Ni-cr-fe alloy sheet and its blooming method from large ingot

Abstract

The present application belongs to the technical field of stainless steel rolling, and relates to a Ni-Cr-Fe alloy plate and a large ingot type rolling and blooming method thereof. The Ni-Cr-Fe alloy large ingot type rolling and blooming method provided by the present application comprises the following steps: (1) smelting molten steel by using a medium-frequency furnace+AOD+LF method, and pouring the molten steel into a large flat ingot; (2) heating and heat-insulating the large flat ingot, and removing phosphorus by using high-pressure water after discharging; (3) rolling, wherein the rolling temperature is greater than or equal to 1080 DEG C, the final rolling temperature is greater than or equal to 850 DEG C, the deformation amount of the first five passes is controlled to be less than or equal to 5%, the rolling overline speed is less than or equal to 2 m / s, and the normal rolling is performed in the later period to obtain an intermediate blank; and (4) rolling the intermediate blank into a finished plate to obtain a Ni-Cr-Fe alloy plate. The Ni-Cr-Fe series nickel-based alloy large ingot type rolling and blooming method provided by the present application directly pours molten steel into a large flat ingot and directly performs one-fire rolling and blooming process, and compared with a traditional process, has the advantages of low production cost, high efficiency, large ingot, large plate, high product quality, and fully meets the use requirements of high-end chemical equipment.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel rolling technology, and relates to a Ni-Cr-Fe alloy plate and its large ingot rolling method. Specifically, it refers to how to achieve large ingot rolling through process optimization and control, replacing the traditional forging method, and achieving low-cost, high-efficiency, and high-quality production. Background Technology

[0002] Nickel-based alloys possess high strength at both room temperature and high temperature, as well as excellent oxidation and corrosion resistance. They are widely used in petrochemical, energy, machinery, and environmental protection industries, making them an indispensable and extremely important class of materials for economic development and national defense. Ni-Cr-Fe nickel-based alloys, due to their superior corrosion resistance, are widely used in petrochemical pipelines and chemical equipment.

[0003] With the increasing scale of high-end chemical equipment, higher requirements have been placed on the size and weight of medium plates. This has led to a further increase in the weight and size of the original ingot billets, generally ≥10 tons. The traditional production process for nickel-based alloy plates is: vacuum induction furnace + electroslag remelting + forging billet + plate rolling, or medium frequency furnace + AOD + LF + electroslag remelting + forging billet + plate rolling. Before forging billet, the electroslag ingots are all round ingots, which need to be forged into flat ingots through multiple forging processes. This results in low production efficiency, high cost, and frequent forging cracking. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a Ni-Cr-Fe alloy sheet and a method for rolling and billet preparation of its large ingot.

[0005] Specifically, the method for rolling and billet preparation of Ni-Cr-Fe alloy large ingots provided by this invention includes:

[0006] (1) Steel is smelted using a medium-frequency furnace + AOD + LF method and cast into large flat ingots;

[0007] (2) The large flat ingot is heated and kept at a constant temperature, and then dephosphorized by high-pressure water after it is taken out of the furnace;

[0008] (3) Rolling, with an initial rolling temperature ≥1080℃ and a final rolling temperature ≥850℃. The deformation amount in the first five passes is controlled at ≤5%, and the rolling speed is ≤2m / s. The subsequent rolling is normal to obtain an intermediate billet.

[0009] (4) The intermediate billet is rolled into a finished plate to obtain Ni-Cr-Fe alloy plate.

[0010] The above-mentioned method for rolling and billeting large Ni-Cr-Fe alloy ingots involves large flat ingots with a thickness of 300-500 mm, a width of 1200-2000 mm, and a weight of 10-20 tons.

[0011] The above-described method for rolling large ingots of Ni-Cr-Fe alloy comprises, by weight percentage, molten steel of the following proportions: C≤0.150%, Si≤0.50%, Mn≤1.00%, P≤0.030%, S≤0.015%, Cr14.00%-17.00%, Ni≥72.00%, Cu≤0.50%, and Fe6.00%-10.00%.

[0012] In the above-mentioned method for rolling and opening large Ni-Cr-Fe alloy ingots, the heating in step (2) is carried out in a steel ingot heating furnace.

[0013] In the above-mentioned method for rolling large ingots of Ni-Cr-Fe alloy, in step (2), the furnace temperature is ≤500℃ when loading the furnace. When the furnace temperature reaches 500℃, it is held for 2-4 hours. Then, the temperature is raised to 1150-1180℃ at a heating rate of ≤100℃ / h and held for 1.2-1.5 min / mm thickness.

[0014] In the above-mentioned method for rolling large ingots of Ni-Cr-Fe alloy, the thickness of the intermediate billet is determined according to the thickness of the finished plate, while ensuring that the rolling compression ratio is ≥2 and the compression ratio of the intermediate billet rolled into the finished plate is ≥5.

[0015] In the above-mentioned method for rolling large ingots of Ni-Cr-Fe alloy, the intermediate billet undergoes surface grinding and length setting before the finished plate is rolled.

[0016] In the above-mentioned method for rolling large ingots of Ni-Cr-Fe alloy, in step (4), during the rolling process of the finished plate, the intermediate billet heating temperature is 1180-1200℃, the initial rolling temperature is ≥1100℃, the final rolling temperature is ≥850℃, and the plate is water-cooled after rolling.

[0017] On the other hand, the present invention also provides a Ni-Cr-Fe alloy sheet, which is obtained by the above-mentioned Ni-Cr-Fe alloy ingot rolling and billet preparation method.

[0018] The Ni-Cr-Fe alloy plate described above, after sensitization treatment at 750℃ for 30 min, has an intergranular corrosion rate of 0.5-3.0 mm / a after 24 h.

[0019] The technical solution of the present invention has the following beneficial effects:

[0020] The present invention provides a method for rolling and billeting large ingots of Ni-Cr-Fe nickel-based alloys, which involves directly pouring molten steel into large flat ingots and rolling them in one heat. Compared with traditional processes, this method has the advantages of low production cost, high efficiency, large ingot weight, large plate weight, and high product quality, and fully meets the requirements of high-end chemical equipment. Detailed Implementation

[0021] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0022] When a range of values ​​is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0023] The technical solution used in the Ni-Cr-Fe alloy large ingot rolling and billet preparation method provided by this invention is described in detail below:

[0024] Preparation of large steel ingots

[0025] Typical standard composition control range for Ni-Cr-Fe alloys is (wt%):

[0026]

[0027] The ingredient control standards refer to ASME SB168.

[0028] To ensure the metallurgical purity and overall quality of the alloy, it is smelted using a medium-frequency furnace + AOD + LF method, and then directly cast into large flat ingots.

[0029] To obtain a high-quality solidification structure, the thickness of the flat ingot should be controlled between 300-500 mm, the width between 1200-2000 mm, the height is unlimited, and the weight of the ingot should be between 10-20 tons.

[0030] roughing

[0031] Nickel-based alloys possess a series of characteristics, including high deformation resistance, narrow hot working temperature range, difficulty in controlling microstructure, and susceptibility to cracking during rolling. Therefore, direct rolling of finished plates is not feasible; instead, the flat ingots must be pre-rolled. This invention directly achieves one-fire rolling pre-rolling. The rolling pre-rolling process is determined as follows:

[0032] Because flat ingots are heavy, they need to be heated in a steel ingot heating furnace.

[0033] When loading the furnace, the furnace temperature should be ≤500℃. After the furnace temperature reaches 500℃, it should be held for 2-4 hours before slowly increasing the temperature again, with a heating rate ≤100℃ / h, to prevent cracking caused by large temperature differences between the inside and outside of the ingot. When the temperature reaches 1150-1180℃, it should be held for a duration determined according to the ingot thickness, designed at 1.2-1.5 min / mm, before being unloaded and rolled.

[0034] Due to the poor thermal conductivity of nickel-based alloys, high-temperature loading into the furnace can cause stress cracking due to the large temperature difference between the inside and outside of the ingot. Similarly, excessively rapid heating can also lead to cracking due to the large temperature difference between the inside and outside of the ingot. Therefore, low-temperature loading is necessary, with preheating and holding at around 500℃. Since the steel ingot has a cast structure and poor thermoplasticity, it should be held at 1150-1180℃ for a designed holding time of 1.2-1.5 min / mm. Too low a temperature will result in excessive temperature drop during rolling, causing deformation outside the optimal thermoplasticity zone and leading to rolling cracking. Too high a temperature, exceeding the optimal thermoplasticity zone during rolling, will also cause rolling cracking.

[0035] Before rolling the billet, a high-pressure water descaling process is performed; no water is sprayed during the rolling process. The initial rolling temperature is ≥1080℃, and the final rolling temperature is ≥850℃. Due to the poor plasticity of the original cast structure of the ingot, the first five passes must adopt the principle of small deformation and low speed rolling, with the deformation controlled at ≤5% and the rolling speed ≤2m / s. Normal rolling is then performed in the later stages. The thickness of the intermediate billet is determined based on the thickness of the finished plate, and it is necessary to simultaneously ensure that the initial billet compression ratio is ≥2 and the intermediate billet-to-finished plate compression ratio is ≥5. After the intermediate billet surface is ground and cut to length, the finished plate is rolled.

[0036] A rolling temperature ≥1080℃ and a final rolling temperature ≥850℃ fall within the optimal thermoplasticity range. Deformation exceeding this range easily leads to rolling cracks. Furthermore, at the start of rolling, due to the cast structure, the deformation per pass should not be excessive. High temperature and low speed promote dynamic recrystallization, transforming the microstructure into a rolled microstructure, significantly improving plasticity. The rolling initial compression ratio must be ≥2. Outside this range, the billet microstructure after initial rolling is in a mixed-crystal state with poor plasticity. The compression ratio of the intermediate billet rolled into the finished plate should be ≥5 to ensure a fine and uniform microstructure and optimal overall performance.

[0037] Finished plate rolling

[0038] The intermediate billet is heated and then rolled.

[0039] The heating temperature is 1180-1200℃, the initial rolling temperature is ≥1100℃, the final rolling temperature is ≥850℃, and the rolling is water-cooled.

[0040] The heating temperature is 1180-1200℃. Above this temperature, the initial grains are too large, resulting in insufficient mechanical properties of the rolled sheet. Below this range, the edges of the rolled sheet are prone to cracking. Therefore, the initial rolling temperature should be ≥1100℃, the final rolling temperature ≥850℃, and water cooling should be applied after rolling.

[0041] The finished plate obtained according to the method of this invention, after heat treatment, fully meets the performance requirements of ASME SB 168. Intergranular corrosion testing was conducted using the ASTM G28 A method. After sensitization treatment at 750℃ for 30 min, the intergranular corrosion rate was 0.5-3.0 mm / a after 24 h, fully meeting the user's specific requirements.

[0042] Example

[0043] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments, unless otherwise specified, are performed according to conventional methods and conditions.

[0044] Summary of the composition and content (wt%) of the large flat ingots in Examples 1-3 and Comparative Example 1

[0045]

[0046] Example 1

[0047] The steel was smelted using a medium-frequency furnace + AOD + LF method, and then directly cast into large flat ingots, with dimensions of 350*1700*2600mm and a weight of approximately 13.5 tons. Heating was performed in an ingot heating furnace. The furnace temperature was 400℃ during loading. After reaching 500℃, the temperature was held for 4 hours, followed by a slow increase at a rate of 100℃ / h. The temperature was then held at 1170℃ for approximately 7.5 hours before being removed from the furnace and rolled. A high-pressure water descaling process was performed before rolling, but no water was sprayed during the rolling process. The initial rolling temperature was 1100℃, and the final rolling temperature was 890℃. The deformation in the first five passes was controlled to ≤5%, and the rolling speed was ≤2m / s. Subsequent passes were rolled normally. The intermediate slab thickness was 160mm, and the initial rolling compression ratio was 2.2. After the intermediate billet surface is ground and cut to length, the finished plate is rolled. The intermediate billet heating temperature is 1180℃, the initial rolling temperature is 1110℃, the final rolling temperature is 870℃, and it is water-cooled after rolling. The finished plate size is 25*2500*8160mm, and the rolling compression ratio is 6.4.

[0048] After heat treatment, the finished panels fully meet the requirements of ASME SB 168. Intergranular corrosion testing was conducted using the ASTM G28A method. After sensitization treatment at 750℃ for 30 minutes, the intergranular corrosion rate after 24 hours was 1.52 mm / a (the measured intergranular corrosion rate of panels processed by traditional methods is generally between 1.3 and 7.4 mm / a), fully meeting the user's specific requirements.

[0049] Example 2

[0050] The steel was smelted using a medium-frequency furnace + AOD + LF method, and then directly cast into large flat ingots, with dimensions of 380*1750*2650mm and a weight of approximately 15 tons. Heating was performed in an ingot heating furnace. The furnace temperature was 450℃ during loading. After reaching 500℃, the temperature was held for 3 hours, followed by a slow increase at a rate of 100℃ / h. The temperature was then held at 1180℃ for approximately 8.5 hours before being removed from the furnace and rolled. A high-pressure water descaling process was performed before rolling, but no water was sprayed during the rolling process. The initial rolling temperature was 1100℃, and the final rolling temperature was 880℃. The deformation in the first five passes was controlled to ≤5%, and the rolling speed was ≤2m / s. Subsequent passes were rolled normally. The intermediate billet thickness was 180mm, and the initial rolling compression ratio was 2.1. After the intermediate billet surface is ground and cut to length, the finished plate is rolled. The intermediate billet heating temperature is 1180℃, the initial rolling temperature is 1100℃, the final rolling temperature is 880℃, and it is water-cooled after rolling. The finished plate size is 32*2800*8900mm, and the rolling compression ratio is 5.6.

[0051] After heat treatment, the finished panels fully meet the requirements of ASME SB 168. Intergranular corrosion testing was conducted using the ASTM G28A method. After sensitization treatment at 750℃ for 30 minutes, the intergranular corrosion rate was 0.81 mm / a after 24 hours (the measured intergranular corrosion rate of panels processed by traditional methods is generally between 1.3 and 7.4 mm / a), fully meeting the user's specific requirements.

[0052] Example 3

[0053] The steel was smelted using a medium-frequency furnace + AOD + LF method, and then directly cast into large flat ingots, with dimensions of 450*1800*2600mm and a weight of approximately 18 tons. Heating was performed in an ingot heating furnace. The furnace temperature was 450℃ during loading. After reaching 500℃, the temperature was held for 4 hours, followed by a slow increase at a rate of 100℃ / h. The temperature was then held at 1180℃ for approximately 9.5 hours before being removed from the furnace and rolled. A high-pressure water descaling process was performed before rolling, but no water was sprayed during the rolling process. The initial rolling temperature was 1110℃, and the final rolling temperature was 910℃. The deformation in the first five passes was controlled to ≤5%, and the rolling speed was ≤2m / s. Subsequent passes were rolled normally. The intermediate slab thickness was 160mm, and the initial rolling compression ratio was 2.8. After the intermediate billet surface is ground and cut to length, the finished plate is rolled. The intermediate billet heating temperature is 1180℃, the initial rolling temperature is 1100℃, and the final rolling temperature is 880℃. After rolling, it is water-cooled. The finished plate size is 22*2600*9500mm, and the rolling compression ratio is 7.3.

[0054] After heat treatment, the finished panels fully meet the requirements of ASME SB 168. Intergranular corrosion testing was conducted using the ASTM G28A method. After sensitization treatment at 750℃ for 30 minutes, the intergranular corrosion rate was 1.03 mm / a after 24 hours (the measured intergranular corrosion rate of panels processed by traditional methods is generally between 1.3 and 7.4 mm / a), fully meeting the user's specific requirements.

[0055] Comparative Example 1

[0056] The steel was smelted using a medium-frequency furnace + AOD + LF + electroslag remelting method, and then directly cast into large round ingots, with ingot dimensions of φ800*2200mm and a weight of approximately 11.5 tons. Heating was performed using an ingot heating furnace. The furnace temperature was 400℃ during loading. After reaching 500℃, the temperature was held for 4 hours, followed by a slow increase in temperature at a rate of 100℃ / h. The temperature was then raised to 1180℃ and held for approximately 8.5 hours before being removed from the furnace and forged into a billet. The billet was forged through six heat treatments, resulting in an intermediate billet thickness of 280mm. The intermediate billet underwent a second heat rolling process, with the initial heating temperature at 1180℃, the initial rolling temperature at 1110℃, and the final rolling temperature at 870℃. After rolling, the billet was water-cooled, resulting in an intermediate billet thickness of 160mm. After the intermediate billet surface is ground and cut to length, it undergoes rolling to become the finished plate. The intermediate billet is heated to 1190℃, the initial rolling temperature is 1120℃, and the final rolling temperature is 890℃, followed by water cooling. The finished plate dimensions are 25*2200*6000mm.

[0057] After heat treatment, the finished plate meets the requirements of ASME SB 168. Intergranular corrosion testing was conducted using the ASTM G28 A method. After sensitization at 750℃ for 30 minutes, the intergranular corrosion rate was 6.7 mm / a after 24 hours, which is worse than that of the rolling process.

[0058] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art should understand that these embodiments are merely illustrative of the invention and should not be construed as limiting its scope. It should be noted that any variations and substitutions equivalent to these embodiments should be considered to be covered within the scope of the claims. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for rolling and billet preparation of large Ni-Cr-Fe alloy ingots, characterized in that, include: (1) The medium-frequency furnace + AOD + LF method is used for smelting and casting into large flat ingots; (2) The large flat ingot is heated and kept warm, and then dephosphorized by high-pressure water after it is taken out of the furnace; When loading the furnace, the furnace temperature should be ≤500℃. When the furnace temperature reaches 500℃, it should be held for 2-4 hours. Then, the temperature should be raised to 1150-1180℃ at a rate of ≤100℃ / h and held for 1.2-1.5 min / mm thickness. (3) Rolling, with an initial rolling temperature of ≥1080℃ and a final rolling temperature of ≥850℃. The deformation amount in the first five passes is controlled at ≤5%, and the rolling speed is ≤2m / s. The subsequent rolling is normal to obtain an intermediate billet. The thickness of the intermediate billet is determined according to the thickness of the finished plate, while ensuring that the rolling blank compression ratio is ≥2. (4) The intermediate billet is rolled into a finished plate. The heating temperature of the intermediate billet is 1180-1200℃, the initial rolling temperature is ≥1100℃, the final rolling temperature is ≥850℃, the compression ratio of the intermediate billet rolled into a finished plate is ≥5, and the Ni-Cr-Fe alloy plate is obtained by water cooling after rolling.

2. The method for rolling and billet preparation of Ni-Cr-Fe alloy large ingots according to claim 1, characterized in that, The large flat ingot has a thickness of 300-500mm, a width of 1200-2000mm, and a weight of 10-20 tons.

3. The method for rolling and billet preparation of Ni-Cr-Fe alloy large ingots according to claim 1, characterized in that, The composition of the large flat ingot, by weight percentage, is: C ≤0.150%, Si ≤0.50%, Mn ≤1.00%, P ≤0.030%, S ≤0.015%, Cr 14.00%-17.00%, Ni ≥72.00%, Cu ≤0.50%, Fe 6.00%-10.00%.

4. The method for rolling and billet preparation of Ni-Cr-Fe alloy large ingots according to claim 1, characterized in that, In step (2), the heating is carried out in a steel ingot heating furnace.

5. The method for rolling and billet preparation of Ni-Cr-Fe alloy large ingots according to claim 1, characterized in that, Before rolling the finished plate, the intermediate billet is surface-grinding and length-fixing.

6. A Ni-Cr-Fe alloy plate, characterized in that, It is obtained by the Ni-Cr-Fe alloy ingot rolling and billet preparation method according to any one of claims 1-5.

7. The Ni-Cr-Fe alloy plate according to claim 6, characterized in that, After sensitization treatment at 750℃ for 30 minutes, the intergranular corrosion rate was 0.5-3.0 mm / a after 24 hours.

Images