Forging method for controlling grain size of nitrogen-control stainless steel TP316LN main pipeline tee joint

Abstract

The invention relates to a forging method for controlling grain size of a nitrogen-controlled austenitic stainless steel TP316LN main pipeline tee joint, which is characterized in that through two-time upsetting and two-time drawing, large deformation of a steel ingot is realized, columnar crystals are broken, macrosegregation is improved, as-cast structures are broken, internal pores are welded, and reasonable fiber direction distribution is obtained. According to the method, the forging ratio of each heating number of the blank is reasonably controlled, the deformation and recrystallization process is balanced, and a more uniform and finer grain structure is obtained. And the manufacturing cost of the product is effectively reduced, various assessment indexes of the forge piece meet the product requirements, and the grain size is higher than grade 4.

Description

Technical Field

[0001] The invention belongs to the technical field of metal forging, and in particular relates to a forging method for controlling the grain size of a nitrogen-controlled stainless steel TP316LN main pipeline tee. Background Art

[0002] Nitrogen-controlled TP316LN austenitic stainless steel material is based on ASME SA376316LN, with the carbon content controlled below ≤0.03%. Due to the use of ultra-low carbon, TP316LN has strong resistance to intergranular corrosion. At the same time, due to the addition of nitrogen, the strength of the steel is significantly improved, while still maintaining a high level of plasticity and toughness; in terms of corrosion resistance, the addition of nitrogen improves the steel's resistance to pitting, crevice corrosion and intergranular corrosion; in terms of organizational stability, nitrogen is added to the steel as an austenite-forming element, which can reduce the ferrite content in the steel, making the austenite more stable, and still maintaining a single austenite structure and non-magnetic in a low temperature environment. In addition to having good resistance to intergranular corrosion, the steel also has excellent mechanical properties, corrosion fatigue resistance and good welding performance. Nitrogen-controlled TP316LN austenitic stainless steel material can be used in non-magnetic, corrosion-resistant, low-temperature, superconducting and nuclear fusion ultra-low-temperature environments with high strength requirements due to its excellent comprehensive mechanical properties and corrosion resistance in various corrosive media. Therefore, it is widely used in industrial technologies such as military industry, energy, aerospace, chemical industry and bioengineering.

[0003] The structure of this steel is single-phase austenite at room temperature, and there is no phase change during heat treatment. Therefore, the grains cannot be refined by heat treatment. The grains can only be refined by forging deformation to break up the grains and cause them to recrystallize.

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

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

[0006] In order to solve the above technical problems, the present invention provides a forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipeline tee, characterized in that the steps are as follows:

[0007] (1) First fire: When the steel ingot is charged into the furnace, the furnace temperature is ≤550℃, and 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 stretched;

[0008] (2) Second fire: After the billet is returned to the furnace, the temperature is raised to 1200±10℃ as soon as possible. The holding time is calculated as (80-120mm) / h. The billet is placed with the original big end facing downward. The billet is upset to half of the height with an upset ratio of 2.0. Then, the billet is pulled out with a deformation amount of 10%-15% and the ingot is pulled into an octagonal shape and then flattened. When flattening, the appropriate forging ratio should be designed according to the step height of the forging. Then, the billet is returned to the furnace for heating;

[0009] (3) Third fire: The furnace temperature drops to 1100±10℃. After the billet is returned to the furnace, the temperature is raised 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, the two ends of the engraved billet are pulled to the appropriate size according to the height of the small step and returned to the furnace for heating;

[0010] (4) Fourth fire: After the billet is returned to the furnace, the temperature is raised to 1100±10℃ as soon as possible, and the holding time is calculated as (80-120mm) / h. After it is taken out of the furnace, the two ends of the small step engraving and one side of the big end of the ingot are pulled to the appropriate size, and then the protruding part of the main pipe direction at the step is pressed into the inside of the main pipe. Finally, the main pipe is pulled into eight sides and returned to the furnace for heating;

[0011] (5) Fifth fire: After the billet is returned to the furnace, the temperature is raised to 1100±10℃ as soon as possible. The holding time is calculated as (80-120mm) / h. After the forging is taken out of the furnace, the main pipe is first pulled to the process size, and then the large and small steps are forged to the process size;

[0012] (6) Solution treatment: Return the forged billet to the furnace and heat it to 1040±10℃. The holding time is calculated as (80-120mm) / h. Then cool it to room temperature after taking it out of the furnace.

[0013] Beneficial effects: The present invention achieves a larger deformation of the steel ingot through two upsetting and two drawing processes, breaks up columnar crystals, improves macrosegregation, breaks up the as-cast structure, welds the internal pores, and obtains a reasonable fiber direction distribution. By reasonably controlling the forging ratio of each fire of the billet and balancing the deformation and recrystallization process, a more uniform and finer grain structure is obtained.

[0014] The manufacturing cost of the product has been effectively reduced. All assessment indicators of the forgings meet the product requirements, and the grain size is higher than level 4.

[0015] Due to the inherent characteristics of this type of steel, a press with sufficient capacity is selected for forging according to the size of the ingot during forging, so as to avoid multiple forgings due to insufficient press capacity during forming, which ultimately leads to mixed crystal phenomenon. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the dimensions of the main pipeline tee forging in the embodiment of the present invention

[0017] Figure 2 Schematic diagram of the size of the electroslag ingot in the embodiment of the present invention

[0018] Figure 3 A schematic diagram of a first-fire forging process in an embodiment of the present invention

[0019] Figure 4 Schematic diagram of the double-fire forging process in the embodiment of the present invention

[0020] Figure 5 Schematic diagram of the three-fire forging process in the embodiment of the present invention

[0021] Figure 6 Schematic diagram of the four-fire forging process in the embodiment of the present invention

[0022] Figure 7 This is a schematic diagram of the five-fire forging process in the embodiment of the patent of this invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below.

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

[0025] (1) First fire: The steel ingot is upset and drawn; when the steel ingot is loaded into the furnace, the furnace temperature is ≤550℃, and the holding time at this temperature 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 the steel ingot is taken out of the furnace for forging, the big end of the steel ingot is placed downward, and the steel ingot is upset to half the height of the ingot body, with an upset ratio of 2.0. Then, the steel ingot is drawn with a deformation amount of 10%-15% and the ingot is drawn into an octagonal shape with the head butted. The drawing ratio is 2.0, and the final forging temperature is controlled to be ≥850℃.

[0026] (2) Second fire: After the billet is returned to the furnace, the temperature is raised to 1200±10℃ as soon as possible, and the holding time is calculated as (80-120mm) / h; the original big end of the billet is placed downward, and the billet is upset to half of the height, with an upset ratio of 2.0, and then the ingot is pulled out with a deformation of 10%-15%, and then it is pulled into an octagonal shape, and then it is flattened. When it is flattened, the appropriate forging ratio should be designed according to the step height of the forging. According to the principle of constant volume, the size is calculated in advance and the line is drawn when engraving. Use a triangular knife to engrave according to the line position, and the engraving depth is 100-200mm; return to the furnace for heating.

[0027] (3) Third fire: The furnace temperature drops 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 as (80-120mm) / h. After leaving the furnace, the two ends of the billet are pulled to the appropriate size according to the height of the small step. The forging ratio of the main pipeline is controlled to be greater than 1.5, and the forging ratio at the step is greater than 1.3. The original big end of the clamped steel ingot is rotated 90° counterclockwise, the size of the small step and each part is calculated, and the line is marked. Use a triangular knife to mark the marked part, the marking depth is 100-200mm, and return to the furnace for heating.

[0028] (4) Fourth fire: After the billet is returned to the furnace, the temperature is raised to 1100±10℃ as soon as possible, and the holding time is calculated as (80-120mm) / h. After leaving the furnace, the two ends of the small step engraving and one side of the big end of the ingot are pulled to the appropriate size, and then the protruding part of the main pipe direction at the step is pressed into the inside of the main pipe. Finally, the main pipe is pulled into eight sides, and 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, and then returned to the furnace for heating.

[0029] (5) Fifth fire: After the billet is returned to the furnace, the temperature is raised to 1100±10℃ as soon as possible, and the holding time is calculated as (80-120mm) / h. After the forging is taken out of the furnace, the main pipe is first pulled to the process size, and then the large and small steps are forged to the process size. When pressing the step height direction, pay attention to controlling the small feed amount and pressing multiple times. Control the forging ratio of each 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. It is then cooled to room temperature by water. The holding time is determined by the wall thickness of the forging.

[0031] The forging diagram of this embodiment is shown in FIG. Figure 1 As shown, the required steel ingot is 8.3 tons of electroslag steel ingot, such as Figure 2 As shown, a 6000-ton hydraulic press is used for forging, and the forming process is described as follows.

[0032] See also Figure 1-7 A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipeline tee, the forging method comprising the following steps:

[0033] Step 1: In the first fire, the steel ingot is upset and stretched. When the steel ingot is loaded into the furnace, the furnace temperature is ≤550℃. Keep it at 550℃ for 4h, heat it to 1000±10℃ as soon as possible and keep it for 10h, then heat it to 1200±10℃ as soon as possible and keep it for 8h. After being taken out of the furnace for forging, the big end of the steel ingot is placed downward, and the steel ingot is upset to 800mm with an upsetting ratio of 2.0. Then, it is stretched with a deformation amount of 10%-15% and the ingot is stretched into an 850mm square with the ends butted. The stretching ratio is 2.0, the final forging temperature is ≥850℃, and it is returned to the furnace for heating. The schematic diagram of the steel ingot deformation process in step 1 is as follows: Figure 3 shown.

[0034] Step 2: Second fire: After the billet is returned to the furnace, the temperature is raised to 1200±10℃ as soon as possible and kept warm for 10h. Place the original big end of the billet downward, upset the billet to 850mm, the upsetting ratio is 2.0, and then the ingot is stretched with a deformation of 10%-15%, and the ingot is pulled into an octagonal shape, and then becomes a 950mm×750mm flat square with a stretching ratio of 1.8. The manipulator clamps the original small end of the ingot, and places the 750mm wide surface on the platform facing up. According to the principle of constant volume, the dimensions calculated in advance are marked, and then a round steel with a diameter of 10mm is used to stamp the marked position. A triangular knife is used to engrave according to the marked position, and the engraving depth is 100-200mm. During the engraving process, the right-angle side of the triangular knife must always be kept vertically on the forging. When pulling out the knife after the engraving is completed, the manipulator and the upper hammer head are used to collide at the right angle of the triangular knife to loosen the triangular knife and facilitate the pulling out of the knife. The schematic diagram of the billet structure change and engraving during the forging process in step 2 is as follows: Figure 4 shown.

[0035] Step 3: Third fire: The furnace temperature drops to 1100±10℃, and after the billet is returned to the furnace, it is raised to 1100±10℃ as soon as possible and kept warm for 8h. After taking out of the furnace, first pull the billet I, III, and V parts to 750mm square, and then press the width of IV (step) from 950mm to 750mm, and finally pull the billet I, III, and V parts to 750mm square. The forging ratio of the main pipeline is 1.53, and the forging ratio at the step is 1.3. Clamp the original big head end of the steel ingot and place the billet on the platform with the step facing up, and then rotate it 90° counterclockwise. The operation method for engraving is as described in step 2, and return to the furnace for heating. The schematic diagram of the billet structure change and engraving during the forging process in step 3 is shown as follows. Figure 5 shown.

[0036] Step 4: Four-fire: After the billet is returned to the furnace, the temperature is raised to 1100±10℃ as soon as possible and kept warm for 7 hours. The furnace manipulator clamps the original big end of the steel ingot and pulls the billet parts Ⅰ, Ⅲ, and Ⅴ to 600mm square, then presses the protruding parts at the steps Ⅱ and Ⅳ into the main pipe, and finally pulls the billet parts Ⅰ, Ⅲ, and Ⅴ to 600mm square. The forging ratio of the main pipe is 1.6, the forging ratio at the two steps is 1.3, and then returns to the furnace for heating. The schematic diagram of the billet structure change during the forging process in step 4 is as follows: Figure 6 shown.

[0037] Step 5: Fifth fire: After the billet is returned to the furnace, the temperature is raised to 1100±10℃ as soon as possible and kept at this temperature for 6 hours. After the forging is taken out of the furnace, the middle part of the two steps of the main pipe is stretched by 10%-15% deformation, and the distance between the centers of the two steps is measured while stretching. When the center distance is 1786±20mm, the stretching is stopped, and then the parts on both sides of the large and small steps are stretched to Finally, the height and width of the steps are pressed to the process size. The forging ratio of the main pipe is 2.1, the forging ratio of the small step is 1.8, and the forging ratio of the large step is 1.7. The schematic diagram of the change of the billet structure during the forging process of step 5 is as follows Figure 7 shown.

[0038] Step 6: Solution treatment: heat the forged billet to 1040±10℃, keep it warm for 4h, and then cool it to room temperature with water.

[0039] The present invention achieves a larger deformation of the steel ingot by two upsetting and two drawing, breaks up the columnar crystals, improves the macro segregation, breaks up the cast structure, welds the internal pores, and obtains a reasonable fiber direction distribution. The method reasonably controls the forging ratio of each fire of the billet, balances the deformation and recrystallization process, and obtains a more uniform and finer grain structure. The product manufacturing cost is effectively reduced, and all the assessment indicators of the forgings meet the product requirements, and the grain size is higher than level 4.

[0040] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as 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 pipeline tee. It is characterized in that Here are the steps: (1) First fire: When the steel ingot is charged into the furnace, the furnace temperature is ≤550℃, and 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 stretched; (2) Second fire: After the billet is returned to the furnace, the temperature is raised to 1200±10℃ as soon as possible. The holding time is calculated as (80-120mm) / h. The billet is placed with the original big end facing downward. The billet is upset to half of the height with an upset ratio of 2.

0. Then, the billet is pulled out with a deformation amount of 10%-15% and the ingot is pulled into an octagonal shape and then flattened. When flattening, the appropriate forging ratio should be designed according to the step height of the forging. Then, the billet is returned to the furnace for heating; (3) Third fire: The furnace temperature drops to 1100±10℃. After the billet is returned to the furnace, the temperature is raised 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, the two ends of the engraved billet are pulled to the appropriate size according to the height of the small step and returned to the furnace for heating; (4) Fourth fire: After the billet is returned to the furnace, the temperature is raised to 1100±10℃ as soon as possible, and the holding time is calculated as (80-120mm) / h. After it is taken out of the furnace, the two ends of the small step engraving and one side of the big end of the ingot are pulled to the appropriate size, and then the protruding part of the main pipe direction at the step is pressed into the inside of the main pipe. Finally, the main pipe is pulled into eight sides and returned to the furnace for heating; (5) Fifth fire: After the billet is returned to the furnace, the temperature is raised to 1100±10℃ as soon as possible. The holding time is calculated as (80-120mm) / h. After the forging is taken out of the furnace, the main pipe is first pulled to the process size, and then the large and small steps are forged to the process size; (6) Solution treatment: Return the forged billet to the furnace and heat it to 1040±10℃. The holding time is calculated as (80-120mm) / h. Then cool it to room temperature after taking it out of the furnace.

2. A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipeline tee according to claim 1, Features: The forging is made of nitrogen-controlled austenitic stainless steel TP316LN.

3. A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipeline tee according to claim 1, Features: The forging is a double-nozzle main pipeline tee, and the two nozzles are at 90 degrees to each other.

4. A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipeline tee according to claim 1, Features: In step (1), the steel ingot is placed with the big end facing downward, and the steel ingot is upset to half the height of the ingot body, with an upset ratio of 2.0, and then the steel ingot is stretched with a deformation amount of 10%-15% on the full anvil, and the steel ingot is pulled into eight sides, with the head butted, and the stretching ratio is 2.0, and the final forging temperature is controlled to be ≥850°C.

5. A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipeline tee according to claim 1, Features: The forging temperature of the steel ingot is controlled to be 1200° C. during upsetting, and the forging temperature is reduced to 1100° C. during forming.

6. A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipeline tee according to claim 1, Features: When forging the billet, the forging ratio of each part in each firing should be controlled, and the forging ratio of the main pipe part should be greater than 1.5, and the forging ratio of the tee step should be greater than 1.

3.

7. A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipeline tee according to claim 1, Features: When the blank is engraved with a triangular cutter during forging, the engraving depth must be greater than 100 mm.

8. A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipeline tee according to claim 1, Features: When the steel ingots are loaded into the furnace, the furnace temperature is ≤550℃, and the holding time at this temperature is calculated as (100-200mm) / h.

9. A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipeline tee according to claim 1, Features: The blank will become square after each firing during the forming process.

10. A forging method for controlling the grain size of nitrogen-controlled stainless steel TP316LN main pipeline tee according to claim 1, Features: During the fifth tempering, the forging ratio of each part of the forging must be greater than 1.6.

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