Coarse carbide reinforced ultra-fine grain laser cladding layer cutter and preparation method thereof

Abstract

The invention discloses a coarse carbide reinforced ultra-fine grain laser cladding layer cutter and a preparation method thereof. A coarse carbide reinforced ultra-fine grain cladding layer is prepared on an M2 high-speed steel base material by using a pulse laser cladding three-layer process; the cladding of the three layers is that after the next cladding layer is solidified, the next cladding layer is cladded again under the same cladding condition until the cutter material with the three cladding layers is obtained; and the section of the cladding layer in the thickness direction serves as the rear tool face of the tool, and a chamfer is machined between the front tool face and the rear tool face. According to the method, the coarse carbide enhanced ultrafine grain cladding layer is prepared on the M2 high-speed steel base material by adopting a method of synchronously feeding powder and cladding three layers by pulse laser, so that the hardness and the wear resistance of the base material can be effectively improved. And the cladding layer matrix grains reach the submicron scale.

Description

Technical Field

[0001] The invention relates to the technical field of laser cladding, and in particular to a coarse carbide reinforced ultrafine grain laser cladding layer tool and a preparation method thereof. Background Art

[0002] During the cutting process, the tool tip needs to withstand huge impact force and severe friction. The wear of the tool will not only shorten its service life, but also lead to frequent shutdowns for tool replacement or re-sharpening, seriously affecting production efficiency. With the development of modern industrial manufacturing, improving the performance and life of mechanical components has become a continuous pursuit. Strengthening treatment of high-speed steel tools can improve the hardness, wear resistance and service life of the tools, which has far-reaching significance for improving resource utilization.

[0003] Among many surface treatment technologies, laser cladding, as an advanced surface modification technology, can achieve good metallurgical bonding between the cladding layer and the substrate. It also has a small dilution rate and heat-affected zone, high efficiency and wide material applicability. These advantages make laser cladding show broad application potential in the field of strengthening mechanical parts. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a coarse carbide reinforced ultrafine grain laser cladding layer tool with good hardness and wear resistance and a preparation method thereof.

[0005] In order to solve the above technical problems, the preparation method of the coarse carbide reinforced ultrafine grain laser cladding layer tool of the present invention comprises the following steps: S1 preparation of laser cladding layer material: using a pulsed laser cladding three-layer process to prepare a coarse carbide reinforced ultrafine grain cladding layer on an M2 high speed steel substrate, the three-layer cladding is to wait for the next cladding layer to solidify and then clad another layer on the next cladding layer under the same cladding conditions until a three-layer cladding layer tool material is obtained;

[0006] S2 tool making: the top surface of the cladding layer of the tool material is used as the front cutting surface of the tool, the cross section in the thickness direction of the cladding layer is used as the back cutting surface of the tool, and a chamfer is machined between the front cutting surface and the back cutting surface.

[0007] The cladding adopts the synchronous powder feeding method. The alloy powder used for cladding is composed of 32.36wt.% of ferrovanadium powder, 6.1wt.% of graphite powder and 61.54wt.% of reduced iron powder, wherein the ferrovanadium powder adopts FeV50, the vanadium mass content of the ferrovanadium powder is 48%, the particle size range of the ferrovanadium powder, graphite powder and reduced iron powder is 100-200 mesh, the laser power is 1000W, the spot diameter is 2.0mm, the pulse frequency is 4500Hz, the duty cycle is 95%, the defocus amount is 25mm, the scanning speed is 12mm / s, the overlap rate is 35%, the powder feeding rate is 7.2g / min, and the protective argon gas flow rate is 15L / min.

[0008] Preferably, the surface of the substrate is polished and rust-removed before cladding, and the substrate is ultrasonically cleaned with anhydrous ethanol for 5 minutes to 10 minutes, blown dry, and then placed in a blast drying oven at a temperature of 120 degrees for 1.5 hours.

[0009] Preferably, the powder is mixed in a V-shaped powder mixer for 2 hours and dried in a vacuum drying oven at 120° C. for 2 hours to remove moisture.

[0010] Preferably, the S2 includes the steps of: S21 dividing the tool material into multiple square areas and cutting out a square body on the top surface of the cladding layer, the top surface of the cladding layer serving as the front cutting surface of the tool, and the cross section in the thickness direction of the cladding layer serving as the back cutting surface of the tool, S22 polishing the square body and chamfering the front cutting surface and the back cutting surface.

[0011] The coarse carbide reinforced ultrafine crystal laser cladding layer tool of the present invention is prepared by adopting any one of the above-mentioned preparation methods of the coarse carbide reinforced ultrafine crystal laser cladding layer tool.

[0012] The beneficial effects of the present invention are:

[0013] The present invention adopts a three-layer method of synchronous powder feeding pulse laser cladding on an M2 high-speed steel substrate to prepare a coarse carbide reinforced ultrafine grain cladding layer, which can effectively improve the hardness and wear resistance of the substrate. The hardness of the obtained cladding layer can reach up to 1100HV. 0.2 The wear scar width, depth and wear volume are approximately 0.5 mm, 1.11 μm and 0.184×10 -7 μm 3 The grains of the cladding layer matrix reach submicron scale, and the prepared carbides are in-situ generated VC, which are coarse carbides; the main cutting force of the prepared cladding layer tool is reduced by 8.6% compared with the high-speed steel tool, the cutting distance is increased by 75%, and the minimum roughness of the processed surface reaches 2.5Ra.

[0014] A metal-based cladding layer containing a ceramic phase is prepared on the surface of a substrate with low hardness and low wear resistance. It not only retains the strength and toughness of the metal phase material, but also significantly improves the wear resistance of the cladding layer by introducing the high hardness characteristics of the ceramic phase. The coarse carbides generated in situ by the laser have excellent wear resistance and hardness. Adding strong carbides to the powder can greatly improve the hardness and wear resistance of the cladding sample. Coarse carbides have stronger wear resistance than fine carbides. Fine grain strengthening can increase the hardness of the cladding layer. Since laser cladding has the characteristics of rapid heating and rapid cooling, combined with the three-layer cladding process, it is easier to obtain submicron or nanometer grains. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1XRD diffraction patterns of cladding layers a and b;

[0016] Figure 2 The optical microscopic morphology of the top layer of the cladding layer a prepared in Example 1 of the present invention;

[0017] Figure 3 The optical microscopic morphology of the top layer of the cladding layer b prepared in Comparative Example 1 of the present invention;

[0018] Figure 4 The secondary electron morphology of the top layer of the cladding layer a prepared in Example 1 of the present invention;

[0019] Figure 5 The secondary electron morphology of the top layer of the cladding layer b prepared in Comparative Example 1 of the present invention;

[0020] Figure 6 The microhardness distribution of the high-speed steel substrate and the cladding layers a and b prepared in the embodiments of the present invention and the comparative example along the depth direction of the cross section;

[0021] Figure 7 The grain size diagram of the substrate of the cladding layers a and b prepared in the embodiment of the present invention and the comparative example;

[0022] Figure 8 The friction coefficient curves of the friction and wear of the cladding layers a and b prepared in the embodiment of the present invention and the comparative example;

[0023] Fig. 9 The cross-sectional depth and width of the friction and wear profiles of the high-speed steel substrate and the cladding layers a and b prepared in the embodiments of the present invention and the comparative example;

[0024] Fig.10 The wear volume of friction and wear of the high-speed steel substrate and the cladding layers a and b prepared in the embodiments of the present invention and the comparative example;

[0025] Fig.11 A schematic diagram of the manufacturing process of the cladding layer a and b cutting tools prepared in the embodiment of the present invention and the comparative example;

[0026] Fig.12 The cladding layers a and b prepared in the embodiment of the present invention and the comparative example are the front and rear tool faces and geometric parameters and the schematic diagram of the tool face;

[0027] Fig.13 The cutting forces of the high-speed steel tool and the cladding layers a and b prepared in the embodiments of the present invention and the comparative example;

[0028] Fig.14 The rear tool wear amount of the high-speed steel tool and the cladding layer a and b tools prepared in the embodiment of the present invention and the comparative example;

[0029] Fig.15The roughness of the machined surface of the high-speed steel tool and the cladding layer a and b tools prepared in the embodiments of the present invention and the comparative example;

[0030] Fig.16 Secondary electron morphology images of the front and rear tool faces wear of high-speed steel tools and cladding layers a and b prepared in the embodiments of the present invention and the comparative example; DETAILED DESCRIPTION

[0031] The specific embodiment and the comparative example both prepare the coarse carbide reinforced ultrafine grain laser cladding layer tool according to the following method: Specific steps:

[0032] S1 laser cladding material:

[0033] The cladding layer was prepared on the M2 high-speed steel substrate by synchronous powder feeding pulse laser cladding method. Before cladding, the surface of the M2 high-speed steel substrate was polished and rusted, and the substrate was ultrasonically cleaned with anhydrous ethanol for 5min-10min, blown dry, and then placed in a blast drying oven at a temperature of 120 degrees for 1.5h; the alloy powder used for cladding was mixed for 2 hours using a V-shaped powder mixer and dried in a vacuum drying oven at 120℃ for 2 hours to remove moisture.

[0034] The alloy powder used for cladding is composed of ferrovanadium powder, graphite powder and reduced iron powder, wherein the ferrovanadium powder is FeV50, the vanadium mass content of the ferrovanadium powder is 48%, the particle size range of the ferrovanadium powder, graphite powder and reduced iron powder is 100-200 mesh, and the alloy powder composition is: 32.36wt.% of ferrovanadium powder, 6.1wt.% of graphite powder and 61.54wt.% of reduced iron powder.

[0035] The M2 high-speed steel substrate was clad by synchronous powder feeding pulse laser cladding. The laser power was 1000W, the spot diameter was 2.0mm, the pulse frequency was 4500Hz, the duty cycle was 95%, the defocus amount was 25mm, the scanning speed was 12mm / s, the overlap rate was 35%, the powder feeding rate was 7.2g / min, and the protective argon gas flow rate was 15L / min.

[0036] The phase of the cladding layer was characterized by an X-ray diffractometer in the 2θ range of 20-90° and a scanning speed of 20° / min.

[0037] The cross-sectional morphology was characterized using scanning electron microscopy.

[0038] The microhardness of the cladding layer was measured using a microhardness tester with a load of 1.96N and a holding time of 15s.

[0039] A reciprocating friction and wear tester was used to carry out a dry friction test at room temperature to determine the dry sliding wear behavior of the cladding layer. The test force was 50N, the stroke was 8mm, the frequency was 5Hz, and the friction time was 30min. The wear profile was measured by a three-dimensional optical microscope to obtain the wear volume loss.

[0040] S2 makes knives:

[0041] S21 divides the tool material into multiple square areas and cuts out a square body on the top surface of the cladding layer. The high-speed steel and the cladding layers a and b prepared in the embodiments of the present invention and the comparative example are made into samples with a size of 13.0 mm×13.0 mm×6.0 mm using an electric spark wire cutting machine. The top surface of the cladding layer is used as the rake face of the tool, and the cross section in the thickness direction of the cladding layer is used as the back face of the tool. S22 polishes the square body and chamfers the rake face and the back face.

[0042] A horizontal machine tool was used to carry out dry cutting test on 45# steel. The surface roughness and tool wear of the machined surface were recorded and observed using a roughness meter and a three-dimensional ultra-depth-of-field digital microscope.

[0043] In addition, Example 1:

[0044] The process parameters of the pulsed laser cladding three-layer process are: laser power 1000W, spot diameter 2.0mm, pulse frequency 4500Hz, duty cycle 95%, defocusing amount 25mm, scanning speed 12mm / s, overlap rate 35%, powder feeding rate 7.2g / min, protective argon gas flow rate 15L / min, and cladding layer a is obtained.

[0045] In addition, in Comparative Example 1:

[0046] The process parameters of the pulsed laser cladding two-layer process are: laser power 1000W, spot diameter 2.0mm, pulse frequency 4500Hz, duty cycle 95%, defocusing amount 25mm, scanning speed 12mm / s, overlap rate 35%, powder feeding rate 7.2g / min, protective argon gas flow rate 15L / min, and cladding layer b is obtained.

[0047] Cladding three or two layers means that after the next cladding layer solidifies, another layer is clad on the next cladding layer under the same cladding conditions until a tool material with a corresponding number of cladding layers is obtained.

[0048] See also Figure 1 , XRD diffraction diagrams of cladding layers a and b. Cladding layers a and b are composed of α-Fe, γ, VC, Cr7C3, Cr 23 It is composed of C6, Fe3C, Mo2C and WC phases.

[0049] See also Figure 2-3, Optical microscopic morphology of the top layers of cladding layers a and b. The average grain sizes of the substrates of cladding layers a and b are 0.96μm and 0.91μm, respectively, reaching submicron ultrafine grain scale.

[0050] See also Figure 4-5 , the secondary electron morphology of the top layers of cladding layers a and b, the secondary electron morphology of the carbides in the top layers of cladding layers a and b are different, among which coarse carbides are generated in situ in the third layer of cladding layer a, and the cladding processes of cladding layers a and cladding layers b are the same, and the formation mechanism of the coarse carbides generated in cladding layer a is: when cladding the first layer, the inside of the molten pool will produce Marangoni motion under the action of the pulsed laser, and VC is in the form of fine particles. When cladding the second layer, due to the dilution effect of laser cladding, the part of the solidified first layer will be remelted, and the solidified material in the first layer will be diluted into the second layer, and VC will begin to agglomerate and grow. When cladding the third layer, the laser remelts part of the second layer. Due to the low density of carbide VC, VC will condense and float, and VC will agglomerate and grow into coarse carbides in the third layer. Repeated experiments have shown that when the cladding reaches four layers, the further increase in the number of coarse carbides leads to increased brittleness of the cladding layer, which is prone to cracks during cutting and affects the toughness of the material.

[0051] See also Figure 6 , the microhardness distribution of cladding layer a and b along the depth direction of the cross section, from Fig.12 It can be seen that the microhardness of the cladding layer a is the highest, which is 1100HV 0.2 , indicating that the coarse carbides generated in the cladding layer a have a positive effect on improving the hardness of the cladding layer.

[0052] See also Figure 7 , Grain size diagram of the substrate of cladding layer a and b. When three layers are clad, the minimum grain size of cladding layer a is 0.91μm, reaching the sub-micron ultrafine grain scale.

[0053] See also Figure 8 , the friction coefficient curves of cladding layers a and b, the average friction coefficient of cladding layer a is 0.441. Cladding layer a has higher hardness than M2 high-speed steel substrate and cladding layer b. There are a large number of coarse carbides in cladding layer a. During the wear process, the friction pair will continuously rub the coarse carbides, which will be more hindered during the wear process. The wear surface is not easy to deform, resulting in a larger friction coefficient. The hardness of M2 high-speed steel substrate and cladding layer b is lower than that of cladding layer a, and it is more likely to deform during the wear process, resulting in a smaller friction coefficient.

[0054] See also Figure 9-10The cross-sectional depth, width and wear volume of the friction and wear profiles of cladding layers a and b are shown in Table 2. The cross-sectional depth and width of the wear profile of cladding layer a are lower than those of the high-speed steel substrate and cladding layer b. The wear volume of the M2 high-speed steel substrate is 1.491×10 -7 μm 3 The wear volume of cladding layer b is 0.345×10 -7 μm 3 The wear volume of cladding layer a is the smallest, which is 0.184×10 -7 μm 3 This can be attributed to the fact that during the wear process, the coarse carbides of the cladding layer a are exposed to the outside, playing a supporting role, reducing the contact area between the cladding layer and the friction pair, and the fine and dense grains in the cladding layer a are conducive to hindering dislocation slip, increasing the grinding resistance of the cladding layer a to the friction pair, and reducing the depth of friction wear. As the friction and wear proceed, under the action of friction force and friction heat on the wear surface, the elements in the cladding layer react with O to continuously generate oxidation products. The generated oxides are enriched around the coarse carbides, forming an oxide film that has the effect of reducing friction.

[0055] See also Fig.11 The manufacturing process of the cladding layer a and b tools prepared in the embodiments of the present invention and the control example is to use an electric spark wire cutting machine to make the cladding completed sample into a sample with a size of 13.0 mm×13.0 mm×6.0 mm, and grind and chamfer the cut sample to make a tool.

[0056] See also Fig.12 , the geometric parameters and tool face schematic diagram of the cladding layer a and b tools prepared in the embodiment of the present invention and the control example, the top surface with the cladding layer is used as the front tool face, and the cross section in the thickness direction of the cladding layer is used as the back tool face. When in use, the front tool face and the back tool face jointly cut the workpiece. According to the wear standard of the turning tool durability test recommended by the international standard ISO, the tool is considered to have failed when VB is greater than or equal to 0.3mm.

[0057] See also Fig.13 The cutting forces of the high-speed steel tool and the cladding layer a and b tools prepared in the embodiments of the present invention and the control example are shown in FIG. 1 . The main cutting force of the cladding layer a tool is reduced by 8.6% compared with the high-speed steel tool.

[0058] See also Fig.14 The flank wear of the high-speed steel tool and the cladding layer a and b tools prepared in the embodiments of the present invention and the control example shows that the cutting distance of the cladding layer a tool is increased by 75% compared with the high-speed steel tool.

[0059] See also Fig.15The roughness of the processed surface of the high-speed steel tool and the cladding layer a and b tools prepared in the embodiments of the present invention and the control example is that the roughness of the processed surface of the cladding layer a tool is as low as 2.5Ra.

[0060] See also Fig.16 , secondary electron morphology of the wear of the front and rear blades of the high-speed steel tool and the cladding layer a and b tools prepared in the embodiments of the present invention and the control example. The wear of the cladding layer a tool is reduced compared with the high-speed steel tool and the cladding layer b tool. The high-speed steel tool has serious built-up edge and chipping during cutting. The built-up edge phenomenon is caused by the high temperature and pressure at the contact point between the high-speed steel tool and the workpiece during cutting, which produces a serious bonding phenomenon. At this time, the chips flow through the bottom layer adhered to the blade surface and accumulate to form a built-up edge. Severe built-up edge not only affects the service life of the tool, but also reduces the surface roughness of the cutter. The coarse carbides in the cladding layer a will be exposed during the cutting process. The exposed coarse carbides play a skeleton role, have high hardness and excellent wear resistance, and are not easy to fall off during the cutting process, resulting in reduced wear on the back blade of the cladding layer a.

[0061] The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will appreciate that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a coarse carbide reinforced ultrafine grain laser cladding tool, characterized in that: The following steps are involved: S1 Preparation of laser cladding layer material: Use pulsed laser cladding three-layer process to prepare coarse carbide reinforced ultrafine grain cladding layer on M2 high speed steel substrate. Cladding three layers is to wait for the next cladding layer to solidify and then clad another layer on the next cladding layer under the same cladding conditions until a tool material with three cladding layers is obtained; S2 tool making: the top surface of the cladding layer of the tool material is used as the front cutting surface of the tool, the cross section in the thickness direction of the cladding layer is used as the back cutting surface of the tool, and a chamfer is machined between the front cutting surface and the back cutting surface.

2. The method for preparing a coarse carbide reinforced ultrafine-grained laser cladding tool according to claim 1, characterized in that: The cladding adopts the synchronous powder feeding method. The alloy powder used for cladding is composed of 32.36wt.% of ferrovanadium powder, 6.1wt.% of graphite powder and 61.54wt.% of reduced iron powder, wherein the ferrovanadium powder adopts FeV50, the vanadium mass content of the ferrovanadium powder is 48%, the particle size range of the ferrovanadium powder, graphite powder and reduced iron powder is 100-200 mesh, the laser power is 1000W, the spot diameter is 2.0mm, the pulse frequency is 4500Hz, the duty cycle is 95%, the defocus amount is 25mm, the scanning speed is 12mm / s, the overlap rate is 35%, the powder feeding rate is 7.2g / min, and the protective argon gas flow rate is 15L / min.

3. The method for preparing a coarse carbide reinforced ultrafine-grained laser cladding tool according to claim 1, characterized in that: Before cladding, the surface of the substrate was polished and rust-removed, and the substrate was ultrasonically cleaned with anhydrous ethanol for 5 minutes to 10 minutes, blown dry, and then placed in a blast drying oven at a temperature of 120 degrees for 1.5 hours.

4. The method for preparing a coarse carbide reinforced ultrafine-grained laser cladding tool according to claim 1, characterized in that: The powders were mixed using a V-shaped mixer for 2 hours and dried in a vacuum drying oven at 120° C. for 2 hours to remove moisture.

5. The method for preparing a coarse carbide reinforced ultrafine-grained laser cladding tool according to claim 1, characterized in that: The S2 includes the steps of: S21 dividing the tool material into multiple square areas and cutting out a square body on the top surface of the cladding layer, the top surface of the cladding layer serving as the front cutting surface of the tool, and the cross section in the thickness direction of the cladding layer serving as the back cutting surface of the tool, and S22 polishing the square body and chamfering the front cutting surface and the back cutting surface.

6. A coarse carbide reinforced ultrafine grain laser cladding tool, characterized in that: The tool is prepared by adopting the method for preparing a coarse carbide reinforced ultrafine grain laser cladding layer tool as claimed in any one of claims 1 to 5.

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