A cycle of continuous connection and continuous punching of stainless steel forging process

Abstract

The application discloses a stainless steel forging process with cyclic connection and continuous forging, which comprises three processes of AOD refining, LF refining and forging, wherein the AOD refining comprises the steps of refining preparation, decarburization, primary reduction and secondary reduction; the LF refining comprises the steps of LF refining preparation and refining; and the forging comprises the steps of fast forging, heat preservation and refining. The application has the advantages of high stability, high repeatability, convenient industrialized batch production, high production efficiency and low cost.

Description

Technical Field

[0001] This invention relates to the field of stainless steel production technology, and more specifically to a continuous stainless steel forging process. Background Technology

[0002] Stainless steel forging is a process of manufacturing metal workpieces through hot working deformation. It utilizes recrystallization to refine the grain structure and optimize the original defects of the steel ingot, such as segregation and porosity, thereby improving its mechanical properties. These forgings are widely used in high-load, complex operating conditions in the mechanical field, such as key components like nuclear power plant sealing chambers, pressure vessels, and heavy-duty bearings.

[0003] In stainless steel forging, fast forging and precision forging are two core processes, each with its own emphasis in terms of equipment, process characteristics, and applicable scenarios. Fast forging is suitable for billet preparation and preliminary forming, while precision forging is used for the final forming of high-precision, complex shapes. Fast forging achieves efficient billet preparation with high cycle time and large deformation, while precision forging achieves near-net-shape forming and high precision with little or no cutting. The two often form a combined process chain of "fast forging billet preparation + precision forging finished parts".

[0004] In actual production, some manufacturers have fast forging furnaces and precision forging furnaces far apart. After the steel ingots are rolled, they need to be transported to the precision forging furnace. The billets will experience a significant temperature drop during transportation. In order to improve the microstructure after forging, the holding time of the steel ingots in the furnace should not be too long, otherwise overheating may occur. Even if this process is used, the stainless steel products after forging still have poor ultrasonic testing performance, usually at the level of GB / T 4162 B, but cannot reach the A level standard.

[0005] Therefore, there is an urgent need for a continuous stainless steel forging process. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a cyclic continuous forging process for stainless steel to solve the problems in the background art.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows.

[0008] A continuous stainless steel forging process includes the following steps: S1, AOD Refining S11. Refining preparation: After raising the temperature of the AOD refining furnace to ≥800℃, add 18-24t of molten steel with a temperature of ≥1550℃ into the AOD refining furnace. S12, Decarburization: The gas supply method of "main O2 and auxiliary N2 + Ar" is adopted. O2 is blown in from the top of the converter, while N2 and Ar are blown in from the bottom of the furnace for stirring. The temperature of the molten steel is maintained at 1680-1740℃ when adding slag material for blowing. S13, Primary Reduction: Sampling and analyzing carbon content. When C in the furnace is ≤0.013%, ferrosilicon is added to the AOD refining furnace for reduction, with a reduction time ≥7 minutes. S14: Secondary reduction: After sampling and analysis, the Si content reaches the control target of 0.30%-0.40%, the reduction ends. The furnace temperature is measured by shaking, sampling is performed, and slag is skimmed off at a rate of ≥90%. Reduction slag is added, and the reduction time is >5 minutes. S2, LF Refining S21, LF refining preparation: Argon gas is connected to the LF refining furnace. The slag shell is broken by stirring with a large flow of argon gas. After the ladle car is driven to the heating station, the temperature is measured, and full component samples and gas samples are taken. The ladle is heated to above 1560℃. S22. Refining: After the slag turns white and the temperature is ≥1560℃, take a sample and continue to keep the white slag for ≥20 minutes; after the composition is qualified, start stirring with a large flow of argon gas, stir for 8 minutes, then blow softly for ≥15 minutes; after standing for 3 minutes, cast in a ladle at a temperature of 1530~1540℃. S3. After casting is completed, the casting is loaded into the furnace for heating and heat preservation; S4, Forging S41. Rapid forging: The castings that have been kept warm in step S3 are subjected to longitudinal and transverse forging to obtain bars, and the rapid forging time m1 of one bar is recorded. S42. Heat preservation: Transport the bar stock to the precision forging heating furnace and heat and preserve it at the target temperature of 1080-1110℃ for 60 minutes, and record the transport time of the bar stock in m2. S43. Precision forging: When the fast forging billet reaches the nth bar, the first bar is transported from the furnace to the precision forging machine for precision forging. It is forged from a 280 octagon through 5 passes to the finished bar, thus achieving a continuous forging cycle. After precision forging, the finished bar is air-cooled to a surface temperature ≥900℃, held for 6-8 hours, and then air-cooled again to obtain the finished product.

[0009] To further optimize the technical solution, the amount of ferrosilicon added in step S13 is calculated based on the oxygen consumption: (Total oxygen consumption - oxygen consumption during decarbonization - oxygen consumption during desiliconization) 1.66 = Amount of ferrosilicon required for alloying.

[0010] To further optimize the technical solution, the reducing slag material in step S14 includes 350-400 kg / furnace of quicklime, 150-250 kg / furnace of fluorite, and 0.6-1 kg / t of Al particles.

[0011] To further optimize the technical solution, in step S21, during the heating process at the heating station, lime and fluorite are added to the furnace to adjust the slag alkalinity and fluidity, and the composition is finely adjusted based on the analysis results.

[0012] To further optimize the technical solution, in step S21, during the heating process at the heating station, FeSi powder is added for diffusion deoxidation, with an addition amount of 50-120 kg / furnace; during heating, a good reducing atmosphere is maintained inside the ladle, and the oxygen control target is ≤25 ppm.

[0013] To further optimize the technical solution, the FeSi powder is added in small batches multiple times.

[0014] To further optimize the technical solution, in step S22, the diameter of the Ar gas ring should be ≥300mm, and it should not be exposed above the molten steel surface.

[0015] Further optimize the technical solution. The heating and heat preservation process in step S3 is as follows: after the casting is kept at 500±10℃ for 2 hours, it is heated to 800±10℃ at a heating rate of ≤100℃ / h and kept for 2 hours; then it is heated to 1160±10℃ at a heating rate of ≤100℃ / h and kept for 4-5 hours.

[0016] The technical solution was further optimized, and the blanking deformation amount in the fast forging in step S41 was 60.56%.

[0017] Further optimize the technical solution. In step S43, the precision forging time m3 is: m3=m1+m2; n={(60+m2) / m1}+1.

[0018] Due to the adoption of the above technical solutions, the technical progress achieved by this invention is as follows.

[0019] This invention provides a continuous, cyclic forging process for stainless steel, combining the production efficiency of fast forging and precision forging. It allows for the simultaneous fast forging and transport of new bars after the bar's holding time has elapsed, achieving coordinated production between fast and precision forging. This continuous forging process ensures each ingot is fully heated without overheating, resulting in excellent microstructure after forging. The forging process utilizes timely converter holding to prevent overheating caused by excessive holding time. Simultaneously, the close integration of fast and precision forging ensures uninterrupted production, further refining the grain size and improving the performance of the stainless steel. This invention offers advantages such as high stability, high repeatability, ease of industrial mass production, high production efficiency, and low cost. Attached Figure Description

[0020] Figure 1 This is an overall flowchart of the present invention; Figure 2 This is a process flow diagram of the AOD refining to forging stage of the present invention; Figure 3 This is a heating curve of the casting before forging according to the present invention; Figure 4 This is a metallographic diagram of Embodiment 1 of the present invention; Figure 5 This is a metallographic diagram of Embodiment 2 of the present invention; Figure 6 This is a metallographic diagram of Comparative Example 1 of the present invention; Figure 7 This is a metallographic diagram of Comparative Example 2 of the present invention. Detailed Implementation

[0021] A continuous, cyclical stainless steel forging process, such as... Figure 1 As shown, the process includes electric furnace smelting, AOD refining, LF refining, casting, furnace charging and holding, rapid forging, furnace return and holding, precision forging, machining, and physical and chemical testing and flaw detection. The main process from AOD refining to precision forging is as follows: Figure 2 As shown, the specific steps include: S1, AOD Refining S11. Refining preparation: After raising the temperature of the AOD refining furnace to ≥800℃, add 18-24t of molten steel with a temperature of ≥1550℃ into the AOD refining furnace.

[0022] S12, Decarburization: The main O2 and auxiliary N2+Ar gas supply method is adopted, and the temperature of molten steel is maintained at 1680-1740℃ when adding slag material; the slag material is quicklime and fluorite.

[0023] S13. Primary reduction: Sampling and analyzing carbon content. When C in the furnace is ≤0.013%, ferrosilicon is added to the AOD refining furnace for reduction. The reduction time is ≥7 minutes. The amount of ferrosilicon added is calculated according to the following formula.

[0024] (Total oxygen consumption - oxygen consumption during decarbonization - oxygen consumption during desiliconization) 1.66 = Amount of ferrosilicon required for alloying; where oxygen content is in m³ and ferrosilicon content is in kg.

[0025] S14: Secondary Reduction: After sampling and analysis, the Si content reaches the control target of 0.30%-0.40%, the reduction ends. The furnace temperature is measured by shaking, sampling is performed, and slag is skimmed off at a rate ≥90%. Reducing slag is added, and the reduction time is >5 minutes. The reducing slag includes 350-400 kg / furnace of quicklime, 150-250 kg / furnace of fluorite, and 0.6-1 kg of Al particles per ton of molten steel.

[0026] S2, LF Refining S21, LF refining preparation: Argon gas is connected to the LF refining furnace. A large flow of argon gas is used to stir and break the slag shell. After the ladle car is driven to the heating station, the temperature is measured, and all components and gas samples are taken. The ladle is heated to above 1560℃.

[0027] During the heating process at the heating station, lime and fluorite are added to the furnace to adjust the alkalinity and fluidity of the slag, and the composition is finely adjusted based on the analysis results.

[0028] During the heating process at the heating station, FeSi powder is added for diffusion deoxidation, at a rate of 50-120 kg / furnace. A good reducing atmosphere is maintained inside the ladle during heating, with oxygen control targeting ≤25 ppm. FeSi powder is added in small batches multiple times, and Al powder can be added when Si levels are high.

[0029] S22. Refining: After the slag has turned white and the temperature is ≥1560℃, take a sample and continue to keep the white slag for ≥20 minutes; after the composition is qualified, start stirring with a large flow of argon gas, stir for 8 minutes, and then blow softly for ≥15 minutes; after standing for 3 minutes, cast in a ladle with a ladle temperature of 1530~1540℃; the diameter of the Ar gas ring is ≥300mm and does not expose the surface of the molten steel.

[0030] S3. After casting is completed, the casting is loaded into the furnace for heating and heat preservation. The heating and heat preservation process is as follows: after holding the casting at 500±10℃ for 2 hours, the temperature is increased to 800±10℃ at a heating rate of ≤100℃ / h and held for 2 hours; then the temperature is increased to 1160±10℃ at a heating rate of ≤100℃ / h and held for 4-5 hours.

[0031] S4, Forging S41. Rapid Forging: The casting completed in step S3 is subjected to longitudinal and transverse forging to obtain a bar stock, and the rapid forging time m1 of one bar stock is recorded. The initial deformation of the rapid forging in this step is 60.56%.

[0032] S42. Heat preservation: Transport the bar stock to the precision forging furnace and heat it at the target temperature of 1080-1110℃ for 60 minutes to ensure that the steel ingot can be thoroughly heated without overheating, resulting in excellent microstructure after forging; at the same time, record the transport time of the bar stock in m2.

[0033] S33, Precision Forging: When the billet reaches the nth bar, the first bar is transported from the furnace to the precision forging machine for precision forging. It is forged from a 280 octagon through 5 passes to the finished bar, thus achieving a continuous forging cycle. The fine forging time m3 is: m3=m1+m2; n={(60+m2) / m1}+1.

[0034] The precision forging process is as follows: 280 octagonal bar is forged into finished bar stock through 5 passes, the 5 passes being: 280 octagonal bar - Φ270 - Φ225 - Φ225 (air run with temperature control) - Φ185 - Φ176; after precision forging, the finished bar stock is air cooled to a surface temperature ≥900℃ and held for 6-8 hours; then it is air cooled again to obtain the product.

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Example 1:

[0036] S1, AOD Refining S11. Refining preparation: After raising the temperature of the AOD refining furnace to ≥800℃, add 20t of molten steel at 1560℃ into the AOD refining furnace.

[0037] S12, Decarburization: The gas supply method of "main O2 and auxiliary N2 + Ar" top and bottom blowing is adopted, that is, O2 is blown in from the top of the converter, while N2 and Ar are blown in from the bottom of the furnace for stirring; the temperature of molten steel is maintained at 1700℃ when slag is added and the blowing is carried out.

[0038] S13. Primary reduction: Sampling and analyzing carbon content. When C in the furnace is ≤0.013%, ferrosilicon is added to the AOD refining furnace for reduction, and the reduction time is ≥7 minutes.

[0039] S14: Secondary Reduction: After sampling and analysis, the Si content reaches the control target of 0.30%-0.40%, the reduction ends. The furnace is shaken for temperature measurement, sampling, and slag removal ≥90%. Reduction slag is added, and the reduction time is 6 minutes. The reduction slag includes 400 kg of quicklime, 200 kg of fluorite, and 16 kg of Al particles.

[0040] S2, LF Refining S21, LF Refining Preparation: Argon gas is connected to the LF refining furnace. The slag shell is broken by stirring with a large flow of argon gas. After the ladle car is driven to the heating station, the temperature is measured, and all components and gas samples are taken. The ladle is heated to 1580℃.

[0041] During the heating process at the heating station, lime and fluorite are added to the furnace to adjust the slag basicity and fluidity, and the composition is fine-tuned based on the analysis results. During the heating process at the heating station, 100 kg of FeSi powder is added to the furnace for diffusion deoxidation; a good reducing atmosphere is maintained inside the ladle during heating, with oxygen control targeting ≤25 ppm. S22, Refining: After the slag has fully turned white and the temperature is ≥1560℃, a sample is taken, and the slag is kept white for 20 minutes; after the composition is found to be qualified, high-flow-rate argon gas stirring is started, and after stirring for 8 minutes, soft blowing is performed for 15 minutes. After standing for 3 minutes, the ladle is lifted for casting, with the ladle temperature at 1540℃. During the refining process, the diameter of the Ar gas ring inside the furnace is ≥300 mm to ensure that the molten steel surface is not exposed.

[0042] S3. After casting is completed, the casting is loaded into the furnace for heating and heat preservation. The heating and heat preservation process is as follows: after holding the casting at 500℃ for 2 hours, the temperature is increased to 800℃ at a rate of 100℃ / h and held for 2 hours; then the temperature is increased to 1160℃ at a rate of 100℃ / h and held for 5 hours.

[0043] S4, Forging S41. Rapid Forging: The casting completed in step S3 is subjected to longitudinal and transverse forging to obtain a bar stock, and the rapid forging time for one bar stock is recorded. In this step, the initial deformation of the rapid forging is 60.56%, and the rapid forging time is 10 minutes.

[0044] S42. Heat preservation: The bar stock is transported to the precision forging furnace and heated and preserved at the target temperature of 1100℃ for 60 minutes; and the transport time of the bar stock is recorded. In this embodiment, the time for the bar stock to be transported from the fast forging station to the precision forging furnace is 10 minutes.

[0045] S43, Precision Forging: When the fast forging billet reaches the nth bar, the first bar is transported from the furnace to the precision forging machine for precision forging. It is forged from a 280 octagon through 5 passes to the finished bar, thus achieving a continuous forging cycle.

[0046] Among them, the precision forging time = rapid forging time + transportation time = 20 minutes. n = {(60min + transportation time) / rapid forging time} + 1 = {(60min + 10min) / 10min} + 1 = 8.

[0047] The precision forging process is as follows: 280 octagonal bar is forged into finished bar stock through 5 passes, the 5 passes being: 280 octagonal bar - Φ270 - Φ225 - Φ225 (air run with temperature control) - Φ185 - Φ176; after precision forging, the finished bar stock is air cooled to a surface temperature of 900℃ and held for 6 hours; then it is air cooled again to obtain the product. Example 2:

[0048] The difference between this embodiment and Embodiment 1 lies in the process of step S4. In this application, step S4 is as follows: S4, Forging S41. Rapid Forging: The casting completed in step S3 is subjected to longitudinal and transverse forging to obtain a bar stock, and the rapid forging time for one bar stock is recorded. In this step, the initial deformation of the rapid forging billet is 60.56%, and the rapid forging time is 12 minutes.

[0049] S42. Heat preservation: The bar stock is transported to the precision forging furnace and heated and preserved at the target temperature of 1110℃ for 60 minutes; and the transport time of the bar stock is recorded. In this embodiment, the time for the bar stock to be transported from the fast forging station to the precision forging furnace is 8 minutes.

[0050] S43, Precision Forging: When the fast forging billet reaches the nth bar, the first bar is transported from the furnace to the precision forging machine for precision forging. It is forged from a 280 octagon through 5 passes to the finished bar, thus achieving a continuous forging cycle.

[0051] Among them, the precision forging time = rapid forging time + transportation time = 20 minutes. n = {(60min + transport time) / rapid forging time} + 1 = {(60min + 8min) / 12min} + 1 = 7.

[0052] The precision forging process is as follows: 280 octagonal bar is forged into finished bar stock through 5 passes, the 5 passes being: 280 octagonal bar - Φ270 - Φ225 - Φ225 (air run with temperature control) - Φ185 - Φ176; after precision forging, the finished bar stock is air cooled to a surface temperature of 900℃ and held for 8 hours; then it is air cooled again to obtain the product. Comparative Example 1:

[0053] The difference between this comparative example and Example 1 is that the bar stock transportation time is not recorded in step S31, and after the heat preservation in step S33 is completed, the bar stock after the heat preservation in step S32 is directly sent into the precision forging furnace. Comparative Example 2:

[0054] The difference between this comparative example and Example 2 is that the bar stock transportation time is not recorded in step S31, and after the heat preservation in step S33 is completed, the bar stock after the heat preservation in step S32 is directly sent into the precision forging furnace.

[0055] The bars prepared in Examples 1-2 and Comparative Examples 1-2 were machined and polished to obtain stainless steel finished products. The grain size grades were then observed using an optical microscope, and were found to be 6, 6, 5, and 5, respectively. The images are attached. Figures 4-7 As shown in the figure. The test results show that, because the bar stock in this invention is subjected to continuous forging cycles, the stainless steel can be thoroughly heated without overheating. Therefore, the microstructure after forging is more uniform and the grains are finer than those in the comparative example.

[0056] The stainless steel products prepared in Examples 1-2 and Comparative Examples 1-2 were tested for quality grade using longitudinal wave according to the method of GB / T 4162. The experimental results are shown in Table 1.

[0057] Table 1: Group Single defect flat bottom hole diameter Multiple defect flat bottom hole diameter Multiple defect spacing Long strip defect flat bottom hole diameter Long strip defect length Quality rating Example 1 black skin 3.2 2.0 25 2.0 25 B Example 1 black finish 2.0 1.2 25 1.2 25 A Example 2 black skin 3.2 2.0 25 2.0 25 B Example 2 black finish 2.0 1.2 25 1.2 25 A Comparative Example 1 black skin 4.0 3.2 25 3.2 25 C Comparative Example 1 black finish 3.2 2.0 25 2.0 25 B Comparative Example 2 black skin 4.0 3.2 25 3.2 25 C Comparative Example 2 black finish 3.2 2.0 25 2.0 25 B As shown in Table 1, the stainless steel prepared by this invention exhibits superior black skin flaw detection results compared to GB / T 4162 Class B, and its flaw detection after finishing meets GB / T 4162 Class A. In Comparative Examples 1-2, due to overheating during bar remelting, the black skin flaw detection results were at GB / T 4162 Class C, and the final finishing flaw detection effect was also poor, with test results at GB / T 4162 Class B.

[0058] In summary, this invention combines the production efficiency of fast forging and precision forging. By coordinating the production of fast forging and precision forging, new bars can be forged and transported simultaneously after the holding time is reached, achieving a continuous forging effect. This ensures that each steel ingot is fully heated without overheating, resulting in excellent microstructure after forging. Furthermore, the forging process of this invention further refines the grain size and improves the performance of stainless steel.

Claims

1. A continuous stainless steel forging process, characterized in that, Specifically, the following steps are included: S1, AOD Refining S11. Refining preparation: After raising the temperature of the AOD refining furnace to ≥800℃, add 18-24t of molten steel with a temperature of ≥1550℃ into the AOD refining furnace. S12, Decarburization: The gas supply method is "main O2, auxiliary N2 + Ar"; the temperature of the molten steel is maintained at 1680-1740℃ when slag is added and the molten steel is blown. S13, Primary Reduction: Sampling and analyzing carbon content. When C in the furnace is ≤0.013%, ferrosilicon is added to the AOD refining furnace for reduction, with a reduction time ≥7 minutes. S14: Secondary reduction: After sampling and analysis, the Si content reaches the control target of 0.30%-0.40%, the reduction ends. The furnace temperature is measured by shaking, sampling is performed, and slag is skimmed off at a rate of ≥90%. Reduction slag is added, and the reduction time is >5 minutes. S2, LF Refining S21, LF refining preparation: Argon gas is connected to the LF refining furnace. The slag shell is broken by stirring with a large flow of argon gas. After the ladle car is driven to the heating station, the temperature is measured, and full component samples and gas samples are taken. The ladle is heated to above 1560℃. S22. Refining: After the slag turns white and the temperature is ≥1560℃, take a sample and continue to keep the white slag for ≥20 minutes; after the composition is qualified, start stirring with a large flow of argon gas, stir for 8 minutes, then blow softly for ≥15 minutes; after standing for 3 minutes, cast in a ladle at a temperature of 1530~1540℃. S3. After casting is completed, the casting is loaded into the furnace for heating and heat preservation; S4, Forging S41. Rapid forging: The castings that have been kept warm in step S3 are subjected to longitudinal and transverse forging to obtain bars, and the rapid forging time m1 of one bar is recorded. S42. Heat preservation: Transport the bar stock to the precision forging heating furnace and heat and preserve it at the target temperature of 1080-1110℃ for 60 minutes, and record the transport time of the bar stock in m2. S43. Precision forging: When the fast forging billet reaches the nth bar, the first bar is transported from the furnace to the precision forging machine for precision forging. It is forged from a 280 octagon through 5 passes to the finished bar, thus achieving a continuous forging cycle. After precision forging, the finished bar is air-cooled to a surface temperature ≥900℃, held for 6-8 hours, and then air-cooled again to obtain the finished product.

2. The stainless steel forging process of continuous cyclic forging according to claim 1, characterized in that: The amount of ferrosilicon added in step S13 is calculated based on the oxygen consumption: (Total oxygen consumption - oxygen consumption during decarbonization - oxygen consumption during desiliconization) 1.66 = Amount of ferrosilicon required for alloying.

3. The cyclic continuous forging process for stainless steel according to claim 2, characterized in that: The reducing slag material in step S14 includes 350-400 kg / furnace of quicklime, 150-250 kg / furnace of fluorite, and 0.6-1 kg / t of Al particles.

4. The cyclic continuous forging process for stainless steel according to claim 4, characterized in that: In step S21, during the heating process at the heating station, lime and fluorite are added to the furnace to adjust the slag alkalinity and fluidity, and the composition is finely adjusted based on the analysis results.

5. The cyclic continuous forging process for stainless steel according to claim 1, characterized in that: In step S21, during the heating process at the heating station, FeSi powder is added for diffusion deoxidation, with an addition amount of 50-120 kg / furnace. During heating, a good reducing atmosphere is maintained inside the ladle, and the oxygen control target is ≤25 ppm.

6. The cyclic continuous forging process for stainless steel according to claim 5, characterized in that: The FeSi powder is added in small batches multiple times.

7. The cyclic continuous forging process for stainless steel according to claim 1, characterized in that: In step S22, the diameter of the Ar gas ring is ≥300mm and does not protrude above the molten steel surface.

8. The cyclic continuous forging process for stainless steel according to claim 1, characterized in that: The heating and holding process in step S3 is as follows: after holding the casting at 500±10℃ for 2 hours, the temperature is increased to 800±10℃ at a heating rate of ≤100℃ / h and held for 2 hours; then the temperature is increased to 1160±10℃ at a heating rate of ≤100℃ / h and held for 4-5 hours.

9. The cyclic continuous forging process for stainless steel according to claim 1, characterized in that: In step S41, the initial deformation of the fast forging billet is 60.56%.

10. The cyclic continuous forging process for stainless steel according to claim 1, characterized in that: In step S43, the fine forging time m3 is: m3 = m1 + m2; n = {(60 + m2) / m1} + 1.

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