CN116516114A - Process method for processing GCr15 steel by using ultrasonic-assisted ECAP - Google Patents
Process method for processing GCr15 steel by using ultrasonic-assisted ECAP Download PDFInfo
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- 239000000314 lubricant Substances 0.000 claims description 23
- 239000000463 material Substances 0.000 claims description 21
- 238000010438 heat treatment Methods 0.000 claims description 20
- 238000001192 hot extrusion Methods 0.000 claims description 17
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 16
- 239000011521 glass Substances 0.000 claims description 12
- 238000000227 grinding Methods 0.000 claims description 11
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- 238000001816 cooling Methods 0.000 claims description 9
- 238000004458 analytical method Methods 0.000 claims description 8
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 6
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/04—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering with simultaneous application of supersonic waves, magnetic or electric fields
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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Abstract
The invention discloses a process method for processing GCr15 steel by using ultrasonic-assisted ECAP, which aims to improve the wear resistance of the GCr15 steel, compares the tribological properties of the GCr15 steel under different load and sliding speed conditions after the GCr15 steel is subjected to the ultrasonic-assisted ECAP process, and discusses the wear mechanism by analyzing the wear surface morphology. Research results show that the ultrasonic-assisted ECAP treatment can remarkably reduce the friction coefficient of GCr15 steel in the friction process; the abrasion loss of the GCr15 steel subjected to the ultrasonic-assisted ECAP treatment is reduced in the same time period as that of the GCr15 steel subjected to the ultrasonic-assisted ECAP treatment; GCr15 steel after annealing treatment and ECAP treatment had a slight sticking and flaking phenomenon than the worn surface before extrusion.
Description
Technical Field
The invention relates to the field of GCr15 steel processing, in particular to a process method for processing GCr15 steel by using an ultrasonic-assisted ECAP.
Background
GCr15 steel is high-carbon chromium bearing steel with excellent friction and wear properties, and is widely applied to the fields of machine manufacturing, railway transportation, automobile manufacturing, national defense industry and the like. In order to improve the wear resistance of the GCr15 steel, the conventional heat treatment process is complicated in process, long in treatment period, insufficient in toughness and low in hardness of the treated material, and often fails due to cracking, cracking and deformation, the service performance is poor, and the GCr15 steel is forged according to the normal process specification and then is subjected to subsequent heat treatment. Generally, heat treatment includes pretreatment and finishing; the conventional pretreatment process is spheroidizing annealing, and the final treatment process is quenching and low-temperature tempering. The common Gcr15 steel spheroidizing annealing process is to heat for 2-3h at 780-810 ℃, isothermal for 4-5h at 710-730 ℃, cool to below 650 ℃ in a furnace, discharge and air cool, and carry out oil quenching at the final treatment process parameters of 820-840 ℃ and then carry out low-temperature tempering at 150-200 ℃.
The publication number is: the patent application CN103484618A discloses a heat treatment method of GCr15 steel, which comprises the following steps: (1) Firstly heating GCr15 steel to 960-980 ℃ for 30-50min; then cooling to 800-820 ℃ in a furnace, and preserving heat for 3-4 hours; then raising the temperature of GCr15 steel to 900-920 ℃ and preserving heat for 20-30min; then cooling to below 620 ℃ in the furnace, discharging and air cooling; (2) heating to 900-920 ℃, and quenching; (3) Cooling to 160-180 deg.c and low temperature tempering.
The publication number is: the patent application CN102758068A discloses a heat treatment method of GCr15 steel, comprising the steps of: heating GCr15 steel to 1045-1055 ℃, preserving heat for 0.4-0.6h, and quenching in oil; cooling to room temperature, heating to 715-725 ℃ and tempering; cooling to room temperature and then preheating; heating to 835-845 ℃, preserving heat for 2-3h, and then quenching in hot oil; cooling and then tempering at 175-185 ℃.
ECAP technology, which is called equal-channel angular pressing, is equal-channel angular extrusion (equal channel angular pressing); also known as ECAE. The beginning of the 70 s of the last century was proposed by the soviet union, segal, with additional pictures for schematic device diagrams. The material is subjected to strong shear deformation at the corners of the die, and the cross section size is basically kept unchanged, so that the extrusion can be repeatedly performed, a large amount of strain is accumulated, and the material can be used for refining the grains of the material.
Ultra-fine grain materials (grain sizes between 10 and 1000 nm) have attracted considerable attention due to their demonstrated unusual series of physical, chemical and mechanical properties. Research shows that strong plastic deformation (Severe Plastic Deformation, SPD for short) can prepare ultrafine grain materials, and a relatively large number of equal channel angular extrusion methods (Equal Channel Angular Pressing) are currently applied, and the equal channel angular extrusion deformation methods proposed by Segal refine grains by pressing a sample into a specially designed die to realize large shear deformation.
In the ECAP process, deformation force and energy consumption increase in the extrusion process due to friction between the test sample and the die, resulting in non-uniformity of deformation and tool wear. Ko et al used graphite lubricant to lubricate the test specimens and the mold, effectively reducing friction during extrusion. Gao Leilei it is believed that graphite lubricant is easily volatilized at high temperature, and will significantly reduce its lubrication and protection effects, while glass lubricant has the characteristics of high viscosity, high activity, high melting point, low friction coefficient, good heat insulation performance, etc., and is suitable for use at high temperature. Besides proper lubricant is selected to ensure smooth ECAP deformation processing, the scholars can also reduce the friction force in extrusion engineering from the aspects of die structure design, external force addition and the like. Nagasekhar et al analyzed the effect of die angle and friction on material deformation and found that friction decreased with increasing die included angle ψ, since increasing included angle ψ helps to reduce the gap between the sample and die during ECAP deformation. With the development of vibration technology, the influence of ultrasonic vibration on plastic forming is also being paid more and more attention to students, and ultrasonic vibration can effectively reduce friction. Blaha and Langencker first studied the effect of ultrasonic vibration on metal plastic forming. Hung et al state that ultrasonic vibration can reduce the friction between the sample and the mold during the material forming process, thereby reducing the forming force required for the forming process. It can be seen that the application of ultrasonic vibration techniques to ECAP processes can reduce the friction between the test specimen and the mold. However, experimental and simulation results related to the ultrasonic vibration assisted ECAE technology have not been found much so far. Djava roodi et al applied ultrasonic vibration to the extrusion process and on the basis of simple experiments and simulations indicated that proper addition of ultrasonic vibration to the extrusion did reduce the friction between the sample and the die. However, djava roodi et al have only been analyzed by a simple set of experiments, and the main work has been accomplished by simulation. In the test, djavaroodi et al applied ultrasonic vibrations of a certain frequency and amplitude to the test specimen in a certain direction. The ultrasonic vibration is used as a special vibration, and the mass points on the surface of the material generate vibration under the action, so that the positive pressure between friction pairs is reduced, and in addition, the mass points on the surface of the friction pairs vibrate, so that abrasive dust is rapidly discharged out of a friction interface, and abrasion of the abrasive dust is avoided. This is also one of the reasons why the learner introduced ultrasonic vibration into ECAP. If the die is reasonably designed, ultrasonic vibration can be applied to the die along a certain direction, so that positive pressure between friction pairs is reduced. It is therefore necessary to investigate the effect of ultrasonic vibration on ECAP (Ultrasonic Vibration-Assisted Equal Channel Angular Pressing) shaping after it has been applied to the mold.
The ultrasonic vibration plastic working effect (Blaha effect) of metals was first discovered in 1955 by Blaha and Langenecker, and when ultrasonic vibration was applied to a test piece or tooling die, the yield stress and flow stress of the material were significantly reduced. The ultrasonic technology is applied to the process of extruding the metal material at the equal channel corners, so that the yield stress and the flow stress of the material can be reduced; friction between the die and the workpiece is reduced; obtaining the ultra-fine grain metal material.
The GCr15 steel is treated by the ultrasonic auxiliary ECAP, and the GCr15 steel is applied to experiments of tribological properties of the GCr15 steel under different load and sliding speed conditions in different occasions. This is also beneficial for the deep research of the abrasion mechanism of the material to improve the surface friction and abrasion performance of GCr15 steel, and is a problem worthy of research.
Disclosure of Invention
In order to solve the problems existing in the prior art, the invention provides a process for improving the surface friction and wear properties of GCr15 steel by performing ultrasonic-assisted ECAP treatment on the GCr15 steel.
The purpose of the invention is realized in the following way:
firstly grinding a cut sample on a grinding machine, then polishing the surface again by using fine sand paper to obtain a sample with the thickness of 9.4mm multiplied by 100mm, chamfering the sample, and paying attention to the chamfering angle; scrubbing the surface of a sample by using acetone, and then lubricating a GCr15 steel sample by using a glass lubricant with the model of FR-35;
the specific operation steps are as follows:
firstly, coating glass lubricant on the surface of a sample to be extruded, wherein the thickness of the lubricant is about 0.2mm; secondly, placing the sample in a box-type resistance furnace, and heating for 15min under the condition that the temperature of the resistance furnace is controlled to be 80 ℃; thirdly, naturally drying the GCr15 steel sample after heating and drying at room temperature;
fourth, each surface of the die is lubricated by graphite lubricant, so that the lubricating performance between the die and the sample is improved;
fifth step: ultrasonic-assisted equal-channel corner extrusion die preparation:
sixth step: sample annealing treatment:
seventh step: high temperature ultrasound assisted ECAP processing of GCr 15:
eighth step: annealing the treated sample.
The ultrasonic-assisted equal-channel angular extrusion die is prepared, the die used in the ultrasonic-assisted equal-channel angular extrusion process consists of an ultrasonic vibration upper die, a lower die and an ultrasonic assembly, wherein the internal angle phi and the external angle ψ of the die are 90 degrees, and the die is manufactured by selecting materials 5Cr4W5Mo2V (RM 2);
in the extrusion process, the magnitude of the load applied to the sample in the extrusion process is greatly influenced by the friction force between the die and the sample; in order to reduce the channel friction force between the sample 4 and the die 5 during ultrasonic auxiliary equal channel angular extrusion, so that the sample can be extruded from a horizontal channel smoothly, an ultrasonic amplitude transformer is combined with a die ejector rod, meanwhile, an ultrasonic vibration support 2 is additionally arranged at the upper part of the amplitude transformer, the universal testing machine 1 directly acts on the ultrasonic vibration support during extrusion, the ultrasonic vibration support transmits the lower pressure to the ejector rod, meanwhile, an ultrasonic transmitter is connected at the upper part of the ejector rod, the ejector rod drives the sample to move downwards, and ultrasonic vibration is applied to the sample during extrusion; meanwhile, the pressure head 3 of the universal testing machine directly acts on the ultrasonic vibration bracket during extrusion, and the ejector rod at the lower part of the ultrasonic vibration bracket is tightly matched with the circular cylinder shape of the lower die, so that the die does not need to be accurately positioned before extrusion begins; therefore, the die is not required to be fastened on a platform of the universal testing machine, and the die is only required to be placed under the pressure head after the sample and the ejector rod are arranged in the lower die; the ultrasonic assembly mainly comprises an ultrasonic generator with power of 2 kW, frequency of 20 kHz and amplitude of 40 mu m, an ultrasonic amplitude transformer and an ultrasonic amplitude transformer fixing bracket; the microcomputer is used for controlling the universal testing machine to apply pressure to the ultrasonic auxiliary equal channel angular extrusion ultrasonic punch 3, and the extrusion process is completed when the ultrasonic is downwards extruded and simultaneously the ultrasonic is vibrated;
the sample annealing treatment is as follows: annealing the GCr15 steel sample which is not subjected to ECAE extrusion treatment at 960 ℃ (AC 3+50 ℃), preserving heat for 20min, and cooling along with a furnace; performing microstructure analysis and mechanical property test on the annealed sample;
the high-temperature ultrasonic-assisted ECAE processing of GCr15 is as follows: firstly grinding and polishing the sample to obtain a 9.4mm multiplied by 100mm sample, scrubbing the surface of the sample by acetone, and then lubricating the GCr15 sample by a glass lubricant. And (3) preserving the heat of the surface-treated sample at 550-750 ℃ for 20min, and simultaneously preserving the heat of the ultrasonic-assisted ECAE mould at 500 ℃ for 1h for preheating. And then taking out the sample and the mould simultaneously, and rapidly putting the sample into the mould for ultrasonic-assisted ECAE hot extrusion.
The annealing treatment of the treated sample is as follows: the samples subjected to the ultrasonic-assisted ECAE treatment are annealed at 800 ℃, 900 ℃ and 960 ℃ for 30min, 60min and 90min respectively. And performing apparent tissue analysis and microhardness test on the annealed sample.
Has the positive beneficial effects that: the application carries out thermal processing experimental study on the GCr15 steel sample through the high-temperature ultrasonic-assisted ECAP process so as to realize the research work of the aspects of microstructure refinement, microhardness enhancement, tribological property improvement and the like of the GCr15 steel sample. The following innovation points are:
(1) The GCr15 sample is subjected to hot extrusion treatment by adopting an ultrasonic-assisted ECAP process for the first time, the temperature which smoothly passes through extrusion is obtained through experiments, the microstructure of the GCr15 is obviously refined, and the action mechanism of the microstructure of the GCr15, which is obviously refined due to factors such as the ultrasonic-assisted ECAP process, precipitation of a second phase, annealing treatment and the like, is analyzed through experimental data.
(2) The influence of various factors such as a high-temperature ultrasonic-assisted ECAP process, load, speed conditions and the like on the tribological performance of the GCr15 sample under the dry friction condition is researched, and the action mechanism of improving the tribological wear performance of the GCr15 sample after being treated by the high-temperature ultrasonic-assisted ECAP process is illustrated.
GCr15 steel was chosen as the subject of the study and was subjected to the ECAP study of ultrasonic vibrations. Conventional ECAP and UV-ECAP extrusion were performed using GCr15 steel bars as an example, and a series of extrusion experiments were performed. Detection experiments were performed on ECAP and UV-ECAP samples using various techniques, and experimental data were analyzed. The influence of high-frequency vibration of ultrasonic waves on ECAP molding of the GCr15 steel material is discussed, and the mechanical properties and the internal microstructure evolution of the material are examined. The UV-ECAP process was evaluated.
Drawings
FIG. 1 is a schematic illustration of an equal channel angular extrusion die of the present invention;
FIG. 2 is an ultrasonic-assisted equal channel angular extrusion die of the present invention;
FIG. 3 is a schematic view of ultrasonic-assisted equal channel angular extrusion and microstructure observation sampling of a sample;
FIG. 4 is a photograph of a cross-sectional microstructure of a GCrl5 steel sample before and after single pass ultrasonic assisted ECAP extrusion; (a) GCr15 cross-sectional microstructure before ultrasound-assisted ECAP extrusion (b) GCr15 cross-sectional microstructure after single-pass ultrasound-assisted ECAP extrusion;
FIG. 5 is a graph showing the change of friction coefficient with time at a load of 100N;
FIG. 6 is a flow chart of the process of the present invention.
Detailed Description
The invention is further described with reference to the accompanying drawings and examples:
as shown in fig. 6, in the process method for processing GCr15 steel by using the ultrasonic-assisted ECAP, firstly grinding a cut sample on a grinding machine, then polishing the surface again by using fine sand paper to obtain a sample with the thickness of 9.4mm multiplied by 100mm, chamfering the sample, and paying attention to the chamfering angle; scrubbing the surface of a sample by using acetone, and then lubricating a GCr15 steel sample by using a glass lubricant with the model of FR-35;
the specific operation steps are as follows:
firstly, coating glass lubricant on the surface of a sample to be extruded, wherein the thickness of the lubricant is about 0.2mm; secondly, placing the sample in a box-type resistance furnace, and heating for 15min under the condition that the temperature of the resistance furnace is controlled to be 80 ℃; thirdly, naturally drying the GCr15 steel sample after heating and drying at room temperature;
fourth, each surface of the die is lubricated by graphite lubricant, so that the lubricating performance between the die and the sample is improved;
fifth step: ultrasonic-assisted equal-channel corner extrusion die preparation:
sixth step: sample annealing treatment:
seventh step: high temperature ultrasound assisted ECAP processing of GCr 15:
eighth step: annealing the treated sample.
Example 1
As shown in fig. 1, the equal channel angular extrusion die is provided with an internal intersection angle Φ=90°, and a die for extrusion is manufactured by using a material 5Cr4W5Mo2V (RM 2). And then an ultrasonic vibration punch is additionally arranged at the upper half part of the equal channel corner extrusion die. The ultrasonic assembly mainly comprises an ultrasonic generator with power of 2 kW, frequency of 20 kHz and amplitude of 5 mu m, an ultrasonic punch and an ultrasonic punch fixing frame.
The test material was a high-quality GCr15 round steel bar having a diameter of 50 mm in a hot rolled state, and then the GCr15 round steel bar was cut into test pieces of 9.6mm×9.6mm×100mm in size by a wire cutting machine, and the chemical composition thereof was as shown in Table 1:
TABLE 1 chemical composition (mass%) of GCr15
Firstly grinding the cut sample on a grinding machine, then polishing the surface again by using fine sand paper to obtain a sample of 9.4mm multiplied by 100mm, and paying attention to the chamfering angle after chamfering the sample; the surface of the sample was scrubbed with acetone and then lubricated with a glass lubricant of type FR-35. The specific operation steps are as follows: firstly, coating glass lubricant on the surface of a sample to be extruded, wherein the thickness of the lubricant is about 0.2mm; secondly, placing the sample in a box-type resistance furnace, and heating for 15min under the condition that the temperature of the resistance furnace is controlled to be 80 ℃; thirdly, naturally drying the GCr15 steel sample after heating and drying at room temperature; and fourthly, lubricating the surfaces of the mold with graphite lubricant to improve the lubricating performance between the mold and the sample.
4. Ultrasonic auxiliary equal channel angular extrusion die preparation before test:
the mould used in the ultrasonic-assisted equal-channel angular extrusion process consists of an ultrasonic vibration upper mould, a lower mould and an ultrasonic assembly, wherein the internal angle phi and the external angle ψ of the mould are 90 degrees, and as shown in fig. 2, the mould is made of 5Cr4W5Mo2V (RM 2).
In the extrusion process, the magnitude of the load applied to the sample in the extrusion process is greatly influenced by the friction force between the die and the sample. In order to reduce the channel friction force between a sample and a die during ultrasonic auxiliary equal channel angular extrusion, the purpose that the sample can be extruded from a horizontal channel smoothly is achieved, the ultrasonic auxiliary equal channel angular extrusion die is arranged on the upper half part of the die, an ultrasonic amplitude transformer is combined with a die ejector rod, meanwhile, an ultrasonic vibration support is additionally arranged on the upper part of the amplitude transformer, a universal testing machine directly acts on the ultrasonic vibration support during extrusion, the ultrasonic vibration support transmits the lower pressure to the ejector rod, meanwhile, an ultrasonic transmitter is connected to the upper part of the ejector rod, the ejector rod drives the sample to move downwards, and ultrasonic vibration is applied to the sample during extrusion, so that the purpose of reducing friction resistance is achieved. Meanwhile, the pressure head of the universal testing machine directly acts on the ultrasonic vibration support during extrusion, and the ejector rod at the lower part of the ultrasonic vibration support is tightly matched with the circular cylinder of the lower die, so that the die is not required to be accurately positioned before extrusion begins. Therefore, the die is not required to be fastened on a platform of the universal testing machine, and the die is only required to be placed under the pressure head after the sample and the ejector rod are arranged in the lower die. The ultrasonic assembly mainly comprises an ultrasonic generator with power of 2 kW, frequency of 20 kHz and amplitude of 40 mu m, an ultrasonic amplitude transformer and an ultrasonic amplitude transformer fixing bracket. The microcomputer-controlled universal testing machine is used for applying pressure to the ultrasonic-assisted equal-channel angular extrusion ultrasonic punch (shown in fig. 5), and the extrusion process is completed by extruding downwards and simultaneously vibrating ultrasonically.
The GCr15 steel sample which is not subjected to ECAP extrusion treatment is annealed at 960 ℃ (AC 3 +50 ℃), and after 20 minutes of heat preservation, the sample is cooled along with the furnace. And carrying out microstructure analysis and mechanical property test on the annealed sample.
Firstly grinding and polishing the sample to obtain a 9.4mm multiplied by 100mm sample, scrubbing the surface of the sample by acetone, and then lubricating the GCr15 sample by a glass lubricant. And (3) preserving the heat of the surface-treated sample at 550-750 ℃ for 20min and simultaneously preheating an ultrasonic-assisted ECAP die at 500 ℃ for 1 h. And then taking out the sample and the mould simultaneously, and rapidly putting the sample into the mould for ultrasonic-assisted ECAE hot extrusion.
The samples treated by the ultrasonic-assisted ECAP are annealed at 800 ℃, 900 ℃ and 960 ℃ for 30min, 60min and 90min respectively. And performing apparent tissue analysis and microhardness test on the annealed sample.
8.1 And (3) microscopic tissue observation:
in order to facilitate the comparison of microstructure structures, test samples are respectively cut and taken out from the outside and the inside of a sample which is not subjected to ultrasonic-assisted equal channel angular extrusion treatment and ECAE treatment and a GCr15 sample which is subjected to single-pass ultrasonic-assisted equal channel angular extrusion treatment.
The treated sample was first cut along the extrusion directions XZ, YZ, specifically as shown in fig. 3 below.
The cut GCr15 sample is subjected to surface polishing treatment, and then the surface of the GCr15 sample is subjected to etching treatment by using 4% nitric alcohol solution. And observing the GCr15 microstructure of the sample which is not extruded, the sample which is processed by ECAE and the GCr15 microstructure which is extruded by single ultrasonic auxiliary equal channel corners by adopting an optical microscope and a scanning electron microscope with the model of BM-4XC, and analyzing the grain refinement effect of the ultrasonic auxiliary equal channel corners and the influence on the structural characteristics of the GCr15 sample by observation.
As shown in fig. 4, the observation of the picture shows that the original structure of the GCr15 steel sample is coarse grains with the equiaxial diameter of about 50 μm before ECAP extrusion treatment, after single-pass ultrasonic assisted ECAP extrusion, the grains are obviously thinned to about 8 μm after extrusion, the microstructure of the GCrl5 steel is greatly changed, the original multi-angle and massive second phase grains are crushed into fine grains and uniformly dispersed in a matrix, the grain size is obviously reduced, but the deformation in the ECAP is uneven, and trace coarse grains still exist.
As can be seen from fig. 4, after single pass ECAP extrusion at a preheating temperature of 950 ℃, the microstructure of the GCrl5 steel is greatly deformed in grain compared to the non-extruded GCrl5 steel sample. From the graph, after single-pass ECAP extrusion, serious plastic deformation occurs in the alloy, and crystal grains are obviously refined. After one ultrasonic assisted ECAP extrusion, the original GCrl5 steel grain equiaxed structure is crushed under the action of shearing force and is obviously elongated along the shearing direction, so that a banded structure is formed.
8.2 hardness test of samples before and after extrusion:
hardness was measured on GCr15 steel samples without ECAP extrusion and with single pass extrusion with ultrasound assisted ECAP. The microhardness of the GCr15 steel sample was measured three times by using an MHV2000 microhardness tester, and the data were averaged.
8.3 test of frictional wear properties of samples before and after extrusion:
1) Friction and wear test sample preparation:
the GCr15 steel sample without ECAP extrusion treatment and the GCr15 steel sample with ultrasonic-assisted ECAE single-pass extrusion treatment were cut to obtain frictional wear samples, and the cut samples were 25mm×7mm in size.
2) Friction wear test parameter selection
The frictional wear test temperature was controlled at room temperature. Load split under dry friction conditions depending on the content of the test
The sliding speeds of the samples on the wearing machine were set to be 50N, 100N, 150N and 200N, respectively, and 0.45m/s and 0.90m/s, respectively. The abrasion test results in this paper were all collected as averages of three data from repeated tests.
3) Friction and wear test method steps
The experiment adopts an M-2000 type multifunctional friction and wear testing machine. The GCr15 steel sample size is 25mm multiplied by 7mm; for the GCr15 steel ring, the sample size is phi 40mm multiplied by 10mm, the temperature is controlled to 850+/-10 ℃, quenching treatment is carried out, and then tempering treatment is carried out at 160+/-5 ℃ for 2 hours, wherein the surface hardness is 58-60 HRC. Both the GCr15 steel coupon and the mating piece were sanded with 900# sandpaper to a surface roughness ra=0.14 μm before frictional wear, and then cleaned with acetone. The test is carried out under the room temperature condition, and the friction environment temperature under the dry friction condition is 24+/-2 ℃, so that the test is carried out by paying attention to the selection of season time, and the humidity is about 45% -55%. Measurement of abrasion loss of GCr15 steel sample the abrasion loss was evaluated by measuring the abrasion loss using a Sartorius BP211D electronic balance with an accuracy of 0.01 mg.
4) Friction and wear test contents
The friction and wear performance of GCr15 steel is tested by adopting a ring-block friction and wear testing machine, and the test contents are as follows:
(1) And researching the friction and wear characteristics of GCr15 steel after ultrasonic-assisted ECAP hot extrusion treatment under a dry friction condition, and the influence of test parameters such as time, load, sliding speed and the like on the friction and wear performance of the GCr15 steel, so as to obtain the friction and wear rule.
(2) The GCr15 steel treated by the ultrasonic-assisted ECAP process is annealed and not treated, and friction and wear performances of the GCr15 steel are researched by comparison to obtain an optimal annealing temperature, and the GCr15 steel has a low friction coefficient at the optimal annealing temperature.
(3) The wear pattern of GCr15 steel was demonstrated by comparing the wear surface topography of GCr15 steel before and after the ultrasound assisted ECAE hot extrusion treatment.
5) Analysis of surface wear topography
(1) Metallographic structure observation analysis
In the experiment, a BM-4 XCS type optical microscope is used for analyzing the microstructure of a sample, and the used etching solution is a mixture of HF, HNO3 and H2O, and the volume ratio is 1:3:10.
(2) Test the wear surface topography of the samples was analyzed by observation using a CSM-950 Scanning Electron Microscope (SEM) from OPTON, germany.
The extrusion force of the GCrl5 steel sample is 2250kN at maximum after one pass of ECAP extrusion, and the extrusion force of the GCrl5 steel ultrasonic auxiliary equal channel angle after one pass is 2000kN at maximum. The extrusion force is reduced by 11.1% compared with the extrusion force before and after. Equal channel angular extrusion and ultrasonic assisted ECAP experiments are respectively carried out under the same conditions, so that the fact that ultrasonic vibration affects the extrusion load of a test press is explained, the extrusion force of GCrl5 steel is reduced by applying ultrasonic vibration, and mainly the yield stress and flow stress of materials are reduced by ultrasonic vibration, and friction between a die and a GCrl5 steel workpiece is reduced.
The waveforms also differ significantly when the extrusion experiments were performed under both protocols. The maximum load of the ultrasonic-assisted ECAP was reduced by 11.1% from the equal channel angular compression. A square wave-like curve appears in the ultrasound-assisted ECAP, mainly when the ultrasound vibration application is intermittent. The equal channel angular extrusion does not add ultrasonic vibration, and the relative waveform is smoother and no square wave appears.
The frictional wear test was performed on a frictional wear tester to obtain a graph of the frictional coefficient of GCr15 before and after extrusion with respect to time, which was shown in FIG. 5, at a sliding speed of 200r/min and a load of 100N. It can be seen from the graph that the coefficient of friction of the GCr15 steel without extrusion treatment is significantly higher than that after extrusion, the average coefficient of friction is 0.89, and the average coefficient of friction after ultrasonic-assisted extrusion treatment is reduced by 0.56, which is reduced by 37%. This demonstrates that the ultrasound-assisted ECAP treatment can significantly reduce the coefficient of friction of GCr15 steel during friction at a load of 100N.
The GCrl5 steel is treated by the ultrasonic-assisted ECAP hot extrusion process, so that the microstructure of the GCrl5 steel can be obviously refined. The refinement of the microstructure of the alloy necessarily has an influence on the hardness of GCrl5 steel. The change of the hardness values of the GCrl5 steel before and after the ultrasonic-assisted ECAP hot extrusion treatment is compared, so that the influence mechanism of the ECAP hot extrusion process on the performance is favorably and deeply discussed, and a processing process capable of obtaining the optimal GCr15 steel performance is formulated.
The hardness of GCrl5 steel varies greatly before and after ultrasonic assisted ECAP hot extrusion. The microhardness of the GCrl5 steel sample which is not subjected to ECAP extrusion treatment is 365HV, the hardness of the sample is obviously improved to 580HV after the sample is subjected to one-pass ultrasonic-assisted ECAE extrusion treatment, and the hardness is improved by 61% relative to the hardness before extrusion. This demonstrates that the hardness of GCrl5 steel is significantly increased after heat treatment with ultrasonic assisted ECAP and that the alloy has a relatively high hardness after single pass ultrasonic assisted ECAP extrusion. The microstructure refinement of GCrl5 steel after one-time extrusion treatment of ultrasonic-assisted ECAP causes hardness increase. The structure of the sample is obviously refined after the ultrasonic-assisted ECAP heat treatment process, the grain size of the alloy is obviously reduced after extrusion, the GCrl5 steel has relatively small grain size after single-pass extrusion, the number of grains is increased, the sample refining effect is obvious, and the hardness of the sample is improved after single-pass extrusion. Meanwhile, the GCrl5 steel is subjected to severe plastic deformation in the extrusion process, the dislocation density in the GCrl5 steel material is increased, the lattice distortion elastic energy is increased, and the hardness and the strength of the GCrl5 steel material are improved.
The GCr15 steel is processed by the ultrasonic-assisted ECAP hot extrusion process, and the GCr15 steel with fine structure and excellent performance is prepared. The action mechanism of tissue refinement and friction and wear performance improvement of the GCr15 steel sample after the ultrasonic-assisted ECAE hot extrusion treatment is researched and analyzed, and the friction and wear rule and wear form of the GCr15 steel sample after the ultrasonic-assisted ECAE hot extrusion treatment are explained, so that the following conclusion is drawn:
1. when the preheating temperature is 950 ℃, the ultrasonic-assisted ECAE hot extrusion of GCr15 steel is successfully realized, the crystal grains are obviously refined, and the crystal grain size is obviously reduced.
After single hot extrusion, the GCR15 steel has raised hardness, obvious plastic deformation of its structure, some refinement of coarse initial grains, and alloy grain size from 50 microns before extrusion to 8 microns after extrusion.
And 3, separating out second-phase fine particles which are dispersed in a tissue after the GCr15 steel is subjected to ultrasonic-assisted ECAE hot extrusion and annealing treatment, wherein the fine second phase dispersedly strengthens a matrix, so that the mechanical property of the sample is improved.
The tribology performance of the GCR15 steel sample after being treated by the high-temperature ultrasonic-assisted ECAE process under the same test condition is better than that of the GCR15 steel sample after being not treated by the ultrasonic-assisted ECAE extrusion process.
And 5, the friction coefficient of the GCr15 steel sample is increased and then reduced along with the increase of the load under the dry friction condition, and an inflection point appears in the experimental process. The friction coefficient of the sample decreases instead with increasing sliding speed, but the amount of wear of the sample increases with increasing load and sliding speed.
The GCr15 steel sample mainly has three wear forms of abrasive particle wear, adhesive wear and surface fatigue wear in the friction wear process, and the three wear forms show different degrees along with the change of experimental conditions and the change of experimental parameters.
The action mechanism of improving the friction and wear performance of the GCr15 steel sample after the ultrasonic-assisted ECAP hot extrusion treatment is as follows: the surface hardness and strength of the GCr15 steel sample are improved through the treatment of the ultrasonic-assisted ECAE, and the abrasion resistance and wear resistance are obviously enhanced. Meanwhile, the GCr15 steel sample is subjected to high-temperature ultrasonic-assisted ECAP process treatment structure is obviously thinned, so that the plastic deformation resistance of the sample is improved, the plow effect between friction and abrasion surfaces is reduced, and the friction and abrasion performance of the GCr15 steel sample is also improved.
In order to improve the wear resistance of the GCr15 steel, after the GCr15 steel is subjected to ultrasonic-assisted ECAP process treatment, the friction performance of the GCr15 steel under different load and sliding speed conditions is compared, and the wear mechanism is studied by analyzing the wear surface morphology. Research results show that the ultrasonic-assisted ECAP treatment can remarkably reduce the friction coefficient of GCr15 steel in the friction process; the abrasion loss of the GCr15 steel subjected to the ultrasonic-assisted ECAP treatment is reduced in the same time period as that of the GCr15 steel subjected to the ultrasonic-assisted ECAP treatment; GCr15 steel after annealing treatment and ECAP treatment had a slight sticking and flaking phenomenon than the worn surface before extrusion.
Claims (5)
1. A process method for processing GCr15 steel by using an ultrasonic-assisted ECAP is characterized by comprising the following steps of: firstly grinding the cut sample on a grinding machine, then polishing the surface again by using fine sand paper to obtain a sample of 9.4mm multiplied by 100mm, and paying attention to the chamfering angle after chamfering the sample; scrubbing the surface of a sample by using acetone, and then lubricating a GCr15 steel sample by using a glass lubricant with the model of FR-35;
the specific operation steps are as follows:
firstly, coating glass lubricant on the surface of a sample to be extruded, wherein the thickness of the lubricant is about 0.2mm; secondly, placing the sample in a box-type resistance furnace, and heating for 15min under the condition that the temperature of the resistance furnace is controlled to be 80 ℃; thirdly, naturally drying the GCr15 steel sample after heating and drying at room temperature;
fourth, each surface of the die is lubricated by graphite lubricant, so that the lubricating performance between the die and the sample is improved;
fifth step: ultrasonic-assisted equal-channel corner extrusion die preparation:
sixth step: sample annealing treatment:
seventh step: high-temperature ultrasonic-assisted ECAE processing of GCr 15:
eighth step: annealing the treated sample.
2. The process for the ultrasonic-assisted ECAP treatment of GCr15 steel according to claim 1, wherein: the ultrasonic-assisted equal-channel angular extrusion die is prepared, the die used in the ultrasonic-assisted equal-channel angular extrusion process consists of an ultrasonic vibration upper die, a lower die and an ultrasonic assembly, wherein the internal angle phi and the external angle ψ of the die are 90 degrees, and the die is manufactured by selecting materials 5Cr4W5Mo2V (RM 2);
in the extrusion process, the magnitude of the load applied to the sample in the extrusion process is greatly influenced by the friction force between the die and the sample; in order to reduce the channel friction force between a sample and a die during ultrasonic-assisted equal channel angular extrusion, the sample can be extruded from a horizontal channel smoothly, an ultrasonic amplitude transformer is combined with a die ejector rod, an ultrasonic vibration support is additionally arranged at the upper part of the amplitude transformer, a universal testing machine directly acts on the ultrasonic vibration support during extrusion, the ultrasonic vibration support transmits the lower pressure to the ejector rod, an ultrasonic transmitter is connected at the upper part of the ejector rod, the ejector rod drives the sample to move downwards, and ultrasonic vibration is applied to the sample during extrusion; meanwhile, the pressure head of the universal testing machine directly acts on the ultrasonic vibration bracket during extrusion, and the ejector rod at the lower part of the ultrasonic vibration bracket is tightly matched with the circular cylinder shape of the lower die, so that the die does not need to be accurately positioned before extrusion begins; therefore, the die is not required to be fastened on a platform of the universal testing machine, and the die is only required to be placed under the pressure head after the sample and the ejector rod are arranged in the lower die; the ultrasonic assembly mainly comprises an ultrasonic generator with power of 2 kW, frequency of 20 kHz and amplitude of 40 mu m, an ultrasonic amplitude transformer and an ultrasonic amplitude transformer fixing bracket; the microcomputer is used for controlling the universal testing machine to apply pressure to the ultrasonic-assisted equal-channel angular extrusion ultrasonic punch, the ultrasonic is extruded downwards, and meanwhile, the ultrasonic is vibrated, so that the extrusion process is completed.
3. The process for the ultrasonic-assisted ECAP treatment of GCr15 steel according to claim 1, wherein: the sample annealing treatment is as follows: annealing the GCr15 steel sample which is not subjected to ECAE extrusion treatment at 960 ℃ (AC 3+50 ℃), preserving heat for 20min, and cooling along with a furnace; and carrying out microstructure analysis and mechanical property test on the annealed sample.
4. The process for the ultrasonic-assisted ECAP treatment of GCr15 steel according to claim 1, wherein: the high-temperature ultrasonic-assisted ECAE processing of GCr15 is as follows: firstly grinding and polishing a sample to obtain a sample with the thickness of 9.4mm multiplied by 100mm, scrubbing the surface of the sample by acetone, and then lubricating a GCr15 sample by a glass lubricant; the sample after surface treatment is kept at 550-750 ℃ for 20min, and simultaneously, an ultrasonic-assisted ECAE mould is kept at 500 ℃ for 1h for preheating; and then taking out the sample and the mould simultaneously, and rapidly putting the sample into the mould for ultrasonic-assisted ECAE hot extrusion.
5. The process for the ultrasonic-assisted ECAP treatment of GCr15 steel according to claim 1, wherein: the annealing treatment of the treated sample is as follows: annealing the sample subjected to the ultrasonic-assisted ECAE treatment at 800 ℃, 900 ℃ and 960 ℃ for 30min, 60min and 90min respectively; and performing apparent tissue analysis and microhardness test on the annealed sample.
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