Laser cladding m2 high toughness coating and preparation method thereof

Abstract

The present application relates to a kind of laser cladding M2 high toughness coating and its preparation method, by multi-pass cladding and semi-solid solidification technology, form a kind of dendritic solidification crystalline organization coated on α-primary crystal;The α-primary crystal phase in this organization and the matrix phase of dendritic solidification crystalline organization are α-Fe, but the order of formation of the two phases is different, alloy composition is not identical, discontinuous component interface exists between the two;Carbonide is formed in the process of solidification and is precipitated in two phases, in dispersed, broken network precipitation state;So as to improve the strength and toughness of coating;The hardness of the obtained coating is 65.3HRC~68.0HRC;Bending strength is 2658~3846MPa;Impact toughness is more than 15.0~18.0J.cm 2 .

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of M2 alloy coating, and relates to a high-toughness laser cladding M2 coating and a preparation method thereof. TECHNICAL BACKGROUND

[0002] M2 high-speed steel is a molybdenum-based high-speed steel containing a large amount of W, Mo, Cr, V and other alloy elements, is a representative of general high-speed steel, is a wear-resistant and heat-resistant tool steel with secondary hardening characteristics, and has been widely used in cutting tools, cold and hot dies and other tools or structural parts requiring heat resistance and wear resistance.

[0003] Casting refers to a method of directly casting a product after melting a material at a high temperature. The material is usually melted in an electric arc furnace and poured into a high-temperature-resistant mold to obtain a finished product through a series of processes such as cooling crystallization, heat treatment and post-treatment. In industrial production, the production efficiency can be ensured by controlling the melting temperature, atmosphere and cooling conditions. The as-cast structure of M2 high-speed steel is composed of martensite and eutectic carbide structure. The eutectic carbide type is mainly M2C, which is distributed in the form of bone or net, and is extremely stable and not easy to break and granulate. This feature makes the hardness, red hardness and fracture toughness of the as-cast M2 high-speed steel not lower than that of the forged state, but the impact toughness is much lower than that of the forged state. The impact toughness of the as-cast M2 is generally 6.0-8.0 J·cm 2 , and the impact toughness of the forged-heat-treated M2 is more than 15.0 J·cm 2 .

[0004] Forging is a method of producing products with certain shape and mechanical properties by pressing metal blanks through a forging press, which can reduce the defects of porosity in the casting sample to a certain extent, optimize the structure, and improve the mechanical properties. Forging parts are often used to manufacture important mechanical parts with high load and harsh working conditions. Because the original M2 high-speed steel blank has uneven organization and chemical composition, heat treatment cannot change this situation, so it is necessary to use forging to break the too large eutectic carbide in the blank and make the carbide distribution uniform, and then to manufacture various cutters and dies. However, in actual production, a series of defects such as corner cracks and cross cracks often occur. The main reasons for the defects can be summarized as follows: first, when the temperature decreases, the difficulty of metal flow caused by the metal flow leads to cracking, accompanied by the precipitation of carbide, which accelerates the formation of cracks. Second, when the temperature rises, there is a shear stress at the corner of the blank. When the high-speed steel is subjected to such shear stress, due to its poor high-temperature plasticity, the whole high-speed steel tends to harden, especially at the corner, thereby cracks are generated. In the study of forged M2 high-speed steel, the method of low-temperature furnace charging and slow heating below 800-900 ℃ can ensure the heat penetration of the blank, so that the structure transits smoothly and the internal stress reaches the minimum, thereby avoiding heating cracks. By increasing the heating speed, the furnace temperature is increased, and the stable performance of the forged M2 high-speed steel is obtained.

[0005] With the progress and continuous development of industry, the demand for engineering machinery is increasing, and engineering machinery is often subjected to wear, fracture and other forms of damage in harsh working conditions. The damage of these key components not only affects the service performance of the overall engineering machinery, but also has great safety hazards. In order to solve this problem, laser cladding technology emerges as the times require and develops rapidly. Laser cladding uses laser to melt metal powder, which is combined with the base material to form a metal surface coating, thereby playing a surface strengthening role of the base material. M2 high-speed steel can be used as the raw material of laser cladding coating due to its high hardness, high toughness and high wear resistance.

[0006] However, the M2 coating of laser cladding undergoes a melting process, and the eutectic carbide type mainly in the form of M2C is often formed, which is distributed in the form of skeleton or network. The subsequent forging process cannot break the coarse eutectic carbide formed during melting and cooling, and the distribution of carbide is uneven, which reduces the toughness of the coating and the mechanical properties cannot reach the performance level of the forged structure. SUMMARY

[0007] The application aims to provide a laser cladding M2 high-toughness coating and a preparation method thereof.

[0008] To achieve the above-mentioned purpose, the technical scheme provided by the application is as follows:

[0009] The M2 alloy powder is prepared by a gas atomization method, and the average particle size of the powder ranges from 30 to 45 microns; the laser cladding process is adopted to form a dendritic solidification crystalline structure coated on an alpha-primary crystal on the substrate through multi-pass cladding and semi-solid solidification technology; the alpha-primary phase and the matrix phase of the dendritic solidification crystalline structure are both alpha-Fe, but the two phases are formed in different sequences and have different alloy compositions, and there is a discontinuous composition interface between the two phases; the carbide formed in the solidification process is precipitated in the two phases in a dispersed and broken network state.

[0010] The substrate used in the application includes medium-carbon and low-carbon carbon structural steel, such as 42CrMo, 45 steel, 16Mn, and 16Cr; and also includes alloy tool steel, such as H13 steel.

[0011] The multi-pass cladding and semi-solid solidification technology used in the application is mainly performed through the alternation of three laser cladding process parameters, including the first pass: the laser power is 4.5-5.0 KW, the laser scanning speed is 1.5-2 m / min, the powder feeding rate is 10-15 g / min, the laser spot diameter is 1.8-2.2 mm, and the argon gas flow rate is 5-5.5 L / min; the second pass: the laser power is 2.5-3.96 KW, the laser scanning speed is 5-12 m / min, the powder feeding rate is 15-25 g / min, the laser spot diameter is 1.2-2.5 mm, the laser pass overlap rate is 50-70%, and the argon gas flow rate is 6-7 L / min; and the third pass: the laser power is 2.5-3.96 KW, the laser scanning speed is 10-20 m / min, the powder feeding rate is 8-18 g / min, the laser spot diameter is 1.2-2.5 mm, the laser multi-pass overlap rate is 70%-90%, and the argon gas flow rate is 6-7 L / min.

[0012] The first pass is characterized by high laser power and low laser scanning speed, and is used to preheat the substrate and to make the M2 powder fully molten; the second pass is characterized by low laser power and high laser scanning speed, and is used to re-melt the first-pass coating metal in solidification process to realize semi-solid crystallization; the third pass is characterized by laser power equivalent to that of the second pass, but the scanning speed is increased and the powder feeding rate is decreased, so as to mix the coating structure of the third pass with that of the second pass to realize overall semi-solid crystallization. After the above three passes are continuously completed, the above process is repeated alternately, and the laser overlap rate of the first pass is 50-60%.

[0013] After the coating is completed, air cooling is performed to room temperature to realize normalizing treatment; the hardness of the obtained coating is 65.3 HRC-68.0 HRC; the bending strength is 2658-3846 MPa; and the impact toughness is more than 15.0-18.0 J.cm 2 The laser cladding has the characteristics of high hardness, high strength and high toughness.

[0014] The preparation method of the above laser cladding M2 high-toughness coating comprises the following steps:

[0015] (1) substrate surface pretreatment; the surface of the cladding area of the substrate is preheated, polished and cleaned, the treatment temperature is 250-450 °C, and the time is 2-6 h; then the surface of the substrate after heat treatment is oxidized and peeled off and polished, and finally the surface of the substrate is cleaned by ultrasonic cleaning with anhydrous ethanol.

[0016] (2) laser cladding process; the substrate pretreated in step (1) is sent into the laser cladding system. The dried M2 alloy powder is put into the powder feeding device. The coaxial powder feeding method and multi-pass overlapping cladding technology are used to perform cladding on the surface of the substrate. Argon is delivered as a protective gas while cladding. Three kinds of laser cladding process parameters are used to alternately perform cladding passes for coating preparation;

[0017] The three laser cladding process parameters are alternately carried out, including the first pass: laser power is 4.5-5.0 KW, laser scanning speed is 1.5-2 m / min, powder feeding rate is 10-15 g / min, laser spot diameter is 1.8-2.2 mm, and argon flow rate is 5-5.5 L / min; the second pass: laser power is 2.5-3.96 KW, laser scanning speed is 5-12 m / min, powder feeding rate is 15-25 g / min, laser spot diameter is 1.2-2.5 mm, laser pass overlap rate is 50-70%, and argon flow rate is 6-7 L / min; the third pass: laser power is 2.5-3.96 KW, laser scanning speed is 10-20 m / min, powder feeding rate is 8-18 g / min, laser spot diameter is 1.2-2.5 mm, laser multi-pass overlap rate is 70%-90%, and argon flow rate is 6-7 L / min;

[0018] After the above three passes are continuously completed, the first pass is repeatedly carried out alternately, and the laser overlap rate of the first pass is 50-70%;

[0019] (3) Post-treatment of the cladding layer; the cladding layer obtained in step (2) is subjected to air cooling and normalizing treatment. After the cladding process is completed, the M2 coating is obtained after cooling to room temperature;

[0020] In the above laser cladding process, the faster laser scanning speed and high overlap rate of the second and third cladding passes can reduce the non-overlapping area in the coating and increase the semi-solidified overlapping structure; the secondary melting of the first cladding pass is caused by the second and third cladding passes, so as to form semi-solidified structure and reduce the network carbide structure. The M2 coating prepared by the present application has the following advantages:

[0021] The mechanical properties of the M2 coating can be improved by changing the laser cladding mode and process parameters. The laser cladding passes of the three process parameters are alternately carried out, so that the first cladding metal is subjected to secondary melting and mixed with the second cladding metal, and the third cladding metal is melted with the second cladding metal, thereby effectively improving the overlapping degree and greatly improving the mechanical properties of the M2 coating; the hardness of the obtained coating is 65.3 HRC-68.0 HRC; the bending strength is 2658-3846 MPa; and the impact toughness is more than 15.0-18.0 J·cm 2 The laser cladding mode produced by the present application has the advantages of simple process flow, simple equipment, low cost, etc. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 SEM surface structure diagram of D1 in Example 1

[0023] Figure 2 SEM surface structure diagram of G1 in Example 1

[0024] Figure 3 Metallographic structure diagram of G1 in Example 1 DETAILED DESCRIPTION

[0025] Example 1

[0026] 1. Surface pretreatment of the substrate: the surface of the substrate is subjected to deoxidation and polishing treatment, and is ultrasonically cleaned with anhydrous alcohol. Then, preheating treatment is carried out, the treatment temperature is 250℃, and the time is 2h.

[0027] 2. Laser cladding process: the pretreated substrate is sent into a Tru Diode 4006 high-speed optical fiber laser cladding system. After drying, the M2 alloy powder with different chemical compositions is put into the powder feeding device. The coaxial powder feeding mode and the multi-pass cladding technology are used to carry out cladding processing on the surface of the substrate. Argon is delivered as a protective gas while cladding.

[0028] The sample is prepared by using the conventional laser cladding process parameters on the substrate, which is denoted as D1, and the process parameters are as follows: laser power 4.5KW, laser scanning speed 1.5m / min, powder feeding speed 10g / min, laser spot diameter 1.8mm, and argon flow rate 5L / min. Figure 1 From the SEM surface structure image of the D1 coating, it can be found that the carbide presents a skeleton or network distribution, and is very stable and not easy to break and granulate. This organization has an adverse effect on the mechanical properties of the coating.

[0029] The sample is prepared by alternately carrying out the cladding passes of the three laser cladding process parameters of the application on the substrate, which is denoted as G1, including the first pass: laser power 4.5KW, laser scanning speed 1.5m / min, powder feeding rate 10g / min, laser spot diameter 1.8mm, and argon flow rate 5L / min; the second pass: laser power 2.5KW, laser scanning speed 5m / min, powder feeding rate 15g / min, laser spot diameter 1.2mm, laser pass overlap rate 50%, and argon flow rate 6L / min; the third pass: laser power 2.5KW, laser scanning speed 10m / min, powder feeding rate 8g / min, laser spot diameter 1.2mm, laser multi-pass overlap rate 70%, and argon flow rate 6L / min; after the above three passes are continuously completed, the alternation is repeated, and at this time, the laser overlap rate of the first pass is 50%.

[0030] 3. Air cooling normalizing treatment is carried out on the cladding layer. After the cladding process is completed, the M2 coating is obtained after cooling to room temperature. Figure 2The SEM surface structure image of G1 coating is dendritic solidification crystalline structure coated on alpha-primary crystal; the alpha-primary phase and the matrix phase of the dendritic solidification crystalline structure are both alpha-Fe, but the two phases are different in sequence and alloy composition, and there is a discontinuous composition interface between the two phases; the carbide formed during solidification is dispersed and broken network. Figure 3 The metallographic photo of G1 coating, Figure 3 The discontinuously distributed white substance is carbide. The structure makes the hardness of the M2 coating reach 65.3 HRC, the bending strength reach 2658 MPa, and the impact toughness reach 15 J·cm 2 , which has the characteristics of high hardness, high strength and high toughness.

[0031] Example 2

[0032] 1. Substrate surface pretreatment: the substrate surface is subjected to deoxidation and polishing treatment, and is subjected to ultrasonic cleaning with anhydrous alcohol. Then, preheating treatment is carried out, the treatment temperature is 280 DEG C, and the treatment time is 3h.

[0033] 2. Laser cladding process: the pretreated substrate is sent into a Tru Diode 4006 high-speed optical fiber laser cladding system. After drying, M2 alloy powder with different chemical compositions is put into a powder feeding device, and is subjected to cladding processing on the substrate surface by adopting coaxial powder feeding mode and multi-pass cladding technology. Argon gas is supplied as a protective gas during cladding. First, the conventional laser cladding process parameters are used to carry out cladding to prepare a sample, and the sample is denoted as D2, and the process parameters are as follows: laser power 4.6 KW, laser scanning speed 1.6 m / min, powder feeding speed 11 g / min, laser spot diameter 1.9 mm, and argon gas flow rate 5.2 L / min.

[0034] The sample prepared by alternately carrying out cladding passes with three kinds of laser cladding process parameters on the substrate is denoted as G2, and includes the following three passes: the first pass: laser power 4.6 KW, laser scanning speed 1.6 m / min, powder feeding speed 11 g / min, laser spot diameter 1.9 mm, and argon gas flow rate 5.2 L / min; the second pass: laser power 3 KW, laser scanning speed 6 m / min, powder feeding speed 18 g / min, laser spot diameter 1.6 mm, laser multi-pass overlapping rate 55%, and argon gas flow rate 6.2 L / min; and the third pass: laser power 2.8 KW, laser scanning speed 12 m / min, powder feeding speed 10 g / min, laser spot diameter 1.6 mm, laser multi-pass overlapping rate 75%, and argon gas flow rate 6.2 L / min. After the above three passes are continuously completed, the above three passes are repeatedly and alternately carried out, and the laser overlapping rate of the first pass is 55% at this time.

[0035] 3. Air cooling and normalizing treatment is carried out on the cladding layer. After the cladding process is completed, the M2 coating is obtained after cooling to room temperature. The carbides in the D2 coating structure are in a skeletal or reticular distribution, and are very stable and not easy to break and granulate. This organization will have an adverse effect on the mechanical properties of the coating. In the G2 coating structure, a dendritic solidification crystalline organization is formed which is coated on the α-primary crystal; the α-primary phase and the dendritic solidification crystalline organization in this organization are both α-Fe, but the order of formation of the two phases is different, the alloy composition is not the same, and there is a discontinuous composition interface between the two. The carbides formed during solidification are precipitated in the two phases, in a dispersed and broken network precipitation state. This organization makes the hardness of the M2 coating reach 67.0 HRC, the bending strength can reach 2985 MPa, and the impact toughness can reach 15.6 J.cm 2 , which has the characteristics of high hardness, high strength and high toughness.

[0036] Example 3

[0037] 1. Substrate surface pretreatment: The substrate surface is subjected to deoxidation and polishing treatment, and is ultrasonically cleaned with anhydrous alcohol. Then, preheating treatment is carried out, the treatment temperature is 320°C, and the time is 4h.

[0038] 2. Laser cladding process: The pretreated substrate is sent into the Tru Diode 4006 high-speed optical fiber laser cladding system. After drying, M2 alloy powder with different chemical compositions is placed in the powder feeding device, and the coaxial powder feeding method and multi-pass overlapping cladding technology are used to carry out cladding processing on the substrate surface. Argon is supplied as a protective gas while cladding. First, the sample is cladded on the substrate using conventional laser cladding process parameters, and the sample is marked as D3, and the process parameters are: laser power 4.7 KW, laser scanning speed 1.7 m / min, powder feeding speed 12 g / min, laser spot diameter 2 mm, and argon flow rate 5.2 L / min.

[0039] The present application alternately carries out three laser cladding process parameters on the substrate to prepare a sample, which is recorded as G3, including the first pass: laser power 4.7 KW, laser scanning speed 1.7 m / min, powder feeding speed 12 g / min, laser spot diameter 2 mm, argon flow rate 5.2 L / min; the second pass: laser power 3.2 KW, laser scanning speed 8 m / min, powder feeding rate 20 g / min, laser spot diameter 1.8 mm, laser multi-pass overlap rate 60%, argon flow rate 6.5 L / min. The third pass: laser power 3 KW, laser scanning speed 15 m / min, powder feeding rate 12 g / min, laser spot diameter 1.8 mm, laser multi-pass overlap rate 80%, argon flow rate 6.5 L / min. After the above three passes are continuously completed, the above is repeatedly alternately carried out, and the laser overlap rate of the first pass is 60% at this time.

[0040] 3. Air cooling normalizing treatment is carried out on the cladding layer. After the cladding process is completed, the M2 coating is obtained after cooling to room temperature; the carbide in the D3 coating structure presents a skeleton or reticular distribution, and is extremely stable and not easy to break and granulate. This organization has an adverse effect on the mechanical properties of the coating. In the G3 coating structure, a dendritic solidification crystalline organization coated on the α-primary crystal is formed; the α-primary phase and the matrix phase of the dendritic solidification crystalline organization in the organization are both α-Fe, but the order of formation of the two phases is different, the alloy composition is not the same, and there is a discontinuous composition interface between the two phases; the carbide formed in the solidification process is precipitated in the two phases, in a dispersed and broken network precipitation state. This organization makes the hardness of the M2 coating reach 66.4 HRC, the bending strength can reach 2856 MPa, and the impact toughness can reach 16.2 J·cm 2 , which has the characteristics of high hardness, high strength and high toughness.

[0041] Example 4

[0042] 1. Substrate surface pretreatment: the substrate surface is subjected to deoxidation and polishing treatment, and is subjected to ultrasonic cleaning with anhydrous alcohol. Then, preheating treatment is carried out, the treatment temperature is 350℃, and the time is 5h.

[0043] 2. Laser cladding process: The pretreated substrate is sent into the Tru Diode 4006 high-speed fiber laser cladding system. After drying, the M2 alloy powder with different chemical compositions is put into the powder feeding device, and the coaxial powder feeding mode and multi-pass cladding technology are used to perform cladding processing on the surface of the substrate. Argon is delivered as a protective gas at the same time of cladding. First, the sample is prepared by cladding on the substrate using conventional laser cladding process parameters, and the sample is marked as D4, and the process parameters are: laser power 4.8 KW, laser scanning speed 1.8 m / min, powder feeding speed 13 g / min, laser spot diameter 2 mm, and argon flow rate 5.3 L / min.

[0044] The present application alternately performs cladding passes with three laser cladding process parameters on the substrate to prepare a sample, which is marked as G2, including a first pass: laser power 4.8 KW, laser scanning speed 1.8 m / min, powder feeding speed 13 g / min, laser spot diameter 2 mm, and argon flow rate 5.3 L / min; a second pass: laser power 3.5 KW, laser scanning speed 10 m / min, powder feeding rate 22 g / min, laser spot diameter 2.0 mm, laser multi-pass overlap rate 65%, and argon flow rate 6.7 L / min. A third pass: laser power 3.2 KW, laser scanning speed 18 m / min, powder feeding rate 15 g / min, laser spot diameter 2.0 mm, laser multi-pass overlap rate 85%, and argon flow rate 6.7 L / min. After the above three passes are continuously completed, the alternation is repeated, and at this time the laser overlap rate of the first pass is 65%.

[0045] 3. Air cooling normalizing treatment is performed on the cladding layer. After the cladding process is completed, the M2 coating is obtained after cooling to room temperature; the carbides in the D4 coating are in a skeletal or reticular distribution, and are very stable and not easy to break and granulate. This organization has an adverse effect on the mechanical properties of the coating. In the G4 coating, a dendritic solidification crystalline organization is formed which is coated on the α-primary crystal; the α-primary phase and the dendritic solidification crystalline organization in the matrix phase are both α-Fe, but the order of formation of the two phases is different, the alloy composition is not the same, and there is a discontinuous composition interface between the two phases; the carbides formed during solidification are dispersed and broken in the two phases. This organization makes the hardness of the M2 coating reach 65.3 HRC, the bending strength can reach 3236 MPa, and the impact toughness can reach 16.4 J.cm 2 , which has the characteristics of high hardness, high strength and high toughness.

[0046] Example 5

[0047] 1. Substrate surface pretreatment: The substrate surface is deoxidized and polished, and then ultrasonic cleaned with anhydrous alcohol. Then, preheating treatment is performed at a temperature of 380℃ for 5.5h.

[0048] 2. Laser cladding process: The pretreated substrate is sent into a Tru Diode 4006 high-speed fiber laser cladding system. After drying, M2 alloy powder with different chemical compositions is put into a powder feeding device, and cladding is performed on the substrate surface by using coaxial powder feeding and multi-pass cladding technology. Argon is delivered as a protective gas during cladding. First, cladding is performed on the substrate using conventional laser cladding process parameters to prepare a sample, which is denoted as D5, and the process parameters are as follows: laser power 4.9KW, laser scanning speed 1.9m / min, powder feeding speed 14g / min, laser spot diameter 2.1mm, and argon flow rate 5.4L / min.

[0049] The present application alternately performs cladding passes with three laser cladding process parameters on the substrate to prepare a sample, which is denoted as G5, and includes the following steps: first pass: laser power 4.9KW, laser scanning speed 1.9m / min, powder feeding speed 14g / min, laser spot diameter 2.1mm, and argon flow rate 5.4L / min; second pass: laser power 3.75KW, laser scanning speed 12m / min, powder feeding speed 25g / min, laser spot diameter 2.3mm, laser multi-pass overlap rate 70%, and argon flow rate 7.0L / min; and third pass: laser power 3.6KW, laser scanning speed 20m / min, powder feeding speed 18g / min, laser spot diameter 2.3mm, laser multi-pass overlap rate 90%, and argon flow rate 7.0L / min. After the above three passes are continuously completed, the first pass is repeated alternately, and the laser overlap rate of the first pass is 65%.

[0050] 3. Air cooling normalizing treatment is performed on the cladding layer. After the cladding process is completed, the sample is cooled to room temperature to obtain an M2 coating;

[0051] The carbides in the D5 coating are in a skeletal or reticular distribution and are very stable and not easy to break and granulate. This organization has an adverse effect on the mechanical properties of the coating. In the G5 coating, a dendritic solidification crystalline organization is formed which is coated on the α-primary crystal; the α-primary crystal phase and the dendritic solidification crystalline organization in the matrix phase are both α-Fe, but the two phases are formed in different sequences and have different alloy compositions, and there is a discontinuous composition interface between the two phases; the carbides formed during solidification are dispersed and broken in the two phases. This organization makes the hardness of the M2 coating reach 67.5HRC, the bending strength reach 3678MPa, and the impact toughness reach 17.2J.cm 2It has the characteristics of high hardness, high strength and high toughness.

[0052] Example 6

[0053] 1. Substrate surface pretreatment: the substrate surface is subjected to deoxidation and polishing treatment, and is ultrasonically cleaned with anhydrous alcohol. Then, preheating treatment is carried out, the treatment temperature is 420 DEG C, and the time is 6h.

[0054] 2. Laser cladding process: the pretreated substrate is sent into a Tru Diode 4006 high-speed optical fiber laser cladding system. After drying, the M2 alloy powder with different chemical compositions is put into the powder feeding device, and the coaxial powder feeding mode and the multi-pass overlapping cladding technology are used to carry out cladding processing on the substrate surface. Argon is delivered as a protective gas while cladding. First, the conventional laser cladding process parameters are used to carry out cladding on the substrate to prepare a sample, and the sample is marked as D6, and the process parameters are as follows: laser power 5.0KW, laser scanning speed 2.0m / min, powder feeding speed 15g / min, laser spot diameter 2.2mm, and argon flow rate 5.5L / min.

[0055] The present application alternately carries out cladding passes with three kinds of laser cladding process parameters on the substrate to prepare a sample, and the sample is marked as G6, including the first pass: laser power 5.0KW, laser scanning speed 2.0m / min, powder feeding speed 15g / min, laser spot diameter 2.2mm, and argon flow rate 5.5L / min. The second pass: laser power 3.96KW, laser scanning speed 12m / min, powder feeding rate 25g / min, laser spot diameter 2.5mm, laser pass overlapping rate 70%, and argon flow rate 7L / min. The third pass: laser power 3.96KW, laser scanning speed 20m / min, powder feeding rate 18g / min, laser spot diameter 2.5mm, laser multi-pass overlapping rate 90%, and argon flow rate 7L / min. After the above three passes are continuously completed, the alternation is repeated, and at this time, the laser overlapping rate of the first pass is 70%.

[0056] 3. Air-cooling normalizing treatment is carried out on the cladding layer. After the cladding process is completed, the M2 coating is obtained after cooling to room temperature.

[0057] The carbides in the D6 coating have a bone-like or net-like distribution and are very stable and not easy to break and granulate. This kind of structure has a bad influence on the mechanical properties of the coating. In the G6 coating, a dendritic solidification crystalline structure is formed which is coated on the α-primary crystal; the α-primary crystal phase and the matrix phase of the dendritic solidification crystalline structure are both α-Fe, but the two phases are formed in different sequences and have different alloy compositions, and there is a discontinuous composition interface between the two phases; the carbides formed during solidification are precipitated in the two phases and are in a dispersed and broken net precipitated state. This kind of structure makes the hardness of the M2 coating reach 68.0 HRC, the bending strength reach 3846 MPa, and the impact toughness reach 18 J.cm 2 which has the characteristics of high hardness, high strength and high toughness.

Claims

1. A laser-clad M2 high-toughness coating, characterized in that: M2 alloy powder, prepared by gas atomization, was used as raw material, with an average particle size ranging from 30 to 45 μm. A dendritic solidified crystalline structure, coated on α-primary crystals, was formed on the substrate through multi-pass cladding and semi-solid solidification. Both the α-primary crystal phase and the matrix phase of the dendritic solidified crystalline structure are α-Fe, but they form in different orders, have different alloy compositions, and exhibit discontinuous compositional interfaces. During solidification, carbides precipitate within both phases in a dispersed, discontinuous precipitation state. The multi-pass cladding and semi-solid solidification technology mainly involves alternating cladding passes using three different laser cladding process parameters: Pass 1: Laser power 4.5-5.0 KW, laser scanning speed 1.5-2 m / min, powder feed rate 10-15 g / min, laser spot diameter 1.8-2.2 mm, argon flow rate 5-5.5 L / min; Pass 2: Laser power 2.5-3.96 KW, laser scanning speed 5-12 m / min. For the first pass: the powder feeding rate is 15-25 g / min, the laser spot diameter is 1.2-2.5 mm, the laser pass overlap rate is 50-70%, and the argon flow rate is 6-7 L / min; for the third pass: the laser power is 2.5-3.96 KW, the laser scanning speed is 10-20 m / min, the powder feeding rate is 8-18 g / min, the laser spot diameter is 1.2-2.5 mm, the laser multi-pass overlap rate is 70%-90%, and the argon flow rate is 6-7 L / min. The first pass is characterized by high laser power and low laser scanning speed, used to preheat the substrate and bring the M2 powder to a fully molten state; the second pass is characterized by low laser power and high laser scanning speed, used to remelt the metal parts of the first pass coating that are in the solidification process, achieving semi-solidification and crystallization; the third pass is characterized by laser power comparable to the second pass, but with increased scanning speed and decreased powder feeding rate, to achieve the purpose of mixing the coating structure of the third pass with the coating structure of the second pass, thus achieving overall semi-solidification and crystallization; In the laser cladding process described above, the faster laser scanning speed and higher overlap rate of the second and third cladding passes can reduce the non-overlapping area in the coating and increase the semi-solidified overlap structure. The second and third cladding passes cause the first cladding pass to melt again, forming a semi-solidified structure and reducing the network carbide structure. After the above three passes are completed consecutively, they are repeated alternately. At this time, the laser overlap rate of the first pass is 50-60%. After coating, the coating is air-cooled to room temperature for normalizing treatment; the resulting coating has a hardness of 65.3 HRC to 68.0 HRC; a flexural strength of 2658 to 3846 MPa; and an impact toughness exceeding 15.0 to 18.0 J / cm². 2 This laser cladding exhibits high hardness, high strength, and high toughness.

2. The method for preparing a laser cladding M2 high-toughness coating as described in claim 1, characterized in that: Includes the following steps: (1) Pretreatment of substrate surface: The surface of the cladding area of ​​the substrate is preheated, polished and cleaned at a temperature of 250-450℃ for 2-6 hours; the surface of the substrate after heat treatment is then oxidized, peeled and polished, and the surface of the substrate is ultrasonically cleaned with anhydrous ethanol. (2) Laser cladding process: The pretreated substrate in step (1) is sent into the laser cladding system; the dried M2 alloy powder is placed into the powder feeding device; the coaxial powder feeding method and multi-pass overlapping cladding technology are used to perform cladding on the substrate surface; argon gas is supplied as a protective gas during cladding; the coating is prepared by alternating cladding passes with three laser cladding process parameters. (3) Post-treatment of cladding layer: The cladding layer obtained in step (2) is subjected to air cooling normalizing treatment; After the cladding process is completed, the coating is cooled to room temperature to obtain the M2 coating.

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