Ultrahigh-chromium grinding ball and preparation method thereof

Abstract

The invention provides an ultrahigh chromium grinding ball which comprises the following chemical components in percentage by weight: 2.5 to 4.0 percent of C (carbon), 1.0 to 2.0 percent of Si (silicon), 0.8 to 2.5 percent of Mn (manganese), 28.0 to 35.0 percent of Cr (chromium), 0.01 to 0.5 percent of Mo (molybdenum), 0.01 to 0.5 percent of Cu (copper), 0.01 to 0.5 percent of Ni (nickel) and the balance of Fe (iron) and inevitable impurities. By increasing the usage amount of Si and Mn elements and adding a proper amount of Mo / Cu / Ni alloy elements for strengthening, the high-hardness chromium grinding ball is obtained.

Description

Technical Field

[0001] This invention relates to an ultra-high chromium grinding ball, and more particularly to an ultra-high chromium grinding ball and its preparation method. Background Technology

[0002] High-chromium cast iron grinding balls are a cost-effective wear-resistant material widely used in mining, building materials, cement and other industries. Traditional high-chromium white cast iron grinding balls have high hardness, and their metallographic structure is mainly composed of martensite and carbides. While the martensite provides sufficient hardness, it lacks toughness. When the product is subjected to significant impact or stress, microcracks will appear at the locations where the martensite and carbides intertwine.

[0003] Chromium forms hard eutectic carbides (such as M7C3) with carbon, which can give chromium grinding balls high hardness and wear resistance. However, when the content is less than 10.0 wt%, the wear resistance decreases significantly. When the content exceeds 12.0 wt%, the improvement in wear resistance is not significant, and the castability of the molten steel will decrease.

[0004] Currently, there are relatively few manufacturers in China producing ultra-high chromium grinding balls, especially those producing large-diameter grinding balls. The main challenges lie in the element ratio and heat treatment processes. Currently, the heat treatment used by manufacturers of ultra-high chromium grinding balls is uniformly air quenching. This is primarily because air quenching has a faster cooling rate than oil quenching, which can lead to cracking. However, air-quenched products generally have lower overall hardness, typically around 58 HRC, resulting in insufficient wear resistance in practical applications.

[0005] Therefore, in order to obtain high-hardness chromium grinding balls, it is crucial to select the appropriate element ratio and adapt it to the relevant processing technology, which is also an urgent problem to be solved. Summary of the Invention

[0006] To address the technical problems existing in the background art, the present invention proposes an ultra-high chromium grinding ball, the chemical composition of which includes: C: 2.5-4.0 wt%, Si: 1.0-2.0 wt%, Mn: 0.8-2.5 wt%, Cr: 28.0-35.0 wt%, Mo: 0.01-0.5 wt%, Cu: 0.01-0.5 wt%, Ni: 0.01-0.5 wt%, with the balance being Fe and unavoidable impurities.

[0007] The Si+Mn ≥ 3wt%, and the Mo+Cu+Ni ≥ 0.5wt%.

[0008] In this invention, the elemental ratio of Si+Mn≥3wt% and Mo+Cu+Ni≥0.5wt% significantly increases the wear resistance of the ultra-high chromium grinding ball. Among them, Si and Mn are strong ferrite forming elements, which preferentially dissolve in the austenitic matrix during solidification. When the content of Si and Mn increases, they occupy the positions in the matrix that should be occupied by Cr, causing Cr to be "squeezed" out of the matrix. Since Cr is a strong carbide forming element, these squeezed-out Cr are more likely to combine with carbon in the matrix to form high-hardness primary chromium carbide. Alloying elements such as Mo, Cu, and Ni will synergistically increase the hardness of the ultra-high chromium grinding ball.

[0009] When the Si content increases, Si can effectively occupy the positions of Cr in the matrix, displacing more Cr to combine with C to form carbides, increasing the Cr / C ratio, and increasing the proportion of M7C3 type carbides. More dispersed Cr can combine to form more carbide nucleation sites. The increase in nucleation sites effectively refines the size of the carbides, reduces the cutting of the matrix material by the carbides, reduces stress concentration points, and lowers the risk of internal stress and later cracking in the product. At the same time, the increase of Mn enhances the strength of the matrix, expands the austenite phase region, and reduces the risk of matrix cracking. The above adjustments effectively reduce the risk of cracking and breakage during subsequent heat treatment, providing a good foundation for improving the hardness of the product.

[0010] This invention also proposes a method for preparing the above-mentioned ultra-high chromium grinding balls, comprising the following steps:

[0011] S1. Melt the raw materials into molten iron;

[0012] S2. After treating the molten iron with a slag-collecting agent, the ultra-high chromium grinding balls are obtained by casting using a sand-covering process with an iron mold.

[0013] S3. The crude ultra-high chromium grinding balls are placed in quenching oil for oil quenching, and then tempered to obtain the finished ultra-high chromium grinding balls.

[0014] In this invention, Mo and C readily form fine MoC, which can act as in-situ generated second-phase particles to increase nucleation cores, thereby refining the grain size; while Ni can effectively expand the austenite phase region, thereby increasing the impact toughness of the grinding ball and reducing the risk of grinding ball breakage and spalling; Cu only acts in the matrix structure, which can improve the strength of the matrix material and increase corrosion resistance.

[0015] In step S1, the raw materials include low-carbon ferrochrome, ferrosilicon, ferromanganese and scrap steel.

[0016] In step S2, the slag-collecting agent is perlite or quartz sand.

[0017] In step S2, the pouring temperature is 1400-1500℃.

[0018] In step S3, the crude ultra-high chromium grinding balls are heated to 900-1100℃ before oil quenching.

[0019] In step S3, the temperature of the quenching oil is 80-120℃, and the quenching time is 3-6 minutes.

[0020] The method for preparing ultra-high chromium grinding balls according to any one of claims 3-8 is characterized in that, in step S3, the tempering temperature is 400-500℃ and the tempering time is 5-8h.

[0021] Beneficial effects of this invention:

[0022] By increasing the amount of Si and Mn elements and adding appropriate amounts of Mo / Cu / Ni alloying elements for strengthening, the grains are refined and the matrix strength is enhanced, preventing cracking during subsequent oil quenching. Oil quenching and tempering will increase the precipitation of carbides, making the product hardness reach 62-64 HRC. Detailed Implementation

[0023] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0025] The technical solution of the present invention will now be described more clearly and completely with reference to specific embodiments and comparative examples.

[0026] Example 1

[0027] This embodiment proposes an ultra-high chromium grinding ball and its preparation method:

[0028] Ultra-high chromium grinding balls:

[0029] The chemical composition of the high-chromium wear-resistant ball, by weight percentage, includes: C: 3.2wt%, Si: 1.3wt%, Mn: 1.9wt%, Cr: 30.0wt%, Mo: 0.35wt%, Cu: 0.1wt%, Ni: 0.07wt%, with the balance being Fe and unavoidable impurities, wherein Si+Mn=3.2wt%≥3wt%, and Mo+Cu+Ni=0.52wt%≥0.5wt%.

[0030] Preparation method of ultra-high chromium grinding balls:

[0031] (1) Clean and dry low-carbon ferrochrome, ferrosilicon, ferromanganese and scrap steel are put into a high-frequency induction melting furnace for melting according to the chemical composition and ratio of ultra-high chromium grinding balls. When the temperature of the molten iron reaches 1600℃, the chemical composition of the molten iron is tested to see if it meets the requirements. If the content of any element is low, it is supplemented until the chemical composition meets the ratio requirements.

[0032] (2) Add slag-collecting agent perlite to the molten iron, remove the slag twice, sprinkle another layer of slag-collecting agent, and then cast the mixture at a temperature of 1450℃ to obtain the crude product of ultra-high chromium grinding balls.

[0033] (3) Heat the crude ultra-high chromium grinding ball to 1050℃, place it in quenching oil at 100℃, quench it for 4 minutes, then heat the crude ultra-high chromium grinding ball to 450℃ and temper it for 5 hours to obtain the finished ultra-high chromium grinding ball.

[0034] Example 2

[0035] This embodiment proposes an ultra-high chromium grinding ball and its preparation method:

[0036] Ultra-high chromium grinding balls:

[0037] The chemical composition of the high-chromium wear-resistant ball, by weight percentage, includes: C: 2.7wt%, Si: 1.6wt%, Mn: 2.2wt%, Cr: 28.0wt%, Mo: 0.23wt%, Cu: 0.25wt%, Ni: 0.05wt%, with the balance being Fe and unavoidable impurities, wherein Si+Mn=3.8wt%≥3wt%, and Mo+Cu+Ni=0.53wt%≥0.5wt%.

[0038] Preparation method of ultra-high chromium grinding balls:

[0039] (1) Clean and dry low-carbon ferrochrome, ferrosilicon, ferromanganese and scrap steel are put into a high-frequency induction melting furnace for melting according to the chemical composition and ratio of ultra-high chromium grinding balls. When the temperature of the molten iron reaches 1600℃, the chemical composition of the molten iron is tested to see if it meets the requirements. If the content of any element is low, it is supplemented until the chemical composition meets the ratio requirements.

[0040] (2) Add slag-collecting agent perlite to the molten iron, remove the slag three times, sprinkle another layer of slag-collecting agent, and then cast the mixture at a temperature of 1450℃ to obtain the crude product of ultra-high chromium grinding balls.

[0041] (3) Heat the crude ultra-high chromium grinding ball to 1030℃, place it in quenching oil at 90℃, quench it for 4 minutes, then heat the crude ultra-high chromium grinding ball to 420℃ and temper it for 7 hours to obtain the finished ultra-high chromium grinding ball.

[0042] Example 3

[0043] This embodiment proposes an ultra-high chromium grinding ball and its preparation method:

[0044] Ultra-high chromium grinding balls:

[0045] The chemical composition of the high-chromium wear-resistant ball, by weight percentage, includes: C: 4.0 wt%, Si: 1.8 wt%, Mn: 2.5 wt%, Cr: 35.0 wt%, Mo: 0.27 wt%, Cu: 0.21 wt%, Ni: 0.06 wt%, with the balance being Fe and unavoidable impurities, wherein Si+Mn=4.3 wt% ≥ 3 wt%, and Mo+Cu+Ni=0.54 wt% ≥ 0.5 wt%.

[0046] Preparation method of ultra-high chromium grinding balls:

[0047] (1) Clean and dry low-carbon ferrochrome, ferrosilicon, ferromanganese and scrap steel are put into a high-frequency induction melting furnace for melting according to the chemical composition and ratio of ultra-high chromium grinding balls. When the temperature of the molten iron reaches 1600℃, the chemical composition of the molten iron is tested to see if it meets the requirements. If the content of any element is low, it is supplemented until the chemical composition meets the ratio requirements.

[0048] (2) Add slag-collecting agent perlite to the molten iron, remove the slag twice, sprinkle another layer of slag-collecting agent, and then cast the mixture at a temperature of 1450℃ to obtain the crude product of ultra-high chromium grinding balls.

[0049] (3) Heat the crude ultra-high chromium grinding ball to 1070℃, place it in quenching oil at 105℃, quench it for 5 minutes, then heat the crude ultra-high chromium grinding ball to 465℃ and temper it for 6 hours to obtain the finished ultra-high chromium grinding ball.

[0050] Comparative Example 1

[0051] This comparative example presents an ultra-high chromium grinding ball and its preparation method, which is the same as that in Example 1, except that "Mn: 1.9wt%" is replaced with "Mn: 0.9wt%", that is, Si+Mn=2.2wt%≤3wt%, Mo+Cu+Ni=0.52wt%≥0.5wt%.

[0052] Comparative Example 2

[0053] This comparative example presents an ultra-high chromium grinding ball and its preparation method, which is the same as in Example 1, except that "Mo: 0.35wt%" is replaced with "Mo: 0.15wt%", that is, Si+Mn=3.4wt%≥3wt%, Mo+Cu+Ni=0.34wt%≤0.5wt%.

[0054] Comparative Example 3

[0055] This comparative example presents an ultra-high chromium grinding ball and its preparation method, which is the same as that in Example 1, except that oil quenching is replaced by air quenching.

[0056] Metallographic examination, hardness testing, and impact toughness testing were performed on Examples 1-3 and Comparative Examples 1-3. The hardness test was performed according to GB / T230.1-2009, and the impact toughness test was performed according to GB / T229-2020. The test data are shown in Table 1.

[0057] Table 1 Performance test data for each embodiment and comparative example

[0058]

[0059]

[0060] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-chromium grinding ball, characterized in that, The chemical composition of the ultra-high chromium grinding ball includes: C: 2.5-4.0 wt%, Si: 1.0-2.0 wt%, Mn: 0.8-2.5 wt%, Cr: 28.0-35.0 wt%, Mo: 0.01-0.5 wt%, Cu: 0.01-0.5 wt%, Ni: 0.01-0.5 wt%, with the balance being Fe and unavoidable impurities.

2. The ultra-high chromium grinding ball according to claim 1, characterized in that, The Si+Mn ≥ 3wt%, and the Mo+Cu+Ni ≥ 0.5wt%.

3. A method for preparing the ultra-high chromium grinding ball according to claim 1 or 2, characterized in that, Includes the following steps: S1. Melt the raw materials into molten iron; S2. After treating the molten iron with a slag-collecting agent, the ultra-high chromium grinding balls are obtained by casting using a sand-covering process with an iron mold. S3. The crude ultra-high chromium grinding balls are placed in quenching oil for oil quenching, and then tempered to obtain the finished ultra-high chromium grinding balls.

4. The method for preparing ultra-high chromium grinding balls according to claim 3, characterized in that, In step S1, the raw materials include low-carbon ferrochrome, ferrosilicon, ferromanganese and scrap steel.

5. The method for preparing ultra-high chromium grinding balls according to claim 3 or 4, characterized in that, In step S2, the slag-collecting agent is perlite or quartz sand.

6. The method for preparing ultra-high chromium grinding balls according to any one of claims 3-5, characterized in that, In step S2, the pouring temperature is 1400-1500℃.

7. The method for preparing ultra-high chromium grinding balls according to any one of claims 3-6, characterized in that, In step S3, the crude ultra-high chromium grinding balls are heated to 900-1100℃ before oil quenching.

8. The method for preparing ultra-high chromium grinding balls according to any one of claims 3-7, characterized in that, In step S3, the temperature of the quenching oil is 80-120℃, and the quenching time is 3-6 minutes.

9. The method for preparing ultra-high chromium grinding balls according to any one of claims 3-8, characterized in that, In step S3, the tempering temperature is 400-500℃ and the tempering time is 5-8h.

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