Production method of steel fine grains for high-carbon grinding balls

Abstract

The invention belongs to the technical field of metallurgy, and particularly relates to a production method of fine grains of steel for high-carbon grinding balls, which comprises the following steps: 1) controlling part of chemical components in the steel: controlling the content of Al to be 0.025-0.040%, the content of Mn to be 0.65-0.80% and the content of Cr to be 0.60-0.90% in percentage by weight; (2) the binary alkalinity of LF refining slag is controlled to be 4.5-6.0, the nitrogen content of molten steel after RH refining is 26-38 ppm, and (3) the final rolling temperature of continuous rolling is controlled to be 950-1000 DEG C. According to the method, the technical requirements of steel for large-specification high-carbon steel wear-resistant steel balls are met, the requirement for fine grains of the grinding ball steel at the grade of 7 or above is met, and meanwhile the requirement for high hardenability of the grinding ball steel and the requirement for low-grade inclusions are also met.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and particularly relates to a method for producing fine-grained steel for high-carbon grinding balls. Background Art

[0002] With the development of the mining industry, the demand for steel for wear-resistant steel balls is increasing day by day, and the quality requirements for steel for wear-resistant steel balls are getting higher and higher. It is not only required that the raw materials have good internal quality, high hardenability and hardenability, but also the requirements for grain size from different manufacturers are gradually on the rise, from not less than grade 5.0 to as high as not less than grade 7.0 (the industry is generally at grade 6.0). Therefore, it is very necessary to study the grain size of steel for grinding balls, especially low-alloy medium-high carbon steel with a large size of more than φ90mm, and the influence of grain size on hardenability and inclusions must be systematically considered in the process design. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for producing fine-grained steel for high-carbon grinding balls, which meets the technical requirements of steel for large-size high-carbon wear-resistant steel balls, not only meets the requirement of fine grains of grade 7 or above for grinding ball steel, but also meets the requirement of high hardenability and lower-grade inclusions for grinding ball steel.

[0004] In order to achieve the above purpose, the present invention is realized by adopting the following technical solutions: A method for producing fine-grained steel for high-carbon grinding balls, the production process includes: converter smelting, LF refining, RH refining, continuous casting, charging and heating, blooming, continuous rolling and slow cooling; the specific method is as follows: 1) Control of some chemical components in the steel: by weight percentage, the Al content is controlled at 0.025% - 0.040%, the Mn content is controlled at 0.65% - 0.80%, and the Cr content is controlled at 0.60% - 0.90%; 2) The binary basicity of the LF refining slag is controlled at 4.5 - 6.0; the nitrogen content of the molten steel after RH refining is 26 - 38 ppm; 3) The finish rolling temperature of continuous rolling is controlled at 950 - 1000 °C.

[0005] Preferably, for the control of some chemical components in the steel: by weight percentage, the Al content is controlled at 0.030%, the Mn content is controlled at 0.75%, and the Cr content is controlled at 0.77%.

[0006] For the LF refining, the temperature for entering the refining is 1493 - 1513 °C.

[0007] The charging and heating process adopts four-stage heating. The temperature in the first heating stage is 600 - 750°C, and the residence time in the furnace is 125 - 165 min; the temperature in the second heating stage is 850 - 1050°C, and the residence time in the furnace is 110 - 150 min; the temperature in the third heating stage is 1160 - 1250°C, and the soaking temperature is 1180 - 1250°C. The total residence time in the third heating stage and the soaking stage is 215 - 285 min; the total residence time in the furnace is 450 - 600 min.

[0008] The rolling temperature of the blooming mill is 1050 - 1150°C, the temperature for entering the continuous rolling is 1000 - 1060°C, and the finishing rolling temperature is controlled at 950 - 1000°C; after the rolled piece is sawed, the cooling bed adopts fast-forward collection to ensure that the temperature for entering the slow cooling pit is ≥320°C, and the temperature for leaving the slow cooling pit is ≤100°C.

[0009] The chemical composition in the steel is by weight percentage: C: 0.60% - 0.66%, Si: 1.60% - 1.90%, Mn: 0.65% - 0.80%, Cr: 0.60% - 0.90%, Al: 0.025% - 0.040%, P ≤ 0.025%, S ≤ 0.010%, and the balance is iron and inevitable impurities.

[0010] The grain size of the steel is above grade 7. For the end hardenability of round steel with a specification of φ100mm and above: J9 ≥ 61HRC, J15 ≥ 59HRC, J25 ≥ 53HRC, J30 ≥ 44HRC.

[0011] In the steel of the present invention, the fine series of class B inclusions is grade 0 - 1.5, with an average of 0.53; the fine series of class D inclusions is grade 0 - 1.0, with an average of 0.567; the class Ds inclusions are grade 0.

[0012] In the present invention, an aluminum content control of 0.025% - 0.040% is adopted in the chemical composition design to ensure the formation amount of aluminum nitride under the condition of low nitrogen (26 - 38 ppm) after RH vacuum, laying a foundation for achieving fine and uniform grains. At the same time, combined with the working conditions of the steel mill, a reasonable rolling process is equipped, and the finishing rolling temperature is designed in the range of 950 - 1000°C to ensure that the average grain size is above grade 7.

[0013] The present invention matches the chemical composition design with the refinement of the grain size, comprehensively considers the grain size and hardenability, and makes systematic technical improvements: After the grain size is increased from the original average of grade 6.0 to above average of grade 7.0, it will lead to a decrease in hardenability. In the present invention, the target chemical components of Mn and Cr are respectively controlled at Mn: 0.65% - 0.80% and Cr: 0.60% - 0.90%. Especially when Mn and Cr are 0.75% and 0.77% respectively, it can ensure that the hardenability of the grinding balls will not decrease. On the premise that the alloy cost does not increase significantly, grain refinement is achieved, the hardness does not decrease, and the wear resistance is significantly improved, and the cost performance of the grinding balls is improved.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. After the implementation of the present invention, the grain size of the steel can reach above average of grade 7.0.

[0015] 2. By controlling the basicity of the refining slag in the present invention, the fine series of type B inclusions in the molten steel is improved to grade 0 - 1.5 (average 0.53), the average grade of the fine series of type D reaches 0.567, and the type Ds is basically 0, ensuring good overall inclusion level.

[0016] 3. For the round steel products with a diameter of more than φ100mm in the present invention, it is experimentally verified that the end hardenability does not decrease. The end hardenability of the round steel with a diameter of more than φ100mm is: J9≥61HRC, average 61.6HRC; J15≥59HRC, average 60.3HRC; J25≥53HRC, average 55HRC; J30≥44HRC, average 45.3HRC. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is the austenitization and solid-liquid phase temperature range calculated by JMatPro software.

[0018] Figure 2 It is the metallographic diagram of the grain size (grade 0.7) of the product in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] The following further illustrates the specific implementation manners of the present invention in conjunction with the embodiments. The following embodiments are used to specifically illustrate the content of the present invention. These embodiments are only general descriptions of the content of the present invention and do not limit the content of the present invention.

[0020] The production process of the present invention is as follows: hot metal - converter smelting - deoxidation alloying - LF refining - RH refining - continuous casting - slow cooling - out of storage - charging and heating - blooming - continuous rolling - sawing - cooling and collecting - slow cooling in the pit - out of the pit - straightening - flaw detection - packaging - weighing - warehousing.

[0021] 1. Combining with the pearlite-based microstructure characteristics of the steel used for grinding balls, as well as the requirements for hardenability and the actual situation of relatively low nitrogen content after RH treatment, if the grain size is adjusted from an average of grade 6.0 to above an average of grade 7.0, the target Al content needs to be increased to 0.025% - 0.040%. Considering that the increase in grain size will lead to a decrease in hardenability, it is necessary to finely adjust the target chemical compositions of Mn and Cr to reduce their impact on hardenability and wear resistance. The theoretical adjustment amounts of Mn and Cr elements under the condition of little change in hardenability are calculated by two methods: empirical formula and JMatPro software. The composition design of specific examples is shown in Table 1.

[0022] Table 1: Composition of Optimized Grinding Ball Steel

[0023] 2. By adjusting the basicity of the LF refining slag, the present invention reduces the influence of inclusions: Considering the current grade requirements for various fine inclusions and the influence of the designed change in Al content on inclusions, it is necessary to adjust the binary basicity of the LF refining slag to 5.5 to reduce the highest grade of type B inclusions and appropriately increase the grade of type D inclusions to ensure good overall inclusion level.

[0024] After entering the refining, ensure that the melting effect of the ladle top slag is good, and the average refining temperature is 1503°C. The consumption of lime after argon and during LF furnace refining is about 9.58 kg / t, the consumption of pre-melted calcium aluminate is about 10.0 kg / t, the consumption of calcium carbide during LF furnace refining is about 1.20 kg / t, and the consumption of aluminum pellets is about 0.19 kg / t. The final slag is all white slag. The designed CaO content in the LF refining slag sample is about 52%, SiO2 is about 9.5%, Al2O3 is about 29%, and FeO is about 0.4%, that is, the basicity R is about 5.5. The average power-on treatment time is 55 min, and the average refining cycle is 120 min.

[0025] 3. By optimizing the rolling process, promote uniform grains, and the average grade reaches above grade 7.0: Considering that this grade is mainly composed of pearlite microstructure, and due to the large size of the specification and the lack of controlled rolling and controlled cooling means in the unit, it is impossible to perform large reduction rolling in the austenite non-recrystallization zone of the rolled piece, that is, it is impossible to refine grains through austenite non-recrystallization or two-phase zone rolling. At the same time, calculate the austenitization and solid-liquid phase temperature ranges of this grade through JMatPro software (see Figure 1 ), that is, the solid phase temperature is about 1340°C, and the Ar3 temperature is about 790°C, so as to determine whether the optimized heating system is scientific and reasonable and operable. The process system of specific examples is shown in Table 2, and the product performance indicators of the examples are shown in Table 3. The grain size (grade 0.7) of the product in Example 1 is shown in the metallographic Figure 2 .

[0026] Table 2: Heating System for 390*510mm Cross-section Continuous Casting Slab

[0027] Table 3: Product Performance Indicators of the Examples (φ100mm) 。

Claims

1. A production method for fine grains of steel used for high-carbon grinding balls, and the production process includes: Converter smelting, LF refining, RH refining, continuous casting, charging and heating, blooming, continuous rolling and slow cooling; it is characterized in that the specific method is as follows: 1) Control of some chemical components in steel: By weight percentage, the Al content is controlled at 0.025% - 0.040%, the Mn content is controlled at 0.65% - 0.80%, and the Cr content is controlled at 0.60% - 0.90%; 2) The binary basicity of the LF refining slag is controlled at 4.5 - 6.0; the nitrogen content of the molten steel after RH refining is 26 - 38 ppm; 3) The finish rolling temperature of continuous rolling is controlled at 950 - 1000 °C.

2. The method for producing fine grains of steel for high-carbon grinding balls according to claim 1, characterized in that, Control of some chemical components in steel: By weight percentage, the Al content is controlled at 0.030%, the Mn content is controlled at 0.75%, and the Cr content is controlled at 0.77%.

3. A method for producing fine grains of steel for high-carbon grinding balls according to claim 1, characterized in that, For the said LF refining, the refining temperature is 1493 - 1513 °C.

4. A method for producing fine grains of steel for high-carbon grinding balls according to claim 1, characterized in that, The said charging and heating adopts four-stage heating. The temperature of heating section I is 600 - 750 °C, and the residence time in the furnace is 125 - 165 min; the temperature of heating section II is 850 - 1050 °C, and the residence time in the furnace is 110 - 150 min; the temperature of heating section III is 1160 - 1250 °C, the soaking section temperature is 1180 - 1250 °C, and the sum of the residence times in the furnace for heating section III and the soaking section is 215 - 285 min; the total residence time in the furnace is 450 - 600 min.

5. A production method for fine grains of steel for high-carbon grinding balls according to claim 1, characterized in that, The starting rolling temperature of the blooming mill for rolling steel is 1050 - 1150 °C, the temperature for entering continuous rolling is 1000 - 1060 °C, and the finish rolling temperature is controlled at 950 - 1000 °C; the temperature for entering the slow cooling pit is ≥320 °C, and the temperature for leaving the slow cooling pit is ≤100 °C.

6. A method for producing fine grains of steel for high-carbon grinding balls according to claim 1, characterized in that, The chemical components in steel by weight percentage are: C: 0.60% - 0.66%, Si: 1.60% - 1.90%, Mn: 0.65% - 0.80%, Cr: 0.60% - 0.90%, Al: 0.025% - 0.040%, P ≤ 0.025%, S ≤ 0.010%, and the balance is iron and unavoidable impurities.

7. A method for producing fine grains of steel for high-carbon grinding balls according to any one of claims 1-6, characterized in that, The grain size of the steel is above grade 7.

0. The end hardenability of round steel with a specification of φ100 mm and above is: J9 ≥ 61 HRC, J15 ≥ 59 HRC, J25 ≥ 53 HRC, J30 ≥ 44 HRC.

8. A production method for fine grains of steel for high-carbon grinding balls according to any one of claims 1-6, characterized in that, The fine series of B-type inclusions in the steel is grade 0 - 1.5; the fine series of D-type is grade 0 - 1.0; the Ds type is grade 0.

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