Annealing method and application of high alloy steel pickling steel coil

Abstract

The invention provides an annealing method and application of a high alloy steel pickled steel coil, and the annealing method comprises the following steps: in a cover annealing furnace, pre-purging the pickled steel coil in N2, and carrying out hydrogen blowing treatment, heating treatment and cooling treatment after the pre-purging is completed; the hydrogen blowing treatment is divided into three sections of blowing, the blowing flow of the first-time large-flow hydrogen blowing treatment is 1-10m < 3 > / h higher than that of the second-time large-flow hydrogen blowing treatment, and the duration of the first-time large-flow hydrogen blowing treatment accounts for 15-35% of the total duration of the two-time large-flow hydrogen blowing treatment; the heating treatment adopts a three-stage heating method, and the cooling treatment adopts a four-stage cooling method. According to the method, three-stage blowing is creatively adopted in the hydrogen blowing process, the flow and duration of three-time hydrogen blowing are optimally designed, and a three-stage heating mode and a four-stage cooling method are adopted in the heating process, so that the structure spheroidizing grade and the uniformity form of the high-alloy steel are obviously improved, matrix decarburization is prevented, the rolling difficulty is reduced, and the yield of the high-alloy steel is improved. Therefore, the cold rolling reduction rate is obviously improved.

Description

Technical Field

[0001] The invention relates to the technical field of hot-rolled pickled steel manufacturing, in particular to an annealing method for a high-alloy steel pickled steel coil and its application. Background Art

[0002] X32 bimetallic saw blade backing steel, a high-alloy steel, is primarily used to manufacture saw blade backing for cutting hard products such as steel, non-ferrous metals, hard and precious woods, and polymer materials, as well as cutting segments for high-end saw chains. It is a top-tier tool steel and a foundation for industrial development. Currently, domestic market demand for this material is 20,000 to 30,000 tons annually. However, its high alloying element content of 8% creates extremely high strength and quality requirements, making rolling extremely challenging.

[0003] Therefore, in order to prepare the organizational morphology for subsequent cold rolling, optimize the microstructure of the material, and improve the cold rolling rollability and mechanical properties, it is urgent to develop an annealing process suitable for X32 high alloy steel. Summary of the Invention

[0004] The main purpose of the present invention is to provide an annealing method for a high-alloy steel pickled steel coil to solve the problems of imperfect grain structure, great rolling difficulty and low cold rolling reduction rate of X32 high-alloy steel.

[0005] To achieve the above object, the present invention provides a method for annealing a high-alloy steel pickled coil, comprising:

[0006] In the bell annealing furnace, the pickled steel coil is pre-purged in N2, and after the pre-purging is completed, hydrogen blowing treatment, heating treatment and cooling treatment are carried out in sequence;

[0007] The hydrogen blowing treatment includes two large-flow hydrogen blowing treatments and one small-flow hydrogen blowing treatment in sequence, wherein the purge flow rate of the first large-flow hydrogen blowing treatment is not less than 25m 3 / h, and the purge flow rate of the first large-flow hydrogen blowing treatment is 1-10m higher than the purge flow rate of the second large-flow hydrogen blowing treatment 3 / h, the duration of the first high-flow hydrogen blowing treatment accounts for 15-35% of the total duration of the two high-flow hydrogen blowing treatments;

[0008] The heating treatment adopts a three-stage temperature rising method, and the cooling treatment adopts a four-stage temperature lowering method.

[0009] Furthermore, the purge flow rate of the first high-flow hydrogen blowing treatment is 5-10m higher than the purge flow rate of the second high-flow hydrogen blowing treatment. 3 / h.

[0010] Furthermore, the duration of the first high-flow hydrogen blowing treatment accounts for 18-32% of the total duration of the two high-flow hydrogen blowing treatments.

[0011] Preferably, the conditions for the first large flow hydrogen blowing treatment include at least: a purge flow rate of 25-35m 3 / h, the purge time is 3-9h.

[0012] Preferably, the conditions for the second large flow hydrogen blowing treatment include at least: a blowing flow rate of 20-30m 3 / h, the purge time is 6-12h.

[0013] Furthermore, the low-flow hydrogen blowing treatment includes the following steps: when the bell furnace temperature is 580-600°C, a low-flow purge method is used to blow hydrogen, and the purge flow rate is less than 3m 3 / h until annealing is completed.

[0014] Furthermore, the pre-purge conditions include at least: a pre-purge time of 10-25 minutes, a volume of 30-50m 3 .

[0015] Furthermore, the heating treatment steps include:

[0016] The first stage: free heating to 180-200℃ and keeping warm;

[0017] The second stage: continue heating to 380-420℃ at a certain heating rate and keep warm;

[0018] The third stage: continue heating to 730-780℃ at a certain heating rate and keep warm.

[0019] Furthermore, the cooling process comprises the following steps:

[0020] The first stage: cooling from 730-780℃ to 600-650℃ with the furnace cover, which takes 3-5 hours;

[0021] The second stage: after being lifted off the outer cover, air cooling is adopted, and the furnace temperature is reduced from 600-650℃ to 360-400℃;

[0022] The third stage: using water cooling, the furnace temperature is reduced from 360-400℃ to 100-120℃;

[0023] Stage 4: Remove from oven and cool to room temperature.

[0024] The present invention also provides an application of the annealing method of the high-alloy steel pickled steel coil in X32 high-alloy steel.

[0025] The beneficial effects of the present invention are as follows:

[0026] The annealing method for pickled high-alloy steel coils provided by the present invention, through the development of a reasonable hood annealing process, pioneering the use of two high-flow purges and one low-flow purge during the hydrogen blowing process, optimizing the flow rate and duration of the two high-flow hydrogen blowing stages, adopting a three-stage heating method during the heating process, and a four-stage cooling method during the cooling process, can significantly improve the microstructure spheroidization level and uniformity of the high-alloy steel, prevent matrix decarburization, reduce rolling difficulty, and thus significantly increase the cold rolling reduction rate. Specifically, the high-alloy steel substrate treated by the annealing method of the present invention has a single cold rolling reduction rate of up to 60%, which can significantly reduce the number of cold rolling passes and rolling range, reduce production costs, and achieve short-cycle rolling delivery.

[0027] The annealing method for pickled high-alloy steel coils provided by the present invention has simple process, convenient operation, high production efficiency, low production cost and stable process, and is particularly suitable for the hood annealing process of pickled X32 high-alloy structural steel coils. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0029] Figure 1 This is a microstructure diagram of the X32 high alloy steel hot-rolled pickled steel coil after treatment in Example 1 of the present invention.

[0030] Figure 2 This is a microstructure diagram of the X32 high alloy steel hot-rolled pickled steel coil after treatment in Example 3 of the present invention.

[0031] Figure 3 This is a microstructure diagram of the X32 high alloy steel hot-rolled pickled steel coil after treatment in Example 4 of the present invention.

[0032] Figure 4 This is a microstructure diagram of the X32 high alloy steel hot-rolled pickled steel coil after treatment in Example 5 of the present invention.

[0033] Figure 5 This is a microstructure diagram of the X32 high alloy steel hot-rolled pickled steel coil after being processed in Comparative Example 1 of the present invention.

[0034] Figure 6 This is a microstructure diagram of the X32 high alloy steel hot-rolled pickled steel coil after being processed in Comparative Example 2 of the present invention.

[0035] The realization of the objectives, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0036] The following will be combined with the accompanying 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 embodiments described 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 making creative efforts are within the scope of protection of the present invention.

[0037] In addition, in the present invention, descriptions such as "first" and "second" are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. Moreover, the technical solutions between the various embodiments of the present invention can be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0038] It should be noted that the room temperature or normal temperature mentioned in the present invention refers to 25±2°C.

[0039] The present invention provides a method for annealing a high-alloy steel pickled steel coil, comprising the following steps:

[0040] In the bell annealing furnace, the pickled steel coil is pre-purged in N2, and after the pre-purging is completed, hydrogen blowing treatment, heating treatment and cooling treatment are carried out in sequence;

[0041] The hydrogen blowing treatment includes two large-flow hydrogen blowing treatments and one small-flow hydrogen blowing treatment in sequence, wherein the purge flow rate of the first large-flow hydrogen blowing treatment is not less than 25m 3 / h, and the purge flow rate of the first large-flow hydrogen blowing treatment is 1-10m higher than the purge flow rate of the second large-flow hydrogen blowing treatment 3 / h, the duration of the first high-flow hydrogen blowing treatment accounts for 15-35% of the total duration of the two high-flow hydrogen blowing treatments;

[0042] The heating treatment adopts a three-stage temperature rising method, and the cooling treatment adopts a four-stage temperature lowering method.

[0043] It should be noted that the specific operating steps of the annealing method include: loading the pickled steel coil into the bell-type annealing furnace, then tightening the inner bell. After completing the hydrogen valve, inner bell, and furnace table sealing tests, N2 pre-purge is performed. After the pre-purge is completed, hydrogen purge, heating, and cooling are sequentially performed.

[0044] It should be noted that the pickled steel coil is pickled once on the basis of the hot-rolled steel coil to eliminate the oxides on the surface of the hot-rolled steel coil (the hot-rolled coil has a high rolling temperature, and the steel coil will be oxidized after it is taken off the line, forming oxides on the surface), so as to prepare the surface quality for subsequent cold rolling, prevent the oxides from being pressed into the steel coil during cold rolling, and prevent the oxides from affecting the surface quality.

[0045] According to the characteristics of pickled steel coils, the present invention adopts two sections of large flow rate purge and one section of small flow rate in the hydrogen blowing process, optimizes the flow rate and duration of the two sections of large flow rate hydrogen blowing, and especially sets the difference between the two sections of large flow rate hydrogen blowing to 1-10m 3 / h and a reasonable distribution of the duration ratio of the two sections of large-flow hydrogen blowing, combined with a three-stage heating method during the heating process and a four-stage cooling method during the cooling process, can increase the first-time cold rolling reduction rate of the treated high-alloy steel substrate to 60%, thereby significantly reducing the number of cold rolling passes and rolling process, lowering production costs, and achieving short-cycle rolling delivery.

[0046] In some specific embodiments, the purge flow rate of the first high-flow hydrogen blowing treatment is 5-10m higher than the purge flow rate of the second high-flow hydrogen blowing treatment. 3 / h.

[0047] The inventors found that, combined with the characteristics of high alloy steel with high alloy content, high hardness and high strength, two sections of large flow hydrogen blowing were used continuously, and the difference between the two sections of hydrogen blowing flow was set at 5-10m 3 / h range, through the gradient design of hydrogen blowing flow rate, it can not only improve the thermal conductivity efficiency, accelerate the spheroidization process of steel coils in the bell-type furnace, and improve the spheroidization rate of the organization, but also better optimize the microstructure and reduce the yield strength of high alloy steel, thereby achieving the purpose of reducing the difficulty of rolling.

[0048] In some specific embodiments, the duration of the first high-flow hydrogen blowing treatment accounts for 18-32% of the total duration of the two high-flow hydrogen blowing treatments.

[0049] Through research, the inventors found that by setting the difference between the two sections of high-flow hydrogen blowing and reasonably allocating the duration ratio of the two high-flow hydrogen blowing sessions, specifically, setting the duration of the first high-flow hydrogen blowing treatment to 18-32% of the total duration of the two high-flow hydrogen blowing sessions, a substrate with uniform structure can be better formed, thereby reducing the difficulty of subsequent rolling and increasing the reduction rate of a single cold rolling.

[0050] According to a particularly preferred embodiment, the conditions for the first large flow hydrogen blowing treatment include at least: a purge flow rate of 25-35m 3 / h, the purge time is 3-9h.

[0051] According to a particularly preferred embodiment, the conditions for the second large flow hydrogen blowing treatment include at least: a purge flow rate of 20-30m 3 / h, the purge time is 6-12h.

[0052] It should be noted that the use of high-flow purge in the early stage of bell annealing is beneficial to remove moisture adsorbed on the surface of the steel coil in the bell furnace, oil and grease that may exist on the surface of the steel coil, and moisture generated by the reaction of iron oxide scale and hydrogen.

[0053] In some specific embodiments, the low-flow hydrogen blowing treatment includes the following steps: when the bell furnace temperature is 580-600°C, a low-flow purge method is used to blow hydrogen, and the purge flow rate is less than 3m 3 / h until annealing is completed.

[0054] It's important to note that when the furnace temperature reaches 580-600°C, a very low-flow hydrogen blowing mode is employed, similar to a suffocating furnace, and this continues until the coils are removed from the furnace. Within this temperature range, the carbon in the steel begins to react with hydrogen to produce methane, leading to decarburization. Based on the principle of chemical equilibrium shift, stopping the hydrogen blowing allows the methane produced by the decarburization reaction to remain in the gas, inhibiting the reaction and thus preventing decarburization.

[0055] In some specific embodiments, the pre-purge conditions include at least: a pre-purge time of 10-25 minutes, a volume of 30-50 m 3 .

[0056] According to a particularly preferred embodiment, the heating treatment step comprises:

[0057] The first stage: free heating to 180-200℃ and keeping warm;

[0058] The second stage: continue heating to 380-420℃ at a certain heating rate and keep warm;

[0059] The third stage: continue heating to 730-780℃ at a certain heating rate and keep warm.

[0060] In some specific embodiments, the first stage comprises heating to 180-200°C at a free-flowing temperature and maintaining the temperature for 1-2 hours. The inventors have discovered that, when using the aforementioned preferred embodiment for pickling high-alloy steel coils, water adsorbed on the coil surface is vaporized into water vapor. Under high-flow hydrogen blowing conditions, the water vapor can be quickly removed, preventing decarburization during the subsequent annealing process and preventing oxidation of metal elements on the coil surface.

[0061] In some specific embodiments, the second stage comprises heating the steel coil at a rate of 60-90°C / h to a temperature of 380-420°C and maintaining the temperature for 1-2 hours. The inventors have discovered that, under the aforementioned preferred embodiment, oil and grease on the surface of the pickled steel coil volatilize due to heat and are quickly discharged from the bell-type furnace. Furthermore, the overall temperature of the steel coil is uniformized below the recrystallization temperature, resulting in a more uniform annealed structure.

[0062] In some specific embodiments, the third stage comprises: continuing to heat the material to 730-780°C at a heating rate of 30-50°C / h and maintaining the temperature for 16-20 hours. The inventors have discovered that excessively high temperatures can lead to excessive spheroidization and growth of cementite, resulting in coarse austenite, which is not conducive to subsequent cold rolling and quenching processes. Excessively low temperatures can result in low spheroidization and uneven microstructure, making the material susceptible to edge cracking and band breakage during rolling. Annealing at the aforementioned temperatures can provide a substrate with a uniform microstructure and refined cementite.

[0063] In some specific embodiments, the cooling process comprises:

[0064] The first stage: cooling from 730-780℃ to 600-650℃ with the furnace cover, which takes 3-5 hours;

[0065] The second stage: after being lifted off the outer cover, air cooling is adopted, and the furnace temperature is reduced from 600-650℃ to 360-400℃;

[0066] The third stage: using water cooling, the furnace temperature is reduced from 360-400℃ to 100-120℃;

[0067] Stage 4: Remove from oven and cool to room temperature.

[0068] It should be noted that in the actual process, you can perform slow cooling with the cover on by power off or directly replace the cooling cover with air cooling, and then water cooling to 100-120℃.

[0069] The present invention also provides an application of the annealing method of the high-alloy steel pickled steel coil in X32 high-alloy steel.

[0070] It should be noted that X32 high-alloy steel is a high-grade alloy tool steel primarily used to manufacture the backing material of bimetallic saw blades. It contains high proportions of carbon, chromium, molybdenum, cobalt, and other alloying elements, with an alloy content of up to 8%, resulting in high hardness, strength, wear resistance, and good fatigue resistance.

[0071] According to a particularly preferred embodiment, the X32 high alloy steel used in the present invention includes the following chemical elements in weight percentage:

[0072] Carbon 0.27-0.35%, silicon 0.20-0.35%, manganese 0.90-1.10%, sulfur ≤0.005%, phosphorus ≤0.015%, chromium 3.50-4.0%, nickel 0.30-0.80%, vanadium 0.30-0.50%, molybdenum 1.0-1.4%, and the rest are Fe and impurity elements remaining in the smelting process.

[0073] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, all raw materials and instruments used are commercially available.

[0074] It should be noted that the X32 high alloy steel in the following embodiments all comes from X32 high alloy steel coils produced by Hunan Valin Lianyuan Iron and Steel Co., Ltd.

[0075] Example 1

[0076] This embodiment provides an annealing method for a hot-rolled pickled coil of X32 high-alloy steel, wherein the chemical composition and weight percentage of the X32 high-alloy steel are as follows: C 0.3%, Si 0.22%, Mn 0.99%, P 0.01%, S 0.001%, Cr 3.91%, Ni 0.75%, V 0.39%, Mo 1.38%, and the remainder is Fe and unavoidable impurities. The method specifically comprises the following steps:

[0077] Four X32 hot-rolled pickled steel coils with a coil weight of 18 tons and a specification of 2.8×1250mm were loaded into the bell-type annealing furnace for annealing. The inner cover was pressed tightly. After the hydrogen valve, inner cover and furnace table sealing tests were completed in sequence, N2 pre-purge was carried out for 20 minutes, and the volume was 50m 3 , after purging, start hydrogen blowing and heating operations;

[0078] Hydrogen blowing treatment: 30m in high flow mode 3 / h hydrogen blowing for 4 hours, then press 25m 3 / h and continue blowing hydrogen for 9 hours. At this time, the temperature inside the inner cover reaches about 600℃, and then press the automatic pressure maintaining low flow mode for 3m 3 / h hydrogen blowing until annealing is completed;

[0079] Heating treatment: adopt three-stage heating mode;

[0080] The first stage: free heating to 200℃ and keeping warm for 1 hour;

[0081] The second stage: heating to 400℃ in 5 hours and keeping it at that temperature for 2 hours;

[0082] The third stage: heat to 730℃ at 40℃ / h and keep warm for 18h.

[0083] Cooling treatment: adopt four-stage cooling mode;

[0084] Stage 1: After the insulation is completed, the furnace is cooled with the hood for 3 hours, at which time the temperature reaches about 650℃;

[0085] The second stage: after being lifted from the outer cover, air cooling is adopted to 380℃;

[0086] The third stage: using water cooling, the furnace temperature is reduced to 100℃ before being taken out of the furnace;

[0087] Stage 4: Remove from oven and cool to room temperature.

[0088] After annealing, the steel coil is sampled and tested to find that the material structure is uniform, and cold rolling can be produced at a 60% reduction rate.

[0089] Example 2

[0090] This embodiment provides an annealing method for a hot-rolled pickled X32 high-alloy steel coil. The grade of the X32 high-alloy steel used is the same as that in Example 1. The method specifically includes the following steps:

[0091] Four X32 hot-rolled pickled steel coils with a coil weight of 24 tons and a specification of 3.7×1250mm were loaded into the bell-type annealing furnace for annealing. The inner cover was pressed tightly. After the hydrogen valve, inner cover and furnace table sealing tests were completed in sequence, N2 pre-purge was carried out for 20 minutes, and the volume was 50m 3 , after purging, start hydrogen blowing and heating operations;

[0092] Hydrogen blowing treatment: 30m in high flow mode 3 / h hydrogen blowing for 4 hours, then press 25m 3 / h and continue blowing hydrogen for 9 hours. At this time, the temperature inside the inner cover reaches about 600℃, and then press the automatic pressure maintaining low flow mode for 2m 3 / h hydrogen blowing until annealing is completed;

[0093] Heating treatment: adopt three-stage heating mode;

[0094] The first stage: free heating to 200℃ and keeping warm for 1 hour;

[0095] The second stage: heating to 400℃ in 5 hours and keeping it at that temperature for 2 hours;

[0096] The third stage: heating to 750℃ at 40℃ / h and keeping it for 20h;

[0097] Cooling treatment: adopt four-stage cooling mode;

[0098] Stage 1: After the insulation is completed, the furnace is cooled with the hood for 4 hours, at which time the temperature reaches about 650℃;

[0099] The second stage: after being lifted from the outer cover, air cooling is adopted to 380℃;

[0100] The third stage: water cooling is used to reduce the furnace temperature to 110℃ before being taken out of the furnace;

[0101] Stage 4: Remove from oven and cool to room temperature.

[0102] After annealing, the steel coil is sampled and tested to find that the material structure is uniform, and cold rolling can be produced at a 60% reduction rate.

[0103] Example 3

[0104] This embodiment provides an annealing method for a hot-rolled pickled steel coil of X32 high-alloy steel, wherein the chemical composition and weight percentage of the X32 high-alloy steel are: C 0.32%, Si 0.31%, Mn 1.01%, P 0.01%, S 0.002%, Cr 3.75%, Ni 0.55%, V 0.37%, and Mo 1.2%.

[0105] The specific steps include:

[0106] Four X32 hot-rolled pickled steel coils with a coil weight of 24 tons and a specification of 3.0×1250mm were loaded into the bell-type annealing furnace for annealing. The inner cover was pressed tightly. After the hydrogen valve, inner cover and furnace table sealing tests were completed in sequence, N2 pre-purge was carried out for 20 minutes, and the volume was 40m 3 , after purging, start hydrogen blowing and heating operations;

[0107] Hydrogen blowing treatment: 35m in high flow mode 3 / h hydrogen blowing for 3 hours, then press 25 3 / h and continue blowing hydrogen for 10 hours. At this time, the temperature inside the inner cover reaches about 600℃, and then press the automatic pressure maintenance low flow mode 2m 3 / h hydrogen blowing until annealing is completed;

[0108] Heating treatment: adopt three-stage heating mode;

[0109] The first stage: free heating to 200℃ and keeping warm for 2 hours;

[0110] The second stage: heating to 380℃ in 4 hours and keeping warm for 2 hours;

[0111] The third stage: heating to 740℃ at 45℃ / h and keeping warm for 18h;

[0112] Cooling treatment: adopt four-stage cooling mode;

[0113] Stage 1: After the insulation is completed, the furnace is cooled with the hood for 3 hours, at which time the temperature reaches about 640℃;

[0114] The second stage: after being lifted from the outer cover, air cooling is adopted to 380℃;

[0115] The third stage: water cooling is used to reduce the furnace temperature to 110℃ before being taken out of the furnace;

[0116] Stage 4: Remove from oven and cool to room temperature.

[0117] After annealing, the steel coil is sampled and tested to find that the material structure is uniform, and cold rolling can be produced at a 60% reduction rate.

[0118] Example 4

[0119] This embodiment provides an annealing method for hot-rolled pickled steel coils of X32 high alloy steel. The type of X32 high alloy steel used is the same as that in Example 1. The difference is that the purge flow rate of the first hydrogen blowing treatment is 28m 3 / h, the purge flow rate of the second hydrogen blowing treatment is 25m 3 / h. Specifically includes the following steps:

[0120] Four X32 hot-rolled pickled steel coils with a coil weight of 18 tons and a specification of 2.8×1250mm were loaded into the bell-type annealing furnace for annealing. The inner cover was pressed tightly. After the hydrogen valve, inner cover and furnace table sealing tests were completed in sequence, N2 pre-purge was carried out for 20 minutes, and the volume was 50m 3 , after purging, start hydrogen blowing and heating operations;

[0121] Hydrogen blowing treatment: 28m in high flow mode 3 / h hydrogen blowing for 2 hours, then press 25m 3 / h and continue blowing hydrogen for 9 hours. At this time, the temperature inside the inner cover reaches about 600℃, and then press the automatic pressure maintaining low flow mode for 2m 3 / h hydrogen blowing until annealing is completed;

[0122] Heating treatment: adopt three-stage heating mode;

[0123] The first stage: free heating to 200℃ and keeping warm for 1 hour;

[0124] The second stage: heating to 400℃ in 5 hours and keeping it at that temperature for 2 hours;

[0125] The third stage: heating to 730℃ at 40℃ / h and keeping warm for 18h;

[0126] Cooling treatment: adopt four-stage cooling method;

[0127] Stage 1: After the insulation is completed, the furnace is cooled with the hood for 3 hours, at which time the temperature reaches about 650℃;

[0128] The second stage: after being lifted from the outer cover, air cooling is adopted to 380℃;

[0129] The third stage: water cooling is used to reduce the furnace temperature to 120℃ before being taken out of the furnace;

[0130] Stage 4: Remove from oven and cool to room temperature.

[0131] After annealing, the steel coil is sampled and tested to ensure uniform material structure, and cold rolling can be produced at a 50% reduction rate.

[0132] Example 5

[0133] This embodiment provides an annealing method for a hot-rolled pickled X32 high-alloy steel coil. The grade of the X32 high-alloy steel used is the same as that in Example 1. The method specifically includes the following steps:

[0134] Four X32 hot-rolled pickled steel coils with a coil weight of 18 tons and a specification of 2.8×1250mm were loaded into the bell-type annealing furnace for annealing. The inner cover was pressed tightly. After the hydrogen valve, inner cover and furnace table sealing tests were completed in sequence, N2 pre-purge was carried out for 20 minutes, and the volume was 50m 3 , after purging, start hydrogen blowing and heating operations;

[0135] Hydrogen blowing treatment: 30m in high flow mode 3 / h hydrogen blowing for 2 hours, then press 25m 3 / h and continue blowing hydrogen for 12 hours. At this time, the temperature inside the inner cover reaches about 600℃, and then press the automatic pressure maintenance low flow mode 2m 3 / h hydrogen blowing until annealing is completed;

[0136] Heating treatment: adopt three-stage heating mode;

[0137] The first stage: free heating to 200℃ and keeping warm for 1 hour;

[0138] The second stage: heating to 400℃ in 5 hours and keeping it at that temperature for 2 hours;

[0139] The third stage: heating to 730℃ at 40℃ / h and keeping warm for 18h;

[0140] Cooling treatment: adopt four-stage cooling method;

[0141] Stage 1: After the insulation is completed, the furnace is cooled with the hood for 3 hours, at which time the temperature reaches about 650℃;

[0142] The second stage: after being lifted from the outer cover, air cooling is adopted to 380℃;

[0143] The third stage: using water cooling, the furnace temperature is reduced to 100℃ before being taken out of the furnace;

[0144] Stage 4: Remove from oven and cool to room temperature.

[0145] After annealing, the steel coil is sampled and tested to find that the material structure is uniform, and cold rolling can be produced at a 40% reduction rate.

[0146] Comparative Example 1

[0147] This comparative example provides an annealing method for hot-rolled pickled steel coils of X32 high alloy steel. The type of X32 high alloy steel used is the same as that in Example 1, except that hydrogen blowing is performed only once in a high flow mode, with a hydrogen blowing flow rate of 30m 3 / h.

[0148] The specific steps include:

[0149] Four X32 hot-rolled pickled steel coils with a coil weight of 24 tons and a specification of 3.7×1250mm were loaded into the bell-type annealing furnace for annealing. The inner cover was pressed tightly. After the hydrogen valve, inner cover and furnace table sealing tests were completed in sequence, N2 pre-purge was carried out for 20 minutes, and the volume was 50m 3 , after purging, start hydrogen blowing and heating operations;

[0150] Hydrogen blowing treatment: 30m in high flow mode 3 / h hydrogen blowing for 7 hours, at which time the temperature inside the inner cover reaches about 600℃, and then press the automatic pressure maintaining small flow mode 2m 3 / h hydrogen blowing until annealing is completed;

[0151] Heating treatment: adopt three-stage heating mode;

[0152] The first stage: free heating to 200℃ and keeping warm for 1 hour;

[0153] The second stage: heating to 400℃ in 5 hours and keeping it at that temperature for 2 hours;

[0154] The third stage: heating to 720℃ at 40℃ / h and keeping warm for 20h;

[0155] Cooling treatment: adopt four-stage cooling method;

[0156] Stage 1: After the insulation is completed, the furnace is cooled with the hood for 2 hours, at which time the temperature reaches about 650℃;

[0157] The second stage: after being lifted from the outer cover, air cooling is adopted to 380℃;

[0158] The third stage: using water cooling, the furnace temperature is reduced to 100℃ before being taken out of the furnace;

[0159] Stage 4: Remove from oven and cool to room temperature.

[0160] After annealing, the steel coil is sampled and tested to ensure uniform material structure, and cold rolling can be produced at a 20% reduction rate.

[0161] Comparative Example 2

[0162] This comparative example provides an annealing method for hot-rolled pickled X32 high alloy steel coils. The type of X32 high alloy steel used is the same as that in Example 1, except that the first hydrogen purge flow rate is 20 m 3 / h.

[0163] The specific steps include:

[0164] Four X32 hot-rolled pickled steel coils with a coil weight of 24 tons and a specification of 3.7×1250mm were loaded into the bell-type annealing furnace for annealing. The inner cover was pressed tightly. After the hydrogen valve, inner cover and furnace table sealing tests were completed in sequence, N2 pre-purge was carried out for 20 minutes, and the volume was 50m 3 , after purging, start hydrogen blowing and heating operations;

[0165] Hydrogen blowing treatment: 20m in high flow mode 3 / h hydrogen blowing for 2 hours, then press 25m 3 / h and continue blowing hydrogen for 4 hours. At this time, the temperature inside the inner cover reaches about 600℃, and then press the automatic pressure maintenance low flow mode 2m 3 / h hydrogen blowing until annealing is completed;

[0166] Heating treatment: adopt three-stage heating mode;

[0167] The first stage: free heating to 200℃ and keeping warm for 1 hour;

[0168] The second stage: heating to 400℃ in 5 hours and keeping it at that temperature for 2 hours;

[0169] The third stage: heating to 720℃ at 40℃ / h and keeping warm for 20h;

[0170] Cooling treatment: adopt four-stage cooling method;

[0171] The first stage: After the insulation is completed, the furnace is cooled with the cover for 2 hours, at which time the temperature reaches about 700℃;

[0172] The second stage: after being lifted from the outer cover, air cooling is adopted to 380℃;

[0173] The third stage: using water cooling, the furnace temperature is reduced to 100℃ before being taken out of the furnace;

[0174] Stage 4: Remove from oven and cool to room temperature.

[0175] After annealing, the steel coil is sampled and tested to ensure uniform material structure, and cold rolling can be produced at a 20% reduction rate.

[0176] After spheroidizing annealing of the above-mentioned Examples 1-5 and Comparative Examples 1-2, the steel coils were sampled and tested to determine their yield strength, tensile strength, and microspheroidization rate. The specific test results are shown in Table 1.

[0177] Among them, the test method for tensile strength is: GB / T 228.1-2021 "Tensile tests on metallic materials - Part 1: Room temperature test method";

[0178] The test method for yield strength is: GB / T 228.1-2021 "Tension tests on metallic materials - Part 1: Room temperature test methods";

[0179] The test method for the spheroidization rate of the structure is: GB / T 38770-2020 "Inspection and rating of spheroidized structure of low and medium carbon steel".

[0180] Table 1

[0181] Yield strength, MPa Tensile strength, MPa Tissue spheroidization rate, % Example 1 489 672 80 Example 2 478 666 80 Example 3 503 669 80 Example 4 573 749 70 Example 5 612 784 70 Comparative Example 1 707 850 40 Comparative Example 2 724 896 /

[0182] Through comparison, it was found that by formulating a reasonable hood annealing process, two sections of large flow purge and one section of small flow purge were pioneered in the hydrogen blowing process, and the flow rates of the two sections of large flow hydrogen blowing were optimized. In particular, the difference between the two sections of large flow hydrogen blowing was set to 1-10m 3 / h and a reasonable distribution of the duration ratio of the two hydrogen blowing times, combined with a three-stage heating method in the heating process and a four-stage cooling method in the cooling treatment, can increase the cold rolling reduction rate of the treated high-alloy steel substrate to 60%, thereby significantly reducing the number of cold rolling passes and rolling process, lowering production costs, and achieving short-cycle rolling delivery.

[0183] The table above also shows that the annealing method provided by the present invention can produce steel coils with superior spheroidized structures. For example, the spheroidization rates in Examples 1-3 all reached Level 5, indicating that the annealing method according to the preferred embodiment of the present invention can provide a substrate with uniform structure and refined cementite. In contrast, the spheroidization rate in Comparative Example 1 was less than 50%, indicating a low spheroidization grade and uneven structure. The steel coil in Comparative Example 2 had uneven structure distribution and large variations in spheroidization rates in different locations, making it difficult to obtain a representative value during testing.

[0184] Analysis example 1

[0185] The microstructure of the X32 high alloy steel hot rolled pickled steel coils treated by the annealing methods of Example 1, Examples 3-5 and Comparative Examples 1-2 was observed. The specific observation results are shown in Figures 1-6 .

[0186] in, Figure 1 This is the microstructure of the X32 high alloy steel hot rolled pickled steel coil after treatment in Example 1. Figure 2 This is the microstructure of the X32 high alloy steel hot rolled pickled steel coil after treatment in Example 3. Figure 3 This is the microstructure of the X32 high alloy steel hot rolled pickled coil after treatment in Example 4. Figure 4 This is the microstructure of the X32 high alloy steel hot rolled pickled steel coil after treatment in Example 5. Figure 5 This is the microstructure of the X32 high alloy steel hot rolled pickled steel coil after treatment in Comparative Example 1. Figure 6This is the microstructure diagram of the X32 high alloy steel hot rolled pickled steel coil after treatment in Comparative Example 2.

[0187] As can be seen from the figure, the steel coil obtained after treatment by the annealing method provided by the present invention has good internal microstructure uniformity, relatively uniform chemical composition distribution, and basically no matrix decarburization phenomenon occurs; while the steel coils obtained in Comparative Examples 1 and 2 both have decarburization phenomena, uneven grain size, and uneven phase distribution.

[0188] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0189] The above technical solutions of the present invention are only preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention's description and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for annealing a high alloy steel pickled steel coil, characterized in that: include: In the bell annealing furnace, the pickled steel coil is pre-purged in N2, and after the pre-purging is completed, hydrogen blowing treatment, heating treatment and cooling treatment are carried out in sequence; The hydrogen blowing treatment includes two large-flow hydrogen blowing treatments and one small-flow hydrogen blowing treatment in sequence, wherein the purge flow rate of the first large-flow hydrogen blowing treatment is not less than 25m 3 / h, and the purge flow rate of the first large-flow hydrogen blowing treatment is 1-10m higher than the purge flow rate of the second large-flow hydrogen blowing treatment 3 / h, the duration of the first high-flow hydrogen blowing treatment accounts for 15-35% of the total duration of the two high-flow hydrogen blowing treatments; The heating treatment adopts a three-stage temperature rising method, and the cooling treatment adopts a four-stage temperature lowering method.

2. The annealing method according to claim 1, wherein The purge flow rate of the first high-flow hydrogen blowing treatment is 5-10m higher than the purge flow rate of the second high-flow hydrogen blowing treatment. 3 / h.

3. The annealing method according to claim 1, wherein The duration of the first high-flow hydrogen blowing treatment accounts for 18-32% of the total duration of the two high-flow hydrogen blowing treatments.

4. The annealing method according to claim 2 or 3, characterized in that The conditions for the first large flow hydrogen blowing treatment include at least: a blowing flow rate of 25-35m 3 / h, the purge time is 3-9h.

5. The annealing method according to claim 2 or 3, characterized in that: The conditions for the second large flow hydrogen blowing treatment include at least: a purge flow rate of 20-30m 3 / h, the purge time is 6-12h.

6. The annealing method according to claim 1, wherein: The low-flow hydrogen blowing treatment comprises the following steps: when the bell furnace temperature is 580-600°C, a low-flow purge method is used to blow hydrogen, and the purge flow rate is less than 3m 3 / h until annealing is completed.

7. The annealing method according to claim 1, characterized in that The pre-purge conditions include at least: a pre-purge time of 10-25 minutes, a volume of 30-50 m 3 .

8. The annealing method according to claim 1, wherein: The heat treatment steps include: The first stage: free heating to 180-200℃ and keeping warm; The second stage: continue heating to 380-420℃ at a certain heating rate and keep warm; The third stage: continue heating to 730-780℃ at a certain heating rate and keep warm.

9. The annealing method according to claim 8, characterized in that The cooling process comprises the following steps: The first stage: cooling from 730-780℃ to 600-650℃ with the furnace cover, which takes 3-5 hours; The second stage: after being lifted off the outer cover, air cooling is adopted, and the furnace temperature is reduced from 600-650℃ to 360-400℃; The third stage: using water cooling, the furnace temperature is reduced from 360-400℃ to 100-120℃; Stage 4: Remove from oven and cool to room temperature.

10. Use of the annealing method for pickled high alloy steel coils according to any one of claims 1 to 9 in X32 high alloy steel.

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