Manufacturing method of high-strength ferrum-stainless steel thin-wall seamless hexagonal pipe

Abstract

The invention discloses a manufacturing method of a high-strength ferrum-stainless steel thin-wall seamless hexagonal pipe. The manufacturing method comprises the steps that multi-pass cold rolling or cold drawing deformation and heat treatment are conducted, and an intermediate product round pipe is machined; performing one-pass cold-drawing on an intermediate product through a cold-drawing die with six arc edges, and processing the intermediate product into a special-shaped pipe with six arc edges; solid solution heat treatment; performing cold drawing on a secondary intermediate product to finish forming of the seamless hexagonal pipe; and carrying out vacuum heat treatment on the formed seamless hexagonal pipe to finish manufacturing and the like. Aiming at the characteristics of high strength, high hardness and poorer plasticity of a ferrum steel material, a seamless hexagonal tube blank is subjected to multi-pass cold rolling and heat treatment, is subjected to transition by adopting a cold-drawing mold with six arc edges, and is subjected to two-time special cold-drawing forming. By means of the method, the problem that forming difficulty is large can be well solved, and the manufactured seamless hexagonal pipe intermediate product special-shaped pipe and the manufactured finished hexagonal pipe are convenient and easy to adjust in size specification, accurate in finished product size control and excellent in inner surface quality and outer surface quality.

Description

Technical Field

[0001] The invention belongs to the technical field of heat transfer tubes for high-end equipment and new energy systems, and in particular relates to a method for manufacturing a high-strength iron horse steel thin-wall seamless hexagonal tube. Background Art

[0002] With the rapid development of science and technology, nuclear energy, a clean energy, has been vigorously developed by many parties due to its wide and efficient application prospects. On this basis, general round seamless steel pipes can no longer fully meet the application of new materials in nuclear energy-related fields. Aiming at specific equipment structures and corresponding physical and chemical parameters, a high-strength iron horse steel thin-walled seamless hexagonal pipe design came into being.

[0003] Ferrite / martensite steel has become a candidate structural material for lead-based nuclear reactors due to its excellent radiation resistance, thermal conductivity and high-temperature mechanical properties; the structure of ferrite / martensite steel contains both ferrite and martensite phases, which makes the material combine the high strength and wear resistance of ferrite with the excellent toughness and corrosion resistance of martensite. m ≥800MPa, yield strength R p0.2 ≥600MPa, elongation ≤20%, and the hardness of iron horse steel HV ≥280; while the tensile strength of conventional 300 series austenitic stainless steel is R m ≥480MPa, yield strength is R p0.2 ≥175MPa, elongation ≥35%, hardness HV≤220. In comparison, the characteristics of high strength and low plasticity of Tiema steel materials are more prominent.

[0004] As the outer sleeve of nuclear fuel assemblies, the design and manufacture of hexagonal tubes are crucial to the normal operation of nuclear reactors. The structural and material optimization of hexagonal tubes can ensure that the fuel assemblies will not be damaged during transportation and operation, thereby ensuring the safe operation of nuclear reactors. In the past, hexagonal tubes were mostly made of stainless steel. Compared with iron horse steel, its strength is relatively low and its plasticity is relatively high. It can be produced by a variety of processing methods such as cold rolling, cold drawing, and machining. Hexagonal tubes made of iron horse steel have the characteristics of high strength, high hardness, and low plasticity. During the rolling process of conventional processing methods, stress concentration will occur on the six edges of the hexagonal tube, resulting in cracking. Therefore, new manufacturing steps need to be adopted for iron horse steel to ensure the quality of the final product. Summary of the invention

[0005] The purpose of the present invention is to provide a method for manufacturing high-strength iron horse steel thin-wall seamless hexagonal tubes suitable for iron horse steel materials in view of the defects of the existing hexagonal tube processing methods, so as to prevent the product from cracking during the rolling process, thereby ensuring the product quality.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme: A method for manufacturing a high-strength iron horse steel thin-wall seamless hexagonal tube, characterized in that it comprises the following specific steps: Step 1: Perforation of round steel, starting from the iron horse steel tube billet, through multiple cold rolling deformation and heat treatment, to the final intermediate round tube; Step 2: cold drawing the intermediate round tube in step 1 to form a special-shaped tube with six arc edges; Step 3: solution heat treatment; Step 4: cold drawing the shaped tube after solution heat treatment in step 3 to complete the forming of seamless hexagonal tube; Step 5: Vacuum heat treatment is performed on the formed seamless hexagonal tube to complete the manufacturing.

[0007] In view of the high strength and low plasticity of Tiema steel materials, two passes of cold drawing are used to stretch and shape the seamless hexagonal tube, while ensuring production quality and efficiency, preventing stress concentration on the six edges and causing cracking.

[0008] It is further characterized in that: in the step 2, the six vertices of the special-shaped tube coincide with the six vertices of the finished hexagonal tube and have a smooth transition; the distance from the highest point to the center point of the six arc surfaces of the special-shaped tube is H=1 / 2(R-Lcos30°)+Lcos30°; R is the radius of the intermediate round tube, and L is the side length of the finished hexagonal tube; the circumference contraction ratio of the intermediate special-shaped tube compared to the intermediate round tube: D2 / D1=90%~95%; the circumference contraction ratio of the hexagonal tube compared to the intermediate special-shaped tube: D3 / D2=R / (95%×π / 3R).

[0009] During the cold drawing process of the hexagonal tube of Tiema Steel material, stretching and shaping are performed simultaneously, which will generate great stress at the six vertices of the special-shaped tube. The use of a mold with arc edges for cold drawing can reduce the stress at the vertices and prevent edge cracking while ensuring production efficiency.

[0010] Preferably, during the cold drawing process of step 2 and step 4, the drawing rate is ≤9 m / min and is kept at a constant speed, and the drawing force is 280-500 N.

[0011] Preferably, the temperature of the solution heat treatment of the special-shaped tube in step 3 is controlled at 760-780°C, the temperature difference does not exceed 10°C, and the holding time is 15×S minutes; S is the wall thickness of the steel tube, in mm. Since the strength of the iron horse steel material is high and the plasticity is low, the heat treatment ensures that the steel tube has a certain strength and plasticity, which is convenient for the second cold drawing.

[0012] Preferably: the heat treatment temperature in step 5 is 780-800°C, the temperature difference does not exceed 10°C, and the holding time is 15×S minutes; S is the wall thickness of the steel pipe, in mm; after heat treatment, the inner and outer surfaces of the hexagonal pipe are polished with 200-mesh sandpaper. The subsequent heat treatment makes the finished steel pipe reach the preset strength. The oxide layer on the surface of the finished steel pipe is removed by polishing to meet the surface requirements of the steel pipe.

[0013] Preferably, the inner and outer surface roughness of the high-strength iron horse steel thin-wall seamless hexagonal tube is Ra≤0.8μm, the outer margin distance is 100-160mm, the wall thickness is 2-3mm, the outer margin distance tolerance is ±1.0mm, and the wall thickness tolerance is ±0.1mm. The finished iron horse steel thin-wall seamless hexagonal tube has a smooth surface and high precision.

[0014] Preferably, the size of the outer die hole in step 2 and step 4 is the same as the outer surface size of the drawn pipe fitting, and the width of the contact surface between the inner and outer dies and the drawn pipe fitting is 5-10 mm. If the contact surface between the cold drawing die and the drawn pipe fitting is too small during the cold drawing process, the metal flow cannot be controlled, thus forming a non-ideal shape; if the contact surface is too large, the friction is too large, resulting in excessive stress in some areas and causing the pipe fitting to break. Therefore, the contact surface width is designed to be 5-10 mm, which can ensure the final quality of the finished steel pipe.

[0015] In view of the high strength, high hardness and poor plasticity of the iron horse steel material, the seamless hexagonal tube blank is subjected to multiple cold rolling and heat treatment, and then a cold drawing die with six arc edges is used for transition, and two special cold drawing processes are performed. The method of the present invention can well solve the problem of high forming difficulty, and the manufactured seamless hexagonal tube intermediate product special-shaped tube and finished hexagonal tube have convenient and simple size adjustment, precise finished product size control, and excellent internal and external surface quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a diagram showing the deformation process of a round tube cold-drawn intermediate product, a shaped tube, and then drawn into a finished hexagonal tube.

[0017] Figure 2 is a schematic diagram of the outer mold for the round tube cold-drawn intermediate product special-shaped tube.

[0018] Figure 3 is a schematic diagram of the inner mold of the round tube cold-drawn intermediate product special-shaped tube.

[0019] Figure 4 is a schematic diagram of the outer mold of the finished hexagonal tube of the special-shaped tube cold drawing.

[0020] Figure 5 is a schematic diagram of the inner mold of the finished hexagonal tube of the special-shaped tube cold drawing. DETAILED DESCRIPTION

[0021] The present invention will be further described with reference to the accompanying drawings.

[0022] like Figure 1As shown, a process flow chart of a method for manufacturing a high-strength iron horse steel thin-walled seamless hexagonal tube is obtained. According to this process, the outer edge distance is 100~160mm, the wall thickness is 1~3mm, the outer edge distance tolerance is ±1.0mm, the wall thickness tolerance is ±0.1mm, the inner and outer surface roughness Ra≤0.8μm, the material is iron horse steel, and the vertical cross-section is a closed regular hexagon, which is a high-strength thin-walled seamless hexagonal tube.

[0023] The specific production steps are as follows: Step 1: subject the rough tube of Tiema Steel material to multiple cold rolling or cold drawing deformation and heat treatment to process into the final intermediate round tube; each heat treatment process: the heat treatment temperature is 780~800℃, the temperature difference does not exceed 10℃, and the insulation time is 15×S minutes (S is the wall thickness of the round tube, unit is mm). Through different heat treatment processes, the performance of the intermediate round tube is adjusted to ensure its high strength while achieving the best plasticity; straightening is carried out after heat treatment, and the straightness should meet the requirement of 0.8mm / m.

[0024] Step 2: Heading and lubricating the round tube in step 1; the iron horse steel material is not easy to weld and the outer diameter of the round tube is too large to roll the head, so the heading method is selected. Due to the poor plasticity of the material, the pipe end can only be heated before heading, and the heating temperature cannot exceed 700℃; the lubrication method is similar to the lubrication method of conventional stainless steel products, and butter lime is used to evenly apply the inner and outer surfaces of the steel pipe.

[0025] Step 3: After the heading and lubrication treatment in step 2, use the following Figure 2 , 3 The cold drawing die shown in the figure is used to cold draw the steel tube to form an intermediate shaped tube with six arc edges. The drawing rate during the cold drawing process is ≤9m / min and is kept at a constant speed, and the drawing force is 280~500N; during the cold drawing process, the inner die is preferably inserted into the round tube and placed in the initial position of the cold drawing of the pipe fitting, and the shape and size of the cold drawn shaped tube are controlled by the outer die. The six vertices of the shaped tube coincide with the six vertices of the finished hexagonal tube and the transition is smooth; the distance from the highest point to the center point of the six arc surfaces of the shaped tube is H=1 / 2(R-Lcos30°)+Lcos30°; R is the radius of the intermediate round tube, and L is the side length of the finished hexagonal tube; the circumference shrinkage ratio of the intermediate shaped tube compared to the intermediate round tube: D2 / D1= 90%~95%; the circumference shrinkage ratio of the hexagonal tube compared to the intermediate shaped tube: D3 / D2= R / (95%×π / 3R).

[0026] Step 4: Heat treat the intermediate special-shaped tube drawn in step 3. Since the strength of the iron horse steel material is high and the plasticity is low, it is necessary to consider that the plasticity of the intermediate product cannot be too low while ensuring the strength of the finished product. If the plasticity is too low, the special-shaped tube will be fractured due to stress concentration during the drawing process of the finished product; Two factors need to be considered during the heat treatment of the intermediate special-shaped tube. One is whether the pipe fittings will bend and deform during the heat treatment process, and the other is whether the pipe fittings will collapse during the heat treatment process. In view of these two factors, it is necessary to design an inner mold to be inserted into the special-shaped tube. The material must be resistant to high temperature and not deformed and not miscible at high temperature. Its shape is a columnar structure similar to the special-shaped tube. The size must just match the inner wall of the special-shaped tube and it must be easy to take out after heat treatment to ensure that the special-shaped tube does not deform during the heat treatment process; Heat treatment process: The heat treatment temperature is 760~780℃, the temperature difference does not exceed 10℃, and the insulation time is 15×S minutes (S is the wall thickness of the round tube, unit mm).

[0027] Step 5: After the heat treatment in step 4, the special-shaped tube is Figure 4 , 5 The cold drawing die shown is used for final cold drawing of finished products, and a regular hexagonal finished hexagonal tube is drawn; the drawing rate during the cold drawing process should be ≤9m / min, the drawing process should maintain a uniform speed, and the drawing force is 280~500N; if the contact surface between the cold drawing die and the drawn tube is too small during the cold drawing process, the metal flow cannot be controlled, thus forming a non-ideal shape; if the contact surface is too large, the friction will be too large, which will cause excessive stress in some areas and cause the tube to break, so the contact surface width is designed to be 8mm. The size of the cold drawing inner die is the same as the inner hole size of the drawn tube, and the inner die needs to be connected to the mandrel rod. During the cold drawing process, the inner die needs to be placed in the initial position of the cold drawing of the tube. The inner die and the outer die need to be kept on the same plane, and the gap between the inner and outer dies just controls the metal flow, thereby forming the desired product shape structure; to ensure the size of the finished hexagonal tube, the six corners of the inner and outer dies should be exactly opposite.

[0028] Step 6: The finished hexagonal tube is subjected to vacuum furnace heat treatment. Heat treatment process: the heat treatment temperature is 780~800℃, the temperature difference does not exceed 10℃, the insulation time needs to be combined with the wall thickness S of the steel tube, and the insulation time is 15×S minutes; after heat treatment, the inner and outer surfaces of the hexagonal tube are polished with 200-mesh sandpaper.

Claims

1. A method for manufacturing a high-strength iron horse steel thin-wall seamless hexagonal tube, characterized in that: The specific steps include: Step 1: Perforation of round steel, starting from the iron horse steel tube billet, through multiple cold rolling deformation and heat treatment, to the final intermediate round tube; Step 2: cold drawing the intermediate round tube in step 1 to form a special-shaped tube with six arc edges; Step 3: solution heat treatment; Step 4: cold drawing the shaped tube after solution heat treatment in step 3 to complete the forming of seamless hexagonal tube; Step 5: Vacuum heat treatment is performed on the formed seamless hexagonal tube to complete the manufacturing.

2. The method for manufacturing a high-strength seamless hexagonal steel thin-wall tube according to claim 1, characterized in that: In the step 2, the six vertices of the special-shaped tube coincide with the six vertices of the finished hexagonal tube and have a smooth transition; the distance from the highest point to the center point of the six arc surfaces of the special-shaped tube is H=1 / 2(R-Lcos30°)+Lcos30°; R is the radius of the intermediate round tube, and L is the side length of the finished hexagonal tube; the circumference contraction ratio of the intermediate special-shaped tube compared to the intermediate round tube: D2 / D1 = 90%~95%; the circumference contraction ratio of the hexagonal tube compared to the intermediate special-shaped tube: D3 / D2 = R / (95%×π / 3R).

3. The method for manufacturing a high-strength seamless hexagonal steel thin-wall tube according to claim 2, characterized in that: During the cold drawing process of step 2 and step 4, the drawing rate is ≤9m / min and is kept at a constant speed, and the drawing force is 280~500N.

4. The method for manufacturing a high-strength seamless hexagonal steel thin-wall tube according to any one of claims 1 to 3, characterized in that: In the step 3, the solution heat treatment temperature of the special-shaped tube is controlled at 760-780°C, the temperature difference does not exceed 10°C, and the insulation time is 15×S minutes; S is the wall thickness of the steel tube, in mm.

5. The method for manufacturing a high-strength seamless hexagonal steel thin-wall tube according to any one of claims 1 to 3, characterized in that: In step 5, the heat treatment temperature is 780-800°C, the temperature difference does not exceed 10°C, and the insulation time is 15×S minutes; S is the wall thickness of the steel pipe, in mm; after heat treatment, the inner and outer surfaces of the hexagonal tube are polished with 200-mesh sandpaper.

6. The method for manufacturing a high-strength seamless hexagonal steel thin-wall tube according to any one of claims 1 to 3, characterized in that: The inner and outer surface roughness of the high-strength iron horse steel thin-wall seamless hexagonal tube is Ra≤0.8μm, the outer edge distance is 100-160mm, the wall thickness is 2-3mm, the outer edge distance tolerance is ±1.0mm, and the wall thickness tolerance is ±0.1mm.

7. The method for manufacturing a high-strength seamless hexagonal steel thin-wall tube according to any one of claims 1 to 3, characterized in that: In step 2 and step 4, the size of the outer die hole is the same as the outer surface size of the drawn tube fitting, and the width of the contact surface between the inner and outer dies and the drawn tube fitting is 5-10 mm.

Images