Production method for improving manganese sulfide form of medium-carbon high-sulfur free-cutting steel wire rod and medium-carbon high-sulfur free-cutting steel wire rod

Abstract

The invention discloses a production method for improving the manganese sulfide form of a medium-carbon high-sulfur free-cutting steel wire rod and the medium-carbon high-sulfur free-cutting steel wire rod, and the production method comprises the following steps: adding a silicon-manganese alloy and a high-manganese alloy into molten steel for deoxidation alloying in the tapping process of a converter or an electric furnace, and adding lime, ferro-aluminum is not used in the tapping process, and the oxygen content of molten steel in an argon station behind the furnace is 20-40 PPm; lime, calcium carbide and ferrosilicon powder are adopted for slagging in the refining process, and aluminum-containing materials are strictly prohibited from being adopted; the refining outbound oxygen content is controlled to be 10-25 PPm; a weak cooling and slow drawing process is adopted for continuous casting, and the degree of superheat of molten steel is controlled to be 25-35 DEG C in the continuous casting process; during hot rolling, rolling is carried out by adopting 60-70% of large rolling reduction from initial rolling to 1080 DEG C; according to the method, the manganese sulfide form and distribution state of the medium-carbon high-sulfur free-cutting steel can be improved, the cutting performance of the medium-carbon high-sulfur free-cutting steel wire rod is improved, and the machining cracking rate is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of free-cutting steel, and specifically relates to a production method for improving the morphology of manganese sulfide in a medium-carbon high-sulfur free-cutting steel wire rod and a medium-carbon high-sulfur free-cutting steel wire rod. Background Art

[0002] The cutting mechanism of high-sulfur free-cutting steel is to use manganese sulfide in the steel as a stress concentration source to destroy the continuity of the metal matrix and play a role in cutting embrittlement. In order to improve the morphology of manganese sulfide in high-sulfur free-cutting steel, it is usually adopted to increase the free oxygen content in the steel and add other free-cutting phases, such as Sn, Te, Bi, Pb, Se, etc. However, due to the low free oxygen content in medium-carbon free-cutting steel, generally 15-30PPm, it is impossible to improve the morphology of manganese sulfide by the production method of increasing the free oxygen content in the steel. Instead, the method of adding other free-cutting methods will significantly increase the production cost of the steel on the one hand, and on the other hand, the low melting point free-cutting phase will lead to an increase in the surface defect rate of the ingot.

[0003] Chinese patent CN113913676A discloses a metallurgical method for improving the morphology of cast sulfides of medium-carbon high-sulfur free-cutting steel, including: converter or electric furnace smelting, LF refining, soft stirring, and continuous casting. During LF refining, the refining time is controlled to 60 to 70 minutes, which is divided into the early, middle and late stages of refining; among them, in the early stage of refining, a strict slag making system is implemented to ensure the appropriate slag composition; in the middle stage of refining, alloying and oxygen content control are carried out; in the late stage of refining, carbon wire is added for carbon alloying. This patent mainly improves the morphology of cast sulfides, and does not pay attention to the morphology of cast sulfides after rolling. The morphology of manganese sulfide after rolling is a key factor affecting the cutting performance and processing cracking rate of medium-carbon high-sulfur free-cutting steel products. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a production method for improving the morphology of manganese sulfide in medium carbon high sulfur free cutting steel wire rod. Through this production method, the morphology of manganese sulfide in medium carbon high sulfur free cutting steel is improved, the cutting performance is improved and the processing cracking rate is reduced.

[0005] The present invention also provides a medium-carbon high-sulfur free-cutting steel wire rod, in which no other free-cutting phases are added and the production cost is low.

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

[0007] A production method for improving the morphology of manganese sulfide in medium-carbon high-sulfur free-cutting steel wire rod, the production method comprising the following steps:

[0008] (1) During the steel-making process of the converter or electric furnace, silicon-manganese alloy and high-manganese alloy are added to the molten steel for deoxidation and alloying, and lime is added. No aluminum iron is used in the steel-making process, and the oxygen content of the molten steel at the argon station after the furnace is 20-40PPm;

[0009] (2) During the refining process, lime, calcium carbide and ferrosilicon powder are used for slag making. Aluminum-containing materials are strictly prohibited. The oxygen content at the refining station is controlled at 10-25PPm;

[0010] (3) Continuous casting adopts weak cooling and slow pulling process, and the water volume of the crystallizer is 110-120m 3 / h, secondary cooling adopts mist cooling, cooling water volume is 0.5-0.6l / kg, casting speed is 1.2-1.4m / min, and the superheat of molten steel in continuous casting process is controlled at 25-35℃;

[0011] (4) During hot rolling, a large reduction of 60 to 70% is used from the start of rolling to 1080°C.

[0012] In step (1), the added amounts of silicon manganese alloy, high manganese alloy and lime are 0.8-1.5 kg / t, 1.5-2.5 kg / t and 2.5-3.5 kg / t respectively; the manganese content in the high manganese alloy is 80-85%.

[0013] In step (2), the weight percentages of the main components in the refined slag are controlled to be: CaO 35-40%, SiO2 20-25%, Al2O3 1-5%, MnO 15-20%, and MgO 10-15%.

[0014] In step (2), the added amounts of lime, calcium carbide and ferrosilicon powder are 1-1.5 kg / t, 0.2-0.8 kg / t and 0.2-0.7 kg / t respectively.

[0015] In step (2), the chemical composition weight percentage of the ingot obtained by continuous casting is: C 0.40-0.45%, Si 0.25-0.40%, Mn 1.40-1.50%, P 0.020-0.040%, S 0.20-0.30%, Al≤0.0005%, and the balance is Fe and unavoidable impurities.

[0016] In step (4), during hot rolling, the temperature of the soaking section of the heating furnace is controlled at 1200-1250° C., and the soaking section is maintained for ≥60 min.

[0017] In step (4), during hot rolling, the rough rolling start temperature is 1150-1170°C.

[0018] The present invention also provides a medium-carbon high-sulfur free-cutting steel wire rod, which is produced by the production method of the present invention.

[0019] The chemical components of the medium carbon high sulfur free-cutting steel wire rod are as follows by weight: C 0.40-0.45%, Si 0.25-0.40%, Mn 1.40-1.50%, P 0.020-0.040%, S 0.20-0.30%, Al≤0.0005%, and the balance is Fe and unavoidable impurities.

[0020] The equivalent diameter of sulfides in the medium-carbon high-sulfur free-cutting steel wire rod is 3.5-4.5um, and the aspect ratio is ≤3.

[0021] In the production method for improving the morphology of manganese sulfide in medium-carbon high-sulfur free-cutting steel wire rod provided by the present invention, the deoxidation product of silicon and manganese alloy is used as the adsorption core of manganese sulfide inclusions, so that it is not easy to deform during the rolling process; and a large reduction is used in the high-temperature section of the rolling process to break large-sized manganese sulfide into a dispersed distribution, thereby improving the morphology of manganese sulfide in medium-carbon high-sulfur free-cutting steel, improving its cutting performance and reducing the processing cracking rate.

[0022] In order to increase the content of silicon and manganese oxides in steel, the present invention, on the one hand, utilizes the high oxygen content of molten steel during the converter steelmaking process and uses silicon manganese and high manganese alloys for deoxidation and alloying. On the other hand, the addition of aluminum-containing materials is strictly controlled to control the Al content in the steel to ≤0.0005%.

[0023] In order to break up the large-sized manganese sulfide in the steel, the condition that the temperature of the rolled piece is high and the plasticity of the manganese sulfide is poor in the rough rolling stage is utilized, and the reduction amount is increased in the temperature range from 1080℃ to make the manganese sulfide dispersed.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The invention overcomes the characteristic of low free oxygen content of medium carbon high sulfur free cutting steel, avoids the risk of high production cost and increased quality defect rate caused by adding other free cutting phases, and the production method is more economical and practical.

[0026] The present invention utilizes silicon manganese deoxidation products as the core of solidification and precipitation of manganese sulfide, which can effectively inhibit the manganese sulfide inclusions from plastically deforming into slender strip-shaped sulfides during the rolling process, and is beneficial to maintaining the morphology of the sulfide in a spindle shape; utilizing the poor plasticity of manganese sulfide inclusions in a high temperature section, adopts a large reduction amount of rolling in a temperature range of 1080°C from rough rolling to break the long strip-shaped manganese sulfide, and makes the manganese sulfide dispersed, thereby significantly improving the cutting performance of the product and reducing the risk of processing cracking of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an electron microscope image of the distribution state of manganese sulfide in the medium carbon high sulfur free cutting steel wire rod in Example 1;

[0028] Figure 2This is an electron microscope image of the distribution state of manganese sulfide in the medium carbon high sulfur free cutting steel wire rod in Comparative Example 1;

[0029] Figure 3 The cutting morphologies of the medium carbon and high sulfur free-cutting steel wire rods in the embodiments and comparative examples are shown. DETAILED DESCRIPTION

[0030] The present invention is described in detail below with reference to the embodiments.

[0031] The high manganese alloy used in each embodiment and comparative example has a manganese content of 83%.

[0032] In each embodiment and comparative example, the main components of the refined slag are controlled at 35-40% CaO, 20-25% SiO2, 1-5% Al2O3, 15-20% MnO, and 10-15% MgO.

[0033] Example 1

[0034] A production method for improving the morphology of manganese sulfide in medium-carbon high-sulfur free-cutting steel wire rod, comprising the following steps:

[0035] (1) During the steel-making process of the converter or electric furnace, 1kg / t of silicon-manganese alloy and 2kg / t of high-manganese alloy are added to the molten steel for deoxidation and alloying, and 3kg / t of lime is added. No aluminum iron is used in the steel-making process, and the oxygen content of the molten steel at the argon station after the furnace is 23PPm.

[0036] (2) During the refining process, 1kg / t of lime, 0.3kg / t of calcium carbide and 0.2kg / t of ferrosilicon powder are used for slag making. The use of aluminum-containing materials is strictly prohibited; the oxygen content at the refining station is controlled at 15PPm.

[0037] (3) Continuous casting adopts weak cooling and slow pulling process. The superheat of molten steel is controlled at 25℃ during continuous casting, and the water volume of the crystallizer is 110m 3 / h, the secondary cooling water volume is 0.6L / kg, and the pulling speed is 1.4m / min; the chemical composition weight percentage of the ingot obtained by continuous casting is: C 0.40%, Si 0.27%, Mn 1.50%, P 0.030%, S0.20-0.30%, Al 0.0002%, and the balance is Fe and unavoidable impurities.

[0038] (4) The temperature of the soaking section of the heating furnace is controlled at 1200°C, the soaking section is maintained for 80 minutes, and the starting rolling temperature is 1150°C. Taking advantage of the poor plasticity of manganese sulfide in the high temperature section, a 60% reduction is used for rolling from the start rolling to 1080°C.

[0039] Example 2

[0040] A production method for improving the morphology of manganese sulfide in medium-carbon high-sulfur free-cutting steel wire rod, comprising the following steps:

[0041] (1) During the steel-making process of the converter or electric furnace, 1.5 kg / t of silicon-manganese alloy and 1.5 kg / t of high-manganese alloy are added to the molten steel for deoxidation and alloying, and 3.3 kg / t of lime is added. No aluminum iron is used in the steel-making process, and the oxygen content of the molten steel at the argon station after the furnace is 28 PPm.

[0042] (2) During the refining process, 1.3kg / t of lime, 0.6kg / t of calcium carbide and 0.4kg / t of ferrosilicon powder are used for slag making. The use of aluminum-containing materials is strictly prohibited; the oxygen content of the refining outlet is controlled at 20PPm.

[0043] (3) Continuous casting adopts weak cooling and slow pulling process. The superheat of molten steel is controlled at 30℃ during continuous casting, and the water volume of the crystallizer is 115m 3 / h, the secondary cooling water volume is 0.55L / kg, and the pulling speed is 1.3m / min; the chemical composition weight percentage of the ingot obtained by continuous casting is: C 0.43%, Si 0.37%, Mn 1.40%, P 0.030%, S0.20-0.30%, Al 0.0004%, and the balance is Fe and unavoidable impurities.

[0044] (4) The temperature of the soaking section of the heating furnace is controlled at 1250°C, the soaking section is maintained for 60 min, and the start rolling temperature is 1160°C. Taking advantage of the poor plasticity of manganese sulfide in the high temperature section, a 65% reduction is used for rolling from the start rolling to 1080°C.

[0045] Example 3

[0046] A production method for improving the morphology of manganese sulfide in medium-carbon high-sulfur free-cutting steel wire rod, comprising the following steps:

[0047] (1) During the steel-making process of the converter or electric furnace, 0.8kg / t of silicon-manganese alloy and 2.5kg / t of high-manganese alloy are added to the molten steel for deoxidation and alloying, and 2.7kg / t of lime is added. No aluminum iron is used in the steel-making process, and the oxygen content of the molten steel at the argon station after the furnace is 20-40PPm.

[0048] (2) During the refining process, 1.2kg / t of lime, 0.8kg / t of calcium carbide and 0.5kg / t of ferrosilicon powder are used for slag making. The use of aluminum-containing materials is strictly prohibited; the oxygen content at the refining station is controlled at 10-25PPm.

[0049] (3) Continuous casting adopts weak cooling and slow drawing process. The superheat of molten steel is controlled at 35℃ during continuous casting, and the water volume of crystallizer is 120m 3 / h, the secondary cooling water volume is 0.5L / kg, and the pulling speed is 1.2m / min; the chemical composition weight percentage of the ingot obtained by continuous casting is: C 0.45%, Si 0.25%, Mn 1.50%, P 0.040%, S 0.30%, Al 0.0005%, and the balance is Fe and unavoidable impurities.

[0050] (4) The temperature of the soaking section of the heating furnace is controlled at 1225°C, the soaking section is maintained for 70 minutes, and the start rolling temperature is 1170°C. Taking advantage of the poor plasticity of manganese sulfide in the high temperature section, a 70% reduction is used for rolling from the start rolling to 1080°C.

[0051] Comparative Example 1

[0052] The rest is the same as in Example 1, except that in step (1), 200 kg of aluminum iron is added during the steel-making process; and in step (2), 0.2 kg / t of aluminum particles are used for slag making during the refining process.

[0053] Comparative Example 2

[0054] The rest is the same as in Example 2, except that in step (3), the superheat of the molten steel during the continuous casting process is controlled at 22°C, and the water volume in the crystallizer is controlled at 130m 3 / h, the secondary cooling water volume is 0.7L / kg, and the pulling speed is 1.8m / min.

[0055] Comparative Example 3

[0056] The rest is the same as in Example 3, except that in step (4), a 40% reduction is used for rolling from the start of rolling to 1080°C.

[0057] The specifications, manganese sulfide morphology, cutting performance and processing cracking risk of the medium carbon high sulfur free-cutting steel wire rods produced by the above embodiments and comparative examples are shown in Table 1.

[0058] Table 1

[0059]

[0060] In Table 1, the test method for cutting performance is turning on a CNC machine tool. The turning conditions are: feed rate 0.05mm / r, cutting depth 1mm, cutting speed 1600r / min. Statistics are made based on the cutting morphology of the wire rod and the proportion of C-type chips. The higher the proportion of C-type chips, the better the cutting performance.

[0061] Processing cracking ratio: Statistics based on data feedback from downstream manufacturers.

[0062] The above-mentioned reference embodiments provide a detailed description of a production method for improving the manganese sulfide morphology of medium carbon high sulfur free-cutting steel wire rod and a medium carbon high sulfur free-cutting steel wire rod. 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 production method for improving the morphology of manganese sulfide in medium carbon high sulfur free cutting steel wire rod, characterized in that: The production method comprises the following steps: (1) During the steel-making process of the converter or electric furnace, silicon-manganese alloy and high-manganese alloy are added to the molten steel for deoxidation and alloying, and lime is added. No aluminum iron is used in the steel-making process, and the oxygen content of the molten steel at the argon station after the furnace is 20-40PPm; (2) During the refining process, lime, calcium carbide and ferrosilicon powder are used for slag making. Aluminum-containing materials are strictly prohibited. The oxygen content at the refining station is controlled at 10-25PPm; (3) Continuous casting adopts weak cooling and slow pulling process, and the water volume of the crystallizer is 110-120m 3 / h, secondary cooling adopts mist cooling, cooling water volume is 0.5-0.6l / kg, casting speed is 1.2-1.4m / min, and the superheat of molten steel in continuous casting process is controlled at 25-35℃; (4) During hot rolling, a large reduction of 60 to 70% is used from the start of rolling to 1080°C.

2. The method for improving the morphology of manganese sulfide in medium carbon high sulfur free cutting steel wire rod according to claim 1, characterized in that: In step (1), the added amounts of silicon manganese alloy, high manganese alloy and lime are 0.8-1.5 kg / t, 1.5-2.5 kg / t and 2.5-3.5 kg / t respectively; the manganese content in the high manganese alloy is 80-85%.

3. The method for improving the morphology of manganese sulfide in medium carbon high sulfur free cutting steel wire rod according to claim 1, characterized in that: In step (2), the weight percentages of the main components in the refined slag are controlled to be: CaO 35-40%, SiO2 20-25%, Al2O3 1-5%, MnO 15-20%, and MgO 10-15%.

4. The method for improving the morphology of manganese sulfide in medium carbon high sulfur free cutting steel wire rod according to claim 1 or 3, characterized in that: In step (2), the added amounts of lime, calcium carbide and ferrosilicon powder are 1-1.5 kg / t, 0.2-0.8 kg / t and 0.2-0.7 kg / t respectively.

5. The method for improving the morphology of manganese sulfide in medium carbon high sulfur free cutting steel wire rod according to claim 1, characterized in that: In step (2), the chemical composition weight percentage of the ingot obtained by continuous casting is: C 0.40-0.45%, Si 0.25-0.40%, Mn 1.40-1.50%, P 0.020-0.040%, S 0.20-0.30%, Al≤0.0005%, and the balance is Fe and unavoidable impurities.

6. The method for improving the morphology of manganese sulfide in medium carbon high sulfur free cutting steel wire rod according to claim 1, characterized in that: In step (4), during hot rolling, the temperature of the soaking section of the heating furnace is controlled at 1200-1250° C., and the soaking section is maintained for ≥60 min.

7. The method for improving the morphology of manganese sulfide in medium carbon high sulfur free cutting steel wire rod according to claim 1, characterized in that: In step (4), during hot rolling, the rough rolling start temperature is 1150-1170°C.

8. A medium carbon high sulfur free-cutting steel wire rod, characterized in that: The product is produced by the production method according to any one of claims 1 to 7.

9. The medium carbon high sulfur free-cutting steel wire rod according to claim 8, characterized in that: The chemical components of the medium carbon high sulfur free-cutting steel wire rod are as follows by weight: C 0.40-0.45%, Si 0.25-0.40%, Mn 1.40-1.50%, P0.020-0.040%, S 0.20-0.30%, Al≤0.0005%, and the balance is Fe and unavoidable impurities.

10. The medium carbon high sulfur free-cutting steel wire rod according to claim 8, characterized in that: The equivalent diameter of sulfides in medium carbon and high sulfur free-cutting steel wire rod is 3.5-4.5um, and the aspect ratio is ≤3.

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