A process for spheroidizing annealing of a bolt steel material

Abstract

The application discloses a bolt steel spheroidizing annealing process and relates to the technical field of a steel spheroidizing annealing process.The bolt steel spheroidizing annealing process steps of the application successively comprise the following process steps: firstly, under the protection of a nitrogen atmosphere, temperature is raised to 760-800 DEG C for heat preservation, while nitrogen mixed with propylene is introduced, under the catalysis of nickel metal in the bolt steel, then slow cooling and repeated pressurization are adopted to perform primary pressurization cooling, secondary depressurization cooling and tertiary pressurization cooling, more cementite spheroids are obtained, and the uniformity is better, and the problems of uneven spheroidizing structure due to too fast cooling speed or difficulty in breaking flaky cementite due to too slow cooling speed and poor spheroidizing effect are avoided; the process of temperature rising, heat preservation, primary pressurization cooling, secondary depressurization cooling and tertiary pressurization cooling is adopted, spheroidizing annealing effect is good, the bolt steel has good toughness, and the cracking rate is low.

Description

Technical Field

[0001] This invention relates to the field of spheroidizing annealing process technology for steel, specifically a spheroidizing annealing process for bolt steel. Background Technology

[0002] Spheroidizing annealing is one of the fundamental methods to improve the microstructure and properties of steel. The main purpose of spheroidizing annealing is to spheroidize the carbides in the microstructure of steel, reducing the material's hardness, increasing its plasticity, reducing its deformation resistance, and making it easier to plastically process and shape. In the production of screw wire, the key to obtaining ideal properties and microstructure is selecting a suitable spheroidizing annealing process.

[0003] Currently, in the production of low-carbon alloy steel bolts, after the bolt wire is slowly cooled or annealed according to the existing process, the hardness is too high and the toughness is poor. The bolt steel is very prone to cracking. In mild cases, the cracked part needs to be cut off and reused. In severe cases, the bolt steel produced will be scrapped, which seriously affects the quality and yield of bolt steel.

[0004] Therefore, it is urgent to improve the spheroidizing annealing process of bolt steel to make the bolt steel more tough. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a spheroidizing annealing process for bolt steel, comprising the following process steps: heating, heat preservation, primary pressurization cooling, secondary depressurization cooling, and tertiary pressurization cooling.

[0006] Furthermore, the following process steps are included:

[0007] (1) Heating and holding: Place the bolt steel in a heat treatment furnace, evacuate the furnace, and fill it with inert gas. Then, raise the temperature to 760-800℃ at a rate of 90-110℃ / h, and continue heating at a rate of 2-3m / h. 3 Inert gas mixture is introduced at a rate of 30–60 min, followed by heat treatment for 4–6 h.

[0008] (2) First pressurization and cooling: pressurize to 0.1-0.2 MPa and cool the temperature inside the furnace to 560-600℃ by air cooling at a rate of 15-25℃ / h.

[0009] (3) Secondary decompression cooling: Continue to evacuate the vacuum and cool the temperature inside the furnace to 380-400℃ by air cooling at a rate of 75-85℃ / h.

[0010] (4) Three-stage pressurization and cooling: continue to increase the pressure to 0.1-0.2 MPa, and the bolt steel is naturally cooled to room temperature and taken out of the furnace.

[0011] Furthermore, the bolt steel is a low-carbon alloy steel with a nickel content of 2-3%.

[0012] Furthermore, the inert gas is industrial nitrogen with a purity of 99.9%.

[0013] Furthermore, the ratio of industrial nitrogen with a purity of 99.9% to propylene in the inert gas mixture is 1:0.4 to 1:0.6.

[0014] Furthermore, the vacuum level of the vacuum pump is 1 mba.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0016] The spheroidizing annealing process for bolt steel of this invention first involves heating to 760–800°C under nitrogen protection and holding for a period of time. This allows cementite to fully and uniformly dissolve in austenite, forming a single and uniform austenite structure. According to spheroidization theory, uniform austenite is difficult to transform into spheroidized cementite. Simultaneously, nitrogen gas mixed with propylene is introduced. Under the catalytic effect of nickel metal in the bolt steel, a large number of carbon nanowires are formed within the bolt steel, dispersed in a "pinning" manner, enhancing the toughness of the bolt steel. Then, slow cooling and repeated pressurization are used for primary pressurized cooling, secondary depressurized cooling, and tertiary pressurized cooling. This results in more cementite spheroidization and better uniformity, avoiding the problems of uneven spheroidization due to excessively rapid cooling or poor spheroidization due to insufficient fragmentation of lamellar cementite caused by excessively slow cooling. This invention achieves good spheroidizing annealing effect, good toughness of bolt steel, and low cracking rate by employing a process of heating, holding, primary pressurized cooling, secondary depressurized cooling, and tertiary pressurized cooling. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] To more clearly illustrate the method provided by the present invention, the following embodiments are provided in detail. The testing methods for various indicators of the bolt steel obtained in the following embodiments are as follows:

[0019] Toughness: Bolt steel of the same mass as the example and comparative example was prepared and tested on an INSTRON-450 impact testing machine. The impact energy was tested at a test temperature of 0°C to test the toughness.

[0020] Example 1

[0021] A spheroidizing annealing process for bolt steel includes the following steps: heating, holding, primary pressurization cooling, secondary depressurization cooling, and tertiary pressurization cooling.

[0022] Furthermore, the following process steps are included:

[0023] (1) Heating and holding: Place the bolt steel in a heat treatment furnace, evacuate the furnace, and fill it with inert gas. Then, raise the temperature to 76℃ at a rate of 90℃ / h, and continue heating at a rate of 2m / h. 3 Inert gas mixture was introduced at a rate of 1 / min for 30 min, followed by heat treatment for 4 h.

[0024] (2) First pressurization and cooling: pressurize to 0.1MPa and cool the temperature inside the furnace to 560℃ at a rate of 15℃ / h by air cooling.

[0025] (3) Secondary pressure reduction and cooling: Continue to evacuate the vacuum and cool the temperature inside the furnace to 380°C at a rate of 75°C / h by air cooling.

[0026] (4) Three-stage pressurization and cooling: Continue to increase the pressure to 0.1MPa, and the bolt steel will naturally cool to room temperature and be taken out of the furnace.

[0027] Furthermore, the bolt steel is a low-carbon alloy steel with a nickel content of 2%.

[0028] Furthermore, the inert gas is industrial nitrogen with a purity of 99.9%.

[0029] Furthermore, the ratio of industrial nitrogen with a purity of 99.9% to propylene in the inert gas mixture is 1:0.4.

[0030] Furthermore, the vacuum level of the vacuum pump is 1 mba.

[0031] Example 2

[0032] A spheroidizing annealing process for bolt steel includes the following steps: heating, holding, primary pressurization cooling, secondary depressurization cooling, and tertiary pressurization cooling.

[0033] Furthermore, the following process steps are included:

[0034] (1) Heating and holding: Place the bolt steel in a heat treatment furnace, evacuate the furnace, and fill it with inert gas. Then, heat the furnace to 780℃ at a rate of 100℃ / h, and continue heating at a rate of 2.5m / h. 3 Inert gas mixture was introduced at a rate of 1 / min for 45 min, followed by heat treatment for 5 h.

[0035] (2) First pressurization and cooling: pressurize to 0.15MPa and cool the temperature inside the furnace to 580℃ at a rate of 20℃ / h by air cooling.

[0036] (3) Secondary pressure reduction and cooling: Continue to evacuate the vacuum and cool the temperature inside the furnace to 390℃ at a rate of 80℃ / h by air cooling.

[0037] (4) Three-stage pressurization and cooling: Continue to increase the pressure to 0.15MPa, and the bolt steel will naturally cool to room temperature and be taken out of the furnace.

[0038] Furthermore, the bolt steel is a low-carbon alloy steel with a nickel content of 2.5%.

[0039] Furthermore, the inert gas is industrial nitrogen with a purity of 99.9%.

[0040] Furthermore, the ratio of industrial nitrogen with a purity of 99.9% to propylene in the inert gas mixture is 1:0.5.

[0041] Furthermore, the vacuum level of the vacuum pump is 1 mba.

[0042] Example 3

[0043] A spheroidizing annealing process for bolt steel includes the following steps: heating, holding, primary pressurization cooling, secondary depressurization cooling, and tertiary pressurization cooling.

[0044] Furthermore, the following process steps are included:

[0045] (1) Heating and holding: Place the bolt steel in a heat treatment furnace, evacuate the furnace, fill the furnace with inert gas, and then heat it to 800℃ at a rate of 110℃ / h, continuing at a rate of 3m 3 Inert gas mixture was introduced at a rate of 6 min for 60 min, followed by heat treatment for 6 h.

[0046] (2) First pressurization and cooling: pressurize to 0.2MPa and cool the temperature inside the furnace to 600℃ by air cooling at a rate of 25℃ / h.

[0047] (3) Secondary pressure reduction and cooling: Continue to evacuate the vacuum and cool the temperature inside the furnace to 400℃ at a rate of 85℃ / h by air cooling.

[0048] (4) Three-stage pressurization and cooling: Continue to increase the pressure to 0.2MPa, and the bolt steel will naturally cool to room temperature and be taken out of the furnace.

[0049] Furthermore, the bolt steel is a low-carbon alloy steel with a nickel content of 3%.

[0050] Furthermore, the inert gas is industrial nitrogen with a purity of 99.9%.

[0051] Furthermore, the ratio of industrial nitrogen with a purity of 99.9% to propylene in the inert gas mixture is 1:0.6.

[0052] Furthermore, the vacuum level of the vacuum pump is 1 mba.

[0053] Comparative Example 1

[0054] A spheroidizing annealing process for bolt steel includes the following steps: heating, holding, primary pressurization cooling, secondary depressurization cooling, and tertiary pressurization cooling.

[0055] Furthermore, the following process steps are included:

[0056] (1) Heating and holding: Place the bolt steel in a heat treatment furnace, evacuate the furnace, and fill it with inert gas. Then, heat the furnace to 650℃ at a rate of 100℃ / h, and continue heating at a rate of 2.5m / h. 3 Inert gas mixture was introduced at a rate of 1 / min for 45 min, followed by heat treatment for 5 h.

[0057] (2) First pressurization and cooling: pressurize to 0.15MPa and cool the temperature inside the furnace to 580℃ at a rate of 20℃ / h by air cooling.

[0058] (3) Secondary pressure reduction and cooling: Continue to evacuate the vacuum and cool the temperature inside the furnace to 390℃ at a rate of 80℃ / h by air cooling.

[0059] (4) Three-stage pressurization and cooling: Continue to increase the pressure to 0.15MPa, and the bolt steel will naturally cool to room temperature and be taken out of the furnace.

[0060] Furthermore, the bolt steel is a low-carbon alloy steel with a nickel content of 2.5%.

[0061] Furthermore, the inert gas is industrial nitrogen with a purity of 99.9%.

[0062] Furthermore, the ratio of industrial nitrogen with a purity of 99.9% to propylene in the inert gas mixture is 1:0.5.

[0063] Furthermore, the vacuum level of the vacuum pump is 1 mba.

[0064] Comparative Example 2

[0065] A spheroidizing annealing process for bolt steel includes the following steps: heating, holding, primary pressurization cooling, secondary depressurization cooling, and tertiary pressurization cooling.

[0066] Furthermore, the following process steps are included:

[0067] (1) Heating and heat preservation: Place the bolt steel in the heat treatment furnace, evacuate the bolt steel in the heat treatment furnace, fill the heat treatment furnace with inert gas, and then heat it to 780℃ at a rate of 100℃ / h, and then keep it at the temperature for 5h.

[0068] (2) First pressurization and cooling: pressurize to 0.15MPa and cool the temperature inside the furnace to 580℃ at a rate of 20℃ / h by air cooling.

[0069] (3) Secondary pressure reduction and cooling: Continue to evacuate the vacuum and cool the temperature inside the furnace to 390℃ at a rate of 80℃ / h by air cooling.

[0070] (4) Three-stage pressurization and cooling: Continue to increase the pressure to 0.15MPa, and the bolt steel will naturally cool to room temperature and be taken out of the furnace.

[0071] Furthermore, the bolt steel is a low-carbon alloy steel with a nickel content of 2.5%.

[0072] Furthermore, the inert gas is industrial nitrogen with a purity of 99.9%.

[0073] Furthermore, the vacuum level of the vacuum pump is 1 mba.

[0074] Comparative Example 3

[0075] A spheroidizing annealing process for bolt steel includes the following steps: heating, holding, primary pressurization cooling, secondary depressurization cooling, and tertiary pressurization cooling.

[0076] Furthermore, the following process steps are included:

[0077] (1) Heating and holding: Place the bolt steel in a heat treatment furnace, evacuate the furnace, and fill it with inert gas. Then, heat the furnace to 780℃ at a rate of 100℃ / h, and continue heating at a rate of 2.5m / h. 3 Inert gas mixture was introduced at a rate of 1 / min for 45 min, followed by heat treatment for 5 h.

[0078] (2) First pressurization and cooling: pressurize to 0.15MPa, cool the temperature inside the furnace to 580℃ at a rate of 20℃ / h by air cooling, continue to evacuate, and cool the temperature inside the furnace to 390℃ at a rate of 20℃ / h by air cooling.

[0079] (3) Three-stage pressurization and cooling: continue to increase the pressure to 0.15MPa, and the bolt steel is naturally cooled to room temperature and taken out of the furnace.

[0080] Furthermore, the bolt steel is a low-carbon alloy steel with a nickel content of 2.5%.

[0081] Furthermore, the inert gas is industrial nitrogen with a purity of 99.9%.

[0082] Furthermore, the ratio of industrial nitrogen with a purity of 99.9% to propylene in the inert gas mixture is 1:0.5.

[0083] Furthermore, the vacuum level of the vacuum pump is 1 mba.

[0084] Comparative Example 4

[0085] A spheroidizing annealing process for bolt steel includes the following steps: heating, holding, primary pressurization cooling, secondary depressurization cooling, and tertiary pressurization cooling.

[0086] Furthermore, the following process steps are included:

[0087] (1) Heating and holding: Place the bolt steel in a heat treatment furnace, evacuate the furnace, and fill it with inert gas. Then, heat the furnace to 780℃ at a rate of 100℃ / h, and continue heating at a rate of 2.5m / h. 3 Inert gas mixture was introduced at a rate of 1 / min for 45 min, followed by heat treatment for 5 h.

[0088] (2) First pressurization and cooling: pressurize to 0.15MPa and cool the temperature inside the furnace to 580℃ at a rate of 80℃ / h by air cooling; continue to evacuate and cool the temperature inside the furnace to 390℃ at a rate of 80℃ / h by air cooling.

[0089] (3) Three-stage pressurization and cooling: continue to increase the pressure to 0.15MPa, and the bolt steel is naturally cooled to room temperature and taken out of the furnace.

[0090] Furthermore, the bolt steel is a low-carbon alloy steel with a nickel content of 2.5%.

[0091] Furthermore, the inert gas is industrial nitrogen with a purity of 99.9%.

[0092] Furthermore, the ratio of industrial nitrogen with a purity of 99.9% to propylene in the inert gas mixture is 1:0.5.

[0093] Furthermore, the vacuum level of the vacuum pump is 1 mba.

[0094] Example of effect

[0095] Table 1 below shows the analysis results of the toughness of the bolt steels prepared using Examples 1 to 3 and Comparative Examples 1 to 4 of the present invention.

[0096] Table 1

[0097]

[0098] Table 1 shows that the bolt steel prepared in Examples 1, 2, and 3 has good toughness. A comparison of the experimental data from Examples 1, 2, and 3 and Comparative Example 1 shows that bolt steel prepared by heating to 760–800°C and holding at that temperature has good toughness. A comparison of the experimental data from Examples 1, 2, and 3 and Comparative Example 2 shows that bolt steel prepared by holding at a temperature mixed with nitrogen has good toughness. The experimental data from Examples 1, 2, and 3 and Comparative Examples 3, 4, and 5 shows that bolt steel prepared using a single pressurized cooling, a second depressurized cooling, and a third pressurized cooling method has good toughness.

[0099] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A spheroidizing annealing process for bolt steel, characterized in that, The process includes the following steps: heating, holding, primary pressurization and cooling, secondary depressurization and cooling, and tertiary pressurization and cooling. (1) Heating and holding: Place the bolt steel in a heat treatment furnace, evacuate the furnace, fill the furnace with inert gas, and then heat it to 760-800℃ at a rate of 90-110℃ / h, and continue heating at a rate of 2-3m 3 Inert gas mixture is introduced at a rate of / min for 30-60 min, followed by heat treatment for 4-6 h; (2) First pressurization and cooling: pressurize to 0.1~0.2MPa and cool the temperature inside the furnace to 560~600℃ by air cooling at a rate of 15~25℃ / h; (3) Secondary pressure reduction and cooling: Continue to evacuate the vacuum and cool the temperature inside the furnace to 380-400℃ by air cooling at a rate of 75-85℃ / h; (4) Three-stage pressurization and cooling: continue to increase the pressure to 0.1~0.2MPa, and the bolt steel is naturally cooled to room temperature and taken out of the furnace.

2. The spheroidizing annealing process for bolt steel according to claim 1, characterized in that, The bolts are made of low-carbon alloy steel with a nickel content of 2-3%.

3. The spheroidizing annealing process for bolt steel according to claim 2, characterized in that, The inert gas is industrial nitrogen with a purity of 99.9%.

4. The spheroidizing annealing process for bolt steel according to claim 1, characterized in that, The ratio of industrial nitrogen (99.9% purity) to propylene in the inert gas mixture is 1:0.4 to 1:0.

6.

5. The spheroidizing annealing process for bolt steel according to claim 4, characterized in that, The vacuum level of the vacuum pump is 1 mba.

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