Preparation method of small-specification ultra-high-strength steel hot-rolled bar billet for fastener

Abstract

The invention belongs to the technical field of non-ferrous metal processing, and relates to a preparation method of a small-specification ultra-high-strength steel hot-rolled bar billet for a fastener. The method specifically comprises the following steps that firstly, a blank with the specification of phi 120 mm to phi 160 mm is subjected to multiple times of heat preservation rolling at the specified temperature to form a blank with the specification of phi 10.5 mm to phi 12.5 mm, and the deformation in the heat preservation rolling process ranges from 70% to 90%; carrying out normalizing heat treatment on the blank with the specification of phi 10.5 mm to phi 12.5 mm, and then carrying out high-temperature tempering heat treatment; and finally, the blank with the specification of phi 10.5 mm to phi 12.5 mm is machined into a finished bar with the specification of phi 10 mm. The grain size of a finished bar (a bar blank with the specification of phi 10 mm) is controlled to be at 8.5 level by controlling the heating temperature, the finish rolling temperature and the temperature rise of the core of the bar in the rolling process.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal processing and relates to a method for preparing a small-size ultra-high-strength steel hot-rolled bar blank for fasteners. Background Art

[0002] AerMet100 ultra-high strength steel is a high-cobalt-nickel high-alloy steel with good comprehensive mechanical properties. It is an ideal material for key aviation parts. Some aviation fasteners have very high requirements for the strength and plasticity of the material, and AerMet100 steel has both high strength and high plasticity, but its application in aviation fasteners is relatively small. Therefore, it is necessary to develop the preparation process of AerMet100 steel billets for fasteners to promote its application in fasteners.

[0003] The main strengthening methods of AerMet100 steel are precipitation strengthening, phase transformation strengthening and fine grain strengthening. On the one hand, increasing the carbon content will produce greater lattice distortion after the martensitic phase transformation, and the phase transformation strengthening effect will be enhanced; on the other hand, the number of precipitates formed during tempering will increase, and the precipitation strengthening effect will be enhanced. Therefore, we increase the tensile strength of the bar by controlling the carbon content above 0.23%. Although fine grain strengthening can improve the strength and plasticity of the material at the same time, thermal deformation will have an important impact on the fine grain strengthening of the bar. During the rolling process, the bar is prone to a large temperature rise in the core of the bar due to the large deformation amount and deformation rate, which can easily lead to significant coarsening of the grains. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a method for preparing a small-sized ultra-high strength steel hot-rolled bar billet for fasteners.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing a small-sized ultra-high-strength steel hot-rolled bar for fasteners comprises the following steps:

[0007] Step 1: forming a Φ10.5mm-Φ12.5mm billet through multiple heat-insulating rolling at a specified temperature, wherein the deformation amount during the heat-insulating rolling process is 70%-90%;

[0008] Step 2: subjecting the blank with a size of Φ10.5mm to Φ12.5mm to normalizing heat treatment and then to high temperature tempering heat treatment;

[0009] Step 3: Machining the Φ10.5mm-Φ12.5mm billet after high temperature tempering heat treatment into a Φ10mm finished bar.

[0010] Furthermore, in step 1, the heat preservation rolling is performed for multiple times, and the process is as follows:

[0011] In the first heat-insulating rolling, the billet with a specification of Φ160mm is kept at a specified temperature and then rolled into a billet with a size of Φ50mm~Φ56mm; in the second heat-insulating rolling, the billet with a specification of Φ50mm~Φ56mm is kept at a specified temperature and then rolled into a billet with a size of Φ23.5mm~Φ29.5mm; in the third heat-insulating rolling, the billet with a specification of Φ23.5mm~Φ29.5mm is kept at a specified temperature and then rolled into a billet with a size of Φ10.5mm~Φ12.5mm.

[0012] Furthermore, during the first heat preservation rolling and the second heat preservation rolling, the charging temperature is ≤900°C, the temperature is increased to 1020°C to 1060°C at a heating rate of 2°C to 8°C / min, the heat preservation time is 1.5h to 3h, the material is taken out of the furnace and rolled after the heat preservation, and the material is air-cooled after the rolling;

[0013] Furthermore, in the third heat-insulating rolling, the charging temperature is ≤900°C, and the temperature is increased to 1020°C-1060°C at a heating rate of 2°C-8°C / min, and the heat-insulating time is 1h-2h. After the heat-insulating period, the material is taken out of the furnace and rolled, and after the rolling period, the material is air-cooled.

[0014] Furthermore, in the step 2, the normalizing heat treatment is specifically: heating to 890°C to 910°C, keeping the temperature for 2h to 4h, and air cooling after the heating is completed.

[0015] Furthermore, in the step 2, the tempering heat treatment is specifically: heating to 670°C to 690°C, keeping the temperature for 18h to 20h, and air cooling after the heating is completed.

[0016] Furthermore, the grain size of the finished rod with a specification of Φ10 mm is grade 8.5.

[0017] Furthermore, the tensile strength of the finished rod with a specification of Φ10mm is ≥1960MPa, and the elongation is ≥12%.

[0018] Furthermore, the carbon content of the finished bar is 0.23% to 0.25%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) By controlling the heating temperature, final rolling temperature and the temperature rise of the core of the bar during rolling, the grain size of the finished bar (Φ10mm bar billet) is controlled at level 8.5.

[0021] (2) The finished bar has finer grains and higher carbon content (0.23% to 0.25%), so that the tensile strength of the Φ10mm bar is ≥1960MPa, the elongation is ≥12%, and the comprehensive mechanical properties are excellent.

[0022] (3) By lowering the billet heating temperature, the bar can have fine austenite grains before hot rolling, providing favorable conditions for recrystallization and grain refinement. In addition, by setting a reasonable deformation amount and deformation pass during the rolling process, the temperature rise in the core of the bar can be controlled to avoid significant coarsening of the bar grains. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are incorporated in and constitute a part of this specification and, together with the description, serve to explain the principles of the present invention.

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0025] Figure 1 It is a process flow chart of the method for preparing small-sized ultra-high strength steel hot-rolled bar billets for fasteners in the present invention;

[0026] Figure 2 Schematic diagram of the grain size of the head-R / 2 100× of the Φ10 mm rod blank in Example 1 of the present invention;

[0027] Figure 3 Schematic diagram of the grain size of the tail of the Φ10 mm rod blank - R / 2 100× in Example 1 of the present invention;

[0028] Figure 4 Schematic diagram of the grain size of the head-R / 2 100× of the Φ10 mm rod blank in Example 2 of the present invention;

[0029] Figure 5 Schematic diagram of the grain size of the tail of the Φ10 mm rod blank - R / 2 100× in Example 2 of the present invention;

[0030] Figure 6 Schematic diagram of the grain size of the head-R / 2 100× of the Φ10 mm rod blank in Example 3 of the present invention;

[0031] Figure 7 Schematic diagram of the grain size of the tail -R / 2 100× of the Φ10 mm rod in Example 3 of the present invention. DETAILED DESCRIPTION

[0032] Here, exemplary embodiments will be described in detail, and the embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are only examples of devices consistent with some aspects of the present invention as detailed in the appended claims.

[0033] In the embodiment of the invention, the grain size rating adopts GB / T 6394 standard, samples are taken at R / 2 of the head and tail of the rod, and quenched after being kept at 885°C for 1 hour. Then, the sample is polished and the structure is observed with a metallographic microscope.

[0034] The tensile properties test in the embodiment of the invention adopts GB / T 228 standard, samples are taken at the head and tail of the rod, and the properties are tested after heat treatment. Heat treatment process: 885℃, 1h, oil cooling; (-73)℃, 60min, reheating in air; 482℃, 5.5h, air cooling.

[0035] like Figure 1 As shown, a method for preparing a small-sized ultra-high strength steel hot-rolled bar for fasteners specifically comprises the following steps:

[0036] Step 1: forming a Φ10.5mm-Φ12.5mm billet through multiple heat-insulating rolling at a specified temperature, wherein the deformation amount during the heat-insulating rolling process is 75%-90%;

[0037] Step 2: subjecting the blank with a size of Φ10.5mm to Φ12.5mm to normalizing heat treatment and then to high temperature tempering heat treatment;

[0038] Step 3: Machining the Φ10.5mm-Φ12.5mm billet after high temperature tempering heat treatment into a Φ10mm finished bar.

[0039] Example 1

[0040] A method for preparing a small-sized ultra-high-strength steel hot-rolled bar for fasteners comprises the following steps:

[0041] The forged Φ120mm billet was kept at 1020℃ for 2h before rolling, and the setting was as follows: Φ120mm→Φ50mm, total deformation 80%, and air cooling after rolling;

[0042] Φ50mm billet, after being kept at 1020℃ for 1.5h, was rolled with the following settings: Φ50mm→Φ23.5mm, total deformation 75%, and air cooling after rolling;

[0043] The Φ23.5mm billet was rolled after being kept at 1020℃ for 1.5h, with the following settings: Φ23.5mm→Φ10.5mm, total deformation 81%, and air cooling after rolling;

[0044] The Φ10.5mm billet was subjected to normalizing heat treatment, heated to 890°C, kept at this temperature for 2h, and then air-cooled after heating.

[0045] The Φ10.5mm billet was subjected to high temperature tempering heat treatment, heated to 670°C, kept at this temperature for 18h, and then air-cooled after heating.

[0046] The Φ10.5mm billet after high temperature tempering heat treatment is machined into Φ10mm finished bar billet.

[0047] Among them: the deformation amounts of the first insulation rolling, the second insulation rolling and the third insulation rolling are 75% to 90%. Preferably, during these three insulation rolling processes, the deformation amounts can be: 75%, 80%, 81%, 82.5%, 85% and 90%.

[0048] The grain size of the finished bar billet is graded according to GB / T 6394, and the core grain size of the head and tail is 8.5. Figure 2-3 .

[0049] The mechanical properties of the finished rod blank are tested according to GB / T 228, the head and tail tensile strength is ≥1960MPa, the elongation is ≥12%, and the comprehensive mechanical properties are excellent, see Table 1.

[0050] Table 1 Mechanical properties test results of Φ10mm bar blank

[0051] Location Sampling direction σb(MPa) σ0.2(MPa) δ5(%) Ψ(%) standard Vertical ≥1930 ≥1620 ≥10 ≥55 head Vertical 1963 / 1961 / 1963 1762 / 1761 / 1768 15.0 / 13.0 / 15.0 69 / 69 / 70 tail Vertical 1965 / 1967 / 1964 1748 / 1749 / 1749 14.0 / 14.5 / 13.5 71 / 71 / 70

[0052] Example 2

[0053] A method for preparing a small-sized ultra-high-strength steel hot-rolled bar for fasteners comprises the following steps:

[0054] The forged Φ140mm billet was heated at 1040℃ for 1.5h and then rolled. The setting was as follows: Φ140mm→Φ53mm, total deformation 85%, and air cooling after rolling.

[0055] The Φ53mm billet was rolled after being kept at 1040℃ for 2h, with the following settings: Φ53mm→Φ26.5mm, total deformation 75%, and air cooling after rolling;

[0056] The Φ26.5mm billet was rolled after being kept at 1040℃ for 2h, with the following settings: Φ26.5mm→Φ11.5mm, total deformation 81%, and air cooling after rolling;

[0057] The Φ11.5mm billet after high temperature tempering heat treatment was subjected to normalizing heat treatment, heated to 900°C, kept at this temperature for 3h, and air-cooled after heating.

[0058] The Φ11.5mm billet was subjected to high temperature tempering heat treatment, heated to 680°C, kept at this temperature for 18h, and then air-cooled after heating.

[0059] The Φ11.5mm billet is machined into Φ10mm finished bar billet.

[0060] Among them: the deformation amounts of the first insulation rolling, the second insulation rolling and the third insulation rolling are 75% to 90%. Preferably, during these three insulation rolling processes, the deformation amounts can be: 75%, 80%, 81%, 82.5%, 85% and 90%.

[0061] The grain size of the finished bar billet is graded according to GB / T 6394, and the core grain size of the head and tail is 8.5. Figure 4-5 .

[0062] The mechanical properties of the finished rods are tested according to GB / T 228, with the head-tail tensile strength ≥1960MPa, the elongation ≥12%, and the comprehensive mechanical properties are excellent, see Table 2.

[0063] Table 2 Mechanical properties test results of Φ10mm bar blank

[0064] Location Sampling direction σb(MPa) σ0.2(MPa) δ5(%) Ψ(%) standard Vertical ≥1930 ≥1620 ≥10 ≥55 head Vertical 1964 / 1972 / 1964 1694 / 1696 / 1694 14.6 / 14.4 / 13.0 72 / 73 / 74 tail Vertical 1958 / 1972 / 1965 1686 / 1706 / 1713 14.0 / 13.9 / 15.2 74 / 74 / 74

[0065] Example 3

[0066] A method for preparing a small-sized ultra-high-strength steel hot-rolled bar for fasteners comprises the following steps:

[0067] The forged Φ160mm billet was kept at 1040℃ for 2.5h and then rolled with the following settings: Φ160mm→Φ56mm, total deformation 90%, and air cooling after rolling;

[0068] The Φ56mm billet was rolled after being kept at 1060℃ for 1h, with the following settings: Φ56mm→Φ29.5mm, total deformation 75%, and air cooling after rolling;

[0069] The Φ29.5mm billet was rolled after being kept at 1060℃ for 1h, with the following settings: Φ29.5mm→Φ12.5mm, total deformation 81%, and air cooling after rolling;

[0070] The Φ12.5mm billet after high temperature tempering heat treatment was subjected to normalizing heat treatment, heated to 910°C, kept at this temperature for 4h, and air-cooled after heating.

[0071] The Φ12.5mm billet was subjected to high temperature tempering heat treatment, heated to 690°C, kept at this temperature for 20h, and then air-cooled after heating.

[0072] The Φ12.5mm billet is machined into Φ10mm finished bar billet.

[0073] Among them: the deformation amounts of the first insulation rolling, the second insulation rolling and the third insulation rolling are 75% to 90%. Preferably, during these three insulation rolling processes, the deformation amounts can be: 75%, 80%, 81%, 82.5%, 85% and 90%.

[0074] The grain size of the finished bar billet is graded according to GB / T 6394, and the core grain size of the head and tail is 8.5. Figure 6-7 .

[0075] The mechanical properties of the finished rod blank are tested according to GB / T 228, the head and tail tensile strength is ≥1960MPa, the elongation is ≥12%, and the comprehensive mechanical properties are excellent, see Table 3.

[0076] Table 3 Mechanical properties test results of Φ10mm bar blank

[0077]

[0078]

[0079] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention.

[0080] It should be understood that the present invention is not limited to what has been described above and that various modifications and changes may be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing a small-sized ultra-high strength steel hot-rolled bar for fasteners, characterized in that: The specific steps include: Step 1: forming a Φ10.5mm-Φ12.5mm billet through multiple heat-insulating rolling at a specified temperature, wherein the deformation amount during the heat-insulating rolling process is 75%-90%; Step 2: subjecting the blank with a size of Φ10.5mm to Φ12.5mm to normalizing heat treatment and then to high temperature tempering heat treatment; Step 3: Machining the Φ10.5mm-Φ12.5mm billet after high temperature tempering heat treatment into a Φ10mm finished bar.

2. The method for preparing a small-sized ultra-high strength steel hot-rolled bar for fasteners according to claim 1, characterized in that: The process of multiple heat-insulating rolling in step 1 is as follows: In the first heat-insulated rolling, the billet with a size of Φ120mm to Φ160mm is kept at a specified temperature and then rolled into a billet with a size of Φ50mm to Φ56mm; In the second heat-insulating rolling, the billets with specifications of Φ50mm~Φ56mm are kept at a specified temperature and then rolled into billets with specifications of Φ23.5mm~Φ29.5mm; in the third heat-insulating rolling, the billets with specifications of Φ23.5mm~Φ29.5mm are kept at a specified temperature and then rolled into billets with specifications of Φ10.5mm~Φ12.5mm.

3. The method for preparing a small-sized ultra-high strength steel hot-rolled bar for fasteners according to claim 2, characterized in that: During the first and second heat-insulating rolling processes, the charging furnace temperature is ≤900°C, and the temperature is increased to 1020°C-1060°C at a heating rate of 2°C-8°C / min, and the heat-insulating time is 1.5h-2.5h. After the heat-insulating process, the material is taken out of the furnace and rolled, and the material is air-cooled after the rolling process.

4. The method for preparing a small-sized ultra-high strength steel hot-rolled bar for fasteners according to claim 2, characterized in that: In the third heat-insulating rolling, the charging temperature is ≤900°C, and the temperature is raised to 1020°C-1060°C at a heating rate of 2°C-8°C / min, and the heat-insulating time is 1h-2h. After the heat-insulating is completed, the material is taken out of the furnace and rolled, and the material is air-cooled after the rolling is completed.

5. The method for preparing a small-sized ultra-high strength steel hot-rolled bar for fasteners according to claim 1, characterized in that: In the step 2, the normalizing heat treatment is specifically: heating to 890° C. to 910° C., keeping the temperature for 2 h to 4 h, and air cooling after heating.

6. The method for preparing a small-sized ultra-high strength steel hot-rolled bar for fasteners according to claim 1, characterized in that: In the step 2, the tempering heat treatment is specifically: heating to 670° C. to 690° C., keeping the temperature for 18 h to 20 h, and air cooling after heating.

7. The method for preparing a small-sized ultra-high strength steel hot-rolled bar for fasteners according to claim 1, characterized in that: The grain size of the finished rod with a specification of Φ10 mm is 8.

5.

8. The method for preparing a small-sized ultra-high strength steel hot-rolled bar for fasteners according to claim 1, characterized in that: The tensile strength of the finished bar with a specification of Φ10mm is ≥1960MPa and the elongation is ≥12%.

9. The method for preparing a small-sized ultra-high strength steel hot-rolled bar for fasteners according to claim 1, characterized in that: The carbon content of the finished bar is 0.23% to 0.25%.

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