Process for improving the grain coarsening of near-surface metal of austenitic stainless steel valve body type forgings

Abstract

The application discloses a process for improving the grain coarsening of the near-surface layer of an austenitic stainless steel valve body type forging, which comprises the following steps: pre-drawing the ingot by using an upper flat anvil and a lower V-shaped anvil; once-upsetting deformation of the blank by using upper and lower conical surface plates; wide-anvil strong-pressing process and round-rolling blanking; turning the blank by 90 degrees along the axial direction, twice-upsetting deformation of the blank by using upper and lower conical surface plates; turning the blank by 90 degrees along the axial direction, once-drawing of the blank by using upper and lower multi-ribbed anvils, and round-rolling blanking; turning the blank by 90 degrees along the axial direction, three times-upsetting deformation of the blank by using upper and lower conical surface plates; turning the blank by 90 degrees along the axial direction, twice-drawing of the blank by using upper and lower multi-ribbed anvils; first six-face finishing of the blank by using a tooth-shaped anvil; and second six-face finishing of the blank by using a tooth-shaped anvil after rotating the blank by 90 degrees. The application not only ensures that the internal metal grains are sufficiently refined, but also improves the stress state of the near-surface layer of the forging, and realizes precise control of the grain size of the near-surface layer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of forging, and particularly relates to a process for improving the coarse grain of near-surface metal of an austenitic stainless steel valve body type forging. BACKGROUND

[0002] With the rapid development of the economy of China, the demand for stainless steel products is rapidly increasing in the fields of chemical industry, military industry, power plants, biological materials, marine facilities, heat exchangers, petroleum and the like. Due to the excellent characteristics of austenitic stainless steel, the steel grade of the austenitic stainless steel is the most and the use amount is the largest among stainless steels, accounting for about 65% of the entire stainless steel output. The grain size is one of the important indexes affecting the corrosion resistance of the austenitic stainless steel, and the better the grain size and uniformity, the stronger the corrosion resistance of the material. Due to the material characteristics of the austenitic stainless steel, the grain refinement cannot be achieved through the phase change principle of traditional heat treatment, and only the fine and uniform grain structure can be obtained through forging deformation and process control.

[0003] At present, the austenitic valve body type forging adopting the traditional forging process has coarse grain size of the near-surface metal, which affects the ultrasonic flaw detection effect. The reason is that the internal metal flow rate of the forging adopting the traditional forging process method is fast, the internal pores are quickly pressed and deformed, and the fine grain structure can be obtained. However, the contact area of the auxiliary tool with the blank is large, the friction is large, the metal flow of the near-surface metal of the forging is difficult, the forging deformation is small, and the coarse grains generated during high-temperature holding are not fully deformed and refined.

[0004] In recent years, with the development of forging process, the process method of wide anvil strong pressure + controlled temperature narrow anvil deformation has been gradually developed for the grain size difference and near surface metal grain coarsening of austenitic stainless steel forgings. For example, the Chinese patent application with publication number CN111790865A discloses a forging process method for refining the grain of austenitic stainless steel, which can solve the problem of coarse grain structure of forgings and improve the corrosion resistance of austenitic stainless steel. According to the flow deformation of the metal in each region of the forging during the forging process, the invention proposes a wide anvil strong pressure deformation method and a controlled temperature narrow anvil uniform deformation method, that is, the forging is first forged by the wide anvil strong pressure deformation method to make the inner layer of the forging fully deform, and then the subsequent forging is completed by the controlled temperature narrow anvil uniform deformation method to make the surface layer of the forging also fully deform. According to the operation steps and key points described in the invention, the internal pores of the forging can be quickly compressed, and the surface layer and the inner layer of the forging can obtain fine grain structure, meeting the requirement of grain size≥4 level. However, the above process method controls the contact area of the auxiliary tool and the billet to promote the full deformation of the near-surface metal, and the smaller the anvil amount, the more fully the near-surface metal deforms, which is more conducive to controlling the coarsening of the near-surface metal. However, due to the small anvil amount, it is difficult to control the synchronous deformation of the metal in different parts, which also seriously restricts the forging efficiency, resulting in repeated heating in high temperature furnace, which is not conducive to accurately controlling the grain size of the near-surface metal.

[0005] The Chinese invention patent with publication number CN110935827B discloses a forging method for large specification fine-grained austenitic valve steel SNCrW, aiming to solve the problems of serious segregation of primary carbides in the as-cast structure of the ingot, massive precipitation of secondary carbides in the corner of the billet, and coarse structure in the core. The technical solution of the invention is to produce an electric ingot with qualified chemical composition by adopting EAF / non-vacuum induction furnace+LF+VOD / VHD+ESR smelting process, and to adopt radial fast forging combined forging method to solve the problems of the as-cast structure of the ingot by controlling high-temperature homogenization treatment before forging, heating temperature of the billet, re-burning time of the billet, upsetting amount, lengthening and pressing amount, deformation amount and deformation mode of each heating, and length of radial forging billet. The invention has the beneficial effect that the product is large specification fine-grained austenitic stainless steel SNCrW rod with qualified macrostructure, grain size≥6 level, and A-level of GB / T 4162, meeting the requirements of domestic valve manufacturing. However, the above-mentioned patent adopts smelting control and forging temperature control method to promote the refinement of the metal grain of the forging, but does not provide specific control method for the control of the near-surface metal grain size. SUMMARY

[0006] In view of the shortcomings of the existing methods, the present application provides a process for improving the near-surface metal grain coarsening of austenitic stainless steel valve body forgings.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0008] The application discloses a process for improving the grain coarsening of near-surface metal of an austenitic stainless steel valve body type forging, which comprises the following steps:

[0009] Step one: pre-drawing of the steel ingot by using an upper flat anvil and a lower V-shaped anvil;

[0010] Step two: once-upsetting deformation of the blank obtained in step one by using upper and lower conical surface plates;

[0011] Step three: strong pressing process of the blank obtained in step two by using a wide anvil to round the blank;

[0012] Step four: 90-degree axial turning of the blank obtained in step three, and twice-upsetting deformation of the blank by using upper and lower conical surface plates;

[0013] Step five: 90-degree axial turning of the blank obtained in step four, and once-drawing of the blank by using upper and lower multi-edge anvils to round the blank;

[0014] Step six: 90-degree axial turning of the blank obtained in step five, and three times-upsetting deformation of the blank by using upper and lower conical surface plates;

[0015] Step seven: 90-degree axial turning of the blank obtained in step six, and twice-drawing of the blank by using upper and lower multi-edge anvils;

[0016] Step eight: first six-face finishing of the blank obtained in step seven by using a tooth-shaped anvil;

[0017] Step nine: 90-degree rotation of the blank obtained in step eight, second six-face finishing of the blank by using a tooth-shaped anvil, and finishing of the product.

[0018] Preferably, the pre-drawing reduction in step one is not less than 50 mm.

[0019] Preferably, the reduction of the wide-anvil strong pressing method in step three is 16%-20%.

[0020] Preferably, the reduction of the multi-edge anvil in step five is 16%-20%.

[0021] Preferably, the reduction of the multi-edge anvil in step seven is 16%-20%.

[0022] Preferably, the finishing amount in steps eight and nine is 30-40 mm.

[0023] The application has the following positive effects:

[0024] 1. The pre-drawing process in step one realizes preliminary deformation of the near-surface metal along the diameter direction, and the main purpose is to change the as-cast structure of the near-surface metal along the diameter direction into a forged structure, which is beneficial to the deformation of the near-surface metal in a good plastic state.

[0025] The step two, the step four and the step six of the present application are conducted three times of up and down taper face plate upsetting deformation, which gradually transits from point contact to line contact, improves the stress state of the surface layer metal on the basis of achieving the purpose of traditional upsetting method, realizes sufficient deformation of the near surface layer metal at both ends, avoids deformation dead zone and prevents cracking of the near surface layer metal under large deformation.

[0026] The step three of the present application adopts wide anvil strong pressing process, mainly aims to improve the effect of welding core casting defects by large anvil amount and large reduction, and the step five and the step seven are conducted twice of up and down multi-rib anvil elongation. In the multi-rib anvil elongation stage, the near surface layer metal in the deformation area is divided into several parts to be formed respectively due to the special design of the hammer anvil. The convex surface anvil position area is deformed first and simultaneously contacted and deformed respectively, and the concave surface anvil position area is deformed later and simultaneously contacted and formed respectively, which not only ensures the increase of the deformation area at each hammer reduction, but also realizes local small anvil amount forging deformation. Compared with traditional narrow anvil forging, the control efficiency is higher, the fire times are less, and the near surface layer metal structure improvement effect is better.

[0027] The step eight and the step nine of the present application are conducted twice of six surface finishing. Due to the tooth-shaped structure design of the hammer anvil, the near surface layer metal in the deformation area is divided into several parts to be formed respectively during forging. The deformation area is gradually increased with the deformation, and the purpose of multi-anvil position deformation at each hammer reduction is achieved (synchronous and asynchronous, simultaneous and non-simultaneous deformation). The main purpose is to change the stress state of the near surface layer metal, increase the deformation amount of the near surface layer metal in the last fire time, and accurately control the near surface layer grain size.

[0028] The present application adopts taper face plate multiple upsetting, wide anvil, multi-rib anvil elongation and tooth-shaped anvil finishing, which ensures sufficient forging ratio, fully welds the inherent metallurgical defects in the core, and improves the near surface layer metal grain size. The taper face plate upsetting not only realizes the end near surface stage deformation, but also improves the stress state and controls the cracking. The taper face plate multiple upsetting and wide anvil, multi-rib anvil multiple elongation are alternately conducted, which not only avoids the metal deformation "blind area" of the contact part between the near surface and the auxiliary tool, but also ensures that the near surface metal bears multiple stress states in the repeated upsetting and elongation process, and improves the deformation of the near surface metal at multiple angles. The control of internal grain size is beneficial to improving the near surface layer metal grain size.

[0029] 2. The present application adopts multi-directional forging process and different deformation stage different auxiliary shape deformation control method, proposes main deformation taper face plate upsetting and wide anvil strong pressing process, and adopts multi-rib anvil elongation and tooth-shaped anvil finishing process control method for finished products. Not only the internal metal grain is fully refined, but also the stress state of the near surface layer metal is improved, the synchronization of the near surface layer metal deformation is ensured, the near surface layer metal grain size is controlled, the coarse problem of the near surface layer grain size is improved, the forging efficiency is high and the quality is stable. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A schematic diagram of the conical surface plate structure of the present application;

[0031] Figure 2 A schematic diagram of the multi-rib anvil structure of the present application;

[0032] Figure 3 A schematic diagram of the tooth-shaped anvil structure of the present application;

[0033] Figure 4 A schematic diagram of the upsetting of the conical surface plate of the present application;

[0034] Figure 5 A schematic diagram of the wide anvil strong pressing of the present application;

[0035] Figure 6 A schematic diagram of the elongation of the multi-rib anvil of the present application;

[0036] Figure 7 A schematic diagram of the finishing of the tooth-shaped anvil of the present application;

[0037] Figure 8 A process flow diagram for improving the grain coarsening of the near-surface metal of an austenitic stainless steel valve body forging;

[0038] Figure 9 A microstructure grain diagram of the near-surface of the forging obtained in Example 1 of the present application;

[0039] Figure 10 A microstructure grain diagram of the near-surface of the forging obtained in Example 2 of the present application;

[0040] Figure 11 A microstructure grain diagram of the near-surface of the forging obtained in Example 3 of the present application. DETAILED DESCRIPTION

[0041] The embodiments of the present application are described in detail in conjunction with the specific embodiments, which are based on the technical solutions of the present application, and give detailed implementation manners and specific operation processes, but the protection scope of the present application is not limited to the following embodiments.

[0042] Reference Figures 1-8 A process for improving the grain coarsening of the near-surface metal of an austenitic stainless steel valve body forging, which adopts the following steps: overall pre-elongation of the steel ingot, upsetting of the upper and lower conical surface plates, wide anvil strong pressing elongation, round rolling and blanking, upsetting of the upper and lower conical surface plates, elongation of the upper and lower multi-rib anvil, upsetting of the upper and lower conical surface plates, elongation of the upper and lower multi-rib anvil, first finishing of the upper and lower tooth-shaped anvil, second finishing of the upper and lower tooth-shaped anvil, trimming and product delivery, which are described in detail as follows:

[0043] Example 1

[0044] A process for improving the grain coarsening of the near-surface metal of an austenitic stainless steel valve body forging, which includes the following steps:

[0045] Step one, according to the weight of the forging process to match the ingot type, select 32T top pouring ingot type, adopt the upper flat anvil and the lower V anvil to pre-draw to the diameter of 1150mm and the length of 3200mm, the pre-drawing reduction is 50mm;

[0046] Step two, adopt the upper and lower conical surface plate to upset the blank of step one to the height of 1100mm and the diameter of 1980mm;

[0047] Step three, take the blank of step two to perform the wide anvil strong pressing process, according to eight passes to design: the first pass reduction is 320mm, the second pass reduction is 330mm, the third pass reduction is 280mm, the fourth pass reduction is 300mm, the fifth pass reduction is 250mm, the sixth pass reduction is 270mm, the seventh pass reduction is 230mm, and the eighth pass reduction is 240mm, after the square drawing, the rolling down is performed: the diameter is 1285mm and the length is 2540mm, the wide anvil strong pressing reduction is 16%;

[0048] Step four, turn the blank of step three by 90° along the axial direction, adopt the upper and lower conical surface plate to upset the deformation, the upset control size is the height of 1100mm and the diameter of 1960mm;

[0049] Step five, turn the blank of step four by 90° along the axial direction, adopt the upper and lower multi-edge anvil to square draw and lengthen, the reduction is controlled according to 20%, and the rolling down is: the diameter is 750mm and the length is 1250mm;

[0050] Step six, turn the blank of step five by 90° along the axial direction, adopt the upper and lower conical surface plate to upset, the upset control size is the height of 860mm and the diameter of 905mm;

[0051] Step seven, turn the blank of step six by 90° along the axial direction, adopt the upper and lower multi-edge anvil to square draw and lengthen, the reduction is controlled according to 20%;

[0052] Step eight, adopt the tooth-shaped anvil to perform the first six-face finishing on the blank of step seven, the finishing amount is 35mm;

[0053] Step nine, turn the blank of step eight by 90° (crossed with the direction of the first finished blank), adopt the tooth-shaped anvil to perform the second six-face finishing, the finishing amount is 35mm, and the finished product is obtained after the trimming.

[0054] Referring to Figure 9 , by adopting the forging technology of the embodiment, the valve body forging has fine and uniform near-surface grain structure, and the grain size is 5 levels.

[0055] Embodiment 2

[0056] A process for improving the grain coarsening of the near-surface metal of an austenitic stainless steel valve body forging, comprising the following steps:

[0057] Step one, according to the weight of the forging process to match the ingot type, select 32T top pouring ingot type, adopt the upper flat anvil and the lower V anvil to pre-draw to the diameter of 1150mm and the length of 3200mm, the pre-drawing reduction is 50mm;

[0058] Step two, adopt the upper and lower conical surface plate to upset the blank of step one to the height of 1100mm and the diameter of 1980mm;

[0059] Step three, take the blank of step two to perform the wide anvil strong pressing process, according to eight passes to design: the first pass reduction is 360mm, the second pass reduction is 370mm, the third pass reduction is 310mm, the fourth pass reduction is 330mm, the fifth pass reduction is 280mm, the sixth pass reduction is 300mm, the seventh pass reduction is 250mm, and the eighth pass reduction is 270mm, after the square drawing, the rolling down is performed: the diameter is 1245mm and the length is 2700mm, the wide anvil strong pressing reduction is 18%;

[0060] Step four, turn the blank of step three by 90° along the axial direction, adopt the upper and lower conical surface plate to upset the deformation, the upset control size is the height of 1100mm and the diameter of 1960mm;

[0061] Step five, turn the blank of step four by 90° along the axial direction, adopt the upper and lower multi-edge anvil to square draw and lengthen, the reduction is controlled according to 18%, and the rolling down is performed: the diameter is 750mm and the length is 1250mm;

[0062] Step six, turn the blank of step five by 90° along the axial direction, adopt the upper and lower conical surface plate to upset, the upset control size is the height of 860mm and the diameter of 905mm;

[0063] Step seven, turn the blank of step six by 90° along the axial direction, adopt the upper and lower multi-edge anvil to square draw and lengthen, the reduction is controlled according to 18%;

[0064] Step eight, adopt the tooth-shaped anvil to perform the first six-face finishing on the blank of step seven, the finishing amount is 40mm;

[0065] Step nine, turn the blank of step eight by 90° (cross the direction of the first finished blank), adopt the tooth-shaped anvil to perform the second six-face finishing, the finishing amount is 40mm, and the finished product is obtained after the finishing.

[0066] Referring to Figure 10 , by adopting the forging technology of the embodiment, the valve body forging near the surface layer has fine and uniform grain structure, and the grain size is 5 levels.

[0067] Embodiment 3

[0068] A process for improving the grain coarsening of the near-surface layer metal of an austenitic stainless steel valve body forging, comprising the following steps:

[0069] Step one, according to the weight of the forging process, the ingot type is matched, the 32T upper injection ingot type is selected, the upper flat anvil and the lower V anvil are used, the integral pre-drawing is carried out to 1150mm in diameter and 3200mm in length, and the pre-drawing reduction is 52mm;

[0070] Step two, the blank in step one is upset to 1100mm in height and 1980mm in diameter by using the upper and lower conical surface plates for full cross-section upsetting;

[0071] Step three, the blank in step two is subjected to wide anvil strong pressing process, which is designed in eight passes: the first pass reduction is 400mm, the second pass reduction is 420mm, the third pass reduction is 330mm, the fourth pass reduction is 360mm, the fifth pass reduction is 300mm, the sixth pass reduction is 320mm, the seventh pass reduction is 270mm, and the eighth pass reduction is 290mm, and after the square bar drawing, the rolling down is carried out: the diameter is 1260mm, and the length is 2700mm, and the wide anvil strong pressing reduction is 20%;

[0072] Step four, the blank in step three is turned by 90° along the axial direction, and is subjected to upsetting deformation by using the upper and lower conical surface anvil, and the upsetting control size is 1100mm in height and 1960mm in diameter;

[0073] Step five, the blank in step four is turned by 90° along the axial direction, and is subjected to square bar drawing and lengthening by using the upper and lower multi-edge anvil, and the reduction is controlled according to 16%, and the rolling down is: the diameter is 750mm, and the length is 1250mm;

[0074] Step six, the blank in step five is turned by 90° along the axial direction, and is subjected to upsetting by using the upper and lower conical surface plate, and the upsetting control size is 860mm in height and 905mm in diameter;

[0075] Step seven, the blank in step six is turned by 90° along the axial direction, and is subjected to square bar drawing and lengthening by using the upper and lower multi-edge anvil, and the reduction is controlled according to 16%;

[0076] Step eight, the first six-face finishing of the blank in step seven is carried out by using the tooth-shaped anvil, and the finishing amount is 30mm;

[0077] Step nine, the blank in step eight is rotated by 90° (crossed with the direction of the first finished blank), and the second six-face finishing is carried out by using the tooth-shaped anvil, and the finishing amount is 40mm, and the finished product is obtained after trimming.

[0078] Referring to Figure 11 By using the forging technology in the embodiment, the valve body forging has fine and uniform near-surface grain structure, and the grain size is 5 levels.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the present application, and other modifications or equivalent replacements to the technical solutions of the present application made by those skilled in the art should be covered in the scope of the claims of the present application.

Claims

1. A process for improving the grain coarsening of near-surface metal of an austenitic stainless steel valve body type forging, characterized by, It comprises the following steps: Step one: pre-drawing of the ingot by using upper flat anvil and lower V anvil; Step two: 1 time upsetting deformation of the billet obtained in step one by using upper and lower conical anvil; Step three: round rolling of the billet obtained in step two by using wide anvil and strong pressing process; Step four: 2 times upsetting deformation of the billet obtained in step three by using upper and lower conical anvil after turning the billet by 90° along the axial direction; Step five: 1 time drawing of the billet obtained in step four by using upper and lower multi-edge anvil after turning the billet by 90° along the axial direction, and round rolling of the billet; Step six: 3 times upsetting deformation of the billet obtained in step five by using upper and lower conical anvil after turning the billet by 90° along the axial direction; Step seven: 2 times drawing of the billet obtained in step six by using upper and lower multi-edge anvil after turning the billet by 90° along the axial direction; Step eight: 1 time six-surface finishing of the billet obtained in step seven by using tooth-shaped anvil; Step nine: 2 times six-surface finishing of the billet obtained in step eight by using tooth-shaped anvil after turning the billet by 90°, and finishing and delivery of the product.

2. The process for improving the grain coarsening in the near surface metal of a wrought austenitic stainless steel valve body according to claim 1, wherein The pre-drawing reduction in step one is not less than 50 mm.

3. The process for improving the grain coarsening in the near surface metal of a wrought austenitic stainless steel valve body according to claim 1, wherein The reduction in the wide anvil and strong pressing method in step three is 16%-20%.

4. The process for improving the grain coarsening in the near surface metal of austenitic stainless steel valve body type forgings of claim 1, wherein The reduction in the multi-edge anvil in step five is 16%-20%.

5. The process for improving the grain coarsening in the near surface metal of a wrought austenitic stainless steel valve body according to claim 1, wherein The reduction in the multi-edge anvil in step seven is 16%-20%.

6. The process for improving the grain coarsening in the near surface metal of a wrought austenitic stainless steel valve body according to claim 1, wherein The finishing amount in steps eight and nine is 30-40 mm.

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