TP316LN thin-wall hollow pipe forming and grain size control method

Abstract

The invention relates to a TP316LN thin-wall hollow pipe forming and grain size control method which comprises the steps of steel ingot blank making, steel ingot extrusion cogging, inner hole machining, hollow forging forming and solution treatment. Columnar crystals are broken, macrosegregation is improved, as-cast structures are broken, internal pores are welded, and reasonable fiber direction distribution is obtained. Through hollow forging forming and blank forging ratio control, the blank is stressed uniformly in three directions, the deformation and recrystallization process is balanced, a more uniform grain structure is obtained, and meanwhile a large number of raw materials are saved. According to the method, through coordination and cooperation of extrusion cogging and hollow forging, the product manufacturing cost is effectively reduced, all assessment indexes of the forged piece meet the product requirements, and the grain size is higher than 7.5 level.

Description

Technical Field

[0001] The invention belongs to the technical field of metal forging, and in particular relates to a TP316LN thin-wall hollow tube forming and grain size control method. Background Art

[0002] At present, for some thin-walled tube forgings, the performance requirements for materials are extremely strict, and 316LN is usually used, which brings severe challenges to subsequent forging, especially in terms of grain size control.

[0003] 316LN is a Cr-Ni-Mo type ultra-low carbon N-containing austenitic stainless steel. 316LN austenitic stainless steel is widely used because of its good corrosion resistance and high temperature mechanical properties. The addition of N element can not only improve its comprehensive performance, but also reduce the cost of raw materials. Due to the characteristics of austenitic steel, such forgings cannot refine the grains through heat treatment phase transformation, and can only rely on the forming process to control the grain size.

[0004] Traditionally, large forgings are generally produced using hydraulic presses, but the forging frequency of large hydraulic presses is slow, and the forging temperature range of secondary forgings is narrow, which makes it difficult to control the final forging temperature during the production process, and it is easy to produce defects such as mixed crystals and cracks. There is also a direct extrusion forming method, but because its wall thickness is particularly thin, the material flow is uneven during extrusion, the wall thickness difference is difficult to control, and the scrap rate is very high. If the wall thickness is increased, the material utilization rate of the finished product will be very low, and the grain size is also difficult to control, and mixed crystals are prone to occur.

[0005] Due to the narrow deformation temperature range and fast temperature drop of 316LN, the above production methods cannot accurately determine the grain size of thin-walled parts. Summary of the invention

[0006] The invention provides a TP316LN thin-wall hollow tube forming and grain size control method, and the technical problem to be solved is: solving the problems of thin-wall tube forging forming and forging grain size control, so that the mechanical properties and isotropy of the forging are significantly improved.

[0007] In order to solve the above technical problems, the present invention provides a TP316LN hollow tube forming and grain size control method, the steps are as follows:

[0008] (1) Ingot billet making

[0009] Process flow: sawing both ends of the steel ingot - heating the steel ingot - glass powder lubrication - 150 billet making machine billet - air cooling - billet processing - spraying anti-oxidation coating;

[0010] Sawing the two ends of the ingot: Cut off enough of the two ends of the ingot to ensure that there are no defects in the ingot body. Ingot heating: The ingot is loaded into the furnace at ≤550℃, and the temperature is raised to 850±10℃ as soon as possible for insulation. The insulation time is calculated as (0.8-1.2h) / 100mm, and then the temperature is raised to 1190±10℃ as soon as possible for insulation. The insulation time is calculated as (0.8-1.2h) / 100mm. Glass powder lubrication: After being taken out of the furnace, it is transferred to the glass powder spraying station for automatic spray lubrication. The glass powder model is DG844-7. 150 billet making machine billet making: After lubrication, place the big end of the ingot billet downward, and directly upset it on the 150MN billet making machine, and use a suitable piercing needle to pierce. Air cooling: After billet making, air cool to room temperature. Billet processing: The inner hole and outer surface of the billet after billet making are processed to obtain a regular and smooth surface. At the same time, the billet size must meet the mold requirements. Spraying anti-oxidation coating: Preheat the blank to 80-100℃ first, then apply anti-oxidation coating (P35-a3) to the inner and outer surfaces and end faces with a brush to prevent oxidation of the blank surface.

[0011] (2) Ingot extrusion and billeting

[0012] Process flow: billet heating - embedded lubrication - 360 vertical extruder billet opening - water cooling.

[0013] Billet heating: Place the billet with the imprint end (ingot tail) downward, load the furnace at ≤550℃, heat up to 850±10℃ and keep warm as soon as possible, the holding time is calculated as (0.8-1.2h) / 100mm, heat up to 1190±10℃ and keep warm as soon as possible, the holding time is calculated as (0.8-1.2h) / 100mm, and finally heat up to 1210±10℃ and keep warm for 40-80min. Pre-embedded lubrication: After leaving the furnace, place the billet in the pre-embedded lubrication cylinder for lubrication. Use a lubrication cylinder of suitable size, place excess glass powder in the inner hole, and fill the inner hole and outer circle of the billet with glass powder. 360 vertical extruder billet opening: Place the fully lubricated billet on the 360 ​​extruder, insert the core rod into the inner hole, and extrude the billet. Water cooling: Quickly put the extruded billet into water and cool it to room temperature.

[0014] (3) Inner hole processing

[0015] The inner hole of the extruded billet is processed to remove the oxide scale on the surface of the inner hole of the billet, while meeting the subsequent hollow forging size requirements.

[0016] (4) Hollow forging

[0017] Process flow: billet pretreatment - billet heating - forging pretreatment - hollow forging - water cooling.

[0018] Pretreatment of billet: Anti-oxidation coating is applied to the inner hole of the billet, and the billet is preheated after being sealed with aluminum silicate asbestos blanket. Billet heating: Load the billet at ≤720℃, keep it at the charging temperature for a period of time, quickly heat it to 820℃ and keep it, the holding time is calculated as (0.8-1.2h) / 100mm, quickly heat it to 1080±10℃ and keep it, the holding time is calculated as (0.8-1.2h) / 100mm. Pretreatment before forging: After taking out the insulation, spray enough glass powder into the inner hole, apply lubricant about 1mm thick on the surface of the core rod, and preheat the hammer used in the forging process in advance, the preheating temperature is ≥200℃. Hollow forging forming: Insert the core rod into the inner hole of the billet, and use a special hammer for hollow forging for forging. The forging time is controlled at 10-15min, the final forging temperature is ≥850℃, and the forging ratio is ≥2. Water cooling: After forging, quickly enter water to cool to room temperature.

[0019] (5) Solution treatment

[0020] After forging and water cooling, the billet is heated to 1000°C and kept warm, then heated to 1050±10°C and kept warm, and then taken out of the furnace and water-cooled to room temperature. The holding time is determined by the wall thickness of the forging.

[0021] Beneficial effects: The present invention is manufactured by extrusion blanking + precision forging forming method. Both forming methods have one thing in common, that is, the forming process is short in time, which conforms to the characteristics of 316LN with narrow deformation temperature range and fast temperature drop. Through extrusion blanking, a larger deformation of the steel ingot can be achieved, columnar crystals can be broken, macro-segregation can be improved, the cast structure can be broken, internal pores can be welded, and a reasonable fiber direction distribution can be obtained. The precision forging machine belongs to radial forging, which puts the metal in a three-dimensional compressive stress state, which is beneficial to improving the plasticity of the metal. Due to its fast forging speed, it is particularly suitable for forging some high-alloy steels with a narrow forging temperature range and a fast temperature drop rate.

[0022] Through hollow forging, the forging ratio of the billet is controlled, the billet is subjected to uniform stress in three directions, the deformation and recrystallization process are balanced, a more uniform grain structure is obtained, and a large amount of raw materials are saved. This method effectively reduces the manufacturing cost of the product through the coordination of extrusion billet opening and hollow forging. All the assessment indicators of the forgings meet the product requirements, and the grain size is higher than grade 7.5. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the size of the electroslag ingot in the embodiment of the present invention

[0024] Figure 2 Schematic diagram of the steel ingot heating process curve in the embodiment of the present invention

[0025] Figure 3 Schematic diagram of the size of blank 1 in the embodiment of the present invention

[0026] Figure 4Schematic diagram of the heating process curve of blank 1 in the embodiment of the present invention

[0027] Figure 5 Schematic diagram of the size of blank 2 in the embodiment of the present invention

[0028] Figure 6 Schematic diagram of the heating process curve of blank 2 in the embodiment of the present invention

[0029] Figure 7 This is a schematic diagram of the forging process structure in the embodiment of the present invention.

[0030] Figure 8 Schematic diagram of the solid solution treatment process curve in the embodiment of the present invention

[0031] Fig. 9 This is a schematic diagram of the forging structure in the embodiment of the patent of this invention. DETAILED DESCRIPTION

[0032] 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.

[0033] The specifications of the steel ingots and billets in different processes of this example are shown in Table 1.

[0034] Table 1 Specifications of ingots and billets in different processes

[0035]

[0036] See also Figure 1-9 , a TP316LN thin-wall hollow tube forming and grain size control method, the forging method comprises the following steps:

[0037] Step 1: Ingot billeting, electroslag ingot size diagram as shown Figure 1 As shown, the ingot is cut 100mm at each end, heated to 1190±10℃ according to the specified curve, and kept warm for 8h. The ingot heating process curve is as follows Figure 2 After being taken out of the furnace, it is transferred to the glass powder spraying station for automatic spraying lubrication. After lubrication, the big end (marked end) of the steel ingot is placed downward, directly upsetting on the 150MN billet making machine, and piercing with a 355 piercing needle. After billet making is completed, it is air-cooled to room temperature. Then the billet is processed, and the processed billet is billet 1, with dimensions such as Figure 3 shown.

[0038] Step 2: The steel ingot is extruded and opened. The marked end (ingot tail) of billet 1 is placed downward, and the furnace is loaded at ≤550℃. The temperature is raised to 850±10℃ as soon as possible and kept for 6h, then raised to 1190±10℃ as soon as possible and kept for 6h, and finally raised to 1210±10℃ as soon as possible and kept for 40min. The heating process curve of billet 1 is as follows: Figure 4As shown. After coming out of the furnace, the blank is placed in the embedded lubricating cylinder for lubrication. Use the 900 series lubricating cylinder, place excessive glass powder in the inner hole, and fill the inner hole and outer circle of the blank with lubricating powder. Place the fully lubricated blank on the 360 ​​extruder, insert a φ250mm core rod into the inner hole, and use the 360 ​​vertical extruder with a core rod to open the blank. The specifications after opening are φ370×φ240×5500. Then quickly put the extruded blank into a water pool to cool to room temperature.

[0039] Step 3: Billet processing: Cut a 2800mm long section of the hollow billet obtained by extrusion in step 2 to process the inner hole to remove the defects caused by extrusion. At the same time, the surface of the inner hole of the billet becomes smooth to facilitate subsequent forging. The billet specifications after processing are φ370×φ250×2800, and billet 2 is obtained. The size diagram of billet 2 is as follows Figure 5 shown.

[0040] Step 4: Hollow forging, the inner hole of the billet is coated with anti-oxidation coating, and sealed with aluminum silicate asbestos blanket. The furnace is kept at 720℃ for 1.5h, quickly heated to 820℃ for 4.0h, quickly heated to 1080±10℃, and kept for 5.0h. The heating process curve of billet 2 is as follows: Figure 6 As shown. After the insulation is taken out, a sufficient amount of glass powder is sprayed into the inner hole, and the surface of the core rod is lubricated with a lubricant about 1mm thick. The hammer used in the forging process is preheated in advance, and the preheating temperature is ≥200℃. A hollow forging hammer is used for forging at one end of the billet. The feeding time is controlled at about 5min. The billet is forged in one pass. The forging time is controlled at about 10min, and the final forging temperature is 850℃. The forging ratio is 2.5, and the forging is quickly water-cooled after forging. The structural diagram of the forging process is shown in Figure 7 shown.

[0041] Step 5: Solution treatment: heat the forged and water-cooled billet to 1000℃ and keep it for 4h, then heat it to 1050±10℃ and keep it for 0.5h-1h, then take it out of the furnace and water-cool it to room temperature. The solution treatment process curve is as follows: Figure 8 As shown, the size of the forging is Fig. 9 shown.

[0042] Compared with the prior art, the technical effects of the present invention include: by extrusion blanking, a larger deformation of the steel ingot is achieved, columnar crystals are broken, macro-segregation is improved, the cast structure is broken, the internal pores are welded, and a reasonable fiber direction distribution is obtained. Through hollow forging, the blank forging ratio is controlled, the blank is subjected to uniform stress in three directions, the deformation and recrystallization process are balanced, a more uniform grain structure is obtained, and a large amount of raw materials are saved. This method effectively reduces the manufacturing cost of the product through the coordination of extrusion blanking and hollow forging. All assessment indicators of the forgings meet the product requirements, and the grain size is higher than grade 7.5.

[0043] 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 TP316LN hollow tube forming and grain size control method, It is characterized in that Here are the steps: (1) Ingot billet making (2) Ingot extrusion and billeting (3) Inner hole processing (4) Hollow forging (5) Solution treatment 2. A TP316LN hollow tube forming and grain size control method according to claim 1, Features: The process flow of step (1) is: sawing the two ends of the steel ingot - heating the steel ingot - lubricating the glass powder - making the ingot by a billet making machine - air cooling - billet processing - spraying anti-oxidation coating.

3. A TP316LN hollow tube forming and grain size control method according to claim 2, Features: In step (1), sawing the two ends of the steel ingot: a sufficient amount of the two ends of the steel ingot should be cut off to ensure that the ingot body has no defects; heating the steel ingot: the steel ingot is loaded into the furnace at ≤550°C, and the temperature is raised to 850±10°C as soon as possible for insulation, and the insulation time is calculated as (0.8-1.2h) / 100mm, and then the temperature is raised to 1190±10°C as soon as possible for insulation, and the insulation time is calculated as (0.8-1.2h) / 100mm; glass powder lubrication: after being taken out of the furnace, it is transferred to the glass powder spraying station for automatic spraying lubrication; blank making machine blank making: after lubrication, the big end of the steel ingot blank is placed downward, and it is directly upset on the blank making machine, and a suitable piercing needle is selected for perforation; air cooling: after blank making is completed, air cooling is performed to room temperature.

4. A TP316LN hollow tube forming and grain size control method according to claim 2, Features: In step (1), the blank is processed: the inner hole and outer surface of the finished blank are processed to obtain a regular and smooth surface, and the size of the blank must meet the requirements of the mold; the anti-oxidation coating is sprayed: the blank is first preheated to 80-100°C, and then the inner and outer surfaces and the end face are coated with the anti-oxidation coating with a brush.

5. A TP316LN hollow tube forming and grain size control method according to claim 4, Features: The coating model is P35-a3, which prevents the surface of the blank from being oxidized.

6. A TP316LN hollow tube forming and grain size control method according to claim 1, Features: The process flow of step (2) is: billet heating - embedded lubrication - 360 vertical extruder billet opening - water cooling.

7. A TP316LN hollow tube forming and grain size control method according to claim 6, Features: Step (2) is specifically as follows: heating the blank: place the marked end of the blank downward, load the furnace at ≤550°C, heat it to 850±10°C as quickly as possible and keep it warm, and the insulation time is calculated as (0.8-1.2h) / 100mm, heat it to 1190±10°C as quickly as possible and keep it warm, and the insulation time is calculated as (0.8-1.2h) / 100mm, and finally heat it to 1210±10°C as quickly as possible and keep it warm for 40-80min; embedded lubrication: after taking out of the furnace, place the blank in a embedded lubrication cylinder for lubrication, use a lubrication cylinder of suitable size, place excess glass powder in the inner hole, and fill the inner hole and outer circle of the blank with glass powder; 360 vertical extruder blanking: place the fully lubricated blank on the 360 ​​vertical extruder, insert a core rod into the inner hole, and extrude and open the blank; water cooling: quickly put the extruded blank into water and cool it to room temperature.

8. A TP316LN hollow tube forming and grain size control method according to claim 1, Features: The process flow of step (4) is: billet pretreatment - billet heating - forging pretreatment - hollow forging - water cooling.

9. A TP316LN hollow tube forming and grain size control method according to claim 8, Features: Step (4) is specifically as follows: pretreatment of the billet: coating the inner hole of the billet with an anti-oxidation coating, and sealing it with an aluminum silicate asbestos blanket before loading the billet into a furnace for preheating; heating the billet: loading the billet into a furnace at ≤720°C, keeping it at the loading temperature for a period of time, rapidly heating it to 820°C for keeping it, the keeping time is calculated as (0.8-1.2h) / 100mm, rapidly heating it to 1080±10°C for keeping it, the keeping time is calculated as (0.8-1.2h) / 100mm; pretreatment before forging: after keeping it warm and taking it out, spraying a sufficient amount of glass powder into the inner hole, applying a lubricant on the surface of the core rod for lubrication, and preheating the hammer used in the forging process in advance, the preheating temperature is ≥200°C; hollow forging forming: inserting the core rod into the inner hole of the billet, forging it with a special hammer for hollow forging, and the final forging temperature is ≥850°C; Water cooling: After forging, quickly put it into water to cool to room temperature.

10. A TP316LN hollow tube forming and grain size control method according to claim 1, Features: Step (5) is specifically as follows: heating the forged and water-cooled billet to 1000°C and keeping it warm, then heating it to 1050±10°C and keeping it warm, then taking it out of the furnace and water-cooling it to room temperature, wherein the holding time is determined by the wall thickness of the forging.

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