CN104741499B - Sandwich layer forging die and preparation method of forging die sandwich layer surfacing - Google Patents

Abstract

The invention discloses a sandwich layer forging die and a method for preparing the sandwich layer surfacing welding of the forging die. The sandwich layer forging die is between a cast steel base body and a bimetallic gradient surfacing material layer, and the surfacing layer is more plastic than the two. The soft welding material of the sandwich layer with lower yield strength; the preparation method of the forging die sandwich layer overlay welding comprises the following steps: using cast steel as the forging die matrix, welding the soft material of the sandwich layer on the matrix layer; The substrate of the welding sandwich layer material is then surfacing with the transition layer material, and the sandwich layer material is completely welded and covered to form a surfacing transition layer; finally, the high-temperature wear-resistant layer material is welded; after welding, temper to relieve stress, and then perform mechanical processing to obtain Mold; the sandwich layer forging die of the present invention has a long service life and high pressure bearing capacity of the cast steel matrix; the method of the present invention fundamentally solves the key bottleneck problem of low forging die life and high mold manufacturing cost, and can support various types of molds under high temperature and high pressure The die forging of materials provides a new manufacturing method for forging die manufacturing.

Description

A kind of preparation method of sandwich layer forging die and forging die sandwich layer surfacing welding

technical field

The invention belongs to the technical field of moulds, and in particular relates to a forging die with a sandwich layer and a preparation method for surfacing welding of the sandwich layer of the forging die.

Background technique

With the development of the country's heavy equipment manufacturing industry, equipment manufacturing industries such as large aircraft and shipbuilding need to rapidly upgrade their capabilities. The world's largest large-scale die forging hydraulic press (80,000 tons press) came into being. The forging dies used have been widely used in the production of large die forgings in aviation, aerospace, nuclear power, petrochemical and other fields, such as large aircraft fuselages Frames, landing gear, engine turbine discs, etc. The forging materials of these forgings mainly include aluminum alloys, high-temperature alloys, titanium alloys, etc., all of which need to be formed by forging dies. However, the forming temperature of large forgings of difficult-to-deform materials (high temperature alloys, titanium alloys, etc.) is high. During the forging process, due to the long contact time between the forgings and the mold, the mold bears high pressure, and the temperature rises rapidly on the surface of the cavity, and the temperature rises rapidly to Above 700°C, the strength and hardness of the working area of the mold will decrease rapidly, resulting in large deformation and serious wear of the mold, and the life of the mold is extremely low. After forging 1-2 pieces, the deformation of the mold is as high as 10mm or more, and the mold is seriously invalid and can no longer be used. .

At present, only H13 steel and other materials are used to prepare forging dies for large-scale forging hydraulic presses, which can meet the production needs of large-scale forging die hydraulic presses; however, although the life of forging dies is prolonged by using forged H13 steel modules to manufacture forging dies, H13 steel is expensive , The cost of forging billet material and post-forging heat treatment is nearly double that of ordinary process methods, and the manufacturing cost of forging die is quite high. Therefore, high manufacturing cost and extremely low die life have become the key bottlenecks restricting the production of large-scale hard-to-deform material die forging, and also become the key bottleneck of whether large-scale die forging hydraulic presses can be used. Finding a forging die preparation method that can significantly increase the service life of the forging die and reduce the manufacturing cost of the die has become an urgent problem in this technical field.

Contents of the invention

In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a sandwich layer forging die with a longer service life and a higher pressure bearing capacity.

Another object of the present invention is to provide a method for preparing forging die sandwich layer surfacing, which can prolong the life of the forging die, shorten the new product development cycle, and at the same time reduce the cost of die manufacturing, fundamentally solve the problem of The key bottleneck problems of the extremely low life of the die forging for large-scale difficult-to-deform materials and the high cost of die manufacturing have been solved.

To achieve the above object, the present invention adopts the following technical solutions: a sandwich layer forging die, including a cast steel matrix A, a transition layer C and a high-temperature wear-resistant layer D; Layer B; the sandwich layer B has better plasticity and lower yield strength than the cast steel matrix A and the transition layer C;

Among them, the plasticity range of the sandwich layer B is: δ elongation ≥ 14.7%, ψ shrinkage ≥ 31.2%; the yield strength range is: σs yield strength ≥ 550MPa.

Preferably, the δ elongation rate of the sandwich layer B is 14.7%-20%, the ψ shrinkage rate is 31.2%-36%, and the σs yield strength is 550-570 MPA.

A preparation method for overlay welding of a forging die sandwich layer, comprising the steps of:

1) Use cast steel as the mold matrix material to pour out the mold matrix to be welded; among them, the surfacing welding allowance is reserved for the cavity; the thickness of the surfacing welding allowance reserved depends on the specific mold type and model, and generally can be reserved 40~90mm.

2) On the base of the mold to be welded in step 1), along the shape of the reserved surfacing place, surfacing welding soft welding consumables with good plasticity and low yield strength for the sandwich layer are welded to 14~ below the contour line of the mold cavity. 16 mm; the good plasticity and low yield strength mean that its mechanical properties can meet the following standards: σ _s yield strength ≥ 550MPa, σ _b tensile strength ≥ 760MPa, δ elongation ≥ 14.7%, ψ shrinkage ≥ 31.2% , with a hardness of 30 to 35HRC; in this way, when the prepared mold is subjected to the high-pressure peak stress, the sandwich layer acts as a cushion between the transition layer and the cast steel matrix, and firstly produces elastic deformation or even a small amount of plastic deformation, which rapidly reduces the high-pressure peak stress. The diffusion is weakened, effectively protecting the safety of the cast steel matrix, and the cast steel matrix will not be cracked due to the high peak stress value of the cast steel matrix.

3) On the mold base with the sandwich layer welded in step 2), along the shape of the reserved surfacing welding margin and the shape of the sandwich layer, the transition layer welding materials with higher surfacing strength and hardness, cover all the sandwich layer materials Wrap it and continue welding to 8~11 mm below the contour of the mold cavity; the high strength and hardness means that its mechanical performance index can meet the following standards: σ _s yield strength ≥ 790MPa, σ _b tensile strength ≥ 1100MPa , δ elongation ≥ 11.7%, ψ shrinkage ≥ 28.9%, hardness 45-50HRC; in this way, the transition layer can not only combine well with the sandwich layer, but also effectively connect with the cast steel matrix in the upper area of the mold, and can also be connected with the subsequent The high-temperature wear-resistant layer is well bonded. Due to the addition of the sandwich layer material, the stress diffusion between the transition layer and the cast steel matrix becomes more uniform, and the stress concentration area under the cavity can effectively protect the safety of the cast steel matrix and prevent the transition layer material from being subjected to transverse tensile stress. source of cracks.

4) On the mold substrate with the transition layer welded in step 3), surfacing welding materials for the high-temperature wear-resistant layer cover the main wear-resistant working area or all wear-resistant areas of the mold, and weld to 4~6 mm on the contour line of the cavity; The mechanical performance index of the high-temperature wear-resistant layer welding material can reach the following standards: σ _s yield strength ≥ 1000MPa, σ _b tensile strength ≥ 1400MPa, δ elongation ≥ 9.6%, ψ shrinkage ≥ 26.5%, hardness 50～ 55HRC; the strength and hardness of this layer are higher than that of the transition layer and the sandwich layer, and the elongation, shrinkage, impact toughness and high temperature performance are good. It is a wear-resistant and thermal fatigue-resistant layer and plays a major role in the work of forging dies. Through the synergistic compatibility and combination of the above three layers of surfacing layer materials, the service life of the high-temperature wear-resistant layer and the transition layer can be extended because the sandwich layer material has a certain yield when subjected to high pressure.

5) Repeat the slow cooling process after three times of tempering for the mold after three times of surfacing, and then place the mold after the second slow cooling in the air and air cool to room temperature; among them, the tempering temperature is 530~570°C , slow cooling temperature to 160~180°C; this is because the mold will produce unstable structures such as martensite and austenite in the welding heat-affected zone, and there will be large internal stress at the same time; and if the cooling speed of the mold is too fast, it is easy to Produces hardened structure, leading to defects such as cracks; tempering and slow cooling treatment to obtain stable tempered martensite, which can improve the stability of the structure, so that the mold will no longer undergo structure transformation during use, so that its geometric size and performance remain stable ; At the same time, eliminate internal stress in order to improve the performance of the mold and stabilize its geometric dimensions; also improve its ductility or toughness , adjust the mechanical properties of the mold to meet the requirements of use; in order to prevent the first type of temper brittleness, high temperature tempering is adopted Fire, that is, the tempering temperature is controlled at 530 ° C ~ 570 ° C; in order to prevent the second type of temper brittleness, a second tempering slow cooling process is adopted; after the second slow cooling, the mold is placed in the air for air cooling to room temperature ; This is because after slow cooling to below 180 ℃, the structure and performance are basically stable, and can be cooled to room temperature in the air.

6) Machining the air-cooled mold in step 5) so that the dimensions of each part of the mold are in place, and the above-mentioned sandwich layer forging die is obtained. The part after overlay welding of the forging die has high hardness, and general machining cannot guarantee the size. The surface of the cavity after surfacing welding is very uneven, and the plane can be processed by a surface grinder or a CNC machined disc cutter first. Cutting, or directly grinding with a grinding wheel, makes the dimensions of each part of the mold in place.

As an optimization, in the step 1), the poured mold to be welded needs to be quenched at 920°C and tempered at 650°C, and oil-cooled to room temperature. In this way, the residual as-cast structure can be eliminated, and the structure can not be overheated, and the annealed structure can be avoided, so that the comprehensive mechanical properties can meet the product requirements.

In steps 2), 3) and 4) of the above technology, as an optimization, before the surfacing, the surface of the mold to be welded needs to be cleaned, and the oxide scale and welding slag on the surface of the surfacing layer are removed after the third surfacing is completed. Wherein the surface cleaning treatment refers to removing sand, scale, oil, rust, burrs and casting defects. Specifically, carbon arc gouging can be used to remove casting defects such as shrinkage cavities and cracks, and then sand, scale, oil stains, rust, burrs, etc. can be removed with a wind grinder gun to clean the mold surface.

As an optimization, in the above steps 2), 3) and 4), during the surfacing process, the mold is knocked intermittently to make it vibrate, and the vibration frequency is 20-40 times/minute; in this way, the deposited metal can be extended , to prevent hydrogen embrittlement, refine the grains of strengthened parts, smooth edges and corners, reduce stress concentration, improve the stability of dimensional accuracy, eliminate micro cracks and slag defects on the surface of surfacing welding, suppress the occurrence of cracks, and improve the fatigue life of surfacing welding metal ; Among them, refining the grain can not only improve the strength of the material, but also improve its plasticity and toughness; the stress generated in the strengthening process of double-layer metal surfacing welding can be better released, and the combination of hardness and toughness of each surfacing layer can be better. it is good.

As a further optimization, in the above steps 2) and 3), the material of the sandwich layer only covers part of the radian (40-60%) of the base layer according to the maximum stress distribution state, instead of the conformal welding completely covering the reserved area of the base; this It is because the yield strength of the sandwich layer material is very low, and the ideal state is even a semi-solid material. The main function is to spread the maximum stress, and then use the transition layer material to completely wrap the sandwich layer. The sandwich layer is between the transition layer and the cast steel matrix. Playing the role of a cushion, it first produces elastic deformation or even a small amount of plastic deformation, which quickly spreads and weakens the peak stress of high pressure, and effectively protects the safety of the cast steel matrix.

As a further optimization, in steps 2), 3) and 4) of the above technology, a mixed gas of CO ₂ and Ar is required for protection during surfacing welding, and the volume ratio of the gas is: Ar80%~90%, CO ₂ 10% to 20%; the mixed gas of CO ₂ and Ar is used to protect the molten pool and droplets, isolate them from the air, and prevent defects such as pores in the weld; the heat of the arc is concentrated under the compression of the protective gas flow , the welding speed is fast, the molten pool is small, the heat-affected zone is narrow, and the deformation of the weldment after welding is small; and because of the argon-rich mixed gas method, the spatter during the welding process is also significantly reduced, and the welding quality is improved.

In the above steps 2), 3) and 4), as a further optimization step, the wire feeding speed during welding is 5-8M/min, the welding current is 360-440A, and the welding voltage is 35-36V; the selection of the above parameter range is because , when the welding voltage is too low, there is a tendency to stick to the base metal; if the voltage is too high, the arc phenomenon will increase significantly, the molten pool will be unstable, and the spatter will also increase; the welding current will increase, and the penetration depth, fusion width and stack height of the weld bead will be uniform. It increases accordingly, while the dilution rate decreases slightly, but if the current is too large, the spatter will increase; with the increase of welding speed, the weld width and pile height of the weld bead decrease, and the penetration depth and dilution rate increase, but the welding speed is too high , will increase the occurrence rate of arc. In order to control a certain dilution rate and ensure the performance of the surfacing layer, the welding speed is generally controlled at 5-8M/min; appropriate welding parameters can stabilize the molten pool, prevent spatter, and control the dilution rate. Improves the properties of the resulting weld overlay.

In the above steps 2), 3) and 4), as a further step of optimization, the mold needs to be preheated to 450-500°C before surfacing, and the mold temperature must be kept above 300°C during the surfacing process; It can maintain a certain temperature during surfacing welding, so that the influence of temperature difference between the deposited metal and the base metal can be reduced, and various defects caused by the heat-affected zone can be avoided. Cold, as a result, the high-carbon cast steel base metal will generate martensite, the weld will be hardened, the microstructure and mechanical properties will deteriorate, and even fatal accidents such as cracks will occur.

The traditional forging industry currently mainly uses 5CrNiMo, 5CrMnMo, H13, etc. as die steels. These steels have certain hardenability, high temperature strength and impact toughness, but their service life is very low under high temperature and high pressure, and the general price is high, so it is difficult to apply Forging dies for die forging of difficult-to-deform materials. If the applicant's original invention "a method for preparing forging dies based on double-metal layer surfacing welding of cast steel substrate (ZL200910104604X)" is used to prepare forging dies for forging difficult-to-deform materials (high-temperature alloys, titanium alloys), the problem of die forging The forming temperature is higher, the contact time between the forging and the mold is longer due to the holding pressure, and the deformation resistance is greater, so it is difficult to guarantee a higher life. Therefore, the applicant proposed a new method for manufacturing the sandwich layer of the forging die, which is based on the applicant's original invention "a method for preparing forging dies based on double metal layer surfacing welding of cast steel substrate (ZL200910104604X)", and then Between the cast steel matrix and the transition layer, a closed layer of soft material with better plasticity than the two——sandwich layer welding consumables is surfacing. Under high pressure, the sandwich layer is allowed to undergo large elastic deformation or even small plastic deformation. The concentrated peak stress below the cavity rapidly diffuses and attenuates, and is transmitted to the cast steel matrix layer in an approximately uniformly distributed stress, thereby reducing the maximum stress on the cast steel matrix, making the cast steel matrix safer when under pressure, and avoiding peak stress directly This leads to cracks in the cast steel matrix, which in turn causes the mold to break and fail. Due to the addition of the sandwich layer material, the stress diffusion between the transition layer and the cast steel matrix becomes more uniform, and the stress concentration area under the cavity can effectively protect the safety of the cast steel matrix and prevent the transition layer material from being subjected to transverse tensile stress. source of cracks. In addition, since the material of the sandwich layer has a certain concession when subjected to high pressure, the service life of the high-temperature wear-resistant layer and the transition layer can be extended; this method can support difficult-to-deform materials under higher pressure and higher temperature under high temperature conditions die forging.

Forging of large-scale difficult-to-deform materials is prepared with a new method of manufacturing sandwich layers of forging dies, so that low-cost materials for cast steel substrates can be used, and resource saving and material recycling can be realized, which meets the requirements of sustainable development of the country and society; At the same time, because it is a casting mold, the production time is correspondingly shortened, saving time and cost; the proposal of the sandwich layer in the present invention greatly reduces the welding materials and welding workload for surfacing welding, and the function of the cushion improves the pressure bearing safety of the cast steel matrix It also improves the safety of the mold; when the mold is repaired after failure, because the transition layer and high-temperature wear-resistant layer materials are quite good, the wear-resistant layer material can be directly surfacing, the connection strength is good, and the repair cost is low; Not only that, the present invention adopts sandwich layer surfacing manufacturing technology to strengthen and toughen the surface of the forging die, so that the working area can reach or even exceed the performance of ordinary die steel 5CrNiMo, 5CrMnMo or H13, and realize cost reduction, energy saving and consumption reduction and improvement Purpose of mold life.

After the promotion of the present invention, it will surely encourage other types of mold fields in the industry to establish a batch of high-tech with huge market prospects, chain-promoting the sustainable development of this field, and becoming a demonstration project of energy saving, consumption reduction, and circular and healthy development.

Compared with the prior art, the present invention has the following beneficial effects:

1. The service life of the sandwich layer forging die of the present invention is increased by more than 50%. Through the surfacing of each gradient functional layer, the different effects of each gradient layer are synergistically brought into play, and the performance of the cast steel forging die is comprehensively improved, and the strength and strength of the working area are improved. Toughness; a layer of soft sandwich layer welding material is surfacing in the middle of the sandwich layer forging die. When the mold is subjected to high pressure stress, the sandwich layer acts as a cushion between the transition layer and the cast steel matrix, so that the cast steel matrix layer The stress distribution is more uniform, and the high pressure peak stress is rapidly diffused and weakened, so that the peak stress value of the cast steel matrix can be reduced, and the peak stress can not directly cause cracks in the cast steel matrix, resulting in mold fracture and failure, thereby improving the pressure bearing capacity of the cast steel matrix Safety, improve the pressure bearing capacity and overall safety performance of the sandwich layer mold.

2. The addition of the sandwich layer material of the present invention makes the stress diffusion between the transition layer and the cast steel matrix more uniform, and the stress concentration area under the cavity can effectively protect the safety of the cast steel matrix, and prevent the transition layer material from Crack sources appear when subjected to transverse tensile stress. In addition, because the material of the sandwich layer has a certain yield when subjected to high pressure, the service life of the high-temperature wear-resistant layer and the transition layer can be extended.

3. The proposal of the sandwich layer of the present invention greatly reduces the welding material and welding workload for overlay welding, and saves raw materials and workload; The high-temperature wear-resistant layer material is quite good, and can be directly welded with wear-resistant layer materials, with good connection strength and low repair cost; in the fields of forging die design, manufacture and remanufacturing, key part repair, material preparation, resource recycling, and green cycle manufacturing It has broad application value and development prospect.

4. The method of the present invention can be applied to the preparation of large-scale hard-to-deform material forging dies, can significantly extend the life of the forging dies, improve the pressure bearing capacity of the cast steel matrix forging dies, and increase the life of the sandwich layer forging dies by more than 50%; Fundamentally solve the key bottleneck problems of extremely low die life and high cost of die manufacturing for large die forging hydraulic presses for large hard-to-deform materials, and provide a revolutionary and innovative method for forging die manufacturing, which can support high temperatures Die forging forming of various materials under high pressure has inestimable significance to the mold industry.

5. By adopting the sandwich layer surfacing manufacturing technology of the present invention, the surface of the forging die is strengthened and toughened, so that the pressure bearing capacity of the cast steel matrix die is greatly improved, and the working area reaches or even exceeds the performance of ordinary die steel 5CrNiMo, 5CrMnMo or H13 , can be used for the preparation of forging dies for large-scale forging hydraulic presses, instead of using expensive H13 etc. to prepare forging dies for large-scale forging hydraulic presses, which saves more than 20% of the overall cost, reduces mold manufacturing costs, and reduces forging allocation The manufacturing cost is more economical and the development cycle of new products is shortened.

6. The present invention enables the utilization of low-cost cast steel matrix materials, and can realize resource saving and material recycling, meeting the requirements of sustainable development of the country and society; using relatively cheap cast steel as the mold matrix material, the entire to-be The strengthened mold is directly poured into the shape to be welded. Compared with the original new mold, it saves the forging process and machining time, reduces the cost, has a high utilization rate of the base material, shortens the development cycle of the new mold, and saves time and cost.

Description of drawings

Fig. 1 is the structural representation of the sandwich layer forging die cited in the specific embodiment;

Fig. 2 is the mold cross-sectional structure schematic diagram that is used to illustrate each surfacing layer situation in the specific embodiment;

In Figure 2, A is the mold base to be welded; B is the sandwich layer; C is the transition layer; D is the high temperature wear-resistant layer; E is the cavity contour.

detailed description

The present invention will be described in further detail below in conjunction with accompanying drawing and specific embodiment, and the raw material used in the embodiment is common commercially available unless otherwise specified.

Take the preparation process of the sandwich layer forging die as shown in Figure 1 below to further describe the present invention in detail, because the present invention makes creative contributions to the prior art in each step of the inventive method, rather than in forging The selection of die shape and type, so this specific embodiment only enumerates a forging die with a specific structure to describe the method in detail, but each step in the method of the present invention should be regarded as forging dies of different shapes and types. is suitable.

The sandwich layer forging die that needs to be prepared in this specific embodiment is the lower die of a common forging die, and its shape is shown in Figure 1, including a cast steel matrix A, a transition layer C and a high-temperature wear-resistant layer D; A layer of sandwich layer B is welded between the layers C; the sandwich layer B has better plasticity and lower yield strength than both the cast steel matrix A and the transition layer C;

Among them, the plasticity of the sandwich layer B is: δ elongation rate 14.7%, ψ shrinkage rate 31.2%; yield strength: σs yield strength 550MPa.

The sandwich layer surfacing preparation method of the above-mentioned sandwich layer forging die comprises the following steps:

a. Use cast steel as the mold base material to pour out the mold base A to be welded. Among them, the thickness of the surfacing welding allowance for the cavity is 40 mm; Process, the mold cavity is in the shape of a semi-circular arc, and the machining allowance is reserved; the poured forging die is quenched at 920°C and tempered at 650°C, and then oil-cooled to room temperature to improve its mechanical properties.

b. On the base body of the mold to be welded, A is firstly surfacing the soft welding material B of the sandwich layer with good plasticity and low yield strength along the pre-designed shape at the reserved surfacing margin. The thickness of the sandwich layer and the welding length are determined by the stress distribution state. It was decided to cover 40% of the radian of the base layer; under the action of stress diffusion in the sandwich layer, the peak stress should be reduced to the safe use range of the cast steel base, and welded to about 15 mm below the contour line of the mold cavity; wherein, the plasticity is good and Low yield strength means that its mechanical properties can meet the following standards: σ _s (yield strength) ≥ 550MPa, σ _b (tensile strength) ≥ 760MPa, δ (elongation) ≥ 14.7%, ψ (shrinkage) ≥ 31.2% , hardness 35 ~ 36HRC. In practice, you can choose low-hydrogen surfacing welding wires that are similar in composition to the cast steel matrix, or have similar properties in terms of plasticity and other properties after the same heat treatment, such as CD126. In this way, the sandwich layer can be well combined with the matrix, which improves the weldability and strength of the cast steel matrix, effectively connects the matrix layer with the transition layer and the high-temperature wear-resistant layer, and reduces the cost of welding materials.

c. On the substrate of the welded sandwich layer material, follow the shape of the reserved surfacing allowance and the shape of the sandwich layer, and the transition layer C with higher secondary surfacing welding strength and hardness, completely wrap the sandwich layer material, and continue Welded to about 10 mm below the contour line of the mold cavity; where the high strength and hardness mean that its mechanical performance indicators can meet the following standards: σ _s (yield strength) ≥ 790MPa, σ _b (tensile strength) ≥ 1100MPa, δ (elongation) ≥ 11.7%, ψ (shrinkage) ≥ 28.9%, hardness 45 ~ 50HRC. Due to the addition of the sandwich layer material, the stress diffusion between the transition layer and the cast steel matrix becomes more uniform, and the stress concentration area under the cavity can effectively protect the safety of the cast steel matrix and prevent the transition layer material from appearing under transverse tensile stress. source of cracks. In practice, you can choose a low-hydrogen surfacing welding wire, such as CD650, which is similar in composition to the cast steel matrix and sandwich layer, or has similar performance in terms of strength, hardness and toughness after the same heat treatment. In this way, the transition layer can be well combined with the sandwich layer and the matrix, effectively connecting the matrix layer, the sandwich layer and the high-temperature wear-resistant layer, and reducing the cost of welding materials.

d. Surfacing the high-temperature wear-resistant layer D three times on the transition layer, welding to about 5 mm on the contour line of the cavity; usually, the thickness of the three-time surfacing strengthening layer is about 40 mm, covering the working part of the mold; where the contour line is 5 mm About mm is the reserved machining allowance; the mechanical performance index of the reinforced layer D is: σ _s (yield strength) ≥ 1000MPa, σ _b (tensile strength) ≥ 1400MPa, δ (elongation) ≥ 9.6%, ψ( Shrinkage rate) ≥ 26.5%, hardness 50 ~ 55HRC; through the organic compatibility combination of three layers of surfacing layer materials, because the sandwich layer material has a certain concession when under high pressure, the service life of the high temperature wear-resistant layer and the transition layer can be improved. get extended. During specific implementation, the low-hydrogen surfacing welding wire with high hardness and good toughness can be selected, such as CDCo; The wear-resistant and thermal-fatigue-resistant performance layer plays a major role in the work of the forging die.

e. Repeat the tempering and slow cooling process twice for the mold after three times of surfacing, wherein the tempering temperature is 550°C and the slow cooling temperature is 180°C. After the second slow cooling, the mold is placed in the air for air cooling to room temperature.

f. Carry out mechanical processing to the mold after air cooling, make the size of each part of the mold in place, and make the sandwich layer forging mold as shown in Figure 1. The part after overlay welding of the forging die has high hardness, and general machining cannot guarantee the size. The surface of the cavity after surfacing welding is very uneven, and the plane can be processed by a surface grinder or a CNC machined disc cutter first. Cutting, or directly grinding with a grinding wheel, makes the dimensions of each part of the mold in place.

In the specific implementation, before the surfacing welding in the above step b, it is necessary to carry out pre-treatment of surfacing welding strengthening on the mold to be welded, including: 1) cleaning the surface of the mold to remove sand, scale, oil, rust, burrs and casting defects;

2) Overall preheating of the mold to 450°C;

3) The insulation material covers the mold, exposing the mold cavity to be surfacing; the process temperature is ≥300°C.

During the surfacing process of steps b, c and d, it is necessary to:

1) Adopt automatic CO ₂ , Ar mixed gas (protective gas volume ratio: Ar80%, CO ₂ 20%) protective surfacing welding process, and use Miller wire machine to perform one-time surfacing welding of sandwich layer B along the cavity on the surface of the mold to be strengthened , The welding wire feeding speed is 7M/min, the welding current is 400A, and the welding voltage is 36V. This layer is welded to about 15 mm below the contour of the cavity.

2) Adopt automatic CO ₂ , Ar mixed gas (protective gas ratio: Ar80%, CO ₂ 20%) to protect the metal surfacing welding process, and use the Miller wire machine to carry out the transition layer C secondary stacking on the surface of the mold to be strengthened along the cavity Welding, the welding wire feeding speed is 7M/min, the welding current is 400A, and the welding voltage is 36V. This layer is welded to about 10 mm below the contour of the cavity.

3) The strengthening process is carried out in multiple layers. After surfacing a layer of alloy material, remove the oxide skin and welding slag on the surface of the surfacing layer.

4) Three surfacing welding: surfacing special alloy material D (high temperature wear-resistant layer) on the welding layer after surface cleaning. The welding wire feeding speed is 7M/min, the welding current is 400A, and the welding voltage is 36V. The thickness of this layer is about 15 mm.

5) Finally, remove the scale and welding slag on the surface of the surfacing layer.

During the whole welding process, if the mold temperature is lower than 300°C, the furnace must be preheated again; during the welding process, beating hard with a hammer while welding. Among them, the structure of each surfacing layer is shown in Figure 2. In the figure, A is the cast steel mold base, B is the surfacing sandwich layer, C is the surfacing transition layer, D is the surfacing strengthening layer, and E is the actual cavity of the mold. contour line.

The above step e is used to complete the post-weld heat treatment, and the specific implementation includes:

1) The first stress relief and tempering: return to the furnace to heat up immediately after the surfacing, the furnace temperature is ≤450 ° C, the heating time is 0.4 h, the heating temperature is 550 ° C ± 20 ° C, and the holding time is based on the maximum geometric size of the module every 50 mm. Calculated in 1 hour, the holding time should ensure that the mold is preheated and heated thoroughly.

2) The first slow cooling: After the first stress relief and tempering, place the mold body in the thermal insulation bunker; the thermal insulation bunker is composed of ordinary river sand with an average particle diameter of 1 mm, and the temperature of the thermal insulation bunker is maintained at 180°C ;Use sand to completely bury the mold body, keep the heat preservation time ≥12h, and then take the mold out of the bunker; the temperature monitoring during the process is completed by an infrared thermometer.

3) The second stress-relief tempering: Take the mold body out of the heat preservation bunker and enter the second stress-relief tempering, and the process specification is the same as the first stress-relief tempering.

4) The second slow cooling: After the mold completes the second stress relief and tempering, place the mold body in the heat preservation sand pit to start the second slow cooling, and the process specification is the same as the first slow cooling.

5) Air cooling: After the mold completes the second slow cooling, the temperature is 180°C, it is taken out from the heat preservation bunker and placed in the air for air cooling to room temperature. At this time, most of the residual austenite in the mold transforms into martensite, and the martensite eliminates the internal stress. At this time, the hardness of the surfacing welding part is higher than that of the mold body.

The mold obtained after the above step e is finally mechanically processed through step f, and finally a complete forging mold with a sandwich layer of the shape shown in Figure 1 is obtained. The average surface hardness of the finished mold cavity is 50~55HRC, without cracks, inclusions and other defects. The sandwich layer can be well combined with the matrix to reduce the maximum stress on the cast steel matrix. The transition layer C can be well combined with the sandwich layer and the matrix, and the mechanical performance index is slightly better than that of the cast steel matrix after quenching and tempering treatment, which plays the role of transition connection and strengthens the matrix mold at the same time. The strength and hardness of the strengthening layer D are much higher than that of the transition layer C, and the elongation, shrinkage, impact toughness and high temperature performance are good, which can improve the hardness and toughness of the mold cavity. Through the synergistic compatibility of each gradient functional layer, the G35CrNiMo mold can be comprehensively improved, and the strength, toughness and other properties of its working area can be improved, which can replace the forging mold produced by integral forging.

In the actual experiment of this forging die, the die life of the sandwich layer forging die can be increased by more than 50%, which significantly prolongs the life of the forging die; and reduces the number of die changes, reduces downtime, and shortens the new product development cycle; The labor intensity of workers is reduced, and the utilization rate of equipment is greatly improved.

Because the most important part of the present invention's creative contribution to the prior art lies in the steps of the method itself, so in the specific implementation, many data or values are published optimized values, and are not listed for each specific numerical range. Explain different values. It should be considered that as long as these numerical values belong to the numerical range described in the description of the present invention, the present invention can be implemented and the purpose of the invention can be achieved, but the implementation effect may be relatively poor.

Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the invention can be carried out Modifications or equivalent replacements without departing from the spirit and scope of the technical solution of the present invention shall be covered by the claims of the present invention.

Claims (5)

1. a sandwich layer forging die, comprising a cast steel substrate, a transition layer and a high-temperature wear-resistant layer; it is characterized in that, a layer of sandwich layer is welded between the cast steel substrate and the transition layer; the plastic range of the sandwich layer is : δ elongation rate 14.7~20%, ψ shrinkage rate 31.2~36%; yield strength range: σs yield strength 550~570MPa; the plasticity of the sandwich layer is higher than that of the cast steel matrix and the transition layer, and the yield of the sandwich layer The strength is lower than the yield strength of the cast steel matrix and the transition layer. 2. a preparation method for forging die sandwich layer surfacing, is characterized in that, comprises the steps: 1) Use cast steel as the mold matrix material to pour out the mold matrix to be welded; among them, the surfacing welding allowance is reserved for the cavity; 2) On the base of the mold to be welded in step 1), along the shape of the reserved surfacing, surfacing welding materials with good plasticity and low yield strength for the sandwich layer; the sandwich layer surfacing covers 40~60 of the arc of the base layer %; The good plasticity and low yield strength of surfacing welding means that its mechanical performance index can meet the following standards: σ _s yield strength ≥ 550MPa, σ _b tensile strength ≥ 760MPa, δ elongation ≥ 14.7%, ψ shrinkage ≥ 31.2 %, hardness 30~35HRC; 3) On the mold base with the sandwich layer welded in step 2), along the shape of the reserved surfacing welding margin and the shape of the sandwich layer, the transition layer welding materials with higher surfacing strength and hardness, cover all the sandwich layer materials Wrap it and continue welding to 8~11 mm below the mold cavity contour; 4) On the mold substrate with the transition layer welded in step 3), surfacing welding materials for the high-temperature wear-resistant layer cover the main wear-resistant working area or all wear-resistant areas of the mold, and weld to 4~6 mm on the contour line of the cavity; The mechanical performance index of the high-temperature wear-resistant layer welding material can reach the following standards: σ _s yield strength ≥ 1000MPa, σ _b tensile strength ≥ 1400MPa, δ elongation ≥ 9.6%, ψ shrinkage ≥ 26.5%, hardness 50～ 55HRC; 5) Repeat the slow cooling process after three times of tempering for the mold after three times of surfacing, and then place the mold after the second slow cooling in the air and air cool to room temperature; among them, the tempering temperature is 530~570°C , slow cooling temperature to 160~180°C; 6) Machining the air-cooled mold in step 5), so that the dimensions of each part of the mold are in place, and the sandwich layer forging die described in claim 1 is obtained. 3. The method for preparing the surfacing welding of the sandwich layer of the forging die according to claim 2, characterized in that, in the step 1), the base of the mold to be welded is cast with high-carbon chromium-manganese steel. 4. The method for preparing the surfacing welding of the sandwich layer of the forging die according to claim 2, characterized in that the thickness of the surfacing welding allowance reserved in the step 1) is 40-90 mm. 5 . The method for preparing the surfacing welding of the sandwich layer of the forging die according to claim 2 , wherein the sandwich layer is welded to 14-16 mm below the contour line of the mold cavity in the step 2).