CN108132277B - Method for predicting vermicular rate of hypereutectic composition vermicular graphite cast iron - Google Patents

Abstract

The invention discloses a method for predicting the vermicular rate of hypereutectic composition vermicular cast iron, which relates to the technical field of testing materials by applying a thermal analysis method through the state of the tested materials, recording the change of the temperature of the hypereutectic composition vermicular cast iron molten iron along with time through a computer measurement and control system and drawing a cooling curve, obtaining a differential curve through differential processing of the cooling curve, and further calculating the vermicular rate of the molten iron, thereby predicting the vermicular effect of the molten iron and overcoming the defect that the vermicular rate of the hypereutectic composition vermicular cast iron cannot be predicted in the prior art.

Description

A method for predicting the creep rate of vermicular graphite cast iron with hypereutectic composition

technical field

The technical scheme of the present invention relates to the application of thermal analysis method to test the material by testing the state of the material, specifically a method for predicting the creep rate of hypereutectic vermicular graphite cast iron.

Background technique

Vermicular graphite iron not only has the good thermal conductivity, shock absorption and casting performance of gray cast iron, but also has the advantages of high strength and good toughness of ductile iron, and its wear resistance and thermal fatigue resistance are superior to these two materials. Excellent overall performance. In the 1970s, vermicular graphite cast iron began to be used in the manufacture of motor casings, crankshaft drive boxes, brake drums, steel ingot molds and high-horsepower diesel engine cylinder heads to replace high-strength gray iron, alloy cast iron, malleable iron and some ductile iron. . By the end of the 20th century, with the development of the automobile industry, it was found that vermicular graphite iron was the best choice for the production of engine block and cylinder head castings. The drive of the automobile industry made the research and application of vermicular graphite iron enter a new stage of rapid development .

The biggest difficulty in the production of vermicular graphite cast iron is that the range of its vermicular process parameters is too narrow, such as charge ratio, smelting temperature, holding time, ladle preheating temperature, molten iron weight, vermicularizing agent inoculant composition, and holding time in molten iron ladle. , the change of pouring time and the working habits and proficiency of operators will affect the matrix structure of the final vermicular graphite cast iron product. Its mechanical properties and physical properties fluctuate greatly, and it is very difficult to control production stably. In order to solve this problem, a thermal analysis method was introduced, that is, a thermal analysis device was used to collect the cooling curve during the cooling process of the molten iron after creeping, that is, the "temperature-time" curve, and the composition and structure of the molten iron were analyzed by analyzing the cooling curve. Predict and evaluate the vermicular state of molten iron, and guide the next corrective measures, so as to assist in the production of qualified vermicular graphite iron products.

In the chemical composition of vermicular graphite cast iron, the percentage value of the carbon equivalent contained varies in a relatively wide range from the hypoeutectic composition to the hypereutectic composition, but in order to make the molten iron have good casting performance, high Density, low whitish tendency, and percentage of carbon equivalents are usually used in the range of values close to eutectic or hypereutectic. Documents "Production of Compacted Graphite Cast Iron" [Zhang Wenhe, Ding Jun, Nie Furong.. Modern Cast Iron, 006, (02): 54-55] and "Production and Quality Control of Compacted Graphite Iron Castings" [Xu Ming. Foundry Equipment He Technology, 2009, (03): 50-52] recommends that the percentage value of carbon equivalent should be selected from the hypereutectic composition of vermicular graphite cast iron, that is, the percentage value of carbon equivalent should be in the range of 4.3% to 4.6%. The actual investigation and research found that most of the vermicular graphite iron production enterprises in my country currently use some methods of pre-furnace thermal analysis to detect the vermicular rate of vermicular graphite iron. To meet the actual industrial production of qualified hypereutectic vermicular graphite cast iron products.

CN103728333A discloses a double-sample cup ductile iron or vermicular iron furnace rapid analysis method, which is a type of double-cavity analysis sample cup which coats a transfer coating containing antimony strong anti-spheroidizing or anti-creeping elements on a double-cavity analytical sample cup On the inner surface of the cavity, pour the processed molten iron into two cavities at the same time, detect the cooling curves of the molten iron solidification in the two cavities, and use the differential method to find the solidification liquidus temperature T _L1 and T _L2 of the molten iron in the two samples, Eutectic temperatures T _E1 and T _E2 , temperature rises ΔT ₁ and ΔT ₂ caused by the release of latent heat of solidification, and analyzed and compared to calculate the creep rate or spheroidization rate of molten iron solidification, but there is no obvious difference on the cooling curve. The liquidus temperature of the detection of the hypereutectic composition of compacted graphite cast iron, this technique is not given a discussion, so this method cannot achieve the prediction of the vermicular rate of the hypereutectic composition of the compacted graphite iron.

CN1359428A discloses a method for determining the amount of modifier to be added to cast iron by taking a sample from the cast iron molten pool, the temperature of which is recorded simultaneously by two temperature-sensitive devices when the sample solidifies, one for A temperature-sensitive device is arranged in the middle of the sample and the other is near the wall of the vessel. The cooling curve representing the sample temperature of the cast iron melt as a function of time is recorded by these two temperature-sensitive devices, and then by measuring the melting point. These curves were evaluated as a function of time for the pure heat generated in the middle of the bulk sample as a determination of the amount of structural modifier that must be added to the melt to produce dense graphite cast iron (CGI). This prior art evaluates the possibility of recording cooling curves in near-eutectic cast iron melts, although applicable to both hypoeutectic and hypoeutectic cast irons, when it comes to hypereutectic cast irons, due to This type of eigenvalue does not have an obvious turning point or a wide time-varying range of the minimum temperature of eutectic solidification, and the heating curve in the middle does not include any detectable peaks, so it is not suitable for predicting the creep rate of vermicular graphite iron with hypereutectic composition .

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is: a method for predicting the vermicular rate of hypereutectic component vermicular graphite cast iron, by using a computer measurement and control system to record the temperature change of the hypereutectic component vermicular graphite iron molten iron with time and draw a cooling curve , the cooling curve is subjected to differential processing to obtain a differential curve, and the creep rate of the molten iron is further calculated, thereby predicting the creep effect of the molten iron, which overcomes the fact that the existing technology cannot predict the creep of vermicular graphite cast iron with hypereutectic composition. Defects in conversion rate.

The technical scheme adopted by the present invention to solve the technical problem is: a method for predicting the vermicular rate of hypereutectic composition vermicular graphite cast iron, and the specific steps are as follows:

The first step is to record the change of the temperature of the molten iron with the hypereutectic composition of the compacted graphite iron over time through the computer measurement and control system and draw the cooling curve:

The vermicular graphite cast iron molten iron that has undergone vermicularization and inoculation treatment is poured into a sample cup for pre-furnace thermal analysis temperature collection. The temperature signal is converted into an electromotive force signal, and the electromotive force signal is transmitted to a computer measurement and control system through a data transmission line. cooling curve;

The second step is to determine the type of cooling curve:

Use the computer measurement and control system to differentiate the cooling curve drawn in the first step above, and obtain the differential curve of the cooling curve. By detecting the maximum value of the differential curve, it is judged whether there is cooling of the hot metal of hypereutectic vermicular graphite cast iron on the cooling curve. The inflection point TGL of the curve, the inflection point TGU of the cooling curve of the hypereutectic vermicular graphite iron molten iron and/or the inflection point TGR of the cooling curve of the hypereutectic vermicular graphite iron molten iron, and then determine the cooling curve of the detected hypereutectic vermicular graphite iron molten iron to which the cooling curve belongs. The types are as follows: for the type I curve, there will be three maximum values on the differential curve, namely MAX1, MAX2, MAX3; for the type II curve, because there is no inflection point TGL characteristic point of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron , so there are only two maxima MAX2 and MAX3 on the differential curve, but no MAX1; for the type III curve, there is only a maximum value MAX3 on the differential curve; There are three maxima on the differential curve of the cooling curve of molten iron, which means that there are both the inflection point TGL of the cooling curve of the hot metal of hypereutectic vermicular graphite iron and the inflection point TGU and The inflection point TGR of the cooling curve of the hot metal of hypereutectic vermicular graphite cast iron determines that the cooling curve is a type I curve; when it is found that there are two maximum values on the differential curve of the cooling curve of the molten iron of On the cooling curve, there is no inflection point TGL of the cooling curve of the hypereutectic vermicular graphite iron molten iron, but there is the inflection point TGU of the cooling curve of the hypereutectic vermicular graphite iron molten iron and the inflection point TGR of the cooling curve of the hypereutectic vermicular graphite iron molten iron. The cooling curve is the type II curve of the cooling curve; when it is found that there is only one maximum value on the differential curve of the cooling curve of the detected hypereutectic vermicular graphite cast iron molten iron, it means that there is no hypereutectic vermicular graphite iron molten iron on the cooling curve. The inflection point TGL of the cooling curve does not have the inflection point TGU of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron and the inflection point TGR of the cooling curve of the hypereutectic vermicular graphite iron molten iron, and the cooling curve is determined to be a type III curve;

The third step is to predict the creep rate of vermicular graphite cast iron with hypereutectic composition:

Use the computer measurement and control system to determine the characteristic values of the cooling curve obtained in the first step above. If it is determined in the second step that the cooling curve obtained in the first step is a type I curve, the characteristic values include ΔT ₁ , ΔT ₂ , K ₁ , K _2. TEU, TES, TGU, TGL; if it is determined in the second step that the cooling curve obtained in the first step is a type II curve, the characteristic values include △T ₁ , △T ₂ , K ₁ , K ₂ , TEU, TES, TGU ; If it is determined in the second step that the cooling curve obtained in the first step is a type III curve, the characteristic values include ΔT ₁ , ΔT ₂ , K ₁ , K ₂ , TEU, TES, where TEU is a total of hypereutectic vermicular graphite cast iron. The lowest temperature of the crystal, TES is the eutectic end temperature of the hypereutectic vermicular graphite cast iron, TGU is the minimum temperature of austenite precipitation before the eutectic of the hypereutectic vermicular graphite cast iron, TGL is the precipitation temperature of the primary graphite of the hypereutectic vermicular graphite cast iron, △T ₁ is the eutectic re-glow of hypereutectic vermicular graphite cast iron, ΔT ₂ is the temperature difference between TEU and TES of hypereutectic vermicular graphite cast iron, K ₁ is the time proportion of the eutectic stage of hypereutectic vermicular graphite cast iron in the whole solidification process, K ₂ is the inflection point of the cooling curve of the hypereutectic vermicular graphite cast iron. The solidification before TEU accounts for the time proportion of the whole solidification process. Then the computer measurement and control system automatically selects the following corresponding formula according to the type of the cooling curve obtained in the first step to calculate and predict the hypereutectic The vermicular rate of vermicular graphite cast iron with crystal composition:

Formula (1): VGR _I =c ₀ +c ₁ ·ΔT ₁ +c ₂ ·ΔT ₂ +c ₃ ·K ₁ +c ₄ ·K ₂ +c ₅ ·TEU+c ₆ ·TES+c ₇ · TGU+c ₈ TGL,

Formula (2): VGR _II =c ₀ +c ₁ ·ΔT ₁ +c ₂ ·ΔT ₂ +c ₃ ·K ₁ +c ₄ ·K ₂ +c ₅ ·TEU+c ₆ ·TES+c ₇ · TGU,

Formula (3): VGR _III =c ₀ +c ₁ ·ΔT ₁ +c ₂ ·ΔT ₂ +c ₃ ·K ₁ +c ₄ ·K ₂ +c ₅ ·TEU+c ₆ ·TES,

Among them, VGR _Ⅰ , VGR _Ⅱ and VGR _Ⅲ represent the predicted creep rate of the tested hypereutectic vermicular graphite iron molten iron shown by the type I curve, the type II curve and the type III curve respectively; for the type I curve, K ₁ =t _{TES -TER} /t _TES-TGL , K ₂ =t _TEU-TGL /t _TES-TGL ; for Type II curves, K ₁ =t _TES-TER /t _TES-TGU , K ₂ =t _TEU-TGU /t _{TES- TGU} ; for the type III curve, K ₁ =t _TES-TER /t _TES-TEU , K ₂ =0; ΔT ₁ =TER-TEU, ΔT ₂ =TEU-TES; t _TES-TER is the ratio of TER to TES Time, t _TES-TGL is the time from TGL to TES, t _TEU-TGL is the time from TGL to TEU, t _TEU-TGU is the time from TGU to TEU, t _TES-TGU is the time from TGU to TES, t _TES-TEU is the time from TEU to TES; c ₀ is a constant, c ₁ , c ₂ , c ₃ , c ₄ , c ₅ , c ₆ , c ₇ , c ₈ are the coefficients of each item in the prediction formula, c ₀ and the prediction formula The coefficient of each item is recorded by recording the change of the temperature of vermicular graphite iron molten iron with time and drawing the above characteristic value of the cooling curve as an independent variable, and the actual creeping of the casting corresponding to each cooling curve measured by the rapid metallographic method. The rate was obtained by multiple linear regression as the dependent variable.

The above-mentioned method for predicting the creep rate of hypereutectic composition vermicular graphite cast iron, the sample cup for collecting the temperature for thermal analysis in front of the furnace is the sample cup for collecting the temperature for thermal analysis in front of the furnace disclosed in the prior art CN206002472U; the computer measurement and control system is composed of The RT-2009 compacted graphite cast iron intelligent online measurement and control system jointly developed by Hebei University of Technology and Tianjin Sabrans Detection Instrument Co., Ltd. The fast metallographic method and other operating techniques are well known in the technical field.

The beneficial effects of the present invention are as follows:

Compared with the prior art, the present invention has the following outstanding substantive features:

The invention adopts the computer measurement and control system to differentiate the cooling curve of the detected hypereutectic vermicular graphite cast iron molten iron, obtains the differential curve of the cooling curve, and then judges the principle of the type of the detected hypereutectic vermicular graphite iron molten iron cooling curve as follows:

(1) the present invention shows through a large amount of experimental results that the cooling curve of hypereutectic vermicular graphite cast iron molten iron has the following three types:

Type I curve: hypereutectic vermicular graphite cast iron with sufficient eutectic degree, a large amount of primary graphite is precipitated during solidification, and a large amount of latent heat is released. , with the precipitation of the initial graphite, resulting in depletion of carbon around it, a large amount of pre-eutectic austenite begins to nucleate and grow, releasing latent heat, making the cooling curve rise, resulting in the inflection point TGU and over- The inflection point TGR characteristic point of the cooling curve of eutectic compacted graphite cast iron molten iron, and then into the eutectic solidification of vermicular graphite and austenite, this type of cooling curve is a type I curve;

Type II curve: The hypereutectic vermicular graphite cast iron with a slightly lower eutectic degree has a small latent heat generated by the primary graphite, which is not enough to make the cooling curve produce an obvious inflection point TGL of the cooling curve of the eutectic vermicular graphite iron molten iron, but the subsequent The latent heat generated by the growth of austenite before the eutectic can still generate the inflection point of the cooling curve of the hypereutectic vermicular graphite iron molten iron TGU and the inflection point of the cooling curve of the hypereutectic vermicular graphite iron molten iron TGR characteristic point, this type of cooling curve Recognized as type II curve;

Type III curve: eutectic or near-hypereutectic composition of compacted graphite cast iron, its eutectic degree is smaller than the first two types, although it also produces primary graphite and pre-eutectic austenite, but its latent heat is not enough Make the cooling curve appear the inflection point before eutectic, that is, there is neither the inflection point TGL of the cooling curve of the hypereutectic vermicular graphite iron molten iron, nor the inflection point TGU of the cooling curve of the hypereutectic vermicular graphite iron molten iron and the hypereutectic vermicular graphite iron molten iron The inflection point TGR characteristic point of the cooling curve, this type of cooling curve is a type III curve;

(2) The inflection point TGL of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron is the precipitation temperature of the primary graphite of the hypereutectic vermicular graphite cast iron. The larger the TGL, the higher the liquidus, which means the more primary graphite. A large number of experimental studies have found that the final shape of primary graphite growth is spherical or blooming, and the precipitation of primary graphite will reduce the creep rate, and easily cause graphite to float, and lead to shrinkage porosity in castings.

If the differential curve of the cooling curve has a maximum value MAX1, the temperature on the cooling curve corresponding to MAX1 is the inflection point TGL value of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron. If the differential curve does not have a maximum value MAX1, there is no inflection point TGL of the cooling curve of the hypereutectic vermicular graphite iron molten iron on the cooling curve.

(3) The inflection point TGU of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron is the lowest temperature of austenite precipitation before the eutectic of the hypereutectic vermicular graphite cast iron, and the inflection point TGR of the cooling curve of the hypereutectic vermicular graphite iron molten iron is the hypereutectic Austenite precipitation in vermicular graphite cast iron before eutectic rises to the highest temperature. The size of the inflection point TGU of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron and the inflection point TGR of the hypereutectic vermicular graphite iron molten iron also affects the diffusion of carbon atoms and the growth of graphite and austenite before eutectic.

If there is a maximum value MAX2 on the differential curve of the cooling curve, the temperature corresponding to the point where the differential value is zero on the left side of MAX2 is the inflection point TGU of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron, and the nearest differential value on the right side of MAX2 is the inflection point TGU. The temperature corresponding to the point with a value of zero is the inflection point TGR of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron. If the differential curve does not have a maximum value MAX2, there is no inflection point of the cooling curve of the hypereutectic vermicular graphite iron molten iron on the cooling curve. TGU or the inflection point TGR of the cooling curve of the hypereutectic compacted graphite iron molten iron.

(4) The inflection point TEU of the cooling curve of the hypereutectic vermicular graphite iron molten iron is the lowest temperature of the hypereutectic vermicular graphite iron eutectic, and the inflection point of the cooling curve of the the maximum temperature of the crystal. When the common gray cast iron eutectic solidifies, the flake graphite tip penetrates deep into the liquid phase, ahead of the eutectic austenite. The diffusion rate of carbon atoms in the liquid phase is 20 times faster than that in austenite. The rapid growth of graphite leads to carbon depletion around it, which in turn promotes the rapid growth of austenite. Eutectic requires less driving force, so hypereutectic The inflection point TEU of the cooling curve of the compacted graphite iron molten iron is high. When the ductile iron eutectic solidifies, the spheroidal graphite is surrounded by an austenite shell, and the growth of the graphite nodule requires carbon atoms to pass through the austenite shell and enriched to the surface of the graphite nodule, but the diffusion rate of carbon atoms in the austenite It is very slow, so the eutectic growth rate is relatively slow, and the released latent heat of crystallization is small, so the inflection point TEU of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron is low, and the eutectic re-glow △T1 is small. For the vermicular graphite cast iron eutectic, the eutectic graphite begins to be small spherical, so the inflection point TEU of the cooling curve of the hypereutectic vermicular graphite iron molten iron is comparable to that of the ductile iron, and then the graphite distorts and grows into a vermicular shape, which is similar to a flake. The characteristic of graphite grows rapidly and releases a large amount of latent heat, which increases the inflection point TER of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron, so the eutectic re-glow △T1 increases. Therefore, for vermicular graphite cast iron, different vermicular rates also mean that there are correspondingly different inflection points TEU of the cooling curve of the hypereutectic vermicular graphite iron molten iron, inflection points TER of the cooling curve of the hypereutectic vermicular graphite iron molten iron and common Jing Zaihui ΔT1, ΔT ₁ =TER-TEU.

The temperature corresponding to the point where the differential value is zero on the left of MAX3 is the inflection point TEU of the cooling curve of the hypereutectic vermicular graphite cast iron, and the temperature corresponding to the point where the differential value is zero on the right side of MAX3 is the hypereutectic vermicular The inflection point TER of the cooling curve of graphite cast iron molten iron.

The inflection point TES of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron is the eutectic end temperature, and the temperature corresponding to the minimum value after MAX3 on the differential curve of the cooling curve is TES.

(5) When studying the supercooling of gray cast iron, it is found that when the molten iron solidifies to the point where its temperature is lower than the inflection point TEU of the cooling curve of the molten iron of hypereutectic vermicular graphite cast iron, it will nucleate again in the liquid phase, and this stage is supercooled. The nucleation and growth of graphite will bring a certain risk of high spheroidization rate, that is, the size of ΔT ₂ =TEU-TES will affect the creep rate of hypereutectic vermicular graphite cast iron.

(6) K ₁ is the time proportion of the eutectic stage of hypereutectic vermicular graphite cast iron in the whole solidification process. The more spherical graphite, the slower the diffusion of carbon atoms in the late eutectic stage, the slower the heat dissipation of the sample, and the longer the eutectic stage lasts. _K2 is the time proportion of the solidification before TEU at the inflection point of the cooling curve of the hypereutectic vermicular graphite iron molten iron in the whole solidification process. The solidification stage before the inflection point of the cooling curve of the hypereutectic vermicular graphite cast iron hot metal consumes more carbon, and the resulting graphite grows into a spherical or blooming shape, which reduces the creep rate, and the eutectic shrinkage tends to be large in the later stage, and the casting is easy to be cast. produce shrinkage.

For the I-type curve, there is _an obvious inflection point _TGL characteristic point of the cooling curve of the hypereutectic _vermicular graphite cast iron molten iron. _-TGL , the inflection point of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron, the solidification before TEU accounts for the time proportion of the whole solidification process K ₂ =t _TEU-TGL /t _TES-TGL ; for the type II curve, there is no obvious hypereutectic Inflection point TGL characteristic point of the cooling curve of vermicular graphite iron molten iron, K ₁ =t _TES-TER /t _TES-TGU , K ₂ =t _TEU-TGU /t _TES-TGU ; for type III curve, hypereutectic vermicular graphite iron There is no inflection point on the curve before the inflection point TEU of the cooling curve of molten iron, K ₁ =t _TES-TER /t _TES-TEU , K ₂ =0.

Compared with the prior art, the present invention has the following remarkable progress:

(1) the method of the present invention records the variation of the temperature of the hot metal of the hypereutectic composition vermicular graphite cast iron with time through the computer measurement and control system and draws a cooling curve, the cooling curve obtains a differential curve through differential processing, and further calculates the creep of the molten iron. Therefore, the creeping effect of the molten iron can be predicted, which overcomes the defect that the existing technology cannot predict the creeping rate of the hypereutectic component vermicular graphite cast iron.

(2) The method of the present invention can intelligently identify the hypereutectic vermicular graphite cast iron, and predict the creeping effect of the hypereutectic vermicular graphite cast iron. The method is fast and accurate, and the error of the calculated creep rate does not exceed ±5%, which can help improve the stability of the production of compacted graphite iron.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 is a schematic block diagram of the flow of the method of the present invention.

Fig. 2 is the cooling curve-I type curve and the corresponding differential curve of the vermicular graphite cast iron molten iron in Example 1 of the present invention.

Fig. 3 is the cooling curve - II type curve and the corresponding differential curve of the vermicular graphite cast iron molten iron in Example 2 of the present invention.

Fig. 4 is the cooling curve-III type curve and the corresponding differential curve of the vermicular graphite cast iron molten iron in Example 3 of the present invention.

Figure 5(a) is a body metallographic photograph of the vermicular graphite cast iron glass mold casting obtained in Example 1 of the present invention.

Figure 5(b) is a metallographic photograph of the body of the vermicular graphite cast iron piston ring casting obtained in Example 2 of the present invention.

Figure 5(c) is a body metallographic photograph of the vermicular graphite cast iron glass mold casting obtained in Example 3 of the present invention.

Detailed ways

The embodiment shown in FIG. 1 shows that the process of the method of the present invention is: the computer measurement and control system draws the cooling curve → determines the type of the cooling curve, including type I curve, type II curve and type III curve → predicts the hypereutectic composition of vermicular graphite cast iron The creep rate, the calculation formulas are:

Formula (1): VGR _I =c ₀ +c ₁ ·ΔT ₁ +c ₂ ·ΔT ₂ +c ₃ ·K ₁ +c ₄ ·K ₂ +c ₅ ·TEU+c ₆ ·TES+c ₇ · TGU+c ₈ TGL,

Formula (2): VGR _II =c ₀ +c ₁ ·ΔT ₁ +c ₂ ·ΔT ₂ +c ₃ ·K ₁ +c ₄ ·K ₂ +c ₅ ·TEU+c ₆ ·TES+c ₇ · TGU,

Formula (3): VGR _III =c ₀ +c ₁ ·ΔT ₁ +c ₂ ·ΔT ₂ +c ₃ ·K ₁ +c ₄ ·K ₂ +c ₅ ·TEU+c ₆ ·TES.

Further explanation: VGR _Ⅰ , VGR _Ⅱ and VGR _Ⅲ represent the predicted creep rate of the tested hypereutectic vermicular graphite iron molten iron shown by the I-type curve, the II-type curve and the III-type curve, respectively, and TEU is the total hypereutectic vermicular graphite cast iron. The lowest temperature of the crystal, TES is the eutectic end temperature of the hypereutectic vermicular graphite cast iron, TGU is the minimum temperature of austenite precipitation before the eutectic of the hypereutectic vermicular graphite cast iron, TGL is the precipitation temperature of the primary graphite of the hypereutectic vermicular graphite cast iron, △T ₁ is the eutectic re-glow of the hypereutectic vermicular graphite cast iron, △T ₂ is the temperature difference between the TEU and TES of the hypereutectic vermicular graphite iron, K ₁ is the time proportion of the eutectic stage of the hypereutectic vermicular graphite cast iron in the whole solidification process, K ₂ is the time proportion of the solidification before the inflection point TEU of the cooling curve of the hypereutectic vermicular graphite cast iron in the whole solidification process, c ₀ is a constant, c ₁ , c ₂ , c ₃ , c ₄ , c ₅ , c ₆ , c ₇ and c ₈ are coefficients of each item in the prediction formula.

Example 1

Preparation of hypereutectic vermicular graphite cast iron glass mold castings, the product requires creep rate greater than 80%.

The first step is to record the change of the temperature of the molten iron with the hypereutectic composition of the compacted graphite iron over time through the computer measurement and control system and draw the cooling curve:

The vermicular graphite cast iron molten iron that has undergone vermicularization and inoculation treatment is poured into a sample cup for temperature collection for thermal analysis in front of a furnace disclosed by CN206002472U, and a K-type thermocouple set in the center of the sample cup tests the vermicular graphite iron iron molten iron in the sample cup. The temperature signal during the solidification process of the sample is converted into an electromotive force signal, and the electromotive force signal is transmitted to a computer measurement and control system RT-2009 compact graphite cast iron intelligent online measurement and control system through the data transmission line. Record the change of the temperature of the vermicular graphite iron molten iron with time and draw the cooling curve, the cooling curve is shown in Figure 2;

The second step is to determine the type of cooling curve:

Use computer measurement and control system-RT-2009 type vermicular graphite cast iron intelligent online measurement and control system to differentiate the cooling curve drawn in the first step above to obtain the differential curve of the cooling curve, and use the above computer measurement and control system to find the detected hypereutectic vermicular graphite cast iron. There are 3 maximum values on the differential curve of the cooling curve of molten iron, namely MAX1, MAX2, and MAX3, indicating that the cooling curve has both the inflection point TGL of the cooling curve of the hot metal of hypereutectic vermicular graphite cast iron and the hypereutectic vermicular graphite cast iron. The inflection point TGU of the cooling curve of the molten iron and the inflection point TGR of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron, and then it is judged that the type of the cooling curve obtained in the first step of the detected hypereutectic vermicular graphite iron molten iron belongs to the type I curve;

The third step is to predict the creep rate of vermicular graphite cast iron with hypereutectic composition:

Use computer measurement and control system-RT-2009 type vermicular graphite cast iron intelligent online measurement and control system to detect the characteristic values of the cooling curve described in the first step, including TGL, TGU, TGR, TEU, TER, TES, ΔT ₁ , ΔT ₂ , The results of K ₁ and K ₂ are shown in Table 1 and Table 2. In the formula of predicted creep rate obtained by multiple linear regression, the constant c ₀ =108.946, the coefficients of the terms, c ₁ =24.765, c ₂ =-25.272 , c ₃ =24.186, c ₄ =-57.693, c ₅ =-0.062, c ₆ =1.322, c ₇ =-0.034, c ₈ =-0.123,

Then use the following formula to calculate and predict the creep rate of vermicular graphite cast iron with hypereutectic composition:

Formula (1): VGR _I =c ₀ +c ₁ ·ΔT ₁ +c ₂ ·ΔT ₂ +c ₃ ·K ₁ +c ₄ ·K ₂ +c ₅ ·TEU+c ₆ ·TES+c ₇ · TGU+c ₈ TGL

The creep rate was calculated to be 81% by the computer measurement and control system. After inspection, the creep rate of the cast vermicular graphite cast iron glass mold casting body is 82%, which meets the product requirements.

Fig. 2 is the cooling curve-I type curve and the corresponding differential curve of the vermicular graphite cast iron molten iron in the present embodiment, indicating that the hypereutectic vermicular graphite iron with sufficient eutectic degree precipitates a large amount of primary graphite during solidification, and is accompanied by the release of With a lot of latent heat, the curve shows a clear inflection point TGL. With the precipitation of the initial graphite, the surrounding carbon is depleted, and a large amount of pre-eutectic austenite begins to nucleate and grow, releasing latent heat, making the curve rise, producing TGU and TGR characteristic points, and then entering the co-existence of vermicular graphite and austenite. Crystal solidification.

Fig. 5 (a) is the body metallographic photograph of the vermicular graphite cast iron glass mold casting obtained in the present embodiment, and its vermicular rate is 82%. The crystallinity is larger, so the size is larger.

Example 2

Preparation of hypereutectic vermicular graphite cast iron piston rings, the product requires creep rate greater than 80%.

The first step is to record the change of the temperature of the molten iron with the hypereutectic composition of the compacted graphite iron over time through the computer measurement and control system and draw the cooling curve:

The vermicular graphite cast iron molten iron that has undergone vermicularization and inoculation treatment is poured into a sample cup for temperature collection for thermal analysis in front of a furnace disclosed by CN206002472U, and a K-type thermocouple set in the center of the sample cup tests the vermicular graphite iron iron molten iron in the sample cup. The temperature signal during the solidification process of the sample is converted into an electromotive force signal, and the electromotive force signal is transmitted to a computer measurement and control system RT-2009 compact graphite cast iron intelligent online measurement and control system through the data transmission line. Record the change of the temperature of the vermicular graphite iron molten iron with time and draw the cooling curve. The cooling curve is shown in Figure 3;

The second step is to determine the type of cooling curve:

Use computer measurement and control system-RT-2009 type vermicular graphite cast iron intelligent online measurement and control system to differentiate the cooling curve drawn in the first step above to obtain the differential curve of the cooling curve, and use the above computer measurement and control system to find the detected hypereutectic vermicular graphite cast iron. There are only two maxima MAX2 and MAX3 on the differential curve of the cooling curve of molten iron, but there is no MAX1, which means that there is no inflection point TGL of the cooling curve of the hot metal of hypereutectic vermicular graphite iron on the cooling curve, but there is a hypereutectic vermicular graphite iron. The inflection point TGU of the cooling curve of the molten iron and the inflection point TGR of the cooling curve of the hypereutectic vermicular graphite iron molten iron, and then it is judged that the cooling curve obtained in the first step of the detected hypereutectic vermicular graphite iron molten iron belongs to the type II curve;

The third step is to predict the creep rate of vermicular graphite cast iron with hypereutectic composition:

Use computer measurement and control system-RT-2009 type vermicular graphite cast iron intelligent online measurement and control system to detect the eigenvalues of the cooling curve mentioned in the first step, including TGU, TGR, TEU, TER, TES, △T ₁ , △T ₂ , K ₁ , K ₂ , the results are shown in Table 1 and Table 2, the constant c ₀ =-66.332 in the predicted creep rate formula obtained by multiple linear regression, the coefficients of the terms, c ₁ =19.367, c ₂ =-31.641, c ₃ =20.379, c ₄ =-42.268, c ₅ =-0.037, c ₆ =1.562, c ₇ =-0.025,

Then use the following formula to calculate and predict the creep rate of vermicular graphite cast iron with hypereutectic composition:

Formula (2): VGR _II = c ₁ ·ΔT ₁ +c ₂ ·ΔT ₂ +c ₃ ·K ₁ +c ₄ ·K ₂ +c ₅ ·TEU+c ₆ ·TES+c ₇ ·TGU

The creep rate was calculated to be 89% by the computer measurement and control system. The cast vermicular graphite cast iron piston ring body has a creep rate of 86%, which meets the product requirements.

Fig. 3 is the cooling curve of the vermicular graphite cast iron molten iron in the present embodiment-type II curve and the corresponding differential curve, showing that the latent heat generated by the primary graphite during solidification of the hypereutectic vermicular graphite iron with a slightly lower eutectic degree is small, which is not enough to make The cooling curve produces a distinct TGL inflection point.

Fig. 5(b) is the body metallographic photograph of the vermicular graphite cast iron piston ring casting obtained in the present embodiment, and its vermicular rate is 82%. The larger spheroidal graphite in the figure is primary graphite, because its eutectic degree is not large enough , so the primary graphite does not grow as large spherical or flower-like shape as shown in Fig. 5(a).

Example 3

Preparation of hypereutectic vermicular graphite cast iron glass mold castings, the product requires creep rate greater than 80%.

The first step is to record the change of the temperature of the molten iron with the hypereutectic composition of the compacted graphite iron over time through the computer measurement and control system and draw the cooling curve:

The vermicular graphite cast iron molten iron that has undergone vermicularization and inoculation treatment is poured into a sample cup for temperature collection for thermal analysis in front of a furnace disclosed by CN206002472U, and a K-type thermocouple set in the center of the sample cup tests the vermicular graphite iron iron molten iron in the sample cup. The temperature signal during the solidification process of the sample is converted into an electromotive force signal, and the electromotive force signal is transmitted to a computer measurement and control system RT-2009 compact graphite cast iron intelligent online measurement and control system through the data transmission line. Record the change of the temperature of the vermicular graphite iron molten iron with time and draw the cooling curve, the cooling curve is shown in Figure 4;

The second step is to determine the type of cooling curve:

Use computer measurement and control system-RT-2009 type vermicular graphite cast iron intelligent online measurement and control system to differentiate the cooling curve drawn in the first step above to obtain the differential curve of the cooling curve, and use the above computer measurement and control system to find the detected hypereutectic vermicular graphite cast iron. There is only one maximum value MAX3 on the differential curve of the cooling curve of molten iron, which means that there is neither the inflection point TGL of the cooling curve of the hot metal of hypereutectic vermicular graphite cast iron nor the inflection point of the cooling curve of the molten iron of hypereutectic vermicular graphite iron. TGU and the inflection point TGR of the cooling curve of the hypereutectic vermicular graphite cast iron molten iron, and then determine that the type of the cooling curve obtained in the first step of the detected hypereutectic vermicular graphite iron molten iron belongs to the type III curve;

The third step is to predict the creep rate of vermicular graphite cast iron with hypereutectic composition:

Use computer measurement and control system-RT-2009 type vermicular graphite cast iron intelligent online measurement and control system to detect the characteristic values of the cooling curve described in the first step, including TEU, TER, TES, ΔT ₁ , ΔT ₂ , K ₁ , K ₂ , The results are shown in Tables 1 and 2. In the predicted creep rate formula obtained by multiple linear regression, the constant c ₀ =87.337, the coefficients of the terms, c ₁ =7.543, c ₂ =-38.349, c ₃ =18.361, c ₄ =0, c ₅ =-0.124, c ₆ =1.717,

Then use the following formula to calculate and predict the creep rate of vermicular graphite cast iron with hypereutectic composition:

Formula (3): VGR _III =c ₀ +c ₁ ·ΔT ₁ +c ₂ ·ΔT ₂ +c ₃ ·K ₁ +c ₄ ·K ₂ +c ₅ ·TEU+c ₆ ·TES

The creep rate was calculated to be 93% by the computer measurement and control system. . After inspection, the creep rate of the cast vermicular graphite cast iron glass mold casting body is 90%, which meets the product requirements.

Fig. 4 is the cooling curve of the vermicular graphite cast iron molten iron in the present embodiment - the type III curve and the corresponding differential curve, showing that the eutectic or near-hypereutectic composition of vermicular graphite iron also produces primary graphite and pre-eutectic austenite when solidified However, the latent heat generated by it is not enough to make the cooling curve appear at the pre-eutectic inflection point.

Fig. 5(c) is the bulk metallographic photograph of the vermicular graphite cast iron glass mold casting obtained in the present embodiment, and its vermicular rate is 90%. Because it is a near-eutectic composition, there is no obvious primary graphite in the metallographic phase. .

Table 1. List of physical meanings of each eigenvalue in the cooling curve of hypereutectic vermicular graphite iron molten iron

Table 2. Results of detected eigenvalues for each embodiment

In the above embodiments, the rapid metallographic method and other operating techniques are well known in the technical field.

Claims (1)

1. A method for predicting the vermicular rate of hypereutectic vermicular cast iron is characterized by comprising the following specific steps:

firstly, recording the change of the temperature of the hypereutectic vermicular cast iron molten iron along with time through a computer measurement and control system and drawing a cooling curve:

pouring vermicular cast iron molten iron subjected to vermicularizing and inoculation into a stokehold thermal analysis temperature collection sample cup, converting a temperature signal in a solidification process of a vermicular cast iron molten iron sample in the sample cup into an electromotive force signal by a K-type thermocouple arranged in the center of the sample cup, transmitting the electromotive force signal to a computer measurement and control system through a data transmission line, converting the electromotive force signal into a temperature value by the computer measurement and control system, and recording the change of the temperature of the vermicular cast iron molten iron along with time and drawing a cooling curve;

secondly, determining the type of the cooling curve:

differentiating the cooling curve drawn in the first step by using a computer measurement and control system to obtain a differential curve of the cooling curve, judging whether the cooling curve has an inflection point TGL of the cooling curve of the hypereutectic vermicular cast iron molten iron, an inflection point TGU of the cooling curve of the hypereutectic vermicular cast iron molten iron and/or an inflection point TGR of the cooling curve of the hypereutectic vermicular cast iron molten iron by detecting the number of maximum values on the differential curve, and further judging the type of the cooling curve of the detected hypereutectic vermicular cast iron molten iron as follows: for the type I curve, 3 maximum values are MAX1, MAX2 and MAX3 on the differential curve; for the type II curve, because the characteristic point of the inflection point TGL of the cooling curve of the hypereutectic vermicular cast iron molten iron does not exist, only 2 maximum values MAX2 and MAX3 are formed on the differential curve, and MAX1 is not formed; for the type III curve, the differential curve has a maximum value MAX 3; therefore, when the computer measurement and control system finds that 3 maximum values exist on the differential curve of the cooling curve of the detected hypereutectic vermicular cast iron molten iron, the cooling curve is judged to be an I-type curve, wherein the inflection point TGL of the cooling curve of the hypereutectic vermicular cast iron molten iron, the inflection point TGU of the cooling curve of the hypereutectic vermicular cast iron molten iron and the inflection point TGR of the cooling curve of the hypereutectic vermicular cast iron molten iron exist on the cooling curve; when 2 maximum values are found on the differential curve of the cooling curve of the detected hypereutectic vermicular cast iron molten iron, the cooling curve is judged to be a II-type curve without the inflection point TGL of the cooling curve of the hypereutectic vermicular cast iron molten iron, and when 1 maximum value is found on the differential curve of the cooling curve of the detected hypereutectic vermicular cast iron molten iron, the cooling curve is judged to be a III-type curve without the inflection point TGL of the cooling curve of the hypereutectic vermicular cast iron molten iron, the inflection point TGU of the cooling curve of the hypereutectic vermicular cast iron molten iron and the inflection point TGR of the cooling curve of the hypereutectic vermicular cast iron molten iron on the cooling curve;

and thirdly, predicting the vermicular rate of hypereutectic vermicular cast iron:

determining characteristic value of the cooling curve obtained in the first step by using a computer measurement and control system, and if the cooling curve obtained in the first step is determined to be a type I curve in the second step, the characteristic value comprises △ T₁、△T₂、K₁、K₂TEU, TES, TGU, TGL, and if the cooling curve obtained in the first step is determined to be a type II curve in the second step, the characteristic values include △ T₁、△T₂、K₁、K₂TEU, TES, TGU, if the cooling curve obtained in the first step is determined to be type III curve in the second step, the characteristic values include △ T₁、△T₂、K₁、K₂TEU and TES, wherein TEU is the eutectic minimum temperature of hypereutectic vermicular cast iron, TES is the eutectic ending temperature of hypereutectic vermicular cast iron, TGU is the austenite precipitation minimum temperature before hypereutectic vermicular cast iron eutectic, TGL is the precipitation temperature of primary graphite of hypereutectic vermicular cast iron, △ T₁△ T for eutectic recalescence of hypereutectic vermicular cast iron₂Is the temperature difference, K, of the TEU and TES of hypereutectic vermicular cast iron₁The time proportion of the later eutectic period of the hypereutectic vermicular cast iron to the whole solidification process, K₂The method is characterized in that the solidification before the inflection point TEU of the cooling curve of hypereutectic vermicular cast iron molten iron accounts for the time proportion of the whole solidification process, and then a computer measurement and control system automatically selects the following corresponding formula according to the type of the cooling curve obtained in the first step to calculate and predict the vermicular cast iron vermicular rate of hypereutectic components:

formula (1): VGR_Ⅰ＝c₀+c₁·△T₁+c₂·△T₂+c₃·K₁+c₄·K₂+c₅·TEU+c₆·TES+c₇·TGU+c₈·TGL，

Formula (2): VGR_Ⅱ＝c₀+c₁·△T₁+c₂·△T₂+c₃·K₁+c₄·K₂+c₅·TEU+c₆·TES+c₇·TGU，

Formula (3): VGR_Ⅲ＝c₀+c₁·△T₁+c₂·△T₂+c₃·K₁+c₄·K₂+c₅·TEU+c₆·TES，

Wherein, VGR_Ⅰ、VGR_ⅡAnd VGR_ⅢRespectively representing the predicted creep rates of the detected hypereutectic vermicular graphite cast iron molten iron shown by the type I curve, the type II curve and the type III curve; for curve I, K₁＝t_TES-TER/t_TES-TGL，K₂＝t_TEU-TGL/t_TES-TGL(ii) a For type II curves, K₁＝t_TES-TER/t_TES-TGU，K₂＝t_TEU-TGU/t_TES-TGU(ii) a For type III curves, K₁＝t_TES-TER/t_TES-TEU，K₂＝0；△T₁＝TER-TEU，△T₂＝TEU-TES；t_TES-TERTime of TER to TES, t_TES-TGLTime from TGL to TES, t_TEU-TGLTime of TGL to TEU, t_TEU-TGUTime of TGU to TEU, t_TES-TGUTime from TGU to TES, t_TES-TEUThe time from TEU to TES; c. C₀Is a constant number c₁、c₂、c₃、c₄、c₅、c₆、c₇、c₈As coefficients of terms in the prediction formula, c₀And the coefficients of all items in the prediction formula are obtained by performing multiple linear regression by taking the actual creep rate of the casting corresponding to each cooling curve measured by a rapid metallographic method as a dependent variable, and taking the characteristic value of the cooling curve which is drawn by recording the change of the molten iron temperature of the vermicular cast iron along with time as an independent variable; the physical significance of the TGR is the austenite precipitation rising maximum temperature before the hypereutectic vermicular cast iron is eutectic; the physical meaning of TER is the highest eutectic rising temperature of hypereutectic vermicular cast iron.

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