Preparation method of hot-rolled bar billet for nickel-iron-based high-temperature bolt

Abstract

The invention discloses a preparation method of a hot-rolled bar billet for a ferronickel-based high-temperature bolt, which belongs to the technical field of nonferrous metal processing, and comprises the following steps: (1) adopting a billet with the specification of phi 160mm, comprising the following chemical components in percentage by mass: 22-30% of Fe, 17-21% of Cr, 0.2-0.6% of Mo, 3-6% of Al + Ti, 0.2-0.8% of W, 0.03-0.06% of C, 1.5-3.0% of Co, 0.002-0.008% of B and the balance of Ni, keeping the billet at 1000-1050 DEG C, rolling the billet into a billet with the specification of phi 70mm, and with the deformation of 70-90%; (2) the blank with the specification of phi 70 mm is subjected to heat preservation at the temperature of 1000-1050 DEG C and then rolled into a blank with the specification of phi 38 mm, and the deformation amount ranges from 70% to 90%; and (3) the blank with the diameter phi being 38 mm is subjected to solid solution heat treatment, and the hot-rolled blank with the diameter being 36 mm for the nickel-iron-based high-temperature bolt is obtained after solid solution heat treatment is completed. The rolling rod for the high-temperature bolt is prepared by adopting a low-temperature large-deformation rolling technology, so that the structure of a rod blank is uniform and fine, and carbides are fine and are dispersed and distributed.

Description

Technical Field

[0001] The invention relates to a field, in particular to a method for preparing a hot-rolled rod blank for nickel-iron-based high-temperature bolts. Background Art

[0002] With the development of the national economy and the improvement of people's living standards, the demand for electricity is increasing. Promoting the development of ultra-supercritical coal-fired power generation technology and improving the efficiency of thermal power generation are important measures for my country to cope with global climate change and achieve energy conservation and emission reduction goals. Increasing the temperature and pressure of steam is an important means to improve the thermal efficiency of thermal power generating units. However, the increase in steam parameters also increases the failure risk of certain key materials in thermal power generating units. Steam turbine high-temperature bolts are extremely critical materials for thermal power generating units. If they fail during long-term service, they may cause huge casualties and economic losses. The presence of coarse grains and aggregated carbides will aggravate the local stress concentration generated by high-temperature bolts during service, thereby increasing the direction of failure. Therefore, a suitable thermal processing process is needed to obtain uniform and fine structures and dispersed carbides, improve the mechanical properties and quality of high-temperature bolts, and ensure the safe operation of thermal power generating units.

[0003] There are many primary carbides in the cast structure of the high-temperature alloy used in the present invention, which are difficult to completely eliminate by high-temperature homogenization, and the carbides can only be refined by deformation and crushing. And when the size of the billet is smaller, it is easier for carbides to be distributed, thereby increasing the potential safety hazards of the material during service. In addition, the billet is likely to form mixed crystals during the hot rolling process, which will also reduce the mechanical properties of the material. Therefore, if you want to promote the application of this material in high-temperature bolts for steam turbines, you need to develop a reasonable method for preparing rolled billets so that the material has a uniform and fine structure and the carbides are dispersed. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a hot-rolled rod blank for nickel-iron-based high-temperature bolts to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for preparing a hot-rolled rod blank for a nickel-iron-based high-temperature bolt, using a Φ160 mm billet, the chemical composition mass percentage of which is: Fe: 22%-30%, Cr: 17%-21%, Mo: 0.2%-0.6%, Al+Ti: 3%-6%, W: 0.2%-0.8%, C: 0.03%-0.06%, Co: 1.5%-3.0%, B: 0.002%-0.008%, the remainder is Ni, and a rod blank with a specification of Φ36 mm, a grain size of ≥3 levels, and a carbide rating of ≤2 levels is prepared through a rolling process, characterized in that the method comprises the following steps:

[0007] S1.Φ160mm billet is kept at 1000℃~1050℃ and then rolled into Φ70mm billet, with a deformation of 70%~90%;

[0008] S2.Φ70mm billet is kept at 1000℃~1050℃ and then rolled into Φ38mm billet, with a deformation of 70%~90%;

[0009] S3.Φ38mm billet is subjected to solution heat treatment.

[0010] Preferably, in step S1, the billet with a specification of Φ160 mm is heated with a charging temperature ≤ 800°C, and the temperature is raised to 1000°C-1050°C at a heating rate of 3°C-6°C / min, and the insulation time is 1h-2h. After the insulation, the billet is taken out of the furnace and rolled, and the material is air-cooled after the rolling.

[0011] Preferably, in step S2, the Φ70mm billet is heated with a furnace charging temperature ≤800°C, and the temperature is raised to 1000°C-1050°C at a heating rate of 3°C-6°C / min, and the insulation time is 1h-2h. After the insulation, the billet is taken out of the furnace and rolled, and the material is air-cooled after the rolling.

[0012] Preferably, the step S3 is heating to 1020° C. to 1080° C., keeping the temperature for 1 h to 2 h, and air cooling after heating.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention makes carbides finer and more dispersed through large deformation rolling, and the carbide rating is level 2; by controlling the rolling heating temperature and the final rolling temperature, the grains are refined, and the grain size of the Φ36mm specification bar billet after heat treatment is controlled at level 4 to 5, thereby improving the grain size and organizational uniformity of the bar billet. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Carbides of Φ36mm rod: (a) edge 100×; (b) R / 2100×; (c) core 100×;

[0015] Figure 2 High magnification of Φ36mm rod: (c) core 100×. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] See also Figure 1 and Figure 2

[0018] In the embodiment of the present invention, the carbide rating adopts the GB / T 14999.6-2010 standard, and the sample is taken from the center, R / 2, and edge of the rod billet and then polished and the structure is observed with a metallographic microscope;

[0019] In the embodiment of the invention, the grain size rating adopts the ASTM E 112 standard, and samples are taken from the center, R / 2, and edge of the rod billet and then the structure is observed with a metallographic microscope;

[0020] The present invention provides a technical solution:

[0021] A method for preparing a hot-rolled rod blank for a nickel-iron-based high-temperature bolt, using a Φ160 mm billet, the chemical composition mass percentage of which is: Fe: 22%-30%, Cr: 17%-21%, Mo: 0.2%-0.6%, Al+Ti: 3%-6%, W: 0.2%-0.8%, C: 0.03%-0.06%, Co: 1.5%-3.0%, B: 0.002%-0.008%, the remainder is Ni, and a rod blank with a specification of Φ36 mm, a grain size of ≥3 levels, and a carbide rating of ≤2 levels is prepared through a rolling process, characterized in that the method comprises the following steps:

[0022] S1.Φ160mm billet is kept at 1000℃~1050℃ and then rolled into Φ70mm billet, with a deformation of 70%~90%;

[0023] S2.Φ70mm billet is kept at 1000℃~1050℃ and then rolled into Φ38mm billet, with a deformation of 70%~90%;

[0024] S3.Φ38mm billet is subjected to solution heat treatment.

[0025] Furthermore, in step S1, the Φ160mm billet is heated, the charging temperature is ≤800°C, the temperature is increased to 1000°C-1050°C at a heating rate of 3°C-6°C / min, the insulation time is 1h-2h, and after the insulation is completed, the billet is taken out of the furnace and rolled, and the material is air-cooled after the rolling is completed.

[0026] Furthermore, in step S2, the Φ70mm billet is heated, the charging temperature is ≤800°C, the temperature is increased to 1000°C-1050°C at a heating rate of 3°C-6°C / min, the insulation time is 1h-2h, and after the insulation is completed, the billet is taken out of the furnace and rolled, and the material is air-cooled after the rolling is completed.

[0027] Furthermore, in step S3, the temperature is heated to 1020° C. to 1080° C., and the temperature is kept for 1 hour to 2 hours, and the mixture is water-cooled after the heating is completed.

[0028] Example 1

[0029] A method for preparing a hot-rolled rod blank for a nickel-iron-based high-temperature bolt, using a Φ160 mm billet, the chemical composition mass percentage of which is: Fe: 22%, Cr: 17%, Mo: 0.2%, Al+Ti: 3%, W: 0.2%, C: 0.03%, Co: 1.5%, B: 0.002%, and the balance is Ni, and preparing a rod blank with a specification of Φ36 mm, a grain size of ≥3 levels, and a carbide rating of ≤2 levels through a rolling process, characterized in that the method comprises the following steps:

[0030] S1. Heat the Φ160mm billet, the charging temperature is ≤800℃, and the temperature is raised to 1000℃ at a heating rate of 3℃ / min, and the holding time is 1h. After the holding time is over, the billet is rolled out of the furnace. After the rolling is completed, the material is air-cooled. The Φ160mm billet is held at 1000℃ and then rolled into a Φ70mm billet with a deformation of 70%;

[0031] S2. The Φ70mm billet is heated, the charging temperature is ≤800℃, the temperature is raised to 1000℃ at a heating rate of 3℃min, the holding time is 1h, the billet is rolled out of the furnace after the holding period is over, and the material is air-cooled after the rolling period is over. The Φ70mm billet is held at 1000℃ and then rolled into a Φ38mm billet, with a deformation of 70% to 90%;

[0032] S3. Heat to 1020℃, keep warm for 1h, water cool after heating, and perform solution heat treatment on the Φ38mm billet.

[0033] Example 2

[0034] A method for preparing a hot-rolled rod blank for a nickel-iron-based high-temperature bolt, using a Φ160 mm billet, the chemical composition mass percentage of which is: Fe: 25%, Cr: 18%, Mo: 0.5%, Al+Ti: 5%, W: 0.6%, C: 0.05%, Co: 1.7%, B: 0.005%, and the balance is Ni, and preparing a rod blank with a specification of Φ36 mm, a grain size of ≥3 levels, and a carbide rating of ≤2 levels through a rolling process, characterized in that it includes the following steps:

[0035] S1. Heat the Φ160mm billet, the charging temperature is ≤800℃, and the temperature is raised to 1025℃ at a heating rate of 5℃ / min, and the holding time is 1.5h. After the holding time is over, the billet is rolled out of the furnace. After the rolling is completed, the material is air-cooled. The Φ160mm billet is kept at 1025℃ and then rolled into a Φ70mm billet with a deformation of 80%;

[0036] S2. The Φ70mm billet is heated, the charging temperature is ≤800℃, the temperature is raised to 1025℃ at a heating rate of 5℃ / min, the holding time is 1.5h, and the billet is rolled after the holding time is over. After the rolling, the material is air-cooled. The Φ70mm billet is held at 1025℃ and then rolled into a Φ38mm billet with a deformation of 80%;

[0037] S3. Heat to 1020℃, keep warm for 1.5h, air cool after heating, and perform solution heat treatment on the Φ38mm billet.

[0038] Example 3

[0039] A method for preparing a hot-rolled rod blank for a nickel-iron-based high-temperature bolt, using a Φ160 mm billet, the chemical composition mass percentage of which is: Fe: 30%, Cr: 21%, Mo: 0.6%, Al+Ti: 6%, W: 0.8%, C: 0.06%, Co: 3.0%, B: 0.008%, and the balance is Ni, and preparing a rod blank with a specification of Φ36 mm, a grain size of ≥3 levels, and a carbide rating of ≤2 levels through a rolling process, characterized in that the method comprises the following steps:

[0040] S1. Heat the Φ160mm billet, the charging temperature is ≤800℃, and the temperature is raised to 1050℃ at a heating rate of 6℃ / min, and the holding time is 2h. After the holding time is over, the billet is rolled out of the furnace. After the rolling is completed, the material is air-cooled. The Φ160mm billet is held at 1050℃ and then rolled into a Φ70mm billet with a deformation of 90%;

[0041] S2. The Φ70mm billet is heated, the charging temperature is ≤800℃, the temperature is raised to 1050℃ at a heating rate of 6℃ / min, the holding time is 2h, and the billet is rolled out of the furnace after the holding period is completed. After the rolling period is completed, the material is air-cooled. The Φ70mm billet is held at 1050℃ and then rolled into a Φ38mm billet with a deformation of 90%;

[0042] S3. Heat to 1020℃, keep warm for 2h, air cool after heating, and perform solution heat treatment on the Φ38mm billet.

[0043] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing hot-rolled rod blanks for nickel-iron-based high-temperature bolts, using a Φ160mm billet, the chemical composition mass percentage is: Fe: 22% to 30%, Cr: 17% to 21%, Mo: 0.2% to 0.6%, Al+Ti: 3% to 6%, W: 0.2% to 0.8%, C: 0.03% to 0.06%, Co: 1.5% to 3.0%, B: 0.002% to 0.008%, the balance is Ni, the billet is kept at 1000°C to 1050°C and then rolled into a Φ70mm billet, the deformation amount is 70% to 90%, and a rod blank with a specification of Φ36mm, a grain size ≥3, and a carbide rating ≤2 is prepared by a rolling process, characterized in that The following steps are involved: S1.Φ160mm billet is kept at 1000℃~1050℃ and then rolled into Φ70mm billet, with a deformation of 70%~90%; S2.Φ70mm billet is kept at 1000℃~1050℃ and then rolled into Φ38mm billet, with a deformation of 70%~90%; S3.Φ38mm billet is subjected to solution heat treatment.

2. The method for preparing a hot-rolled rod for nickel-iron-based high-temperature bolts according to claim 1, characterized in that: In step S1, the Φ160 mm specification billet is heated, the charging temperature is ≤800°C, the temperature is increased to 1000°C-1050°C at a heating rate of 3°C-6°C / min, the insulation time is 1h-2h, and after the insulation is completed, the billet is taken out of the furnace and rolled, and the material is air-cooled after the rolling is completed.

3. The method for preparing a hot-rolled rod for nickel-iron-based high-temperature bolts according to claim 2, characterized in that: In step S2, the Φ70mm billet is heated, the charging temperature is ≤800°C, the temperature is increased to 1000°C-1050°C at a heating rate of 3°C-6°C / min, the insulation time is 1h-2h, and after the insulation is completed, the billet is taken out of the furnace and rolled, and the material is air-cooled after the rolling is completed.

4. The method for preparing a hot-rolled rod for nickel-iron-based high-temperature bolts according to claim 3, characterized in that: In step S3, the temperature is heated to 1020° C. to 1080° C., and the temperature is kept for 1 hour to 2 hours, and air-cooled after the heating is completed.

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