Method for repairing injection mold by using plasma spray welding ceramic particle TiC reinforced iron-based spray welding layer

Abstract

The invention relates to the technical field of material surface modification, in particular to a method for improving corrosion resistance and wear resistance of a repaired mold through ceramic particles TiC. The plasma spray welding layer disclosed by the invention is composed of 0.5%-1.5% of TiC powder and 98.5%-99.5% of 440C iron-based main body powder. The powder is adopted on plasma transfer arc spray welding equipment, a relevant spray welding process is combined, a failed injection mold is subjected to spray welding repair, a spray welding layer is subjected to metallurgical fusion welding, the welding layer is well combined with base metal, a passivation film rich in Cr is formed, and the service life of the injection mold is prolonged. The repaired injection mold spray welding layer has the advantages of being good in bonding performance, high in corrosion resistance, high in abrasion resistance, low in cost and the like. The mold repaired through the method is high in corrosion potential, low in corrosion current density and high in abrasion resistance, the cost of mold scrapping caused by corrosion or abrasion of the injection mold in the production process is greatly reduced, the technical vacancy of injection mold repairing is filled up, and good application prospects are achieved in the field of injection mold repairing.

Description

Technical Field

[0001] The invention relates to the technical field of material surface modification, and in particular to a method for improving the corrosion resistance and wear resistance of a repaired mold by using ceramic particles TiC. Background Art

[0002] China's plastics industry is developing rapidly, and the amount of molds used is large. The S136 molds and some high-wear-resistant molds on the market generally show poor corrosion resistance and wear resistance, short mold life, and no effective means of repair after scrapping. Scrapped molds can only be replaced with new ones, causing huge economic losses.

[0003] With the increasing production demand, the comprehensive performance of injection molds, especially corrosion resistance and wear resistance, has been challenged. Applying plasma spray welding technology to mold repair not only fills the technical gap of mold repair, but also makes the molds repaired by plasma spray welding have better corrosion resistance and wear resistance than before, and greatly reduces the cost of mold scrapping due to corrosion or wear.

[0004] Metal-based composite materials with iron-based powder and ceramic particles as reinforcement materials have become very attractive and potential materials due to their excellent performance. Among various ceramic reinforcements, TiC has excellent wear resistance and is an excellent choice for reinforcement of iron-based composite materials. Because the iron-based powder 440C has a high Cr content, after being mixed with TiC powder in the correct proportion, through plasma spray welding, a Cr-rich passivation film is formed on the welding layer, which greatly improves the corrosion resistance and wear resistance of the mold after repair. Summary of the invention

[0005] The present invention aims to provide a plasma spray-welded ceramic particle TiC reinforced iron-based repair injection mold spray-welded layer and a preparation method thereof, which can improve the corrosion resistance and wear resistance of the mold at the same time, extend the service life, improve the performance, and reduce the mold investment cost.

[0006] In order to achieve the above technical purpose, the technical solution provided by the present invention is as follows:

[0007] A method for repairing an injection mold by using plasma sprayed ceramic particles TiC to strengthen an iron-based sprayed layer comprises the following steps:

[0008] S1. Mold pretreatment

[0009] Cut the mold to be repaired to remove the corroded or worn parts; after cutting, clean and preheat, and remove the surface oxide layer;

[0010] S2. Configure spray welding powder

[0011] The ceramic particle TiC powder and the iron-based powder are placed in a ball mill for ball milling to prepare a TiC / iron-based composite powder;

[0012] S3. Spray welding

[0013] The TiC / iron-based composite powder is sprayed onto the mold to be repaired which has been preheated and polished in S1 by using plasma spray welding equipment to form a spray welding layer;

[0014] S4. Insulation and cooling

[0015] After the spray welding operation is completed, the mold repaired by spray welding should be kept warm and cooled slowly to prevent cracks;

[0016] S5. Mold post-processing

[0017] After cooling, the surface of the spray-welded repaired mold is repaired to ensure the mold's size and surface quality requirements.

[0018] As an improvement, the iron-based powder is 440C powder.

[0019] As an improvement, the mass percentages of the ceramic particle TiC powder and the iron-based powder in step S2 are: TiC powder 0.5%-1.5%; iron-based powder 98.5%-99.5%.

[0020] As an improvement, the purity of the TiC powder is 99.8%, and the purity of the 440C powder is 99.5%.

[0021] As an improvement, the cleaning in step S1 is to remove rust, oxide layer, oil stains and impurities on the surface of the mold.

[0022] As an improvement, the preheating temperature in step S1 is 350-420°C.

[0023] As an improvement, the spray welding method in step S3 is: using high-purity argon gas protection in the plasma spray welding equipment to eliminate oxygen pollution during the plasma spray welding process; and adopting a plasma spray welding strategy of rotating 90° on the previous layer during the spraying process to avoid defects caused by uneven heating.

[0024] As an improvement, the particle size of the TiC powder and the iron-based powder is 325 mesh.

[0025] As an improvement, the composition of the 440C iron-based powder is as follows in mass percentage: C: 0.95% to 1.20%; Si: <1.00%; Cr: 16.00% to 18.00%; Ni: <0.60%; Mo: 0.40% to 1.00%.

[0026] As the geometric shapes of commercial injection molded products become more and more complex, the lack of a good repair method for complex structural mold steel after use is an important challenge that mold steel on the market needs to face. Traditional processing methods have almost no way to repair damaged molds. Plasma spray welding technology (PTA) can repair damaged molds without processing tools, providing a potential technical route for mold repair.

[0027] The advantages of the present invention are:

[0028] The present invention can achieve the advantages of the preparation method based on adding ceramic particles TiC and PTA, and improve the required corrosion resistance, wear resistance and bonding performance by changing and controlling the mass fraction of ceramic particles TiC and iron-based powder 440C, PTA spray welding power, spray welding speed, and spray welding powder feeding amount. It is well achieved that the purpose of further improving the corrosion resistance and wear resistance while ensuring the normal use performance of the mold after repair is achieved, thereby achieving the repair of the mold to make the mold more corrosion-resistant and more wear-resistant, prolonging the service life, and reducing the cost of scrapping the mold due to corrosion or wear in actual production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a flow chart of a method for preparing a plasma spray-welded ceramic particle TiC reinforced iron-based repair injection mold spray-welded layer.

[0030] Figure 2 The weld layer microstructures of the original samples prepared in Examples 1-3 and the molds repaired with TiC / 440C composite materials in different proportions, wherein (a) is the weld layer microstructure of the original S136 steel, (b) is the weld layer microstructure of Example 1 with 99.5% 440C powder and 0.5% TiC powder added, (c) is the weld layer microstructure of Example 2 with 99% 440C powder and 1% TiC powder added, and (d) is the weld layer microstructure of Example 3 with 98.5% 440C powder and 1.5% TiC powder added.

[0031] Figure 3 The Tafel curve results of electrochemical testing on the S136 mold steel original part and the mold weld layer repaired with TiC / 440C composite materials in different proportions for this secondary repair. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0033] The original S136 die steel block sample with the size of 8mm×8mm×6mm was taken for electrochemical testing. The electrochemical test results showed that the corrosion current density of the coating was 1.10±0.07×10 -6 Acm 2 , the self-corrosion potential is -0.19±0.03V SCE .

[0034] The original S136 mold steel block sample with the size of 8mm×8mm×6mm was taken for hardness test. The test results showed that the hardness of the original S136 steel base that needed to be repaired this time was 49.7HRC.

[0035] Example 1

[0036] This embodiment discloses a plasma sprayed ceramic particle TiC reinforced iron-based repair injection mold spray layer: its composition is 99.5% 440C powder and 0.5% TiC powder, and the TiC is added to the matrix by ball milling.

[0037] The method of repairing the injection mold using the plasma sprayed ceramic particles TiC to strengthen the iron-based sprayed layer in this embodiment is as follows:

[0038] S1. Mold pretreatment

[0039] The damaged S136 mold steel is cut and polished with a milling machine to remove the damaged part until the metallic luster is exposed; then the mold to be repaired is degreased and cleaned with potassium hydroxide degreaser and cleaning aid organic chelating agent, the cleaning temperature is about 25°C, rinse with clean water after cleaning, and finally wipe the surface of the steel plate with anhydrous ethanol and dry for use.

[0040] S2. Configure spray welding powder

[0041] The weighed S136 powder and TiC powder were placed in a ball mill, and the TiC / 440C composite material was ball milled in an argon protection environment. In order to make the TiC particles evenly dispersed around the 440C matrix powder, the process parameters of the ball mill were a ball-to-powder weight ratio of 4:1, a main disk speed of 200 rpm, and a ball milling time of 6 hours; the mixed powder was dried at 70°C in a vacuum environment for 12 hours to obtain a ceramic particle reinforced metal composite material;

[0042] S3. Spray welding

[0043] The ceramic particle reinforced metal composite powder is loaded into the powder feeding tank of the instrument, the S136 mold steel to be repaired after S1 treatment is preheated to 350°C, and the preheated damaged S136 mold steel is sprayed and repaired by plasma spray welding equipment in an argon environment to obtain a mold repaired by plasma spray welding;

[0044] S4. Insulation and cooling

[0045] After the spray welding operation is completed, the mold repaired by spray welding should be kept warm and cooled slowly to prevent cracks;

[0046] S5. Mold post-processing

[0047] After cooling, the surface of the spray-welded repaired mold is repaired to ensure the mold's size, surface quality and other requirements.

[0048] In this embodiment, the sample is prepared under the following conditions: spray welding current 120A; plasma arc length 15-17mm; plasma gas flow rate 9L / min; shielding gas flow rate 2.4L / min; spray distance: 5-6mm.

[0049] The electrochemical test results show that the corrosion current density of the coating in 3.5% NaCl solution is 4.87±0.06×10 -7 Acm 2 The self-corrosion potential of the coating is -0.15±0.03V SCE .

[0050] A block sample with a size of 8mm×8mm×6mm was taken for hardness test. The test results showed that the hardness of the weld layer was 50.2HRC.

[0051] Example 2

[0052] This embodiment discloses a plasma sprayed ceramic particle TiC reinforced iron-based repair injection mold spray layer: its composition is 99% 440C powder and 1% TiC powder, and the TiC is added to the matrix by ball milling.

[0053] This embodiment adopts the same repair method as that of Embodiment 1.

[0054] The electrochemical test results show that the corrosion current density of the coating in 3.5% NaCl solution is 3.53±0.04×10 -7 Acm 2 The self-corrosion potential of the coating is -0.17±0.02V SCE .

[0055] A block sample with a size of 8mm×8mm×6mm was taken for hardness test. The test results showed that the hardness of the weld layer was 52.1HRC.

[0056] Example 3

[0057] This embodiment discloses a plasma sprayed ceramic particle TiC reinforced iron-based repair injection mold spray layer: its composition is 98.5% 440C powder and 1.5% TiC powder, and the TiC is added to the matrix by ball milling.

[0058] This embodiment adopts the same repair method as that of Embodiment 1.

[0059] The electrochemical test results show that the corrosion current density of the coating in 3.5% NaCl solution is 1.01±0.05×10 -6 Acm 2 The self-corrosion potential of the coating is -0.18±0.04V SCE .

[0060] A block sample with a size of 8mm×8mm×6mm was taken for hardness test. The test results showed that the hardness of the weld layer was 53.6HRC.

[0061] Take the S136 mold steel original parts to be repaired in Examples 1 to 3 and the mold welding layers repaired by TiC / 440C composite materials with different proportions, and observe the microstructure. The microstructure results are as follows: Figure 2 shown.

[0062] The S136 mold steel original parts to be repaired in Examples 1 to 3 and the mold welding layers repaired by TiC / 440C composite materials with different ratios were tested by electrochemical Tafel curves. The results are as follows: Figure 3 shown.

[0063] Depend on Figures 2-3 It can be seen that the plasma sprayed ceramic particle TiC reinforced iron-based repair injection mold sprayed welding layer of the present invention can further improve the corrosion resistance, and the corrosion current density of the welding layer is in the range of 3.53±0.04×10 -7 Acm 2

[0064] ~1.01±0.05×10 -6 Acm 2 , in the range of TiC mass percentage 0.5% to 1.5%, it is significantly smaller than the original S136 mold iron matrix; self-corrosion potential -0.15±0.03~-0.18±0.04V SCE , which is higher than the original S136 mold iron matrix in the range of TiC mass percentage of 0.5% to 1.5%.

[0065] The above results show that the plasma sprayed ceramic particle TiC reinforced iron-based repair injection mold spray welding layer of the present invention has better corrosion resistance than the original material itself. According to the hardness test and wear resistance test results, the corrosion resistance of the present invention is better than the original S136 mold steel, and with the increase of TiC within the percentage range of the present invention, the overall wear resistance is also improved. However, as the TiC content increases, the overall proportion of 440C is also decreasing, which leads to a decrease in the proportion of Cr-rich passivation film on the surface of the weld layer, thereby slightly reducing the corrosion resistance. The results of the present invention show that 99% 440C mixed with 1% TiC as a repair material can make the corrosion resistance and wear resistance of the mold after repair reach the optimal balance.

[0066] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for repairing an injection mold by using plasma sprayed ceramic particles TiC to strengthen an iron-based sprayed layer, characterized in that: The steps include: S1. Mold pretreatment Cut the mold to be repaired to remove the corroded or worn parts; after cutting, clean and preheat, and remove the surface oxide layer; S2. Configure spray welding powder The ceramic particle TiC powder and the iron-based powder are placed in a ball mill for ball milling to prepare a TiC / iron-based composite powder; S3. Spray welding The TiC / iron-based composite powder is sprayed on the mold to be repaired which has been preheated and polished in S1 by using plasma spray welding equipment to form a spray welding layer; S4. Insulation and cooling After the spray welding operation is completed, the mold repaired by spray welding should be kept warm and cooled slowly to prevent cracks; S5. Mold post-processing After cooling, the surface of the spray-welded repaired mold is repaired to ensure the mold's size and surface quality requirements.

2. A method for repairing an injection mold using a plasma sprayed ceramic particle TiC reinforced iron-based sprayed layer according to claim 1, characterized in that: The iron-based powder is 440C powder.

3. A method for repairing an injection mold using a plasma sprayed ceramic particle TiC reinforced iron-based sprayed layer according to claim 1 or 2, characterized in that: The mass percentages of the ceramic particle TiC powder and the iron-based powder in step S2 are: TiC powder 0.5%-1.5%; iron-based powder 98.5%-99.5%.

4. A method for repairing an injection mold using a plasma sprayed ceramic particle TiC reinforced iron-based sprayed layer according to claim 3, characterized in that: The purity of the TiC powder is 99.8%, and the purity of the 440C powder is 99.5%.

5. A method for repairing an injection mold using a plasma sprayed ceramic particle TiC reinforced iron-based sprayed layer according to claim 1, characterized in that: The cleaning in step S1 is to remove rust, oxide layer, oil stains and impurities on the surface of the mold.

6. A method for repairing an injection mold using a plasma sprayed ceramic particle TiC reinforced iron-based sprayed layer according to claim 1, characterized in that: The preheating temperature in step S1 is 350-420°C.

7. A method for repairing an injection mold using a plasma sprayed ceramic particle TiC reinforced iron-based sprayed layer according to claim 1, characterized in that: The spray welding method in step S3 is: using high-purity argon gas protection in the plasma spray welding equipment to eliminate oxygen pollution during the plasma spray welding process; In addition, during the spraying process, a plasma spraying strategy of rotating 90° on the previous layer is adopted to avoid defects caused by uneven heating.

8. A method for repairing an injection mold using a plasma sprayed ceramic particle TiC reinforced iron-based sprayed layer according to claim 1, characterized in that: The particle size of the TiC powder and the iron-based powder is 325 mesh.

9. A method for repairing an injection mold using a plasma sprayed ceramic particle TiC reinforced iron-based sprayed layer according to claim 2, characterized in that: The composition of the 440C iron-based powder is as follows in percentage by mass: C: 0.95% to 1.20%; Si: <1.00%; Cr: 16.00% to 18.00%; Ni: <0.60%; and Mo: 0.40% to 1.00%.

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