Process for forging a large ship shaft with a medium and small forging press

Abstract

The present invention relates to a new process for forging large ship shafts on medium and small forging presses. The 31.5MN hydraulic press is used to forge the ship shaft forging into a 40-ton ingot shaft forging with end flanges. The flange has a diameter of ￠1140mm, the shaft body has a diameter of ￠718mm, the total length is 8525mm, the single weight of the forging is 31.56t, the weight of the material ingot is 40t, and the forging ratio is 4.4. On the basis of the original sizing ring dimensions, the outer diameter of the sizing ring is increased by the scheme of shrinking on a ring-shaped part to meet the upsetting requirements of the large ingot and the forging ratio of the flange. Secondly, the hot-charged ingot is fed into the furnace when the surface temperature is ≥550°C. After being kept warm at the starting forging temperature, the large ingot is upset and drawn out by using the process of high temperature, forging wide flat plates, and large reduction in area. Two upsetting and drawing operations are carried out on the large ingot, which is completed in four heating passes, and there is sufficient holding time between each heating pass to achieve through forging. After forging, it is heat-charged into the furnace for heat preservation and cooling, and then normalized and tempered to make the structure fully transformed, reduce the existence of austenitized structure, and make the forging obtain more ideal mechanical properties.

Description

Technical Field

[0001] The invention relates to a process for forging a large ship axle by using a 31.5MN hydraulic press and a small and medium-sized forging press for forging a 40-ton ingot ship axle, and belongs to the field of forging. Background Art

[0002] The existing large ship shaft forgings are made of marine carbon manganese steel, with mechanical properties requirements: tensile strength Rm ≥ 600MPa, yield strength Re ≥ 300 MPa, elongation A5 ≥ 18%, shrinkage Z ≥ 40%, impact energy AKv ≥ 18 J, and the internal quality must meet the requirements of IACS: No. 68-2000 standard. The flange diameter of the shaft forgings is Φ1140mm, the shaft diameter is Φ718mm, and the total length is 8525mm. It belongs to the large flange long shaft forgings. (Specific dimensions are as attached Figure 8 As shown in the figure, the weight of the forging is 31.56t, the weight of the material ingot is 40t, and the forging ratio is 4.4. In this regard, the forging plants with large forging equipment currently produce shaft forgings. Due to the use of existing processes in materials, forging processes and heat treatment, the delivered products have excessive defects after flaw detection and re-inspection, none of which are qualified, and the products are scrapped, which seriously affects the delivery period.

[0003] Its technical difficulties are as follows: (1) Under the traditional material composition scheme, it is very difficult to ensure that the mechanical property indexes of a ship shaft with such a large cross-section meet the specified requirements. (2) The existing largest forging equipment is a 31.5 MN hydraulic press, and the maximum forging capacity is upsetting of carbon steel ingots below 30 tons, while forging this ship shaft requires a 40-ton ingot, which obviously exceeds the expected forging capacity. At the same time, the outer diameter of the existing forging auxiliary tooling - the upsetting leak plate is only Φ1800 mm. If the existing upsetting leak plate is used for ingot upsetting, the raw material will run to the area outside the leak plate, and after the drawing process, forging defects will occur on the product, resulting in insufficient machining allowance and the risk of product rejection. (3) Generally, there will be residual tensile stress when a large steel ingot cools after casting. Coupled with certain internal defects, when a steel ingot in this state is rapidly heated, tensile thermal stress will be generated inside due to the temperature difference between the inner and outer layers of the steel ingot, and internal cracking and breakage will occur when it reaches a certain degree. At the same time, when heating a cold ingot, in order to achieve a sufficient forging effect and prevent the occurrence of one-sided deformation (yin-yang surface), it must be evenly heated and thoroughly burned at an appropriate temperature. (4) The commonly used forging process for large ship shaft forgings is to produce finished products after one upsetting and drawing of the steel ingot on a large forging press. However, large ship shaft forgings produced by this process plan often have a large number of dense defects in the flange area, and the grain size of the structure is seriously coarse. The main reason is that one upsetting and drawing cannot meet the forging ratio requirements at the flange, which will lead to the flange not being forged through and compacted, and it is very easy to have problems such as coarse grain size of the structure and unqualified non-destructive testing. At the same time, when producing finished products in one heat during the forging process, low-temperature forging will occur, which is likely to cause cracks and mixed crystals in the forgings. (5) In terms of heat treatment, due to the large difference in the effective cross-section of large ship shaft forgings and the long total length, it is easy to occur phenomena such as uneven heat treatment of each part, serious deformation of the rod part, and coarse grains at the flange end during the heat treatment process, affecting the performance indexes. Summary of the Invention

[0004] Design purpose: To avoid the deficiencies in the background technology. One is to optimize the material composition ratio and add alloying elements to improve the strength of the forging and refine the grain size. The other is to increase the outer diameter of the upsetting leak plate through the scheme of shrinking on a ring-shaped part based on the existing size of the upsetting leak plate, to meet the forging requirements of large steel ingots for forging large ship shafts with medium and small forging presses.

[0005] Design scheme: To achieve the design purpose of the present invention. The present invention starts from aspects such as composition optimization, process innovation, and strict control of process parameters, so that the large ship shaft forgings produced meet the technical requirements of the product in terms of appearance size, internal quality, and mechanical properties. The specific innovation points are as follows:

[0006] (1) Optimize the material composition ratio. Adding alloying elements can improve the strength of forgings and refine the grain size. The addition of Mn not only increases the strength but also improves its impact toughness. However, if the Mn content is too high, it is easy to cause defects such as segregation of MnS inclusions in forgings, resulting in unqualified ultrasonic flaw detection of forgings. Therefore, in this invention, the Mn content is controlled at 0.70 - 0.90%. In addition, Cr can also effectively improve the strength of forgings, refine the grains, and improve the mechanical properties. So, the Cr content in this invention is controlled at 0.20 - 0.25%; C can effectively increase the strength, so we control C at 0.45 - 0.50%. The optimized chemical composition (mass fraction %) is as Figure 9 .

[0007] (2) Combine the current existing equipment and improve the existing tooling to meet the primary condition for forging large ship shaft forgings on medium and small presses. Based on the original size of the upsetting leak plate, increase the outer diameter of the upsetting leak plate through the scheme of shrinking on a ring-shaped part to meet the upsetting requirements of large steel ingots, thereby improving the upsetting effect of large steel ingots and ensuring the forging ratio of the flange of large ship shaft forgings.

[0008] (3) Adopt hot charging of steel ingots for heating instead of cold ingot heating. The surface temperature of the hot-charged steel ingot should be ≥550°C before entering the furnace, which not only avoids the adverse effects brought by rapid heating in the temperature range where the plasticity of steel is insufficient below 550°C but also reduces the energy consumption of natural gas.

[0009] (4) After holding at the starting forging temperature, adopt the process of high-temperature, forging wide flat plates, and large reduction in area for drawing out. Upset and draw out the large steel ingot twice to create a good hydrostatic stress state in the core, completely improve the as-cast structure of the steel ingot, make the dense impurities disperse, and complete the entire forging production process in four heating times. Ensure sufficient holding time between each heating time to achieve the effect of forging through.

[0010] (5) After forging, adopt the method of hot charging into the furnace for holding and cooling, and then carry out normalizing and tempering heat treatment to make the structure transform fully and reduce the existence of austenitized structure; the cooling after normalizing and tempering adopts the method of blower spraying to inhibit the growth of lamellar ferrite and make the forgings obtain more ideal mechanical properties.

[0011] Technical solution: A process for forging large ship shafts with small and medium-sized forging presses. The ship shaft forgings are forged with a 31.5MN hydraulic press as 40-ton ingot shaft forgings with end flanges. The flange diameter is Φ1140mm and the shaft body diameter is Φ718. mm, total length 8525mm, single forging weight 31.56t, material ingot weight 40t, forging ratio 4.4; material composition: C0.45~0.50, Si≤0.45, Mn0.70~0.90, P≤0.025, S≤0.020, Cr0.20~0.25, Mo≤0.15, Ni≤0.40; and on the basis of the original size of the upsetting leak plate, the outer diameter of the upsetting leak plate is increased through the scheme of the red sleeve ring to meet the upsetting requirements of large steel ingots, thereby improving the upsetting effect of large steel ingots and ensuring the flange forging ratio of large ship shaft forgings; secondly, hot delivery ingot heating is used instead of cold ingot heating, and the surface temperature of the hot delivery ingot is ≥550 ℃ before entering the furnace, and after keeping warm at the initial forging temperature, the large ingot is upset and drawn twice by adopting the process of high temperature, forging wide flat plate, and large reduction drawing, which creates a good hydrostatic stress state in the core, completely improves the cast structure of the ingot, and makes the dense impurities dispersed. The whole forging production process is completed in four fires, and sufficient insulation time is guaranteed between each fire to achieve the effect of forging through; after forging, the hot charging furnace is used for insulation cooling, and then normalizing and tempering heat treatment is carried out to make the structure fully transformed and reduce the existence of austenitized structure; the cooling after normalizing and tempering adopts the blower spray method to inhibit the growth of lamellar ferrite and make the forgings obtain more ideal mechanical properties.

[0012] Compared with the background technology, the present invention improves the strength, grain refinement and impact toughness of forgings by optimizing the Mn content, Cr content and C content, thereby solving the problem of unqualified ultrasonic flaw detection in the background technology; secondly, on the basis of the size of the original upsetting leak plate, the outer diameter of the upsetting leak plate is increased by a red sleeve ring solution to meet the upsetting requirements of large steel ingots, thereby improving the upsetting effect of large steel ingots and ensuring the flange forging ratio of large ship shaft forgings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a diagram of the forging blank of a large ship axle forging.

[0014] Figure 2 This is a schematic diagram of the first fire forging.

[0015] Figure 3 This is a schematic diagram of the second fire steel ingot upsetting (Φ750mm) leaking plate to Φ1950mm.

[0016] Figure 4 This is the side view of the steel ingot being upset during the second fire.

[0017] Figure 5This is a schematic diagram of the upsetting (Φ750mm) of the steel ingot in the third fire from the leak plate to Φ1950mm.

[0018] Figure 6 This is the side view of the steel ingot being upset during the third fire.

[0019] Figure 7 This is the finished product picture of the Ⅳth fire.

[0020] Figure 8 It is the normalizing + tempering heat treatment process curve of large ship shaft forgings.

[0021] Figure 9 It is a background technology picture.

[0022] Figure 10 This is the optimized chemical composition table.

[0023] Figure 11 This is the composition table of large ship axle forgings.

[0024] Figure 12 It is a table of mechanical properties of large ship shaft forgings. DETAILED DESCRIPTION

[0025] Example 1: Refer to the attached Figure 1 A process for forging large ship axles with small and medium-sized forging presses. The ship axle forgings are 40-ton ingot axle forgings with end flanges using a 31.5MN hydraulic press. The flange diameter is Φ1140mm and the shaft diameter is Φ718. mm, total length 8525mm, single forging weight 31.56t, material ingot weight 40t, forging ratio 4.4; material composition: C0.45~0.50, Si≤0.45, Mn0.70~0.90, P≤0.025, S≤0.020, Cr0.20~0.25, Mo≤0.15, Ni≤0.40; and on the basis of the original size of the upsetting leak plate, the outer diameter of the upsetting leak plate is increased through the scheme of the red sleeve ring to meet the upsetting requirements of large steel ingots, thereby improving the upsetting effect of large steel ingots and ensuring the flange forging ratio of large ship shaft forgings; secondly, hot delivery ingot heating is used instead of cold ingot heating, and the surface temperature of the hot delivery ingot is ≥550 ℃ before entering the furnace, and after keeping warm at the initial forging temperature, the large ingot is upset and drawn twice by adopting the process of high temperature, forging wide flat plate, and large reduction drawing, which creates a good hydrostatic stress state in the core, completely improves the cast structure of the ingot, and makes the dense impurities dispersed. The whole forging production process is completed in four fires, and sufficient insulation time is guaranteed between each fire to achieve the effect of forging through; after forging, the hot charging furnace is used for insulation cooling, and then normalizing and tempering heat treatment is carried out to make the structure fully transformed and reduce the existence of austenitized structure; the cooling after normalizing and tempering adopts the blower spray method to inhibit the growth of lamellar ferrite and make the forgings obtain more ideal mechanical properties.

[0026] 1. Forging process: The design process parameters of the large marine shaft forging are as follows: It is forged from marine carbon manganese steel KSF60, with a forging weight of 31.560 t. The material specification is a 40 t hexagonal ingot, and one ingot is forged into one piece, with a forging ratio of 4.4. Forging temperature: 1270 °C to 750 °C.

[0027] The first heat treatment: The ingot is clamped at the jaws, the excess riser is removed, and it is reheated in the furnace and kept warm for more than 12 hours. See Figure 2 ;

[0028] The second heat treatment: The ingot is upset (Φ750 mm) to Φ1950 mm with a leakage plate; it is drawn out to an octagon of 1500 mm with a large reduction in thickness using the upper flat plate and the lower platform, and then reheated in the furnace and kept warm for more than 12 hours. See Figure 3 and 4 ;

[0029] The third heat treatment: The ingot is upset for the second time (Φ750 mm) to Φ1950 mm with a leakage plate; it is drawn out to an octagon of 1240 mm with a large reduction in thickness using the upper flat plate and the lower platform, marked and divided into parts, and then reheated in the furnace and kept warm for more than 6 hours. See Figure 5 and 6 ;

[0030] The fourth heat treatment: Each step is drawn out to the size of the process blank, the flange is rolled round, and the finished product is finished. See Figure 7 .

[0031] 2. Rough machining: After forging, 10 mm of allowance is reserved on each side based on the finish turning size for rough turning. After rough turning, ultrasonic flaw detection is carried out to ensure that the forging meets the requirements of the IACS: No. 68 - 2000 standard.

[0032] 3. Performance heat treatment: In order to ensure that the large marine shaft forging obtains high strength and good impact toughness values, a normalizing and tempering heat treatment process of heating in the furnace to 860 ± 10 °C, holding for 12 hours and then air cooling; then heating in the furnace to 580 ± 10 °C, holding for 20 hours and then air cooling and spraying before taking out of the furnace is specially formulated. The specific process curve is as Figure 8 shown.

[0033] 4. Test results: 1) The composition of the large marine shaft forging is shown in Figure 11 .

[0034] 2) The mechanical property results of the large marine shaft forging (as shown in Figure 12 ) meet the enterprise standard and the technical requirements of the customer's drawing.

[0035] 3) No excessive defects are found in the large marine shaft forging through ultrasonic flaw detection, and it meets the requirements of the IACS: No. 68 - 2000 standard.

[0036] It should be understood that although the above embodiments have made a relatively detailed textual description of the design concept of the present invention, these textual descriptions are only simple textual descriptions of the design concept of the present invention, rather than limitations on the design concept of the present invention. Any combination, addition or modification that does not exceed the design concept of the present invention falls within the protection scope of the present invention.

Claims

1. A process for forging large ship shafts using medium and small forging presses, characterized by: The 31.5MN hydraulic press is used to forge the ship shaft forging, which is a 40-ton ingot shaft forging with an end flange. The flange diameter size reaches Φ1140mm, the shaft body diameter is Φ718mm, the total length is 8525mm, the single weight of the forging is 31.56t, the weight of the material ingot is 40t, and the forging ratio is 4.4; the material composition: C 0.45 - 0.50, Si ≤ 0.45, Mn 0.70 - 0.90, P ≤ 0.025, S ≤ 0.020, Cr 0.20 - 0.25, Mo ≤ 0.15, Ni ≤ 0.40; and on the upsetting cauldrons, the outer diameter of the upsetting cauldrons is increased by shrinking on the ring parts to meet the upsetting requirements of large steel ingots, thereby improving the upsetting effect of large steel ingots and ensuring the forging ratio of the flange of large ship shaft forgings; secondly, hot charging of steel ingots for heating is adopted instead of cold ingot heating. The surface temperature of the hot-charged steel ingot is ≥550°C before entering the furnace. After holding at the starting forging temperature, a process of high temperature, forging wide flat plates, and large reduction in length is used to perform two upsetting and drawing processes on the large steel ingot, creating a good hydrostatic stress state in the core, completely improving the as-cast structure of the steel ingot, making the dense impurities disperse, and the entire forging production process is completed in four heating times, ensuring sufficient holding time between each heating time to achieve the effect of forging through; after forging, the method of hot charging into the furnace for holding and cooling is adopted, and then normalizing and tempering heat treatment is carried out to make the structure fully transformed and reduce the existence of austenitized structure; the cooling after normalizing and tempering adopts the method of blower spraying to inhibit the growth of lamellar ferrite and make the forging obtain more ideal mechanical properties.

2. The process for forging large ship shafts with medium and small forging presses according to claim 1, characterized in that: 1) Forging process: The marine carbon manganese steel KSF60 with the above-mentioned material composition is forged and formed. The weight of the forging is 31.560t, the material specification is a 40t hexagonal ingot, one ingot is forged into one piece, the forging ratio is 4.4, and the forging temperature: 1270°C - 750°C; The first heating time: The steel ingot is clamped at the jaws, the excess riser is cut off, and it is returned to the furnace for heating and holding for more than 12 hours; The second heating time: The steel ingot is upset from a Φ750mm caulron to Φ1950mm; it is drawn to an octagon of 1500mm with large reduction in length using the upper flat plate and the lower platform, and then returned to the furnace for heating and holding for more than 12 hours; The third heating time: The steel ingot is upset again from a Φ750mm caulron to Φ1950mm; it is drawn to an octagon of 1240mm with large reduction in length using the upper flat plate and the lower platform, marked and divided into parts, and then returned to the furnace for heating and holding for more than 6 hours; The fourth heating time: Each step is drawn to the process blank size, the flange is rolled round, and the finished product is finished; 2) Rough machining: After forging, 10mm allowance is reserved on one side based on the finish turning size for rough turning. After rough turning, ultrasonic flaw detection is carried out to ensure that the forging meets the requirements of the IACS: No. 68 - 2000 standard; 3) Performance heat treatment: The forging that meets the IACS: No. 68 - 2000 standard after rough machining is heated in the furnace to 860 ± 10°C, held for 12 hours and then air-cooled; then it is heated in the furnace to 580 ± 10°C, held for 20 hours and then air-cooled and sprayed out of the furnace for the normalizing and tempering heat treatment process.

3. The process for forging a large ship shaft by a medium and small-sized forging press according to claim 1 or 2, characterized in that: Actual chemical composition values (mass fraction %) of the large ship shaft after normalizing and tempering heat treatment: C 0.47 - 0.48, Si 0.20 - 0.22, Mn 0.76 - 0.81, P 0.008 - 0.009, S 0.001 - 0.002, Cr 0.22 - 0.23, Mo 0.05 - 0.07, Ni 0.02 - 0.03, the balance being iron.

4. The process for forging a large ship shaft using a medium and small-sized forging press according to claim 3, characterized in that: Actual chemical composition values (mass fraction %) of the large ship shaft after normalizing and tempering heat treatment: C 0.47, Si 0.20, Mn 0.81, P 0.009, S 0.001, Cr 0.23, Mo 0.05, Ni 0.

03.

5. The process for forging large ship shafts on medium and small forging presses according to claim 4, characterized in that: Tensile strength Rm 650 Mpa, yield strength ReL 331 MPa, elongation at break A 21.0%, reduction of area Z 42.5%, average value of impact energy absorbed Kv2 at 0°C 25 J.

6. The process for forging a large ship shaft using a medium and small-sized forging press according to claim 3, characterized in that: Actual chemical composition values (mass fraction %) of the large ship shaft after normalizing and tempering heat treatment: C 0.48, Si 0.22, Mn 0.76, P 0.008, S 0.002, Cr 0.22, Mo 0.07, Ni 0.

02.

7. The process for forging a large ship shaft on a medium and small-sized forging press according to claim 3, characterized in that: Tensile strength Rm 668 MPa, yield strength ReL 353 MPa, elongation at break A 23.0%, reduction of area Z 49.0%, average value of impact energy absorbed Kv2 at 0°C 23 J.

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