Processing method of high-strength medium alloy carburizing steel

Abstract

The invention relates to the field of metal processing, and discloses a processing method of high-strength medium alloy carburizing steel, which comprises the following steps of: assembling parts and welding to form a product: aligning all the parts forming the product through corresponding grooves in a contact manner, and assembling all the parts to be welded to form a product prototype; carrying out integral preheating treatment on the to-be-welded parts which are integrally placed and assembled before welding, wherein the preheating temperature is 200-250 DEG C; after the temperature of all the to-be-welded parts is reached, welding the groove contact edges of the two to-be-welded parts which are placed and contacted one by one, so that a welding seam with a certain width is formed between the base materials of the two parts; all to-be-welded parts of the whole product are continuously heated in the welding process, and it is guaranteed that the temperature of the to-be-welded parts is always kept at 200-250 DEG C in the welding process; dehydrogenating the whole product; performing stress relief annealing on the whole product; and integrally tempering the product. According to the scheme, the overall performance of a welding product is effectively improved, and the performance homogenization of welding seams and part base metal is effectively improved.

Description

Technical Field

[0001] The invention relates to the field of metal processing, and in particular to a processing method of high-strength medium-alloy carburizing steel. Background Art

[0002] 18Cr2Ni4W is a high-strength medium alloy carburizing steel. Due to its good strength, toughness and wear resistance, it is widely used in the manufacture of high-strength parts, such as helicopter journals, gears, turbine shafts and compressor shafts of aircraft engines. However, the material itself has poor weldability. Since the surface of 18Cr2Ni4W reaches a high carbon state after carburizing and quenching, it is easy to increase brittleness after welding, and sometimes even break after welding. Therefore, at present, products made of 18Cr2Ni4W cannot be welded, and can only be cast, forged, etc. Summary of the invention

[0003] The present invention aims to provide a processing method for high-strength medium-alloy carburizing steel to solve the problem that the existing processing technology cannot complete the welding of 18Cr2Ni4W material.

[0004] To solve the above problems, the present invention adopts the following technical solutions:

[0005] A method for processing high-strength medium-alloy carburizing steel comprises the following steps:

[0006] Step 1: Assemble and weld parts to form products: Align all parts that constitute the product through corresponding grooves, so that all parts to be welded are assembled to form a product prototype; preheat the entire assembled parts to be welded before welding, and the preheating temperature is 200℃-250℃; after the temperature of all parts to be welded is reached, start welding the groove contact edges of the two parts to be welded one by one, so that a certain width of weld is formed between the parent materials of the two parts; during the welding process, continue to heat and ignite all parts to be welded of the entire product to ensure that the temperature is always maintained at 200℃-250℃ during the welding process;

[0007] Step 2, dehydrogenation of the product as a whole;

[0008] Step 3: Stress relief annealing of the product as a whole;

[0009] Step 4: Overall conditioning of the product;

[0010] Step 5: Sandblast the entire product.

[0011] Furthermore, in step 2, the entire product after welding is heated to 250°C-300°C and kept warm for 2 hours for dehydrogenation treatment.

[0012] Furthermore, in step three, the dehydrogenated product is subjected to stress relief annealing as a whole. When the furnace temperature reaches 300°C, the product is loaded into the furnace and heated at a rate of 70-90°C / h. After heating to 500±20°C, the product is kept warm for 5-7h. The product is cooled with the furnace at a rate of 70-100°C / h. When the product is cooled to 280-300°C, it is taken out of the furnace and air-cooled.

[0013] Further, in step 4, the stress-relieved product is tempered as a whole. When the furnace temperature reaches 300°C, the product is loaded into the furnace, heated to 830±20°C within 5-9 hours, and then kept warm. After 5-9 hours of warming time, it is taken out of the furnace and cooled to 50-100°C in oil; then heated to 520±20°C within 3-5 hours, and then kept warm. After 5-12 hours of warming time, it is taken out of the furnace and cooled to room temperature in the air; the performance requirements of the tempered product are met: tensile strength Rm≥1050MPa, yield strength Rel≥835MPa, elongation A≥10%, impact toughness AKv≥78J.

[0014] Furthermore, in step five, the entire product is shot peened with a hand-held spray gun, with the nozzle 200±30 mm away from the surface of the workpiece, and the spray gun is moved evenly and smoothly to remove rust and debris on the surface of the product.

[0015] Further, the method further comprises the following steps:

[0016] Step 6: Overall flaw detection of the product: ultrasonic flaw detection of each weld on the surface of the product;

[0017] Step 7: Overall machining of the product: The product that meets the requirements of the flaw detection standard is processed as a single workpiece to the corresponding size to form a new part to be processed, and participate in the assembly and welding of the new product.

[0018] Furthermore, the part in step 1 is formed by turning the 18Cr2Ni4W base material workpiece.

[0019] Furthermore, the 18Cr2Ni4W base material workpiece is formed by forging a steel ingot and then processed by normalizing + tempering heat treatment.

[0020] Further, when the furnace temperature reaches 500°C, the 18Cr2Ni4W workpiece is loaded into the furnace, and the temperature is increased to 930±30°C within 5-10 hours, and then the workpiece is kept warm. After the holding time is 6-9 hours, the workpiece is taken out of the furnace and cooled to room temperature in the air; then the temperature is increased to 700±20°C within 5-7 hours, and then the workpiece is kept warm. After the holding time is 5-12 hours, the workpiece is taken out of the furnace and cooled to room temperature in the air to obtain the processed 18Cr2Ni4W base material workpiece.

[0021] The principles and advantages of this solution are:

[0022] This solution overcomes technical prejudice, solves the design defects in the existing processing technology, and designs a new processing method for the welding defects of the 18Cr2Ni4W material itself, so that the processed protruding 18Cr2Ni4W material can not only be welded to form a welded product, but also the overall performance of the welded product is effectively improved.

[0023] Because 18Cr2Ni4W is not weldable, welding is rarely used for the processing of 18Cr2Ni4W materials. Although casting, forging and other methods can also complete the manufacturing of 18Cr2Ni4W material products, welding has more advantages. Welding can make material utilization higher, cost lower, operation more flexible and precision higher.

[0024] Although some people have tried to weld 18Cr2Ni4W materials by adding heat treatment, the qualified rate of welded products is extremely low. In this process, the product parts are first quenched and tempered, and then assembled and welded after the parent material performance meets the product requirements. After the product parts are quenched and tempered and then welded, the inconsistent temperatures of various parts are more likely to cause welding defects. During the welding process of quenched and tempered steel, the heat-affected zone is heated to an area that exceeds the tempering temperature of the quenching and tempering treatment, which easily causes the joint strength and hardness to be lower than the softening zone of the parent material, becoming a weak area that reduces the joint strength. At the same time, when the carbon and alloying element content of the material is high, when the welding pool solidifies during the welding process, the crystal segregation tendency is greater, and thermal cracks are easily generated.

[0025] The present solution first assembles the product prototype, and during welding, heats the entire product to keep the overall temperature of the product in the same temperature environment, thereby reducing the brittleness of the 18Cr2Ni4W material during welding and improving its weldability. The subsequent dehydrogenation, stress relief annealing and tempering are all treatments for the welded product as a whole, so that after the weld is formed, the welded product including the weld is continuously treated as a whole, which not only heats the welded joint of the parts and the parent material at the same time, improves the reduction in joint strength caused by softening of the heat affected zone, restores joint strength and toughness, but also effectively improves the overall welding quality and service life of the welded product. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The figure is a schematic flow chart of a processing method according to an embodiment of the present invention.

[0027] Figure 2 This is a weld bead division diagram of a welding product according to an embodiment of the present invention.

[0028] Figure 3 This is a macroscopic metallographic diagram of the weld of the welding product according to an embodiment of the present invention.

[0029] Figure 4 This is a microscopic metallographic image of the adjacent fusion lines between the weld and the base material of the part of the welding product according to the embodiment of the present invention at 200 microns.

[0030] Figure 5 This is a microscopic metallographic image of the adjacent fusion lines between the weld and the part base material of the welding product of an embodiment of the present invention at 50 microns. DETAILED DESCRIPTION

[0031] The following is further described in detail through specific implementation methods:

[0032] Example

[0033] The high-strength medium-alloy carburizing steel 18Cr2Ni4W to be processed in this embodiment has good hardenability and high strength, toughness and wear resistance, and is suitable for manufacturing parts that withstand high loads and impacts. It is widely used in the manufacture of high-strength parts, such as helicopter journals, gears, turbine shafts of aircraft engines, compressor shafts, etc.

[0034] Among them, the chemical composition of 18Cr2Ni4W is:

[0035] Carbon (C): 0.17%-0.23%,

[0036] Chromium (Cr): 1.50%-1.80%,

[0037] Nickel (Ni): 3.50%-4.00%,

[0038] Tungsten (W): 0.60%-0.90%,

[0039] Silicon (Si): ≤0.40%,

[0040] Manganese (Mn): ≤0.60%,

[0041] Phosphorus (P): ≤0.035%,

[0042] Sulfur (S): ≤0.035%.

[0043] However, the weldability of 18Cr2Ni4W material itself is poor. In the process of using 18Cr2Ni4W material to weld and process to form welded products, the quality of welded products cannot be well guaranteed, and the unqualified rate of welded products is high. Since the surface of 18Cr2Ni4W reaches a high carbon state after carburizing and quenching, it is easy to cause increased brittleness after welding, and sometimes even break by itself after welding. In order to ensure the quality of welded products, it is generally quenched and tempered first on the base material of the parts to be welded. After the performance of the base material meets the product requirements, assembly and welding are carried out, and hydrogen is removed after welding, and then stress relief annealing is performed to obtain the final welded product. Among them, in order to change the welding performance of the 18Cr2Ni4W base material, it is particularly important during the quenching and tempering process.

[0044] First, quenching is performed: the 18Cr2Ni4W material is heated above the critical temperature and then rapidly cooled to form a martensitic structure, thereby increasing the hardness and strength of the material.

[0045] Then, tempering is carried out: the quenched 18Cr2Ni4W material is reheated to a certain temperature (below the critical temperature), and then slowly cooled to reduce the internal stress caused by quenching and improve the toughness and plasticity of the material.

[0046] According to the actual situation, choosing appropriate quenching and tempering treatment before welding can improve the comprehensive mechanical properties of 18Cr2Ni4W materials, including hardness, strength, toughness and plasticity. Reduce internal stress. After quenching, large internal stress will be generated inside the 18Cr2Ni4W material. Tempering can effectively reduce these internal stresses and prevent the 18Cr2Ni4W material from deformation or cracking during subsequent processing or use. Improve the microstructure. Quenching and tempering treatment can improve the microstructure of 18Cr2Ni4W materials, making them more uniform and dense, and improve the overall performance of 18Cr2Ni4W materials. Finally, the parent parts composed of 18Cr2Ni4W materials can have better welding performance and be assembled with other parts to form a complete product, avoiding cracking and improving the qualified rate of products.

[0047] Although the above existing quenching and tempering operations can reduce the number of cracks caused by direct welding of 18Cr2Ni4W material parts to a certain extent, the overall performance of the final welded product has not reached the expected goal. Although the weld between the 18Cr2Ni4W base material and other materials is not easy to crack, the cracking phenomenon is reduced, but as a whole product, the strength of the weld and its surrounding areas is obviously not comparable to that of the 18Cr2Ni4W base material and other parts, and even the strength of the weld and its surrounding areas has affected the overall strength of the welded product.

[0048] In view of this, after careful research, the inventor found that there are major defects in the existing 18Cr2Ni4W processing technology. In order to overcome the welding defects of the 18Cr2Ni4W material itself and the design defects of the existing processing technology, the inventor studied and obtained the solution of this embodiment.

[0049] This embodiment aims at the original 18Cr2Ni4W processing technology, overcomes the technical prejudice of technical personnel in this field, solves the design defects of the existing processing technology, and cleverly designs the processing process. While avoiding the occurrence of welding cracks, it ensures that the overall mechanical properties of the product meet the requirements, making the overall performance of the product more similar, especially the overall strength is effectively improved.

[0050] The processing method of the high-strength medium-alloy carburizing steel in this embodiment comprises the following steps:

[0051] S1. Forging of steel ingot: Forging the steel ingot to obtain 18Cr2Ni4W workpiece.

[0052] S2. Heat treatment after forging, normalizing + tempering: improve the grain size of 18Cr2Ni4W base material and improve the performance of 18Cr2Ni4W base material. Use a trolley natural furnace or a trolley resistance furnace to heat treat the 18Cr2Ni4W workpiece. When the furnace temperature reaches 500℃, load the 18Cr2Ni4W workpiece into the furnace, heat it to 930±30℃ within 5-10 hours, and then keep it warm. After keeping it warm for 6-9 hours, take it out of the furnace and cool it to room temperature in the air; then heat it to 700±20℃ within 5-7 hours, and then keep it warm. After keeping it warm for 5-12 hours, take it out of the furnace and cool it to room temperature in the air to obtain the treated 18Cr2Ni4W base material workpiece.

[0053] S3. Part machining: The 18Cr2Ni4W base material workpiece is machined to the required size through turning to form parts.

[0054] S4. Parts flaw detection: Perform ultrasonic flaw detection on parts according to GB / T6402 Level I requirements; proceed to the next step after passing the inspection.

[0055] S5. Part groove processing: Grind the groove angle of each part to 30°-50°, and clean the oil stains on the groove surface before welding so that the parts can be better aligned and assembled. After the groove grinding is completed, proceed to the next step.

[0056] S6. Assemble and weld to form products: Align all parts that constitute the product through corresponding groove contacts, so that all parts to be welded are assembled to form a product prototype; before welding, the entire assembled parts to be welded are preheated as a whole, and the preheating temperature is 200℃-250℃; after the temperature of all parts to be welded is reached, start welding the groove contact edges of the two parts to be welded that are placed in contact one by one, so that a welding area of ​​a certain width is formed between the parent materials of the two parts, that is, a weld is formed; during the welding process, all parts to be welded of the entire product are continuously heated and ignited to ensure that the temperature is always maintained at 200℃-250℃ during the welding process, so that all parts that constitute the entire product are in the same temperature environment, and the performance of the weld and the parent materials of the surrounding parts are increased. The product is formed after all the welding parts are welded.

[0057] When welding, Figure 2 The weld is zoned and welded as shown in Table 1.

[0058] Table 1 Welding parameters

[0059]

[0060] The macroscopic metallographic image of the weld formed by welding is as follows Figure 3 As shown in Figure 2, the width of the back weld is about 23 mm, and the width of the front weld is less than or equal to 30 mm. The microstructure of the fusion line of the welded product in the adjacent area between the single part and the weld is shown in Figure 2. Figure 4 and Figure 5 shown.

[0061] S7. Dehydrogenation of the entire product: Heat the entire product after welding to 250℃-300℃ and keep it warm for 2 hours for dehydrogenation treatment, so that the performance of each area of ​​the product is similar, further improving the overall performance of the product.

[0062] S8. Overall stress relief annealing of the product: Use a trolley natural furnace or a trolley resistance furnace to perform stress relief annealing on the entire product after dehydrogenation. When the furnace temperature reaches 300℃, load the product into the furnace and heat it up at a rate of 70-90℃ / h. After heating to 500±20℃, keep it warm for 5-7h, cool it with the furnace at a rate of 70-100℃ / h. When it cools to 280-300℃, take it out of the furnace and air cool it.

[0063] S9. Overall quenching and tempering of the product: Use a trolley natural furnace or a trolley resistance furnace to quench and temper the product after stress relief. When the furnace temperature reaches 300℃, load the product into the furnace, heat it to 830±20℃ within 5-9 hours, and then keep it warm. After 5-9 hours of heat preservation, take it out of the furnace and cool it to 50-100℃ in oil; then heat it to 520±20℃ within 3-5 hours, and then keep it warm. After 5-12 hours of heat preservation, take it out of the furnace and cool it to room temperature in the air; the performance requirements of the quenched and tempered product are as follows: Rm≥1050MPa, Rel≥835MPa, A≥10%, AKv≥78J (normal temperature);

[0064] Among them, Rm: represents the tensile strength of the material, which is required to be at least 1050MPa, that is, the product must be able to withstand at least 1050MPa of stress in the tensile test to avoid breaking. Rel: represents the yield strength of the material, which is required to be at least 835MPa, that is, the product must be able to withstand at least 835MPa of stress in the tensile test to begin plastic deformation. A: represents the elongation of the material, which is required to be at least 10%, that is, the ratio of the elongation of the product before breaking in the tensile test to the original length must be greater than or equal to 10%. AKv: represents the impact toughness of the material, which is required to be at least 78J at room temperature, that is, the product must be able to absorb at least 78J of energy in the Charpy impact test without breaking.

[0065] S10. Overall sandblasting of the product: Use a hand-held spray gun to blast the entire product. The nozzle should be 200±30mm away from the surface of the workpiece. Move the spray gun evenly and steadily to remove rust and debris on the surface of the product.

[0066] S11. Overall flaw detection of products: ultrasonic flaw detection shall be carried out on each weld on the surface of the product according to the requirements of CB / Z125-2012 Level I. Products that meet the flaw detection requirements can be packaged and put into storage according to actual needs, or further machined as a whole according to needs.

[0067] S12. Overall machining of the product: the product that meets the requirements of the flaw detection standard is processed as a single workpiece to the corresponding size to form a new part to be processed, and steps S5-S11 are repeated, or new processing steps are performed to participate in new product assembly and welding.

[0068] The performance parameters of the welded product finally obtained by the processing method of this embodiment are shown in Table 2. The overall performance of the welded product obtained by this embodiment is much higher than that of the product processed by the existing method, especially the strength of the weld and its surrounding area is greatly improved to be homogeneous with the performance of the base material of the part:

[0069] The mechanical properties of the quenched and tempered product obtained in this embodiment are as follows: yield strength ≥ 835MPa, tensile strength ≥ 1050MPa, elongation at fracture ≥ 10%, impact energy of U-notch impact test ≥ 78J, actual weld metal measurement values: yield strength 968MPa, tensile strength 1064MPa, elongation at fracture 11%, impact energy (according to the standard requirements, the impact energy of each group of three samples) are 83J, 86J, 80J respectively, and the bending test joint is qualified without cracks. The mechanical properties of the weld meet the requirements of the parent material.

[0070] Table 2 Performance parameters of welding products

[0071]

[0072] The advantages of this embodiment are:

[0073] 1. Use this process route to change the product processing steps, and perform overall quenching and tempering after the parts are welded. Compare the metallographic structure of the weld and heat-affected zone with that of the parent material. There is no obvious coarse grains and structural transformation in the weld area;

[0074] 2. There is no increase in brittleness of the weld, and the mechanical properties meet the standard requirements of high strength and high toughness.

[0075] Through the method of this embodiment, not only can the 18Cr2Ni4W material be welded, but also the overall performance of the welding product can be effectively improved, and the welding qualification rate can be greatly improved.

[0076] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for processing high-strength medium-alloy carburizing steel, characterized in that: The following steps are involved: Step 1: Assemble and weld parts to form a product: Align all parts that make up the product through corresponding grooves, so that all parts to be welded are assembled to form a product prototype; Before welding, the entire assembled parts to be welded are preheated at a temperature of 200℃-250℃. After the temperature of all the parts to be welded is reached, the contact edges of the grooves of the two parts to be welded that are placed in contact with each other are welded one by one to form a weld of a certain width between the parent materials of the two parts. During the welding process, all the parts to be welded of the entire product are continuously heated and refrigerated to ensure that the temperature is always maintained at 200℃-250℃ during the welding process. Step 2, dehydrogenation of the product as a whole; Step 3: stress relief annealing of the product as a whole; Step 4: Overall conditioning of the product; Step 5: Sandblast the entire product.

2. The method for processing high-strength medium alloy carburizing steel according to claim 1, characterized in that: In step 2, the entire welded product is heated to 250°C-300°C and kept warm for 2 hours for dehydrogenation treatment.

3. The processing method of high-strength medium-alloy carburizing steel according to claim 1, characterized in that: In step three, the dehydrogenated product is subjected to stress relief annealing as a whole. When the furnace temperature reaches 300°C, the product is loaded into the furnace and heated at a rate of 70-90°C / h. After heating to 500±20°C, it is kept warm for 5-7h. After cooling with the furnace at a rate of 70-100°C / h, it is cooled to 280-300°C and air-cooled.

4. The method for processing high-strength medium alloy carburizing steel according to claim 1, characterized in that: In step 4, the stress-relieved product is tempered as a whole. When the furnace temperature reaches 300°C, the product is loaded into the furnace, heated to 830±20°C within 5-9 hours, and then kept warm. After 5-9 hours of warming time, it is taken out of the furnace and cooled to 50-100°C in oil; then heated to 520±20°C within 3-5 hours, and then kept warm. After 5-12 hours of warming time, it is taken out of the furnace and cooled to room temperature in the air; the performance requirements of the tempered product are as follows: tensile strength Rm≥1050MPa, yield strength Rel≥835MPa, elongation A≥10%, and impact toughness AKv≥78J.

5. The method for processing high-strength medium-alloy carburizing steel according to claim 1, characterized in that: In step five, the entire product is shot blasted with a hand-held spray gun, with the nozzle 200±30mm away from the surface of the workpiece. The spray gun moves evenly and steadily to remove rust and debris on the surface of the product.

6. The method for processing high-strength medium-alloy carburizing steel according to claim 1, characterized in that: The following steps are also included: Step 6: Overall flaw detection of the product: ultrasonic flaw detection of each weld on the surface of the product; Step 7: Overall machining of the product: The product that meets the requirements of the flaw detection standard is processed as a single workpiece to the corresponding size to form a new part to be processed, and participate in the assembly and welding of the new product.

7. The method for processing high-strength medium-alloy carburizing steel according to claim 1, characterized in that: The part in step 1 is formed by turning the 18Cr2Ni4W base material workpiece.

8. The method for processing high-strength medium-alloy carburizing steel according to claim 7, characterized in that: The 18Cr2Ni4W base material workpiece is forged from a steel ingot and then processed through normalizing + tempering heat treatment.

9. The method for processing high-strength medium-alloy carburizing steel according to claim 8, characterized in that: When the furnace temperature reaches 500°C, the 18Cr2Ni4W workpiece is loaded into the furnace, and the temperature is raised to 930±30°C within 5-10 hours, and then the workpiece is kept warm. After the holding time is 6-9 hours, the workpiece is taken out of the furnace and cooled to room temperature in the air; then the temperature is raised to 700±20°C within 5-7 hours, and then the workpiece is kept warm. After the holding time is 5-12 hours, the workpiece is taken out of the furnace and cooled to room temperature in the air to obtain the processed 18Cr2Ni4W base material workpiece.

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