Outer die hole pattern structure for cold drawing forming of stainless steel flat rectangular pipe and process of outer die hole pattern structure

Abstract

The invention discloses an outer die hole pattern structure for cold drawing forming of a stainless steel flat rectangular pipe and a process thereof, belongs to the technical field of metal material processing, and solves the technical problem that long edges of a stainless steel round pipe are concave after cold drawing forming. According to the solution, the stainless steel flat rectangular pipe cold-drawing forming outer die hole pattern comprises a set of outer die long edges arranged symmetrically and a set of outer die short edges arranged symmetrically, the outer die long edges and the outer die short edges are in transition connection through outer die arcs, and each outer die long edge comprises two arc long edges which are arranged symmetrically and concave inwards; the chord height h of the long edge of the outer mold and the included angle alpha are in the relation of h = 0.5 L1 * tan alpha; and on the basis, performing one-pass cold drawing and bright annealing treatment on the thin-wall stainless steel round pipe by using an outer die hole pattern structure. The prepared stainless steel flat rectangular tube has the comprehensive advantages of being high in precision, high in performance and low in cost, economic benefits are obvious, and the stainless steel flat tube can meet the requirements of generator liquid inner-cooling hollow wires.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material processing, and specifically relates to an outer die hole structure and a process for cold drawing a stainless steel flat rectangular tube. Background Art

[0002] Stainless steel has the advantages of high strength and corrosion resistance. The generator liquid internal cooling hollow conductor tube adopts a stainless steel seamless tube with a flat rectangular shape. Referring to the JB / T10415.22019 "Generator Liquid Internal Cooling Hollow Conductor Part 2: Stainless Steel Hollow Conductor" standard, the various performance indicators and inspection requirements of the generator liquid internal cooling hollow conductor are clarified, mainly including chemical composition, size and deviation, mechanical properties, surface quality, airtightness test, eddy current detection, intergranular corrosion, grain size inspection and other performance indicators. The standard mentions that the use of hollow conductors should be "drawn and delivered in a solid solution state", but it does not specify the specific drawing forming method. After consulting relevant literature, it does not involve the detailed mold structure for manufacturing the product. Therefore, it is necessary to design a stainless steel flat rectangular tube cold drawing forming die that can meet the use requirements of the generator liquid internal cooling hollow conductor.

[0003] When cold-drawing a stainless steel round tube into a flat rectangular tube, the deformation ratio between the round tube size and the flat tube size must also be considered. When designing the round tube size, the prior art usually calculates the outer circumference of the finished stainless steel flat tube. For example, Figure 1 As shown, assuming that the perimeter of the finished stainless steel flat tube is S = 2 × (L1 + L2) + 4C, L1 is the length of the long side of the finished product, L2 is the length of the short side of the finished product, and C is the length of the outer arc of the finished product, then the theoretical diameter of the stainless steel round tube before deformation is D = S / π. However, the round tube obtained by theoretical calculation is very likely to have an insufficient outer arc during the "round to square" cold drawing deformation. The reason is that the stainless steel material has a certain plasticity. In addition to the change in appearance during cold drawing deformation, the wall thickness will also change slightly. Therefore, when designing the size of the stainless steel round tube, the perimeter ratio K before and after deformation must be considered. Therefore, the diameter of the round tube is D = KS / π, and K is generally 1.02-1.05. The thinner the wall thickness, the greater the K value.

[0004] If the cold-drawn outer die hole structure is designed according to the theoretical nominal size of the flat tube, the cold-drawn flat tube will have a concave long side (such as Figure 2 The reason for the concave is that the cold drawing deformation causes work hardening. The cold drawn flat tube has residual stress caused by strain after leaving the outer die. The release of residual stress at room temperature causes dimensional change, that is, the long side L1 becomes concave, while the short side L2 remains straight. Summary of the invention

[0005] The main purpose of the present invention is to overcome the deficiencies in the prior art and solve the technical problem of concave phenomenon on the long sides of stainless steel round tubes after cold drawing. The present invention provides an outer die hole structure and process for cold drawing of stainless steel flat rectangular tubes.

[0006] The present invention is achieved through the following technical solutions:

[0007] A stainless steel flat rectangular tube cold drawing outer die hole structure, the stainless steel flat rectangular tube cold drawing outer die hole comprises a group of symmetrically arranged outer die long sides and a group of symmetrically arranged outer die short sides, the outer die long sides and the outer die short sides are connected by an outer die arc transition, when designing the stainless steel flat rectangular tube cold drawing outer die hole structure, the outer die long sides are designed to have a certain curvature shape (such as Figure 3 As shown in the figure, in order to compensate for the dimensional change caused by the residual stress release of the stainless steel flat rectangular tube, the shape and size of the long side of the outer mold are determined by three parameters: h, L1 and α, wherein: the long side of the outer mold includes two symmetrically arranged and inwardly concave arc long sides, and the central angle of the arc long side is Assume that the finished long side of the stainless steel flat rectangular tube is L1, the wall thickness of the stainless steel flat rectangular tube is δ, and the angle between the chord length of the long side of the arc and the long side L1 of the finished product is α, then the relationship between the chord height h of the long side of the outer mold and the angle α is:

[0008] h=0.5L1×tanα; ①

[0009] tanα=2h / L1; ②

[0010] In formula ① and formula ②, the value of α is 3° to 8°, and the larger the value of δ is, the smaller the value of α is.

[0011] A cold drawing forming process for preparing a stainless steel flat rectangular tube using the outer die hole structure as described above comprises the following steps:

[0012] S1. Calculate the design dimensions of thin-walled small-diameter stainless steel round tubes:

[0013] The perimeter S of the finished stainless steel flat rectangular tube is:

[0014] S=2×(L1+L2)+4C; ③

[0015] In formula ③, L1 is the length of the long side of the finished product, L2 is the length of the short side of the finished product, and C is the length of the outer arc of the finished product;

[0016] The theoretical diameter D of the initial stainless steel round tube is:

[0017] D=KS / π; ④

[0018] In formula ④, K = 1.02 to 1.05;

[0019] S2. Design of the outer die hole structure for cold drawing of stainless steel flat rectangular tube:

[0020] S2-1. Determine the chord height h of the outer die long side: The outer die hole type of the cold-drawn stainless steel flat rectangular tube includes a group of symmetrically arranged outer die long sides and a group of symmetrically arranged outer die short sides. The outer die long sides and the outer die short sides are connected by an outer die arc transition. The length of the outer die short side is equal to the length L2 of the short side of the finished product, and the arc length of the outer die arc is equal to the arc length C of the finished product outer arc. The wall thickness of the stainless steel flat rectangular tube is δ, and the angle between the chord length of the arc long side and the long side L1 of the finished product is α. The relationship between the chord height h of the outer die long side and the angle α is:

[0021] h=0.5L1×tanα; ①

[0022] tanα=2h / L1; ②

[0023] In formula ① and formula ②, the value of α is 3° to 8°, and the larger the value of δ is, the smaller the value of α is.

[0024] S2-2. Determine the long side of the outer mold: connect the vertex of the chord height to the endpoint of one end of the long side of the arc, connect the outer mold arc to the endpoint of the other end of the corresponding long side of the arc, and the central angle of the long side of the arc is The two symmetrically arranged arc long sides are connected to form the long side of the outer mold;

[0025] S3, passing the thin-walled small-diameter stainless steel round tube determined in step S1 through the stainless steel flat rectangular tube cold drawing forming outer die determined in step S2, and performing cold drawing to obtain a stainless steel flat rectangular tube blank;

[0026] S4, stainless steel flat rectangular tube blank heat treatment:

[0027] The cold-drawn stainless steel flat rectangular tube billet has increased strength and decreased plasticity due to work hardening, so it is necessary to carry out solid solution treatment of the finished product to ensure the final performance of the product. The solid solution treatment adopts bright annealing under a hydrogen protective atmosphere. The annealing temperature is 1030℃~1080℃, and the holding time is 1.5~2 times of the wall thickness. The stainless steel flat rectangular tube is obtained. After annealing, the cold deformation work hardening is eliminated, and the internal microstructure is recovered and recrystallized. The banded crystal structure is transformed into an equiaxed crystal structure, and the grains are refined.

[0028] Furthermore, the stainless steel flat rectangular tube obtained in step S4 has a grain size of 6, a tensile strength of 529 MPa, a yield strength of 252 MPa, and an elongation of 65.5%.

[0029] The beneficial effect of the present invention is that the stainless steel flat rectangular tube prepared by the outer mold hole structure and the cold drawing forming process provided by the present invention has the comprehensive advantages of high precision, high performance and low cost in its appearance profile, and has obvious economic benefits. The stainless steel flat tube can meet the needs of liquid internal cooling hollow conductors of generators. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the longitudinal section of a finished stainless steel flat rectangular tube;

[0031] Figure 2 It is a schematic diagram of the longitudinal section of a stainless steel flat rectangular tube produced by the prior art;

[0032] Figure 3 A schematic longitudinal section diagram of a stainless steel flat rectangular tube produced by using the cold-drawn outer die hole structure of the present invention;

[0033] Figure 4 It is a partial enlarged schematic diagram of the long side of the outer die in the cold drawing forming outer die hole structure of the present invention;

[0034] Figure 5 It is a schematic longitudinal section diagram of a finished stainless steel flat rectangular tube prepared in a specific implementation manner.

[0035] In the figure, 1 is the long side of the outer mold, 1-1 is the long side of the arc, 2 is the short side of the outer mold, and 3 is the arc of the outer mold. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0037] like Figure 3 and Figure 4 The outer die hole structure of the cold-drawn stainless steel flat rectangular tube shown in the figure comprises a group of symmetrically arranged outer die long sides 1 and a group of symmetrically arranged outer die short sides 2, and the outer die long sides 1 and the outer die short sides 2 are transitionally connected by an outer die arc 3, wherein: the outer die long side 1 comprises two symmetrically arranged and inwardly concave arc long sides 1-1, and the center angle of the arc long side 1-1 is Assume that the finished long side of the stainless steel flat rectangular tube is L1, the wall thickness of the stainless steel flat rectangular tube is δ, and the angle between the chord length of the arc long side 1-1 and the finished long side L1 is α, then the relationship between the chord height h of the outer mold long side 1 and the angle α is:

[0038] h=0.5L1×tanα; ①

[0039] tanα=2h / L1; ②

[0040] In formula ① and formula ②, the value of α is 3° to 8°, and the larger the value of δ is, the smaller the value of α is.

[0041] Taking 022Cr19Ni10 stainless steel flat rectangular tube as an example, the chemical composition of 022Cr19Ni10 stainless steel flat rectangular tube is shown in Table 1 below.

[0042] Table 1.022Cr19Ni10 stainless steel chemical composition (wt) / %

[0043]

[0044] The finished product is a 022Cr19Ni10 stainless steel flat rectangular tube with a width of 8.15±0.05mm, a height of 4±0.05mm, and a wall thickness of 1±0.05mm, that is, the inner and outer diameter tolerances are controlled to be ±0.05mm, and the length is not less than 2000mm. The required inner diameter, outer diameter and length dimensions are obtained by cold rolling or cold drawing. It must be in a solution treatment state. The plasticity index requires that the elongation of the tensile test is not less than 50%, and the inner and outer surfaces are polished with a finish of ≤0.8μm.

[0045] like Figures 3 to 5 The cold drawing forming process for preparing a stainless steel flat rectangular tube with an outer die hole structure shown includes the following steps:

[0046] S1. Calculate the design dimensions of thin-walled small-diameter stainless steel round tubes:

[0047] The perimeter S of the finished stainless steel flat rectangular tube is:

[0048] S=2×(L1+L2)+4C; ③

[0049] In formula ③, L1 is the length of the long side of the finished product, L2 is the length of the short side of the finished product, and C is the length of the outer arc of the finished product;

[0050] like Figure 5 As shown, in this specific embodiment, L1 = 6.15 mm, L2 = 2 mm, C = 1.25 mm (the radius of the finished product outer arc R = 0.8 mm), then the perimeter S of the finished stainless steel flat rectangular tube is: S = 2 × (L1 + L2) + 4C = 2 × (6.15 + 2)

[0051] +4×1.25=21.3mm;

[0052] The theoretical diameter D of the initial stainless steel round tube is:

[0053] D=KS / π; ④

[0054] In formula ④, K = 1.02 to 1.05;

[0055] In this specific implementation, K = 1.02, then the theoretical diameter of the initial stainless steel round tube is D = KS / π = 1.02 × 21.3 / π = 6.92 mm;

[0056] S2. Design of the outer die hole structure for cold drawing of stainless steel flat rectangular tube:

[0057] S2-1. Determine the chord height h of the outer die long side 1: The outer die hole type of the cold-drawn stainless steel flat rectangular tube includes a group of symmetrically arranged outer die long sides 1 and a group of symmetrically arranged outer die short sides 2. The outer die long side 1 and the outer die short side 2 are transitionally connected by the outer die arc 3. The length of the outer die short side 2 is equal to the length L2 of the finished product short side, and the arc length of the outer die arc 3 is equal to the arc length C of the finished product outer arc. The wall thickness of the stainless steel flat rectangular tube is δ, and the angle between the chord length of the arc long side 1-1 and the finished product long side L1 is α. Then the relationship between the chord height h of the outer die long side 1 and the angle α is:

[0058] h=0.5L1×tanα; ①

[0059] tanα=2h / L1; ②

[0060] In formula ① and formula ②, the value of α is 3° to 8°, and the larger the value of δ is, the smaller the value of α is;

[0061] S2-2, determine the outer mold long side 1: the vertex of the chord height is connected to the end point of one end of the arc long side 1-1, the outer mold arc 3 is connected to the end point of the other end of the corresponding arc long side 1-1, and the central angle of the arc long side 1-1 is The two symmetrically arranged arc long sides 1-1 are connected to form the outer mold long side 1;

[0062] In this specific implementation, α=5°, δ=1mm, then the chord height h=0.5×6.15×tan5°≈0.27mm, and then the two endpoints of the long side of the finished product are the two ends of the arc, the center angle of the long side 1-1 of the arc is 10°, combined with the chord height h=0.27mm, it can be determined that the center angle of the long side 1 of the outer mold is 20° and the arc length is 6.19mm;

[0063] S3, passing the thin-walled small-diameter stainless steel round tube determined in step S1 through the stainless steel flat rectangular tube cold drawing forming outer die determined in step S2, and performing cold drawing to obtain a stainless steel flat rectangular tube blank;

[0064] S4. Heat treatment of stainless steel flat rectangular tube billet: The solution treatment adopts bright annealing under hydrogen protective atmosphere. The annealing temperature is 1030℃~1080℃ and the holding time is 2min to obtain stainless steel flat rectangular tube. The grain size of stainless steel flat rectangular tube reaches 6 level, the tensile strength reaches 529MPa, the yield strength reaches 252MPa, the elongation reaches 65.5%, and the test results of intergranular corrosion, chemical composition, etc. meet the product requirements.

[0065] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A stainless steel flat rectangular tube cold-drawn outer die hole structure, the stainless steel flat rectangular tube cold-drawn outer die hole comprises a group of symmetrically arranged outer die long sides (1) and a group of symmetrically arranged outer die short sides (2), the outer die long sides (1) and the outer die short sides (2) are transitionally connected by an outer die arc (3), characterized in that: The outer mold long side (1) comprises two symmetrically arranged and inwardly concave arc long sides (1-1), and the central angle of the arc long side (1-1) is Assuming that the finished long side of the stainless steel flat rectangular tube is L1, the wall thickness of the stainless steel flat rectangular tube is δ, and the angle between the chord length of the arc long side (1-1) and the finished long side L1 is α, the relationship between the chord height h of the outer mold long side (1) and the angle α is: h=0.5L1×tanα; ① tanα=2h / L1; ② In formula ① and formula ②, the value of α is 3° to 8°, and the larger the value of δ is, the smaller the value of α is.

2. A cold drawing forming process for preparing a stainless steel flat rectangular tube using the outer die hole structure as claimed in claim 1, characterized in that: The following steps are involved: S1. Calculate the design dimensions of thin-walled small-diameter stainless steel round tubes: The perimeter S of the finished stainless steel flat rectangular tube is: S=2×(L1+L2)+4C; ③ In formula ③, L1 is the length of the long side of the finished product, L2 is the length of the short side of the finished product, and C is the length of the outer arc of the finished product; The theoretical diameter D of the initial stainless steel round tube is: D=KS / π; ④ In formula ④, K = 1.02 to 1.05; S2. Design of the outer die hole structure for cold drawing of stainless steel flat rectangular tube: S2-1. Determine the chord height h of the outer die long side (1): The outer die hole profile of the cold-drawn stainless steel flat rectangular tube includes a group of symmetrically arranged outer die long sides (1) and a group of symmetrically arranged outer die short sides (2). The outer die long side (1) and the outer die short side (2) are transitionally connected by an outer die arc (3). The length of the outer die short side (2) is equal to the length L2 of the short side of the finished product, and the length of the outer die arc (3) is equal to the arc length C of the finished product outer arc. The wall thickness of the stainless steel flat rectangular tube is δ, and the angle between the chord length of the arc long side (1-1) and the long side L1 of the finished product is α. Then the relationship between the chord height h of the outer die long side (1) and the angle α is: h=0.5L1×tanα; ① tanα=2h / L1; ② In formula ① and formula ②, the value of α is 3° to 8°, and the larger the value of δ is, the smaller the value of α is; S2-2, determine the outer mold long side (1): the vertex of the chord height is connected to the end point of one end of the arc long side (1-1), the outer mold arc (3) is connected to the end point of the other end of the corresponding arc long side (1-1), and the central angle of the arc long side (1-1) is Two symmetrically arranged arc long sides (1-1) are connected to form the outer mold long side (1); S3, passing the thin-walled small-diameter stainless steel round tube determined in step S1 through the stainless steel flat rectangular tube cold drawing forming outer die determined in step S2, and performing cold drawing to obtain a stainless steel flat rectangular tube blank; S4. Heat treatment of stainless steel flat rectangular tube blank: The solution treatment adopts bright annealing under hydrogen protective atmosphere, the annealing temperature is 1030℃~1080℃, and the holding time is 1.5~2 times of the wall thickness δ to obtain a stainless steel flat rectangular tube.

3. The cold drawing forming process for preparing a stainless steel flat rectangular tube with an outer die hole structure according to claim 2, characterized in that: The stainless steel flat rectangular tube obtained in step S4 has a grain size of 6, a tensile strength of 529 MPa, a yield strength of 252 MPa, and an elongation of 65.5%.

Images