PDC drill bit surface hardening method

Abstract

The invention provides a PDC drill bit surface hardening method, and belongs to the technical field of well drilling drill bit treatment.The method comprises the following steps that the surface of a PDC drill bit is subjected to oil and rust removal, polishing treatment, cleaning and drying, and the pretreated PDC drill bit is obtained; cladding the bonding layer mixture on the surface of the pretreated PDC drill bit to form a bonding layer; cladding the hardened layer mixture on the surface of the bonding layer to form a hardened layer; and then the hardened layer is subjected to heating hardening treatment, and the hardened PDC drill bit is obtained. By means of the method, the hardening strength, abrasion resistance and erosion resistance of the hardening layer on the surface of the PDC drill bit are improved, the service life of the hardening layer is prolonged, and the drill bit is better protected.

Description

Technical Field

[0001] The present invention relates to the technical field of drilling bit treatment, and in particular to a method for surface hardening of a PDC bit for oil and gas exploitation. Background Art

[0002] The PDC bit is short for Polycrystalline Diamond Compact bit, which is a commonly used drilling tool in the geological drilling industry and evolved from the diamond drill. The PDC bit is divided into two types according to the matrix material: matrix body and steel body, but the manufacturing processes are completely different. The shape of the steel body bit is not restricted by the strength of the cutter wings, with high production efficiency and low production cost, and has more advantages than the matrix body bit. With the continuous improvement of the high-pressure jet bit technology and the continuous increase of the bit pump pressure, the erosion failure problem of the steel body bit has become increasingly serious, seriously affecting the drilling speed. Therefore, the existing technology studies how to improve the erosion resistance of the bit to expand the application range of the steel bit.

[0003] At present, the PDC bit has the advantages of flexible design, high machining accuracy, simple process, short development cycle, etc., so it has been more and more widely used in oil drilling. However, the existing PDC bit has the problem that the surface strength of the bit is insufficient, resulting in easy wear of the PDC bit and peeling of the surface layer. Therefore, how to improve the surface hardening strength, wear resistance and erosion resistance of the PDC bit is an urgent problem to be solved. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a method for surface hardening of a PDC bit, which solves the problem that the existing PDC bit has insufficient surface strength, resulting in easy wear of the PDC bit and peeling of the surface layer.

[0005] Another purpose of the present invention is to provide a PDC bit obtained by treating with the method for surface hardening of the PDC bit.

[0006] In order to achieve the above purposes of the present invention, the following technical solutions are specifically adopted:

[0007] In the first aspect, the present invention provides a method for surface hardening of a PDC bit, including the following steps:

[0008] S1. Degrease, derust and polish the surface of the PDC bit, clean and dry it to obtain a pretreated PDC bit;

[0009] S2. Clad the bonding layer mixture on the surface of the pre-treated PDC bit to form a bonding layer. The bonding layer mixture includes the following raw materials in parts by weight: 30 - 50 parts of iron powder, 16 - 28 parts of nickel powder, 11 - 25 parts of copper powder, 12 - 24 parts of aluminum carbide, 2 - 10 parts of itaconic acid epoxy, 5 - 11 parts of aluminum phosphate gel, and 1 - 5 parts of silicon dioxide gel.

[0010] S3. Clad the hardening layer mixture on the surface of the bonding layer to form a hardening layer. The hardening layer mixture includes the following raw materials in parts by weight: 30 - 60 parts of silicon carbide, 20 - 40 parts of vanadium nitride, 35 - 38 parts of zirconium oxide, 10 - 12 parts of boron oxide, 5 - 6 parts of silicon dioxide gel, 23 - 25 parts of magnesium oxide, 2 - 3 parts of talcum powder, 2 - 8 parts of tin powder, 1 - 9 parts of boron powder, 3 - 7 parts of zinc powder, 4 - 6 parts of lead powder, 5 - 11 parts of titanium powder, and 1 - 5 parts of binder. Then, perform heat hardening treatment on the hardening layer to obtain the hardened PDC bit.

[0011] The following is a detailed description of each step:

[0012] S1. Surface pre-treatment:

[0013] In this step, use a degreasing and rust-removing agent to degrease and remove rust from the surface of the PDC bit, then use a grinding mechanism to grind stubborn stains, and after the treatment, use a cleaning agent to clean the surface of the PDC bit and put it into a drying device for drying.

[0014] In some embodiments, the degreasing and rust-removing agent includes the following raw materials in parts by weight: 15 - 35 parts of hydrochloric acid, 10 - 30 parts of emulsifier (such as Peregal O, EL, OP (such as OP-10)), 1 - 6 parts of penetrant (such as JFC, sodium dodecylbenzenesulfonate), 3 - 6 parts of thiourea, 2 - 4 parts of sodium chloride, 0.1 - 0.3 parts of defoamer (such as dimethyl silicone oil, polyester modified silicone oil, tributyl phosphate, higher alcohols), 0.1 - 0.3 parts of flavoring agent, 12 - 17 parts of phosphoric acid, 0.2 - 0.6 parts of tartaric acid, 0.2 - 0.6 parts of accelerator (such as nickel), and 100 parts of water. Weigh the corresponding amounts of raw materials as needed and put them into a blender and mix evenly to obtain the degreasing and rust-removing agent.

[0015] In some embodiments, the cleaning agent is one or two selected from acetone and alcohol.

[0016] In some embodiments, the drying temperature is 90 - 120 °C and the drying time is 10 - 20 min.

[0017] S2. Clad the bonding layer:

[0018] The bonding layer raw material is put into a grinding, mixing and stirring device for uniform stirring to obtain a bonding layer mixture. The preferred stirring speed is 120-240 r / min and the stirring time is 15-45 min.

[0019] The bonding layer mixture includes the following raw materials in parts by weight: 30-50 parts of iron powder, for example 30, 32, 35, 36, 38, 40, 42, 45, 46, 48, 50 parts; 16-28 parts of nickel powder, for example 16, 18, 20, 22, 24, 26, 28 parts; 11-25 parts of copper powder, for example 12, 13, 15, 17, 18, 19, 20, 21, 22, 23, 24, 25 parts; 12-24 parts of aluminum carbide, for example 12, 14, 16, 18, 20, 22, 24 parts; 2-10 parts of itaconic acid epoxy, for example 2, 4, 6, 8, 10 parts; 5-11 parts of aluminum phosphate gel, for example 5, 6, 7, 8, 9, 10, 11 parts; 1-5 parts of silica gel, for example 1, 2, 3, 4, 5 parts.

[0020] Silica gel mainly plays a role in corrosion prevention.

[0021] Cladding refers to the process of melting the deposits on the surface of the drill bit and covering them onto the surface of the drill bit by means of laser.

[0022] In some embodiments, the cladding temperature is 500-600° C., and the cladding time is 30-90 min.

[0023] In some embodiments, after the adhesive layer is formed, the step of using a cleaning agent to clean the surface of the adhesive layer is further included, and then placing the adhesive layer in a drying device for drying.

[0024] Preferably, the cleaning agent is one or two selected from acetone and alcohol.

[0025] Preferably, the drying temperature is 120-160° C. and the drying time is 15-30 min.

[0026] S3, cladding hardened layer:

[0027] The hardened layer raw material is put into a grinding, mixing and stirring device for uniform stirring, thereby obtaining a hardened layer mixture. The preferred stirring speed is 300-400 r / min and the stirring time is 20-60 min.

[0028] The hardened layer mixture includes raw materials in the following parts by weight: 30 - 60 parts of silicon carbide, such as 30, 32, 34, 35, 36, 38, 40, 42, 44, 45, 46, 48, 50, 52, 54, 55, 56, 58, 60 parts; 20 - 40 parts of vanadium nitride, such as 20, 22, 24, 25, 26, 27, 28, 30, 32, 34, 36, 38, 40 parts; 35 - 38 parts of zirconia, such as 35, 36, 37, 38 parts; 10 - 12 parts of boron oxide, such as 10, 11, 12 parts; 5 - 6 parts of silica gel, such as 5, 5.5, 6 parts; 23 - 25 parts of magnesium oxide, such as 23, 24, 25 parts; 2 - 3 parts of talcum powder, such as 2, 2.5, 3 parts; 2 - 8 parts of tin powder, such as 2, 3, 4, 5, 6, 7, 8 parts; 1 - 9 parts of boron powder, such as 1, 2, 3, 4, 5, 6, 7, 8, 9 parts; 3 - 7 parts of zinc powder, such as 3, 4, 5, 6, 7 parts; 4 - 6 parts of lead powder, such as 4, 5, 6 parts; 5 - 11 parts of titanium powder, such as 5, 6, 7, 8, 9, 10, 11 parts; 1 - 5 parts of binder (such as methyl cellulose, polyvinyl alcohol, dextrin), such as 1, 2, 3, 4, 5 parts.

[0029] In some embodiments, the cladding temperature is 500 - 600 °C and the cladding time is 30 - 90 min.

[0030] In some embodiments, the heat hardening treatment includes three - stage heating. The heating rate in the first stage is 6 - 8 °C / min, and it is heated to 650 - 800 °C with a holding time of 20 - 30 min. The heating rate in the second stage is 5 - 6 °C / min, and it is heated to 800 - 1400 °C with a holding time of 30 - 40 min. The heating rate in the third stage is 4 - 5 °C / min, and it is heated to 1400 - 2200 °C with a holding time of 45 - 55 min.

[0031] In a second aspect, the present invention provides a PDC bit, which is obtained by the surface hardening method of the above - mentioned PDC bit.

[0032] The PDC bit obtained by the treatment of the present invention has excellent hardness, strength, wear resistance and erosion resistance, and a long service life.

[0033] Beneficial effects

[0034] 1. In the present invention, by cladding an adhesive layer on the surface of the PDC bit and then cladding a hardening layer, since the aluminum phosphate gel and silica gel contained in the adhesive layer can enhance the diffusion and fusion between material molecules, the bonding strength between the hardening layer and the PDC bit is further improved, which is beneficial to solving the problem of surface layer peeling of the PDC bit, and also solves the problems of non-wetting and non-adhesion between the hardening layer and the metal layer on the surface of the PDC bit. Due to the strong physical bonding force between particles, the generation of cracks, voids and other problems during the use of the PDC bit is greatly reduced, thereby reducing the friction coefficient and wear amount, improving the hardening strength, wear resistance and erosion resistance of the hardening layer on the surface of the PDC bit, prolonging the service life of the hardening layer, and better protecting the bit.

[0035] 2. By adding substances such as tin, boron, zinc, lead, titanium, etc. to the hardening layer mixture in the present invention, not only can the oxidation resistance and wear resistance of the hardening layer on the surface of the PDC bit be improved, but also the internal structure and performance of the hardening layer on the surface of the PDC bit can be improved, and the thermal weight loss rate can be reduced, thereby improving the thermal stability of the hardening layer on the surface of the PDC bit, solving the problems of reduced thermal stability and weak strength existing in the hardening layer on the surface of the PDC bit, which is beneficial to protecting the PDC bit and prolonging the service life of the PCD bit.

[0036] The present invention has been described in detail above, but the above embodiments are essentially illustrative only and are not intended to limit the present invention. In addition, the present invention is not limited by any theory described in the foregoing prior art or the invention content or the following embodiments. Specific Embodiments

[0037] The following further illustrates the present invention in conjunction with embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation to the scope of protection required by the present invention.

[0038] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the embodiments are all conventional raw materials, reagents, methods in the art.

[0039] The particle size of silica in the silica gel is 5 - 10 μm, the bulk density is 350 - 360 mg / cm 3 , and the pH value is between 7.7 - 7.8;

[0040] The water content of the aluminum phosphate gel is 14 - 16%, and the pH value is 1.8 - 2.0.

[0041] Example 1

[0042] A method for hardening the surface of a PDC bit for oil and gas exploitation, comprising the following steps:

[0043] Step 1: Use a degreasing and derusting agent to treat the surface of the PDC bit to remove oil and rust, and then use a grinding mechanism to grind stubborn stains. After the treatment, clean the surface of the PDC bit with acetone and alcohol, and put it into a drying device to dry at 90 °C for 10 minutes;

[0044] The degreasing and derusting agent includes the following raw materials in parts by weight: 15 parts of hydrochloric acid, 10 parts of emulsifier (OP-10), 1 part of penetrant (JFC), 3 parts of thiourea, 2 parts of sodium chloride, 0.1 part of defoamer (tributyl phosphate), 0.1 part of flavoring agent, 12 parts of phosphoric acid, 0.2 part of tartaric acid, 0.2 part of accelerator (nickel), and 100 parts of water. Weigh the corresponding amounts of raw materials and put them into a blender to mix evenly to obtain the degreasing and derusting agent;

[0045] Step 2: Weigh the hardening layer raw materials by weight: 30 parts of silicon carbide, 20 parts of vanadium nitride, 35 parts of zirconium oxide, 10 parts of boron oxide, 5 parts of silica gel, 23 parts of magnesium oxide, 2 parts of talcum powder, 2 parts of tin powder, 1 part of boron powder, 3 parts of zinc powder, 4 parts of lead powder, 5 parts of titanium powder, and 1 part of binder (methyl cellulose);

[0046] Weigh the bonding layer raw materials by weight: 30 parts of iron powder, 16 parts of nickel powder, 11 parts of copper powder, 12 parts of aluminum carbide, 2 parts of itaconic acid epoxy, 5 parts of aluminum phosphate gel, and 1 part of silica gel;

[0047] Step 3: Put the bonding layer raw materials in Step 2 into a grinding, mixing and stirring device 1 and stir evenly at a stirring speed of 120 r / min for 15 minutes to prepare the bonding layer mixture for later use;

[0048] Step 4: Put the hardening layer raw materials in Step 2 into a grinding, mixing and stirring device 2 and stir evenly at a stirring speed of 300 r / min for 15 minutes to prepare the hardening layer mixture for later use;

[0049] Step 5: Heat the PDC bit treated in Step 1 at 500 °C for 30 minutes. After heating, take the bonding layer mixture in Step 3 and cladding it on the surface of the PDC bit to form a bonding layer. Then clean the surface of the bonding layer with acetone and alcohol, and put it into a drying device to dry at 120 °C for 15 minutes;

[0050] Step 6: After the adhesive layer is dried, weigh the hardening layer mixture in Step 4 and form a hardening layer on the surface of the adhesive layer by cladding. Then, perform a three-stage heating and hardening treatment on the hardening layer. The heating rate in the first stage is 6 °C / min, and it is heated to 650 °C with a holding time of 20 min. The heating rate in the second stage is 5 °C / min, and it is heated to 800 °C with a holding time of 30 min. The heating rate in the third stage is 4 °C / min, and it is heated to 1400 °C with a holding time of 45 min, thereby obtaining a PDC bit with completed hardening.

[0051] Example 2

[0052] A method for surface hardening of a PDC bit for oil and gas exploitation, comprising the following steps:

[0053] Step 1: Use a degreasing and rust-removing agent to treat the surface of the PDC bit to remove oil and rust, and then use a grinding mechanism to grind stubborn stains. After the treatment, clean the surface of the PDC bit with acetone and alcohol, and put it into a drying device to dry at 105 °C for 15 min;

[0054] The degreasing and rust-removing agent comprises the following raw materials in parts by weight: 25 parts of hydrochloric acid, 20 parts of emulsifier (OP-10), 3 parts of penetrant (JFC), 4 parts of thiourea, 3 parts of sodium chloride, 0.2 part of defoamer (tributyl phosphate), 0.2 part of flavoring agent, 15 parts of phosphoric acid, 0.4 part of tartaric acid, 0.4 part of accelerator (nickel), and 100 parts of water. Weigh the corresponding amounts of raw materials and put them into a blender and mix evenly to obtain the degreasing and rust-removing agent;

[0055] Step 2: Weigh the hardening layer raw materials by weight: 45 parts of silicon carbide, 30 parts of vanadium nitride, 36 parts of zirconium oxide, 11 parts of boron oxide, 5.5 parts of silica gel, 24 parts of magnesium oxide, 2.5 parts of talcum powder, 5 parts of tin powder, 5 parts of boron powder, 5 parts of zinc powder, 5 parts of lead powder, 8 parts of titanium powder, and 3 parts of binder (methyl cellulose);

[0056] Weigh the adhesive layer raw materials by weight: 40 parts of iron powder, 22 parts of nickel powder, 18 parts of copper powder, 18 parts of aluminum carbide, 6 parts of itaconic acid epoxy, 6 parts of aluminum phosphate gel, and 3 parts of silica gel;

[0057] Step 3: Put the adhesive layer raw materials in Step 2 into a grinding, mixing and stirring device 1 and stir evenly at a stirring speed of 180 r / min for 30 min to prepare the adhesive layer mixture for standby;

[0058] Step 4: Put the hardening layer raw materials in Step 2 into a grinding, mixing and stirring device 2 and stir evenly at a stirring speed of 350 r / min for 40 min to prepare the hardening layer mixture for standby;

[0059] Step Five: Heat the PDC bit processed in Step One at 550 °C for 60 min. After heating, take the bonding layer mixture in Step Three and clad it on the surface of the PDC bit to form a bonding layer. Then, clean the surface of the bonding layer with acetone and alcohol. After cleaning, put it into a drying device and dry it at 140 °C for 22 min;

[0060] Step Six: After the bonding layer is dried, weigh the hardening layer mixture in Step Four and clad it on the surface of the bonding layer to form a hardening layer by cladding. Then, perform a three-stage heating and hardening treatment on the hardening layer. The heating rate in the first stage is 7 °C / min, and it is heated to 740 °C with a holding time of 25 min. The heating rate in the second stage is 5.5 °C / min, and it is heated to 1100 °C with a holding time of 35 min. The heating rate in the third stage is 4.5 °C / min, and it is heated to 1700 °C with a holding time of 50 min, thereby obtaining the PDC bit with hardening completed.

[0061] Example 3

[0062] A method for hardening the surface of a PDC bit for oil and gas exploitation, comprising the following steps:

[0063] Step One: Use a degreasing and rust-removing agent to treat the surface of the PDC bit to remove oil and rust, and then use a grinding mechanism to grind stubborn stains. After treatment, clean the surface of the PDC bit with acetone and alcohol, and put it into a drying device and dry it at 120 °C for 20 min;

[0064] The degreasing and rust-removing agent comprises the following raw materials in parts by weight: 35 parts of hydrochloric acid, 30 parts of emulsifier (OP-10), 6 parts of penetrant (JFC), 6 parts of thiourea, 4 parts of sodium chloride, 0.3 parts of defoamer (tributyl phosphate), 0.3 parts of flavoring agent, 17 parts of phosphoric acid, 0.6 parts of tartaric acid, 0.6 parts of accelerator (nickel), and 100 parts of water. Weigh the corresponding amounts of raw materials and put them into a mixer and mix evenly to obtain the degreasing and rust-removing agent;

[0065] Step Two: Weigh the hardening layer raw materials by weight: 60 parts of silicon carbide, 40 parts of vanadium nitride, 38 parts of zirconium oxide, 12 parts of boron oxide, 6 parts of silica gel, 25 parts of magnesium oxide, 3 parts of talcum powder, 8 parts of tin powder, 9 parts of boron powder, 7 parts of zinc powder, 6 parts of lead powder, 11 parts of titanium powder, and 5 parts of binder (methyl cellulose);

[0066] Weigh the bonding layer raw materials by weight: 50 parts of iron powder, 28 parts of nickel powder, 25 parts of copper powder, 24 parts of aluminum carbide, 10 parts of itaconic acid epoxy, 11 parts of aluminum phosphate gel, and 5 parts of silica gel;

[0067] Step 3: Put the raw materials of the adhesive layer in Step 2 into the first grinding, mixing and stirring equipment and stir evenly at a stirring speed of 240 r / min for 45 min to obtain the adhesive layer mixture for standby;

[0068] Step 4: Put the raw materials of the hardening layer in Step 2 into the second grinding, mixing and stirring equipment and stir evenly at a stirring speed of 400 r / min for 60 min to obtain the hardening layer mixture for standby;

[0069] Step 5: Heat the processed PDC bit in Step 1 at 600 °C for 90 min. After heating, take the adhesive layer mixture in Step 3 and clad it on the surface of the PDC bit to form an adhesive layer. Then, clean the surface of the adhesive layer with acetone and alcohol. After cleaning, put it into the drying equipment and dry it at 160 °C for 30 min;

[0070] Step 6: After the adhesive layer is dried, weigh the hardening layer mixture in Step 4 and clad it on the surface of the adhesive layer to form a hardening layer by cladding. Then, perform a three-stage heating and hardening treatment on the hardening layer. The heating rate in the first stage is 8 °C / min, and it is heated to 800 °C with a holding time of 30 min. The heating rate in the second stage is 6 °C / min, and it is heated to 1400 °C with a holding time of 40 min. The heating rate in the third stage is 5 °C / min, and it is heated to 2200 °C with a holding time of 55 min to obtain the hardened PDC bit.

[0071] Comparative Example 1

[0072] The difference from Example 1 is that the adhesive layer raw materials do not contain aluminum phosphate gel.

[0073] Comparative Example 2

[0074] The difference from Example 1 is that the adhesive layer raw materials do not contain silicon dioxide gel.

[0075] Comparative Example 3

[0076] The difference from Example 1 is that the adhesive layer raw materials do not contain aluminum phosphate gel and silicon dioxide gel.

[0077] Comparative Example 4

[0078] The difference from Example 1 is that the hardening layer raw materials do not contain tin powder.

[0079] Comparative Example 5

[0080] The difference from Example 1 is that the hardening layer raw materials do not contain boron powder.

[0081] Comparative Example 6

[0082] The difference from Example 1 is that the hardening layer raw materials do not contain zinc powder.

[0083] Comparative Example 7

[0084] It is different from Example 1 in that the hardening layer raw material does not contain lead powder.

[0085] Performance Test

[0086] The following performance tests were carried out on the PDC bits after treatment in the examples and comparative examples:

[0087] 1. Coefficient of friction: Detect the coefficient of friction of the PDC bit after hardening is completed

[0088] 2. Life-related indicators: Refer to the percentage reduction in wear volume. The larger the percentage reduction in wear volume, the longer the life of the bit.

[0089] Percentage reduction in wear volume: The original PDC bit and the PDC bit after hardening are respectively rubbed with a grinding wheel, and the stopwatch is timed for 180 seconds. Detect the mass reduction of the original PDC bit after grinding and the mass reduction of the PDC bit after hardening is completed, and calculate the percentage reduction in wear volume = (mass reduction of the original PDC bit - mass reduction of the PDC bit after hardening is completed) / mass reduction of the original PDC bit. The matrix is all in the size of 5mm×5mm×5mm; the grinding wheel is a silicon carbide grinding wheel.

[0090] 3. Hardness: Detect the Rockwell hardness / HRC of the PDC bit after hardening is completed.

[0091] 4. Erosion resistance: Detect the impact work of the PDC bit after hardening is completed. The larger the impact work, the better the erosion resistance.

[0092] The results are shown in Table 1.

[0093] Table 1

[0094] Sample Coefficient of friction Reduction in wear amount (%) Rockwell hardness / HRC <![CDATA[Impact energy / (J / m 2 )]]> Example 1 0.31 ＞99 86 19.6 Example 2 0.35 ＞99 92 20.2 Example 3 0.39 ＞99 94 20.5 Comparative example 1 0.20 38 73 16.8 Comparative example 2 0.17 26 71 16.4 Comparative example 3 0.13 21 70 16.1 Comparative example 4 0.24 47 75 17.7 Comparative example 5 0.23 44 74 17.3 Comparative example 6 0.24 46 75 17.5 Comparative example 7 0.22 41 73 17.1

[0095] The above examples are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that: without departing from the spirit and essence defined by the claims of the present invention, the technical solutions described in the foregoing examples can be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A method for surface hardening of a PDC bit, characterized in that, It includes the following steps: S1. Degrease, derust and polish the surface of the PDC bit, clean and dry it to obtain the pretreated PDC bit; S2. Clad the bonding layer mixture on the surface of the pretreated PDC bit to form a bonding layer; the bonding layer mixture includes the following raw materials in parts by weight: 30-50 parts of iron powder, 16-28 parts of nickel powder, 11-25 parts of copper powder, 12-24 parts of aluminum carbide, 2-10 parts of itaconic acid epoxy, 5-11 parts of aluminum phosphate gel and 1-5 parts of silicon dioxide gel; S3. Clad the hardening layer mixture on the surface of the bonding layer to form a hardening layer; the hardening layer mixture includes the following raw materials in parts by weight: 30-60 parts of silicon carbide, 20-40 parts of vanadium nitride, 35-38 parts of zirconium oxide, 10-12 parts of boron oxide, 5-6 parts of silicon dioxide gel, 23-25 parts of magnesium oxide, 2-3 parts of talcum powder, 2-8 parts of tin powder, 1-9 parts of boron powder, 3-7 parts of zinc powder, 4-6 parts of lead powder, 5-11 parts of titanium powder and 1-5 parts of binder; then heat and harden the hardening layer to obtain the hardened PDC bit.

2. The method for surface hardening of a PDC bit according to claim 1, characterized in that, In step S1, the degreasing and derusting agent includes the following raw materials in parts by weight: 15-35 parts of hydrochloric acid, 10-30 parts of emulsifier, 1-6 parts of penetrant, 3-6 parts of thiourea, 2-4 parts of sodium chloride, 0.1-0.3 parts of defoamer, 0.1-0.3 parts of flavoring agent, 12-17 parts of phosphoric acid, 0.2-0.6 parts of tartaric acid, 0.2-0.6 parts of accelerator and 100 parts of water; Preferably, the cleaning agent is one or both selected from acetone and alcohol; Preferably, the drying temperature is 90-120 °C and the drying time is 10-20 min.

3. The method for surface hardening of a PDC bit according to claim 1, characterized in that, The preparation method of the bonding layer mixture in step S2 includes: Put the bonding layer raw materials into a grinding, mixing and stirring device for uniform stirring to obtain the bonding layer mixture; preferably, the stirring speed is 120-240 r / min and the stirring time is 15-45 min.

4. The method for surface hardening of a PDC bit according to claim 1, characterized in that, The cladding temperature in step S2 is 500-600 °C and the cladding time is 30-90 min.

5. The method for surface hardening of a PDC bit according to claim 1, characterized in that, After forming the bonding layer in step S2, it further includes the steps of cleaning the surface of the bonding layer with a cleaning agent and then putting it into a drying device for drying; Preferably, the cleaning agent is one or both selected from acetone and alcohol; Preferably, the drying temperature is 120-160 °C and the drying time is 15-30 min.

6. The method for surface hardening of a PDC bit according to claim 1, characterized in that, The preparation method of the hardening layer mixture in step S3 includes: Put the hardening layer raw materials into a grinding, mixing and stirring device for uniform stirring to obtain the hardening layer mixture; preferably, the stirring speed is 300-400 r / min and the stirring time is 20-60 min.

7. The method for surface hardening of a PDC bit according to claim 1, characterized in that, The cladding temperature in step S3 is 500-600 °C and the cladding time is 30-90 min.

8. The method for surface hardening of a PDC bit according to claim 1, characterized in that, The heat hardening treatment includes three-stage heating with temperature increase. In the first stage, the heating rate is 6 - 8 °C / min, and the temperature is increased to 650 - 800 °C with a holding time of 20 - 30 min. In the second stage, the heating rate is 5 - 6 °C / min, and the temperature is increased to 800 - 1400 °C with a holding time of 30 - 40 min. In the third stage, the heating rate is 4 - 5 °C / min, and the temperature is increased to 1400 - 2200 °C with a holding time of 45 - 55 min.

9. A PDC bit obtained by treating with the method for surface hardening of a PDC bit according to any one of claims 1-8.