KR940003890B1 - Ferrochromium alloy - Google Patents

Abstract

An erosion and corrosion resistant ferrochromium alloy comprising the following composition, in wt. %, 34 - 50 chromium, 1.5 - 2.5 carbon, up to 5 manganese, up to 5 silicon, up to 5 molybdenum, up to 10 nickel, up to 5 copper, up to 1 % of each of one or more micro-alloying elements selected from the group consisting of titanium, zirconium, niobium, boron, vanadium and tungsten, and balance, iron and incidental impurities. The alloy has a microstructure comprising eutectic chromium carbides in a matrix comprising one or more of ferrite, retained austenite and martensite, as herein defined. Optionally, the microstructure further comprises one of primary chromium carbides, primary ferrite or primary austenite in the matrix.

Description

Corrosion-resistant ferrochromium alloy and its manufacturing method

1 is a micrograph showing the microstructure of an Abex alloy.

2-5 are micrographs showing the microstructure of a preferred alloy of the present invention.

The present invention relates to ferrochrome alloys, in particular ferrochrome alloys having corrosion resistance and corrosion resistance.

The present invention relates to materials for use in the manufacture of internal pumps, pipes, nozzles, mixers, and other device components that can be used for mixtures containing corrosive fluids and erosive particles.

Typical fields for melting such parts include fuel gas desulfurization operations in which the parts are exposed to sulfuric acid and limestone, and also in the production of fertilizers in which the parts are exposed to phosphoric acid, nitric acid and gypsum.

US Pat. Nos. 4,536,232 and 4,080,198 (Abex Corpotation "Abex US Patents") provide 1.6tw% carbon and 28wt% characterized by primary chromium carbide and ferrite in a methyleneite or austenite matrix containing chromium solids. Ferrochrome alloys containing chromium are disclosed. Excellent corrosion resistance due to chromium in the alloy. However, the production of such alloys is not sufficient from the standpoint of corrosion resistance.

It is an object of the present invention to provide a ferrochrome alloy with improved corrosion resistance and corrosion resistance compared to the alloy disclosed in the Abex U.S. patent.

Abex U.S. The erosion and corrosion mechanism of the patented alloys shows that the corrosion phenomenon is accelerated as the erosive particles in the fluid stream continue to remove the passive corrosion resistant layer. In order to replenish the water resistant layer, the chromium must be concentrated to the highest possible content in the matrix.

However, if the chromium content is improved simply by increasing the chromium content, it forms an undesirable sigma phase in view of the problem of softness.

The present invention Abex U.S. By increasing both the chromium and carbon concentrations in the alloys of the type disclosed in the patent, it is possible to increase the chromium carbide volume fraction and thereby improve the wear resistance of the ferrochrome alloy, while increasing the chromium content to prevent the formation of large amounts of sigma phase. Announced that it can maintain an excitation matrix. As mentioned above, the corrosion resistance of the ferrochrome alloy can be realized by improving the wear resistance of the ferrochrome alloy in the mechanism of erosion and corrosion.

In the present invention, there is provided a corrosion-resistant ferrochrome alloy having the following weight percent composition.

34-50 chrome

1.5-2.5 carbon

Manganese up to 5

Silicon up to 5

Molybdenum up to 5

Up to 10 nickel

Up to 5

One or more micro-alloy forming elements selected from titanium, zirconium, niobium, boron, vanadium and tungsten up to 1% and the remainder also contain eutectic chromium carbide in a matrix composed of one or more ferrites, residual austenite and martensite It is composed of ancillary impurities and iron in the microstructure.

"Ferrite" means a body centered cubic (alpha or / or delta) containing chromium solid solution.

"Austenite" refers to face centered cubic iron containing carbon and chromium solid solutions.

"Martensite" refers to a modified product of austenite. The matrix preferably contains 25-35wt% chromium solid solution. In addition, the microstructure preferably contains one of primary chromium carbide, primary ferrite or primary austenite in the matrix.

The amounts of elements such as chromium, carbon, manganese, silicon, molybdenum, nickel and copper are in weight percent as follows:

36-40 chrome

1.9-2.1 carbon

1-2 manganese

0.5-1.5 silicone

1-2 molybdenum

1-5 nickel

1-2 dong

In such a composition it is more preferred that the matrix contains 29-32 wt% chromium solid solution.

In the present invention, the chromium and carbon content in the above ferrochrome alloy is Abex U.S. By increasing the content more than the patent to increase the volume ratio of the rigid carbide to improve the wear resistance. More specifically, the stoichiometric equilibrium between chromium and carbon content enables the chromium carbide volume ratio to be increased without increasing the chromium content of the matrix to the critical level just before the occurrence of sigma phase phenomena.

Preferred alloys of the present invention are Abex U.S. It shows better corrosion resistance than the alloy published in the patent. This is shown in Table 1 below and Abex U.S. Lab scale potential dynamic corrosion and disc wear test results for the alloys disclosed in the patent and the preferred alloys of the present invention are shown. The compositions of the alloys are listed in Table 2 below.

TABLE 1

Corrosion and Erosion Test Results

* 10% sulfuric acid, 25 ° C ASTM G61

** 40 wt% silica sand slurry 18 m / s

TABLE 2

Composition of the alloys of Table 1

* U.S. As-shares with compositions within the scope of Patent 4,536,232

** U.S. Heat treatment alloys with compositions within the scope of Patent 4,536,232

Table 1 shows that the alloy of the present invention has much better corrosion resistance than Abex alloys.

The alloy of the present invention is Abex U.S. It has a different microstructure than the alloy disclosed in the patent. The difference is that the alloy of the present invention and Abex U.S. It is shown in the accompanying drawings, which are micrographs of the alloy of the patent.

Figure 1 shows the microstructure of an Abex alloy consisting of 28.4% chromium, 1.94% carbon, 0.97% manganese, 1.48% silicon, 2.10% molybdenum, 2.01% nickel, 1.49% copper and the rest iron. This microstructure consists of a primary austenite dendritic structure (50% by volume) and, on the other hand, a process structure consisting of process ferrite, retained austenite and martensite.

Figure 2 shows the microstructure of the preferred alloy of the present invention consisting of 35.8% chromium, 1.94% carbon, 0.96% manganese, 1.48% silicon, 2.06% molybdenum, 2.04% nickel, 1.48% copper and the rest iron. The microstructure consists of primary ferrite dendritic tissue (20% by volume) as a eutectic form and process ferrite containing finely dispersed eutectic carbides in a matrix of process ferrite. Abex U.S. Compared to the microstructure of the patent, the microstructure of FIG. 2 reflects the presence of a reduced volume of primary dendritic tissue and an enlarged volume of the process matrix, and the stiffness in the alloy compared to the Abex alloy due to its relatively high carbide ratio. The carbide volume ratio is generally larger. It should be noted that this phenomenon is clearly magnified when compared with the microstructures shown in FIGS. 3 to 5 and FIG.

3 shows the microstructure of another alloy of the present invention consisting of 40.0% chromium, 1.92% carbon, 0.96% manganese, 1.59% silicon, 1.95% molybdenum, 1.95% nickel, 1.48% copper and the remainder iron. This microstructure contains process carbides in the process ferrite matrix.

4 shows the microstructure of another alloy of the present invention consisting of 40.0% chromium, 2.30% carbon, 2.77% manganese, 1.52% silicon, 2.04% molybdenum, 1.88% nickel, 1.43% copper and the remainder iron. This microstructure is different from the process form with primary MC carbides, but with process carbides in the process ferrite matrix.

5 shows the microstructure of another alloy of the present invention consisting of 43% chromium, 2.02% carbon, 0.92% manganese, 1.44% silicon, 1.88% molybdenum, 1.92% nickel, 1.2% copper and the remainder iron. The microstructure in this case is a subprocess with a very small amount of primary MC carbides and a process structure with process carbides in the process ferrite matrix.

Suitable conventional casting and heat treatment techniques are used to prepare the alloy of the present invention. However, after forming the alloy by the casting method, it is preferable to heat-treat and air cool at a temperature in the range of 600 to 1,000 ℃.

It is also possible to produce the alloy by various modification methods without departing from the spirit and scope of the invention.

Claims (5)

34-50 wt% chromium 1.5-2.3 wt% carbon 0.5-3 wt% manganese 0.5-2 wt% silicon 1-2 wt% molybdenum 1-5 wt% nickel 1-2 wt% copper and titanium, Containing up to 1% by weight of each element of at least one selected from zirconium, niobium, boron, vanadium and tungsten, the remainder being composed of iron and ancillary impurities, while at least one ferrite, retained austenite, and also martensite Corrosion-resistant ferrochrome alloy characterized by the microstructure of the (eute ctic) chromium contained in the matrix. The alloy of claim 1, wherein the microstructure comprises one of primary chromium carbide, primary ferrite or primary austenite in the matrix. The alloy of claim 1, wherein the matrix contains 25-35% by weight of chromium solid solution. The alloy according to claim 1, wherein the chromium content is 36-40% by weight, the carbon content is 1.9-2.1% by weight, the manganese content is 1-2% by weight, and the silicon content is 0.5-1.5% by weight. . 34-50 wt% chromium 1.5-2.3 wt% carbon 0.5-3 wt% manganese 0.5-2 wt% silicon 1-2 wt% molybdenum 1-5 wt% nickel 1-2 wt% copper and titanium, Containing up to 1% by weight of each element of at least one selected from zirconium, niobium, boron, vanadium and tungsten, the remainder being composed of iron and ancillary impurities, while at least one ferrite, retained austenite, and also martensite A process for producing a corrosion-resistant ferrochrome alloy, characterized in that the microstructured ferrochrome alloy containing eutectic chromium in a matrix formed by a conventional casting method, then heat-treated and air cooled at a temperature of 600-1,000 ℃.