CN102676909B - Method for manufacturing high-chrome cast iron grinding balls - Google Patents

Abstract

The invention discloses a method for manufacturing high-chromium cast iron grinding balls. The melting and casting process is as follows: the sample blank is melted in a 100KW, 10kg medium-frequency induction furnace, the melting temperature is 1450°C-1500°C, high-temperature casting is adopted, and the furnace temperature is 1400°C About; the heat treatment process is: quenching at 980 ° C, air cooling to room temperature, tempering temperature is 400 ° C at medium temperature, air cooling to room temperature after tempering; the alloy content of the sample blank is: the carbon content is selected at 2.5% to 3.5%; The content of chromium is less than 20%; the content of manganese is less than 2.2%; the content of Si is 0.4-1.2%; the content of molybdenum, copper, vanadium and tungsten is all less than 1.0%. The wear resistance of cast balls is closely related to its heat treatment process. Through the experimental research on the composition design and heat treatment process of high chromium alloy balls, the metallographic structure and performance changes of high chromium alloy balls are analyzed, and a proposal to improve the wear resistance of high chromium alloy balls is proposed. manufacturing method.

Description

A kind of manufacturing method of high chromium cast iron grinding ball

technical field

The invention relates to the technical field of metallurgy, in particular to a method for manufacturing high-chromium cast iron grinding balls. the

Background technique

Ball mill is widely used in cement, electric power, mineral processing, building materials and other industries. As the grinding medium in the ball mill, the grinding ball must have high wear resistance and high toughness. the

In recent years, with the rapid development of my country's industry, the consumption of grinding balls is very large. How to improve the performance of grinding balls, improve their service life and production efficiency, has a wide range of economic benefits. the

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for manufacturing high-chromium cast iron grinding balls in view of the deficiencies in the prior art. the

Technical scheme of the present invention is as follows:

A method for manufacturing high-chromium cast iron grinding balls. The melting and casting process is as follows: the sample blank is smelted in a 100KW, 10kg medium-frequency induction furnace, the melting temperature is 1450°C-1500°C, high-temperature casting is adopted, and the furnace temperature is about 1400°C; heat treatment process It is: quenching at 980°C, air cooling to room temperature, tempering temperature is 400°C at medium temperature, and air cooling to room temperature after tempering. the

In the manufacturing method of the high chromium cast iron grinding ball, the alloy content of the sample blank is as follows: the carbon content is selected from 2.5% to 3.5%; the chromium content is less than 20%; the manganese content is less than 2.2%; 1.2%; molybdenum, copper, vanadium, tungsten content are all less than 1.0%. the

The wear resistance of cast balls is closely related to its heat treatment process. Through the experimental research on the composition design and heat treatment process of high chromium alloy balls, the metallographic structure and performance changes of high chromium alloy balls are analyzed, and a proposal to improve the wear resistance of high chromium alloy balls is proposed. manufacturing method. the

Description of drawings

Figure 1 is a heat treatment process diagram for wear-resistant balls;

Figure 2 is the metallographic structure diagram (400X) of wear-resistant balls after heat treatment in different processes; a, 3# sample without heat treatment b, 4# sample quenched at 980 °C c, 5# sample quenched at 980 °C and tempered at 400 °C; d. 6# sample was quenched at 980°C and tempered at 600°C;

Figure 3 is a comparison of the hardness of wear-resistant balls under different heat treatment processes;

Figure 4 is a comparison of abrasive wear of wear-resistant balls under different heat treatment processes. the

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments. the

Embodiment 1, chemical composition optimization design

Based on the requirements for the matrix and carbide type, the chemical composition of the wear-resistant ball is optimized as follows under laboratory and factory conditions:

(1) Carbon: C has an important influence on the matrix structure and carbides of high chromium cast iron. C is the main element for forming eutectic carbides (Cr, Fe) ₇ C ₃ and plays an important role in wear resistance. The carbon content determines the number of carbides. Selecting a higher carbon content can obtain more high-hardness carbides, improve hardenability and excellent wear resistance, thermal crack resistance and spalling resistance, but impact toughness and The flexural strength decreases linearly. Therefore, it is appropriate to choose the carbon content in the range of 2.5% to 3.5%.

(2) Chromium: Cr is the basic alloying element for high chromium white cast iron to ensure excellent wear resistance and toughness, and its content determines the type of carbide. When the Cr content is greater than 10%, the eutectic carbides in high-chromium cast iron are basically M ₇ C ₃ , starting from obtaining Austrian and Baky bodies, the chromium content in high-chromium cast iron must be controlled to be less than 20%. When Cr reaches a certain amount, it is not obvious to continue to increase the wear resistance, and if it is too small, carbides (Cr, Fe) ₇ C ₃ with high hardness cannot be formed.

(3) Manganese: Mn is an effective element for forming austenite and improving hardenability. The role of Mn in high chromium cast iron: one is to deoxidize; the other is to strengthen the matrix and carbide. When the Mn content is too high, austenite will appear in the structure, and the austenite structure is not suitable for grinding balls, because austenite grinding balls will cause a lot of crushing and peeling in both dry grinding and wet grinding, but due to Manganese is used for both deoxidation and desulfurization, so the content of manganese in wear-resistant balls should not be too high, less than 2.2%. the

(4) Silicon: Since Si is a non-carbide forming element, hardenability can be significantly reduced. The main function of Si is to increase the Ms point and reduce the retained austenite. On the one hand, Si dissolves in the matrix, which significantly reduces the hardenability. As the Si content increases, the carbides become finer, and Si dissolves in the matrix to reduce the carbon content of the austenite; on the other hand, Si makes the austenite dendrites more refined, and the carbides become finer, and Si content increases, carbides increase, hardness and wear resistance increase, but impact toughness decreases. When producing as-cast high-chromium spherical troostite grinding balls, appropriately increase the Si content, 0.4-1.2%, which is beneficial to the tendency of Si to dissolve in the base to promote the transformation of troostite and improve the corrosion resistance of cast iron. the

5) Micro-alloying: In high-chromium cast iron, since most of the added chromium enters carbides, the concentration of chromium in the matrix is not enough to inhibit the transformation of pearlite. In order to improve the as-cast hardenability of the grinding ball, it is necessary to add molybdenum, copper, vanadium and tungsten for microalloying, and the content is less than 1.0%. the

Molybdenum is a strengthening carbide forming element, and its main function is to refine the matrix and refine carbides. Molybdenum can shift the C curve to the right and improve hardenability. When molybdenum and copper are used in combination, the effect of improving hardenability is greater. Molybdenum can also improve the tempering stability and prevent tempering brittleness, thereby improving the comprehensive mechanical properties. Under the condition of metal mold casting, adding a small amount can play a significant role, and it is suitable for wear-resistant steel balls with special requirements. 

Vanadium is a trace alloying element, which can form carbonitrides with high hardness and disperse in the matrix, which is conducive to improving the microhardness and wear resistance of the matrix, and is also beneficial to the refinement of grains. the

Table 1 Composition range of high chromium cast iron balls (unit: %)

serial number C Mn Si Cr Mo V W Ti Nb S P Fe 1# sample 2.99 2.01 1.15 14.90 0.01 0.21 ＜0.02 0.07 0.22 0.039 0.046 Surplus

Embodiment 2, high chromium wear-resistant ball melting and casting process

The sample blank is melted in a 100KW, 10kg medium frequency induction furnace. The casting mold used is an ordinary sand mold, the melting temperature is 1450°C to 1500°C, high temperature casting is adopted, and the furnace temperature is about 1400°C. the

Embodiment 3, grinding ball heat treatment process

Heat treatment is a necessary process for the production of high chromium cast iron grinding balls. Reasonable heat treatment can eliminate the internal stress of the ball, make the hardness and toughness of the material well matched, and improve the wear resistance of the material. the

The heat treatment process of high chromium cast iron grinding balls is actually a dynamic process of secondary carbide precipitation and dissolution. To obtain good wear resistance, high chromium cast iron must undergo quenching treatment, and the choice of quenching temperature and holding time is heat treatment. crucial factor in the process. the

In a certain temperature range, the higher the quenching temperature, the higher the hardenability. With the increase of chromium content in the alloy, the temperature range at which secondary carbides start to precipitate moves to the high temperature direction, so the quenching temperature will also change with the chromium content. Due to the good hardenability of high chromium white cast iron, in actual production, air cooling with weak cooling strength is generally used for quenching to avoid hot cracking of castings and improve the service life of materials. High chromium castings can be used in the quenched state, but the quenched structure has high internal stress and more retained austenite. Timely tempering treatment can not only eliminate the quenched internal stress, but also produce residual austenite. Martensitic transformation causes secondary hardening of high chromium cast iron. Through the research on the heat treatment process of high chromium white cast iron, it is found that under the working conditions of low stress and high stress abrasive wear, the tempering process can be omitted, and it can be put into use after air quenching. In addition, the heat treatment process of chromium-based white cast iron includes stabilization treatment, agglomeration treatment, etc. the

heat treatment process

Quenching and tempering experiments were carried out on the grinding balls using a box-type resistance furnace. Quenching at 980°C, air cooling to room temperature, tempering temperature is 400°C, 600°C respectively, air cooling to room temperature after tempering. the

The heat treatment process carried out in this experiment is shown in Figure 1, and the heat treatment processes adopted by 3#, 4#, 5#, and 6# samples are shown in Table 2. the

Table 2 Heat treatment process of different samples

the Heat treatment process 3# sample No heat treatment 4# sample Quenching at 980°C 5# sample Quenching at 980°C and tempering at 400°C 6# sample Quenching at 980°C Tempering at 600°C

Note: 3#, 4#, 5#, 6# alloys have the same composition as 1#, but the heat treatment process is different. the

Heat treatment experiments show that the matrix structure obtained at room temperature after quenching at 980°C is dominated by acicular quenched martensite. At this time, the wear-resistant ball has high hardness and wear resistance, but internal stress often exists in the quenched structure, which easily leads to wear The grinding ball is cracked and deformed, so it must be tempered to eliminate the internal stress and improve the toughness of the wear-resistant ball; after tempering at a medium temperature of 400°C, the matrix structure at room temperature is dominated by tempered troostite, and the wear-resistant ball has Higher hardness and wear resistance; after tempering at 600°C, the matrix structure at room temperature is mainly tempered sorbite, and contains many coarse cementite and ferrite, which leads to the hardness and wear resistance of wear-resistant balls. The wear resistance is poor; the best heat treatment process is quenching at 980°C and tempering at medium temperature at 400°C. the

microstructure analysis

In this experiment, a metallographic microscope was used to observe the metallographic structure of high-chromium white cast iron grinding balls in the as-cast state and after heat treatment, and to study the relationship between structure and performance. the

Use wire electric discharge cutting to take a sample with a size of 10mm×10mm×8mm at the center of the grinding ball, and polish it with 200# to 1500# metallographic sandpaper. The etching agent is 4% nitric acid alcohol, and the etching time is 10s. The structure was observed and analyzed with MDS metallographic microscope. the

The metallographic structure of the grinding balls treated by different heat treatment processes is shown in Figure 2. From the metallographic microstructure of wear-resistant balls after different heat treatment processes in Figure 2, it can be seen that the microstructure of the 3# sample without heat treatment (Fig. a) at room temperature is pearlite P + carbide + metamorphic ledeburite Ld', and The cementite content is less, the cementite content is more, and the carbides are mostly mesh-like carbides; Figure b shows the metallographic micrograph of the sample obtained after quenching at 980 ° C and air cooling to room temperature, and the matrix structure is quenched Martensite M + carbide + a small amount of retained austenite A, martensite is mainly acicular martensite, and carbides are mainly dispersed in the matrix as granular carbides; Figure c shows that after quenching at 980 ° C and air cooling to room temperature, then tempered at 400°C at medium temperature, and air-cooled to room temperature to obtain a micrograph of the sample. The matrix structure is tempered troostite T + carbide + a small amount of retained austenite A, and the martensite is mainly mixed martensite. The carbides are mainly granular carbides; quenched at 980°C and air-cooled to room temperature, then tempered at 600°C, and air-cooled to room temperature, the obtained matrix structure is tempered sorbite + carbide + a small amount of residual austenite Body A, high temperature tempering causes martensite to decompose to form sorbite, and ferrite and carbide are relatively coarse. the

Hardness Analysis

Hardness is an important index to measure wear resistance. The uniformity of the hardness of the ball reflects the uniformity of wear. This experiment uses the HR-150A Rockwell hardness tester to test the hardness value of high chromium white cast iron in the as-cast state and after heat treatment. And make a comparison to study the influence of composition and heat treatment process on the hardness of the material. the

Measure the hardness value at intervals of 5 mm along the two vertical diameters from the center to the edge, and take the average value as the final value of hardness. The hardness measurement sample is shown in Figure 3. From the hardness comparison in Figure 3, it can be seen that after quenching at 980 °C, the hardness of the wear-resistant ball is the highest, which is consistent with the matrix structure of quenched martensite; after tempering at 400 °C, The hardness of the wear-resistant ball is still higher than that of the non-heat-treated wear-resistant ball, indicating that the hardness of tempered martensite is lower than that of quenched martensite, but it is still higher than that of ledeburite + pearlite; and after 600 ° C The hardness of the wear-resistant ball after high temperature tempering is lower than that of the unheated wear-resistant ball. Combined with the analysis of Figure 2, it can be seen that the structure of the wear-resistant ball without heat treatment at room temperature is based on transformed ledeburite, and contains pearlite and carbide, and the hardness value is not high; after quenching at 980 ° C and air-cooled to room temperature, the structure of the wear-resistant ball is as follows: The quenched state is dominated by acicular martensite, and the hardness is very high; after quenching at 980 ° C and air cooling to room temperature, and then tempering at 400 ° C and air cooling to room temperature, the matrix structure of the wear-resistant ball is mainly tempered martensite, and the hardness is After quenching at 980°C and air-cooling to room temperature, then tempering at 600°C and air-cooling to room temperature, the martensite in the structure of the wear-resistant ball decomposes to form tempered sorbite, resulting in a serious decrease in the hardness of the wear-resistant ball. the

wear analysis

The test evaluates wear resistance by comparing the wear amount of each sample under the same wear conditions. ML-10 type abrasive wear testing machine is used, the motor speed is 90r/min, the quartz sandpaper is 140#, and the loads are 200g, 400g, 800g respectively. After wear and tear, its mass was measured with an electronic analytical balance (with an accuracy of 0.1 mg). Wear amount ΔM = mass M ₁ before wear - mass M ₂ after wear. The results are shown in FIG. 4 . It can be seen from Figure 4 that after quenching at 980°C, the amount of wear is the smallest, which may be related to the high hardness of the structure, but internal stress is likely to exist in the quenched structure; after quenching at 980°C and tempering, the wear amount is 980°C The wear amount of the quenched wear-resistant ball is large, which shows that the tempering treatment reduces the wear resistance of the wear-resistant ball, but the wear amount after tempering at 400°C is lower than that after tempering at 600°C, which means that the wear-resistant ball after tempering at medium temperature The wear resistance of the ball is better than that of the wear-resistant ball after high temperature tempering.

Heat treatment experiment conclusion

In this experiment, a high-temperature heating furnace is used to heat-treat the wear-resistant ball samples in different processes, and a metallographic microscope, a Rockwell hardness tester, and an abrasion testing machine are used to analyze the structure and wear resistance of the wear-resistant ball after heat treatment, and the following conclusions are drawn :

1) After the wear-resistant ball is quenched at 980°C, the matrix structure obtained at room temperature is mainly acicular quenched martensite. At this time, the wear-resistant ball has high hardness and wear resistance, but internal stress often exists in the quenched structure, which is easy to Lead to cracking and deformation of the wear-resistant ball, so it must be tempered to eliminate internal stress and improve the toughness of the wear-resistant ball;

2) After tempering at a medium temperature at 400°C, the matrix structure at room temperature is dominated by tempered troostite, and the wear-resistant ball has high hardness and wear resistance; after tempering at a high temperature at 600°C, the matrix structure at room temperature is tempered It is mainly sorbite and contains many coarse ferrite and carbides, which lead to poor hardness and wear resistance of wear-resistant balls;

3) The best heat treatment process is quenching at 980°C and tempering at medium temperature at 400°C. the

It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the protection scope of the appended claims of the present invention. the

Claims (1)

1. A method for manufacturing high chromium cast iron grinding balls, characterized in that the melting and casting process is as follows: the sample blank is smelted in an intermediate frequency induction furnace at a melting temperature of 1450°C to 1500°C, high temperature casting is adopted, and the furnace temperature is about 1400°C The heat treatment process is: quenching at 980 ° C, air cooling to room temperature, tempering temperature is 400 ° C at medium temperature, air cooling to room temperature after tempering; the alloy content of the sample blank is: the carbon content is selected at 2.99%; the manganese content is 2.01 %; Si content 1.15%; Chromium content 14.90%; Mo content 0.01%, Vanadium content 0.21%; Tungsten content less than 0.02%; Titanium content 0.07%; quantity.

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