Forming method for improving influence of internal structure of quenched and tempered steel forging on magnetic particle inspection

Abstract

The present application belongs to the field of forging hot working, and relates to a forming method for improving the influence of internal organization of a quenched and tempered steel forging on magnetic particle inspection. The method comprises the following steps: using the forging fluidity of 35Cr2Ni4MoA / E to quickly form in a required direction, i.e. lengthening by a die anvil, to obtain a formed forging; using a method for pre-treating the internal organization of the formed forging, i.e. stress relief annealing, cooling according to the annealing temperature of 580-620 DEG C; holding in the temperature range, cooling after the temperature reduction treatment, surface processing after the heat treatment, and finally physical and chemical treatment.

Description

Technical Field

[0001] This invention belongs to the field of hot forging and relates to a forming method for improving the influence of the internal structure of quenched and tempered steel forgings on magnetic particle testing. Background Technology

[0002] 35Cr2Ni4MoA / E is a quenched and tempered steel within the alloy structural steel category, primarily used for manufacturing parts that bear heavy loads, such as turbine shafts for aero engines, rotor shafts for helicopter main gearboxes, and load-bearing components for aircraft landing gear. This type of steel requires excellent comprehensive mechanical properties, meaning it simultaneously possesses high strength, hardness, and good plasticity and toughness. The carbon content of quenched and tempered steel is generally between 0.25% and 0.5%. 35Cr2Ni4MoA / E belongs to medium carbon steel; too low a carbon content affects strength, while too high a carbon content results in insufficient toughness. The main alloying elements added to this steel are Cr, Ni, and Mo, which enhance the hardenability of the steel and strengthen the tempered martensite.

[0003] Due to varying requirements for the internal microstructure of 35Cr2Ni4MoA / E alloy forgings, the control over the production method, specifically the post-forging cooling method, differs. Inappropriate production methods and post-forging cooling can lead to changes in the internal microstructure, directly affecting the final magnetic particle testing results. This can result in products failing to meet the final testing requirements, leading to product scrap and significant resource waste. Therefore, selecting a suitable forging method and cooling regime is crucial for improving the internal microstructure and magnetic particle testing performance of 35Cr2Ni4MoA / E forgings. The following are the magnetic particle testing results for 35Cr2Ni4MoA / E forgings produced using conventional forging methods.

[0004] Conventional forging methods:

[0005] Material cutting - heating - forging - drawing - rolling - cooling - heat treatment - physical and chemical treatment - machining - flaw detection; conventional forging is done on a flat anvil, with the heat applied as needed, but the forging time is long, the final temperature is not easy to control, and it affects the physical and chemical testing and magnetic particle testing of the forgings.

[0006] Conventional forging processes, due to their long forging time and difficulty in controlling the final forging temperature, fail to meet the requirements for magnetic particle testing of the forgings. Therefore, selecting a reasonable forging method to shorten the forging time and increase the final forging temperature is crucial to the microstructure and properties of the material. In particular, conventional forging methods increase the number of forging passes, leading to localized dry burning in the later forgings, longer forging times, and difficulty in maintaining the final forging temperature, significantly affecting the physical and chemical properties of the forgings and resulting in a large number of defective forgings. Summary of the Invention

[0007] The purpose of this invention is to provide a method for shortening the forging time of 35Cr2Ni4MoA / E by changing the post-forging cooling method to improve the original microstructure of the raw material, using forging to meet the design requirements of the forging and a reasonable forging forming scheme, and obtaining qualified and stable magnetic particle testing indicators.

[0008] Technical solution:

[0009] A forming method for improving the influence of the internal microstructure of quenched and tempered steel forgings on magnetic particle testing, comprising:

[0010] 35Cr2Ni4MoA / E is rapidly formed in the desired direction by forging fluidity, i.e., the anvil is drawn out to obtain the formed forging;

[0011] The method for pre-treating the internal structure of formed forgings is stress-relieving annealing, with cooling at an annealing temperature of 580℃~620℃.

[0012] The insulation material is cooled after a cooling treatment, then heat-treated, surface-processed, and then physicochemically treated, before finally undergoing heat treatment.

[0013] 35Cr2Ni4MoA / E is rapidly formed in the desired direction using forging fluidity, i.e., anvil drawing, to obtain formed forgings, including:

[0014] The raw materials are divided according to the dimensions such as the volume required for the size of the forging step;

[0015] Pre-set the required anvil shape. The required anvil shape consists of two pieces, one above the other, that is, completely symmetrical. The external dimensions of the anvil shape need to meet the external dimensions of the commonly used hammer anvils of the required equipment.

[0016] The segmented billet is put into the furnace at ≤800℃ and heated to 800℃±50℃, then further heated to 1130℃±20℃ with a holding coefficient of 0.5min / mm. The hammer and anvil are preheated to 200℃~350℃. After the forging is held at the set temperature, it is immediately taken out of the furnace and forged on a free forging hammer using a special anvil, while controlling the intermediate and final forging temperatures and forging time.

[0017] The heated billet is removed from the furnace and transferred to a preheated special anvil, where one end of the forging is forged to the required size.

[0018] The billet that has been produced at one end is immediately reheated in the furnace. The reheated billet is then removed from the furnace and transferred to the aforementioned special anvil. The other end of the forging is then forged to the required forging size to obtain the finished part.

[0019] Stress-relief annealing includes:

[0020] Before forging, a natural gas furnace or electric furnace should be prepared for annealing.

[0021] The formed parts should be immediately subjected to stress-relief annealing. The procedure is to directly transfer them to a natural gas furnace at 550-630℃ after forging and hold for 5.5-6.5 hours, then cool them down to 450-550℃ and hold for 0.5-1.5 hours. After taking them out of the furnace, cover them with high-temperature cotton in a sheltered place and let them cool to room temperature before removing the high-temperature cotton. Air cooling after forging is not allowed before transferring them to the furnace.

[0022] After stress-relief annealing, the furnace door must not be opened, and the furnace door must be fully closed. The dial markings are allowed to rise ≤50℃. Stress-relief annealing must be completed within 24 hours before the conventional heat treatment process is carried out.

[0023] Material sorting methods include:

[0024] Using the required length from the maximum cross section of the stepped shaft as a reference, the belt shape is machined along both sides of the maximum cross section of the stepped shaft with a width-to-depth ratio of 4.5 / 1, and the required bar diameter with a fillet radius R = 1 / 10 is used for smooth transition.

[0025] The calculation method for the external dimensions of this type of anvil includes:

[0026] The pre-designed anvil has a semi-circular through hole at its length center, extending along its width, with a diameter D of the semi-circular through hole. 大 =1 / 2D 小 +10mm, D 小 The minimum diameter of the forging is required; the center axis of the semi-circular through hole should coincide with the center line of the anvil along its length, and a tangent line of the semi-circle should be made at a 45-degree angle on both sides of the center line. The intersection of the tangent line and the anvil should be smoothly transitioned using the diameter of the required feed material, R = 3 / 7.

[0027] The shape and size of the pre-set anvil can be perfectly symmetrical along its length.

[0028] From one end of the forging to the desired forging size, including:

[0029] The forging process employs a split-drawing method, forging one end to the required forging size. This step requires completion in one pass, and the forging size should be 0.02% larger than the dimensions specified in the drawing. The hammer reduction and feed rate should be controlled within 1 / 3 to 1 / 2 of the drawing size. During the drawing and rounding process, a manipulator should be used to rotate the billet, and repeated hammering and rounding at the same forging location are not permitted to prevent localized coarse grains in the forging. No interruptions are allowed during forging to allow for shorter forging time and better control of the final temperature. The forging dimensions should be measured promptly after forging.

[0030] The forging temperature for split-length drawing is controlled at W of the flat anvil forging temperature. 型锻造 ≥W 平锻造 (between 0.5 and 0.6).

[0031] The beneficial effects of this invention are:

[0032] 35Cr2Ni4MoA / E material is a quenched and tempered steel among alloy structural steels. After forging with an anvil and subsequent stress-relief treatment, the internal structure of the forging undergoes the required changes. This invention lays the foundation for providing the internal structure required for magnetic particle testing of the forging, ultimately meeting the requirements of the forging. Attached Figure Description

[0033] To more clearly illustrate the technical solutions implemented in this invention, the accompanying drawings used in the embodiments of this invention will be briefly explained below. Obviously, the drawings described below are merely some embodiments of this invention. Those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0034] Figure 1 This is a schematic diagram of the special-purpose anvil from Example 1;

[0035] Figure 2 This is a schematic diagram of the forging process in Example 1.

[0036] Figure 3 This is a schematic diagram of the forging process in Example 1. Detailed Implementation

[0037] A method for shortening the forging time of 35Cr2Ni4MoA / E by designing a mold that closely resembles the shape of a forging, and a forging method that improves the original microstructure of the raw material by changing the post-forging cooling method. The method employs a rapid forming method for 35Cr2Ni4MoA / E in the desired direction by forging fluidity, i.e., anvil elongation, and a reasonable cooling method for symmetrical forgings. It also includes a method for pre-treating the internal microstructure, i.e., stress-relieving annealing, i.e., cooling at an annealing temperature of 580℃~620℃; holding in the heat after cooling, followed by heat treatment, surface machining, physical and chemical treatment, and finally heat treatment.

[0038] The method includes the following steps:

[0039] Step 1: Machining the required bar stock. This involves dividing the material required for the forging into the required dimensions based on the size of the forging step. The method is to use the required length from the maximum cross-section of the step axis as a reference, and machine it into a belt shape with a width-to-depth ratio of 4.5 / 1 on both sides of the maximum cross-section of the step axis. The required bar diameter with a fillet radius of R = 1 / 10 is used to smoothly transition the material.

[0040] Step 2: Pre-set the required anvil. The required anvil consists of two pieces, one above the other, that is, completely symmetrical. The external dimensions of the anvil need to meet the external dimensions of the commonly used hammer anvil of the required equipment. The cavity dimensions are as follows.

[0041] The pre-set anvil is positioned at the center of its length according to the minimum diameter D required for the forging. 大 =1 / 2D 小 A +10mm dimension is set for a semi-circular through-hole along the width direction. The center axis of the semi-circular through-hole must coincide with the center line of the anvil along its length. A tangent line to the semi-circle is drawn at a 45-degree angle on both sides of the center line. The intersection of the tangent line and the anvil is smoothly transitioned using a radius of R = 3 / 7 of the required material diameter. The pre-set shape and dimensions of the anvil should be perfectly symmetrical along its length.

[0042] Step 3: The billet is heated to ≤800℃ and then heated to 800℃±50℃ in the furnace, followed by a further increase to 1130℃±20℃. The holding temperature coefficient is 0.5min / mm. The hammer and anvil are preheated to 200℃~350℃. After the forging is held at the set temperature for the set time, it is immediately taken out of the furnace and forged on a free forging hammer using a special anvil. At the same time, the intermediate and final forging temperatures and forging time are controlled.

[0043] Step 4: At one end of the forging step shaft on the hammer, the heated billet is removed from the furnace and transferred to a pre-heated special anvil. The forging time is less than or equal to half of the original forging time; that is, S 型转 ≤1 / 2S 平转 The forging process employs a split-drawing method to forge the required stepped shaft-type forging dimensions. This step is generally required to be completed in one pass, and the forging dimensions should be 0.02% larger than the dimensions shown in the drawing. The hammer reduction and feed rate should be controlled within 1 / 3-1 / 2 of the drawing size. During the drawing and rounding process, a manipulator should be used to rotate the billet, and repeated hammering and rounding at the same forging location are not allowed to prevent localized coarse grains in the forging. No interruptions are allowed during forging to allow for shorter forging time to control the final temperature. The forging dimensions should be measured promptly after forging. The final temperature should meet the material requirements. The split-drawing forging temperature is controlled at W of the flat anvil forging temperature. 型锻造 ≥W 平锻造 The value should be between 0.5 and 0.6.

[0044] Step 5: Forging the other end of the stepped shaft on the hammer: Immediately return the billet produced at one end to the furnace and heat it to the required forging temperature. The heating requirement is a furnace temperature rise of 1130℃±20℃, with a holding coefficient controlled at 0.35min / mm-0.5min / mm. The transfer time is the same as above. Using the same method as in Step 1, transfer it to a special anvil and forge the other end to the required stepped shaft forging size. The forging heats, forging dimensions, and forging requirements of Step 2 are the same as in Step 1. The main consideration is that the coaxiality of the forging should be corrected on the hammer in a timely manner after forging, which can be checked using a special template.

[0045] Step 6: Stress Annealing

[0046] Before forging, a natural gas furnace or electric furnace should be prepared for annealing. The formed parts should be subjected to stress-relief annealing immediately. The procedure is to transfer them directly to a 600℃ natural gas furnace after forging and hold them for 6 hours (air cooling after forging is not allowed), then cool them down to 500℃ and hold them for 1 hour. After removing them from the furnace, cover them with high-temperature cotton in a sheltered place and let them cool (exposed parts are not allowed). After air cooling to room temperature, remove the high-temperature cotton.

[0047] After stress-relief annealing, the furnace door must not be opened (the furnace door must be fully closed, and the dial markings can be raised by ≤50°C). Stress-relief annealing must be completed within 24 hours before proceeding to the conventional heat treatment process.

[0048] Step 7, Heat Treatment: Normalizing + Tempering; Quenching + Tempering

[0049] Step 8: Perform 100% mechanical property checks and magnetic particle testing on the forgings.

[0050] Example 1

[0051] (1) Design process flow: forging bar stock → sawing to the required length → processing into the required forging billet → forging one end → forging the other end → stress relief treatment → heat treatment → physical and chemical treatment.

[0052] (2) The blank material with the following specifications required by the process (Φ350×855)

[0053] (3) Process the raw material blanks (see Figure 1 )

[0054] (4) First draw the bar stock with a length of Φ350×415 at the large end to Φ260±5×680±5;

[0055] After dividing the Φ260±5×680±5 material, draw it to Φ230±5×850+10 (excluding the bulge) (see forging process for details). Figure 3 The forging deformation amount should be controlled at 30% to 35%;

[0056] (5) Forging Figure 2 and Figure 3 Completed in one forging cycle; record the actual forging time and final forging temperature; return the hot material to the furnace (place the unforged end in the rear area of ​​the heating furnace), and forge the small end (the end of the bar stock with a length of Φ350×355) with the following forging dimensions: first draw the bar stock with a length of Φ350×355 at the small end to Φ245±5×680±5;

[0057] (6) Next, stretch Φ245±5×680±5 to Φ210±5×870±5 (excluding the bulge).

[0058] (7) Record the actual forging time and final forging temperature; straighten the workpiece after forging and check whether the dimensions meet the requirements of the forging drawing. The coaxiality should be ≤5mm; and check the length, allowing the length dimension of the forging to exceed the positive tolerance.

[0059] (8) One natural gas furnace should be prepared in advance for stress-relief annealing. Stress-relief annealing is carried out in a natural gas furnace. Annealing process: After forging, transfer to a 600℃ natural gas furnace and hold for 6 hours, then cool to 500℃ and hold for 1 hour. Remove from the furnace and air-cool to room temperature in a sheltered place; cover with special high-temperature insulation cotton, and do not expose. After stress-relief annealing, it is not allowed to open the furnace door containing the annealed forging. The rest is carried out according to the original forging process. Next, a reasonably designed die is used to forge the rough shape for final shaping.

[0060] (9) The physical and chemical properties of the forgings after heat treatment meet the requirements shown in the figure.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A forming method for improving the influence of the internal structure of quenched and tempered steel forgings on magnetic particle testing, characterized in that, include: 35Cr2Ni4MoA / E is rapidly formed in the desired direction by forging fluidity, i.e., the anvil is drawn out to obtain the formed forging; The method for pre-treating the internal structure of formed forgings is stress-relieving annealing, with cooling at an annealing temperature of 580℃~620℃. The insulation material is cooled after a cooling treatment, then heat-treated, surface-processed, and then subjected to physical and chemical treatments, and finally heat-treated. 35Cr2Ni4MoA / E is rapidly formed in the desired direction using forging fluidity, i.e., anvil drawing, to obtain formed forgings, including: The raw materials are divided according to the volume dimensions required for the size of the forging steps; Pre-set the required anvil shape, which consists of two pieces, top and bottom; The segmented billets are fed into the furnace at ≤800℃ and heated to 800℃±50℃, then further heated to 1130℃±20℃ with a holding coefficient of 0.5min / mm. The hammer and anvil are preheated to 200℃~350℃. After the forgings are held at the set temperature for the set time, they are immediately taken out of the furnace and forged on a free forging hammer using a special anvil, while controlling the intermediate and final forging temperatures and forging time. The heated billet is removed from the furnace and transferred to a preheated special anvil, where one end of the forging is forged to the required size. The billet that has been produced at one end is immediately reheated in the furnace. The reheated billet is then removed from the furnace and transferred to the special anvil mentioned above. The other end of the forging is forged to the required forging size to obtain the formed part. Material sorting methods include: Using the required length at the maximum cross-section of the stepped shaft as a reference, the belt shape is machined along both sides of the maximum cross-section of the stepped shaft with a width-to-depth ratio of 4.5 / 1, and the required bar diameter with a fillet radius R = 1 / 10 is used to smoothly transition the shape. The calculation method for the external dimensions of this type of anvil includes: The pre-designed anvil has a semi-circular through hole at its length center, extending along its width, with a diameter D of the semi-circular through hole. 大 =D 小 +10mm, D 小 The minimum diameter of the forging is required; the center axis of the semi-circular through hole should coincide with the center line of the anvil along its length, and a tangent line of the semi-circle should be made at a 45-degree angle on both sides of the center line. The intersection of the tangent line and the anvil should be smoothly transitioned using the diameter of the required bar stock, R = 3 / 7. The shape and dimensions of the pre-designed anvil are perfectly symmetrical along the length direction. From one end of the forging to the desired forging size, including: The forging process employs a split-drawing method, forging one end to the required forging size. This step requires completion in one pass, and the forging size should be 0.02% larger than the dimensions specified in the drawing. The hammer reduction and feed rate should be controlled within 1 / 3 to 1 / 2 of the drawing size. During the drawing and rounding process, a manipulator should be used to rotate the billet, and repeated hammering and rounding at the same forging location are prohibited to prevent localized coarse grains in the forging. No interruptions are allowed during forging to allow for shorter forging time and better control of the final temperature. The forging dimensions should be measured promptly after forging. The forging temperature for split-lengthening is controlled at the same level as that for flat anvil forging (W-type forging ≥ W-flat forging (0.5-0.6)).

2. The method according to claim 1, characterized in that, Stress-relief annealing includes: Before forging, a natural gas furnace or electric furnace should be prepared for annealing. The formed parts should be immediately subjected to stress-relief annealing. The procedure is to directly transfer them to a natural gas furnace at 550-630℃ after forging and hold for 5.5-6.5 hours, then cool them down to 450-550℃ and hold for 0.5-1.5 hours. After taking them out of the furnace, cover them with high-temperature cotton in a sheltered place and let them cool to room temperature before removing the high-temperature cotton. Air cooling after forging is not allowed before transferring them to the furnace.

3. The method according to claim 2, characterized in that, After stress-relief annealing, the furnace door must not be opened, and the furnace door must be fully closed. The dial markings are allowed to rise ≤50℃. Stress-relief annealing must be completed within 24 hours before the conventional heat treatment process is carried out.

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