DE2757114A1 - PROCESS FOR MANUFACTURING HIGH STRENGTH GRAPHITE CASTING - Google Patents

Description

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Process for producing high-strength nodular cast iron

The invention relates to a method for producing a high-strength spheroidal graphite cast iron with a low carbon equivalent.

In general, nodular cast iron (also referred to as nodular cast iron or spherulitic cast iron) is a product with a relatively high carbon content and
high silicon content, in which the carbon has largely crystallized in spheroidal form as pre-eutectic graphite during the treatment in the liquid phase. Such a cast iron has a
increased strength compared to the usual gray cast iron, in which most of the carbon is in the form of flake

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shaped or flaky graphite is present, and The cause of the insufficient strength of the product is a so-called constriction effect. The gray cast iron is mostly used without additional special heat treatment. Molten iron for making of nodular cast iron requires an amount of carbon which is sufficient for the crystallization of graphite during the casting process, with additional sufficient Amounts of silicon are added to favor graphite formation and to achieve good castability. In addition, it is necessary to add a graphite-forming agent to the molten iron, which includes Mg as an essential component. The carbon and silicon content of cast iron are usually expressed by the carbon equivalent (CA) as follows: CÄ (%) - C (%) + -1 (Si + P) (%). With nodular cast iron the carbon equivalent is known to lie within the range of approximately 4, O to 5> O%

As is well known, spheroidal graphite cast iron is produced by sand casting and, as a result, it tends to have its own imperfections, such as the formation of shrinkage cavities caused by the movement of relatively weak cast iron walls caused. Another disadvantage of spheroidal graphite cast iron is that it is caused by the heat treatment of the castings inevitably an increase in volume or cracking occurs on the surface in particular when the 'castings have internal defects. The nodular cast iron is supplied to its use in the encapsulated state or after a short heat treatment which the casting is made stress-free in particular.

There is also another type of high quality cast iron known as the so-called forgeable cast iron or is referred to as malleable cast iron. This material has a

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relatively low carbon and silicon content. The carbon equivalent of this cast iron is roughly in the range of 2.5 to 3 »5% as a major difference For spheroidal graphite cast iron, a solidification or solidification process is used in the manufacture of malleable cast iron (Sand mold casting) performed so that you can get the structure of a white cast iron, with no graphite crystallizing out during solidification. The production of malleable cast iron is finished when the white cast iron is subjected to a heat treatment that takes a long time has been used to cause precipitation of so-called compact graphite or heap-shaped graphite, which improves the toughness of the product. A disadvantage of malleable cast iron is the necessity an excessive time for the heat treatment to convert the white cast iron to graphitized cast iron or convert. The heat treatment generally takes 20 to 50 hours, and in some cases, it takes it extends to approximately 100 hours for large-sized castings.

The invention aims to provide a method for producing spheroidal graphite cast iron with a view to the toughness is better than usual high quality cast iron.

Preferably, the invention is concerned with a method for producing high-strength spheroidal graphite cast iron, which a more economical way of implementation allows and more advantageous than the usual way of manufacturing malleable cast iron is.

According to the invention, a method for producing nodular cast iron is characterized in that an iron melt with relatively low carbon and silicon content with the addition of an agent for graphite precipitation in

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Spherical shape, which mainly contains magnesium a metal mold casting is solidified quickly, giving a casting with a structure of white cast iron obtained, and that the casting is subjected to a brief heat treatment to prevent precipitation of to effect fine spheroidal graphite.

Preferably, the carbon equivalent of the molten iron in the process according to the invention is within a range of 2.0 to 4.3 % and the spheroidal graphite precipitating agent is added in such an amount that the amount of bound Mg in the molten iron is 0.01 to 0 .2% by weight. The agent for spheroidal graphite formation is selected from the agents customary for this purpose for cast iron. The metal mold casting in the method of the invention includes any kind of conventional permanent mold casting method insofar as a metal mold is used, and also includes gravity metal mold casting, low pressure casting, pressure injection molding and metal forging in the molten state. The use of a die casting process, which can be formed from a die injection molding process, is preferred. The heat treatment for graphite formation and precipitation is carried out for approximately 0.2 to 10 hours at temperatures between 750 and 1200 ^° C., but the heat treatment is usually ended after less than 5 hours.

A nodular cast iron produced by the method according to the invention is that which is otherwise usually produced Superior in both tensile strength and wear resistance.

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A preferred idea of the invention is the production of a high-strength and wear-resistant spheroidal graphite cast iron from molten iron with a carbon equivalent value of 2.0 to 4.3% using a metal mold casting process, which is preferably formed by a die-casting process. An agent for the precipitation or formation of graphite, which mainly contains magnesium, is added to the melt. This is also followed by a heat treatment for graphite precipitation, which is carried out at 750 to 1200 ^° C. for a few hours. The rapid solidification in metal mold casting gives the white cast iron a fine structure and the precipitation of fine spheroidal graphite ends quickly during heat treatment.

Further details, features and advantages of the invention emerge from the following description of FIG preferred embodiments with reference to the accompanying drawings.

FIG. 1 is a micrograph of the structure of the cast iron in an intermediate state before the heat treatment for graphite precipitation in the method according to the invention in the unetched state,

Figures 2A, 2B, 2C and 2D are micrographs of the structure a nodular cast iron in the unetched state for four produced from the sample according to FIG Test specimens, the heat treatment being carried out over different periods of time is,

FIG. 3 is a micrograph of the structure of the sample Figure 2A in the unetched state,

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Figure 4 is a graph showing the relationship between heating temperature in treatment for Shows graphite formation according to the invention and the time required to complete the Graphite precipitation and formation is required,

Figure 5 is a diagram showing the relationship between heating temperature and time required shows for the complete graphite precipitation in the method according to the invention,

FIG. 6 is a micrograph of the structure of a spheroidal graphite cast iron in the etched state, according to the pressure injection molding produced as metal mold casting in the method according to the invention has been, and

Figure 7 is a graph showing the wear resistance of a nodular cast iron according to the method according to the invention compared to three Kinds of common cast iron is registered.

The composition of the molten metal to carry out Of course, the method according to the invention comes with a view to the advantages that can be achieved Main meaning too. The properties of cast iron are mainly based on the amounts of it contained C and Si, although various other components such as B. Ni, Cr, Mo, Mn, etc. to improve special Properties cannot be neglected. With an increase in the total amount of carbon in the casting

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iron results in larger amounts of graphite being present in the castings formed. A similar effect Si is assigned, but it also fulfills the task of ensuring good castability of the iron melt. The carbon equivalent has therefore become established to specify a basic composition for cast iron, the definition of which has been given above. Cast iron can contain a larger amount of graphite at larger sizes Contains carbon equivalent.

In the method according to the invention, the starting material used is an iron melt, the carbon equivalent of which lies within a range from 2.0 to 4.3%. This is because of the following conditions. If the carbon equivalent is less than 2.0%, it is difficult to describe such iron as cast iron, but then the iron is to be referred to as steel. Such low carbon equivalent iron is very difficult to cast, especially when casting using a permanent and permanent mold. In addition, a high casting temperature is required, which is undesirable in view of the durability of the metal molds. The upper limit value for the carbon equivalent is 4.3%, since a crystallization of graphite in coarse form in the solidification stage is undesirable and since one wants to obtain a cast iron as an intermediate product which has essentially the structure of white cast iron. A composition with a carbon equivalent of more than 4.3% lies in the iron-carbon diagram in a region above a eutectic point, so that pre-eutectic graphite is likely to crystallize out of the iron melt with such a composition. With a carbon content of more than 4.3%

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there is a risk that cast iron with improved toughness will not be obtained in the process according to the invention.

The molten iron in the invention can, as usual, contain elements known per se for modification or improvement the strength, such as Cr, Ni, Mo, Al, B, Nb, Ti and / or V included.

In Table 1 is a composition of the nodular cast iron reproduced, which is obtained in the method according to the invention, this composition being the compositions contrasted by three common types of cast iron.

Table 1

. (Wt%)

C. Si Mn P. S. ,1 Cast iron according to the _{o na}
Invention ^ to- , 0 0.9-3 , 0 0.15-0.9 ^ 0.2 <o , 15 known temper- _pp ,
cast <^ -? , 0 0.9-1, • ⁶ (usual) 50.1 ζο , 025 well-known blacksmith ^, - ^,
hard cast iron? »>" , 2 2.0-3. , 5 0.2-1.0 Ϋ 0.1 ίο usual casting, _Q ,
iron ^ ¹ "^ , 8 1.5-2. .5 0.5-0.9 60.2 * 0

The solidification of the iron melt in the process according to the invention takes place in accordance with the metal mold casting process, which pursues the main goal of a quick termination of the freezing. This solidification method enables multiple advantages over conventional solidification methods using sand casting. A faster one Solidification in the metal molds is extremely beneficial for suppressing the crystallization of graphite during the Solidification of the cast iron in the liquid phase. By a

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Secondly, rapid solidification is achieved in that a casting is obtained which has a fine grain structure. Furthermore, internal stresses in the sense of the crystal lattice theory occur increasingly during casting, which leads to the production of precipitation nuclei in many places during the subsequent heat treatment to precipitate the Nodular graphite from a structure of white cast iron is used. In addition, this procedure allows that a high quality intermediate product is obtained during casting with only minor internal defects, such as shrinkage cavities, since a The increase in the volume of the cast iron in addition to the crystallization of the graphite upon solidification is suppressed so that no movement of the cast walls occurs during solidification.

There is a noticeable difference between pouring and pouring molten iron with a carbon equivalent of 4.3 % or slightly lower by the usual sand casting as compared with a product obtained after metal mold casting of molten iron with the same composition. In the product of a sand casting process, a certain proportion of the carbon is present in the form of crystallized graphite. However, the product of a molten metal casting process has the structure of white cast iron due to faster completion of solidification. The application of the die-casting process using a metal mold, such as pressure injection molding or the forging of molten metal, is particularly advantageous if one wants to achieve rapid solidification, since with these casting processes a favorable contact of the cast molten iron with the molds is ensured, so that the structure of white cast iron can be obtained in a simple manner in such a casting process even if an iron

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melt with a carbon equivalent of 4.3% usage finds. The solidification of the molten iron in the method according to the invention is therefore preferably carried out in a die casting process using a metal mold.

The method according to the invention is somewhat similar to a method known per se for producing Malleable cast iron or malleable cast iron, since both initially have the structure of a white cast iron target. What differs in the method according to the invention is the addition of an agent to support the Spheroidal graphite formation, which is formed by an agent in support of graphite formation as such, and which is added into the molten iron to solidify when pouring with the metal mold. In this regard (apart from the casting process) the process of the invention is similar to a conventional process for making Ductile iron. The shape of the precipitated graphite has a great influence on the tensile strength of the cast iron, As previously mentioned. In this context, more compact, heaped or dendritic graphite is flaky or flake-like graphite, but spheroidal graphite is most preferred. In teaching According to the invention, a precipitation of very fine spheroidal graphite particles is achieved. As with the manufacture Mg is the most important of the usual nodular cast iron Part of the means for graphite formation and spheroidal precipitation of the graphite in the invention. Mg can can also be used alone, but it is preferable to bring Mg in the form of an alloy or a mixture with others Elements in the iron melt. Typical examples of agents containing Mg and for graphite precipitation in spherical shape are suitable from alloys such as Mg-Fe-Si, Mg-Ni-Si, Mg-Fe and

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Mg-Ni formed. Furthermore, alloys or mixtures of Mg either with elements of the rare Earths or the metals of the alkaline earth group can be used. The amount of graphite precipitating agent in spherical shape, which is added to the molten iron in the process according to the invention, is chosen so that the The amount of Mg bound in the casting is within a range of 0.01 to 0.2% by weight of the casting. As is usual with these production methods, an inoculant such as Fe-Si or Ca-Si can be added to the iron melt be added together with the agent containing Mg and for spheroidal graphite precipitation and formation serves.

Due to the presence of the agent, which contains Mg and is used for spheroidal graphite formation, in a Molten iron poured into the metal mold causes a supercooling effect, which in conjunction with a rapid Solidification in the metal mold leads to a very fine grain structure of the cast. Except for the stupor in the presence of Mg, the structure of a white cast iron, the precipitate nuclei, is obtained of spheroidal graphite (or thereby become the basic prerequisites for the production of such precipitates created in the sense of atomic physics), so that the decomposition of cementite and the diffusion and coagulation of separated graphite in the subsequent stage of graphite formation (heat treatment) be promoted with the help of these excretory nuclei or through these basic requirements.

In the method according to the invention, the heat treatment comes to precipitate graphite from the structure white cast iron is of major importance as it can be carried out within a short period of time. This-

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arises from the fine structure of the white cast iron obtained by the previous casting using a ketal mold. The usual production of malleable cast iron requires a great deal of time and several tens of hours to design a heat treatment for graphite formation in such a way that the decomposition of a structure of white cast iron, i.e. a mixed phase of cementite and austenite (or cementite) to form a matrix of pearlite or ferrite or a mixed matrix of pearlite and ferrite with compact or accumulated graphite dispersed therein. In the method according to the invention, on the other hand, the structure of the white cast iron simply decomposes when graphite is precipitated in fine spherical form by a heat treatment which takes considerably less time and a high-strength cast iron is obtained. With regard to a physical metallurgical consideration, this is presumably beneficial with regard to the simple decomposition of the cementite and the migration or diffusion of the carbon during the heat treatment of the finely structured white cast iron. The heat treatment for graphite formation takes place for approximately 0.2 to 10 hours at temperatures between 750 and 1200 ° C. Temperatures between 800 and 95O ⁰ C. are preferably used.

By completing the heat treatment for graphite formation in the method according to the invention in considerably A significantly shorter time compared to similar treatment methods for the manufacture of malleable cast iron is obtained better output or productivity. An additional advantage with the method according to the invention is to be seen in the fact that the fine spheroidal graphite in the manufactured product no significant change in With regard to the shape and particle size is subject even if the heat treatment is prolonged

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to be led. Accordingly, there is a degree of freedom in the heat treatment in the invention as to which one is used Duration too. There is thus no need for a precise time limit and termination the heat treatment.

The heat treatment is preferably carried out in a non-oxidizing atmosphere or a reducing atmosphere, which is particularly advantageous in terms of maintaining a good surface in the cast article, the can be ensured thanks to the previous method of casting using a metal mold. To the step to Graphite formation can be a tempering at elevated temperature and tempering process or a common blowing process, such as inter-stage tempering or graded martensite hardening.

The invention is explained in more detail with the aid of the following examples.

example 1

Pig iron and scrap iron are melted in an electric furnace with the addition of a Pe-Si alloy and a customary deoxidizing agent, so that an iron melt is obtained with a carbon equivalent of 3 »5 % . The iron melt was then placed in a pouring ladle with the addition of 5% by weight of a conventional agent which contains Mg and serves for the formation and precipitation of spheroidal graphite. The molten metal was poured into a metal mold made of die steel with dies formed to produce test pieces. Each die has the shape of a band with dimensions of 100 50 χ 10 mm. The shape was on approximately; 150 C preheated and a means for easy peeling was

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sprayed onto the engraved areas of the mold before pouring the melt. After the solidification has ended of the cast iron, several test pieces were cut from the produced cast product.

FIG. 1 is a micrograph (100 times magnification) of the structure of the casting of one of these test pieces as a cast article, which has been polished and left unetched. The structure is that of a white cast iron. The remaining test pieces were subjected to a heat treatment for formation of graphite, which was carried out in a nitrogen atmosphere at a constant temperature of 900 ⁰ C for different times. The samples were then polished (but not etched), whereby the micro-section images according to FIGS. 2A to 2D are obtained with a 100-fold magnification. FIG. 2A shows the structure with a heat treatment of 0.5 hours and FIGS. 2B, 2C and 2D with a heat treatment of 1, 2 and 5 hours. As can be seen from the figures, graphite has become finely spherical in all four cases eliminated. A matrix of pearlite was common to the structures of nodular cast iron. FIGS. 2A and 2D demonstrate that if the heat treatment is prolonged in the method according to the invention, there is no appreciable conversion or enlargement of the graphite precipitate. When the test piece, which had been subjected to a heat treatment for 0.5 hours, is etched, a micrograph corresponding to FIG. 3 at 100 times magnification results, which is to be regarded as representative. From FIGS. 2A and 3 it can be seen that the structure of the white cast iron shown in FIG. 1 has been completely converted into a nodular cast iron structure during the short time of the heat treatment.

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Example 2

The production of the molten iron was carried out in a similar manner Manner as in example 1 (carbon equivalent was 3.5%) »however the agent according to example 1, which contains magnesium and serves to form nodular graphite, the iron melt in various proportions added so that you could change the amount bound in the casting compound according to Table 2. The pouring using a permanent mold was carried out according to Example 1 and the graphite formation was carried out a heating of the cast samples at 900 C during one hour. Table 2 shows the analytical values of the bound Mg, the form of the precipitated graphite and the type of matrix of the samples of spheroidal graphite cast iron obtained according to this exemplary embodiment have been.

Table 2

sample
No. bound
Mg (wt.%) Shape of graphite matrix 1 0.009 quasi-spherical Cementite and
Perlite 2 0.021 spheroidal Perlite 3 0.052 spheroidal Perlite 0.103 spheroidal Perlite, however
partly ferrite 5 0.188 spheroidal Perlite, however
partly ferrite 6th 0.226 quasi-spherical Perlite and ze
mentite

The data listed in Table 2 show the preferred use of the spheroidal graphite formation agent in one such an amount that Mg at 0.01 to 0.2 wt% in

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the solidified casting compound with regard to the shape of the precipitated Graphite in a bound state is beneficial. It's hard to get a good nodular cast iron obtained when the amount of Mg bound is less than 0.01 wt%. The bond of more than 0.2 wt .-% Mg in cast iron is also undesirable, since the graphite tends to deform and this is a unnecessarily large amount of means for spheroidal graphite formation consumed.

Example 3

Several batches of molten iron were produced from pig iron, scrap iron, a common recarburizing agent and an Fe-Si alloy with different values for the coal equivalent according to Table 3. The measurement of the carbon equivalent was carried out with the aid of a commercially available high-speed analyzer. The spheroidal graphite formation agent in Example 1 was added to each batch with the aim of binding 0.05% by weight of Mg in the product. Casting using a metal mold according to Example 1 was carried out for each batch of the molten iron. The castings thus obtained had a structure of white cast iron regardless of the carbon equivalent values. The castings were subjected to a heat treatment for graphite formation at a constant temperature of 900 ^° C. in order to investigate the relationship between the carbon equivalent and the time required to complete the graphite formation during the heat treatment. The result of this experiment is shown in Figure 4-. This experiment was also carried out with regard to castings which were produced essentially according to the procedures described above, but in which no Mg was added to the molten iron. The results obtained are shown in broken line in FIG.

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A tensile strength test using an Amsler universal testing machine was undertaken with the graphitized samples which had been obtained from a heat treatment at 900 ^° C. for 3 hours. For tensile testing, 5 tensile specimens were used for each batch of molten iron, ie for each specific carbon equivalent value. The test results are summarized in Table 3 together with a comparison of conventional cast iron and the hardness values of the samples. The hardness is measured according to the Rockwell hardness scale C.

Table 5

sample
No.

Carbon equivalent

Bound Mg wt .-%)

hardness

Tensile strength _P (kg / mm ² )

1 2.25 0.048 29-31 91-95 2 2.55 0.052 26-30 85-91 3 3.08 0.046 28-33 91-96 4th 3.51 0.055 25-29 89-93 5 4.12 0.051 25-29 85-90

1: common nodular cast iron 2: common malleable cast iron

40-60 35-70

The values in Table 3 show that a nodular cast iron according to the method according to the invention is better Has tensile strength.

Embodiment 3 was repeatedly carried out except that a die-casting process was carried out using a horizontal cold chamber die casting machine instead of the casting process according to Example 3 using gravity was executed. The tensile strength values and hardness values of the specimens obtained during die casting gave im

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essentially the same values listed in Table 3.

Example 4-

The production of the molten iron according to Example 1 and the casting using a metal mold according to Example 1 were repeated. The graphite formation of the white cast iron obtained took place in a nitrogen atmosphere at three different temperatures, 800, 850 and 900 ^° C., with the aim of determining the time required for sufficient precipitation of fine spheroidal graphite at each temperature. The experimental results are shown in the diagram in FIG. 5, from which it can be seen that the graphite formation after continuous heat treatment for only 0.5 to 1 hour at a temperature of 900 ^° C. and approximately 3 hours at a temperature of less than 800 ° C had ended. This allows the rapid graphite formation in the method according to the invention to be demonstrated.

Example 5

A molten iron was prepared in an electric furnace with a carbon equivalent of 4.2 %. About 2 kg of this molten iron was placed in a ladle. Mg was added to the molten iron as in Example 1. The molten iron was cast into a rectangular plate (100 × 50 × 10 mm) by pressure injection molding under the following conditions. A horizontal cold chamber injection molding machine containing tungsten alloy molds was provided for this purpose.

Injection pressure 200 kg / cm Injection speed 0.8 m / sec. Mold temperature 250 ° C. Casting temperature 1350 ⁰ C

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The casting obtained by this procedure had a structure of a white cementite cast iron with a finer grain structure than the cast structures in Samples 2 to 5 in Example 3 Contact of the iron melt with the mold surfaces faster solidification is possible. The graphite formation in this casting took place with the aid of a heat treatment for one hour in a nitrogen atmosphere at 900 ^° C. FIG. 6 shows a micrograph enlarged 100 times of the etched structure of the graphitized casting.

The wear resistance of spheroidal graphite cast iron was determined using this example with the aid of a wear testing machine checked by Ogoshi. The test was carried out under dry abrasion conditions with a wear section of 100 mm and a load of 3 »3 kg with a mild steel surface as a counter surface. For comparison, the usual Needle crystal cast iron, gray cast iron (JIS FC25) and spheroidal graphite cast iron (JIS FCD70) were tested under the same conditions. the Results are entered in FIG. From this figure it can be seen that the cast iron according to the method according to of the invention in terms of wear resistance significantly better than conventional gray cast iron and spheroidal graphite cast iron is. It is comparable to a cast iron with a needle crystal structure, which is a highly wear-resistant cast iron is known.

Example 6

The spheroidal graphite cast iron of Example 5 was annealed quench or at elevated temperature, by passing the sample was immersed in an oil at 850 ⁰ C and it was joined to a heat treatment at 600 ⁰ C. The consideration of the

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The metallurgical structure of a cast iron treated in this way showed that the cementite matrix was converted into tempered martensite, with no significant change in the shape and size of the spheroidal graphite resulting. The tensile strength of the cast iron was 90 to 100 kg / mm and the hardness (H _RC ) was 28-33.

As can be seen from Examples 4 to 6, has a nodular cast iron produced by the method according to the invention, a considerably high tensile strength and at the same time an extremely advantageous wear resistance, if one makes a comparative consideration with tough and high-quality cast iron. The invention is thus of great industrial importance, since the use of cast iron is expanding considerably leaves.

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Claims (14)

Dr. F. Zumstein Sr. - Dr. E. Assmann - Dr. R. Koenigsberger Dipl.-Phys. R. Holzbauer - Dipl.-Ing. F. Klingseisen - Dr. F. Zumstein jun. PATENTANWÄLTE BOOO Munich 2 · BrauhausstraOe 4 · Telephone collection no. 329341 ■ Teleeramme Zumpat · Telex 529979 Case PG23-77175 NISSAN MOTOR COMPANY, UMITED, Yokohama City, Japan Method for producing high-strength ductile iron Patent claims 1. A method for producing a high-strength nodular cast iron, characterized in that an iron melt with a carbon equivalent in the range of 2.0 to 4.3 % is created, a means for nodular graphite formation which contains magnesium as an essential component, the iron melt in such an amount it is added that the amount of bound magnesium in the resulting cast iron is 0.01-0.2% by weight that the molten iron containing magnesium rapidly solidify into a casting having a structure of white cast iron in a casting process using a metal mold is left and that the casting 809827 / 0S07 27 57 ι ι -Z- for about 0.2 to about 10 hours at a temperature between 750 and 1200 ^{° C}
fine spheroidal graphite is heated. Temperature between 750 and 1200 ⁰ G for the excretion of 2. The method according to claim 1, characterized in that the heating takes place at temperatures between 800 and 95O ⁰ C. 3 · The method according to claim 2, characterized in that the heating during approximately 0.5 to about 5 hours. 4. The method according to any one of the preceding claims, characterized in that the heating is carried out in a non-oxidizing atmosphere. 5. Method according to one of the preceding claims, characterized in that the casting process using a metal mold is from a die casting process is formed. 6. The method according to claim 5i, characterized in that the die casting process of one Die injection molding process is formed. 7. The method according to claim 5i, characterized in that the die casting process of one Process for forging molten metal is formed. 8. The method according to any one of the preceding claims, characterized in that the iron melt about 2.0 to 4.0 wt% C and about 0.9 contains up to 3 »0 wt .-% Si. 809827/0807 27571H 9- method according to one of the preceding claims, characterized in that the agent for spheroidal graphite formation contains metallic magnesium. 10. The method according to any one of the preceding claims, characterized in that the means for Nodular graphite formation is formed from a magnesium alloy which has been selected from the group which Ni-Mg, Fe-Mg, Fe-Si-Mg and Fe-Ni-Mg alloys, alloys of magnesium with at least one metal of the rare ones Earths and alloys of magnesium with at least one alkaline earth metal. 11. The method according to any one of the preceding claims, characterized in that the product is remunerated at elevated temperature. 12. The method according to any one of the preceding claims, characterized in that the iron melt has the following composition: 2.0 to 4.0 % C,
0.9 to 3.0 % Si,
0.15 to 0.9% Mn 0.2% P, 0.1% S, all values being given in% by weight. 13. Nodular cast iron, characterized by a carbon equivalent in a range of 2.0 up to 4.3%, caused by the solidification of a molten iron Potting in a metal mold is quickly transformed into a casting with a structure of white cast iron, with the iron melt contains 0.01 to 1.2% by weight of magnesium, 809827/0807 2757 IU and that after potting for about 0.2 to 10 hours has been heated at temperatures between 750 and 1200 ° C for the precipitation of fine spheroidal graphite. 14. Nodular cast iron according to claim 13i characterized by g e, that it is about 2.0 to 4.0 C, about 0.9 to 3.0 Si, about 0.15 to 0.9 Mn and contains up to approximately 0.2% P, all proportions being given in% by weight. 15 · spheroidal graphite cast iron according to claim 14, characterized in that the S content < Is 0.1 wt%. ΒΠ9827 / 0807