DE3509709A1 - Process for producing an austempered nodular cast iron article, and the article thus obtained - Google Patents

Abstract

A process for producing an austempered nodular cast iron article and the resulting cast iron article, which can be a thick-walled article, are described. This is produced using a cast iron composition containing spheroidal graphite and consisting essentially of 3.0-4.0% by weight of C, 1.5-3.0% by weight of Si, 0.005-0.2% by weight of a spheroid-forming agent such as Mg, Ca and/or Ce, 0.3-0.8% by weight of Mn, 0.3-2.0% by weight of Cu, 0.2-2.5% by weight of Mo, and 0-0.3% by weight of Ni, the remainder being iron. The cast iron article is cooled from the austenite stabilisation temperature to the temperature of the transformation to troostite at a suitable cooling rate in such a way that precipitation of perlite is avoided, preferably at a cooling rate of between 10 DEG C/sec and 0.5 DEG C/sec. A fluidised-bed furnace is suitable for cooling. In the cast iron composition, the following relationship is preferably maintained: 3(Mn(% by weight) + Mo(% by weight)) + 2(Cu(% by weight) + Ni(% by weight)) >/= 7% by weight.

Description

description

The invention relates to a spheroidal graphite cast iron, and more particularly a process for the production of an intermediate tempered or heat bath hardened one Iron body with spheroidal graphite (spheroidal tEraphite cast iron) and the resulting Product.

The intermediate tempering or heat hardening of spheroidal graphite cast iron Great interest was devoted as a measure to achieve a cheap, lightweight materials to be used instead of steel grades for various machine elements in motor vehicles or motor vehicles, ships, civil or agricultural Machines, in equipment for steel production, etc. This is due to the fact that intermediate-tempered spheroidal graphite cast irons, which are known as bainitic spheroidal Graphite cast iron can be called a much better combination of Tensile strength and elongation or toughness than usual ferritic or pearlitic spheroidal graphite cast irons. For example, there was a success at Replacement of forged and carburized steel gears for automobiles and motor vehicles thanks to inter-stage tempered gears made of spheroidal graphite cast iron with advantages reported in many ways, such as reducing the overall production cost, the reduction in weight and noise reduction due to a high damping rate of the new material.

In practice, however, the inter-stage of spheroidal Graphite cast iron as only for limited uses for small and thin-walled Parts proved to be an ideal interstage or because it is not easy Utilization of high bainite or troostite by heat treatment of common spheroidal ones To achieve graphite cast iron. The main reason for the difficulty of the Intermediate tempering of spherical graphite cast iron of conventional compositions lies in the fact that the stability of the supercooled austenite is insufficient is. It is therefore necessary to achieve a suitable intermediate level remuneration, that the cast iron from the austenization temperature to bainite or. Troostite transition temperature is cooled at a sufficiently high rate of temperature decrease. In the event of thick-walled parts, however, it is difficult to achieve such a high cooling rate or Realize cooling speed in each part of each cast body and therefore Much pearlite precipitates from supercooled austenite during the cooling process. In some cases a salt bath is used to provide faster cooling than air cooling to achieve. However, in current industry it is generally undesirable to To use salt baths because of the laborious operation, the low productivity and the use of polluting materials. In addition, the tends to Cooling in a salt bath to create stronger stresses in the treated cast body than occurs in the case of air cooling.

As a typical measure to solve the above problem, it is known to use a spheroidal graphite cast iron which has substantial amounts of Mo and / or Ni, for example, in JP Patent Publication No.

47-19496 (1972) and JP-OS Nos. 50-127823 (1975) and 54-133420 (1979). The addition of Mo and / or Ni stabilizes the austenite and it therefore becomes possible to obtain a suitable intermediate grade of the spheroidal To achieve graphite cast iron without pearlite precipitation occurring, even if the cooling from the austenization temperature to the bainite or troostite transition temperature at a relatively low cooling rate or slow cooling speed Air cooling is carried out. The use of a relatively low rate of cooling offers the further advantage that there is less tension in the treated castings be generated.

However, the addition of vast amounts of the very expensive leads Mo and Ni to spheroidal graphite cast iron to a considerable one Increase in material cost and therefore cannot be widely carried out. In addition, when a large amount of Ni is contained, it becomes isothermal Conversion of austenite to bainite or troostite so slowly that the cast iron body for a very long period of time at the temperature for the formation of the troostite must be kept to upon completion of the inter-tier treatment to achieve good mechanical properties.

In EP patent application 84 114 386.0 by the same applicant, accordingly U.S. patent application S.N. 676 929 dated November 30, 1984, it was proposed to use a spheroidal graphite cast iron composition containing 0.3-0.8% by weight Mn and 0.3-2.0% by weight of Cu and optionally up to 0.1% by weight of Mo and / or up to 0.3 wt .- Ni may contain, and the cooling of the cast iron body from the austenite stabilization temperature to the troostite transition temperature to be carried out at a suitable cooling rate or cooling speed, that perlite precipitation is avoided, preferably in a fluidized bed furnace, especially if the cast iron body is a thick-walled part. This method is based on the finding that by using appropriate amounts of Mn and Cu it is possible to maintain the stability of the supercooled austenite at the time of To improve interstage heat treatment without the need to to add large amounts of Mo and / or Ni to the cast iron composition. Accordingly this method leads to low material costs and enables practical achievement of advantages in the inter-stage tempering of spheroidal graphite cast iron parts, even in cases of relatively thick-walled parts, without the need for use a salt bath occurs.

In addition, the isothermal conversion to troostite can be used in the intermediate aging treatment in a relatively short time due to the strict limitation of the salary of Ni in the cast iron. However, there are this method has limitations in terms of their effectiveness, due to the composition of the spheroidal Graphite cast iron, so that the practical application of this method to very thick-walled Sharing does not always produce fully satisfactory results.

It is an object of the invention to provide a method for easy and economical Generation of appropriately inter-stage-tempered or heat-bath-treated spheroidal graphite cast iron bodies provide good mechanical properties have, the method being fully applicable even if the cast iron body is a very thick-walled part.

Another object of the invention is to provide a suitable one Way inter-tier-remunerated resp.

heat bath-treated spheroidal graphite cast iron body, the good Has mechanical properties and requires relatively low material costs.

A method according to the invention for achieving an interstage paid or heat bath-treated spheroidal graphite cast iron body consists of the following Steps (a) Casting a spheroidal graphite composition consisting of 3.0-4.0 % By weight C, 1.5-3.0% by weight Si, 0.005-0.2% by weight of a spheroidizing agent, 0.3-0.8% by weight Mn, 0.3-2.0% by weight Cu, 0.2-2.5% by weight Mo, 0-0.3% by weight Ni and the remainder consists of iron and inevitable impurities, to an in body shaped as desired, and (b) intermediate tempering or

Heat bath treatment ("Austempering") of the cast iron body in that the cast iron body is first held at a temperature at which the austenite is stabilized, the cast iron body from the first temperature to a second Temperature is cooled at which the transformation of austenite to troostite or bainite takes place at such a cooling rate or cooling speed that the Cooling takes place essentially without precipitation of perlite, whereby the cast iron body is held at the second temperature to undergo isothermal conversion from austenite to troostite or bainite, whereupon the cast iron body is quenched or is cooled.

In this method it is preferred if the total amount of Mn, Cu, Mo and Ni in the spheroidal graphite cast iron composition is controlled so that the following conditions are met.

3 (Mn (% by weight) + Mo (% by weight)) + 2 (Cu (% by weight) + Ni (% by weight> = 7% by weight) It is also preferred if the cooling rate or cooling speed set in of step (b) mentioned is in the range of 10 OC / sec to 0.5 OC / sec.

An essential feature of the present invention is coexistence or the combined presence of 0.3 to 0.8% by weight of ANn, 0.3 to 2.0% by weight of Cu and 0.2-2.5 wt. t of Mo in the spheroidal graphite cast iron. By using such Amounts of these three types of alloying elements will increase the stability of the supercooled Austenite greatly improved at the time of the intermediate tempering of the cast iron body, without the need to add a large amount of Ni to the spheroidal graphite cast iron composition to add.

The material used in this method is less expensive than usual spheroidal graphite cast irons with a high nickel content, and also has the advantage that the isothermal conversion to troostite or bainite in the intermediate tempering treatment can be carried out in a relatively short time. The above special area the cooling rate is from the point of view of safe prevention the precipitation of the perlite and the minimization of the body in the cast iron produced stresses generated by the interstage aging heat treatment are preferred. In many cases, the Cooling from the austenite stabilization temperature to the troostite or bainite formation temperature by air cooling. In cases thick-walled cast iron body, it is preferred to use a fluidized bed furnace, the desired cooling rate or cooling speed even in the inner parts to achieve the cast iron body, although it is also possible to use a salt bath or a To use metal bath. Fluidized bed furnaces are free from those mentioned above Problems encountered with salt baths and the intermediate-level products have better mechanical properties when cooling in an oven Type is carried out.

According to the invention, there is a suitable range for the austenite stabilization temperature at about 800 "C to about 1000" C, and preferably 850 to 950 OC. A suitable one The range for the troostite formation temperature is about 200 ° C to about 400 ° C.

The present invention makes it possible to use the interstage coating technique to apply to a relatively inexpensive spheroidal graphite cast iron to thereby not only thin-walled machine parts but also very thick-walled machine parts to form, which have both high strength and high toughness, or to manufacture machine parts that have a high bainite or Exploit troostite content. The invention is applicable to numerous structural parts for machines, such as gearboxes, Connections or joints, cylinders, piston rings, housings, drums, forks, crankshafts, Swivel arms, etc.

The attached figure is briefly explained below. The only Figure is a graph showing the influence of Mo content in a spherical Graphite cast iron for use according to the invention on the position of the pearlite nose shows in the TTT diagram of the cast iron.

The invention is explained in more detail below.

According to the invention, the composition is made of a spherical graphite cast iron as stated above. The effects of the respective alloying elements and the reasons for specifying the limits on the quantities of the respective elements are in listed below. In the following description are the set of elements given in the cast iron as percent by weight.

(1) Carbon Carbon is an alloying element used in cast iron is absolutely necessary. In the spheroidal graphite cast iron of the present invention the content of C is limited to a maximum of 4.0%, since the presence of more than 4.0% C together with Si a crystallization of graphite as primary crystal can cause which is unfavorable for the strength and toughness of the cast iron. If the content of C is too low, the cast iron composition will be deteriorated Pourability on. The minimum content of C is therefore given as 3.0%.

(2) Silicon Silicon is an alloying element that is an important one Plays a role in achieving graphite formation in the cast iron. When the salary Si is too small, the cast iron composition has an unsatisfactory one Castability as well as an unsatisfactory degree of graphite formation. On the other hand, when the content of Si is too high, the cast iron is insufficient Elongation and is unfavorably brittle. Due to such tendencies, the Si content is in a spheroidal graphite cast iron according to the invention to the range of 1.5 limited to 3.0%.

(3) Manganese According to the invention, manganese is used as an alloying element, this makes an important contribution to increasing the stability of supercooled austenite in the spheroidal graphite cast iron. The minimum content of Mn becomes 0.3% set because the effect is believed to be insufficient is when the Mn content is less than 0.3%. The content of Mn is on Limited to a maximum of 0.8%, since the addition of a larger amount of Mn causes a reduction the strength and toughness of the cast iron.

(4) Copper Copper works to improve the suitability of the spheroid Graphite cast iron for heat treatment. The minimum content of Cu will be 0.3 % given because the expected effect is insufficient if the Cu content is less than 0.3 t. On the other hand, due to the presence of relatively large amounts on Cu the spheroid formation of the graphite made more difficult and the addition of an unnecessarily large one Amount of Cu leads to a decrease in the tensile strength and impact strength of the spheroidal graphite cast iron.

Therefore, the content of Cu is limited to a maximum of 2.0%.

(5) Molybdenum According to the invention, molybdenum is an important alloying element, this is very effective in maintaining the stability of supercooled austenite at the time of intermediate tempering of the spheroidal graphite cast iron body increased. To have such an effect of the To achieve Mo sufficient, spheroidal graphite cast irons according to of the invention always made with a content of at least 0.2% Mo.

The Mo content is limited to a maximum of 2.5% mainly because because Mo is an expensive material.

(6) Spheroid-forming agent For a spheroidal one according to the present invention Graphite cast iron can be a spheroid-forming agent freely from known resp.

usual spheroid-forming elements can be chosen, such as Mg, Ca and Ce, with Mg being preferred over the other spheroid-forming elements. To give a good spheroidization of the graphite without the mechanical properties of the cast iron adversely, is a suitable range of the Mg content or another spheroid forming agent in a cast iron composition according to of the invention at 0.005% to 0.2%.

(7) Nickel According to the invention, nickel is an optional alloying element, which can increase the stability of supercooled austenite in the cast iron. The salary of Ni is limited to a maximum of 0.3%, since if the Ni content is above 0.3%, the There is a tendency that Ni undergoes the bainite or troostite transformation instead of the pearlite transformation suppressed, and it therefore takes a longer time to convert to troostite to successfully perform in order to achieve good mechanical properties of the interstage-quenched and tempered To achieve cast iron; Another reason is that Ni is an expensive one Material is.

If one takes the simultaneous effect of Mn, Cu and Mo or of Mn, Cu, Mo and Ni on the latent period or the incubation time t. a so-called Perlite nose into consideration, which in a TTT diagram (time-temperature transformation (conversion) diagram), also known as the isothermal transformation diagram, in the spherical Graphite cast iron occurs, so it is preferred to determine the content (the percentages by weight) to control these alloy-forming elements so that the above in general resp. the summarizing part of the description is safely adhered to will.

In practice it is inevitable and permissible that an inventive spheroidal graphite cast iron has very low levels of impurities in addition to the contains essential and optional alloy elements and Fe mentioned above. Typical examples of such impurities are phosphorus and sulfur. It is favorable if the P content is below 0.1%, since a higher P content is harmful for the processability of the cast iron.

It is also favorable if the S content is below 0.1%, since a higher content of S has a detrimental effect on the spheroid formation of the graphite.

The following examples serve to illustrate the invention, without to restrict them.

Example 1 In this example, spheroidal graphite cast iron compositions were prepared produced according to the invention, by adding Mn, Cu and Mo to a basic composition, which is an example of commonly used spheroidal graphite cast iron compositions was. The cast iron base composition consisted of 3.6% by weight C, 2.8% by weight Si, 0.04 wt. T Mg, 0.02 wt. E P, 0.007 wt.% S and the remainder of Fe. In the alloy In spheroidal graphite cast iron compositions, the Mn content was a constant 0.5 % By weight and the Cu content was a constant 1.5% by weight. The content of Mo was varied, the influence of Mo on the thermal stability of supercooled austenite in a spheroidal graphite cast iron containing a combination of Mn and Cu, to investigate.

Any of the alloyed spheroidal graphite cast iron compositions was cast and made into test pieces for a tensile test having a diameter of of 7 mm in its cylindrical central part, as well as test pieces For the Charpy impact test to process, which are 10 x 10 mm square and 55 mm long and had a slot-like incision 3 mm deep. The test pieces were tempered by a first heating at 900 OC for 4 hours1 then cooled to 250 ° C in a fluidized bed furnace and then 2 hours was kept at 250 ° C and then cooled or quenched in water. By doing Fluidized bed furnace an alumina powder was used, which was replaced by a 0.177 mm sieve (80 mesh) was used as the heat transfer medium. The oven was with electric radiators are provided on the outside of the heating chamber, in which the aluminum oxide powder was included, and nitrogen gas was released into the heating chamber to an extent of 230 1 / min introduced so that the heated aluminum oxide powder layer diffuse was distributed in order to achieve a uniformly heated fluidized bed. The tensile strength and Charpy impact value were measured on the test pieces thus treated measured according to standard methods. The results are summarized in the table below given with the special compositions of the respective samples.

In addition, the degree of stability of the supercooled austenite in the Samples of the alloyed spheroidal graphite cast irons evaluated using a Conversion-expansion-shrinkage measuring device for obtaining a TTT diagram. In this test, each sample underwent an intermediate aging treatment at 900.degree. C. during Subjected for 15 minutes and then refrigerated. The table contains the values for the incubation time t. a pearlite nose that appeared in the TTT diagram. In the single figure of the In the accompanying drawing, the curve "1.5Cu-0.5Mn" represents the result of this test. It can be seen that the larger the value of t. the more stable the austenite and the likelihood of converting to pearlite is less even if the cooling speed is relatively slow.

This means that a large value of ti indicates that the cast iron is excellently suited for the intermediate aging heat treatment, and that a suitable one Intermediate tempering of the cast iron is possible.

Example 2 Cu, Mn, Mo and Ni became those described in Example 1 Basic cast iron composition joined to achieve a spheroidal graphite cast iron composition with a content of 2.0% by weight Cu, 0.8% by weight Mn, 1.01% by weight Mo and 0.29% by weight Ni, d. H. a composition according to Invention that is almost the allowed maximum amounts of Cu, Mn and Ni contained.

This cast iron was also subjected to the tests described in Example 1 subject. The results are shown in the table and in the figure.

Example 2A Example 2 was modified by increasing the nickel content to 2.50 wt%. The resulting spheroidal graphite cast iron was also used subjected to the above tests. The results are shown in the table.

Comparative experiment 1 Example 2 was modified, with none Addition of Mo took place. In the case of this spheroidal graphite cast iron, a Perlite nose in the TTT diagram at the point shown in the figure.

Example 3 Cu, Mn and Mo became the base cast iron composition of Example 1 added to obtain a spheroidal graphite cast iron containing 0.3 wt% Cu, 0.3 wt% Mn and 1.0 wt% Mo, i.e. H. a composition according to of the invention containing the minimal amounts of Cu and Mn.

In the case of this spheroidal graphite cast iron, a pearlite nose was shown in the TTT diagram as indicated in the figure.

Comparative experiment 2 Example 3 was modified, with no Mo was added. In this case a pearlite nose appeared on the TTT diagram at the position shown in the figure.

In the figure, the curve "1.5Cu-0.5Mn" shows that the effect of Mo occurs when its content in the spheroidal graphite cast iron is about 0.2% by weight and that the stability of the austenite in the cast iron is improved considerably becomes when the content of Mo is increased. By comparing the value of ti in Example 2 and that in Comparative Experiment 1 it can be seen that the addition of Mo is equally effective even if the cast iron is relatively large of Cu, Mn and Ni. From a comparison between the value of ti in the example 3 and that in Comparative Experiment 2 it can be seen that the addition of Mo is the same Is effective even if the content of Cu and Mn is relatively low.

Comparative experiments 3-8 Six different comparisons were made for further comparisons spheroidal graphite cast iron compositions made outside of the invention, as shown in the table, using the cast iron base composition mentioned in Example 1 was applied. Furthermore, the tests of Example 1 were also used for the comparative experiments 3-8 carried out. The results are shown in the table.

Table cast iron alloying elements (% by weight) Position of the pearlite tensile strength Charpy blow ----------------------------- nose in TTT-Dia- worth Mn Cu Mo Ni gram, ti (sec) (kgf / mm²) (kgf / m / cm²) Ex. 1A 0.5 1.5 0.20 - # 140 128 0.8-1.0 Ex. 1B 0.5 1.5 0.40 - # 180 129 0.7-1.0 Ex. 1C 0.5 1.5 0.78 - # 240 126 0.7-0.9 Ex. 1D 0.5 1.5 1.49 - # 350 125 0.7-0.9 Ex. 1E 0.5 1.5 2.48 - # 530 123 0.7-1.0 Ex. 2 0.8 2.0 1.01 0.29 # 530 121 0.7-0.9 Ex. 2A 0.8 2.0 2.50 0.29 # 730 123 0.7-0.9 Comp. 3 0.3 0.3 - - # 30 154 1.2-1.5 Comp. 4 0.3 0.3 - - # 130 132 1.2-1.1 Comp. 5 0.3 0.3 - - # 490 113 0.8-1.7 cf. 6 0.3 0.3 - - # 550 102 0.5-1.7 cf. 7 0.3 0.3 - - # 480 110 0.7-1.9 cf. 8 0.3 - 0.50 2.10 # 470 102 0.4-0.6 Note: each Cast iron composition contained 3.6 wt% C, 2.8 wt% Si, 0.04 wt% Mg, 0.02 % By weight of P and 0.007% by weight of S in addition to the alloying elements specified above In of the table, the ti values of Examples 1A to 1E show the same tendency as in the curve of the figure. From a comparison between the data of Example 2 and the data of Examples 1C and 1D can be seen that the addition of an adequate Amount of Ni to the cast iron compositions containing a small amount of Mo, causes a further improvement of the austenite and thus a further improvement the accessibility for the interstage remuneration. The data of Example 2A demonstrate that the suitability of the Ni-containing spheroidal graphite cast iron for the interstage aging can be further improved if the Mo content is up to the allowable maximum Salary is increased.

In contrast, the spheroidal graphite cast irons of the comparative experiments were 3 and 4 poorly suited for the intermediate level remuneration, since Mo is not or only was insufficiently added. In the case of comparative experiment 5, where the content of Mn was too large, and Comparative Experiment 6, where the content of Cu was too large, the mechanical properties of the intermediate tempered samples were deteriorated. The same was found in the case of comparative experiments 7 and 8, where one an excessive amount of Ni was used. Such spheroidal graphite cast irons with high nickel content have decreased tensile strength and impact strength on, probably due to the delay in the conversion to bainite or Troostite. In an additional experiment, the one for the troostite transformation was made at 250 "C required time measured as about 2000 seconds for the sample of the comparative test 7 (Ni 0.48%) and less than 1000 seconds for the samples of Examples 2 and 2A (Ni 0.29%). This test result shows that in the interstage aging heat treatment according to the invention the conversion to troostite is complete in a relatively short time, despite expansion the time of occurrence of the pearlite nose, which indicates an increased stability of the austenite.

Examples 3-5 In Example 3, a spheroidal graphite cast iron composition was consisting of 3.6% by weight of E C, 2.6% by weight of Si, 0.04% by weight of Mg, 0.8% by weight of Mn, 2.0% by weight Cu, 0.2 wt .-% Mo and the remainder of Fe and unavoidable impurities, to one cast cylindrical rod 60 mm in diameter and 180 mm in length. The cast iron rod was made by a first heat treatment at a tempering temperature of 850 ° C Subjected to an intermediate level for 4 hours, then to 350 ° C in the fluidized bed furnace of Example 1, whereupon the temperature 2 Hours at 350 ° C to complete the conversion to Proostit, after which it was cooled or quenched with water.

In Example 4, the spheroidal graphite cast iron composition was used of Example 3 modified by increasing the Mo content to 0.3% by weight. For example 5, the composition of Example 4 was further modified by adding 0.1 wt. E Ni. The modified cast iron compositions each became cylindrical Bars of the dimensions given in Example 3 were cast and these samples were made tempered in the same way as in example 3 between stages.

After the interstage tempering treatment, the cast Iron bars of Examples 3, 4 and 5 divided into sections and the metal structure each sample was examined under the microscope. No pearlite structure was found in any of the samples can be found even in the central core area and confirmed accordingly it turns out that each sample was very well remunerated.

Claims (7)

Process for the production of an intermediate-tempered cast iron body with ball graphite and the body obtained thereby Patent claims 1. Method for Production of an intermediate-tempered or heat bath tempered cast iron body with spheroidal graphite, characterized by the following stages: (a) Casting of spheroidal graphite containing cast iron composition, which consists of 3.0 to 4.0 wt .-% C, 1.5 ins 3.0 Wt% Si, 0.005 to 0.2 wt% of a spheroid-forming agent, 0.3 to 0.8 wt% Mn, 0.3 to 2.0 wt% Cu, 0.2 to 2.5 wt% Mo, 0 to 0.3 wt% Ni and the remainder consists of Fe and unavoidable impurities, to the desired shaped body; and (b) intermediate tempering or heat bath treatment of the cast iron body by that the cast iron body is first held at a first temperature at which Austenite is stabilized, the cast iron body from the first temperature to a second temperature is cooled at which the transformation of austenite to llroostite or bainite takes place, with such a cooling rate or cooling speed, that the cooling is achieved essentially without precipitation of pearlite, hold of the cast iron body at this second temperature to achieve the isothermal conversion of Austenite to troostite or bainite, and subsequent quenching or Hardening of the cast iron body. 2. The method according to claim 1, characterized in that the total amounts on Mn, Cu, Mo and Ni in the composition of the following equation correspond to: 3 (Mn (% by weight) + Mo (% by weight)) + 2 (Cu (% by weight) + Ni (% by weight)) 2 7% by weight. 3. The method according to claim 1 or 2, characterized in that the Cooling rate or the cooling speed in the range from 10 OC / sec to 0.5 OC / sec lies. 4. The method according to claim 3 or one of the other preceding Claims, characterized in that the cooling stage (b) from the first temperature carried out to the second temperature in a fluidized bed furnace or fluidized bed furnace will. 5. The method according to claim 1 or one of the other preceding Claims, characterized in that the first temperature is in the range of about 800 OC to about 1000 OC and the second temperature is in the range of about 200 OC to about 400 OC. 6. The method according to claim 1 or one of the other preceding Claims, characterized in that the spheroid-forming agent comprises an element selected from the group of Mg, Ca and Ce. 7. Intermediate tempered cast iron body with spheroidal graphite, produced according to the method of one of claims 1 to 6.