A kind of ultra-high hardness surface strengthened GGr15 steel and preparation method thereof

Abstract

The invention discloses an ultra-high hardness surface-strengthened GGr15 steel and a preparation method thereof, and belongs to the technical field of heat treatment of metal materials. The invention discloses an ultra-high hardness surface-strengthened GGr15 steel preparation method, which adopts a multi-stage composite carbonitriding process to quickly and efficiently form dispersed granular carbonitriding compounds on the surface of GGr15 bearing steel, which can not only realize high-efficiency carbonitriding on the surface of bearing steel, but also avoid abnormal growth and coarsening of carbonitriding compounds, and significantly improve the surface hardness and wear resistance of steel; the method significantly improves the carbonitriding speed and shortens the processing cycle, thereby realizing the practicality, economy and effectiveness of the carbonitriding treatment process, and the reagent cost used in the method is low, and the processing temperature and processing time are significantly reduced, showing great potential in energy saving, emission reduction and cost reduction.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment of metal materials, and specifically relates to an ultra-high hardness surface-strengthened GGr15 steel and a preparation method thereof. Background Art

[0002] Rolling bearings are an indispensable and important part in all mechanical transmission devices. With the rapid development of industry and science and technology in my country, the demand for high-quality and high-precision bearings is growing. Rolling bearings are subjected to high and complex stresses during work, and are subject to friction, impact and vibration on the contact surface. This leads to two main forms of bearing damage: 1. Pits are generated on the working surface, causing spalling; 2. Contact fatigue damage, which significantly reduces the service life of bearing parts and causes the bearings to fail to operate normally. Therefore, how to obtain high hardness and high fatigue damage resistance on the surface of bearing steel parts has become a key technology that needs to be solved urgently.

[0003] At present, a lot of research has been carried out at home and abroad on how to improve the surface hardness, wear resistance and fatigue damage resistance of bearings. GGr15 steel has become the most widely used high-carbon chromium bearing steel because it has a low alloy content, can obtain good wear resistance and fatigue resistance after quenching and tempering, and is relatively cheap. Domestic bearing companies have only carried out related attempts and experimental research on the carbonitriding treatment of the surface of GGr15 bearing steel workpieces on their own, but the bearing surface still inevitably produces defects such as thick non-martensitic structure and coarse network carbides. In addition, in order to reduce the deformation of finished parts and ensure the accuracy of parts, domestic companies adopt a more conservative strategy, that is, to increase the grinding amount of the product surface by 0.15-0.28mm thickness, thereby increasing the temperature and time of carbonitriding treatment, resulting in increased costs. On the one hand, foreign countries carry out hard chromium plating on the surface, and on the other hand, by increasing the carbon content (1.3%), fine and dispersed compound particles are prepared in the GGr15 steel. Most of the compound particle sizes are less than 0.5μm, but there are still a small number of compound particles larger than 1μm, and banded carbides are also produced. Therefore, the surface modification technology of bearing steel still has the following shortcomings: on the one hand, the carbonitriding treatment temperature is high (≥850℃) and the treatment time is long. For example, in order to obtain a 0.4mm surface layer, it is necessary to treat at 850-860℃ for more than 6h. On the other hand, the current carbonitriding technology has great difficulty in controlling the size and distribution of carbonitride compounds in the bearing steel layer. Carbonitride compounds are often prone to agglomeration and abnormal coarsening, which reduces the mechanical properties of the workpiece. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide an ultra-high hardness surface strengthened GGr15 steel and a preparation method thereof, so as to solve the technical problems of the current carbonitriding process with high temperature, long time and poor economy.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The invention discloses a method for preparing ultra-high hardness surface-strengthened GGr15 steel, comprising the following steps:

[0007] S1: After degreasing the finely processed GGr15 steel workpiece, heat treatment is performed at 700±10° C. in a mixed atmosphere of ammonia and ethanol or methanol solution cracking gas to obtain a pretreated GGr15 steel workpiece;

[0008] S2: Then, the carburizing furnace is heated to 840±5°C, and the pre-pretreated GGr15 steel workpiece is carbonitrided in a mixed atmosphere of ammonia and methanol-isopropanol mixed solution cracking gas. After the carbonitriding, quenching and tempering are performed in sequence to obtain an ultra-high hardness surface-strengthened GGr15 steel.

[0009] Furthermore, in S1, in the mixed atmosphere of ammonia and cracked gas of ethanol or methanol solution, ammonia accounts for 60%-70% of the mixed atmosphere, and cracked gas of ethanol or methanol solution accounts for 30%-40% of the mixed atmosphere, by volume percentage; the amount of ammonia gas and the amount of ethanol or methanol solution dripped are adjusted so that the volume percentage of residual ammonia in the furnace at 700-710°C is 8%-12%.

[0010] Furthermore, in S1, the pretreatment time is 0.5-2h.

[0011] Furthermore, in S2, the mixed atmosphere of the ammonia gas and the cracking gas of the methanol-isopropanol mixed solution has 4%-6% residual ammonia gas by volume percentage, a carbon potential of 1.2%-1.4%, and a nitrogen potential of <0.4%.

[0012] Furthermore, in S2, the carbonitriding treatment time is 1-4 hours; and the quenching method is oil quenching.

[0013] Furthermore, in S2, the process parameters of the tempering treatment are: tempering at 160-200° C. for 1-4 hours.

[0014] The invention also discloses ultra-high hardness surface-strengthened GGr15 steel prepared by the preparation method.

[0015] Furthermore, the ultra-high hardness surface-strengthened GGr15 steel has a hardened layer in which granular carbonitrides are dispersed, and the thickness of the hardened layer is 0.2-0.6 mm; after oil quenching treatment, the ultra-high hardness surface-strengthened GGr15 steel has a hardness of 67.5-69 HRC, and after tempering treatment, the hardness is 64-67 HRC.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The invention discloses a preparation method of ultra-high hardness surface-strengthened GGr15 steel. Firstly, the GGr15 steel is subjected to a pre-infiltration treatment step at 700±10°C, i.e., below the critical temperature, in a mixed atmosphere of ammonia and ethanol or methanol solution cracking gas, thereby providing extremely favorable conditions for subsequent carbonitriding. Subsequently, a high-concentration carbonitriding treatment is carried out in a mixed atmosphere of ammonia and methanol-isopropanol mixed solution cracking gas at the critical temperature of the steel of 840±5°C. Finally, the GGr15 steel is subjected to a quenching and tempering treatment to obtain a hardened layer with dispersed carbonitriding compounds on the surface. A multi-stage composite carbonitriding process is adopted to quickly and efficiently form dispersed granular carbonitriding compounds on the surface of GGr15 bearing steel, which can not only achieve efficient carbonitriding on the surface of the bearing steel, but also avoid abnormal growth and coarsening of carbonitriding compounds, and significantly improve the surface hardness and wear resistance of the steel. This method significantly improves the carbonitriding speed and shortens the treatment cycle, thereby achieving the practicality, economy and effectiveness of the carbonitriding treatment process. At the same time, the reagents used in this method are low in cost, and the treatment temperature and treatment time are significantly reduced. It shows great potential in energy conservation, emission reduction and cost reduction, has a broad market for promotion and application and considerable economic benefits, and has an optimistic prospect.

[0018] The present invention also discloses an ultra-high hardness surface-strengthened GGr15 steel prepared by the above-mentioned preparation method. According to relevant experimental results, the surface layer of the ultra-high hardness surface-strengthened GGr15 steel obtains a high-density granular compound, and the size of the residual austenite and the size of the martensite are uniform and small; at the same time, it has high tempering stability. For example, after tempering at 160°C, the surface hardness can still be as high as 877HV 0.5 (measured at 0.1mm), even when tempered at a higher temperature of 200℃, the surface hardness can still reach 796HV 0.5 After tempering at 160-200℃ for 1-4h, its macro-hardness can still be maintained at 64-67HRC, and the thickness of the hardened layer of carbonitride obtained on its surface is 0.2-0.6mm, which has excellent tempering stability and mechanical properties. Therefore, even with high tempering temperature (such as 200℃) and long tempering time (such as 4h), bearing parts can still retain high hardness and high wear resistance, thereby ensuring high stability and high precision of bearing operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a morphology of the high-density granular compound on the surface of the GGr15 steel after carbonitriding at 840±5℃ / 2h + low-temperature tempering in Example 1;

[0020] Figure 2 This is the microstructure morphology of the surface carbonitride hardened layer of GCr15 steel after carbonitriding at 84075°C / 1h + low temperature tempering in Example 2;

[0021] Among them: a-macroscopic morphology at 200 times the metallographic scale; b-surface carbonitride morphology at 1000 times the metallographic scale;

[0022] Figure 3 It is the Rockwell hardness value of GCr15 steel in oil quenching and tempering state after carbonitriding treatment;

[0023] Figure 4 This is a microstructure morphology of the hardened layer of carbonitride on the surface of the GCr15 steel of Example 4 after carbonitriding at 840±5°C / 1h + low temperature tempering;

[0024] Among them: a-surface macroscopic morphology at 500 times the metallographic scale; b-surface carbonitride morphology at 1000 times the metallographic scale;

[0025] Figure 5 The Rockwell hardness value of the GCr15 steel of Example 5 after being oil-quenched at 840±5°C / 2-4h and tempered at 180°C for 1-4h;

[0026] Figure 6 The microstructure characteristics of the hardened layer of carbonitride on the surface of the GCr15 steel of Example 5 after carbonitriding at 840±5℃ / 2-4h+tempering at 180℃ for 1h;

[0027] Among them: a-840±5℃ / 2h; b-840±5℃ / 3h; c-840±5℃ / 4h. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0029] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0030] Herein, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible sub-ranges and individual values ​​within the range (including integers and fractions).

[0031] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0032] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0033] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0034] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0035] Example 1

[0036] A method for preparing ultra-high hardness surface-strengthened GGr15 steel comprises the following steps:

[0037] S1: First, a GGr15 test block with a size of 15×15×20mm was polished with metallographic sandpaper; then, the sample was wiped with anhydrous ethanol and absorbent cotton, and dried for use; the pit carburizing furnace was heated to 700±10°C at 10°C / min, and 70% ammonia, 30% ethanol or methanol cracking gas, and 12% residual ammonia were introduced by volume percentage, and the GGr15 steel block was placed in the pit furnace for 1 hour to obtain a pretreated GGr15 steel workpiece (pre-infiltration treatment below the critical temperature);

[0038] S2: Continue to heat the pit carburizing furnace to 84075℃ at 15℃ / min to heat the pretreated GGr15 steel workpiece, at a carbon potential of 1.2%, a nitrogen potential of less than 0.4%, and a residual ammonia of 6%, and keep it warm for 2h; then quench the test block into oil for cooling, and its average Rockwell hardness is 67.5HRC, and the maximum value is 68.5HRC. The oil-quenched test block is subjected to low-temperature tempering treatment at a tempering temperature of 160℃, kept warm for 1h, and air-cooled to room temperature, with an average Rockwell hardness of 65.7HRC, to obtain ultra-high hardness surface-strengthened GGr15 steel. Figure 1 It is a high-density granular compound on the surface of GGr15 steel after carbonitriding at 840±5℃ / 2h + low-temperature tempering. It can be seen from the figure that the compound particles are dispersed.

[0039] Example 2

[0040] A method for preparing ultra-high hardness surface-strengthened GGr15 steel comprises the following steps:

[0041] S1: Select a GGr15 bearing jacket workpiece with an outer diameter of 20 mm, and polish the surface of the sample with metallographic sandpaper; then wipe the sample with anhydrous ethanol moistened with absorbent cotton, and dry it for use; heat the pit carburizing furnace to 700-710°C at 10°C / min, and introduce 66% ammonia, 34% ethanol or methanol cracking gas, and 9.4% residual ammonia by volume percentage, and put the GGr15 steel test block into the pit furnace for 1 hour to obtain the pretreated GGr15 steel workpiece (pre-infiltration treatment below the critical temperature);

[0042] S2: Continue to heat the pit carburizing furnace to 84075℃ at 15℃ / min to heat the pretreated GGr15 steel workpiece, at a carbon potential of 1.35%, a nitrogen potential of less than 0.4%, and a residual ammonia of 5.4%, and keep it warm for 1h; then quench the test block into medium-speed cooling oil, and its average Rockwell hardness is 67.1HRC, and the maximum value is 68.2HRC. The oil-quenched test block is subjected to low-temperature tempering treatment at a tempering temperature of 180℃, kept warm for 1h, and air-cooled to room temperature, with an average Rockwell hardness of 64.5HRC, to obtain ultra-high hardness surface-strengthened GGr15 steel. Figure 2 It is a high-density spherical compound on the surface of GGr15 steel after carbonitriding at 840±5℃ / 1h + low-temperature tempering. From the figure, we can see that the thickness of the surface carburized layer is 0.2mm and the surface carbonitriding compounds are dispersed.

[0043] Example 3

[0044] A method for preparing ultra-high hardness surface-strengthened GGr15 steel comprises the following steps:

[0045] S1: Select a GGr15 disc workpiece with a diameter of 40 mm and a thickness of 20 mm, and polish the surface of the sample with metallographic sandpaper; then wipe the sample with anhydrous ethanol moistened with absorbent cotton, and dry it for use; heat the pit carburizing furnace to 700-710°C at 10°C / min, and introduce 64% ammonia, 36% ethanol or methanol cracking gas, and 9.6% residual ammonia by volume percentage, and put the GGr15 steel test block into the pit furnace for 0.5h to obtain the pretreated GGr15 steel workpiece (pre-infiltration treatment below the critical temperature);

[0046] S2: Continue to heat the pit carburizing furnace to 84075℃ at 15℃ / min to heat the pretreated GGr15 steel workpiece, at a carbon potential of 1.3%, a nitrogen potential of less than 0.4%, and a residual ammonia of 4.6%, and keep it warm for 4h; then quench the test block into medium-speed cooling oil, with an average Rockwell hardness of 67.3HRC and a maximum of 68.2HRC. Perform low-temperature tempering treatment on the oil-quenched test block at a tempering temperature of 180℃, keep warm for 4h, and air-cool to room temperature to obtain ultra-high hardness surface-strengthened GGr15 steel.

[0047] Example 4

[0048] A method for preparing ultra-high hardness surface-strengthened GGr15 steel comprises the following steps:

[0049] S1: Select a GGr15 ring sample with an outer diameter of 30 mm and an inner diameter of 20 mm, wipe the sample with anhydrous ethanol and absorbent cotton, and dry it for use; heat the pit carburizing furnace to 700-710°C at 10°C / min, introduce 60% ammonia, 40% ethanol or methanol cracking gas, and 8.0% residual ammonia by volume percentage, put the GGr15 steel test block into the pit furnace for 1.5h, and obtain the pretreated GGr15 steel workpiece (pre-infiltration treatment below the critical temperature);

[0050] S2: Continue to heat the pretreated GGr15 steel workpiece in the pit carburizing furnace at 15℃ / min to 84075℃, keep it warm for 1h at a carbon potential of 1.4%, a nitrogen potential of less than 0.4%, and a residual ammonia of 4.0%; then quench the test block into medium-speed cooling oil, and its average Rockwell hardness is 67.8HRC, and the maximum value is 69HRC. The oil-quenched test block is subjected to low-temperature tempering treatment, and the tempering temperatures are selected at 160℃, 180℃ and 200℃, respectively, and kept warm for 1h, and then air-cooled to room temperature, and the average Rockwell hardness is 65.5HRC, 64.6HRC and 64HRC, respectively. Figure 3 As shown, it has high tempering stability and obtains ultra-high hardness surface strengthened GGr15 steel. Figure 4The figure shows the microstructure of the hardened layer of carbonitride on the surface of GCr15 steel after carbonitriding at 840±5℃ / 1h + low temperature tempering. It can be seen from the figure that when tempered at 160℃ for 1h, the thickness of the surface carburized layer is 320μm. After air cooling, the surface microstructure still retains high-density dispersed spherical carbonitrides, making the hardness at 0.1mm from the surface as high as 877HV 0.5 .

[0051] Example 5

[0052] A method for preparing ultra-high hardness surface-strengthened GGr15 steel comprises the following steps:

[0053] S1: Select a GGr15 bearing sample with an outer diameter of 45 mm and an inner diameter of 35 mm, wipe the sample with anhydrous ethanol and absorbent cotton, and dry it for later use; heat the pit carburizing furnace to 700-710°C at 10°C / min, introduce 65% ammonia, 35% ethanol or methanol cracking gas, and 10% residual ammonia by volume, put the GGr15 steel test block into the pit furnace for 1.5 hours, and obtain the pretreated GGr15 steel workpiece (pre-infiltration treatment below the critical temperature);

[0054] S2: Continue to heat the pit carburizing furnace to 84075℃ at 15℃ / min to heat the pretreated GGr15 steel workpiece, at a carbon potential of 1.28%, a nitrogen potential of less than 0.4%, and a residual ammonia of 5.0%, and keep them warm for 2h / 3h / 4h respectively; then quench the test block into medium-speed cooling oil, and the average Rockwell hardness is 67.8HRC, 68.5HRC and 69HRC respectively. The oil-quenched test block is subjected to low-temperature tempering treatment, and the tempering temperature is selected to be 180℃, and the temperature is kept warm for 1h, 2h, 3h and 4h respectively, and then air-cooled to room temperature. The average Rockwell hardness can be maintained at 64.6-67HRC, which has high tempering stability, such as Figure 5 As shown in the figure, the ultra-high hardness surface strengthened GGr15 steel was obtained. The thickness of the surface carburized layer of the bearings tempered at 180℃ for 1h and treated at 84075℃ for 2h / 3h / 4h was 390μm, 510μm and 600μm respectively. The surface organization still retained high-density dispersed spherical carbonitrides, as shown in the figure. Figure 6 a. Figure 6 b and Figure 6 As shown in c.

[0055] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing ultra-high hardness surface-strengthened GGr15 steel, characterized in that: The following steps are involved: S1: heat treating the GGr15 steel workpiece at 700±10° C. in a mixed atmosphere of ammonia and ethanol solution cracking gas or ammonia and methanol solution cracking gas to obtain a pretreated GGr15 steel workpiece; S2: Then, the carburizing furnace is heated to 840±5° C., and the pretreated GGr15 steel workpiece is subjected to carbonitriding treatment in a mixed atmosphere of ammonia and cracking gas of a methanol-isopropanol mixed solution. After the carbonitriding treatment, quenching and tempering treatment are performed in sequence to obtain an ultra-high hardness surface-strengthened GGr15 steel; In S1, in the mixed atmosphere of ammonia and ethanol solution cracking gas or ammonia and methanol solution cracking gas, ammonia accounts for 60%-70% of the mixed atmosphere, and the cracking gas of ethanol or methanol solution accounts for 30%-40% of the mixed atmosphere by volume percentage; the amount of ammonia gas and the amount of ethanol or methanol solution dripped are adjusted so that the volume percentage of residual ammonia in the furnace at 700±10°C is 8%-12%; In S2, the mixed atmosphere of ammonia and the cracked gas of the methanol-isopropanol mixed solution has 4%-6% residual ammonia by volume, a carbon potential of 1.2%-1.4%, and a nitrogen potential of <0.4%.

2. The method for preparing ultra-high hardness surface-strengthened GGr15 steel according to claim 1, characterized in that: In S1, the heat treatment time is 0.5-2h.

3. The method for preparing ultra-high hardness surface-strengthened GGr15 steel according to claim 1, characterized in that: In S2, the carbonitriding treatment time is 1-4 hours; the quenching method is oil quenching.

4. The method for preparing ultra-high hardness surface-strengthened GGr15 steel according to claim 1, characterized in that: In S2, the process parameters of the tempering treatment are: tempering at 160-200° C. for 1-4 hours.

5. An ultra-high hardness surface-strengthened GGr15 steel, characterized in that: The steel is prepared by the method for preparing ultra-high hardness surface-strengthened GGr15 steel as described in any one of claims 1 to 4.

6. The ultra-high hardness surface-strengthened GGr15 steel according to claim 5, characterized in that: The ultra-high hardness surface-strengthened GGr15 steel has a hardened layer in which granular carbonitrides are dispersed, and the thickness of the hardened layer is 0.2-0.6 mm; the ultra-high hardness surface-strengthened GGr15 steel has a hardness of 67.5-69 HRC after oil quenching treatment, and a hardness of 64-67 HRC after tempering treatment.

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