JP5462568B2 - Method for determining the number of graphite particles in spheroidal graphite cast iron - Google Patents

Description

  The present invention relates to a method for determining the number of graphite particles in spheroidal graphite cast iron, and in particular, a spheroidal graphite cast iron melt obtained by subjecting a cast iron melt obtained by melting in a melting furnace or the like to spheroidizing graphite or inoculation treatment. The present invention relates to a method capable of effectively grasping the number of spheroidal graphite particles after solidification.

  Conventionally, carbon, which is the main component of cast iron, is also apparent in Non-Patent Document 1 (January 30, 1995, published by Sangyo Tosho Co., Ltd., Hideo Nakae, “Casting Engineering”, pp. 17-27). It is known that the solidification temperature of the cast iron melt is lowered to improve the fluidity at the time of melting, and the volume of crystal expands due to the crystallization of carbon as graphite. . And these properties are also the reason why cast iron has been used a lot, and the crystallized graphite phase is overwhelmingly lower in strength than the base ferrite phase and pearlite phase, and it has thermal conductivity and vibration. Since the damping capacity is high, the material properties of cast iron are strongly influenced by the crystallization amount and distribution of graphite.

  Ductile cast iron, that is, spheroidal graphite cast iron, which is one of such cast irons, is intended to improve the strength and ductility by spheroidizing the shape of the crystallized graphite. Increasing the number of grains is expected to improve the properties of the material, such as the increase in strength and elongation, as well as the uniformity of the structure, the tendency to chilling / reducing the occurrence of shrinkage, and the increase in ferrite rate. .

  By the way, in order to confirm the number of graphite particles in spheroidal graphite cast iron, generally, the cast iron melt after the graphite spheroidizing treatment and inoculation treatment is injected into a test piece mold of a predetermined shape, solidified, and then solidified. After completion, a test piece for microscopic inspection is produced from the obtained casting. After such a test piece is cut out from a casting and polished, the number of graphite grains per unit area is obtained from several fields of view by microscopic inspection and image processing, and the average number of graphite grains is obtained. . Alternatively, a test in which a test piece is cut out from a part of a product after casting and the number of graphite grains is similarly obtained may be employed.

  However, although the data regarding the number of graphite grains obtained by such a method is used for quality control of the spheroidal graphite cast iron product, it takes time to obtain the data. It was rarely used to improve the inoculation process or to avoid risk during casting. In addition, if the number of graphite grains in the resulting spheroidal graphite cast iron can be estimated before casting the cast iron melt into the mold, whether or not the cast iron melt inoculation treatment or graphite spheroidization treatment is acceptable, or after solidification It is possible to predict the properties of cast iron products.

  On the other hand, as a method for predicting the properties of cast iron after solidification before casting the cast iron melt into a mold, one of the inventors, together with other inventors, is disclosed in Patent Document 1 (Japanese Patent No. 2750832). Note that, when the cast iron melt solidifies, carbon is crystallized as graphite (stable system) and crystallized as cementite (metastable system). ) And cementite eutectic temperature (TEC), and based on the relationship with the minimum cooling temperature (TEL) of the cast iron melt to be inspected, a method for determining and indexing the graphite nucleation ability was proposed. It has become possible to grasp the properties of molten cast iron and the properties of cast iron after solidification, such as the tendency to chill, including the effects of trace elements in flake graphite cast iron.

  And there are three sampling containers for thermal analysis used, the chilling agent is added to the first container, the cementite eutectic temperature (TEC) is measured, and the second container Without adding additives, grasp the eutectic solidification temperature change of the cast iron melt to be inspected, and further add a graphitizing agent to the third container, measure the graphite eutectic temperature (TEG), From the relationship with the eutectic solidification temperature change obtained from the second container, the properties of the cast iron melt are judged, but such a method is merely to judge the melt properties of flake graphite cast iron. Thus, the number of graphite grains of spheroidal graphite cast iron could not be obtained.

  The method proposed in the above-mentioned Patent Document 1 is merely to grasp the properties of the flake graphite cast iron melt (original hot water), and is a cast iron melt for spheroidal graphite cast iron. In addition, when a chilling agent such as tellurium is added to the first container and the cementite eutectic temperature (TEC) is measured, CV graphite cast iron and spheroidal graphite cast iron In the cast iron melt after spheroidizing treatment, magnesium and tellurium, which are spheroidizing agents, react with each other, making chilling difficult, and therefore, the cementite eutectic temperature (TEC) cannot be measured. It was a thing.

Japanese Patent No. 2750832

Nakao Hideo, “Casting Engineering”, pp. 17-27 (published on January 30, 1995, Sangyo Tosho Co., Ltd.)

  Under such circumstances, the present inventors have intensively investigated the relationship between the cast iron melt subjected to the graphite spheroidizing treatment and the inoculation treatment and the number of graphite particles in the spheroidal graphite cast iron obtained therefrom. While determining at least the supercooling inversion temperature (TSC) from the cooling curve obtained from the cooling process of the cast iron melt subjected to the crystallization treatment and its differential curve, the graphite eutectic temperature (TEG) and cementite eutectic temperature ( TEC) and the degree of graphitization calculated from those temperatures [ΔT1 / ΔTE = (TSC−TEC) / (TEG−TEC)] is calculated with respect to the number of graphite grains in the spheroidal graphite cast iron obtained from the molten cast iron. From the graphitization degree obtained in the same manner from the cast iron melt to be inspected based on the correlation and found to have a good correlation As a result, it has been reached that the number of graphite grains in the cast spheroidal graphite cast iron can be satisfactorily determined or estimated, and the present invention has been completed.

  Therefore, the problem to be solved by the present invention is to quickly and easily determine the number of graphite grains in the spheroidal graphite cast iron obtained from the spheroidal graphite cast iron melt subjected to the spheroidizing treatment and inoculation treatment. It is to provide a possible method.

  And, in order to solve the above-mentioned problems, the present invention can be suitably implemented in various aspects as listed below, but each aspect described below can be combined in any combination, It can be adopted. It should be noted that the aspects or technical features of the present invention are not limited to those described below, and can be recognized based on the description of the entire specification and the inventive concept described in the drawings. Should be understood.

(1) A cast iron melt subjected to inoculation after graphite spheroidization or graphite spheroidization is placed in a predetermined sampling container and cooled, and at least from the cooling curve obtained from the cooling process and its differential curve, While determining the supercooling reversal temperature (TSC), the graphite eutectic temperature (TEG) and the cementite eutectic temperature (TEC) of the molten cast iron were determined, and the degree of graphitization calculated from these temperatures [ΔT1 / ΔTE = ( TSC-TEC) / (TEG-TEC)], and determining the number of graphite grains in spheroidal graphite cast iron obtained from the molten cast iron based on the correlation between the number of graphite grains obtained in advance and the degree of graphitization A method for determining the number of graphite grains in spheroidal graphite cast iron.
(2) The spherical graphite according to the above aspect (1), in which the graphite eutectic temperature is determined as the higher one of the temperature corresponding to the valley in the differential curve of the cooling curve and the maximum eutectic temperature. A method for determining the number of graphite grains in cast iron.
(3) The cementite eutectic temperature is obtained from a cooling curve obtained by cooling the cast iron melt not subjected to the graphite spheroidization treatment together with a chilling agent in a sampling container. A method for determining the number of graphite grains in the spheroidal graphite cast iron according to the aspect (1) or (2).
(4) The above aspect (1), wherein the graphite eutectic temperature and / or the cementite eutectic temperature is determined from a chemical component of the cast iron melt obtained by performing graphite spheroidization treatment or inoculation treatment after graphite spheroidization treatment. The method to determine the graphite particle number in the spheroidal graphite cast iron as described in any one of thru | or (3).
(5) The graphite eutectic temperature (TEG) is expressed by the following formula:
TEG (° C.) = 1149.6 + 4.7 × Si% −4 × Mn% −44 × P% + 2.7 × Cu% + 1.0 × Ni% −10.5 × Cr% −17.7 × Mo% − 14.8 × V% −6.1 × W% −80.3 × B% −9.3 × Sn% −3.7 × Nb% −5.2 × Sb% + 13.9 × Al% + 1.8 × Co%
The method of determining the number of graphite grains in the spheroidal graphite cast iron according to the above aspect (4) calculated based on the above.
(6) The cementite eutectic temperature (TEC) is:
TEC (° C.) = 1142.7-11.6 × Si% −0.75 × Mn% −46.2 × P% −1.4 × Cu% −1.1 × Ni% + 5.9 × Cr% − 14 5 × Mo% + 3.3 × V% −2.8 × W% −26.0 × B% −6. 0 × Sn% −0.0 × Nb% −5.1 × Sb% −1.8 × Al% −0.7 × Co%
The method of determining the number of graphite grains in the spheroidal graphite cast iron according to the above aspect (4) calculated based on the above.
(7) The cast iron melt that has been inoculated after graphite spheroidization or graphite spheroidization is placed in a predetermined sampling container and cooled, and from a cooling curve obtained from the cooling process and its differential curve, at least While determining the supercooling reversal temperature (TSC), the graphite eutectic temperature (TEG) and the cementite eutectic temperature (TEC) of the molten cast iron were determined, and the degree of graphitization [ΔT1 / ΔTE = (TSC−TEC) ) / (TEG-TEC)], and the number of graphite grains in the spheroidal graphite cast iron obtained from the cast iron melt is measured, and the correlation between the number of graphite grains obtained and the degree of graphitization is expressed as follows: A step of obtaining in advance;
For the molten cast iron to be inspected, the step of calculating the degree of graphitization in the same manner as the case of obtaining the above correlation,
Based on the degree of graphitization obtained for the molten cast iron to be inspected, the number of graphite grains in the spheroidal graphite cast iron obtained from the molten iron to be inspected is determined from the correlation between the previously obtained number of graphite grains and the degree of graphitization. And a step of determining the number of graphite grains in the spheroidal graphite cast iron.
(8) The method for determining the number of graphite grains in the spheroidal graphite cast iron according to the above aspect (7), wherein the correlation is determined in consideration of a cooling rate when obtaining the spheroidal graphite cast iron from the molten cast iron to be inspected.

  Thus, in the present invention, before casting the cast iron melt that has been inoculated after the graphite spheroidizing treatment or graphite spheroidizing treatment into a mold, a part thereof is collected from the cooling process, While obtaining a cooling curve and its derivative curve, at least the supercooling inversion temperature (TSC) or the eutectic minimum temperature (TEL) is obtained, and further, the graphite eutectic temperature (TEG) and the cementite eutectic temperature (TEC) are obtained. Thus, only by calculating the degree of graphitization (ΔT1 / ΔTE), based on the calculated degree of graphitization, the number of graphite particles after solidification can be calculated from the correlation between the number of graphite grains determined in advance and the degree of graphitization. Therefore, it is possible to easily confirm whether or not the graphite spheroidization treatment and the inoculation treatment have been properly performed.

  In addition, by predicting the number of graphite particles after solidification of cast iron melt that has been subjected to such graphite spheroidization treatment and inoculation treatment, it becomes possible to optimize the cast iron in the molten state, thereby As a result, it is possible to optimize the feeders installed for this purpose, and in addition to helping to reduce production costs, the quality of spheroidal graphite cast iron products after solidification is stable and Even in the above, a beneficial advantage can be provided.

It is explanatory drawing which shows an example of an apparatus structure suitable for implementation of this invention. It is explanatory drawing which shows the representative example of the cooling curve calculated | required in the method of this invention, and its differential curve. It is explanatory drawing which plotted the relationship between the supercooling degree ((DELTA) T) obtained in the experiment relevant to this invention, and the number of graphite grains (N) in spheroidal graphite cast iron. The degree of graphitization (ΔT1 / ΔTE) determined using the undercooling inversion temperature actually measured in the examples of the present invention, the graphite eutectic temperature and the cementite eutectic temperature calculated from the chemical components of the cast iron melt, and spherical It is explanatory drawing which shows the relationship with the graphite particle number (N) in graphite cast iron. Graphitization degree (ΔT1 / ΔTE) obtained by using the measured values of the undercooling inversion temperature and the graphite eutectic temperature obtained in the examples of the present invention and the cementite eutectic temperature calculated from the chemical components of the molten cast iron It is explanatory drawing which shows the relationship between graphite particle number (N) in spheroidal graphite cast iron. It is explanatory drawing corresponding to FIG. 3 which shows the relationship between the degree of supercooling ((DELTA) T) and the number of graphite grains (N) when the magnitude | sizes of the test piece cast are different. FIG. 5 is an explanatory diagram corresponding to FIG. 4 and showing the relationship between the degree of graphitization (ΔT1 / ΔTE) and the number of graphite grains (N) when the sizes of test pieces to be cast are different. It is explanatory drawing corresponding to FIG. 5 which shows the relationship between the degree of graphitization ((DELTA) T1 / (DELTA) TE) and the number of graphite grains (N) in case the magnitude | size of the test piece cast is different. It is explanatory drawing corresponding to FIG. 3 which shows the relationship between the degree of supercooling ((DELTA) T) and the number of graphite grains (N) in the case where the magnitude | size of the test piece cast is different. It is explanatory drawing corresponding to FIG. 4 which shows the relationship between the degree of graphitization ((DELTA) T1 / (DELTA) TE) and the number of graphite grains (N) in the case where the magnitude | size of the test piece cast is different. It is explanatory drawing corresponding to FIG. 5 which shows the relationship between the degree of graphitization ((DELTA) T1 / (DELTA) TE) and the number of graphite grains (N) in the case where the magnitude | size of the test piece cast is different. An explanation showing the relationship between the cooling rate (R) and the number of graphite grains (N) during casting of the spheroidal graphite cast iron (product) obtained from the results of FIGS. 4, 7, and 10 according to the degree of graphitization. FIG.

  In short, the present invention provides at least a supercooling reversal temperature (TSC) from a cooling curve obtained from a cooling process of a so-called spheroidal graphite cast iron melt that has been subjected to graphite spheroidization treatment or inoculation treatment after graphite spheroidization treatment and its differential curve. On the other hand, the graphite eutectic temperature (TEG) and the cementite eutectic temperature (TEC) of such a cast iron melt are obtained, and the degree of graphitization (ΔT1 / ΔTE) calculated from these three temperatures is such a cast iron melt. The number of graphite grains (N in the target spheroidal graphite cast iron product in the state of the molten cast iron based on having a good correlation with the number (N) of graphite grains in the spheroidal graphite cast iron product obtained from FIG. 1 shows an example of a system that can be suitably used for carrying out such a method according to the present invention.

  In FIG. 1, reference numeral 2 denotes a sampling container equipped with a known temperature detection sensor for detecting the temperature of a thermocouple or the like, in which a cast iron melt to be measured is accommodated. It is like that. Further, the sample collection container 2 is supported by the support base 4 and is electrically connected to the support base 4 so that a signal from the temperature detection sensor can be taken out through the conductor 6. And the conducting wire 6 is connected to the signal converter 8, and detects and amplifies the signal from a temperature detection sensor, and digitizes an analog signal. Further, the signal converter 8 sends the digitized data to the arithmetic unit 10 where a cooling curve and its differential curve as shown in FIG. 2 are created.

  In the system as shown in the figure, the cast iron melt for measurement accommodated in the sampling container 2 is a cast iron melt that has been subjected to a graphite spheroidization treatment or an inoculation treatment after the graphite spheroidization treatment. It is a normal processing melt that gives a spheroidal graphite cast iron product. Here, the graphite spheroidization treatment is generally carried out in the same manner as before using magnesium, and the inoculation treatment is also graphite-based, Ba-based, Ca-Si-based, Ce-based, Bi-based, etc. The known cast inoculum is appropriately used in the same manner as before, and the cast iron melt thus obtained is used.

  Further, the cast iron melt that is inoculated after such graphite spheroidizing treatment or graphite spheroidizing treatment is cooled when a predetermined amount is accommodated in the sampling container 2 and cooled. As shown in FIG. 2, the cooling curve (A) and its differential curve (B) are calculated in the arithmetic unit 10 via the signal converter 8 based on the molten metal temperature signal detected by the temperature detection sensor in FIG. It is created.

  Further, from the obtained cooling curve (A) and differential curve (B), at least the supercooling inversion temperature (TSC), that is, the temperature corresponding to the valley in the cooling curve (A) (the temperature at the point B), so-called The eutectic minimum temperature (TEL) is determined and determined. Further, the eutectic start temperature, in other words, the temperature corresponding to the valley in the differential curve (b) (the temperature at point A) is determined from such a cooling curve (b) and the differential curve (b). Is the eutectic maximum temperature (TEH), which is higher than the temperature corresponding to the peak in the cooling curve (b) (the temperature at the point C), the eutectic start temperature is determined as the graphite eutectic temperature (TEG). ) And lower than that, the eutectic maximum temperature (TEH) is used as the graphite eutectic temperature (TEG).

Here, although partially shown in FIG. 2, the eutectic temperature difference (ΔTE), eutectic minimum temperature (TEL) or subcooling inversion temperature (TSC) and cementite co-defined as defined in the present invention are also shown. The temperature difference (ΔT1) of the crystal temperature (TEC), the degree of graphitization (ΔT1 / ΔTE) and the degree of supercooling (ΔT) are as follows.
ΔTE = TEG-TEC, ΔT1 = TSC-TEC
ΔT1 / ΔTE = (TSC-TEC) / (TEG-TEC)
ΔT = TEH-TSC

Further, the graphite eutectic temperature (TEG ; ° C ) and cementite eutectic temperature (TEC ; ° C ) described above are derived from the chemical components of the cast iron melt subjected to inoculation after graphite spheroidization or graphite spheroidization, or It can be obtained by calculation from the chemical composition of the cast iron melt before the spheroidizing spheroidization process (gentoyu). Specifically, one of the present inventors and others announced with other researchers, As has been clarified in a paper entitled “Effects of various alloying elements on crystal temperature” [“Casting Engineering” Vol. 70 (1998) No. 7, pp. 465 to 470], each was calculated according to the following calculation formula. The Rukoto.
TEG = 1149.6 + 4.7 × Si% −4 × Mn% −44 × P% + 2.7 × Cu% + 1.0 × Ni% −10.5 × Cr% −17.7 × Mo% −14.8 X V%-6.1 x W%-80.3 x B%-9.3 x Sn%-3.7 x Nb%-5.2 x Sb% + 13.9 x Al% + 1.8 x Co%
TEC = 1142.7-11.6 × Si% −0.75 × Mn% −46.2 × P% − 1.4 × Cu% −1.1 × Ni% + 5.9 × Cr% −14.5 × Mo% + 3.3 × V% −2.8 × W% −26.0 × B% −6.0 × Sn% −0.0 × Nb% −5.1 × Sb% −1.8 × Al% -0.7 × Co%

  In the above calculation formulas, the combination of element symbols such as Si% and Mn% and percentage symbols each indicate the content (mass basis) of the element in the molten cast iron. From the point where the chemical component in the molten metal changes slightly due to the addition of the graphite spheroidizing agent and the inoculant, preferably, the chemical component of the molten cast iron that is subjected to the graphite spheroidizing treatment or the inoculating treatment thereafter It will be determined using the quantity. Further, 0.0 × Nb% in the above TEC calculation formula clarifies that the contribution ratio of Nb is zero. Furthermore, since the content of elements other than Si in these two calculation formulas is small, and the contribution ratio is low as a whole, these two calculation formulas are simplified considering only the Si content. Further, TEG = 1149.6 + 4.7 × Si% and TEC = 1142.7-11.6 × Si% can also be used.

  Furthermore, the cementite eutectic temperature (TEC) used in the present invention can also be actually measured according to other known methods. For example, as disclosed in Patent Document 1 described above, graphite spheroidization is possible. Sampling with cast iron melt (source hot water) that has not been treated or inoculated with known chilling agents such as tellurium or a part of which is replaced with Se, Bi, Cr, etc. It is also possible to obtain it from the obtained cooling curve by storing it in a container and allowing it to cool.

  The following thermal analysis experiment was conducted in order to examine how the graphitization degree (ΔT1 / ΔTE) defined above has a relationship with the number of graphite grains in the spheroidal graphite cast iron.

  First, after melting the cast iron material using a high frequency furnace, using magnesium as a graphite spheroidizing agent, a graphite spheroidizing treatment is performed by a pouring method, and the Si content is 1.9%, 2.0%, 50 kg of various cast iron melts of 2.1%, 2.5%, 2.7% or 3.0% were prepared. The other chemical components of each cast iron melt were adjusted to 3.7% C, 0.20% Mn, 0.060% Mg, and 0.0040% Sb, respectively. Here, all the percentages are expressed on a mass basis.

  Next, various types of graphite spheroidized cast iron melts having different Si contents were individually returned to the high-frequency furnace, and a fading test was carried out at 1350 ° C. At this time, graphite-based, Ba-based, Ca-Si-based, Ce-based, or Bi-based inoculums are added to each molten metal at various timings, and 0 minutes, 1 minute, 2.5 minutes, and 5 minutes. 7.5 minutes, 10 minutes, 15 minutes, every 20 minutes, poured into a CE meter cup for thermal analysis (diameter 30 mm x height 50 mm) (sample collection container) and allowed to cool naturally. Based on the apparatus configuration shown in FIG. 1, the supercooling inversion temperature (TSC) and the graphite eutectic temperature (TEG) were determined from the cooling curve obtained from the cooling process and the differential curve, respectively. Moreover, about the cementite eutectic temperature (TEC) of each molten metal, it calculated | required based on the previous formula from the elemental analysis value using the emission analysis apparatus with the graphite eutectic temperature (TEG).

In addition, using a test piece made of spheroidal graphite cast iron (ingot) having a diameter of 30 mm × height of 50 mm obtained from each cast iron melt, a test piece for microscopic inspection was cut out and polished, and then a microscope By inspection, the number of graphite grains per unit area (N, pieces / mm ² ) was measured. The number of graphite particles was counted for large particles having a diameter of 10 μm or more, and smaller particles were cut, and the average value of values measured at 28 locations for each test piece was obtained.

  The relationship between the number of graphite grains (N) thus obtained and the degree of supercooling (ΔT) obtained from the thermal analysis curve (cooling curve) is plotted in FIG. 3, where the number of graphite grains is shown. No correlation can be observed between (N) and the degree of supercooling (ΔT). In addition, in this FIG. 3, the numbers of Si and% shown in parentheses on the right side of each inoculum indicate the Si content in the cast iron molten metal (former hot water), and Ca- In the symbols indicating the results using the Si-based inoculant, only those indicated by arrows were tested using the cast iron melt having the Si content indicated therein, and Ca-Si without arrows. All the system symbols indicate the results when a cast iron melt having a Si content of 2.1% is used. Such a display form is the same in FIGS. 4 to 11 described below.

  In addition, while obtaining the supercooling reversal temperature (TSC) from the cooling curves and their differential curves for various cast iron melts obtained by the thermal analysis described above, the graphite eutectic temperature (TEG) and the cementite coexistence of each melt are obtained. The crystallization temperature (TEC) is calculated from the component analysis results of each molten metal based on the TEG calculation formula and the TEC calculation formula described above, and the graphitization degree [ΔT1 / ΔTE] is calculated from these three temperatures. When the relationship between the obtained graphitization degree and the number of graphite grains (N) in the spheroidal graphite cast iron (test piece) obtained from each cast iron melt is plotted, a good correlation is obtained as shown in FIG. I was able to get a relationship.

  That is, in FIG. 4, even if the type of the inoculum and the content of the chemical component (Si) in the molten metal are changed, a high correlation is observed between the degree of graphitization and the number of graphite grains, If the degree of graphitization is ΔT1 / ΔTE and the number of graphite grains is N, an approximate linear equation (correlation coefficient r = 0.97) shown as N = 613 × (ΔT1 / ΔTE) −126 can be recognized. .

  In addition to the overcooling inversion temperature (TSC), the graphite eutectic temperature (TEG) was measured from the cooling curve obtained by the thermal analysis and its differential curve, and only the cementite eutectic temperature (TEC) was measured. As shown in FIG. 5, the graphitization degree [ΔT1 / ΔTE] was calculated from the above calculation formula, and compared with the number of graphite grains (N) in each spheroidal graphite cast iron (test piece). It was possible to recognize a significant correlation. That is, even if the kind of inoculum and the content of Si as a chemical component in the molten metal are changed, a high correlation is observed between the degree of graphitization and the number of graphite grains, and the degree of graphitization is ΔT1 / ΔTE, When the number of graphite grains is N, N = 614 × (ΔT1 / ΔTE) −205 (correlation coefficient r = 0.95) can be obtained as an approximate linear equation.

  Furthermore, in the above thermal analysis experiment, when the size of the CE tester cup (sampling container) for thermal analysis is changed, the size of the obtained test piece is changed, and the casting conditions, particularly the cooling rate, are changed. Even so, a good relationship is recognized between the degree of graphitization and the number of graphite grains, and the results are shown in FIGS. That is, FIGS. 6 to 8 were obtained when a CE meter cup having a diameter of 40 mm and a height of 50 mm was used, and therefore a test piece having a diameter of 40 mm and a height of 50 mm was cast. FIGS. 9 to 11 show the results obtained when casting a test piece having a diameter of 200 mm and a height of 200 mm, respectively. FIG. 6 is an explanatory diagram corresponding to FIGS. 3 to 5, respectively.

  As shown in FIGS. 7 and 8 showing the relationship between the degree of graphitization and the number of graphite grains when a test piece having a diameter of 40 mm and a height of 50 mm was produced, the degree of graphitization and the number of graphite grains Is a high correlation between the degree of graphitization and the number of graphite grains even when the type of inoculum and the Si content in the melt are changed. In FIG. 7, the approximate linear equation: N = 564 × (ΔT1 / ΔTE) −132 (correlation coefficient r = 0.97) is obtained, and in FIG. 8, the approximate linear equation: N = 529 × (ΔT1 / ΔTE) −173 (correlation coefficient r = 0. 95) is obtained.

  FIGS. 10 and 11 showing the relationship between the degree of graphitization and the number of graphite grains when the test piece size is 200 mm in diameter and 200 mm in height correspond to FIGS. 4 and 5, respectively. However, as in these figures, a high correlation is recognized between the degree of graphitization and the number of graphite grains even when the type of inoculum and the Si content in the molten metal are changed. The approximate linear equation in FIG. 10 is N = 154 × (ΔT1 / ΔTE) −29 (correlation coefficient r = 0.96), and the approximate linear equation in FIG. 11 is N = 155 × (ΔT1 / ΔTE). -48 (correlation coefficient r = 0.97).

  From the above, the number of graphite particles in spheroidal graphite cast iron is proportional to the nucleation capacity taking into account the molten metal component, that is, the degree of graphitization (ΔT1 / ΔTE). Correlation with the degree of graphitization is obtained in advance, based on the graphite spheroidization treatment or the cast iron melt that has been inoculated after the graphite spheroidization treatment and compared with the degree of graphitization obtained in the same procedure. The number of graphite particles in a spheroidal graphite cast iron product obtained from a graphite iron spheroidized / inoculated cast iron melt can be effectively judged or estimated, and such a degree of graphitization is basically Since it can be obtained using the value obtained from the cooling curve and its differential curve or calculation formula, the number of graphite grains can be judged or estimated quickly and easily.

  Note that the correlation between the number of graphite grains and the degree of graphitization is clearly shown in the comparison between FIG. 4 and FIG. 5, the comparison between FIG. 7 and FIG. 8, and the comparison between FIG. 10 and FIG. In calculating the degree of graphitization, depending on whether one actual measurement value (TSC) or two actual measurement values (TSC and TEG) are used, a slightly different approximate linear equation is given. In determining the number of graphite grains in cast iron, the calculation conditions for the degree of graphitization for obtaining the correlation and the calculation conditions for the degree of graphitization of the molten cast iron that gives the spheroidal graphite cast iron are unified, in other words, the actual measurement used. It is desirable to make the number of values the same, and this can improve the accuracy of determination of the number of graphite grains.

  As is clear from the comparison between FIGS. 4 and 5 and FIGS. 7 and 8 and FIGS. 10 and 11, also when the size of the test piece changes, that is, when the casting conditions, particularly the cooling rate (conditions) are different. Since the correlation between the number of graphite grains and the degree of graphitization is affected, the size of the test piece for obtaining the correlation may be matched with the size of the target spheroidal graphite cast iron product. By matching the casting conditions, for example, by matching the cooling conditions during casting, the correlation between the number of graphite grains and the degree of graphitization of those closer to the target spheroidal graphite cast iron product is further obtained. The accuracy of determining the number of graphite grains can be increased.

  Furthermore, apart from the above, the correlation between the number of graphite grains and the degree of graphitization is considered in consideration of the cooling rate when casting the target spheroidal graphite cast iron product from the cast iron melt to be inspected. It is also effective to obtain (in consideration), and an example is shown in FIG. FIG. 12 is a graph plotting the relationship between the cooling rate and the number of graphite grains during the production of each test piece according to the degree of graphitization using the results shown in FIGS. 4, 7 and 10. (However, when the degree of graphitization is 0.3 and 1.0, it is an estimated value from the approximate linear equation, and when the cooling rate is 200 ° C./min, both are shown as empirical values or estimated values. In any case of graphitization, the cooling rate and the number of graphite grains can be related with an effective approximate linear equation. Then, from these approximate linear expressions, the relational expression between the degree of graphitization (ΔT1 / ΔTE) and the number of graphite grains (N) in consideration of the cooling rate (R): N = [4.26 × (ΔT1 / ΔTE) − 0.9] × (R + 30) (correlation coefficient r = 0.99), and the cooling rate (product size) at the time of casting between the test piece and the spheroidal graphite cast iron product is different. However, if the cooling rate of the spheroidal graphite cast iron product is clear, the number of graphite grains in the product can be determined or estimated from the above relational expression using the degree of graphitization required for the test piece. When the graphitization degree is 0.3 or less, “chill” is generated. In FIG. 12, an approximate linear expression with a graphitization degree of 0.3: N = 0.56 × R + 18 is used as a reference. Thus, it can be used to determine the occurrence of chill.

  In addition, the relationship between the number of graphite particles in the test piece and the number of graphite particles in the target spheroidal graphite cast iron product is obtained, and based on the relationship, the correlation is converted and the degree of graphitization of the cast iron melt that gives the test piece In addition, the number of graphite particles in the target spheroidal graphite cast iron product can also be obtained, and furthermore, the degree of graphitization obtained from the cast iron melt giving the test piece is directly determined by the number of graphite particles in the target spheroidal graphite cast iron product. It is also possible to determine the number of graphite grains from the degree of graphitization obtained from the cast iron melt that gives the test piece based on the correlation.

  In any case, there is basically a predetermined correlation between the number of graphite grains in the spheroidal graphite cast iron product and the spheroidal graphite cast iron melt that gives it, and such a correlation. Based on the above, it is possible to effectively determine or estimate the number of graphite grains in the target spheroidal graphite cast iron product.

  By the way, when concretely carrying out the present invention, generally, (a) a cast iron melt subjected to inoculation after graphite spheroidization or graphite spheronization is accommodated in a predetermined sampling container and cooled. From the cooling curve obtained from the cooling process and its differential curve, at least the supercooling inversion temperature (TSC) is obtained, while the graphite eutectic temperature (TEG) and the cementite eutectic temperature (TEC) of the molten cast iron are obtained, and The degree of graphitization [ΔT1 / ΔTE = (TSC-TEC) / (TEG-TEC)] was calculated from the temperature of the steel, and the number of graphite particles in the spheroidal graphite cast iron obtained from the cast iron melt was measured and obtained. The step of obtaining the correlation between the number of graphite grains and the degree of graphitization in advance, and (b) calculating the degree of graphitization in the same manner as the case of obtaining the above correlation for the molten cast iron to be inspected. And (c) a spheroidal graphite obtained from the molten cast iron to be inspected based on the correlation between the number of graphite grains and the degree of graphitization determined in advance based on the degree of graphitization obtained for the molten cast iron to be inspected. A method including a step of determining the number of graphite grains in cast iron is suitably employed. At that time, the molten cast iron for obtaining the correlation and the molten cast iron to be inspected generally contain chemical components other than Si in substantially the same proportion, and basically include the cooling rate. By setting the casting conditions in substantially the same manner, it is possible to further increase the accuracy of determining the number of graphite grains in the target spheroidal graphite cast iron product. In addition, as described above, it is also advantageously employed to obtain the correlation in consideration of the cooling rate when obtaining spheroidal graphite cast iron from the molten cast iron to be inspected.

  The exemplary embodiments of the present invention have been described in detail above, but these are merely examples, and the present invention is not limited in any way by specific descriptions according to such embodiments. It should be understood that this is not to be interpreted.

  For example, it is not necessary to actually show the cooling curve and its differential curve obtained by cooling a cast iron melt subjected to graphite spheroidization treatment or inoculation treatment, as shown in FIG. It is also possible to directly take out the supercooling inversion temperature (TSC) and the graphite eutectic temperature (TEG) by processing on the computer based on this signal, which makes it even faster and simpler The degree of graphitization can be detected, and further, based on the correlation between the degree of graphitization and the number of graphite grains stored in advance by a computer, the graphite grains in the target spheroidal graphite cast iron can be detected. The number can be determined advantageously.

  Further, in the example of the system suitable for carrying out the present invention shown in FIG. 1, the signal conversion device 8 can be integrated and incorporated in the arithmetic device 10, and further, only the exponent is displayed / transmitted. Alternatively, it is possible to provide a printing device and output by printing.

  In addition, although not listed one by one, the present invention can be implemented in a mode with various changes, modifications, improvements, and the like based on the knowledge of those skilled in the art. It goes without saying that any one of them falls within the scope of the present invention without departing from the spirit of the invention.

2 Sampling container 4 Support base 6 Conductor 8 Signal converter 10 Arithmetic unit

Claims (8)

  Cast iron melt that has been inoculated after graphite spheroidizing or graphite spheroidizing treatment is placed in a predetermined sampling container and cooled, and at least supercooling is reversed from the cooling curve obtained from the cooling process and its differential curve. While obtaining the temperature (TSC), the graphite eutectic temperature (TEG) and the cementite eutectic temperature (TEC) of the molten cast iron were obtained, and the degree of graphitization [ΔT1 / ΔTE = (TSC−TEC) calculated from these temperatures. ) / (TEG-TEC)], the number of graphite grains in the spheroidal graphite cast iron obtained from the cast iron melt is determined from the correlation between the number of graphite grains obtained in advance and the degree of graphitization. A method for determining the number of graphite grains in graphite cast iron.   2. The graphite grains in the spheroidal graphite cast iron according to claim 1, wherein the graphite eutectic temperature is determined as a higher one of a temperature corresponding to a valley in the differential curve of the cooling curve and a maximum eutectic temperature. How to determine the number.   The said cementite eutectic temperature is calculated | required from the cooling curve obtained by accommodating the said cast iron molten metal in which the graphite spheroidization process is not given with a chilling agent, and cooling it. Alternatively, a method for determining the number of graphite grains in the spheroidal graphite cast iron according to claim 2.   The graphite eutectic temperature and / or the cementite eutectic temperature is obtained from a chemical component of the cast iron melt obtained by inoculation after graphite spheroidization or graphite spheroidization. A method for determining the number of graphite grains in the spheroidal graphite cast iron according to any one of the above items. The graphite eutectic temperature (TEG) is represented by the following formula:
TEG (° C.) = 1149.6 + 4.7 × Si% −4 × Mn% −44 × P% + 2.7 × Cu% + 1.0 × Ni% −10.5 × Cr% −17.7 × Mo% − 14.8 × V% −6.1 × W% −80.3 × B% −9.3 × Sn% −3.7 × Nb% −5.2 × Sb% + 13.9 × Al% + 1.8 × Co%
The method of determining the number of graphite grains in the spheroidal graphite cast iron according to claim 4 calculated based on the above.
The cementite eutectic temperature (TEC) is expressed by the following formula:
TEC (° C.) = 1142.7-11.6 × Si% −0.75 × Mn% −46.2 × P% −1.4 × Cu% −1.1 × Ni% + 5.9 × Cr% − 14 5 × Mo% + 3.3 × V% −2.8 × W% −26.0 × B% −6. 0 × Sn% −0.0 × Nb% −5.1 × Sb% −1.8 × Al% −0.7 × Co%
The method of determining the number of graphite grains in the spheroidal graphite cast iron according to claim 4 calculated based on the above.
Cast iron melt that has been inoculated after graphite spheroidizing or graphite spheroidizing treatment is placed in a predetermined sampling container and cooled, and at least supercooling is reversed from the cooling curve obtained from the cooling process and its differential curve. While determining the temperature (TSC), the graphite eutectic temperature (TEG) and the cementite eutectic temperature (TEC) of the molten cast iron were determined, and the degree of graphitization [ΔT1 / ΔTE = (TSC−TEC) / ( TEG-TEC)] and calculating the correlation between the number of graphite grains obtained and the degree of graphitization in advance by measuring the number of graphite grains in the spheroidal graphite cast iron obtained from the cast iron melt When,
For the molten cast iron to be inspected, the step of calculating the degree of graphitization in the same manner as the case of obtaining the above correlation,
Based on the degree of graphitization obtained for the molten cast iron to be inspected, the number of graphite grains in the spheroidal graphite cast iron obtained from the molten iron to be inspected is determined from the correlation between the previously obtained number of graphite grains and the degree of graphitization. And a step of determining the number of graphite grains in the spheroidal graphite cast iron.   The method for determining the number of graphite grains in the spheroidal graphite cast iron according to claim 7, wherein the correlation is determined in consideration of a cooling rate when obtaining the spheroidal graphite cast iron from the molten cast iron to be inspected.

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