Method for judging inoculation effect of gray cast iron

Abstract

The invention relates to a method for judging the inoculation effect of gray cast iron in the technical field of casting. The method comprises the steps that a temperature-time curve in the molten iron cooling process is obtained through a thermal analysis technology; performing integral and differential calculation on the temperature-time curve to obtain characteristic values, calculating the graphite precipitation degree of the gray cast iron and the proportion of flake graphite according to the characteristic values, and quantitatively judging the inoculation effect of the gray cast iron according to the graphite precipitation degree and the proportion of flake graphite. According to the method for judging the inoculation effect of the gray cast iron, the inoculation effect of the gray cast iron can be rapidly and quantitatively judged under the condition that the metallographic phase of the casting does not need to be observed, and the inspection efficiency of the casting is improved.

Description

Technical Field

[0001] The present application relates to the field of casting technology, and in particular to a method for judging the inoculation effect of grey cast iron. Background Art

[0002] When producing gray cast iron, it is required to obtain a pearlite matrix plus flake graphite, in which the graphite morphology is mainly controlled by inoculation treatment. At present, the inoculation effect, that is, whether the graphite of gray cast iron is flake graphite of a certain length, is determined by observing the metallographic photos of cast iron. Therefore, it can only be inspected after the casting is completed, which makes the inspection efficiency low. Summary of the invention

[0003] In view of the problems existing in the background technology, the present application provides a method for judging the inoculation effect of grey cast iron. This method can quickly and quantitatively judge the inoculation effect of grey cast iron without observing the metallographic structure of the casting, thereby improving the inspection efficiency of the casting.

[0004] According to one aspect of the present invention, there is provided a method for judging the inoculation effect of grey cast iron, comprising: obtaining a temperature-time curve during the cooling process of molten iron using a thermal analysis technique; integrating and differentiating the temperature-time curve to obtain a characteristic value, calculating the degree of graphite precipitation and the proportion of flake graphite in the grey cast iron according to the characteristic value, and quantitatively judging the inoculation effect of the grey cast iron according to the degree of graphite precipitation and the proportion of flake graphite.

[0005] In some embodiments of the present invention, the temperature-time curve is provided with a eutectic starting point T1 and a eutectic ending point T2; the temperature-time curve between the eutectic starting point T1 and the eutectic ending point T2 and the straight line between the two points are set to form an ideal area S max ; Establish the relationship between different carbon contents C% and ideal area S of gray cast iron max In actual production, the current molten iron is taken for thermal analysis and carbon content detection to obtain the temperature-time curve of the current molten iron and the carbon content C0% of the current molten iron, and the eutectic starting point T10 and the eutectic ending point T20 of the current molten iron are obtained according to the temperature-time curve of the current molten iron; the instantaneous area S of the current molten iron is calculated using the temperature-time curve between the eutectic starting point T10 and the eutectic ending point T20 of the current molten iron and the straight line between the two points ins , using the different carbon content C% of gray cast iron and the ideal area S max The ideal area S of the current molten iron is calculated by the linear relationship between and the carbon content C0% of the current molten iron max-0 ; Compare the current instant area S of the molten iron ins and the ideal area S max-0 , and the degree of graphite precipitation in gray cast iron was obtained.

[0006] In some embodiments of the present invention, according to S ins / Smax-0 The ratio of S is used to determine the degree of graphite precipitation in the gray cast iron; when S ins / S max-0 ≥0.9, it means that graphite is fully precipitated; when 0.7≤S ins / S max-0 When S is less than 0.9, it indicates that graphite precipitation is insufficient; ins / S max-0 When <0.7, it means that there is no graphite precipitation or a small amount of graphite precipitation.

[0007] In some embodiments of the present invention, the eutectic starting point T1 is the first point on the temperature-time curve when the temperature reduction rate starts to be lower than 0.4°C / s before the eutectic minimum temperature TEU; the eutectic ending point T2 is the temperature point on the temperature-time curve corresponding to the maximum value T2" ​​of the second-order differential of the temperature-time curve at the end of solidification.

[0008] In some embodiments of the present invention, the gray cast iron has different carbon contents C% and ideal area S max The linear relationship is: S max =-3913+1857*C.

[0009] In some embodiments of the present invention, the gray cast iron has different carbon contents C% and ideal area S max The linear relationship is obtained by fitting the curve data with the eutectic minimum temperature TEU temperature above 1142℃.

[0010] In some embodiments of the present invention, the first-order differential curve of the temperature-time curve is provided with a t1 point and a t2 point, wherein the t1 point is the lowest point on the first-order differential curve of the corresponding stage between the initial crystallization temperature TL and the eutectic minimum temperature TEU, and the t2 point is the highest point on the first-order differential curve after the eutectic minimum temperature TEU; the time difference of the temperature-time curve between the t1 point and the t2 point is set to Δt; a formula for the influence of the flake graphite ratio of the eutectic minimum temperature TEU and Δt is established; in actual production, the current molten iron is taken for heat treatment. Analyze and detect to obtain the temperature-time curve of the current molten iron, obtain the eutectic minimum temperature TEU0 according to the temperature-time curve of the current molten iron, and calculate the first-order differential curve, obtain the t10 point and the t20 point according to the first-order differential curve of the current molten iron, and then calculate the time difference Δt0 of the temperature-time curve between the t10 point and the t20 point; calculate the flake graphite ratio of gray cast iron using the eutectic minimum temperature TEU and Δt influence formula and the eutectic minimum temperature TEU0 and Δt0 of the current molten iron.

[0011] In some embodiments of the present invention, the influence formula of the ratio of flake graphite on the eutectic minimum temperature TEU and Δt is: ratio of flake graphite = -10.9 + 0.0104 * TEU - 0.00270 (TEU - 1142.29) 2 -0.000243(Δt-59.44) 2 .

[0012] An embodiment of the present application provides a method for judging the inoculation effect of gray cast iron. The method obtains the degree of graphite precipitation and the proportion of flake graphite in the gray cast iron by integrating and differentiating the temperature-time curve during the cooling process of the molten iron. Compared with the current method of determining the inoculation effect by observing the metallographic photographs of the cast iron, the present invention can quickly judge the inoculation effect of the gray cast iron without observing the metallographic phase of the casting, thereby improving the inspection efficiency of the casting. Compared with the current qualitative judgment of the graphite precipitation tendency, the present invention can quantitatively judge the inoculation effect of the gray cast iron, has a higher utilization value, and can be directly used for adjusting production parameters to optimize the casting process. The present invention changes the evaluation of the inoculation effect of the gray cast iron from qualitative to quantitative evaluation, that is, determines two evaluation indicators, the degree of graphite precipitation and the proportion of flake graphite. When the two indicators reach the preset values, it is considered that the inoculation effect of the gray cast iron meets the requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Various other advantages and benefits will become apparent to those skilled in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only used to illustrate the preferred embodiments and are not to be considered as limiting the present application. In the accompanying drawings:

[0014] Figure 1 It is the temperature-time curve of the cooling of grey cast iron;

[0015] Figure 2 It is the temperature-time curve of grey cast iron (A) and its second-order differential curve diagram (B);

[0016] Figure 3 It is a schematic diagram of the area calculation of the temperature-time curve of gray cast iron;

[0017] Figure 4 It is the temperature-time curve of grey cast iron and its first-order derivative (differential) curve;

[0018] Figure 5 It is different from Experimental Example 1 ins / S max Metallographic diagram of the sample with ratio;

[0019] Figure 6 It is the metallographic diagram corresponding to the calculated values ​​of different flake graphite ratios in Experimental Example 2. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will easily recognize multiple non-critical parameters, which can be changed or modified, and the results are substantially the same.

[0021] If no specific technology or conditions are specified in the examples, the technology or conditions described in the literature in this field or the product instructions are used. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased through regular channels. The experimental methods in the following examples are all conventional methods unless otherwise specified. The test materials used in the following examples are all commercially available products unless otherwise specified.

[0022] In the present invention, grey cast iron refers to an iron-carbon alloy in which most of the carbon exists in the form of flake graphite; inoculation treatment refers to the addition of a small amount of other substances to liquid metal during its solidification process to promote nucleation and change its organizational morphology, and the added substance is called an inoculant; thermal analysis technology refers to the use of a thermal analyzer to collect the temperature-time curve of cast iron liquid during cooling to predict the composition and organization of cast iron; eutectic reaction refers to the eutectic reaction of the alloy when the component ratio of the alloy reaches a certain value at a temperature lower than the melting point of any component metal, that is, two different solid phases are simultaneously generated from one liquid phase.

[0023] At present, the determination of the inoculation effect is often based on observing the metallographic photographs of cast iron. Therefore, the inspection can only be carried out after the casting is completed, which makes the inspection efficiency low.

[0024] In addition, if Figure 1 As shown, during the cooling process of cast iron liquid (temperature-time curve), there are nodes such as TL-initial crystallization temperature, TEU-eutectic minimum temperature, TER-eutectic maximum temperature, and TS-eutectic end temperature.

[0025] At present, the lowest eutectic temperature TEU and rebrightness R (the difference between TER and TEU) are also used to judge the inoculation effect. It is believed that the higher the TEU, the better, and the smaller the rebrightness R, the better. However, this method can only qualitatively judge the tendency of graphite precipitation, and the range is wide. It cannot directly judge the amount of graphite precipitation and graphite morphology, and it cannot be used for production parameter control.

[0026] Based on this, the present application provides a method for judging the inoculation effect of gray cast iron. By using thermal analysis technology, the temperature-time curve of the hypoeutectic (gray cast iron) molten iron during the cooling process is obtained, and the temperature-time curve is integrated and differentiated. According to the calculated characteristic value, the inoculation effect of gray cast iron can be quickly judged, and the inoculation effect of gray cast iron can be quantitatively evaluated for the adjustment of production parameters.

[0027] The present invention discloses a method for judging the inoculation effect of gray cast iron, and the method for judging the inoculation effect of gray cast iron comprises the following steps:

[0028] Firstly, the temperature-time curve of the molten iron cooling process is obtained by using thermal analysis technology.

[0029] Then the temperature-time curve is integrated and differentiated to obtain the characteristic value.

[0030] Then, the graphite precipitation degree and flake graphite ratio of grey cast iron are calculated according to the characteristic values, and the grey cast iron inoculation effect is quantitatively judged according to the graphite precipitation degree and flake graphite ratio.

[0031] The method of the present invention obtains the gray cast iron graphite precipitation degree and the flake graphite ratio by integrating and differentiating the temperature-time curve during the cooling process of the molten iron. Compared with the current method of determining the inoculation effect by observing the cast iron metallographic photograph, the present invention can quickly judge the gray cast iron inoculation effect without observing the metallographic phase of the casting, thereby improving the inspection efficiency of the casting. Compared with the current method of qualitatively judging the graphite precipitation tendency, the present invention can quantitatively judge the gray cast iron inoculation effect, has a higher utilization value, and can be directly used for adjusting production parameters to optimize the casting process.

[0032] In some embodiments of the present invention, the calculation of the degree of graphite precipitation in grey cast iron comprises the following steps:

[0033] First, if Figure 2 As shown in A in FIG. 1 , a eutectic starting point T1 and a eutectic ending point T2 are set on the temperature-time curve.

[0034] like Figure 3 As shown, the present invention sets the temperature-time curve between the eutectic starting point T1 and the eutectic ending point T2 and the straight line between the two points to form an ideal area S max .

[0035] In the present invention, the ideal area S max It indicates that the reaction in the eutectic stage is sufficient and carbon has generated graphite to the maximum extent, which serves as a reference value for characterizing the maximum precipitation amount of graphite in gray cast iron.

[0036] Then establish the relationship between different carbon contents C% and ideal area S of gray cast iron max linear relationship.

[0037] Afterwards, during actual production, the current molten iron is taken for thermal analysis and carbon content detection to obtain the temperature-time curve of the current molten iron and the carbon content C0% of the current molten iron. According to the temperature-time curve of the current molten iron, the eutectic start point T10 and the eutectic end point T20 of the current molten iron can be obtained.

[0038] Then, the instantaneous area S of the current molten iron is calculated using the temperature-time curve between the eutectic starting point T10 and the eutectic ending point T20 of the current molten iron and the straight line between the two points. ins , using the different carbon content C% of gray cast iron and the ideal area S max The ideal area S of the current molten iron is calculated by the linear relationship between and the carbon content C0% of the current molten iron max-0 .

[0039] By comparing the current instant area S of the molten iron ins and the ideal area S max-0 , the degree of graphite precipitation in gray cast iron can be obtained.

[0040] It should be understood that the current instantaneous area S of the molten iron is ins The closer to the ideal area S max-0 The higher the degree of graphite precipitation in gray cast iron, the better the gray cast iron inoculation effect.

[0041] In some embodiments of the present invention, the temperature-time curve between the eutectic starting point T10 and the eutectic ending point T20 of the current molten iron and the instantaneous area S of the area enclosed by the straight line between the two points ins Can be calculated by integration.

[0042] In some embodiments of the present invention, according to S ins / S max-0 The ratio of quantifies the degree of graphite precipitation in grey cast iron, specifically:

[0043] When S ins / S max-0 When ≥0.9, it means that graphite is fully precipitated.

[0044] When 0.7≤S ins / S max-0 When it is less than 0.9, it indicates that the graphite precipitation is insufficient, that is, the graphite has been precipitated to a certain extent but has not reached the full precipitation degree.

[0045] When S ins / S max-0 When <0.7, it means that there is no graphite precipitation or a small amount of graphite precipitation.

[0046] In some embodiments of the present invention, Figure 2 As shown in A, the eutectic starting point T1 is the first point on the temperature-time curve when the temperature drop rate starts to be lower than 0.4℃ / s before the eutectic minimum temperature TEU; Figure 2 As shown in B, the eutectic end point T2 is the temperature point on the temperature-time curve corresponding to the maximum value T2" ​​of the second-order differential of the temperature-time curve at the end of solidification.

[0047] In some embodiments of the present invention, gray cast iron with different carbon content C% and ideal area S max The linear relationship is:

[0048] S max = -3913+1857*C (1);

[0049] Gray cast iron with different carbon content C% and ideal area S max The linear relationship is obtained by fitting the curve data with the eutectic minimum temperature TEU temperature above 1142℃.

[0050] In some embodiments of the present invention, the calculation of the proportion of flake graphite in grey cast iron comprises the following steps:

[0051] First, if Figure 4 As shown, the black curve is the thermal analysis temperature-time curve, the blue curve is the first-order differential curve, and the first-order differential curve of the temperature-time curve is provided with points t1 and t2.

[0052] Among them, point t1 is the lowest point on the first-order differential curve of the corresponding stage between the initial crystallization temperature TL and the lowest eutectic temperature TEU, and point t2 is the highest point on the first-order differential curve after the lowest eutectic temperature TEU.

[0053] The time difference of the temperature-time curve between point t1 and point t2 is set to Δt.

[0054] Then, the influence formula of the proportion of flake graphite on the lowest eutectic temperature TEU and Δt was established.

[0055] Afterwards, in actual production, the current molten iron is taken for thermal analysis and detection to obtain the temperature-time curve of the current molten iron, and the lowest eutectic temperature TEU0 is obtained according to the temperature-time curve of the current molten iron, and the first-order differential curve is calculated, and the t10 point and t20 point are obtained according to the first-order differential curve of the current molten iron, and then the time difference Δt0 of the temperature-time curve between the t10 point and the t20 point is calculated.

[0056] Then, the flake graphite ratio of gray cast iron is specifically calculated by using the lowest eutectic temperature TEU and Δt's influence formula and the lowest eutectic temperature TEU0 and Δt0 of the current molten iron.

[0057] It should be understood that the greater the proportion of flake graphite in the current molten iron, the better the grey cast iron inoculation effect.

[0058] In some embodiments of the present invention, the influence formula of the eutectic minimum temperature TEU and the proportion of flake graphite of Δt is:

[0059] A= -10.9+0.0104*TEU-0.00270(TEU-1142.29)2 -0.000243(Δt-59.44) 2 (2);

[0060] Where A is the proportion of flake graphite.

[0061] In order to better explain the present invention, the method for judging the inoculation effect of grey cast iron of the present application is described in detail below in combination with specific experimental data.

[0062] Experimental Example 1

[0063] Under the condition of carbon content of 3.30%, a cylindrical thermal analysis sample cup was used to cast the test block, and the hot metal samples under different inoculation conditions were thermally analyzed. The carbon content of 3.30% was substituted into the above formula (1) to calculate the S ins and S ins / S max The results are shown in Table 1. The metallographic characteristics of the other four samples are shown in Table 1. Figure 5 shown.

[0064] Table 1C-3.30% S under different conditions ins and S ins / S max

[0065]

[0066] Samples 1 and 2 S ins / S max All ≥ 0.9, compared Figure 5 The metallographic images of No. 1 and No. 2 shown in the figure show that graphite is fully precipitated; No. 3 sample S ins / S max =0.84<0.9, contrast Figure 5 The metallographic image of sample 3 shown in the figure shows that graphite precipitation is insufficient; sample 4 S ins / S max =0.65<0.7, contrast Figure 5 The metallographic diagram of No. 4 shown in the figure shows that only a very small amount of graphite is precipitated. By comparing the calculated results of the graphite precipitation degree of the gray cast iron in this experimental example with the metallographic observation results, it is shown that the two are highly consistent. That is to say, the present invention, without relying on metallographic observation, can accurately obtain the graphite precipitation degree of the casting when the casting is completed based on the temperature-time curve obtained by thermal analysis technology and the integral and differential calculation of the temperature-time curve, thereby quantitatively judging the gray cast iron inoculation effect.

[0067] Experimental Example 2

[0068] Using a cylindrical thermal analysis sample cup, the test block was cast and the hot metal samples under different inoculation conditions were thermally analyzed to obtain their TEU and Δt. The TEU and Δt were substituted into the above formula (2) to calculate the flake graphite ratio A, and the metallographic observation values ​​were obtained by metallographic observation. The results are shown in Table 2. The metallographic observation values ​​of samples 6, 8, 11, 12, 15, and 16 are shown in Table 2. Figure 6 shown.

[0069] Table 2 Comparison of the flake graphite ratio A calculated according to the formula and the observed value

[0070] Sample TEU Δt Metallographic observation value Calculated value A error 5 1128.2 96 0％ -9％ 9％ 6 1127.5 87 10％ 2％ 8％ 7 1133.1 72 55％ 60％ -5％ 8 1134.1 96 30％ 31％ -1％ 9 1139.2 72 80％ 86％ -6％ 10 1137.5 89 65％ 59％ 6％ 11 1142.1 50 98％ 95％ 3％ 12 1142.1 60 100％ 97％ 3％ 13 1144.6 55 100％ 99％ 1％ 14 1144.6 49 100％ 97％ 3％ 15 1147.8 41 90％ 89％ 1％ 16 1148.6 42 85％ 89％ -4％

[0071] In this experimental example, when the calculated value reaches more than 95%, the graphite morphology of the gray cast iron sample is mainly flake graphite. By comparing the calculated results of the flake graphite ratio and the metallographic observation results of this experimental example, it is shown that the two are highly consistent, and the error is basically around 5%, especially when the metallographic observation value is above 85%, the error does not exceed 4%. That is to say, the present invention, without relying on metallographic observation, based on the temperature-time curve obtained by thermal analysis technology and the differential calculation of the temperature-time curve, can accurately obtain the flake graphite ratio of the casting when the casting is completed, thereby quantitatively judging the gray cast iron inoculation effect.

[0072] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for judging the inoculation effect of grey cast iron, characterized in that: include: The temperature-time curve of the molten iron cooling process is obtained by using thermal analysis technology; The temperature-time curve is integrated and differentiated to obtain characteristic values, and the degree of graphite precipitation and the proportion of flake graphite in the gray cast iron are calculated according to the characteristic values. The gray cast iron inoculation effect is quantitatively determined according to the degree of graphite precipitation and the proportion of flake graphite.

2. The method according to claim 1, characterized in that The temperature-time curve is provided with a eutectic starting point T1 and a eutectic ending point T2; the temperature-time curve between the eutectic starting point T1 and the eutectic ending point T2 and the straight line between the two points are set to enclose an ideal area S max ; Establish the relationship between different carbon contents C% and ideal area S of gray cast iron max The linear relationship between In actual production, the current molten iron is taken for thermal analysis and carbon content detection to obtain the temperature-time curve of the current molten iron and the carbon content C0% of the current molten iron. According to the temperature-time curve of the current molten iron, the eutectic starting point T10 and the eutectic ending point T20 of the current molten iron are obtained; The instantaneous area S of the current molten iron is calculated using the temperature-time curve between the eutectic starting point T10 and the eutectic ending point T20 of the current molten iron and the straight line between the two points. ins , using the different carbon content C% of gray cast iron and the ideal area S max The ideal area S of the current molten iron is calculated by the linear relationship between and the carbon content C0% of the current molten iron max-0 ; Compare the current instant area S of the molten iron ins and the ideal area S max-0 , and the degree of graphite precipitation in gray cast iron was obtained.

3. The method according to claim 2, characterized in that According to S ins / S max-0 The ratio of is used to obtain the graphite precipitation degree of the grey cast iron; When S ins / S max-0 When ≥0.9, it means that graphite is fully precipitated; When 0.7≤S ins / S max-0 When <0.9, it means that graphite precipitation is insufficient; When S ins / S max-0 When <0.7, it means that there is no graphite precipitation or a small amount of graphite precipitation.

4. The method according to claim 2, characterized in that: The eutectic starting point T1 is the first point on the temperature-time curve when the temperature reduction rate starts to be lower than 0.4°C / s before the eutectic lowest temperature TEU; The eutectic end point T2 is a temperature point on the temperature-time curve corresponding to the maximum value T2" ​​of the second-order differential of the temperature-time curve at the end of solidification.

5. The method according to claim 2, characterized in that: Gray cast iron with different carbon content C% and ideal area S max The linear relationship is: S max =-3913+1857*C。 6. The method according to claim 5, characterized in that Gray cast iron with different carbon content C% and ideal area S max The linear relationship is obtained by fitting the curve data with the eutectic minimum temperature TEU temperature above 1142℃.

7. The method according to claim 1, characterized in that The first-order differential curve of the temperature-time curve is provided with a point t1 and a point t2, wherein the point t1 is the lowest point on the first-order differential curve of the corresponding stage between the initial crystallization temperature TL and the eutectic minimum temperature TEU, and the point t2 is the highest point on the first-order differential curve after the eutectic minimum temperature TEU; the time difference of the temperature-time curve between the point t1 and the point t2 is set to Δt; and a formula for the influence of the eutectic minimum temperature TEU and the proportion of flake graphite on Δt is established; In actual production, the current molten iron is taken for thermal analysis and detection to obtain the temperature-time curve of the current molten iron, and the eutectic minimum temperature TEU0 is obtained according to the temperature-time curve of the current molten iron, and the first-order differential curve is calculated, and the t10 point and t20 point are obtained according to the first-order differential curve of the current molten iron, and then the time difference Δt0 of the temperature-time curve between the t10 point and the t20 point is calculated; The proportion of flake graphite in gray cast iron is calculated using the formula affecting the proportion of flake graphite of the lowest eutectic temperature TEU and Δt and the lowest eutectic temperature TEU0 and Δt0 of the current molten iron.

8. The method according to claim 7, characterized in that The influence formula of the eutectic minimum temperature TEU and the proportion of flake graphite of Δt is: Flake graphite ratio = -10.9 + 0.0104 * TEU - 0.00270 (TEU - 1142.29) 2 -0.000243(Δt-59.44) 2 .

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