DK151103B - PROCEDURE FOR THE MANUFACTURING OF SAID IRON PAYMENT - Google Patents

Description

151103 »*

The present invention relates to a process for making tough iron castings made using permanent molds or sand molds. For many years, the most widely used commercial process for the manufacture of tough iron has consisted in the addition of magnesium in the form of magnesium-containing alloys or in the addition of the pure element. The added magnesium causes the graphite to secrete in the form of spheroids. The formation of graphite in this form leads to the unique strength and toughness of the material.

Methods of this type are e.g. known from French Patent Laid-Open No. 2,072,125 (using combinations of metallic magnesium and metallic, cobalt, in which a portion of the magnesium is optionally replaced by, for example, calcium, yttrium and / or rare earth metals), U.S. Patent No. 2,792,300 (according to which alloys containing about 55% magnesium and 45% mischmetal are used), British Patent No. 829,658 (using an alloy containing 2% cerium, 8% magnesium, and other materials, including magnesium oxide) and British Patent Specification No. 718,177 (using combinations or alloys of magnesium and cerium (or. cerium misch metal) or alloys thereof with nickel or iron, for example, an alloy containing 15% Mg, 4% Ce, 4 % La or other rare earth metals, 1.5% C and 75.5% Ni).

The use of magnesium or magnesium-containing alloys is known to have a number of disadvantages. The most important of these disadvantages is that the reaction that occurs with the addition of magnesium to the molten iron is usually quite violent and accompanied by the formation of thick clouds of white smoke containing magnesium oxide particles. The reaction is also accompanied by a brilliant white light shade which is harmful to the eyesight. Another disadvantage is that the high degree of reactivity makes it difficult to provide a high utilization of the added magnesium, and therefore the magnesium process is not satisfactory. In addition to the poorer utilization usually obtained, the magnesium content of the melt decreases over time due to the loss of magnesium from the melt resulting from evaporation, oxidation and reaction with the sulfur present in the melt. This magnesium loss is usually referred to as "shrinkage".

Some of the disadvantages mentioned above can be partially avoided depending on the way the magnesium or magnesium alloy is added to the metal melt. Eg. the light shade can be shielded from the eyes by means of a protective sheath. Pressurizing magnesium to the melt gives a somewhat greater efficiency than pouring the molten metal on top of the magnesium alloy. These processes are usually disadvantageous from an economic and operational point of view because additional apparatus is required, either to enclose the area where the magnesium addition is taking place or to put pressure on the container in which the addition is made. These methods, especially the printing method, further delay the process.

Furthermore, it is known that cerium is also a spheroidizing element and that it is less reactive when added to the molten sti cave. however, in order to overcome the liquid-iron network, as in the case of the lower reactivity, cerium will, however, exhibit an undesirable rapid decrease. In addition, cerium is usually only effective in hypereutectic cast iron, it is a powerful carbide former, and it has also been found that the shape of the graphite particles formed is not as perfect as when using magnesium as a spheroidizing agent.

The object of the invention is to provide a process for the manufacture of tough cast iron, which avoids some of the problems which have been encountered with the prior art. Thus, it is desirable, 1) to reduce the amount of nodularization element required for the formation of spheroidal graphite in cast iron, 2) to reduce the smoke and light produced by the addition of the spheroidizing material, 3) to reduce the rate of shrinkage. the spheroidizing effect of the treated melt; 4) minimizing the slag content of the tough iron; and 5) providing a method which allows the selection of a number of individual nodularizing agents as well as the amounts of each.

The object of the invention is solved by the addition of a low sulfur cast iron melting element selected from magnesium, cerium, yttrium, lanthanum, neodymium and praseodymium in the form of an alloy or alloy mixture containing at least two of the nodularization elements, after which the material is cast from the melt and the cast material is allowed to solidify, and this method is peculiar in that the total weight of the nodularization elements does not exceed 6% of the weight of the alloy or alloy mixture, the weight of each of the nodularization elements not exceeding 3% of its weight, wherein the weight of the nodularization elements in the blend is from 0.03 to 0.12% by weight of the melt, and the amount of each nodularization element alone is less than that required to form tough iron, in which approx. 90% of graphite is present as well-formed spheroids.

This results in: a) a drastic reduction in smoke and flames when the alloy is added to the melt; b) a dramatically reduced rate of shrinkage in the c) a decrease in the total amount of nodularizing agent required for a given (d) a reduction in the slag content of the castings.

The invention will now be described in more detail with reference to the drawing, in which: FIG. 1 is a schematic representation of the basic steps of the conventional process for the manufacture of tough cast iron which the invention does not concern; FIG. 2 graphically shows the amount of effective nodularization elements remaining in an iron melt as a function of storage time, where one additive of one nodularization element (similar to the prior art) can be compared with the addition of two or more nodularization elements (according to the invention) FIG. Figure 3 is a photomicrograph of the graphite structure of a tube molded after prolonged standing by a melt to which 5 nodularization elements are added according to the invention; 4 graphically shows a comparison of the percent amounts of nodularization element present in a cast iron melt, calculated on the initially added amount, as a function of storage time, when comparing the addition of one nodularization element (according to the prior art) with adding two or more nodularization elements according to the invention, and fig. Figure 5 graphically shows the amount of two nodular elements present in a tube made under production conditions as a function of time after addition according to the invention.

FIG. Figure 1 shows schematically the conventional method of making tough iron castings. The present invention relates to the spheroidizing step, the previous steps being well known to those skilled in the art. The relationship between the nodularizing agents used, the mode of application and the spheroidizing effect forms the basis of the invention.

The present invention is based on the recognition that the total amount of nodularizing agents required to form tough iron can be reduced by adding more than one nodularizing element in appropriate amounts. This allows a reduction of the concentration of the nodularization elements in the melt, which in turn increases the efficiency, provides a longer effective life, ie. reduces shrinkage, minimizes light and smoke incidence and minimizes iron's tendency to slag.

The results shown in Tables I and II are obtained at 5 151103

Table I

Added Total m ^ π,,. ..

Total amount left in the melt after basic added

Test substances amount_1 5_10_15 minutes_ A Mg 0.05 wt% 0.022 0.016 0.011 0.008 B Ce 0.05 wt% 0.037 0.019 0.011 0.003 C Mg + Ce 0.05 wt% 0.041 0.037 0.030 0.027

(0.025 Mg + (0.020) (0.017) (0.015) (0.013) Mg-X

0.025 Ce) (0.021) (0.020) (0.015) (0.014) Ce D Mg 0.05 wt% 0.034 0.029 0.025 0.022 + Ce (0.01 wt% (0.008 0.007 0.006 0.005) Mg + La of each of 5 (0.008 0.006 0.005 0.004) Ce + Nd elements) (0.0085 0.006 0.0025 0.001) La + Y (0.005 0.005 0.0065 0.010) Nd

(0.005 0.005 0.005 0.002) Y

X

- Figures in parentheses represent the amount of individual elements.

Table II

Added Total% of original total amount left in the basic added melt

Attempt substance_ quantity_1_5_10_15 minutes_ A Mg alone 0.05% by weight 44 26.5 22 16 B Ce 0.05% by weight alone 74 38 22 6 C Mg + Ce 0.05% by weight 80 64 60 52 D Mg + Ce + La + 0.05 wt% 69 58 50 44

Nd + Y

For each of the experiments A-D summarized in the above tables, the low sulfur cast iron melt prior to the spheroidization step is composed of the following elements in amounts within the ranges shown:

Total carbon 3.4 -3.6% by weight

Silicon 1.9 -2.1% by weight

Manganese 0.25 - 0.30% by weight

Sulfur 0.005-0.012% by weight

Phosphorus 0.04-0.06% by weight

In experiment A, 0.05 wt% of magnesium, based on the weight of iron, is added in the form of a conventional cerium-free magnesium ferrosilicon with a magnesium content of 6.17 wt%. In experiment B, 0.05 wt. 151103 Ό of pure metallic cerium is added to the melt in the form of chips. In experiment C, magnesium and cerium are added in the form of an alloy containing 3.0% by weight of magnesium plus 3.0% by weight of cerium, 45% by weight of silicon, while the remainder is iron. The total spheroidizing addition of 0.05 wt% consists of 0.025 wt% magnesium plus 0.025 wt% cerium. In experiment D, the total spheroidizing addition again represents 0.05% by weight. In this case, the spheroidizing addition consists of 0.01% by weight of each of the following five elements: magnesium, cerium, lanthanum, neodymium and yttrium. Magnesium and cerium are added in the form of a ferro-silicon alloy containing 3 wt.% Magnesium and 3 wt.% Cerium. Lanthan and neodymium are added in metallic form. The neodymium contains 74% by weight neodymium and 14% by weight praseodyme. Yttrium is added in the form of a ferrosilicon alloy containing 20% by weight of yttrium.

In addition, the results shown in Tables I and II are shown graphically in FIG. 2, wherein the amount of spheroidizing agent present in a cast iron melt for each of experiments A-D is plotted as a function of time, compared to the amount of spheroidizing agent initially added to the melt. From FIG. 2, that the magnesium and cerium contents diminish over time to lower and lower levels and that at some point the contents become insufficient to provide a good spheroidal graphite structure. In centrifugal casting of tubes in metal furnaces, it has been found that for cast iron with a sulfur content of the order of 0.004-0.006 wt% a minimum magnesium content of the order of 0.012-0-0014 wt% is required for securing a graphite structure in a pipe with a diameter of 152.4 mm, in which approx. 90% by weight of graphite consists of well-formed spheroids. If cerium is used, the required residual content has been found to be approx. 0.016% by weight. It is thus seen (cf. the curves A and B in Fig. 2) that after a storage time of 10 minutes, neither magnesium nor cerium will be present in the melt in amounts sufficient to ensure the formation of the desired graphite structure, ie. both amounts are below the "critical level" if magnesium or cerium is added alone.

Contrary to the behavior of magnesium or cerium, when added individually in amounts of 0.05% by weight, the addition of smaller amounts (0.025% by weight) of magnesium and cerium together or 0.01% by weight of each of 5 spheroidizing elements for a more efficient utilization of the spheroidizing addition, obtaining both a greater utilization to begin with and a longer effective life. Thus, curves C and D show that the total spheroidizing content of the melt is greater than 0.02% by weight even 15 minutes after the addition.

Furthermore, it has been found that the spheroidizing ability of the various nodularization elements varies when added to cast iron melts separately. By contrast, when added in combination, it seems that the total sum of the percent of nodularization elements present in the melt can be used to determine their spheroidizing ability in the melt.

To illustrate this point, Table I shows the remaining concentration of five nodularization elements in a cast iron melt at times up to 15 minutes after the addition of 0.01% by weight of each element. A tube with a diameter of 152, 4 mm is cast from this melt (Experiment D) 18 minutes after the addition of the five elements. This tube has an acceptable spheroidal graphite structure shown in FIG. 3. Since the remaining amounts of the individual nodularization elements in this melt are individually so small (cf. Table I), it can be seen in FIG. 3 can only be obtained from the combined spheroidizing ability of all the elements present. It is also apparent from Table I that the total sum of the residual nodularization elements required in the hot melt to form an acceptable graphite structure in the tube is of the same magnitude as the residual amount of magnesium alone or cerium alone, ie. the amount required to form the same acceptable graphite structure.

The 2 is determined by adding only one of the nodularization elements or combinations of the elements to molten cast iron containing the following elements in amounts within the following ranges:

Total carbon 3.4 -3.6% by weight

Silicon 2.7 - 2.9% by weight

Manganese 0.25 - 0.30% by weight

Sulfur 0.004-0.008% by weight

Phosphorus 0.04-0.06% by weight

The contents of Table II derived from Table I are illustrated graphically in FIG. 4, which shows the higher utilization of the nodularizing agents according to the invention, compared to the known nodularizing agents.

In manufacturing experiments, magnesium plus cerium is added to six-ton dortions of iron in a mold. Prior to the addition of magnesium and cerium 8, the iron has the following composition:

Total carbon 3.4 -3.6% by weight

Silicon 1.9 -2.1% by weight

Manganese 0.25 - 0.30% by weight

Sulfur 0.005-0.012% by weight

Phosphorus 0.04 -0.06 wt% 151103 y

Data from these manufacturing experiments are listed in Table III.

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The additions consist of magnesium ferrosilicon (containing 5 wt% magnesium) plus an addition of cerium ferrosilicon (containing 10 wt% cerium). The amounts added are 0.025 wt% magnesium + 0.025 wt% cerium which gives a total addition of nodularizing agent of 0.05 wt%. The experiments show that pipes with a good spheroidal graphite structure can be cast as late as 34 minutes after the addition time. The data shown in Table III are graphically shown in FIG. 5. The curves of FIG. 5 shows that a tube molded 34 minutes after the magnesium and cerium addition contains 0.013 wt% magnesium + 0.010 wt% cerium. The crucial feature of these data is that none of the elements is present in an amount sufficient to ensure the provision of a good spheroidal graphite structure alone. In contrast, the total amount of the nodularization elements (0.023% by weight) is sufficient to form the desired graphite structure. This experiment further illustrates the efficiency and longer effective life provided by small additions of nodularization elements, since the residual content of magnesium + cerium (0.023 wt%) represents a utilization of 46% of the initially added amount of nodularizing agent 34 minutes after the addition. In addition, Table III shows results of mechanical tests showing the quality of the structures provided in the pipe. These pipes meet the stringent requirements of the commercial specifications for notch impact, fracture and tensile strength.

Another test series is conducted under production conditions to determine whether the results obtained by the combined addition of two different alloys (magnesium-ferro-silicon plus cerium-ferrosilicon) can be obtained by the addition of one alloy containing both magnesium and cerium. In these experiments, 6 tons aliquots of cast iron are treated by adding an alloy containing 2.5 wt% magnesium plus 2.4 wt% cerium. In one experiment, 0.83% by weight of this alloy is added. This corresponds to an addition of 0.021 wt% magnesium plus 0.020 wt% cerium, i.e. a total addition of spheroidizing elements of 0.041 wt%. In this experiment, a tube with a diameter of 203.2 mm cast 31 minutes after the spheroidization treatment contains 0.011 wt% magnesium plus 0.012 wt% cerium corresponding to a sum of 0.023 wt% magnesium + cerium. The total weight of the spheroidizing elements in the molten cast iron is between approx. 0.03 and 0.12% by weight, based on the melt. This corresponds to a utilization of 56% of the original amount, and it is seen that the high utilization and longer effective life of the nodularization elements can be achieved by the simultaneous addition of different alloys, each containing one spheroidizing agent or by adding one alloy containing more than one spheroidal agent. In these production experiments, where an alloy containing 2.5 wt% magnesium plus 2.4 wt% cerium is used, practically the annoying light and smoke phenomena usually encountered by the addition of magnesium-containing alloys are avoided.

It can be seen from the above that adding an alloy or a mixture of alloys containing no more than 3% by weight of each of two or more spheroidizing agents will, in small quantities, ensure that sufficient amounts of spheroidizing agents are present over a longer period of time. time than if the same total amount of one spheroidal agent is added. In addition, the violent reaction that usually occurs during the addition is eliminated. This phenomenon is very surprising and cannot be fully explained.

In experiments where this alloy of 2.5 wt.% Magnesium + 2.4 wt.% Cerium is used in the manufacture of castings in sand molds, it has been found that acceptable graphite structures can be obtained by adding nodularization elements which are 20%. less than that required using a standard 5% magnesium ferrosilicon. Thus, a minor alloy addition is required, which in turn leads to a reduction in the amount of slag formed.

Claims (5)

151103 Patent Claims. A process for the manufacture of tough iron castings, in which a low sulfur cast iron melt is prepared, upon which nodularization elements selected from magnesium, cerium, yttrium, lanthanum, neodymium and praseodymium are added to the melt in the form of an alloy or alloy mixture containing at least two of the nodularization elements, after which the goods are cast from the melt and the cast material is allowed to solidify, characterized in that the total weight of the nodularization elements does not exceed 6% of the weight of the alloy or alloy mixture, the weight of each of the nodularization elements not exceeding 3% of its weight. wherein the weight of the nodularization elements in the mixture is from 0.03 to 0.12% by weight of the melt, and the amount of each nodularization element alone is less than that required for the formation of tough iron, in which approx. 90% of graphite is present as well-formed spheroids. Process according to claim 1, characterized in that magnesium is added to the cast iron melt as the one nodularisation element. 3. A process according to claim 2, characterized in that magnesium and cerium are used. Process according to claim 3, characterized in that magnesium and cerium are used in equal amounts. Process according to claim 1, characterized in that the alloy mixture consists of a first alloy and a second alloy, the first alloy containing only magnesium and the second alloy containing up to 3% by weight of each of the other nodularisation elements.