A method for dehydrogenating large thick-wall forgings

Abstract

The present invention provides a method for dehydrogenating a large thick-walled forging with holes, which can make the core and surface of the large thick-walled forging reach a supercooling temperature of 200-350°C at the same time, so as to improve the dehydrogenation effect of the forging, and relates to the technical field of heat treatment of forgings. A method for dehydrogenating a large thick-walled forging, wherein a center hole is provided in the center of the forging, and the method comprises the following steps: forging the forging; rapid cooling; strong cooling: reheating and cooling: cooling the forging at a rate of ≤50°C / hour until the temperature of the inner and outer surfaces of the forging drops to 250-350°C; fully keeping the forging warm, and the insulation temperature is 250-350°C. The present invention ensures the dehydrogenation effect of large thick-walled forgings.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment of forgings, and in particular to a method for dehydrogenating large thick-wall forgings. Background Art

[0002] Mn-Ni-Mo series 16MND5 / 18MND5 and ASME SA508Gr.3Cl.1 / Cl.2 steels are used in the manufacturing of high-grade forgings such as nuclear islands of large nuclear power plants, high-speed centrifuges, and high-pressure vessels because of their good strength, toughness, hardenability, weldability, fatigue resistance, and radiation resistance. In recent years, with the development of the third-generation nuclear power technology, Mn-Ni-Mo steel forgings have met the requirements of high strength and high toughness required for a design life of 60 years and harsh working environments such as high temperature, high pressure, high humidity, and radiation. At the same time, the shape of the forgings has developed towards larger sizes, thicker walls, higher requirements for purity, homogeneity, and integrated structures, making the manufacturing of forgings increasingly difficult. Studies have shown that Mn-Ni-Mo series 16MND5 / 18MND5 and ASMESA508Gr.3Cl.1 / Cl.2 steels have good performance but also high sensitivity to hydrogen-induced cracking. Its hydrogen-free cracking limit hydrogen content requirement is no more than 0.8ppm, which has an extremely high limit threshold value, much higher than the 2-3ppm hydrogen-free cracking sensitivity limit hydrogen content of conventional steels. In order to ensure that the actual hydrogen content of Mn-Ni-Mo forgings is reduced to below the hydrogen-free cracking sensitivity limit hydrogen content, and reduce the aggregation and combination of hydrogen with defects and organizational stress in the center of the forgings, the following methods are usually adopted to remove hydrogen from the steel: Method 1: Use medium and high vacuum smelting + pouring (called double vacuum method) during smelting to remove the hydrogen content in the forging material; Method 2: After forging and before heat treatment, the forging is quickly supercooled to 200-350℃ to produce phase transformation, so as to promote the uniform transformation of austenite in the core of the forging to ferrite + pearlite structure, increase the diffusion coefficient, and accelerate the diffusion of hydrogen accumulation in the steel. After that, it is heated to 620-670℃ to remove it and accelerate the diffusion of hydrogen accumulation in the forging.

[0003] The above method 1 is obviously not suitable for completing forgings. As for the second method, since large thick-walled forgings have thick walls, the core of the forgings cools very slowly after forging. Therefore, the thicker the forgings, the harder and slower the phase change in the core of the forgings, and the harder it is for hydrogen to diffuse. Especially for extra-thick-walled forgings with an effective thickness of 500 mm or more, it is difficult to ensure that the core and surface of the forgings reach a supercooling temperature of 200-350°C at the same time using the above process, resulting in hydrogen accumulation and difficulty in diffusion, and poor dehydrogenation effect. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a large thick-wall forging dehydrogenation method which can make the core and surface of the large thick-wall forging with holes reach the supercooling temperature of 200-350℃ at the same time, so as to improve the dehydrogenation effect of the forging.

[0005] The invention solves the technical problem by adopting a technical solution: a method for dehydrogenating a large thick-walled forging, wherein a center hole is provided at the center of the forging, and the method comprises the following steps:

[0006] Step 1, forging the forging;

[0007] Step 2, rapid cooling: After the forging is completed, the outer surface and inner surface of the forging are cooled at a cooling rate of 8°C / min to 15°C / min at the same time. During the cooling process, the temperature of the outer surface and the inner surface of the forging is measured. When the temperature of either the outer surface or the inner surface is between 480°C and 500°C, the rapid cooling is stopped;

[0008] Step 3, forced cooling: cool the outer surface and inner surface of the forging at a cooling rate of 3°C / min to 7°C / min at the same time, measure the temperature of the outer surface and inner surface of the forging during the cooling process, and stop forced cooling when the temperature of either the outer surface or the inner surface is between 400°C and 450°C;

[0009] Step 4, reheating and cooling: air-cool the forging to transfer the heat in the core of the forging to the outer and inner surfaces of the forging, so that the surface of the forging is reheated. After the reheating is completed, measure the temperature of the outer and inner surfaces of the forging. If the lowest surface temperature of the outer and inner surfaces of the forging exceeds 500°C, perform steps 2, 3 and 4. If the lowest surface temperature of the outer and inner surfaces of the forging exceeds 450°C but is less than 500°C, perform steps 3 and 4. If the lowest surface temperature of the outer and inner surfaces of the forging is less than 450°C, perform step 5.

[0010] Step 5: Cool the forging at a rate of ≤50°C / hour until the temperature of the inner and outer surfaces of the forging drops to 250-350°C;

[0011] Step 6: Fully heat-insulate the forgings at a temperature of 250-350°C;

[0012] Step 7: Heat the forging to 620°C-670°C and keep it warm for more than 100 hours.

[0013] Furthermore, the effective wall thickness of the forging is 500-1500 mm, and the material of the forging is ASME SA508 Gr.3, 16MND5 or 18MND5.

[0014] Furthermore, in the step 2, the outer surface and the inner surface of the forging are cooled simultaneously by spraying.

[0015] Furthermore, in the step three, the outer surface and the inner surface of the forging are cooled simultaneously by means of air jets.

[0016] Furthermore, the step five adopts furnace cooling.

[0017] The beneficial effect of the invention is that: the large thick-wall forging dehydrogenation method of the present invention cools the center hole wall (inner surface of the forging) and the outer surface at a cooling rate of 8°C / min to 15°C / min after the forging is completed, until the temperature of any one of the outer surface and the inner surface stops at 480°C to 500°C, and then cools the outer surface and the inner surface of the forging 1 at a cooling rate of 3°C / min to 7°C / min at the same time, until the temperature of any one of the outer surface and the inner surface stops at 400°C to 450°C, and then repeatedly reheats and cools the forging until the reheated surface temperature is lower than 450°C, and then cools the forging 1 at a rate of ≤50°C / hour to cool the forging to 250-350°C. The above method can avoid the forging from cooling too fast, resulting in a large temperature difference between the core 12 of the forging and the surface and cracking, and can also reduce the temperature of the core 12 of the forging at a relatively fast speed, so that the temperature of the core 12 of the forging is quickly reduced to a temperature close to the surface temperature of the forging. The above process ensures that the core and surface of the forging reach the supercooling temperature of 200-350℃ almost at the same time, ensuring that the core structure of the forging undergoes ferrite + pearlite phase transformation, creating conditions for the diffusion of hydrogen in the forging and improving the dehydrogenation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a flow chart of the present invention;

[0019] Figure 2 It is a schematic diagram of the structure of the forging;

[0020] Shown in the figure: forging 1, center hole 11, core 12. DETAILED DESCRIPTION

[0021] The invention is further described below with reference to the accompanying drawings and embodiments.

[0022] like Figure 1 , Figure 2 As shown, a method for dehydrogenating a large thick-walled forging is invented, wherein a center hole is provided at the center of the forging, and the method comprises the following steps:

[0023] Step 1, forging the forging 1;

[0024] Step 2, rapid cooling: After the forging is completed, the outer surface and the inner surface (the hole wall of the center hole 11) of the forging 1 are cooled at a cooling rate of 8°C / min to 15°C / min. During the cooling process, the temperature of the outer surface and the inner surface of the forging 1 is measured. When the temperature of any of the outer surface and the inner surface is between 480°C and 500°C, the rapid cooling is stopped;

[0025] Step 3, forced cooling: the outer surface and the inner surface of the forging 1 are cooled at a cooling rate of 3°C / min to 7°C / min at the same time, and the temperature of the outer surface and the inner surface of the forging 1 is measured during the cooling process. When the temperature of any one of the outer surface and the inner surface is 400°C to 450°C, the forced cooling is stopped;

[0026] Step 4, reheating and cooling: air-cool the forging 1 to transfer the heat in the core of the forging 1 to the outer surface and the inner surface of the forging 1, so that the surface of the forging 1 is reheated. After the reheating is completed, measure the temperature of the outer surface and the inner surface of the forging 1. If the lowest surface temperature of the outer surface and the inner surface of the forging 1 exceeds 500°C, perform steps 2, 3 and 4. If the lowest surface temperature of the outer surface and the inner surface of the forging 1 exceeds 450°C but is less than 500°C, perform steps 3 and 4. If the lowest surface temperature of the outer surface and the inner surface of the forging 1 is less than 450°C, perform step 5.

[0027] Step 5, cooling the forging 1 at a rate of ≤50°C / hour until the temperature of the inner and outer surfaces of the forging drops to 250-350°C;

[0028] Step 6: Fully heat-insulate the forging 1 to fully cause phase change in its structure, and the heat-insulating temperature is 250-350°C;

[0029] Step 7: Heat the forging 1 to 620° C. to 670° C. and keep it warm for more than 100 hours.

[0030] In step 1, the forging temperature of the forging 1 can be obtained by looking up the table according to the material of the forging 1.

[0031] The method for dehydrogenating a large thick-walled forging of the present invention comprises the following steps: after forging of the forging is completed, the center hole wall (inner surface of the forging) and the outer surface are cooled at a cooling rate of 8°C / min to 15°C / min simultaneously, until the temperature of any one of the outer surface and the inner surface stops at 480°C to 500°C, and then the outer surface and the inner surface of the forging 1 are cooled at a cooling rate of 3°C / min to 7°C / min simultaneously, until the temperature of any one of the outer surface and the inner surface stops at 400°C to 450°C, and then the forging is repeatedly reheated and cooled until the reheated surface temperature is lower than 450°C, and then the forging 1 is cooled at a rate of ≤50°C / hour to cool the forging to 250-350°C. The above method can avoid the forging from cooling too fast, which may cause the temperature difference between the core 12 of the forging and the surface to be too large and crack, and at the same time, the temperature of the core 12 of the forging can be reduced at a relatively fast speed, so that the temperature of the core 12 of the forging is quickly reduced to a temperature close to the surface temperature of the forging. The above process ensures that the core and surface of the forging reach the supercooling temperature of 200-350℃ almost at the same time, ensuring that the core structure of the forging undergoes ferrite + pearlite phase transformation, creating conditions for the diffusion of hydrogen in the forging and improving the dehydrogenation efficiency.

[0032] In step 2 of the present invention, the outer surface and the inner surface of the forging 1 can be cooled simultaneously by spraying. In step 3, the outer surface and the inner surface of the forging 1 can be cooled simultaneously by air jetting. Of course, other existing cooling methods can also be used for cooling in step 2 and step 3. Step 5 can specifically be furnace cooling.

[0033] Example 1

[0034] The material of the forging is: ASME SA508 Gr.3, a center hole is provided at the center of the forging, and the effective wall thickness of the forging is 500 mm; the dehydrogenation method of the forging is:

[0035] Step 1, forging the forging at a temperature of 1050° C.

[0036] Step 2: Rapid cooling: After the forging is completed, the outer surface and inner surface of the forging are cooled at a cooling rate of 8°C / min at the same time. The temperature of the outer surface and inner surface of the forging is measured during the cooling process. When the temperature of either the outer surface or the inner surface is 480°C, the rapid cooling is stopped.

[0037] Step 3, forced cooling: Cool the outer and inner surfaces of the forging at a cooling rate of 3°C / min at the same time. Measure the temperature of the outer and inner surfaces of the forging during the cooling process. When the temperature of either the outer or inner surface reaches 400°C, stop forced cooling.

[0038] Step 4, reheating and cooling: air-cool the forging to transfer the heat in the core of the forging to the outer and inner surfaces of the forging, so that the surface of the forging is reheated. The reheating ends when the surface temperature of the forging no longer rises. After the reheating ends, measure the temperature of the outer and inner surfaces of the forging. If the lowest surface temperature of the outer and inner surfaces of the forging exceeds 500°C, then perform steps 2, 3 and 4. If the lowest surface temperature of the outer and inner surfaces of the forging exceeds 450°C but is less than 500°C, then perform steps 3 and 4. If the lowest surface temperature of the outer and inner surfaces of the forging is less than 450°C, then perform step 5.

[0039] Step 5: Cool the forging at a rate of 50°C / hour until the temperature of the inner and outer surfaces of the forging drops to 250-350°C;

[0040] Step 6: Fully heat-insulate the forgings at a temperature of 250-350°C;

[0041] Step 7: Heat the forging to 620°C and keep it warm for more than 100 hours.

[0042] The forgings obtained by the above method are free of cracks, and the hydrogen content of the forgings is required to be no higher than 0.8ppm, which is qualified.

[0043] Example 2

[0044] The material of the forging is: 16MND5, a center hole is provided at the center of the forging, and the effective wall thickness of the forging is 1000mm; the dehydrogenation method of the forging is:

[0045] Step 1, forging the forging at a temperature of 1050° C.

[0046] Step 2: Rapid cooling: After the forging is completed, the outer surface and inner surface of the forging are cooled at a cooling rate of 12°C / min. During the cooling process, the temperature of the outer surface and inner surface of the forging is measured. When the temperature of either the outer surface or the inner surface is 490°C, the rapid cooling is stopped.

[0047] Step 3: forced cooling: cool the outer and inner surfaces of the forging at a cooling rate of 5°C / min at the same time. During the cooling process, measure the temperature of the outer and inner surfaces of the forging. When the temperature of either the outer or inner surface reaches 430°C, stop forced cooling.

[0048] Step 4, reheating and cooling: air-cool the forging to transfer the heat in the core of the forging to the outer and inner surfaces of the forging, so that the surface of the forging is reheated. After the reheating is completed, measure the temperature of the outer and inner surfaces of the forging. If the lowest surface temperature of the outer and inner surfaces of the forging exceeds 500°C, perform steps 2, 3 and 4. If the lowest surface temperature of the outer and inner surfaces of the forging exceeds 450°C but is less than 500°C, perform steps 3 and 4. If the lowest surface temperature of the outer and inner surfaces of the forging is less than 450°C, perform step 5.

[0049] Step 5: Cool the forging at a rate of 30°C / hour until the temperature of the inner and outer surfaces of the forging drops to 250-350°C;

[0050] Step 6: Fully heat-insulate the forgings at a temperature of 250-350°C;

[0051] Step 7: Heat the forging to 650°C and keep it warm for more than 100 hours.

[0052] The forgings obtained by the above method are free of cracks, and the hydrogen content of the forgings is required to be no higher than 0.8ppm, which is qualified.

[0053] Example 3

[0054] The material of the forging is: 18MND5, a center hole is provided at the center of the forging, and the effective wall thickness of the forging is 1500mm; the dehydrogenation method of the forging is:

[0055] Step 1, forging the forging at a temperature of 1050° C.

[0056] Step 2: Rapid cooling: After the forging is completed, the outer and inner surfaces of the forging are cooled at a cooling rate of 15°C / min. During the cooling process, the temperatures of the outer and inner surfaces of the forging are measured. When the temperature of either the outer or inner surface is 500°C, the rapid cooling is stopped.

[0057] Step 3, forced cooling: cool the outer and inner surfaces of the forging at a cooling rate of 7°C / min at the same time, measure the temperature of the outer and inner surfaces of the forging during the cooling process, and stop forced cooling when the temperature of either the outer or inner surface reaches 450°C;

[0058] Step 4, reheating and cooling: air-cool the forging to transfer the heat in the core of the forging to the outer and inner surfaces of the forging, so that the surface of the forging is reheated. After the reheating is completed, measure the temperature of the outer and inner surfaces of the forging. If the lowest surface temperature of the outer and inner surfaces of the forging exceeds 500°C, perform steps 2, 3 and 4. If the lowest surface temperature of the outer and inner surfaces of the forging exceeds 450°C but is less than 500°C, perform steps 3 and 4. If the lowest surface temperature of the outer and inner surfaces of the forging is less than 450°C, perform step 5.

[0059] Step 5: Cool the forging at a rate of 10°C / hour until the temperature of the inner and outer surfaces of the forging drops to 250-350°C;

[0060] Step 6: Fully heat-insulate the forgings at a temperature of 250-350°C;

[0061] Step 7: Heat the forging to 670°C and keep it warm for more than 100 hours.

[0062] The forgings obtained by the above method are free of cracks, and the hydrogen content of the forgings is required to be no higher than 0.8ppm, which is qualified.

Claims

1. A method for dehydrogenating a large thick-walled forging, wherein a center hole (11) is provided at the center of the forging (1), and the material of the forging is ASM ESA508Gr.3, 16MND5 or 18MND5, characterized in that: The method comprises the following steps: Step 1, forging the forging (1); Step 2, rapid cooling: after the forging is completed, the outer surface and the inner surface of the forging (1) are cooled at a cooling rate of 8°C / min to 15°C / min at the same time, and the temperature of the outer surface and the inner surface of the forging (1) are measured during the cooling process. When the temperature of either the outer surface or the inner surface is between 480°C and 500°C, the rapid cooling is stopped; Step 3, forced cooling: the outer surface and the inner surface of the forging (1) are cooled simultaneously at a cooling rate of 3°C / min to 7°C / min, and the temperatures of the outer surface and the inner surface of the forging (1) are measured during the cooling process. When the temperature of either the outer surface or the inner surface is between 400°C and 450°C, the forced cooling is stopped; Step 4, reheating and cooling: air-cooling the forging (1) so that the heat in the core of the forging (1) is transferred to the outer surface and the inner surface of the forging (1), so that the surface of the forging (1) is reheated, and after the reheating is completed, the temperature of the outer surface and the inner surface of the forging (1) is measured. If the lowest surface temperature of the outer surface and the inner surface of the forging (1) exceeds 500° C., step 2, step 3 and step 4 are performed; if the lowest surface temperature of the outer surface and the inner surface of the forging (1) exceeds 450° C. but is less than 500° C., step 3 and step 4 are performed; if the lowest surface temperature of the outer surface and the inner surface of the forging (1) is less than 450° C., step 5 is performed; Step 5, cooling the forging (1) at a rate of ≤50°C / hour until the temperature of the inner and outer surfaces of the forging drops to 250-350°C; Step 6: fully heat-insulating the forging (1) at a temperature of 250-350° C.; Step 7: heating the forging (1) to 620°C to 670°C and keeping the temperature therefor for more than 100 hours.

2. A method for dehydrogenating a large thick-walled forging according to claim 1, characterized in that: The effective wall thickness of the forging (1) is 500-1500 mm.

3. A method for dehydrogenating a large thick-walled forging according to claim 1, characterized in that: In the second step, the outer surface and the inner surface of the forging (1) are cooled simultaneously by spraying.

4. A method for dehydrogenating a large thick-walled forging according to claim 1, characterized in that: In the step three, the outer surface and the inner surface of the forging (1) are cooled simultaneously by means of air jets.

5. A method for dehydrogenating a large thick-walled forging according to claim 1, characterized in that: The step five is furnace cooling.

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