CN108165890B

CN108165890B - Preparation method of low-cost high-strength nano bainite wear-resistant steel ball

Info

Publication number: CN108165890B
Application number: CN201810018403.7A
Authority: CN
Inventors: 于浩; 余子权; 宋成浩
Original assignee: University of Science and Technology Beijing USTB
Current assignee: University of Science and Technology Beijing USTB
Priority date: 2018-01-09
Filing date: 2018-01-09
Publication date: 2020-08-11
Anticipated expiration: 2038-01-09
Also published as: CN108165890A

Abstract

A preparation method of a low-cost high-strength nano bainite wear-resistant steel ball belongs to the technical field of metal material processing. The steel ball weight percentage is C: 0.45-0.7 wt.%, Si: 1.5-3.0 wt.%, Mn: 0.5-2.0 wt.%, Cr: 0.1-1.5 wt.%, Al: 0.1-2.0 wt.%, Ti: 0.01-0.1 wt.%, and the balance of Fe and inevitable impurities. After smelting and casting the steel, hot rolling or hot forging the steel into steel balls with the diameter phi of 20-160 mm, rapidly cooling the steel balls to 200-400 ℃, and then preserving the heat for 3-8 hours to obtain the complex phase structure. The alloy disclosed by the invention does not contain elements such as Mo, Ni, Nb, V and the like, is low in cost and simple in heat treatment process, avoids heat treatment procedures such as quenching and tempering, is stable in production process, and obviously increases the wear resistance of the steel ball while refining grains.

Description

Preparation method of low-cost high-strength nano bainite wear-resistant steel ball

Technical Field

The invention belongs to the technical field of metal material processing, and relates to a complex phase structure consisting of nano bainite, a small amount of residual austenite and a TiC precipitated phase distributed in a dispersion manner at room temperature and a production process thereof. The steel grade has excellent wear resistance and is mainly applied to the fields of mines, metallurgy, electric power, building materials, chemical industry and the like.

Background

In the major national basic engineering, energy conservation and emission reduction and light weight of traffic equipment are further emphasized, green transformation and upgrading of the manufacturing industry are accelerated, and the development of industries such as steel, petrifaction, engineering machinery, light industry and textile towards the high end of a value chain is promoted. Therefore, the research effort of steel materials needs to be further improved, and the development of novel steel materials with high strength and toughness and light weight is focused on, so that the consumption of energy resources is reduced, and the sustainable development of the economy and the society is promoted. And with the structure adjustment and the industry upgrade of key industries, products with high performance and high added value and a green, efficient and low-carbon production mode are urgently needed. The steel production capacity of China is in a serious surplus stage, but the high value-added products still cannot completely meet the market demand and still need to be made up by means of imports. According to the estimation, the market demand of the high-grade wear-resistant steel in China is 50-80 ten thousand tons per year, and the import quantity is about 10 ten thousand tons. In addition, the economic loss caused by abrasion in countries around the world is about 500 billion dollars per year in the United states, 153 billion Euros per year in Germany and about 1000 billion yuan per year in China, so that the development of advanced wear-resistant materials has great economic significance.

At present, the top wear-resistant steel production enterprises in foreign countries mainly include the HARDOX series of the SSAB company in Sweden, the XAR series of Detisen knuder, the Germany Dilinggen V series, the RAEX series of Finland Roche, the Japanese JFE series, and the like. The domestic high-end wear-resistant steel market is occupied by the foreign enterprises, and the sale price is more than one time of domestic wear-resistant steel of the same grade, for example, the sale price of the Finland RAXE400(8mm) is 17500 yuan/ton, the sale price of the Japanese JFE-EH400(6-10mm) is 14500 yuan/ton, the sale price of the Bao steel B-MARD400(8mm) is 7500 yuan/ton, and the sale price of the Xinyu wear-resistant steel NM500(6mm) is 8000 yuan/ton. The manufacturers capable of producing high-strength wear-resistant steel in China mainly comprise dance steel, armed steel, precious steel, south steel and the like, the main varieties are NM360 and NM400, and the thickness is 6-80mm generally. Some manufacturers have reached or exceeded international levels and export to southeast asia, japan, south africa, the united states, australia, etc. The wear-resistant steel plate for the weldable high-strength structure, which is produced by the dance steel and has the hardness HB of more than or equal to 360, is suitable for occasions with high wear and high impact, and can also be used as high-strength structural steel with the yield strength of more than or equal to 700 MPa. NM360 and NM400 grade wear-resistant steel is developed by Bao steel in turn, and the size range of the steel plate can be 12-60mm in thickness, 4500mm in width 900 and 13000mm in length 8000. The Anshan iron and steel group company cooperates with Beijing university of science and technology to successfully research and develop bainite-martensite wear-resistant steel plates, and deeply research the structure and mechanical properties of the bainite-martensite wear-resistant steel plates, so that NM360 and NM400 grade wear-resistant steel can be produced. In general, today's developments in wear resistant steel technology present an unbalanced current situation: firstly, the technical development at home and abroad is unbalanced, and domestic wear-resistant steel production enterprises fall behind the most advanced international level in the aspects of technical level, product performance and the like; secondly, the production of the product is unbalanced, the specification and the size of the wear-resistant steel plate product are complete, the number of production enterprises is large, and the number of enterprises for producing wear-resistant steel bars and grinding balls is relatively small.

Chinese application patent CN1189542 discloses a multi-element microalloyed air-cooled bainite steel, which does not need a complex heat treatment process, and grinding balls with bainite/martensite as a main structure can be obtained by air cooling after forging or after rolling, but in order to improve the hardenability and hardness of the material, the grinding balls are addedA large number of microalloy elements such as Nb, V, Ti, RE and the like greatly increase the production cost. Chinese application patent CN104651722 discloses a method for preparing a forged steel ball with a martensite structure surface layer and a soft bainite structure inner core, the alloy components of which are C: 0.42-0.48 wt.%, Si: 0.15-0.35 wt.%, Mn: 0.53-0.90 wt.%, Ni: 0.06-0.20 wt.%. The hardness of the martensite structure on the surface is HRC62 or less, and the hardness of the bainite structure on the core is HRC40 or more. Because the hardness difference between the surface and the core is large, the steel ball is easy to lose efficacy after the surface martensite layer is ground off in the using process, and the service life of the material is reduced. Chinese patent application No. CN103225036 discloses a boron carbide reinforced wear-resistant bainite ductile iron grinding ball and a manufacturing method thereof, wherein a bainite matrix with good obdurability is obtained by controlled cooling, and a certain amount of high hardness (Fe, Cr) is obtained by adding boron and chromium elements₂(B, C) boron carbide to improve the wear resistance of the grinding ball. However, in the method, the wear-resistant steel ball is produced by adopting a casting process, and bubbles or looseness is easily generated in the steel ball, so that the internal structure of the steel ball is thick, particularly the position of a pouring gate is easy to cause uneven hardness, and the steel ball is broken due to out-of-round.

In conclusion, based on scientific and reasonable alloy composition design, the steel ball with the diameter phi of 20-160 mm is formed by smelting, casting, hot rolling or hot forging, the steel ball is rapidly cooled to a certain temperature by utilizing hot processing waste heat, and then the steel ball is kept warm for a period of time, so that the complex phase structure consisting of the nano bainite serving as a matrix, the residual austenite and the TiC precipitated phase can be obtained. The innovation of the invention is as follows: 1) the developed steel is medium-high carbon low alloy steel, the alloy content is low, national strategic resources such as Mo and Ni are not contained, and noble metal elements such as Nb and V are not contained; 2) the bainite wear-resistant steel is environment-friendly, energy-saving and emission-reducing, the nano bainite structure with excellent comprehensive performance can be obtained by certain cooling and heat-preserving process treatment by utilizing the heat processing waste heat without reheating, quenching, tempering and other heat treatment processes, the energy consumption is reduced, the time and the production cost are saved, and the cost performance of the product is greatly improved.

Disclosure of Invention

The invention provides a resource-saving and environment-friendly nano bainite wear-resistant steel ball and a preparation method thereof aiming at the requirements of steel for the wear-resistant steel ball on the hardness, toughness and production cost of the material.

The invention provides a preparation method of a low-cost high-strength nano bainite wear-resistant steel ball, which is characterized in that the weight percentage of alloy components is C: 0.45-0.7 wt.%, Si: 1.5-3.0 wt.%, Mn: 0.5-2.0 wt.%, Cr: 0.1-1.5 wt.%, Al: 0.1-2.0 wt.%, Ti: 0.01-0.1 wt.%, the balance being Fe and unavoidable impurities;

the preparation process comprises the following steps:

firstly, smelting, casting, hot rolling or hot forging the alloy components into steel balls with the diameter phi of 20-160 mm, wherein the total reduction rate is 75-90%; the initial rolling temperature or the initial forging temperature is 1050-1150 ℃, and the final rolling temperature or the final forging temperature is 950-1000 ℃;

and step two, air-cooling the steel ball to 800-900 ℃, then rapidly cooling to 200-400 ℃, and preserving heat for 3-8 hours at the temperature to obtain a complex phase structure consisting of a nano bainite matrix, a small amount of residual austenite and a TiC precipitated phase.

Furthermore, Ti is added into the alloy components to form a TiC precipitated phase with nano-scale size and uniform distribution, so that coarse grains of deformed austenite are inhibited, grains are refined, the strength of a matrix is enhanced, and the wear resistance is improved.

Further, the rolled or forged steel ball is air-cooled to 800-900 ℃, the temperature is higher than the upper limit temperature of a pearlite transformation zone and is also in a TiC precipitation temperature range, and the purpose is to promote the precipitation of a large amount of TiC particles.

Further, the speed of the steel ball rapid cooling is more than 5 ℃/s so as to avoid a pearlite transformation zone, and the super-cooled austenite directly enters a bainite transformation zone.

Furthermore, the volume fraction of the steel ball residual austenite structure is 5-20%.

Furthermore, the steel balls have different heat preservation temperatures, different heat preservation times and corresponding structures and properties, and the nano-bainite lamella spacing is reduced, the strength and the hardness are increased and the heat preservation time is correspondingly prolonged along with the reduction of the heat preservation temperature.

Further, the mechanical properties of the bainite abrasion-resistant steel ball are as follows: yield strength R_pGreater than or equal to 1600MPa, tensile strength R_mMore than or equal to 1900MPa, elongation A after fracture more than or equal to 10 percent, Rockwell hardness HRC more than or equal to 55, and room temperature impact toughness ak more than or equal to 20J/cm²。

The main elements in the material of the invention have the following functions:

c: when the carbon content in the steel is less than 0.8 wt.%, the strength and the hardness of the steel can be improved by increasing the carbon content, the Ms point and the Bs point are effectively reduced, the temperature difference between the Ms and the Bs is enlarged, and the formation of low-temperature nano bainite is ensured. Calculations made by Thermo-calc and MUCG83 show that the temperature range for bainite transformation extends to a reasonable range suitable for industrial production at carbon contents greater than 0.45 wt.%. On the other hand, too high carbon content can reduce the transformation driving force and transformation rate of bainite transformation, so that the transformation degree of bainite is low, the isothermal treatment time is prolonged, the production efficiency is reduced, and the production cost is increased. The transition time was about 28h when the carbon content was 0.8 wt.%; when the carbon content is 1.0 wt.%, the transition time exceeds 3000 h. Comprehensively considering the product performance, the production cost and other factors, and increasing the carbon content of the wear-resistant steel ball to 0.45-0.7 wt.%.

Si: silicon is used as a non-carbide forming element, the added silicon can hinder the precipitation of cementite, so that brittle phases harmful to toughness and plasticity are avoided, the carbon content in austenite can be ensured, residual austenite can stably exist at room temperature, the minimum content of silicon capable of effectively hindering the precipitation of cementite is 1.5 wt.%, and 1.5-2.0 wt.% of silicon is usually added into steel. In addition, silicon is used as a solid solution strengthening element, so that the strength of austenite can be increased, and the bainite structure is refined. The silicon element can make the pearlite transformation area move upwards and the bainite transformation area move downwards, so that the transformation curve is pulled up and down, and the transformation of the bainite is easier to control. However, the delay effect of silicon on bainite transformation is significant, so the addition amount of silicon is selected to be 1.5 to 3.0 wt.% in comprehensive consideration.

Mn: manganese can improve the strength of metal through solid solution strengthening, can separate upper and lower C curves, improves hardenability, obviously reduces the phase transformation driving force of bainite, reduces the transformation temperature of bainite, also can reduce the transformation temperature of martensite, can refine laths, and is beneficial to obtaining a bainite structure with small size. However, too high a manganese content decreases the transformation rate of bainite and causes severe carbon segregation. Comprehensively considering, the addition amount of the manganese is selected to be 0.5-2.0 wt.%.

Cr: chromium improves the stability of super-cooled austenite and increases the transformation incubation period of bainite. In addition, Cr can increase the hardenability of steel and lower the martensite start temperature. Comprehensively considering, the addition amount of the chromium is selected to be 0.1-1.5 wt.%.

Al: the aluminum can increase the free energy difference between bainitic ferrite and austenite, accelerate the transformation rate of bainite and refine the structure at the same time. When the adding amount of aluminum is excessive, the fluidity of the molten steel is obviously reduced, the casting difficulty is greatly improved, and meanwhile, Al in the steel is added₂O₃The slag inclusions are also significantly increased. In addition, Al and Co are used together to have better effect of accelerating bainite transformation, but Co is expensive, and the addition of Co increases the production cost, so that Co is not added in the alloy composition designed by the invention. The bainite transformation time, actual production, cost and other factors are comprehensively considered, and the addition amount of the aluminum is selected to be 0.1-2.0 wt.%.

Ti: titanium is a common micro-alloying element in high-quality steel, can form fine carbonitride with C, N, can inhibit the coarsening of crystal grains in the austenitizing process of the steel, improves the temperature of a non-recrystallization zone, and simultaneously, precipitated TiC can play a role in strengthening a matrix, thereby increasing the strength and the wear resistance of the steel. Researches show that when the content of titanium is 0.01-0.1 wt.%, the size, distribution and volume fraction of precipitated TiC particles reach the most reasonable proportion, and the strength and wear resistance of steel are the best. Therefore, the amount of titanium is selected to be 0.01 to 0.1 wt.%.

The invention is provided withThe nano-scale lath bainite wear-resistant steel ball is efficiently prepared by reasonable element proportion through hot rolling or forging and waste heat treatment processes. Yield strength R of the material_pGreater than or equal to 1600MPa, tensile strength R_mNot less than 1900MPa, the elongation A after fracture not less than 10%, the core hardness of 55-56 HRC, the surface hardness of 58-60 HRC, and the room temperature impact toughness ak not less than 20J/cm². The preparation process is simple, does not need the heat treatment steps of reheating, quenching, tempering and the like, reduces the cost, saves energy, reduces consumption and protects the environment. Meanwhile, the added alloy elements are relatively few, the alloy does not contain national strategic resources such as Mo and Ni, and noble metal elements such as Nb and V, and a resource-saving and environment-friendly product is developed. The nano bainite abrasion-resistant steel ball has obvious advantages in the aspects of performance and cost, and has very wide application prospect in the industries of mines, metallurgy, electric power, building materials, chemical engineering and the like.

Drawings

FIG. 1 is a metallographic structure image of bainite in example 1 of the present invention

FIG. 2 is a metallographic structure image of bainite in example 2 of the present invention

FIG. 3 is a metallographic structure image of bainite in example 3 of the present invention

FIG. 4 is an SEM image of bainite in example 1 of the present invention

FIG. 5 is an SEM image of bainite in example 2 of the present invention

FIG. 6 is an SEM image of bainite in example 3 of the present invention

Detailed Description

The technical solution of the present invention is further illustrated by the following specific examples.

Example 1:

firstly, smelting and casting are carried out according to the component range, and then the components of a casting blank are detected, and the table 1 shows.

TABLE 1 composition of cast slab (wt.%)

A casting blank with the diameter of phi 300mm is heated to 1150 ℃ and homogenized for 2h, and the casting blank is rolled into a bar with the diameter of phi 80mm at 1100 ℃, the total rolling reduction rate is 73 percent, the structure of the bar is mainly sorbite, and the mechanical properties are shown in table 2.

TABLE 2 mechanical Properties

The bar is heated to 1050 ℃ and forged into balls at the temperature, and the final forging temperature is 950 ℃. And then, air-cooling the steel ball to 820-830 ℃, then cooling to 300 ℃ at a cooling rate of more than 5 ℃/s, and preserving heat for 5 hours to form a nano bainite structure, wherein the heat treatment process parameters are shown in Table 3. The mechanical properties of the bainite wear-resistant steel ball are shown in Table 4, the metallographic photograph is shown in figure 1, and the scanning photograph is shown in figure 4.

TABLE 3 Heat treatment Process parameters

TABLE 4 mechanical Properties

Example 2:

firstly, smelting and casting are carried out according to the component range, and then the components of the casting blank are detected, and the table 5 shows.

TABLE 5 composition of cast slab (wt.%)

A casting blank with the diameter of phi 300mm is heated to 1150 ℃ and homogenized for 2h, and the casting blank is rolled into a bar with the diameter of phi 80mm at 1100 ℃, the total rolling reduction rate is 73 percent, the structure of the bar is mainly sorbite, and the mechanical properties are shown in table 6.

TABLE 6 mechanical Properties

The bar is heated to 1050 ℃ and forged into balls at the temperature, and the final forging temperature is 950 ℃. And then, air-cooling the steel ball to 820-830 ℃, then cooling to 300 ℃ at a cooling rate of more than 5 ℃/s, and preserving heat for 5 hours to form a bainite structure, wherein the heat treatment process parameters are shown in Table 7. The mechanical properties of the bainite wear-resistant steel ball are shown in a table 8, the metallographic picture is shown in a figure 2, and the scanning picture is shown in a figure 5.

TABLE 7 Heat treatment Process parameters

TABLE 8 mechanical Properties

Example 3:

firstly, smelting and casting are carried out according to the component range, and then the components of the casting blank are detected, and the table 9 shows.

TABLE 9 composition of cast slabs (wt.%)

A casting blank with the diameter of phi 300mm is heated to 1150 ℃ and homogenized for 2h, and the casting blank is rolled into a bar with the diameter of phi 80mm at 1100 ℃, the total rolling reduction rate is 73 percent, the structure of the bar is mainly sorbite, and the mechanical properties are shown in table 10.

TABLE 10 mechanical Properties

The bar is heated to 1050 ℃ and forged into balls at the temperature, and the final forging temperature is 950 ℃. And then, air-cooling the steel ball to 820-830 ℃, then cooling to 300 ℃ at a cooling rate of more than 5 ℃/s, and preserving heat for 5 hours to form a bainite structure, wherein the heat treatment process parameters are shown in Table 11. The mechanical properties of the bainite wear-resistant steel ball are shown in Table 12, the metallographic photograph is shown in FIG. 3, and the scanning photograph is shown in FIG. 6.

TABLE 11 Heat treatment Process parameters

TABLE 12 mechanical Properties

Finally, it should be noted that the above embodiments are only used for the technical solution of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A preparation method of a low-cost high-strength nano bainite wear-resistant steel ball is characterized in that the alloy comprises the following components in percentage by weight: 0.45-0.7 wt.%, Si: 2.48-3.0 wt.%, Mn: 0.5-2.0 wt.%, Cr: 0.1-1.5 wt.%, Al: 0.1-2.0 wt.%, Ti: 0.05-0.1 wt.%, the balance being Fe and unavoidable impurities;

the preparation process comprises the following steps:

secondly, air-cooling the steel ball to 800-900 ℃, then rapidly cooling to 200-400 ℃, and preserving heat for 3-8 hours at the temperature to obtain a complex phase structure consisting of nano bainite, a small amount of residual austenite and a TiC precipitated phase;

the speed of the steel ball rapid cooling is more than 5 ℃/s so as to avoid a pearlite transformation region and ensure that the super-cooled austenite directly enters a bainite transformation region;

rolling or forging steel balls, and air-cooling to 800-900 ℃, wherein the temperature is higher than the upper limit temperature of a pearlite transformation zone and is also in a TiC precipitation temperature range, so that a large amount of TiC particles are precipitated;

the mechanical properties of the bainite wear-resistant steel are as follows: yield strength R_pGreater than or equal to 1600MPa, tensile strength R_mMore than or equal to 1900MPa, elongation A after fracture more than or equal to 10 percent, Rockwell hardness HRC more than or equal to 55, and room temperature impact toughness ak more than or equal to 20J/cm²。

2. The method for preparing the bainite abrasion-resistant steel ball according to claim 1, wherein Ti is added into the alloy components of the steel to form a TiC precipitated phase with nano-scale size and uniform distribution, thereby inhibiting coarse grains of deformed austenite, refining the grains, enhancing the strength of the matrix and improving the abrasion resistance.

3. The method for preparing the bainite abrasion-resistant steel ball according to claim 1, wherein the volume fraction of the steel ball residual austenite structure is 5-20%.

4. The method for preparing the bainite abrasion-resistant steel ball according to claim 1 or 3, wherein the steel ball has different heat preservation temperatures, different heat preservation times and corresponding structures and properties, and the nano-bainite sheet interval is reduced, the strength and the hardness are increased and the heat preservation time is correspondingly prolonged along with the reduction of the heat preservation temperature.