Hot shearing and extruding short-process forming method for thick-wall cylinder based on hollow casting blank

Abstract

The invention discloses a thick-wall cylinder hot shearing extrusion short-process forming method based on a hollow casting blank, and belongs to the technical field of manufacturing of hard-to-deform alloy thick-wall cylindrical parts. The method comprises the following steps that 1, the thick-wall hollow casting blank is prepared; step 2, hot shearing extrusion; step 3, heat treatment; and step 4, finish machining. The hollow casting blank is prepared by adopting electroslag remelting or electroslag liquid pouring refining; according to the hot shearing extrusion, the hollow casting blank is directly subjected to hot extrusion forming through an annular cylindrical part shearing extrusion die, the technological processes of repeated heating, multi-step hot forging blank manufacturing and the like are omitted, one or two heating number forming is directly conducted, the production cost of materials, energy, manpower and the like can be reduced by about 15%-30%, and the forming and manufacturing efficiency of the annular cylindrical part is improved; the forming-forming effect of the thick-wall cylinder is improved, and meanwhile short-process forming manufacturing of the thick-wall cylinder is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of manufacturing thick-walled cylindrical parts of difficult-to-deform alloys, and relates to a short-process forming method of a thick-walled cylinder based on hot shearing and extrusion of a hollow casting. Background Art

[0002] Large thick-walled cylindrical parts are basic parts for major technical equipment such as power equipment, pressure vessels, and petrochemicals. Their quality directly affects the operational reliability of major technical equipment. At present, the commonly used processing and production methods for annular cylindrical parts are solid steel ingot preparation-hot forging-rough processing-heat treatment-finishing-finished products. Traditional large thick-walled cylindrical forgings use solid steel ingots for forging, which has many processes and complicated operations. After the solid steel ingots are drawn, upsetting, punching and other blanking processes, some macro segregation will remain on the inner wall of the cylinder. These defects will have a serious impact on subsequent processing and use. Among them, the hot forging after punching blanking often uses methods such as mandrel drawing + horse bar reaming, rolling reaming, and hot extrusion. The free forging process of mandrel drawing + hole expansion has many forming fires, poor controllability of temperature and deformation during the forming process, and its forming method is intermittent forming with local loading along the circumference of the cylindrical part, which will cause forming defects such as difficult to control the deformation size of the cylindrical part and uneven wall thickness; rolling hole expansion forming has the characteristics of local loading continuous rapid forming, but due to the fast speed, the deformation of the cylindrical part in each circle is small, resulting in poor forging penetration along the wall thickness direction, and the internal structure cannot be fully softened and the performance is poor. The hot extrusion process is used to process the cylindrical part. The metal is under strong three-dimensional compressive stress in the deformation zone, the plastic deformation capacity of the metal is improved, and the grain structure is improved; however, the caliber and wall thickness of the thick-walled cylindrical part are large, requiring a large-tonnage extruder, and the extrusion ratio is limited. The deformation of a single extrusion is small, and the temperature drops quickly, often resulting in "stuffy car" and other situations, which makes the wall thickness deformation of the extruded part uneven, and the structure and performance after extrusion are uneven.

[0003] With the continuous research and development of hollow ingot smelting technology, the hollow ingot has a dense structure and small segregation and looseness, which provides a theoretical basis and experimental guarantee for improving the homogeneity of the inner wall of large cylindrical forgings. Therefore, the use of hollow billets for direct hot forging to produce annular cylindrical products shortens the process flow compared with the traditional forging process, and has the characteristics of low cost and energy saving. However, when hot forging hollow billets directly, how to achieve effective control of the hot forming process of cylindrical parts on the basis of achieving large plastic deformation, and how to achieve strong deformation, fine homogenization, and coarse solidification structure of steel ingots, these problems have become technical problems that restrict the high-quality manufacturing of thick-walled cylindrical parts. Summary of the invention

[0004] The purpose of the embodiments of the present invention is to solve the technical problems such as complex procedures, difficult process control, uneven deformation, and poor organizational performance in the hot forming process of difficult-to-deform alloy thick-walled cylindrical parts, and to provide a thick-walled tube hot shear extrusion short-process forming method based on hollow ingots, which can not only realize the direct extrusion forming of hollow ingots to prepare thick-walled cylindrical parts, but also realize the hot shear extrusion composite large deformation effect under the total continuous deformation of "shear strain + compression / tensile strain + shear strain"; at the same time, through strong shear deformation, the coarse solidification structure of the steel ingot can be effectively refined and homogenized, so as to achieve integrated control of the forming properties of thick-walled cylindrical parts, and can meet the green and environmentally friendly short-process production of large thick-walled cylindrical parts.

[0005] In order to solve the above technical problems, an embodiment of the present invention provides a short-process forming method of a thick-walled tube by hot shear extrusion based on a hollow casting, comprising the following steps: Step 1, preparation of thick-walled hollow ingot; Step 2, hot shear extrusion: after heating and heat preservation, the hollow ingot prepared in step 1 is directly subjected to hot shear extrusion deformation by using a ring-cylinder shear extrusion die under the pressure of an extruder; Step 3, heat treatment: normalizing or quenching and tempering or solution treatment of the thick-walled cylindrical part obtained in step 2; Step 4, finishing: The thick-walled cylindrical part obtained in step 3 is finished by processing equipment so that the inner and outer surfaces and the end face dimensions reach the required dimensions of the finished product.

[0006] Preferably, in step 1, a hollow cast billet is used as a thick-walled tube forming billet. During the axial extrusion deformation process of the traditional hollow billet, continuous shear deformation of the thick-walled billet is introduced by designing a suitable shear angle. The thick-walled tube has radial shear deformation added on the basis of circumferential compression deformation (reduction) or tensile deformation (expansion), thereby improving the extrusion composite large deformation effect of the thick-walled tube and realizing short-process manufacturing of the thick-walled tube.

[0007] Preferably, in step 2, after heating and heat preservation, the hollow casting blank is directly subjected to hot shear extrusion deformation using a ring-cylinder shear extrusion die under the pressure of an extruder device; the steps include: S1, preparing a cylindrical hollow ingot to be formed, and using an annular furnace to heat the hollow ingot to an initial extrusion temperature and keep it warm for later use; S2, preheating the extrusion die, spraying lubricant on the forming surface of the extrusion forming channel; taking out the hollow billet heated in step S1, spraying lubricant on the inner and outer walls of the hollow billet, and then quickly putting it into the extrusion die channel, and placing the extrusion pad on top of the hollow billet; S3, take out the extrusion punch preheated in step S2, and then quickly place it on the extrusion pad, and use a pressure device to perform hot shear extrusion on the hollow billet at an extrusion speed of 30 mm / s to 70 mm / s; S4. After extrusion, cut off the head and tail of the material for subsequent heat treatment.

[0008] Preferably, the heat treatment process in step 3 can adopt multiple normalizing treatments after extrusion, and the multiple normalizing mechanism with gradually lowering normalizing temperature can adjust and refine the grains; the heat treatment process can adopt solid solution treatment, which can make the grains after deformation uniform and improve its plastic mechanical properties; the heat treatment process can adopt quenching and tempering treatment, which can improve the hardness and tensile strength of the product; and rough processing can be performed before heat treatment to remove lubricants and scales on the inner surface and end face of the cylindrical part.

[0009] Preferably, the finishing in step 4 uses processing equipment such as a cylindrical grinder, a milling machine and a machining center to finish the heat-treated cylindrical part so that the inner and outer surfaces and the end face dimensions reach the required dimensions of the finished product.

[0010] Further, in step 1, the thick-walled hollow ingot is prepared by electroslag remelting or electroslag liquid casting refining, the hollow ingot is in the shape of a ring cylinder, the hollow ingot is prepared by electroslag remelting, the electrode melting rate or the slag-metal interface rising rate is controlled below 0.1 mm / s, and the bottom heat transfer coefficient is 500 W / m 2 / ℃; the electroslag liquid casting and refining is used to prepare the hollow ingot, the casting temperature is 1415℃, the casting speed is 25kg / s, the inner and outer surfaces are cooled simultaneously, and the boundary condition is that the inner wall interface heat transfer coefficient is 400W / m 2 / K, outer wall interface heat transfer coefficient 1000W / m 2 / K, heat transfer coefficient of the bottom interface of the steel ingot is 300W / m 2 / K.

[0011] Further, in step 2, the hollow billet is extruded and deformed under the action of the shear extrusion die, the wall thickness of the hollow billet is slightly smaller than the wall thickness of the thick-walled cylindrical part by 2-5mm, and the inner and outer diameters are correspondingly reduced or increased; the extrusion deformation of the hollow billet is two simple shear deformations and one circumferential compression or tensile deformation under the axisymmetric state, and the metal on the meridian plane moves only in the plane under the action of the hollow punch, and there is no circumferential (tangential) displacement; after the hollow casting billet is sheared and deformed twice in opposite directions with the same shear strain, the extruded part can undergo large plastic deformation and the strain distribution along the wall thickness direction after extrusion is uniform; the hollow casting billet mainly undergoes two shear deformations during the extrusion process, the circumferential deformation can be controlled and reduced as much as possible, and the force required for hot extrusion is small. The hot shear extrusion forming technology not only retains the advantages of good three-dimensional compressive stress state of extrusion deformation; more importantly, the introduction of strong shear deformation can not only greatly improve the deformation effect, refine and homogenize the coarse solidified grain structure, but also improve the uniformity of wall thickness deformation and reduce the extrusion force.

[0012] Furthermore, the hot shear extrusion of the thick-walled tube is divided into reducing-diameter hot shear extrusion and expanding-diameter hot shear extrusion. The reducing-diameter hot shear extrusion is an extrusion method in which the diameter of the blank is reduced while the wall thickness remains unchanged under the combined deformation of radial shear-circumferential compression-radial shear; the expanding-diameter hot shear extrusion is an extrusion method in which the diameter of the blank is reduced while the wall thickness remains unchanged under the combined deformation of radial shear-circumferential stretching-radial shear.

[0013] Furthermore, the shearing and extruding equipment used for the thick-walled cylindrical part is an extruder, and the extruder is one of a vertical extruder and a horizontal extruder.

[0014] The above technical solution of the embodiment of the present invention has the following beneficial technical effects: The present invention proposes a short-process forming method for thick-walled tubes based on hot shear extrusion of hollow ingots. The hollow ingots prepared by electroslag remelting can avoid the generation of various metallurgical defects in the center of solid steel ingots, and the steel is pure, basically free of segregation, the crystal structure is uniform and dense, and the chemical composition is uniform, providing high-quality hollow steel ingots for the production of high-quality large cylindrical parts. At the same time, by using a ring-cylindrical part shear extrusion die to directly perform hot extrusion forming on the hollow ingot, the process of multiple heating and multi-step hot forging blanks is omitted, and one to two fires are directly formed, which can reduce the production costs of materials, energy and manpower by about 15% to 30%, and improve the forming and manufacturing efficiency of ring-cylindrical parts. The hot shear extrusion forming technology of thick-walled cylindrical parts can achieve uniform large plastic deformation of thick-walled tubes, obtain thick-walled cylindrical parts with regular shape and uniform structure and performance, and realize the short-process forming and manufacturing of thick-walled tubes while improving the forming-forming effect of thick-walled tubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of a short-process forming method of a thick-walled tube by hot shear extrusion based on a hollow ingot; Figure 2 It is a schematic diagram of a short-process forming method of hot shear extrusion for reducing and expanding the diameter of a thick-walled tube based on a hollow casting billet; Figure 3 This is a schematic diagram of the front and cross-sectional structure of the hot shearing extrusion forming die for the high nitrogen austenitic stainless steel thick-walled cylindrical part in Example 1; Figure 4 This is a schematic diagram of the front and cross-sectional structure of the hot shear extrusion die for the expansion of the high-nitrogen austenitic stainless steel thick-walled cylindrical part in Example 2; Figure 5 It is a schematic diagram of the enlarged structure of the shear-compression / stretch-shear composite deformation zone during the extrusion process in Examples 1 and 2; Figure 6 This is a schematic diagram of the free forging process for stainless steel thick-walled cylindrical parts.

[0016] In the figure, 1-punch pressing plate, 2-extrusion punch, 3-mandrel, 4-extrusion cylinder, 5-extrusion cushion, 6-hollow ingot, 7-core mold, 8-die, 9-die base; 10-extrusion channel, 11-shear deformation channel, 12-extrusion channel. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0018] Example 1: Hot shear extrusion forming of high nitrogen austenitic stainless steel thick-walled cylindrical parts High nitrogen austenitic stainless steel thick wall cylindrical parts shrinking hot shear extrusion short process forming manufacturing method, refer to Figure 1 , Figure 2 , including the following steps: preparation of high nitrogen austenitic stainless steel hollow ingot - hot shearing and hot extrusion - rough machining - solution treatment - high pressure cold bulging strengthening - finishing, etc.

[0019] The high nitrogen austenitic stainless steel hollow ingot is prepared by electroslag remelting or electroslag liquid casting refining. The ingot is a ring-shaped ingot. The high nitrogen austenitic stainless steel hollow ingot is prepared by electroslag remelting. The electrode melting rate or the slag-metal interface rising rate is controlled below 0.1 mm / s, and the bottom heat transfer coefficient is 500 W / m 2 / ℃; the electroslag liquid casting and refining is used to prepare high nitrogen austenitic stainless steel hollow ingots, the casting temperature is 1415℃, the casting speed is 25kg / s, the inner and outer surfaces are cooled simultaneously, and the boundary condition is that the inner wall interface heat transfer coefficient is 400W / m 2 / K, outer wall interface heat transfer coefficient 1000W / m 2 / K, heat transfer coefficient of the bottom interface of the steel ingot is 300W / m 2 / K.

[0020] The hot shear extrusion is carried out under the pressure of the extruder equipment. The extrusion die adopts a ring-cylindrical part shrinkage hot shear extrusion die. The die adopts a rotation angle of 45° to 60°, is lubricated with glass lubricant, and the extrusion speed is controlled between 30 and 70 mm / s.

[0021] The solution treatment is to heat the extruded part to 1050° C., keep the temperature for 2 hours and then cool it with water.

[0022] The high nitrogen austenitic stainless steel thick-walled cylindrical part shrinking hot shearing extrusion equipment is a vertical extruder or a horizontal extruder.

[0023] like Figure 3 As shown, the high nitrogen austenitic stainless steel thick-walled cylindrical part shrinking hot shear extrusion die comprises a punch plate 1, an extrusion punch 2, a mandrel 3, an extrusion barrel 4, an extrusion pad 5, a core die 7, a die 8 and a die base 9, wherein the extrusion punch 2 is arranged in an annular cylindrical shape, the extrusion punch plate 1 is fixedly arranged above the extrusion punch 2, the die base 9 is arranged above the die 7, the extrusion barrel 4 is arranged above the die 7, the core die 6 passes through the die base die hole and the die die hole, and the mandrel 3 is arranged above the core die 6; The annular gap between the outer wall of the core shaft 3 and the inner wall of the extrusion cylinder 4 is defined as an extrusion channel 10, and the extrusion punch 2 is inserted in the extrusion channel 10; the annular gap between the upper part of the outer wall of the core mold 7 and the inner wall of the die hole of the die is defined as a shear deformation channel 11, and the annular gap between the lower part of the outer wall of the core mold 7 and the inner wall of the die hole of the die base is defined as an extrusion channel 12. The extrusion channel 10, the shear deformation channel 11 and the extrusion channel 12 are connected in sequence from top to bottom to form an extrusion forming channel, and the extrusion forming channel is a rotating body structure.

[0024] The high nitrogen austenitic stainless steel thick wall cylindrical part shrinking hot shear extrusion process mainly includes the following operation steps: S1. Prepare an annular or cylindrical hollow ingot 6 to be formed. The hollow ingot 6 is prepared by an electroslag remelting method. The initial extrusion temperature of the hollow ingot 6 is the maximum temperature allowed in the thermal deformation temperature range of the extruded ingot. The dimensions of the thick-walled hollow ingot 6 to be formed in Example 1 are: an outer diameter of 1428 mm, an inner diameter of 1082 mm, a height of 1000 mm, and a thickness of 173 mm. The hollow ingot 6 is heated to the initial extrusion temperature by an annular furnace and kept warm for use in the subsequent step. S2, first, preheat the extrusion punch 2, the mandrel 3, the extrusion cylinder 4, the core mold 7 and the concave mold 8, the preheating temperature is 350-450°C; then, spray lubricant on the forming surface of the extrusion forming channel, the lubricant is a glass powder lubricant; finally, take out the hollow casting 6 heated in step S1, spray lubricant on the inner and outer walls of the hollow casting 6, and then quickly put it into the extrusion channel 10, and place the extrusion pad 5 on the top of the hollow casting 6; S3, take out the extrusion punch 2 preheated in step S2, and then quickly place it above the extrusion cushion 5, use a pressure equipment extrusion machine or a free forging hydraulic press to apply force to the extrusion punch 2 through the punch plate 1, and the extrusion punch 2 passes through the extrusion cushion 5 from top to bottom through the extrusion channel 10, the shear deformation channel 11 and the extrusion channel 12, and the hollow billet 6 is subjected to hot shear extrusion by shrinking, and the extrusion speed is 30-70 mm / s. After the cylindrical hollow billet 6 to be formed is extruded in this embodiment 1, the size of the extruded part is: the outer diameter is 1030 mm, and the inner diameter is 680 mm; S4. After extrusion, the head and tail of the material are cut off, and then the material is processed to the required size of the finished product after subsequent heat treatment and cold expansion strengthening.

[0025] Example 2: Hot shear extrusion forming of high nitrogen austenitic stainless steel thick-walled cylindrical parts High nitrogen austenitic stainless steel thick wall cylindrical parts expansion hot shear extrusion short process forming manufacturing method, such as Figure 1 and Figure 2 As shown, the process includes the following steps: preparation of high nitrogen austenitic stainless steel hollow ingot - hot shear extrusion with diameter expansion - rough machining - solution treatment - high pressure cold bulging strengthening - finishing, etc., and finally an expanded diameter thick wall tube is obtained.

[0026] The process steps involved in the hot shear extrusion forming technology for expanding the diameter of thick-walled cylindrical parts of high-nitrogen austenitic stainless steel in this embodiment 2 are the same as those in embodiment 1; the difference between the extrusion die structure and that in embodiment 1 is only that: the longitudinal section of the core die 3 is set to a "convex" shape, and the diameter of the upper part of the extrusion forming channel is smaller than the diameter of the lower part. The rest is the same as in embodiment 1 and will not be repeated here.

[0027] The high nitrogen austenitic stainless steel thick-walled cylindrical parts expansion hot shear extrusion forming technology, the size of the annular cylindrical hollow ingot 6 to be formed in this embodiment 2 and the extrusion process are the same as those in embodiment 1, and will not be repeated here. The annular cylindrical hollow ingot 6 to be formed after the expansion hot shear extrusion in this embodiment 2 has a thick-walled cylinder size of: an outer diameter of 1830mm and an inner diameter of 1480mm. The main view of the cross-sectional structure of the expansion hot shear extrusion forming die for high nitrogen austenitic stainless steel thick-walled cylindrical parts is as follows Figure 4 As shown, Figure 3 The forming die is a diameter reduction die. During the deformation process, the inner and outer diameters of the cylindrical part are reduced, and the blank undergoes two shear deformations and one compression deformation. Figure 4 The forming die is an expansion die. During the deformation process, the inner and outer diameters of the cylindrical part expand, and the blank undergoes two shear deformations and one tensile deformation.

[0028] like Figure 5 As shown, it can be seen from Example 1 and Example 2 that the hot shear extrusion deformation of the thick-walled cylindrical part is two simple shear deformations and one circumferential compression or tensile deformation under the axisymmetric state. Under the action of the hollow punch, the metal on the meridian plane only moves in the plane in the shear deformation channel 11, and there is no circumferential displacement; therefore, the metal mainly undergoes simple shear deformation in the PDZ1 shear deformation zone and the PDZ2 shear deformation zone, and undergoes circumferential compression deformation of diameter reduction or circumferential tensile deformation of diameter expansion in the PDLZ variable diameter deformation zone between the two shear deformation zones, as well as the axial elongation of diameter reduction or axial shortening of diameter expansion caused by the resulting deformation.

[0029] Example 3 Double-pass shrinking hot shear extrusion forming of high nitrogen austenitic stainless steel ultra-thick wall cylindrical parts High nitrogen austenitic stainless steel thick wall cylindrical parts expansion hot shear extrusion short process forming manufacturing method, such as Figure 1 and Figure 2 As shown, the process includes the following steps: preparation of high nitrogen austenitic stainless steel hollow ingot - first diameter reduction hot shear extrusion - second diameter reduction hot shear extrusion - rough machining - solution treatment - high pressure cold bulging strengthening - finishing, etc., and finally a diameter reduction thick wall tube is obtained.

[0030] The process steps involved in the hot shear extrusion forming technology for expanding the diameter of thick-walled cylindrical parts of high-nitrogen austenitic stainless steel in this embodiment 3 are the same as those in embodiment 1; the difference between the extrusion die structure and that in embodiment 1 is only that: after one diameter reduction shear deformation, the second diameter reduction shear deformation is performed after reheating in the furnace, and the second diameter reduction shear deformation process is consistent with the operation steps of the first diameter reduction shear deformation, and the rest are the same as in embodiment 1 and will not be repeated here.

[0031] High nitrogen austenitic stainless steel thick-walled cylindrical parts expansion hot shear extrusion forming technology, the dimensions of the thick-walled hollow ingot 6 to be formed in this Example 3 are: outer diameter 1825mm, inner diameter 1485mm, height 600mm, thickness 170mm; the ingot is processed in the first pass according to the shrinking deformation process described in Example 1, and the dimensions of the extruded part after deformation are: outer diameter 1425mm, inner diameter 1085mm, wall thickness 173mm; the extruded part processed in the first pass is processed again by the deformation process described in Example 1, and the dimensions of the finished product after deformation are: outer diameter 1030mm, inner diameter 680mm, wall thickness 175mm. The main view and cross-sectional structure schematic diagram of the double-pass shrinking hot shear extrusion forming mold for ultra-thick walled cylindrical parts of high nitrogen austenitic stainless steel is shown in Figure 3 As shown, no further elaboration is given here.

[0032] Comparative Example 4 Comparison of free forging and hot shear extrusion short process forming technology solutions for thick-walled cylindrical parts The free forging process of stainless steel thick-walled cylindrical parts is as follows: Figure 6 As shown, the specific process is: preparation of stainless steel solid ingot - free forging blanking - hot forging - rough machining - solution treatment - cold expansion strengthening - finishing, etc.

[0033] In the free forging process, the stainless steel solid ingot is prepared by electroslag remelting, and the ingot is a cylindrical ingot with an ingot weight of about 19.6 tons.

[0034] The free forging blanking process includes: drawing and blanking - upsetting - rounding and shaping - cone plate upsetting - punching, a total of 4 to 5 heatings to obtain a hollow blank. The specific steps are as follows: (1) The prepared electroslag solid ingot is drawn as a whole to a diameter of 900mm, and blanked to a solid blank with a diameter of 900mm and a length of 1900mm, and enters a heating furnace to be heated to 1200℃ and kept warm; (2) Take out the blank heated to 1200℃ for upsetting deformation, use a flat plate to upset to a diameter of 1100mm and a height of 1270mm, and roll forge the outer circle for shaping, and the blank enters a heating furnace to be heated to 1190℃ and kept warm; (3) Take out the blank for upsetting deformation, upsetting to a diameter of 1100mm and a height of 1270mm, and roll forging the outer circle for shaping. The billet is 1450 mm in diameter and 730 mm in height, and is rolled to an outer circle. The billet is placed in a heating furnace and heated to 1190°C and kept warm. (4) After the billet is taken out, it is punched with a long punch preheated to 200°C until the bottom of the billet is warped by about 20 to 50 mm. The billet is turned over and punched again with a short punch preheated to 200°C until the punching is completed. A hollow billet with an outer diameter of 1500 mm, an inner diameter of 500 mm and a height of 730 mm is obtained. The hollow billet is placed in a heating furnace and heated to 1150°C for subsequent forging.

[0035] The hot forging forming process comprises: mandrel drawing - flattening the end surface - bar hole expansion - flattening the end surface - bar precision expansion, a total of 4 to 5 times of hot forging is completed. The specific steps are as follows: (1) A core rod with a diameter of 480 mm is used for the first drawing, and the length of the billet is drawn to 930 mm. The billet is returned to the furnace and heated to 1150°C for 2 hours; (2) After taking out the sample, a core rod with a diameter of 480 mm is used for the second drawing, and the billet is drawn to a length of 1130 mm, and the end surface is flattened to a height of 1030 mm. The billet is returned to the furnace and heated to 1150°C for 2 hours; (3) After taking out the sample, the inner diameter of the billet is expanded to 910 mm using an expansion anvil, and the end surface is flattened to a billet height of 1030 mm. The billet is returned to the furnace and heated to 1100°C for 1 hour; (4) After taking out the sample, the inner diameter of the billet is expanded to 1050 mm using an expansion anvil, and the end surface is flattened to a billet height of 1030 mm. The end surface is flattened and air-cooled for damage removal in preparation for subsequent processing and heat treatment. After hot forging, the dimensions of the cylindrical part are: outer diameter 1460mm, inner diameter 1050mm, and height 1030mm.

[0036] Hot shear extrusion forming process of stainless steel thick-walled cylindrical parts: preparation of stainless steel hollow ingot - hot shear extrusion - rough processing - solution treatment - cold expansion strengthening - fine processing, etc.

[0037] In the hot shear extrusion forming short process, the stainless steel hollow ingot is prepared by electroslag remelting or electroslag liquid casting refining, and the ingot is a ring-shaped ingot with an ingot weight of about 11.2 tons. The size of the hollow ingot is: outer diameter 1600mm, inner diameter 1200mm, height 1320mm.

[0038] The hot shear extrusion is carried out under the pressure of the hydraulic press equipment. The extrusion die adopts a hot shear extrusion die with a reduced diameter of a ring cylindrical part. The die adopts a rotation angle of 60° and is lubricated with glass lubricant. The extrusion speed is controlled at 50mm / s. The extrusion die structure and the extrusion process are the same as those in Example 1 and are not described in detail here. The size of the cylindrical part after shearing and extrusion deformation is: outer diameter 1450mm, inner diameter 1050mm, height 1400mm. After the extrusion is completed, the head and tail of the material are cut off. The length of the cut head is about 250mm, and the length of the cut tail is about 120mm.

[0039] The solution treatment is to heat the forged cylindrical piece to 1050°C and keep it at that temperature for 2 hours and then cool it with water. The finishing process uses processing equipment such as a cylindrical grinder, a milling machine and a machining center to finish the heat-treated cylindrical part so that the inner and outer surfaces and the end surface dimensions reach the required dimensions of the finished product.

[0040] The utilization rate of solid steel ingots in the free forging process of thick-walled cylindrical parts is 48.4%, and the utilization rate of hollow steel ingots in the short process of hot shear extrusion forming is 82.1%. In the free forging hot forming process, the billet is heated and forged 8 to 10 times, and the hot shear extrusion forming hollow billet is heated and extruded 1 to 2 times. In the free forging hot forming, the billet is heated and forged for multiple times, and the grains are repeatedly grown and recrystallized and refined, the uniformity of the structure is poor, and the temperature and deformation of the last forming fire are limited, making it difficult to effectively control the structure of the cylindrical forging after forming; in the hot shear extrusion short process, the coarse solidified grain structure of the hollow steel ingot is highly refined and homogenized under the shear fragmentation and recrystallization mechanism.

[0041] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modification, equivalent substitution, improvement, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention.

Claims

1. A short-process forming method for thick-walled tube hot shear extrusion based on hollow casting, characterized in that: The steps include: Step 1, preparation of thick-walled hollow ingot; Step 2, hot shear extrusion: after heating and heat preservation, the hollow ingot prepared in step 1 is directly subjected to hot shear extrusion deformation by using a ring-cylinder shear extrusion die under the pressure of an extruder; Step 3, heat treatment: the thick-walled cylindrical part obtained in step 2 is subjected to normalizing treatment, quenching and tempering treatment, or solid solution treatment; Step 4, finishing: The thick-walled cylindrical part obtained in step 3 is finished by processing equipment so that the inner and outer surfaces and the end face dimensions reach the required dimensions of the finished product.

2. The method for forming a thick-walled tube by hot shearing extrusion of a hollow ingot according to claim 1 is characterized in that: In step 1, a hollow cast billet is used as a thick-walled tube forming billet. During the traditional hollow billet axial extrusion deformation process, continuous shear deformation of the thick-walled billet is introduced by designing a suitable shear angle.

3. The short-process forming method of thick-walled tube hot shear extrusion based on hollow casting according to claim 1 is characterized in that: Step 2 includes the following steps: S1, preparing a cylindrical hollow ingot to be formed, and using an annular furnace to heat the hollow ingot to an initial extrusion temperature and keep it warm for later use; S2, preheating the extrusion die, spraying lubricant on the forming surface of the extrusion forming channel; taking out the hollow billet heated in step S1, spraying lubricant on the inner and outer walls of the hollow billet, and then quickly putting it into the extrusion die channel, and placing the extrusion pad on top of the hollow billet; S3, take out the extrusion punch preheated in step S2, and then quickly place it on the extrusion pad, and use a pressure device to perform hot shear extrusion on the hollow billet at an extrusion speed of 30 mm / s to 70 mm / s; S4. After extrusion, cut off the head and tail of the material for subsequent heat treatment.

4. The method for forming a thick-walled tube by hot shearing extrusion of a hollow ingot according to claim 1 is characterized in that: In step 1, the thick-walled hollow ingot is prepared by electroslag remelting or electroslag liquid casting refining, the hollow ingot is in the shape of a ring cylinder, the hollow ingot is prepared by electroslag remelting, the electrode melting rate or the slag-metal interface rising rate is controlled below 0.1 mm / s, and the bottom heat transfer coefficient is 500 W / m 2 / ℃; the pouring temperature of the electroslag liquid casting refining preparation is 1415℃, the pouring speed is 25kg / s, the inner and outer surfaces are cooled simultaneously, and the boundary condition is the inner wall interface heat transfer coefficient of 400W / m 2 / K, outer wall interface heat transfer coefficient 1000W / m 2 / K, heat transfer coefficient of the bottom interface of the steel ingot is 300W / m 2 / K.

5. The method for forming a thick-walled tube by hot shearing extrusion of a hollow ingot according to claim 1 is characterized in that: In step 2, the hollow billet is extruded and deformed under the action of the shear extrusion die, the wall thickness of the hollow billet is 2-5 mm less than the wall thickness of the thick-walled cylindrical part, and the inner and outer diameters are correspondingly reduced or increased; the extrusion deformation of the hollow billet is two simple shear deformations and one circumferential compression or tensile deformation under the axisymmetric state. Under the action of the hollow punch, the metal on the meridian plane only moves in the plane without circumferential displacement; the hollow casting is sheared in two opposite directions with the same shear strain.

6. The method for forming a thick-walled tube by hot shearing extrusion of a hollow ingot according to claim 5 is characterized in that: The hot shear extrusion of the thick-walled tube is divided into the hot shear extrusion of reducing diameter and the hot shear extrusion of expanding diameter. The hot shear extrusion of reducing diameter is an extrusion method in which the diameter of the blank is reduced while the wall thickness remains unchanged under the combined deformation of radial shear, circumferential compression and radial shear; the hot shear extrusion of expanding diameter is an extrusion method in which the diameter of the blank is reduced while the wall thickness remains unchanged under the combined deformation of radial shear, circumferential stretching and radial shear.

7. The method for forming a thick-walled tube by hot shearing extrusion of a hollow ingot according to claim 5, characterized in that: The shearing and extruding equipment used for the thick-walled cylindrical part is an extruder, and the extruder is one of a vertical extruder and a horizontal extruder.

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