloy can withstand the corrosion of all concentrations of HNO3 below 70 °C; when the temperature of HNO3 reaches the boiling point, the alloy can withstand the corrosion of concentration ≤ 25% HNO3. The test results of 0Cr22Ni56Mo6.5Cu6.5 alloy are listed in Table 9-11. The performance of HN03 with a Cr content of about 28% is better than that of 0Cr22Ni56Mo6. 5Cu6. 5 alloy.

Table 9-11 Corrosion resistance of 0Cr22Ni56Mo6.5Cu6.5 alloy in HN03

Since the performance of stainless steel nitric acid is well suited to the needs of engineering, in order to solve the corrosion problem of HN03, it is not necessary to use expensive nickel-chromium-molybdenum-copper alloy. However, for environments that are resistant to HNO3 and H2SO4, H3PO4, etc., for conditions such as resistance to HNO3, H2SO4, H3PO4, etc., for environments resistant to HNO3 media containing F- and Cr, nickel-chromium-molybdenum-copper corrosion-resistant alloys are used. Can be considered.
9.2.3.8 Organic acids
Among organic acids and organic compounds, nickel-chromium-molybdenum-copper alloys are very resistant to most organic acids and organic compounds such as anhydrides, aldehydes, ketones, alcohols, esters and other organic solvents. Corrosive. According to the test in glacial acetic acid vapor at 360~675 ° C, the flow rate is 4.3 m / s, the corrosion rate of 0Cr22Ni56Mo6. 5Cu6. 5 alloy is 0.0050mm / ao
9.2.3.9 Halogen gas
Among the halogen elements and their hydride gases, the nickel-chromium-molybdenum-copper alloy generally has good corrosion resistance in high-temperature drying dentate gas. However, once water is condensed in chlorine, bromine, and iodine, these alloys are rapidly corroded, even at room temperature. At this time, pitting often occurs.

Table 9-12 Corrosion resistance of 0Cr21Ni68Mo5Cu3 alloy in flowing fluorine

9.2.4 Thermal processing, cold working, heat treatment and welding performance
0Cr21Ni68Mo5Cu3 alloy is a deformed alloy, which can be processed by forging, rolling, drawing, stamping, spinning, etc. without special difficulties. The suitable heat distortion temperature of this alloy is 1065 ~ 1230 ft, but slight thermal processing is also allowed between 950 and 1065T. The suitable heat treatment process for 0Cr21Ni68Mo5CU3 alloy is 1120 ~ 11T7T after heating and water cooling. The maximum allowable cold deformation of this alloy after each heat treatment was 25%. For 0Cr21Ni68Mo5Cu3 alloy, it is most suitable to use TIG and MIG welding.
0Cr22Ni56Mo6.5Cu6.5, 0Cr28Ni56Mo8.5Cu5.5Si4B and 0Cr28Ni55Mo8.5Cu5 All three alloys are cast alloys and can only produce castings. Their heat treatment process is water-cooled after heating at 1丨801. 0Cr28Ni50Mo8.5Cu5.5S14B alloy has poor welding performance and generally needs to be preheated to about 960 °C before welding.
9.2.5 Application
0Cr21Ni68Mo5Cu3 alloy is a deformed alloy. Metallurgical products that can be supplied include plates, pipes, rods, strips, wires and forgings, as well as castings. 0Cr22Ni56Mo6. 5Cu6.5, 0Cr28Ni50Mo8.5Cu5.5Si4B, 0Cr28Ni55Mo8.5Cu5.5 three alloys can only be supplied in the form of cast products. Due to their high content of chromium, molybdenum and copper, these nickel-based alloys are particularly resistant to corrosion by sulfuric acid and phosphoric acid (including sulfuric acid containing cr and F_) and are suitable for the manufacture of cast products such as pumps and valves.