Nitrogen increasing method for alloy steel

Abstract

The invention discloses a nitrogen increasing method for alloy steel, and belongs to the technical field of ferrous metallurgy. The nitrogen increasing method comprises an LF refining procedure and a VD vacuum procedure, in the LF refining procedure, the initial nitrogen content in molten steel is measured, then the temperature of an electrode is lowered to 1600-1700 DEG C, when it is ensured that the use amount of lime is larger than or equal to 1.2 t, the ratio of nitrogen to argon is adjusted to be 9: 1-9.5: 1, the flow is controlled to be 500-2000 NL / min, nitrogen blowing operation is conducted, the nitrogen pressure is limited to be 0.6-1.2 MPa in the process, it is ensured that 8-10 ppm of nitrogen is increased in the molten steel every time 1 m < 3 > of nitrogen is blown in, and the nitrogen content in the molten steel is increased; the nitrogen content in the molten steel is increased to 800-1200 ppm within 2-3 h, and at the moment, the total lime dosage is larger than or equal to 1.4 kg / t steel. The nitrogen increasing method is wide in applicability, high in efficiency and high in operability, and nitrogen increasing operation of various kinds of nitrogen-containing alloy steel can be met.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and particularly relates to a method for increasing nitrogen in alloy steel. Background Art

[0002] Alloy steel is a type of steel with excellent properties, but its use effect in harsh environments such as high temperature and high pressure is not very ideal. Therefore, the improvement of alloy steel has always been a hot topic. Among them, adding an appropriate amount of nitrogen is one of the important measures to improve the performance of alloy steel. Nitrogen-containing alloy steel improves the properties of steel by adding a certain amount of nitrogen element to the steel, resulting in some special properties. Nitrogen-containing alloy steel has higher strength, hardness, toughness and plasticity compared to ordinary steel. In addition, since nitrogen elements can form certain chemical bond compounds with iron elements in the steel, resisting the erosion of external oxidation, chlorination and other factors, it helps to improve the mechanical properties and service life of alloy steel, and is widely used in engineering fields such as manufacturing downhole tubing, ships, bridges, buildings, nuclear power plants and offshore platforms.

[0003] There are mainly two methods for increasing nitrogen in alloy steel: one is to achieve the purpose of nitrogen increase by adding nitrogen-containing alloys such as ferric nitride and chromium nitride. This method can more precisely control the nitrogen content and avoid being too high or too low. However, this method is prone to introducing impurity elements, which are difficult to remove in the subsequent steelmaking process, thus deteriorating the quality of the molten steel. The other is to directly add nitrogen-containing substances such as ammonia gas and nitrogen gas to the molten steel during the steelmaking process, which can quickly increase the nitrogen content in the molten steel. However, referring to the current technical solutions, such as the paper "Research on RH Nitrogen Increase Process for Ultra-Low Carbon Cold Rolled Enamel Steel", the average nitrogen recovery rate is only 19.4%. This application conducts technical research on the problem of low nitrogen blowing recovery rate of molten steel, and hopes to further improve the average level in the industry through the technology of the present invention. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a stable and efficient method for increasing nitrogen in alloy steel, aiming to improve the nitrogen increase efficiency of alloy steel and reduce the nitrogen increase cost.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: a method for increasing nitrogen in alloy steel, the nitrogen increase method includes a refining LF process and a VD vacuum process. The initial nitrogen content in the molten steel is measured in the refining LF process, and then the electrodes are lowered to raise the temperature to 1600 - 1700 °C. When the lime consumption per furnace is ≥ 1.2 t, the nitrogen-argon ratio is adjusted to 9:1 - 9.5:1, and the flow rate is controlled to 500 - 2000 NL / min for nitrogen blowing operation. During the process, the nitrogen pressure is limited to 0.6 - 1.2 MPa, ensuring that for every 1 m 3 of nitrogen blown into the molten steel, the nitrogen content in the molten steel increases by 8 - 10 ppm, and the nitrogen content in the molten steel is increased to 800 - 1200 ppm in 2 - 3 h. At this time, the total lime consumption is ≥ 1.4 kg / t of steel.

[0006] In the VD vacuum treatment process of the present invention, the molten steel amount is 100 - 125 t, the vacuum degree is 20 - 40 Pa, and the vacuum holding time is 20 - 30 min.

[0007] In the VD vacuum treatment process of the present invention, after the vacuum is broken, it is continuously evacuated back to a vacuum degree ≥ 200 Pa until the temperature reaches 1558 - 1580 °C, and then rice husk is added for soft blowing at normal pressure for 8 - 18 min, and then the cover is closed for casting the ingot.

[0008] In the refining LF process of the present invention, the initial nitrogen content in the molten steel is measured to be 30 - 80 ppm.

[0009] The alloy steel of the present invention contains N: 0.020% - 0.085%, V: 0.15% - 0.30%, Ni ≤ 0.45%, Al ≤ 0.009% The actual nitrogen recovery rate measured by the method of the present invention is between 30% - 40%. The actual nitrogen recovery rate is expressed as η N = Δ[N]·W / Q N ·t) × 100%. Wherein: Δ[N]: the difference in nitrogen content of the molten steel before and after nitrogen blowing (ppm or %); W: the weight of the molten steel (t); Q N : the nitrogen blowing-in flow rate (NL / min or m³ / min or standard state m³ / h); t: the nitrogen blowing time (min or h).

[0010] The beneficial effects of adopting the above technical solutions are as follows: 1. The present invention strictly controls the nitrogen blowing process, improves the nitrogen blowing system while ensuring good slag-making effect in the LF refining process, and further optimizes the degassing and soft blowing processes in the VD vacuum process, avoiding affecting the quality of the molten steel, too low nitrogen recovery rate or increasing the smelting cost. 2. Compared with the conventional process, the method of the present invention can more accurately control the nitrogen content in the molten steel. The actual nitrogen recovery rate obtained by the method of the present invention is between 30% - 40%, which is more than 10.6% higher than that of the conventional process. 3. The nitrogen increasing method of the present invention has wide applicability, high efficiency and strong operability, and can meet the nitrogen increasing operations of various nitrogen-containing alloy steels. Specific Embodiments

[0011] The following will further explain and illustrate the present invention in combination with specific embodiments, however, such explanations and illustrations should not unduly limit the technical solutions of the present invention. Example 1

[0012] The alloy steel (boron-chromium-molybdenum steel plate) in this example contains N: 0.020%, V: 0.15%, Ni: 0.05%, Al: 0.003%. The nitrogen increasing method includes the refining LF process and the VD vacuum process; the specific control methods are as follows: 1) Refining LF process: Measure the initial nitrogen content in the molten steel as 30 ppm. Then lower the electrode to raise the temperature to 1600 °C. Ensure that when the lime consumption per furnace is 1.2 t, adjust the nitrogen-argon ratio to 9:1, control the flow rate to 500 NL / min for nitrogen blowing operation. During the process, limit the nitrogen pressure to 0.6 MPa, and ensure that for every 1 m 3 The nitrogen increases the nitrogen content in the molten steel by 8 ppm, and raises the nitrogen content in the molten steel to 800 ppm in 3 h. At this time, the total lime consumption is 1.4 kg / t of steel.

[0013] 2) VD vacuum treatment process: The molten steel volume is 100 t, the vacuum degree is 20 Pa, and the vacuum holding time is 20 min. After the vacuum is broken, continue to pump back to a vacuum degree of 200 Pa until 1580 °C, add rice husk and blow softly at normal pressure for 8 min, then cover and cast the ingot. Example 2

[0014] This example of alloy steel (boron-chromium-molybdenum steel plate) contains N: 0.028%, V: 0.19%, Ni: 0.07%, Al: 0.004%. The nitrogen increasing method includes refining LF process and VD vacuum process; the specific control methods are as follows: 1) Refining LF process: Measure the initial nitrogen content in the molten steel as 36 ppm. Then lower the electrode to raise the temperature to 1625 °C. Ensure that when the lime consumption per furnace is 1.27 t, adjust the nitrogen-argon ratio to 9.1:1, control the flow rate to 780 NL / min for nitrogen blowing operation. During the process, limit the nitrogen pressure to 0.66 MPa, and ensure that for every 1 m 3 The nitrogen increases the nitrogen content in the molten steel by 8.4 ppm, and raises the nitrogen content in the molten steel to 850 ppm in 2.8 h. At this time, the total lime consumption is 1.43 kg / t of steel.

[0015] 2) VD vacuum treatment process: The molten steel volume is 106 t, the vacuum degree is 25 Pa, and the vacuum holding time is 22 min. After the vacuum is broken, continue to pump back to a vacuum degree of 210 Pa until 1575 °C, add rice husk and blow softly at normal pressure for 9.5 min, then cover and cast the ingot. Example 3

[0016] This example of alloy steel (boron-chromium-molybdenum steel plate) contains N: 0.038%, V: 0.22%, Ni: 0.08%, Al: 0.005%. The nitrogen increasing method includes refining LF process and VD vacuum process; the specific control methods are as follows: 1) Refining LF process: Measure the initial nitrogen content in the molten steel as 42 ppm. Then lower the electrode to raise the temperature to 1640 °C. Ensure that when the lime consumption per furnace is 1.3 t, adjust the nitrogen-argon ratio to 9.3:1, control the flow rate to 840 NL / min for nitrogen blowing operation. During the process, limit the nitrogen pressure to 0.75 MPa, and ensure that for every 1 m 3Nitrogen increases the nitrogen content in the molten steel by 8.8 ppm and raises the nitrogen content in the molten steel to 900 ppm in 2.5 h. At this time, the total amount of lime used is 1.47 kg / t of steel.

[0017] 2) VD vacuum treatment process: The amount of molten steel is 112 t, the vacuum degree is 30 Pa, and the vacuum holding time is 24 min. After the vacuum is broken, it is continuously pumped back to a vacuum degree of 220 Pa until 1571 °C, and rice husks are added for normal pressure soft blowing for 11 min, then the lid is covered and the ingot is cast. Example 4

[0018] This example of alloy steel (boron-chromium-molybdenum steel plate) contains N: 0.052%, V: 0.24%, Ni: 0.15%, Al: 0.006%. The nitrogen increasing method includes the refining LF process and the VD vacuum process; the specific control methods are as follows: 1) Refining LF process: Measure the initial nitrogen content in the molten steel as 50 ppm, then lower the electrode to raise the temperature to 1650 °C. When ensuring that the amount of lime used per furnace is 1.38 t, adjust the nitrogen-argon ratio to 9.3:1, control the flow rate to 950 NL / min for nitrogen blowing operation, limit the nitrogen pressure to 0.9 MPa during the process, and ensure that for every 1 m 3 Nitrogen increases the nitrogen content in the molten steel by 9 ppm and raises the nitrogen content in the molten steel to 980 ppm in 2.3 h. At this time, the total amount of lime used is 1.53 kg / t of steel.

[0019] 2) VD vacuum treatment process: The amount of molten steel is 118 t, the vacuum degree is 35 Pa, and the vacuum holding time is 26 min. After the vacuum is broken, it is continuously pumped back to a vacuum degree of 230 Pa until 1566 °C, and rice husks are added for normal pressure soft blowing for 13 min, then the lid is covered and the ingot is cast. Example 5

[0020] This example of alloy steel (boron-chromium-molybdenum steel plate) contains N: 0.068%, V: 0.26%, Ni: 0.30%, Al: 0.007%. The nitrogen increasing method includes the refining LF process and the VD vacuum process; the specific control methods are as follows: 1) Refining LF process: Measure the initial nitrogen content in the molten steel as 67 ppm, then lower the electrode to raise the temperature to 1665 °C. When ensuring that the amount of lime used per furnace is 1.4 t, adjust the nitrogen-argon ratio to 9.4:1, control the flow rate to 1300 NL / min for nitrogen blowing operation, limit the nitrogen pressure to 0.92 MPa during the process, and ensure that for every 1 m 3 Nitrogen increases the nitrogen content in the molten steel by 9.2 ppm and raises the nitrogen content in the molten steel to 1050 ppm in 2.2 h. At this time, the total amount of lime used is 1.58 kg / t of steel.

[0021] 2) VD vacuum treatment process: The molten steel volume is 122 t, the vacuum degree is 37 Pa, and the vacuum holding time is 28 min. After the vacuum is broken, it is continuously pumped back to a vacuum degree of 240 Pa until 1562 °C, and then rice husks are added for soft blowing at normal pressure for 16 min, and then the cover is closed for casting the ingot. Example 6

[0022] This example of alloy steel (boron-chromium-molybdenum steel plate) contains N: 0.078%, V: 0.28%, Ni: 0.39%, Al: 0.008%. The nitrogen increasing method includes the refining LF process and the VD vacuum process; the specific control methods are as follows: 1) Refining LF process: Measure the initial nitrogen content in the molten steel as 75 ppm, then lower the electrode to raise the temperature to 1686 °C. Ensure that when the lime consumption per furnace is 1.43 t, adjust the nitrogen-argon ratio to 9.5:1, control the flow rate to 1700 NL / min for nitrogen blowing operation, limit the nitrogen pressure to 1.1 MPa during the process, and ensure that for every 1 m 3 of nitrogen blown into the molten steel, the nitrogen content in the molten steel increases by 9.8 ppm, and the nitrogen content in the molten steel is increased to 1140 ppm in 2.1 h. At this time, the total lime consumption is 1.62 kg / t of steel.

[0023] 2) VD vacuum treatment process: The molten steel volume is 124 t, the vacuum degree is 39 Pa, and the vacuum holding time is 29 min. After the vacuum is broken, it is continuously pumped back to a vacuum degree of 245 Pa until 1560 °C, and then rice husks are added for soft blowing at normal pressure for 17 min, and then the cover is closed for casting the ingot. Example 7

[0024] This example of alloy steel (boron-chromium-molybdenum steel plate) contains N: 0.085%, V: 0.30%, Ni: 0.45%, Al: 0.009%. The nitrogen increasing method includes the refining LF process and the VD vacuum process; the specific control methods are as follows: 1) Refining LF process: Measure the initial nitrogen content in the molten steel as 80 ppm, then lower the electrode to raise the temperature to 1700 °C. Ensure that when the lime consumption per furnace is 1.5 t, adjust the nitrogen-argon ratio to 9.5:1, control the flow rate to 2000 NL / min for nitrogen blowing operation, limit the nitrogen pressure to 1.2 MPa during the process, and ensure that for every 1 m 3 of nitrogen blown into the molten steel, the nitrogen content in the molten steel increases by 10 ppm, and the nitrogen content in the molten steel is increased to 1200 ppm in 2.0 h. At this time, the total lime consumption is 1.68 kg / t of steel.

[0025] 2) VD vacuum treatment process: The molten steel volume is 125 t, the vacuum degree is 40 Pa, and the vacuum holding time is 30 min. After the vacuum is broken, it is continuously pumped back to a vacuum degree of 260 Pa until 1558 °C, and then rice husks are added for soft blowing at normal pressure for 18 min, and then the cover is closed for casting the ingot.

[0026] The actual nitrogen recovery rates measured by the methods of Examples 1-7 are shown in Table 1.

[0027] Table 1 Implementation effects of actual nitrogen yield in each embodiment

[0028] The above are only the preferred embodiments of the present invention, and the scope of the rights of the present invention cannot be limited thereby. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall fall within the scope covered by the present invention.

Claims

1. A method for increasing nitrogen in alloy steel, characterized in that: The nitrogen-increasing method comprises a refining LF process and a VD vacuum process. The refining LF process determines the initial nitrogen content in the molten steel, then lowers the electrode and raises the temperature to 1600-1700°C, ensures that the amount of lime used in each furnace is ≥1.2t, adjusts the nitrogen-argon ratio to 9:1-9.5:1, controls the flow rate to 500-2000NL / min for nitrogen blowing, limits the nitrogen pressure to 0.6-1.2MPa during the process, and ensures that each 1m 3 Nitrogen increases the nitrogen content in the molten steel by 8-10ppm, and in 2-3 hours the nitrogen content in the molten steel is increased to 800-1200ppm. At this time, the total lime consumption is ≥1.4kg / t steel.

2. A method for increasing nitrogen in alloy steel according to claim 1, characterized in that: The amount of molten steel in the VD vacuum treatment process is 100-125t, the vacuum degree is 20-40Pa, and the vacuum holding time is 20-30min.

3. The method for increasing nitrogen content in alloy steel according to claim 1, characterized in that: In the VD vacuum treatment process, after the vacuum is broken, the vacuum is continuously pumped back to a vacuum degree of ≥200Pa and the temperature is 1558-1580°C, and rice husks are added for soft blowing at normal pressure for 8-18 minutes to cover and cast the steel ingot.

4. A method for increasing nitrogen in alloy steel according to any one of claims 1 to 3, characterized in that: The refining LF process determines the initial nitrogen content in the molten steel to be 30-80 ppm.

5. A method for increasing nitrogen in alloy steel according to any one of claims 1 to 3, characterized in that: The alloy steel contains N: 0.020%-0.085%, V: 0.15%-0.30%, Ni≤0.45%, Al≤0.009%.

6. A method for increasing nitrogen in alloy steel according to any one of claims 1 to 3, characterized in that: The actual nitrogen recovery rate measured by the method is between 30% and 40%.

Images