RU2509820C2 - Method of defining machinability of cast iron with vermicular graphite at machine tools - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed method comprises establishing the relationship between cuttability and content of carbide-stabilising elements in cast iron with vermicular graphite. Note here that said relationship is defined empirically from measured cuttability and content of carbide-stabilising elements in multiple specimens of cast iron with vermicular graphite. Said cast iron with vermicular graphite is used to define the content of carbide-stabilising elements in multiple specimens of cast iron with vermicular graphite. It includes definition of cuttability by indicated relationship 1 and contents of carbide-stabilising elements in multiple specimens of cast iron with vermicular graphite. It comprises definition of at least one first preset reference cuttability of cast iron with vermicular graphite for large-scale mechanical assembly. Cuttability of cast iron with vermicular graphite is classified in comparison with cuttability at first preset reference magnitude.

EFFECT: cast iron with vermicular graphite with optimum cuttability and costs.

23 cl, 5 tbl, 7 dwg

Description

Technical field

The present invention relates to a method for determining the ability to cut cast iron with vermicular graphite in accordance with the preamble of claim 1 of the formula.

State of the art

The automotive industry is facing an ever-increasing need for more efficient engines with lower emissions. One way to achieve cleaner combustion is to use a higher combustion pressure in diesel engines, but this entails more exacting requirements for cylinder block materials and cylinder heads. The strength characteristics of the traditionally dominant material, gray cast iron, are insufficient to withstand the loads to which the material will be subjected in future generation diesel engines. Therefore, many automotive companies are switching to the use of vermicular graphite cast iron in diesel engines. Vermicular graphite cast iron, abbreviated as CVG, has at least 45% -75% higher hardness than gray cast iron and twice the fatigue strength. Engine components made from CVG are currently being produced by various car manufacturers.

The production of vermicular graphite cast iron involves the use of scrap containing elements that can lead to the presence of carbides in the material, the so-called carbide-stabilizing elements. Examples of such elements in vermicular graphite iron are molybdenum (Mo), chromium (Cr) and manganese (Mn). Carbide-stabilizing elements: chromium and manganese, are naturally found in scrap, which is melted and used in the production of vermicular graphite iron. Molybdenum is an alloying element that is added to give CVG greater strength at high temperatures.

When using cast iron with vermicular graphite in production, a problem arises that carbides formed by chromium, manganese and molybdenum reduce its ability to cut. Therefore, the high content of carbide-stabilizing elements entail a low ability to cut and lead to low productivity and high cost of machining. In addition, vermicular graphite cast iron with a low content of carbide-stabilizing elements is expensive because cleaner scrap must be used, which leads to a high purchase price of vermicular graphite cast iron. One task for the use of vermicular graphite cast iron in production is to provide CVG that has good cutting ability at a favorable cost, as disclosed in SU 1766962 C21C 1/10, 07.10.1992.

Therefore, the aim of the invention is to develop a method for easy and reliable determination of the ability to cut cast iron with vermicular graphite based on the content of carbide-stabilizing elements in it.

A further object of the invention is also to provide as cheap a method as possible for classifying CVGs for optimum cutting ability.

The essence of the invention

According to the invention, this goal is achieved by a method for determining the ability to cut cast iron with vermicular graphite, characterized by the following steps:

- establishing a relationship between the ability to cut and the content of carbide-stabilizing elements in cast iron with vermicular graphite, and this ratio is determined empirically from the measured ability to cut and the measured contents of carbide-stabilizing elements on many samples of cast iron with vermicular graphite;

- providing cast iron with vermicular graphite;

- determination of the content of carbide-stabilizing elements in cast iron with vermicular graphite;

- determination of the ability to cut the obtained cast iron with vermicular graphite based on the aforementioned ratio and the contents of carbide-stabilizing elements in cast iron with vermicular graphite.

The method allows you to easily and reliably determine the ability to cut in existing cast iron with vermicular graphite, which gives great advantages in the industrial production of parts made of cast iron with vermicular graphite by machining on metal cutting machines, since the method allows you to easily select cast iron with vermicular graphite, which are optimal for the purpose production. Thus, the method contributes to a very cost-effective production when processing cast iron with vermicular graphite on metal cutting machines.

The method may also include the steps of:

- determining at least one first predetermined reference value for the ability to cut cast iron with vermicular graphite;

- classification of the ability to cut cast iron with vermicular graphite from a comparison of the value of its ability to cut with a given reference value.

According to one alternative, the obtained ability to cut cast iron with vermicular graphite is classified as suitable for production if the obtained value of the ability to cut cast iron with vermicular graphite is higher than the specified reference value.

According to one alternative, the method comprises the step of:

- determination of at least one second reference value for the ability to cut cast iron with vermicular graphite, according to which the ability to cut cast iron with vermicular graphite is classified as very suitable for production if the value of its ability to cut is higher than the second reference value.

The ability to cut is mainly determined as the tool life resource when machining cast iron with vermicular graphite on processing machines with chip removal, preferably during milling.

The tool life is determined primarily as the maximum oblique wear of the tool.

The ratio for the ability to cut is based mainly on a model that includes the ratio between the contents of carbide-stabilizing elements in cast iron with vermicular graphite.

According to one alternative, the model is based on linear relationships, cross-relationships and quadratic relationships between the contents of carbide-stabilizing elements.

According to the first embodiment, the ratio is:

Tool life in minutes = 27-50 * Mo-186 * Cr + 127 * Mn-146 * Mn ² + 146 * Cr * Mo + 151 * Cr * Mn.

Thus, the ability to cut, expressed as a tool life resource, can be determined very accurately, based on a large number of ratios between carbide-stabilizing elements.

According to one alternative, the model is based on linear relationships between the contents of carbide-stabilizing elements in vermicular graphite iron.

According to a second embodiment, the ratio is:

Tool life in minutes = 57.20-18.46 * Mn-80.90 * Cr-38.98 * Mo.

This ratio is easy to apply since it is based on a linear model.

According to a third embodiment, a ratio of:

Tool life = 1- (0.32 ± 0.21) * Mn- (1.41 ± 0.39) * Cr- (0.68 ± 0.31) * Mo, where the tool life is normalized.

The fact that this ratio is normalized eliminates external sources of errors, for example, due to changes in the requirements for machining or due to systematic measurement errors.

Carbide-stabilizing elements preferably include at least manganese, molybdenum and chromium.

It is advisable if the content of carbide-stabilizing elements in cast iron with vermicular graphite is as follows:

Mn: 0.1-0.8 wt.%, Cr 0-0.2 wt.%, Mo 0-0.3 wt.%

Preferably, the content of carbide-stabilizing elements in vermicular graphite iron is as follows:

Mn: 0.4-0.8 wt.%, Cr 0-0.2 wt.%, Mo 0-0.3 wt.%

Description of drawings

Figure 1: Schematic illustration of a tool wear measurement site expressed as oblique wear.

Figure 2: Schematic illustration of a sample used in the method according to the invention.

Figure 3: Histogram of coefficients showing the relationship between carbide-stabilizing elements and tool life, taking into account cross-ratios and quadratic ratios.

Figure 4: Histogram of coefficients illustrating statistically significant relationships between carbide-stabilizing elements and tool life, taking into account cross-relationships and quadratic relationships.

Figure 5: A diagram showing the values of R ² and Q ² for the ratios from figure 4.

Figure 6: Graph comparing the tool life, calculated according to the equation according to the first embodiment of the invention, with the measured average values of the tool life for the tested materials.

Figure 7: Graph comparing the tool life, calculated according to the equation according to the third embodiment of the invention, with the measured normalized average values of the tool life for the samples of materials.

Definitions

The term “cutting ability” in this patent application means a measure of how easy or difficult it is to process the material of a tool with chip removal. The ability to cut material is expressed primarily as a tool life, cutting force, surface uniformity, or chip shape. According to one preferred embodiment of the present invention, the cutting ability is expressed as a tool life resource.

The term "tool life" in this patent application means the period during which a tool, for example, a cutter made of sintered hard metal (TC) for drilling, milling or other machining on metal cutting machines, can be actively used before it reaches set wear limit.

The nature of edge wear during metal cutting can vary depending on the different load factors that the tool is subjected to. The most common types of wear are abrasive, diffusion, oxidative, fatigue and adhesive wear (Berglund et al., 2006). Oblique wear is the most commonly measured wear mechanism (Stjernstoft, 2004).

Measuring the oblique wear of a tool cutting edge during machining involves measuring the abrasive wear on the tool edge v _B in mm, according to Stjernstoft, 2004 and Berglund et al., 2006. Figure 1 shows the cutting tool in front and side views. The dashed line in the figure on the right shows the area that has been worn. The image on the left shows where oblique wear is measured. If tool wear is measured as oblique wear on the cutting edge, the specified maximum allowable wear is expressed as v _B in mm.

Description of the invention

Material samples were prepared from 17 cast iron with vermicular graphite (FGM materials) with different levels of Mn, Cr and Mo.

Samples were cast to obtain prototypes measuring 350 * 120 * 49 mm, see Figure 2, schematically showing the prototypes. The crust of the casting from the samples was removed by longitudinal milling of their lower, upper and side surfaces. This was done in order to obtain the desired dimensions after casting and to achieve a more uniform microstructure, since the microstructure of the peel of the casting is different from the microstructure of the rest of the material.

After that, prototypes from 17 different CVG materials were processed on the machine. To ensure sufficient statistical significance, two additional samples of FGM material 17 were also processed. These samples are indicated by numbers 18 and 19. For each material, the tests for machining were carried out twice, thus, a total of 19 * 2 tests for machining were carried out. Processing was performed by longitudinal milling of samples using a CoroMill 365 machine (R365-063Q22-S15H) equipped with three K20W cutters (R365-1505ZNE-KM K20W). Processing was carried out on a multipurpose milling machine manufactured by Mazak. Prototypes were fixed using a magnetic table.

The following cutting parameters were used: cutting depth (a _p ) 3 mm, feed rate (t _z ) 0.2 mm / tooth and cutting speed (v _c ) 200 m / min. After a series of treatment cycles, the tool holder was removed from the cutter and the cutting wear was measured under a microscope as the maximum oblique wear [v _B in mm]. The treatment and measurement of oblique wear was repeated until the average value of the maximum oblique wear of three incisors reached 0.3 mm, or at the moment when two of the three incisors reached a maximum oblique wear of 0.3 mm, which was taken as the specified maximum allowable wear of the cutter. When the oblique wear reached 0.3 mm, the cutters were considered worn. The tool life was measured, i.e. the total time during which processing is carried out until the cutter is worn out and recorded for all materials. Table 1 presents the results of machining.

Table 1
The results of measuring the tool life Material No. Tool life, measurement 1
[mm] Tool life, measurement 1
[mm] Average tool life
[mm] one 52,5 49.9 51,2 2 47.9 45.0 46,4 3 38.3 40.1 39.2 four 37,4 38.7 38,0 5 24.1 23.8 23.9 6 17.0 24.7 20.9 7 23.7 26.0 24.9 8 22.5 22.6 22.6 9 40,2 38,0 39.1 10 33.3 29.4 31,4 eleven 32.9 30.6 31.7 12 25.9 24.3 25.1 13 30.1 28.3 29.2 fourteen 18.5 18.6 18.5 fifteen 24.0 24.5 24.2 16 15.6 15.6 15.6 17 42.5 36.3 39,4 eighteen 41.6 40,0 40.8 19 41.6 39.7 40.8

The chemical composition of 17 materials was measured by the GD-OES method (glow emitting optical emission spectroscopy). Since samples 17, 18 and 19 had the same composition, in chemical analysis they were considered the same material, number 17. Table 2 shows the chemical composition for 17 prototypes.

The results of tests for machining and chemical compositions of materials were used to establish empirical relationships between the ability to cut, expressed as a tool life resource, and the content of carbide-stabilizing elements in the material, according to the following procedure.

The results of tests on the machining and chemical compositions of the materials were analyzed by full-factor analysis using the Modde program from Umetrics (Umetrics, version 7) to establish the relationship between the tool life and the carbide-stabilizing elements Mo, Cr and Mn.

The program starts with a statistical model and compares various levels of carbide-stabilizing elements in the material with the results of various measurements described above. The analysis is carried out by a program that performs repeated calculations, and a statistical analysis of the results of tests for machining and chemical compositions of materials. The relationships established between the ability to cut and the content of carbide-stabilizing elements established as a result of the analysis make it possible to select coefficients in the model so that the model describes the measured values as best as possible.

According to the first alternative, the program proceeds from the first model, see equation 1, which takes into account linear relations, cross-relations and quadratic relations:

Tool life = constant + a * Mo + b * Cr + c * Mn + d * Mo * Mn + e * Mo * Cr + f * Cr * Mn + g * Mo ² + h * Cr ² + i * Mn ²

[equation 1]

According to the second alternative, the program proceeds from the second model, represented by equation 2 below, taking into account only linear relationships:

Tool life = constant + a * Mo + b * Cr + c * Mn

[equation 2]

The relationships analyzed by the program can be described in various ways. It is easy and comprehensive to present them in the form of a histogram of coefficients, see, for example, figure 3. The histogram of coefficients allows you to conclude which of the elements has the greatest effect, how much this effect is comparable to the effect of other elements, and whether this effect is positive or negative . You can also set the coefficient error scale. If the error value is greater than the effect, i.e., if the error scale passes through zero, the ratio is not considered statistically reliable with the selected significance level of 95%.

Figure 3 shows the relationship between carbide-stabilizing elements and tool life when using the upgraded model according to Equation 1. The histogram shows a picture of the effect, taking into account cross-ratio and quadratic ratio.

As can be seen from the error scales in figure 3, most of the coefficients have permissible errors that exceed the effect, i.e. their error scales cross the coordinate axis, which means that the effect is not provided with the selected significance level. These coefficients were removed from the model and a new histogram of coefficients was adopted. Figure 4 shows a histogram of coefficients for a simplified model. This model shows, among other things, that Cr has the largest negative effect on the tool life.

There are different ways of assessing how well the above model corresponds to reality (measured values). The most common and most important is the value of R ² . The value of R ² can vary between 0 and 1, and 1 means that the model perfectly matches reality. Another important quantity is Q ² , which describes how robust the model is. The value of Q ² can vary from 0 to 1, and 1 corresponds to a reliable model that is not sensitive to data changes. Q ^{2 is} always slightly less than R ² , and for a good model the difference between R ² and Q ² is small. Figure 5 shows an improved model that is in good agreement with the measured values. It shows that for this model, the value of R ² is 0.94, and the value of Q ² is 0.87.

The first embodiment uses the calculation results and the above statistical analysis as the basis for establishing a correlation in the form of an equation of how the cutting ability, expressed as the tool life when machining on metal cutting machines, depends on the carbide-stabilizing elements Cr, Mo and Mn. The ratio is described by equation 3 and contains a constant and members that are statistically significant, and the coefficients in front of them:

Tool life = 27-50 * Mo-186 * Cr + 127 * Mn-146 * Mn ² + 146 * Cr * Mo + 151 * Cr * Mn

[equation 3]

In the same empirical way, as described above, the second embodiment of the invention comes to the following ratio. The ratio according to the second embodiment was based on a linear model in accordance with equation 2 and is represented by equation 4 below:

Tool life = 57.20-18.46 * Mn-80.90 * Cr-38.98 * Mo

[equation 4]

The third embodiment is obtained with the normalized equation. This is done by normalizing equation 4 and taking into account the lower and upper limits of the coefficients, according to equation 5:

Tool life = C1 + (min; max) * Mn + (min; max) * Cr + (min; max) * Mo

[equation 5]

Normalization leads to equation 6:

Tool life = 1 + (- 053; -0.12) * Mn + (- 1.81; -1.02) * Cr + (- 0.99; -0.37) * Mo

[equation 6]

The coefficients in equation 6 were recalculated to vary in accordance with equation 7:

Tool life = 1- (0.32 ± 0.21) * Mn- (1.41 ± 0.39) * Cr- (0.68 ± 0.31) * Mo

[equation 7]

This normalized ratio eliminates external error factors that could affect the result, for example, systematic measurement errors or changes in machining parameters due to conditions or adjusting parameters of the machine used for processing.

Cutting classification

To allow classification of cast iron with vermicular graphite in accordance with its ability to cut, reference values were adopted for the suitability of various cast iron with vermicular graphite for large-scale machining.

In accordance with one alternative, predetermined reference values were determined based on equation 7:

Tool life = 1- (0.32 ± 0.21) * Mn- (1.41 ± 0.39) * Cr- (0.68 ± 0.31) * Mo

[equation 7]

All coefficients in equation 7 were taken as their respective mean values. Based on this assumption, reference values were determined for the suitability of vermicular graphite cast iron for large-scale machining with respect to carbide-stabilizing elements (expressed as tool life resource) as follows:

Level 1: tool life> 0.81 Good for production Level 2: tool life 0.68-0.80 Suitable for production Level 3: tool life <0.67 Not suitable for production

According to the following alternative, reference values can also be determined for equations 3 and 4. They can be determined by measuring the actual tool life, measured by large-scale processing of cast iron with vermicular graphite having different contents of carbide-stabilizing elements. After that, the measured tool resources are evaluated at three levels:

Level 1: Good for production Level 2: Suitable for production Level 3: Not suitable for production

It should be emphasized that the assessment of the tool life as suitable for large-scale processing varies with factors such as a cutting tool, the price of a cutting tool, cutting parameters or other types of metal-cutting machines. Therefore, the above levels should be adjusted by specialists for the prevailing conditions. As an example, we can indicate that when machining with K20W cutters on a multipurpose milling machine manufactured by Mazak, a tool life of more than 40 minutes is considered very suitable for production, a tool life of 40 to 20 minutes is considered suitable for production, and the tool life of less than 20 minutes is considered unsuitable for production.

When calculating the reference values, various factors can be taken into account, for example, material costs can be included here. You can apply different weights for the resource tool life or material costs. You can also take the tool life resource statistically as the average value when processing many materials with different contents of carbide-stabilizing elements. Similarly, you can take the average values for the costs of further materials.

Examples

Below the invention is described in relation to two specific tests conducted with calculated ratios, and measurements on real materials.

Test 1

In the first test, a comparison was made between the measured tool resources and the tool resources calculated according to equation 3.

The calculation of the tool life for the corresponding samples 1-19 was carried out by substituting the contents of the carbide-stabilizing elements Mo, Cr and Mn in equation 3. Then, the calculated tool life is compared with the tool life measured for the corresponding samples (see table 1). Figure 6 shows a very good correspondence between the calculated and measured tool resources.

Test 2

In the second test, two different series of samples were used to make comparisons between the measured tool resources and the tool resources calculated according to equation 7.

The previously described group of samples of materials 1-19 (see table 1) was supplemented by a second series of four additional samples of materials, indicated by numbers 20-23.

Samples of materials 20-23 were made (cast) and analyzed in the same way as materials 1-19, but they were processed on a different machine than the one used for materials 1-19. Another machine operator also worked on this machine. The machine used for materials 20-23 was Huller Hille nb-h 150. The measurement of the tool life on samples of materials was carried out similarly to the measurement for samples 1-19.

Table 3 shows the chemical composition of material samples 20-23.

Table 3
The chemical composition of the samples of materials 20-23 Material
No. C Si Mn S P Cr Ni Mo Cu Ti Sn Mg Cek twenty 3.64 2.24 0.13 0.006 0,022 0,03 <0,050 <0.010 0.65 0.014 0,055 <0.010 4.21 21 3.63 2.27 0.34 0.007 0,022 0.05 <0,050 <0.010 0.69 0.014 0,067 <0.010 4.21 22 3.63 2.29 0.41 0.008 0,022 0.09 <0,050 0,03 0.69 0.014 0,062 <0.010 4.21 23 3.60 2.27 0.48 0.007 0,023 0.09 <0,050 <0.010 0.69 0.014 0,062 <0.010 4.18

Table 4 shows the measured tool resources when processing samples of materials 20-23.

Table 4
The results of measuring the tool life for samples of materials 20-23 Material No. Tool life, measurement 1
[mm] Tool life, measurement 1
[mm] Average tool life
[mm] twenty 30.5 30.5 30.5 21 30.5 28,4 29.5 22 31.8 31,4 31.6 23 27.3 24.5 25.9

Table 5 below shows that the measured tool resources in minutes for materials 20-23 differ from the results for materials 1-19, which have the same composition. This is due to factors of systematic errors caused by the use of other machines for the material of groups 1-19 and 20-23. The machine used for group 20-23 was configured differently than the machine used for group 1-19.

To take this into account, the tool resources for materials 1-23 were calculated as follows according to the normalized equation 7, taking all the coefficients in equation 7 equal to their average values:

Tool life = 1-0.32 * Mn-1.41 * Cr-0.68 * Mo.

Table 5 below shows the results.

The tool resources measured for samples 1-23 were then normalized relative to reference materials 17 * and 23. As noted earlier, the first group contained 17 separate samples of materials, and material 17 was used twice more to ensure statistical significance, these samples are indicated by numbers 18 and 19. Thus, reference material 17 * is the average measurement value for materials 17, 18, and 19.

Normalization was carried out as described below.

For reference materials 17 * and 23, the following assumptions were made:

Estimated tool life = measured normalized tool life

Then calculated the normalized measured resource of tool life for each material 1-23 as follows:

Normalized (x) = Measured (x) * [normalized (fl.) / Measured (fl.)]

Materials 1-19 were normalized in relation to material 17 *, and materials 20-22 - in relation to material 23.

The results are shown in table 5.

Table 5
Measured and calculated tool resources for material samples 1-23 Material No. Estimated tool life = 1-0.32Mn-1.41Cr-0.68Mo Average estimated tool life [min] Measured tool life (normalized) one 0.84 51,2 0.82 2 0.77 46,4 0.74 3 0.70 39.2 0.63 four 0.65 38,0 0.61 5 0.57 23.9 0.38 6 0.46 20.9 0.33 7 0.44 24.9 0.40 8 0.36 22.6 0.36 9 0.72 39.1 0.63 10 0.65 31,4 0.50 eleven 0.57 31.7 0.51 12 0.53 25.1 0.40 13 0.48 29.2 0.47 fourteen 0.36 18.5 0.30 fifteen 0.33 24.2 0.39 16 0.24 15.6 0.25 17 0.64 39,4 0.63 17 * (fl.) 0.64 40.1 0.64 eighteen 0.64 40.8 0.65 19 0.64 40,2 0.65 twenty 0.92 30.5 0.84 21 0.82 29.5 0.81 22 0.72 31.6 0.87 23 (floor) 0.72 25.9 0.71

In figure 7, the values of the measured normalized resource of tool life are shown on the graph as a function of calculated tool resources, which are also shown by a solid line corresponding to the condition "Calculated tool life resource = Measured tool life". As can be seen from the graph, the scatter of the measured normalized values relative to the solid line is insignificant, which shows a good correspondence between the measured and calculated tool resources even for a series of samples processed in other conditions.

The above detailed description of particular embodiments of the invention is intended to illustrate but not limit the invention. Obviously, the described embodiments may be combined, and that various changes and modifications may be made to the invention within the scope of protection of the attached claims.

Claims (23)

1. The method of determining the ability to cut cast iron with vermicular graphite, including providing cast iron with vermicular graphite, characterized in stages:
- establishing a relationship between the ability to cut and the contents of carbide-stabilizing elements in cast iron with vermicular graphite, and this ratio is determined empirically from the measured cutting ability and the measured contents of carbide-stabilizing elements on many samples of cast iron with vermicular graphite,
- determination of the content of carbide-stabilizing elements in cast iron with vermicular graphite,
- determining the ability to cut cast iron with vermicular graphite based on this ratio and the contents of carbide-stabilizing elements in the resulting cast iron with vermicular graphite,
- determining at least one first predetermined reference value for the ability to cut cast iron with vermicular graphite for large-scale mechanical assembly,
- classification of the ability to cut cast iron with vermicular graphite from a comparison of the value of its ability to cut with the first specified reference value. 2. The method according to claim 1, in which the ability to cut purchased cast iron with vermicular graphite is classified as suitable for production if the value of the ability to cut cast iron with vermicular graphite is higher than the first specified reference value. 3. The method according to claim 2, comprising the steps of:
- determining at least one second predetermined reference value for the ability to cut cast iron with vermicular graphite, according to which the ability to cut cast iron with vermicular graphite is classified as very suitable for production if the value of its ability to cut is higher than the second reference value. 4. The method according to any one of claims 1 to 3, in which the ability to cut is defined as the tool life resource when machining cast iron with vermicular graphite on a machine with chip removal. 5. The method according to claim 4, in which the tool life is defined as the maximum oblique wear of the tool. 6. The method according to any one of claims 1 to 3, in which the ratio for cutting ability is based on a model that includes the ratio between the contents of carbide-stabilizing elements in cast iron with vermicular graphite. 7. The method according to claim 6, in which the model is based on linear relationships, cross-relationships and quadratic relationships between the contents of carbide-stabilizing elements. 8. The method according to claim 4, in which the ratio is:
tool life in minutes = 27-50 · Mo-186 · Cr + 127 · Mn-146 · Mn ² + 146 · Cr · Mo + 151 · Cr · Mn. 9. The method according to claim 5 or 7, in which the ratio is:
tool life in minutes = 27-50 · Mo-186 · Cr + 127 · Mn-146 · Mn ² + 146 · Cr · Mo + 151 · Cr · Mn. 10. The method according to claim 6, in which the ratio is:
tool life in minutes = 27-50 · Mo-186 · Cr + 127 · Mn-146 · Mn ² + 146 · Cr · Mo + 151 · Cr · Mn. 11. The method according to claim 6, in which the model is based on linear relationships between the contents of carbide-stabilizing elements in cast iron with vermicular graphite. 12. The method according to claim 4, in which the ratio is:
tool life in minutes = 57.20-18.46 · Mn-80.90 · Cr-38.98 · Mo. 13. The method according to claim 5, in which the ratio is:
tool life in minutes = 57.20-18.46 · Mn-80.90 · Cr-38.98 · Mo. 14. The method according to claim 6, in which the ratio is:
tool life in minutes = 57.20-18.46 · Mn-80.90 · Cr-38.98 · Mo. 15. The method according to item 12, in which the ratio is:
tool life in minutes = 57.20-18.46 · Mn-80.90 · Cr-38.98 · Mo. 16. The method according to claim 4, in which the ratio is:
tool life = 1- (0.32 ± 0.21) · Mn- (1.41 ± 0.39) · Cr- (0.68 ± 0.31) · Mo, and the tool life is normalized. 17. The method according to claim 5, in which the ratio is:
tool life = 1- (0.32 ± 0.21) · Mn- (1.41 ± 0.39) · Cr- (0.68 ± 0.31) · Mo, and the tool life is normalized. 18. The method according to claim 6, in which the ratio is:
tool life = 1- (0.32 ± 0.21) · Mn- (1.41 ± 0.39) · Cr- (0.68 ± 0.31) · Mo, and the tool life is normalized. 19. The method according to item 12, in which the ratio is:
tool life = 1- (0.32 ± 0.21) · Mn- (1.41 ± 0.39) · Cr- (0.68 ± 0.31) · Mo, and the tool life is normalized. 20. The method according to any one of claims 1 to 3, 5, 7, 8, 10-19, in which the carbide-stabilizing elements include at least manganese, molybdenum and chromium. 21. The method according to claim 4, in which the carbide stabilizing elements include at least manganese, molybdenum and chromium. 22. The method according to claim 6, in which the carbide stabilizing elements include at least manganese, molybdenum and chromium. 23. The method according to claim 9, in which the carbide stabilizing elements include at least manganese, molybdenum and chromium.

Images