Low-cost smelting method for improving cleanliness of sulfur-containing gear steel

Abstract

The invention discloses a low-cost smelting method for improving cleanliness of sulfur-containing gear steel. The smelting method comprises the following steps of converter blowing, LF refining and vacuum treatment. In the LF refining step, refining final slag components are controlled to be 50%-60% of CaO, 5%-10% of SiO2, 15%-25% of Al2O3, 0-1% of MnO and 5%-15% of MgO; a sulfur line is fed before LF refining is finished; a calcium line is fed after soft blowing is conducted for 3-5 min, and the Ca / S ratio in the steel is controlled to be 0.02-0.08; according to the method, a high-alkalinity slag making and sulfur increasing process is still adopted, but a micro-calcium treatment process is adopted before vacuum treatment, the Ca / S ratio in the steel is controlled within a certain range, the purpose of inclusion denaturation is achieved, then vacuum circulation treatment is conducted, floating removal of the inclusions is promoted, and the cleanliness of the molten steel is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a smelting method for improving the cleanliness of sulfur-containing gear steel at a low cost. Background Art

[0002] Gear steel is widely used in transmission systems such as automobiles and machinery. Increasing the sulfur content in gear steel can improve the cutting performance of gear steel, improve gear processing efficiency and reduce production costs. The increase in sulfur content in steel will increase the chance of oxides being surrounded by sulfides during smelting, resulting in an increase in the number of symbiotic inclusions; at the same time, long strips of MnS will be formed during rolling, increasing the anisotropy of the steel.

[0003] Chinese patent CN 114892070A discloses a sulfur-containing gear steel and a production method thereof. The invention proposes a sulfide modification treatment method, in which the molten steel after LF refining and smelting is subjected to deep vacuum treatment, and iron-tellurium cored wire is fed to spheroidize, refine and disperse the sulfides in the steel to improve the cutting characteristics of the gear steel. Due to the use of iron-tellurium cored wire, the invention not only has strict requirements on the molten steel temperature, free oxygen and slag layer thickness, but also significantly increases the production cost.

[0004] Patent CN 117126975A discloses a method for controlling sulfides in sulfur-containing gear steel. The invention controls the converter, LF refining, RH refining and continuous casting processes to solve the difficulties in controlling the production of sulfur-containing steel and the morphology of sulfides. The sulfur-containing gear steel produced can be continuously pulled for more than 10 furnaces, and the level of Class A inclusions can be stably controlled to be Class A coarse ≤1.0 and Class A fine ≤1.5. The weakly alkaline slag of the invention has a poor deoxidation effect, and the sulfur content is controlled without adding sulfur during the refining process. There is a risk that the sulfur content is lower than the steel grade requirement, the number of non-metallic inclusions is large, and it is difficult to meet the quality requirements of clean steel products. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a low-cost smelting method for improving the cleanliness of sulfur-containing gear steel, which improves the cleanliness of molten steel of sulfur-containing gear steel without increasing production costs.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A low-cost smelting method for improving the cleanliness of sulfur-containing gear steel, the smelting method comprising the following steps: converter blowing, LF refining, and vacuum treatment;

[0008] In the LF refining step, the final slag composition is controlled at 50-60% CaO, 50-60% SiO 2 5-10%, Al 2 O 315-25%, MnO 0-1%, MgO 5-15%; feed into the sulfur line before LF refining leaves the station; feed into the calcium line after soft blowing for 3-5 minutes, and control the Ca / S ratio in the steel at 0.02-0.08.

[0009] In the converter blowing step, the C content at the converter blowing end point is 0.05-0.08%, and the end point temperature is 1610-1630°C.

[0010] In the converter blowing step, alloying is performed during the steel tapping process, and aluminum iron and lime are added during the steel tapping process for pre-deoxidation.

[0011] In the LF refining step, lime, calcium carbide and aluminum particles are used to form slag.

[0012] In the LF refining step, the feeding length of the sulfur line is 250-300m.

[0013] In the LF refining step, the feeding length of the calcium wire is 20-50m.

[0014] In the vacuum treatment step, the steel liquid is vacuumed using a large gas flow rate of 1000-1200 L / min, and the high vacuum is maintained at ≤67 Pa for ≥12 min.

[0015] In the vacuum treatment step, the ladle bottom blowing gas flow rate is adjusted to 80-100 NL / min, and the soft argon blowing time is 15-20 min.

[0016] The composition and weight percentage of the sulfur-containing gear steel are: C 0.15-0.25%, Si 0.17-0.37%, Mn≤1.30%, S 0.022-0.032%, Al 0.015-0.030%, Cr≤1.25%, Ni≤0.50%, Mo≤0.25%, and the balance is Fe and unavoidable impurities.

[0017] The weakly alkaline slag used in the production of sulfur-containing steel has poor metallurgical effects, especially poor deoxidation effects, and a large number of non-metallic inclusions, making it difficult to meet the quality requirements of clean steel products. The present invention still adopts the high-alkalinity slag sulfur-increasing process, but adopts a micro-calcium treatment process before vacuum treatment to control the Ca / S ratio in the steel within a certain range to achieve the purpose of inclusion modification, and then promotes the floating removal of inclusions through vacuum circulation treatment.

[0018] In order to improve the metallurgical effect of refined slag, a high-basicity slag system is used in the LF refining process; in addition, after LF refining, before the molten steel leaves the station, it is fed into the sulfur line for sulfur addition according to the upper limit of the sulfur content agreement required for sulfur-containing steel.

[0019] In order to improve the cleanliness of molten steel and reduce the number of inclusions in the steel, LF refining feeds the sulfur line and soft blows for 3 minutes, then the molten steel is treated with micro-calcium to control the Ca / S ratio in the steel at 0.02-0.08; the vacuum treatment process uses a larger gas flow rate to increase the number of circulations; after the vacuum treatment, the molten steel is soft-blown with argon to further remove non-metallic inclusions in the molten steel.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention overcomes the shortcomings of poor deoxidation effect and unstable sulfur content control in the process of making weak alkaline slag without adding sulfur, and the process of making high alkaline slag with adding sulfur is beneficial to the adsorption and deoxidation effect of refined slag on inclusions.

[0022] 2. The present invention feeds the sulfur line at the end of the LF exit, and performs micro-calcium treatment after a certain period of soft blowing, which can denature the inclusions in the steel and prolong the sufficient floating time of the denatured inclusions.

[0023] 3. The present invention is easy to operate and has a stable process. It does not denature the sulfide by feeding other high-cost cored wires, so the production cost is low. DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to the embodiments.

[0025] In each embodiment and comparative example, the weight of each batch of molten steel is 120t.

[0026] Example 1

[0027] A low-cost smelting method for improving the cleanliness of sulfur-containing gear steel, the smelting method comprising the following steps:

[0028] Converter blowing: The C content at the converter blowing end point is 0.057%, and the end point temperature is 1625°C; silicon manganese, high manganese, low chromium, etc. are added to the molten steel for alloying during the steel tapping process, and 150kg of aluminum iron and 600kg of lime are added for pre-deoxidation during the steel tapping process;

[0029] LF refining: LF refining process uses lime, calcium carbide and aluminum particles to make slag, and the main components of the final slag are controlled at CaO 56%, SiO 2 9%, Al 2 O 3 22%, MnO 0.5%, MgO 6%; LF refining feeds 260m of sulfur line before leaving the station, and feeds 35m of calcium line after soft blowing for 3 minutes, controlling the Ca / S ratio in the steel at 0.04;

[0030] Vacuum treatment: During the steel liquid vacuuming process, a large gas flow rate of 1000L / min is used, and the high vacuum of 55Pa is maintained for 15min; after the vacuum treatment, the ladle bottom blowing gas flow rate is adjusted to 80NL / min, and the soft argon blowing time is 20min.

[0031] After vacuum treatment, the composition of the molten steel was tested. The composition and weight percentage of the molten steel were: C 0.19%, Si 0.23%, Mn 1.04%, S 0.026%, Al 0.024%, Cr 0.18%, Ni 0.34%, Mo 0.23%, Ca 0.0010%, and the balance was Fe and unavoidable impurities.

[0032] Example 2

[0033] A low-cost smelting method for improving the cleanliness of sulfur-containing gear steel, the smelting method comprising the following steps:

[0034] Converter blowing: The C content at the converter blowing end point is 0.07%, and the end point temperature is 1612°C; silicon manganese, high manganese, low chromium, etc. are added to the molten steel for alloying during the steel tapping process, and 120kg of aluminum iron and 500kg of lime are added for pre-deoxidation during the steel tapping process;

[0035] LF refining: LF refining process uses lime, calcium carbide and aluminum particles to make slag, and the main components of the final slag are controlled at CaO 58%, SiO 2 10%, Al 2 O 3 25%, MnO 0.3%, MgO 5%; LF refining feeds 280m of sulfur line before leaving the station, and feeds 45m of calcium line after soft blowing for 5 minutes, controlling the Ca / S ratio in the steel at 0.06;

[0036] Vacuum treatment: During the steel liquid vacuuming process, a large gas flow rate of 1200L / min is used, and the high vacuum of 60Pa is maintained for 16 minutes; after the vacuum treatment, the ladle bottom blowing gas flow rate is adjusted to 100NL / min, and the soft argon blowing time is 15 minutes.

[0037] After vacuum treatment, the composition of the molten steel was tested. The composition and weight percentage of the molten steel were: C 0.21%, Si 0.31%, Mn 1.14%, S 0.030%, Al 0.020%, Cr 1.21%, Ni 0.41%, Mo 0.16%, Ca 0.0016%, and the balance was Fe and inevitable impurities.

[0038] Comparative Example 1

[0039] A method for smelting sulfur-containing gear steel, the smelting method comprising the following steps:

[0040] Converter blowing: The C content at the converter blowing end point is 0.05%, and the end point temperature is 1635°C; silicon manganese, high manganese, low chromium, etc. are added to the molten steel for alloying during the steel tapping process, and 120kg of aluminum iron and 500kg of lime are added for pre-deoxidation during the steel tapping process;

[0041] LF refining: LF refining process uses lime, calcium carbide and aluminum particles to make slag, and the main components of the final slag are controlled at CaO 47%, SiO 2 18%, Al 2 O 3 15%, MnO 0.6%, MgO 10%;

[0042] Vacuum treatment: The steel liquid is vacuumed at a high gas flow rate of 1000L / min and maintained at a high vacuum of 55Pa for 16 minutes;

[0043] After the vacuum treatment, 260m of sulfur line was fed before leaving the station, and then 80m of calcium line was directly fed; the ladle bottom blowing gas flow was adjusted to 80NL / min, and the soft blowing argon time was 18min. The molten steel composition was tested, and the molten steel composition and weight percentage were: C 0.20%, Si 0.22%, Mn 1.05%, S 0.025%, Al 0.020%, Cr 0.18%, Ni 0.35%, Mo 0.22%, Ca0.0022%, and the balance was Fe and unavoidable impurities.

[0044] Comparative Example 2

[0045] A method for smelting sulfur-containing gear steel, the smelting method comprising the following steps:

[0046] Converter blowing: The C content at the converter blowing end point is 0.06%, and the end point temperature is 1630°C; silicon manganese, high manganese, low chromium, etc. are added to the molten steel for alloying during the steel tapping process. At the same time, no aluminum iron is added during the steel tapping process, and only 500kg of lime is added for pre-deoxidation;

[0047] LF refining: LF refining process uses lime, calcium carbide and aluminum particles to make slag, and the main components of the final slag are controlled at CaO 56%, SiO 2 8%, Al 2 O 3 18%, MnO 0.4%, MgO 11%; LF refining feeds into the calcium line 120m before leaving the station, and the Ca / Al ratio in the steel is 0.10;

[0048] Vacuum treatment: The steel liquid is vacuumed with a large gas flow rate of 1000L / min and maintained at a high vacuum of 50Pa for 18 minutes;

[0049] After vacuum treatment, 260m of sulfur line was fed before leaving the station, the ladle bottom blowing gas flow was adjusted to 90NL / min, and the soft blowing argon time was 20min. The molten steel composition was tested, and the molten steel composition and weight percentage were: C 0.21%, Si 0.25%, Mn 1.06%, S0.027%, Al 0.025%, Cr 0.19%, Ni 0.35%, Mo 0.23%, Ca 0.0025%, and the balance was Fe and unavoidable impurities.

[0050] The cleanliness data of molten steel in the above-mentioned embodiments and comparative examples are shown in Table 1.

[0051] Table 1 Comparison of non-metallic inclusion levels in different embodiments and comparative examples

[0052] Classification A thin A thick B thin B thick C Thin C thick D Thin D thick Ds Example 1 0.5 0 0 0 0 0 0.5 0 0 Example 2 0.5 0 0 0 0 0 0.5 0 0 Comparative Example 1 1.0 0.5 0.5 0 0 0 0.5 0.5 0.5 Comparative Example 2 1.5 1.0 0.5 0 0 0 0.5 0.5 1.0

[0053] From the above comparison, it can be seen that by adopting the methods of Example 1 and Example 2, the steel products produced have a low level of non-metallic inclusions and a higher purity of the molten steel.

[0054] The above-mentioned reference embodiment provides a detailed description of a low-cost smelting method for improving the cleanliness of sulfur-containing gear steel. It is illustrative rather than restrictive, and several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A low-cost smelting method for improving the cleanliness of sulfur-containing gear steel, characterized in that: The smelting method comprises the following steps: converter blowing, LF refining, and vacuum treatment; In the LF refining step, the components of the final slag are controlled at CaO 50-60%, SiO2 5-10%, Al2O3 15-25%, MnO 0-5%, and MgO 5-15%; the LF refining is fed into the sulfur line before leaving the station; the calcium line is fed after soft blowing for 3-5 minutes to control the Ca / S ratio in the steel at 0.02-0.

08.

2. The smelting method according to claim 1, characterized in that: In the converter blowing step, the C content at the converter blowing end point is 0.05-0.08%, and the end point temperature is 1610-1630°C.

3. The smelting method according to claim 1, characterized in that: In the converter blowing step, alloying is performed during the steel tapping process, and aluminum iron and lime are added during the steel tapping process for pre-deoxidation.

4. The smelting method according to claim 1, characterized in that: In the LF refining step, lime, calcium carbide and aluminum particles are used to form slag.

5. The smelting method according to claim 1, characterized in that: In the LF refining step, the feeding length of the sulfur line is 250-300m.

6. The smelting method according to claim 1, characterized in that: In the LF refining step, the feeding length of the calcium wire is 20-50m.

7. The smelting method according to claim 1, characterized in that: In the vacuum treatment step, the steel liquid is vacuumed using a large gas flow rate of 1000-1200 L / min, and the high vacuum is maintained at ≤67 Pa for ≥12 min.

8. The smelting method according to claim 1, characterized in that: In the vacuum treatment step, the ladle bottom blowing gas flow rate is adjusted to 80-100 NL / min, and the soft argon blowing time is 15-20 min.

9. The smelting method according to claim 1, characterized in that: The composition and weight percentage of the sulfur-containing gear steel are: C 0.15-0.25%, Si 0.17-0.37%, Mn≤1.30%, S 0.022-0.032%, Al 0.015-0.030%, Cr≤1.25%, Ni≤0.50%, Mo≤0.25%, Ca≤0.0020%, and the balance is Fe and unavoidable impurities.