EP1646732A1

EP1646732A1 - Cast iron material

Info

Publication number: EP1646732A1
Application number: EP04741074A
Authority: EP
Inventors: Milan LAMPIC-OPLÄNDER; Jörg BILLASCH
Original assignee: Fritz Winter Eisengiesserei GmbH and Co KG
Current assignee: Fritz Winter Eisengiesserei GmbH and Co KG
Priority date: 2003-07-16
Filing date: 2004-07-16
Publication date: 2006-04-19
Anticipated expiration: 2024-07-16
Also published as: EP1646732B1; WO2005007913A1; DE502004005766D1; ES2298771T3; MXPA06000901A

Abstract

The invention relates to an iron material comprising lamellar graphite, which permits a simple adjustment of the optimal properties for a wide range of products, by variation of the content of the alloy components. The above is achieved with a cast iron material comprising (in wt.%): 3.4 4.1 % C, 0.9 1.4 % Si, 0.4 0.7 % Mn, 0.4 0.6 % Cu, 0.01 0.04 % S, 0.003 0.007 % O2, = 0.04 % P the remainder being iron and unavoidable impurities. The following can also optionally be contained either individually or in combination: 0.15 0.45 % Mo, 0.005 0.02 % La, 0.0005 0.01 % Sr, 0.05 0.8 % Ni, 0.005 0.1 % V, 0.05 0.15 % Sn, 0.05 0.08 % N and 0.01 0.02 % Ce. For a saturation degree Sc = C %/4,26-0,3*(Si %+P%), then: 0.85 % = Sc = 1.05 % and for the amount %MEG (amount of eutectic graphite) = 2.25 % - 0.2 Si % then: 1.97 % = MEG = 2.07 %.

Description

IRON CAST MATERIAL

The invention relates to a cast iron material with lamellar graphite, which is particularly suitable for the manufacture of brake disks, light and heavy engine blocks and cylinder heads.

Due to its good machinability and very favorable casting properties with little risk of hidden defects, cast iron with lamellar graphite (gray cast iron) is a popular construction material. Therefore, blocks for internal combustion engines are typically cast from cast iron materials of the type in question.

However, the requirements already placed on the tensile strength of the material have reached the limits of the problem-free use of conventional gray cast iron. This is due to the fact that, on the one hand, increased performance is required, for example when casting internal combustion engines, and, on the other hand, lightweight construction is a central goal of modern cast designs. To make matters worse, users not only demand higher tensile strength of usually more than 300 MPa, but also optimization of other properties, such as high thermal conductivity, high resistance to thermomechanical fatigue and high resistance to friction and sliding wear. In addition, the quality of the casting result is subject to strict tests. The requirements regarding high tensile strengths can basically be met by reducing the carbon and silicon content or the degree of saturation and by alloying Cr, Cu, Ni, Mn or Mo up to a total content of the alloyed elements of up to about 2%. The resistance to thermomechanical fatigue can also be set sufficiently high in this way.

However, the measures mentioned lead to a considerable reduction in the pourability and the self-feeding capacity of the processed

Cast iron material. The risk of hidden defects and partial carbide solidification (edge hardness) increases. At the same time, the machinability of the material deteriorates considerably. Therefore, in industrial production for the increase in tensile strength and resistance to thermomechanical fatigue achieved with the measures mentioned, rejection rates of up to 30% have to be accepted.

However, the demand for high thermal conductivity cannot be met by reducing the carbon and silicon content or the degree of saturation or alloying with certain alloying elements, since the thermal conductivity of gray cast iron is known to be a function of the amount of graphite contained in the cast and decreases with decreasing amounts of graphite , The alloyed elements also generally lead to a decrease in thermal conductivity.

The latter is particularly noticeable when high-performance brake discs are to be cast from a correspondingly alloyed, relatively high-strength material. Due to the segregation behavior of these elements, alloying with carbide-forming elements such as Cr and Mo leads to the formation of undesired complex carbides even if this occurs within theoretical limits for the solubility of these elements (rule of thumb: atomic radius of the respective element <1.15 x atomic radius Fe ). In addition to the fact that these carbides are "waste products" with negative effects on machinability, this has the fundamental disadvantage that if the casting material obtained in the casting operation is reused in the circuit, the entropy in the overall system is increased of the cycle comes.

When the material reused in the cycle is reused, the carbides are generally not completely destroyed. Instead, they remain as so-called clusters, which form carbides again when solidified. As a result of the new alloying with the prescribed amount of chromium and molybdenum, new carbides are then formed again. As a result, this process of enriching the processed casting material with carbides leads to a slow but inevitable increase in unusable chromium and molybdenum, which results in a gradual deterioration in the properties of the casting material. As a result of the fact that the segregated elements influence the temperature of the eutectic equilibrium in the Fe-CX system differently and the inactive non-metallic phases that are also present in the melt are also subject to the process of creeping increase, in extreme cases in the casting operation this can be called "reverse hard casting "dreaded casting mistakes are coming. In addition to the prior art explained above, an iron casting material for the production of camshafts is known from EP 1 213 071 A2 which (in% by weight) 3.5 - 3.7% C, 0.9 - 1.1% Si, up to 1% Mn as well as lanthanum not bound to sulfur with a share of 0.02 - 0.05% and optionally 0.3 - 0.6% Cr, 0.1 - 1.0% Cu, 0, May contain 3-0.6% Mo and 0.02-0.05% Ti. The addition of lanthanum to the known material was carried out with the aim of increasing the hardness of the material and causing grain refinement to improve the tribological behavior. The properties of such an alloy composed in this way were explained in detail in EP 1 213 071 A2 using an exemplary embodiment which (in% by weight) 3.69% C, 0.95% Si, 0.05% La, 0.029% S, 0.0035% 0, 0.29% Mn, 0.5% Cr, 0.2% Cu, 0.51% Mo and 0.022% Ti.

Another example of an iron casting material with lamellar graphite is known from EP 1 004 789 AI. This material is used for the production of brake discs, which are characterized by an increased service life. For this purpose, in the casting material known from EP 1 004 789 Al in weight% 3.9-4.2% C, 0.7-1.2% Si, up to 0.02% P, up to 0 , 02% S and up to 0.05% AI included. In addition, the known material may contain Mn, V, Cu and Cr, the total proportion of these alloying elements not exceeding 1.6%. A brake disc made from such a material is characterized by a particularly high thermal conductivity with good toughness. The known alloy was specifically tested on the basis of an exemplary embodiment which (in% by weight) 4.1% C, 1.0% Si, 0.02% P, 0.03% S, 0.3% Mn, 0 , 01% V, 0.4% Cu, 0.3% Mo and 0.015% Al contained. Starting from the prior art explained above, the object of the invention was to create an alloy concept which makes it possible in a simple manner to set the optimum properties for a wide range of products by varying the contents of the respective alloy components.

According to the invention, this object is achieved by an iron casting material with lamellar graphite, which has the following composition (in% by weight):

C: 3.4 - 4.1%, Si: 0.9 - 1.4%, Mn: 0.4 - 0.7%, Cu: 0.4 - 0.6%, S: 0.01 - 0.04%, 0 ₂ : 0.003 - 0.007%, P: <0.04%, remainder made of Fe and unavoidable impurities, the composition optionally additionally containing one or more of the following elements: Mo: 0.15 - 0, 45%, La: 0.005-0.02%, Sr: 0.005-0.01%, V: 0.005-0.1%, Ni: 0.05-0.8%, Sn: 0.05-0 , 15%, N: 0.05 - 0.08% and for the degree of saturation Sc = C% / 4, 26-0, 3 * (Si% + P%) (C%: respective C content, Si%: respective Si content, P%: respective P content) applies 0.85% <S _c <1.05% and for the respective quantity% MEG = 2.25% - 0.2 Si% (Si%: respective Si content) 1.97% <MEG <2.07% applies.

The invention provides an Fe-C-Si-X cast alloy which has in particular a combination of properties which is optimized both with regard to its strength and with regard to its thermal conductivity and castability and in which the risk of a gradual decrease in the good properties occurring in practical casting operation is reduced Minimum is reduced.

The cast iron material according to the invention is largely free of undesired or unnecessary elements and by-products. The sulfur and oxygen levels are measured in such a way that they no longer have a disruptive influence on the properties of the iron material. This ensures that the iron lattice is cleaned and contains sufficient free capacity to hold the required foreign atoms. At the same time, minimum levels of oxygen and sulfur are prescribed because both elements serve as building blocks for the formation of crystallization nuclei.

By complying with the tuning rules according to the invention for the degree of saturation and the amount of eutectic graphite, the contents of carbon and silicon are dimensioned such that even with a comparatively wide variation in the degree of saturation S, the amount of eutectic graphite MEG remains high.

The amount of eutectic graphite MEG present in the cast material according to the invention far exceeds that of normal cast iron. Its MEG value is usually only around 1.85% by weight. In the cast material according to the invention thus a 10% to 20% higher volume share is available. This excess is a decisive advantage of the iron casting material according to the invention compared to conventional iron material. The material according to the invention thus has a significantly superior self-feeding capacity for the purpose of compensating for the shrinkage of the iron by expanding the graphite compared to conventional cast material. In practical casting operations, this property leads to a significant increase in the reliability with which high-quality cast products are produced.

When producing a cast material according to the invention, the reducing melt treatment by inoculation should strictly depend on the respective level of the oxygen and / or sulfur content.

As alloying elements, the invention provides elements whose atomic radius does not differ too much from that of iron. The deviation is preferably up to max. 2%. The alloying elements should not be strong carbide formers and should not directly segregate. According to the invention, it is therefore provided that, if necessary, copper, nickel, manganese or molybdenum is alloyed to the iron material in order to adjust its required properties. Tin can also be added for this purpose, the atomic radius of which is up to 50% larger than that of iron.

Accordingly, the iron casting material according to the invention contains copper in amounts of 0.4% by weight to 0.6% by weight in order to promote the formation of pearlite without negative effects on the desired high graphitization. Another positive effect of the presence of Cu is that directions of segregation are formed on this element. In the manufacture of lighter castings, such as lightweight engine blocks, it has proven to be advantageous if the range of Cu contents is limited to 0.45-0.55 in order to achieve these effects.

In addition, the alloy according to the invention can also contain nickel in contents of 0.05-0.8% by weight, preferably 0.05-0.7% by weight. In combination with Ni or alone, nitrogen contents of 0.05-0.08% by weight can also be provided. Both alloying elements ensure that the strength of the finished casting is maintained even in the event of a partial pearlite fall. Therefore, Ni and N are preferably present in the iron material according to the invention in combination or individually, in particular if cast parts are produced which, due to their shape or mass, cool slowly with the risk that pearlite will decompose. The rule should be that the contents of Ni and / or N are higher, the larger the module of the respective casting.

The technical term "module" here refers to the ratio of the cast part volume to the heat-emitting surface, for which "cm" is usually used as the unit of measurement.

Levels of Mn in the range from 0.4% by weight to 0.7% by weight also support pearlite formation. ^'However, manganese is also added in particular in order to form segregation directions on manganese. For the production of lighter, faster-cooling castings, the Mn contents can be limited to the range from 0.45 to 0.65% by weight in order to achieve this effect. The maximum phosphorus content is limited to 0.04% by weight in order to minimize the formation of phosphideutectic which would be detrimental to the toughness of the material. For this reason, the sulfur content is also limited to a maximum of 0.04% by weight in order to avoid sulfide formation. In the case of the presence of cerium, the contents of at least 0.01% by weight provided according to the invention are used for nucleation, which leads to finely divided oxysulfides. As a rule, it can be assumed that, in the presence of Ce, the higher the respective S content, the higher the Ce content. The oxysulfides formed by cerium in conjunction with sulfur promote the formation of graphite and increase the strength and hardness of the material without reducing the toughness of the material.

Mo can be added to the iron casting material according to the invention in contents of 0.15% by weight to 0.45% by weight in order to block dislocation movements in the event of thermal stress due to diffusion from the iron grid and thereby to prevent crack formation. The security with which the properties of the material according to the invention which are obtained by adding Mo can be increased by limiting the upper limit of the Mo content to 0.35% by weight or the lower limit to 0.2 % By weight is raised.

Tin contents, which are 0.05% by weight to 0.15% by weight, lead to the formation of a micro segregation zone around the graphite lamellae when the casting remains in the mold for a longer time and prevent the carbon from diffusing into the graphite basic matrix. The addition of strontium favors the nucleation and formation of a structure that is favorable in terms of the desired properties. In order to achieve this purpose safely, at least 0.0005 wt% Sr is required. On the other hand, if the content is more than 0.01% by weight, there is no longer any positive effect. Particularly in the case of larger castings, in which the strength is of particular importance, a particularly positive effect is achieved if Sr is present in a content of 0.0005 to 0.002% by weight.

Levels of lanthanum in the range of 0.005-0.02% by weight have a favorable effect on the castability of the cast alloy according to the invention and promote the hardness of the material and its tribological behavior by causing grain refinement.

If necessary, vanadium is added to the alloy according to the invention in order to increase the hardness and tensile strength of the material. Vanadium alloys the cementite of pearlite and leads to the formation of shorter, rounded lamellae of lamellar graphite, with the result that the hardness and toughness increase. If vanadium is added to an alloy according to the invention for this purpose, this can take place depending on the module of the respective component in order to reliably achieve the desired success. The V content should increase with increasing thickness. Practical trials have shown that optimal

Set the cast part properties if the V content is 0.025 - 0.035% by weight for a module of the respective cast part of 0.25 - 0.65 cm, the V content> 0.035 - for a module of 0.65 - 1.2 cm 0.065% by weight and with a module above 1.2 cm the V content is more than 0.055-0.1 % By weight. If the content according to the invention is more than 0.1% by weight, the solubility limit is exceeded.

A variant of the alloy according to the invention which is particularly suitable for the production of brake discs is characterized in that its carbon contents are in the range from 3.8 to 4.1% by weight. The relatively high carbon content leads to strengths in the range of 150 to 200 MPa. At the same time, castings produced from the alloys composed in this way have a high thermal conductivity with equally high toughness. For the same purpose, the silicon content is preferably in the range from 0.9 to 1.2% by weight.

Another variant of the invention provides for the casting of castings in which high strength combined with good thermal conductivity is paramount that the C content is in the range from 3.4 to 3.8% by weight, in particular 3% by weight. 4 - 3.6 wt .-% is.

Tests have shown that the iron casting material according to the invention composed in this way has high tensile strengths, which in the cast state regularly amount to more than 300 MPa.

When casting thick-walled castings, it is also advantageous if the Si content of the alloy is 1.15-1.4% by weight, in particular 1.2-1.4% by weight, in order to avoid the risk of reoxidation during casting counteracted with reduced C contents.

The oxygen content of an iron casting alloy according to the invention is of particular importance. The speed and extent of nucleation are determined by the 0 ₂ content controlled. An increase in the oxygen content leads to rapid particle growth, while lower oxygen contents result in less growth. These effects are achieved at 0 ₂ contents which are in the range from 30 to 70 ppm. If brake disks or similarly designed components are produced from the alloy according to the invention, the structure can be optimally achieved via the oxygen content by limiting the oxygen contents to 30 to 40 ppm. With thin-walled cast parts, such as light engine blocks or the like with a module of 0.1 to 0.4 cm, high 0 ₂ contents of 50 to 70 ppm have proven to be favorable, since they promote rapid grain growth within the short cooling time. In the case of thick-walled components with modules in the range of 0.4-1 cm, for example heavier engine blocks, optimized ge properties are achieved if the 0 ₂ content is 40 to 60 ppm. When casting complex-shaped cast parts, such as cylinder heads, with a module in the range from 1 to 2.5 cm, on the other hand, an optimized grain growth is achieved in relation to the properties required by these components if the 0 ₂ content of the alloy according to the invention is in the range of 30 up to 50 ppm.

The high tensile strengths of a cast material according to the invention can be assured particularly reliably by the fact that in the cast iron material according to the invention more than 50% of the oxygen contained in it is present in an oxide type whose starting temperature for the reduction with oxygen is above 1,700 K. In addition to the improved strength, thermal conductivity, toughness and machinability, the cast iron material according to the invention also has good corrosion resistance. Because of this special combination of properties, the cast iron material according to the invention is particularly suitable for producing brake disks and engine blocks or cylinder heads for internal combustion engines. In particular, the high tensile strengths in combination with the good castability, machinability and high thermal conductivity make the material according to the invention particularly suitable for use as a material for the production of blocks for modern diesel engines, in which the combustion process leads to extremely high pressure loads comes in the area of the combustion chamber.

The properties of cast iron material according to the invention have been demonstrated in a large number of examples.

Thus, cast iron alloys according to the invention have been cast with the compositions B1 - B7 of truck brake disks given in Table 1 in% by weight, whose Sc value,% MEG value, tensile strength R and Brinell hardness HB are given in Table 1b. Table 1b also contains an evaluation of the structure of the products obtained in each case.

It can be seen that the truck brake disks cast from the alloys listed in Table la consistently have tensile strengths in the range from 160 to 230 MPa. The hardness values are in the range from 147 to 220, so that the brake discs not only have high strength, but also good wear resistance. Furthermore, they have excellent thermal conductivity so that they can safely absorb and dissipate the forces acting on them even under high loads.

Table 2a shows the contents of C, Si, S, Mn, Cu, V, Mo, Sn and Ni for alloys Dl-D5 of cast iron materials according to the invention, from which thin-walled car engine blocks with a 0.7-0.8 cm amount module have been cast. In addition, the alloys D1-D6 in question each contained 60 ppm by weight of O ₂ and 0.01% by weight of La. Table 2b contains the associated values% MEG, SC, the tensile strength Rm and the Brinell hardness HB averaged over different measuring locations as well as an evaluation of the structure.

Table 3a shows the contents of C, Si, S, Mn, Cu, V, Mo, Sn and Ni for alloys ZI - Z6 of cast iron materials according to the invention, from which 100 kg (alloys ZI - Z4) and 400 kg (alloys Z5, Z6) heavy cylinder heads have been cast. The module of the 100 kg cylinder heads was between 2.5 - 3 cm, while the module of the 400 kg cylinder heads was 1 cm. In addition, the alloys ZI-Z6 in each case contained 40 ppm by weight of 0 ₂ and 0.01% by weight of La. Table 3b contains the associated values% MEG and SC, the tensile strength Rm and the Brinell hardness HB as well as an evaluation of the structure.

Finally, one (in% by weight) is 3.6% C, 1.35% Si, 0.1% Sn, 0.5% Mn, 0.5% Cu, 0.01% V, 0.2 % Mo, 40 ppm by weight 0 ₂ and 0.03% S and a cast iron alloy according to the invention as the remainder iron and unavoidable impurities, a heavy crankcase was cast. The alloy's SC was 0.93 and its% MEG was 1.98. The finished housing had a tensile strength Rm of 320 MPa and a finely structured pearlitic structure.

The invention thus provides an iron casting material which has a superior range of properties which can be varied over a wide range. The material according to the invention is characterized by particularly good machinability. Its high tensile strength makes it possible to produce known cast structures, which were previously only made from conventional gray cast iron, with higher strengths, without the need for complex redesigns.

Balance iron and unavoidable impurities

Table la

Table lb Balance iron and unavoidable impurities Table 2a

Table 2b

Balance iron and unavoidable impurities Table 3a

Table 3b

Claims

PATENT TO SPEECH

1. Iron casting material with lamellar graphite, with the following composition (in% by weight): C: 3.4 - 4.1%, Si: 0.9 - 1,%, Mn: 0.4 - 0.7%, Cu : 0.4-0.6%, S: 0.01-0.04%, 0 ₂ : 0.003-0.007%, P: <0.04%, remainder made of Fe and unavoidable impurities, the composition additionally optionally one or may contain several of the following elements: Mo 0.15 0.45%, La 0.005 - 0.02%, Sr 0.0005 - 0.01%, Ni: 0.05 - 0.8%, V: 0.005 - 0.1%, Sn: 0.05-0.15%, N: 0.05-0.08%, Ce: 0.01-0.02% and for the degree of saturation Sc = C% / 4, 26- 0.3 * (Si% + P%) (C%: respective C content, Si%: respective Si content, P%: respective P content) applies 0.85% <S _c <1.05% as well for the respective quantity% MEG = 2.25% - 0.2 Si% (Si%: respective Si content) 1.97% <MEG <2.07% applies

2. Iron casting material according to claim 1, d a d u r c h g e k e n n z e i c h n e t, that the C content is 3.8 - 4.1 wt .-%.

3. Iron casting material according to claim 2, d a d u r c h g e k e n n z e i c h n e t, that the Si content is 0.9 - 1.2 wt .-%.

4. cast iron material according to one of claims 2 or 3, characterized in that the 0 ₂ content is 0.003 - 0.004 wt .-%.

5. Cast iron material according to claim 1, d a d u r c h g e k e n n e z e c h n e t, that the C content is 3.4 - 3.6 wt .-%.

6. The cast iron material according to claim 5, wherein the Si content is 1.15-1.4% by weight.

7. cast iron material according to one of claims 5 or 6, d a d u r c h g e k e n n z e i c h n e t, that the Sr content is 0.005 - 0.002 wt .-%.

8. cast iron material according to one of claims 5 to 7, characterized in that the V content is 0.025 - 0.045 wt .-%.

9. cast iron material according to one of claims 5 to 8 d a d u r c h g e k e n n z e i c h n e t that the Sn content is 0.05-0.15% by weight.

10. cast iron material according to one of claims 5 to 9, d a d u r c h g e k e n n z e i c h n e t, -that the Si content is 1.15 - 1.25 wt .-%.

11. cast iron material according to one of claims 5 to 10, characterized in that the 0 ₂ content is 0.003 - 0.005 wt .-%.

12. Iron casting material according to one of claims 5 to 10, characterized in that the 0 ₂ content is 0.004 - 0.006% by weight.

13. Cast iron material according to one of claims 5 to 10, characterized in that the 0 ₂ content is 0.005 - 0.007% by weight.

14. Cast iron material according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, that the S content is at least 0.02 wt .-%.

15. cast iron material according to one of the preceding claims, characterized in that the Mo content is 0.2 - 0.4 wt .-%.

16. Iron casting material according to one of the preceding claims, that the mn content is 0.45-0.65% by weight.

17. Iron casting material according to one of the preceding claims, that the copper content is 0.45-0.55% by weight.

18. Iron casting material according to one of the preceding claims, that a s u s c h g e k e n n z e i c h n e t that his Sr content is at least 0.05 wt .-%.

19. Cast iron material according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t, that in the cast state more than 50% of the oxygen contained in it is present in an oxide type whose starting temperature for the reduction with oxygen is over 1,700 K.