A forging method for controlling the grain size of a tee joint of nitrogen-controlled stainless steel TP316LN main pipeline

Abstract

The present application relates to a kind of control nitrogen austenitic stainless steel TP316LN main pipeline tee grain size forging method, by two upsetting two drawing, realize the larger deformation of ingot, break columnar crystal, improve macrosegregation, break cast structure, weld internal porosity, get reasonable fiber direction distribution.This method balances deformation and recrystallization process by reasonably controlling the forging ratio of each heating of blank, obtains more uniform, more fine grain structure.Effectively reduce the product manufacturing cost, and the various examination indexes of forgings all meet the product requirements, and the grain size is higher than 4 levels.

Description

Technical Field

[0001] This invention belongs to the field of metal forging technology, specifically relating to a forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tee. Background Technology

[0002] Nitrogen-controlled TP316LN austenitic stainless steel is based on ASME SA376316LN, with the carbon content controlled to ≤0.03%. Due to this ultra-low carbon content, TP316LN exhibits strong resistance to intergranular corrosion. Simultaneously, the addition of nitrogen significantly improves the steel's strength while maintaining high ductility and toughness. In terms of corrosion resistance, the addition of nitrogen improves the steel's resistance to pitting corrosion, crevice corrosion, and intergranular corrosion. Regarding microstructure stability, nitrogen, as an austenite-forming element, reduces the ferrite content in the steel, making the austenite structure more stable and maintaining a single austenitic structure and non-magnetic properties even at low temperatures. In addition to its good resistance to intergranular corrosion, this steel also possesses excellent mechanical properties, corrosion fatigue resistance, and good weldability. Nitrogen-controlled TP316LN austenitic stainless steel material is widely used in military, energy, aerospace, chemical and bioengineering industries due to its excellent comprehensive mechanical properties and corrosion resistance in various corrosive media. It can be used in non-magnetic, corrosion-resistant, low-temperature, superconducting and nuclear fusion ultra-low temperature environments with high strength requirements.

[0003] The steel has a single-phase austenite structure at room temperature and does not undergo phase transformation during heat treatment. Therefore, it is impossible to refine the grains through heat treatment. The only way to refine the grains is to break them up by forging and deformation, which will cause recrystallization.

[0004] The problem of grain size control in nitrogen-controlled TP316LN austenitic stainless steel pipe products has not been well resolved, which seriously affects production stability and cost control. Summary of the Invention

[0005] This invention provides a forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tee. The technical problem to be solved is: to solve the problem of grain size control of nitrogen-controlled stainless steel TP316LN main pipe tee forging, while significantly improving the mechanical properties and isotropy of the forging.

[0006] To address the above technical problems, this invention provides a forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tees, characterized by the following steps:

[0007] (1) First heat: When the steel ingot is loaded into the furnace, the furnace temperature is ≤550℃. The temperature is raised to 1000±10℃ as soon as possible, and the holding time is calculated at (80-120mm) / h. Then the temperature is raised to 1200±10℃ as soon as possible, and the holding time is calculated at (80-120mm) / h. After being taken out of the furnace, the steel ingot is upset and drawn out.

[0008] (2) Second heating: After the billet is returned to the furnace, it should be heated to 1200±10℃ as soon as possible. The holding time should be calculated according to (80-120mm) / h. Place the billet with the original large end facing down, and upset the billet to half the height with an upsetting ratio of 2.0. Then, draw it with a full anvil length of 10%-15% deformation to make the steel ingot octagonal and then flat. When flattening, the appropriate forging ratio should be designed according to the step height of the forging. Then, return it to the furnace for heating.

[0009] (3) Third fire: The furnace temperature is reduced to 1100±10℃. After the billet is returned to the furnace, it is raised to 1100±10℃ as soon as possible. The holding time is calculated according to (80-120mm) / h. After the billet is taken out of the furnace, the two ends of the mark are pulled to the appropriate size according to the height of the small step, and then returned to the furnace for heating.

[0010] (4) Fourth fire: After the billet is returned to the furnace, heat it to 1100±10℃ as soon as possible. The holding time is calculated according to (80-120mm) / h. After the billet is taken out of the furnace, pull the two ends of the small step and one side of the large end of the steel ingot to the appropriate size. Then press the part of the main pipe protruding in the direction of the step into the main pipe. Finally, pull the main pipe into an octagon and return it to the furnace for heating.

[0011] (5) Five-stage heating: After the billet is returned to the furnace, it should be heated to 1100±10℃ as soon as possible. The holding time should be calculated as (80-120mm) / h. After the forging is taken out of the furnace, the main pipe should be pulled to the process size first, and then the large and small steps should be forged to the process size.

[0012] (6) Solution treatment: The forged billet is returned to the furnace and heated to 1040±10℃. The holding time is calculated as (80-120mm) / h. After being taken out of the furnace, it is water cooled to room temperature.

[0013] Beneficial effects: This invention achieves significant deformation of the steel ingot through two upsetting and two drawing processes, breaking up columnar crystals, improving macroscopic segregation, breaking up the as-cast structure, welding internal pores, and obtaining a reasonable fiber orientation distribution. By rationally controlling the forging ratio of the billet in each forging pass and balancing the deformation and recrystallization process, a more uniform and finer grain structure is obtained.

[0014] This effectively reduced product manufacturing costs, and all performance indicators of the forgings met product requirements, with grain size exceeding level 4.

[0015] Due to the inherent properties of this type of steel, a press with sufficient capacity should be selected for forging according to the size of the steel ingot during forging. This is to avoid multiple forging processes due to insufficient press capacity during forming, which could ultimately lead to mixed crystal formation. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the dimensions of the main pipe tee forging in an embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the electroslag ingot dimensions in an embodiment of the present invention.

[0018] Figure 3 This is a schematic diagram of the one-fire forging process in an embodiment of the present invention.

[0019] Figure 4 This is a schematic diagram of the two-fire forging process in an embodiment of the present invention.

[0020] Figure 5 This is a schematic diagram of the three-fire forging process in an embodiment of the present invention.

[0021] Figure 6 This is a schematic diagram of the four-fire forging process in an embodiment of the present invention.

[0022] Figure 7 This is a schematic diagram of the five-fire forging process in an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below.

[0024] This invention provides a forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tees, the steps of which are as follows:

[0025] (1) First forging: Upsetting and drawing the steel ingot; When loading the steel ingot into the furnace, the furnace temperature is ≤550℃. At this temperature, the holding time is calculated as (100-200mm) / h. The temperature is raised to 1000±10℃ as soon as possible, and the holding time is calculated as (80-120mm) / h. Then, the temperature is raised to 1200±10℃ as soon as possible, and the holding time is calculated as (80-120mm) / h. After taking it out of the furnace for forging, the large end of the steel ingot is placed downwards. The steel ingot is upset to half the height of the ingot body with an upsetting ratio of 2.0. Then, it is drawn with a full anvil lengthening of 10%-15% to form an octagon. The ingot is then joined together with a lengthening ratio of 2.0. The final forging temperature is controlled at ≥850℃.

[0026] (2) Second heating: After the billet is returned to the furnace, heat it to 1200±10℃ as soon as possible, and keep it at that temperature for (80-120mm) / h. Place the billet with the original large end facing down, and upset it to half its height with an upsetting ratio of 2.0. Then, draw it with a full anvil length of 10%-15% deformation to make the ingot octagonal, and then flatten it. When flattening, the appropriate forging ratio should be designed according to the step height of the forging. Based on the principle of constant volume, calculate the dimensions and mark the lines in advance when marking. Use a triangular knife to mark the lines at the marked positions, with a marking depth of 100-200mm. Then, reheat it in the furnace.

[0027] (3) Third heating: The furnace temperature is reduced to 1100±10℃. After the billet is returned to the furnace, it is quickly raised to 1100±10℃. The holding time is calculated at (80-120mm) / h. After the billet is taken out of the furnace, the two ends of the marking are pulled to the appropriate size according to the height of the small step. The forging ratio of the main pipe is controlled to be greater than 1.5, and the forging ratio at the step is greater than 1.3. The original large end of the clamped steel ingot is rotated 90° counterclockwise. The dimensions of the small step and each part are calculated, and lines are drawn. The marking is made according to the marked lines using a triangular knife. The marking depth is 100-200mm. The billet is then returned to the furnace for heating.

[0028] (4) Fourth heating: After the billet is returned to the furnace, heat it to 1100±10℃ as soon as possible, and keep it at that temperature for (80-120mm) / h. After taking it out of the furnace, pull the two ends of the small step and one side of the large end of the steel ingot to the appropriate size. Then press the part of the main pipe protruding in the direction of the step into the main pipe. Finally, pull the main pipe into an octagonal shape, control the forging ratio of the main pipe to be greater than 1.5, and the forging ratio of the step to be greater than 1.3, and then return it to the furnace for heating.

[0029] (5) Fifth heating: After the billet is returned to the furnace, heat it to 1100±10℃ as soon as possible, and keep it at that temperature for (80-120mm) / h. After the forging is taken out of the furnace, first pull the main pipe to the process dimensions, and then forge the large and small steps to the process dimensions. When pressing the step height direction, pay attention to controlling the small feed rate and pressing multiple times. Control the forging ratio of each part of the forging to be above 1.6.

[0030] (6) Solution treatment: the forged billet is returned to the furnace and heated to 1040±10℃. The holding time is calculated as (80-120mm) / h. The billet is then cooled to room temperature by water after being taken out of the furnace. The holding time is determined by the wall thickness of the forging.

[0031] The forging drawing for this implementation plan is as follows: Figure 1 As shown, the required steel ingots are 8.3 tons of electroslag steel ingots, such as Figure 2 As shown, the forging process is carried out on a 6000-ton hydraulic press, and the forming process is as follows.

[0032] Please see Figure 1-7 A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tees, the forging method comprising the following steps:

[0033] Step 1: First heating. The steel ingot is upset and drawn. When loading the ingot into the furnace, the furnace temperature is ≤550℃. It is held at 550℃ for 4 hours, then quickly raised to 1000±10℃ and held for 10 hours. Then, it is quickly raised to 1200±10℃ and held for 8 hours. After removal from the furnace, the ingot is forged with the larger end facing down. It is upset to 800mm with an upsetting ratio of 2.0. Then, it is drawn with a full anvil lengthening of 10%-15% to form an octagonal shape of 850mm. The ingot is then joined together with a drawing ratio of 2.0. The final forging temperature is ≥850℃. It is then returned to the furnace for reheating. A schematic diagram of the ingot deformation process in Step 1 is shown below. Figure 3 As shown.

[0034] Step 2: Second Heat Treatment: After the billet is returned to the furnace, quickly raise the temperature to 1200±10℃ and hold for 10 hours. Place the billet with its original large end facing down and upset it to 850mm (upsetting ratio 2.0). Then, with a deformation of 10%-15%, draw it at full length on the anvil, shaping the ingot into an octagon, and then into a 950mm×750mm flat square with a drawing ratio of 1.8. The manipulator holds the original small end of the ingot, placing the 750mm wide side upwards on the platform. Based on the principle of constant volume, mark the pre-calculated dimensions. Then, use a 10mm diameter round steel bar to press the mark at the marked position. Use a triangular knife to engrave the mark according to the marked position, with a depth of 100-200mm. During the engraving process, always keep the right-angle side of the triangular knife perpendicular to the forging. After engraving, when removing the knife, use the manipulator and the upper hammer to collide at the right-angle part of the triangular knife to loosen it and facilitate removal. The schematic diagram of the billet structure changes and engraving during the forging process in step 2 is shown below. Figure 4 As shown.

[0035] Step 3: Three-stage heating: The furnace temperature is reduced to 1100±10℃. After the billet is returned to the furnace, it is quickly raised to 1100±10℃ and held for 8 hours. Upon exiting the furnace, sections I, III, and V of the billet are first drawn to a 750mm square shape. Then, the width of section IV (at the step) is reduced from 950mm to 750mm. Finally, sections I, III, and V are drawn to a 750mm octagonal shape. The forging ratio for the main pipe is 1.53, and the forging ratio at the step is 1.3. The billet is placed on a platform with the step facing upwards at the original large end of the ingot, and then rotated 90° counterclockwise. The engraving procedure is as described in Step 2, followed by reheating in the furnace. The schematic diagram of the billet structure changes and engraving during the forging process in Step 3 is shown below. Figure 5 As shown.

[0036] Step 4: Fourth Heating: After the billet is returned to the furnace, quickly raise the temperature to 1100±10℃ and hold for 7 hours. The furnace operator uses the original large end of the ingot to pull sections I, III, and V of the billet to a 600mm square. Then, the protruding parts at steps II and IV are pressed into the main pipe. Finally, sections I, III, and V of the billet are pulled to a 600mm octagon. The forging ratio in the main pipe is 1.6, and the forging ratio at the two steps is 1.3. The billet is then returned to the furnace for heating. A schematic diagram of the billet structure changes during the forging process in Step 4 is shown below. Figure 6 As shown.

[0037] Step 5: Fifth Heat: After the billet is returned to the furnace, raise the temperature to 1100±10℃ as soon as possible and hold for 6 hours. After the forging is removed from the furnace, first elongate the middle part of the two steps of the main pipe with a deformation of 10%-15%, measuring the distance between the centers of the two steps while elongating, until the center distance is 1786±20mm, then stop elongating. Then elongate the parts on both sides of the large and small steps to... Finally, the height and width of the large and small steps are pressed to the process dimensions. The forging ratio for the main pipe is 2.1, the forging ratio for the small steps is 1.8, and the forging ratio for the large steps is 1.7. A schematic diagram of the billet structure changes during the forging process in step 5 is shown below. Figure 7 As shown.

[0038] Step 6: Solution treatment. Heat the forged billet to 1040±10℃, hold for 4 hours, and then cool it to room temperature with water after removing it from the furnace.

[0039] This invention achieves significant deformation of steel ingots through two upsetting and two drawing processes, breaking up columnar crystals, improving macroscopic segregation, disrupting the as-cast structure, welding internal porosity, and obtaining a reasonable fiber orientation distribution. This method balances deformation and recrystallization processes by rationally controlling the forging ratio of each forging pass, resulting in a more uniform and finer grain structure. This effectively reduces product manufacturing costs, and all performance indicators of the forgings meet product requirements, with grain size exceeding grade 4.

[0040] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tees, characterized in that, The forging is a double-nozzle main pipe tee, with the two nozzles at 90° to each other. The steps are as follows: (1) First heat: When the steel ingot is loaded into the furnace, the furnace temperature is ≤550℃. The temperature is raised to 1000±10℃ as soon as possible, and the holding time is calculated as (80-120mm) / h. Then the temperature is raised to 1200±10℃ as soon as possible, and the holding time is calculated as (80-120mm) / h. After the steel ingot is taken out of the furnace for forging, the steel ingot is upset and drawn out. Place the steel ingot with the large end facing down, and upset the steel ingot to half the height of the ingot body with an upsetting ratio of 2.

0. Then, draw it with a full anvil lengthening of 10%-15% to make the steel ingot octagonal, and then make the end. The lengthening ratio is 2.

0. The final forging temperature is controlled at ≥850℃. (2) Second heating: After the billet is returned to the furnace, it should be heated to 1200±10℃ as soon as possible. The holding time should be calculated according to (80-120mm) / h. Place the billet with the original large end facing down, and upset the billet to half the height with an upsetting ratio of 2.

0. Then, draw it with a full anvil length of 10%-15% deformation to make the steel ingot octagonal and then flat. When flattening, the appropriate forging ratio should be designed according to the step height of the forging. Then, return it to the furnace for heating. (3) Third fire: The furnace temperature is reduced to 1100±10℃. After the billet is returned to the furnace, it is raised to 1100±10℃ as soon as possible. The holding time is calculated according to (80-120mm) / h. After the billet is taken out of the furnace, the two ends of the mark are pulled to the appropriate size according to the height of the small step, and then returned to the furnace for heating. (4) Fourth fire: After the billet is returned to the furnace, heat it up to 1100±10℃ as soon as possible. The holding time is calculated as (80-120mm) / h. After the billet is taken out of the furnace, pull the two ends of the small step and one side of the large end of the steel ingot to the appropriate size. Then press the part of the main pipe protruding in the direction of the step into the main pipe. Finally, pull the main pipe into an octagon and return it to the furnace for heating. (5) Five-stage heating: After the billet is returned to the furnace, it should be heated to 1100±10℃ as soon as possible. The holding time should be calculated as (80-120mm) / h. After the forging is taken out of the furnace, the main pipe should be pulled to the process size first, and then the large and small steps should be forged to the process size. (6) Solution treatment: The forged billet is returned to the furnace and heated to 1040±10℃. The holding time is calculated as (80-120mm) / h. After being taken out of the furnace, it is water-cooled to room temperature. During the forging process, the forging ratio of each part in each forging pass must be controlled, and the forging ratio of the main pipe part must be greater than 1.5, while the forging ratio of the tee step part must be greater than 1.

3.

2. The forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tee according to claim 1, characterized in that: The forging material is nitrogen-controlled austenitic stainless steel TP316LN.

3. The forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tees according to claim 1, characterized in that: The forging temperature of the steel ingot is controlled at 1200℃ during upsetting, and the forging temperature is reduced to 1100℃ during forming.

4. The forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tee according to claim 1, characterized in that: When the blank is forged using a triangular knife, the engraving depth must be greater than 100mm.

5. The forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tee according to claim 1, characterized in that: When steel ingots are loaded into the furnace, the furnace temperature is ≤550℃. At this temperature, the holding time is calculated as (100-200mm) / h.

6. The forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tee according to claim 1, characterized in that: The billet must eventually become octagonal after each firing during the forming process.

7. The forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipe tee according to claim 1, characterized in that: During the fifth firing process, the forging ratio at each part of the forging must be greater than 1.6.

Images