Production method of 65Mn high-carbon steel and 65Mn high-carbon steel

Abstract

The embodiment of the invention discloses a production method of 65Mn high-carbon steel and the 65Mn high-carbon steel. The method comprises the following steps that converter treatment is conducted, specifically, molten iron is smelted in a converter, and waste steel is added; refining treatment, specifically, the molten steel is refined, and baking waste steel is added; vacuum refining treatment is conducted, specifically, the temperature of an RH refining furnace is controlled to range from 1552 DEG C to 1562 DEG C, full-pump input is conducted after a main valve of the RH refining furnace is opened, the ultimate vacuum circulation time is longer than or equal to 15 min, and the circulation time is 20-25 min; the argon flow of the molten steel is circularly increased by 100-150 m < 3 > / h; the molten steel is subjected to continuous casting treatment, so that a casting blank is obtained, and the casting blank comprises, by mass, 0.62%-0.7% of C, 0.17%-0.37% of Si, 0.9%-1.2% of Mn, smaller than or equal to 0.018% of P, smaller than or equal to 0.004% of S, 0.015%-0.06% of Als, 0.0001%-0.00015% of H, smaller than or equal to 0.005% of N and the balance Fe and inevitable impurity elements. According to the method, the surface quality and the mechanical property of the 65Mn high-carbon steel coil are improved.

Description

Technical Field

[0001] The present application belongs to the technical field of carbon tool steel production, and in particular relates to a production method of 65Mn high carbon steel. Background Art

[0002] 65Mn high carbon steel is a widely used steel grade in GB / T 1222-2016. It can be used in industries such as automobile springs, cutting tools, saw blade substrates, etc. It is a high-quality high-grade steel with extremely strict requirements among high-quality carbon structural steels. The 65Mn high carbon steel produced by the compact strip production line (CSP production line) has S≤0.004%, P≤0.015%, and A, B, C, D inclusion rating ≤1.5; there is basically no decarburization on the surface; such 65Mn high carbon steel with low phosphorus and sulfur content and low inclusion level can be mass-produced in thin specifications of more than 1.8mm.

[0003] Normally, whether it is thin slab continuous casting or conventional slab continuous casting, the process used to produce this type of steel is converter (BOF)-refining (LF)-continuous casting (CC), and the thin slab continuous casting and rolling production line has only been recorded for production using this process. However, the existing process has a low pass rate when producing high-performance steel products, so it is urgently needed to be improved.

[0004] At the same time, whether it is thin slab continuous casting or conventional slab continuous casting, the current process of producing this type of steel generally requires higher molten iron, requiring it to reach more than 85%, in order to pursue high carbon and low inclusions at the end of the converter to ensure the quality of molten steel. Although this process can meet the quality requirements of molten steel for general purposes, with the increase of scrap steel resources in the market, the cost-effectiveness of scrap steel relative to molten iron will be more obvious, and the long-process green high scrap steel ratio smelting process is the general trend. Summary of the invention

[0005] The embodiment of the present application provides a method for producing 65Mn high carbon steel, aiming to solve the technical problem of low qualified rate of high-performance 65Mn high carbon steel produced by the existing thin slab continuous casting and rolling production line under the condition of long process and high scrap steel ratio, and provide a production method to reduce the nitrogen and hydrogen content and the size and number of inclusions in the steel plate, and improve the surface quality and mechanical properties of the 65Mn high carbon steel coil.

[0006] In a first aspect, the present application provides a method for producing 65Mn high carbon steel, the method comprising the following steps:

[0007] Converter treatment, including smelting molten iron in a converter by a single slag blowing process and adding scrap steel, wherein the molten iron ratio is 65% to 85%, the scrap steel ratio is 15% to 35%, and the slag basicity in the converter is 2.5-3.5; the carbon content in the molten steel is controlled to be 0.03% to 0.06% at the end of the converter treatment, and P < 0.012%;

[0008] Refining treatment, including refining molten steel and adding roasted scrap steel, when the temperature of molten steel reaches 1580℃ to 1620℃, adding roasted scrap steel, the temperature of the scrap steel is 600℃ to 800℃, and the amount of scrap steel added is controlled to be below the edge of the tank and at a height of 15t molten steel;

[0009] Vacuum refining treatment, including controlling the temperature of the RH refining furnace at 1552 to 1562°C, opening the main valve of the RH refining furnace and putting all pumps into operation, the ultimate vacuum cycle time is ≥15min, the cycle time is 20-25min; the circulation increases the argon flow rate of the molten steel by 100-150m 3 / h;

[0010] Continuous casting treatment, continuously casting molten steel to obtain ingots, the water content of the secondary cooling zone of the continuous casting machine is 1.5-1.8L / (kg·min), and the continuous casting pulling speed is 3.6-4.5m / min; the ingots include the following chemical components in mass percentage: C: 0.62%-0.7%, Si: 0.17%-0.37%, Mn: 0.9%-1.2%, P≤0.018%, S≤0.004%, Als: 0.015%-0.06%, H: 0.0001%-0.00015%, N≤0.005%, and the balance is Fe and unavoidable impurity elements.

[0011] In some optional embodiments, after the converter treatment, the method further comprises: adding 2.0 kg / t slag washing lime and 2.0 kg / t pre-melted refined slag respectively when tapping the converter.

[0012] In some optional embodiments, the refining process includes controlling the final refining slag w(TFe)<1% and the final molten steel w(S)<0.004%.

[0013] In some optional embodiments, the refining treatment includes maintaining the white slag for 10 to 15 minutes and then subjecting it to calcium treatment after the composition of the refined molten steel is qualified, ensuring a soft blowing time of 8 to 15 minutes and an outlet temperature of 1557±5°C.

[0014] In some optional embodiments, at the end of the refining treatment, the hydrogen content in the molten steel is 0.0004% to 0.0013%; the nitrogen content in the molten steel is 0.0040% to 0.013%; at the end of the vacuum refining treatment, the hydrogen content in the molten steel is 0.0001% to 0.00015%, and the nitrogen content in the molten steel is 0.0025% to 0.0050%.

[0015] In some optional embodiments, the vacuum refining treatment includes washing the RH smelting furnace before smelting, and the washing meets the following conditions: the RH tank is washed with LF white slag molten steel, the temperature of the molten steel entering the RH tank is 1600°C~1650°C, the vacuum holding time is 15~20 minutes, and the components in the molten steel in the washing tank meet the following conditions: P≤0.02%, S≤0.005%, Ti≤0.005%.

[0016] In some optional embodiments, after the vacuum refining treatment, the method further comprises: calming the molten steel for ≥10 minutes and placing it on a platform for pouring, and the temperature of the molten steel on the platform is 1517±2°C.

[0017] In some optional embodiments, in the continuous casting process, the mold slag is controlled to include the following chemical components in mass percentage: Na 2 O: 10.0% to 12.0%, Li 2 O: 0.6% to 1.5%, F: 8.0% to 11.0%, CaO: 22.0% to 29.0%, SiO 2: 20% to 26.0%, the remainder being carbonate components, the viscosity of the protective slag is controlled to be 0.05 to 0.160 Pa·s, and the melting temperature of the protective slag is controlled to be 860 to 920°C.

[0018] In some optional embodiments, in the continuous casting step, the thickness of the crystallizer copper plate is 15-25 mm, and the water volume of the wide copper plate of the crystallizer copper plate is 5000-5900 L / min.

[0019] In a second aspect, an embodiment of the present application provides a 65Mn high carbon steel, which is produced by the method described in the first aspect.

[0020] The method provided in the embodiment of the present application controls the temperature of the RH refining furnace to be between 1552 and 1562°C by controlling the converter treatment and the refining treatment, as well as the vacuum refining treatment. After the main valve of the RH refining furnace is opened, all pumps are put into operation, the ultimate vacuum cycle time is ≥15min, and the cycle time is 20-25min; the argon flow rate of the molten steel is increased by 100-150m 3 / h, the hydrogen and nitrogen content in the molten steel for continuous casting can be kept within an appropriate range. Excessive nitrogen and hydrogen in the molten steel will affect the strength and toughness of the steel, affect the heat transfer of the crystallizer during the continuous casting process, cause problems with the quality of the ingot, and then reduce the surface quality, strength, plasticity, and impact toughness of the steel. After RH refining treatment, the size and number of inclusions in the steel plate are reduced, and the surface quality and mechanical properties of 65Mn high carbon steel coils are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0022] Figure 1 A process flow chart of converter treatment-refining treatment-vacuum treatment-continuous casting treatment according to an embodiment of the present application is shown;

[0023] Figure 2 The process flow chart of converter treatment-refining treatment-continuous casting treatment of the comparative example of the present application is shown.

[0024] Figure 3 A diagram showing edge cracks in a steel coil produced by the converter treatment-refining treatment-continuous casting process of the comparative example of the present application is shown. DETAILED DESCRIPTION

[0025] In order to make the invention purpose, technical scheme and beneficial technical effect of the present application clearer, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application, not for limiting the present application.

[0026] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range. In addition, although not explicitly stated, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be combined with any other point or single value as its own lower limit or upper limit or with other lower limits or upper limits to form an unambiguous range.

[0027] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” are inclusive of the number itself, and the “multiple” in “one or more” means more than two, and the “multiple” in “one or more” means more than two.

[0028] The above invention summary of the present application is not intended to describe each disclosed embodiment or each implementation in the present application. The following description more specifically illustrates exemplary embodiments. In many places throughout the application, guidance is provided by a series of examples, which can be used in various combinations. In each embodiment, enumeration is only used as a representative group and should not be interpreted as exhaustive.

[0029] The existing process of 65Mn high carbon steel in thin slab continuous casting and rolling production line is converter (BOF)-refining (LF)-continuous casting (CC). Under this process condition, the hydrogen content of molten steel for continuous casting is 7-13ppm. The hydrogen element comes from carbon powder, alloy and flux materials. Especially for southern steel mills, the hydrogen increase of molten steel is particularly serious during the hot weather from April to September. Hydrogen has an important impact on the quality of steel.

[0030] It has been found that it is difficult to control the hydrogen and nitrogen content of molten steel at a low level using the converter (BOF)-refining (LF)-continuous casting (CC) process, especially when a large amount of scrap steel is added to the converter and refining furnace, the hydrogen and nitrogen content of the molten steel is high. When the hydrogen and nitrogen content of molten steel is high, it has a greater impact on the continuous casting heat flow, mainly because when the molten steel begins to solidify on the meniscus of the primary shell in the crystallizer, as the temperature of the molten steel decreases, the solubility of hydrogen and nitrogen in the molten steel decreases, and the molten steel precipitates in the crystallizer. The precipitated hydrogen and nitrogen cannot be removed in time in the molten protective slag, causing the liquid slag to foam, affecting the heat transfer of the protective slag, thereby reducing the strength of the shell and making it easy to come into direct contact with the copper plate and cause bonding and steel leakage.

[0031] In addition, in the subsequent hot working process or in the process of preparing 65Mn high carbon steel into steel products, the pores containing hydrogen and nitrogen in the ingot and steel will be elongated along the processing direction, causing cracks, which will lead to the reduction of strength, plasticity and impact toughness of the steel. The influence of hydrogen embrittlement on the transverse performance of steel is particularly prominent. Due to the characteristics of the crystal structure in steel, hydrogen molecules tend to gather on the boundaries of dendrites or deformed crystals, thereby causing internal stress, resulting in the weakening of intercrystalline tension, thereby reducing the transverse plasticity and impact toughness of the steel. The influence of hydrogen embrittlement increases synchronously with the strength and carbon content of steel, and affects each other.

[0032] At the same time, whether it is thin slab continuous casting or conventional slab continuous casting, the current process of producing this type of steel generally requires higher molten iron, requiring it to reach more than 85%, in order to pursue high carbon and low inclusions at the end of the converter to ensure the quality of molten steel. Although this process can meet the quality requirements of molten steel for general purposes, with the increase of scrap steel resources in the market, the cost-effectiveness of scrap steel relative to molten iron will be more obvious, and the long-process green high scrap steel ratio smelting process is the general trend.

[0033] Based on this, on the basis of converter (BOF)-refining (LF)-continuous casting (CC), we can further increase the addition of scrap steel, increase vacuum refining treatment, and adjust the vacuum refining treatment and continuous casting process to control the hydrogen, nitrogen and inclusion content of molten steel, improve the surface quality and mechanical properties of steel plates, and meet the demand for high-end cold-rolled products.

[0034] An embodiment of the present application provides a method for producing 65Mn high carbon steel, which comprises the following steps: converter treatment, refining treatment, vacuum refining treatment and continuous casting treatment.

[0035] The method provided in the embodiment of the present application controls the temperature of the RH refining furnace to be between 1552 and 1562°C by controlling the converter treatment and the refining treatment, as well as the vacuum refining treatment. After the main valve of the RH refining furnace is opened, all pumps are put into operation, the ultimate vacuum cycle time is ≥15min, and the cycle time is 20-25min; the argon flow rate of the molten steel is increased by 100-150m 3 / h, can make the hydrogen and nitrogen content in the molten steel for continuous casting within the appropriate range. Excessive nitrogen and hydrogen in the molten steel will affect the strength and toughness of the steel. The continuous casting process affects the heat transfer of the crystallizer, causing problems with the quality of the ingot, which in turn leads to a decrease in the surface quality, strength, plasticity, and impact toughness of the steel. RH refining furnace treatment can also reduce the size and number of inclusions in the steel plate. Improve the surface quality and mechanical properties of 65Mn high carbon steel coils.

[0036] The specific implementation methods of the above steps are introduced below.

[0037] The converter treatment includes smelting molten iron in a converter by a single slag blowing process and adding scrap steel, wherein the molten iron ratio is 65% to 85%, the scrap steel ratio is 15% to 35%, and the slag basicity in the converter is 2.5-3.5; the carbon content in the molten steel is controlled to be 0.03% to 0.06% at the end point of the converter treatment, and P is less than 0.012%.

[0038] In this step, the ratio of molten iron can be 68% to 70%, and the ratio of scrap steel can be 28% to 32%.

[0039] As an example, the total loading capacity of the converter is 100t, and the amount of molten steel tapped is 100*0.91%=91t. The tapping process uses carburizer, ferrosilicon, aluminum blocks, and high manganese alloying according to the composition of the steel grade, and the front and rear slag blocks of the slide control the slag under the converter. When the heat of the converter is unbalanced during the blowing process, ferrosilicon and coke powder are added to the converter to supplement heat to avoid severe overoxidation of the molten steel. The use of low end carbon production can improve the converter smelting rhythm, increase the end phosphorus hit rate, reduce the end carbon content, increase the oxidation in the molten steel and slag, create conditions for converter dephosphorization, and greatly improve the dephosphorization efficiency. In addition, more deoxidizers need to be added to the molten steel provided by the converter, and the converter molten steel has relatively more inclusions. However, the scrap ratio of the converter can be increased from the original <15% to 35%.

[0040] The iron-to-metal ratio is the ratio of the weight of iron to the total weight of iron and scrap steel, usually expressed as a percentage. The calculation formula is:

[0041]

[0042] The refining treatment includes refining the molten steel and adding baked scrap steel. When the temperature of the molten steel reaches 1580°C to 1650°C, the baked scrap steel is added. The temperature of the scrap steel is 600°C to 800°C. The amount of scrap steel added is controlled to be below the edge of the tank and at a height of 15t of molten steel.

[0043] In this step, the slag-making in the early stage of the LF refining process can be used to increase the temperature of the molten steel to above 1580°C. The scrap steel is heated to above 600°C by the mixed gas and oxygen designed by the baking device.

[0044] Controlling the amount of scrap steel added to a height below the tank edge and at 15t of molten steel can be understood as: the amount of steel added is controlled to ensure that the molten steel volume is 1.5 layers of ladle bricks below the tank edge, and the height of molten steel in one ladle brick corresponds to about 10t of molten steel. In this way, suitable molten steel can be achieved. At the same time, more scrap steel is added, and the ladle clearance can meet the vacuum refining treatment.

[0045] In this step, after the scrap steel is added, calcium carbide and slag-reducing agent are added in the LF refining process to increase the slag fluidity and improve the arc submerged effect; the bottom blowing flow rate is adjusted to a small extent during the power transmission process to reduce the amount of nitrogen increase caused by low-temperature power transmission in the early stage of refining; and high-basicity, large-volume, and highly reducing ladle slag is produced, in which the amount of lime added is greater than 6.0 kg / t.

[0046] A lower iron-to-water ratio is used in the converter treatment, and a high carbon content at the end point is not pursued. At the same time, scrap steel is added through LF refining to increase the amount of molten steel to meet the clearance requirements of RH vacuum treatment. As a result, the amount of scrap steel added is increased and the economic cost is reduced. The increase in the amount of scrap steel added also increases the amount of hydrogen, nitrogen and inclusions in the refined molten steel. Therefore, by controlling the vacuum refining treatment and adjusting the hydrogen and nitrogen content, the cleanliness of the molten steel after vacuum refining can be further controlled.

[0047] Vacuum refining treatment, including controlling the temperature of the RH refining furnace at 1552 to 1562°C, opening the main valve of the RH refining furnace and putting all pumps into operation, the ultimate vacuum cycle time is ≥15min, the cycle time is 20-25min; the circulation increases the argon flow rate of the molten steel by 100-150m 3 / h.

[0048] In this step, the temperature of the RH refining furnace, the vacuum time and the time of the argon gas in the immersion tube are controlled, so as to effectively control the amount of hydrogen and nitrogen in the molten steel, improve the cleanliness of the molten steel after vacuum refining treatment, and thus improve the quality of the steel plate.

[0049] The gas in the RH cycle vacuum degassing device can be argon or other gases, which drives the molten steel to circulate continuously in the vacuum chamber, so that the molten steel is fully in contact with the vacuum environment, accelerates the degassing, removal of inclusions and other reactions, and promotes the uniformity of the molten steel composition and temperature.

[0050] Continuous casting treatment, continuously casting molten steel to obtain ingots, the water content of the secondary cooling zone of the continuous casting machine is 1.5-1.8L / (kg·min), and the continuous casting pulling speed is 3.6-4.5m / min; the ingots include the following chemical components in mass percentage: C: 0.62%-0.7%, Si: 0.17%-0.37%, Mn: 0.9%-1.2%, P≤0.018%, S≤0.004%, Als: 0.015%-0.06%, H: 0.0001%-0.00015%, N: ≤0.005%, and the balance is Fe and unavoidable impurity elements.

[0051] Figure 1 A process flow chart of converter treatment-refining treatment-vacuum treatment-continuous casting treatment according to an embodiment of the present application is shown; Figure 2 The process flow chart of converter treatment-refining treatment-continuous casting treatment of the comparative example of the present application is shown.

[0052] See also Figure 1 The molten steel passes through a blast furnace, then goes to a converter for converter smelting, then enters a refining furnace for refining, then goes to a RH vacuum furnace for vacuum smelting, and then goes to a continuous casting machine for continuous casting to obtain a slab, then enters a tunnel furnace, and then enters an F1-F7 finishing mill 6 for rolling, and then undergoes ultra-fast cooling and laminar cooling to achieve the preparation of a steel plate. In the related art, the steel plate obtained by not performing vacuum smelting treatment has more inclusions and poor mechanical properties. The smelting process without vacuum smelting treatment is as follows: Figure 2 See also Figure 2 The molten steel passes through the blast furnace 1, then goes to the converter 2 for converter smelting, then enters the refining furnace 3 for refining treatment, and then is continuously casted at the continuous casting machine 4 to obtain a slab, and then enters the tunnel furnace 5, and is subsequently rolled by the lithium salt F1-F7 finishing mill 6 to prepare the steel plate.

[0053] In some optional embodiments, after the converter treatment, the method further comprises: adding 2.0 kg / t slag washing lime and 2.0 kg / t pre-melted refined slag respectively when tapping the converter.

[0054] In some optional embodiments, in order to ensure the cleanliness of molten steel, the refining treatment includes controlling the final slag of refining w(TFe)<1% and the final molten steel w(S)<0.004%. The control of the total iron content in the slag reduces the secondary oxidation of the slag to the molten steel, reduces the oxidizability of the slag, and is conducive to the further refining and composition control of the molten steel. When the steelmaking process reaches the end point, the mass fraction of sulfur in the molten steel should be controlled below 0.004%, which can avoid reducing the toughness, ductility and machinability of the steel, ensure the quality of the steel, and make the steel have good performance and quality stability.

[0055] In some optional embodiments, the refining treatment includes maintaining the white slag for 10 to 15 minutes and then subjecting it to calcium treatment after the composition of the refined molten steel is qualified, ensuring a soft blowing time of 8 to 15 minutes and an outlet temperature of 1557±5°C.

[0056] In some optional embodiments, at the end of the refining treatment, the hydrogen content in the molten steel is 0.0004% to 0.0013%; the nitrogen content in the molten steel is 0.0040% to 0.013%; at the end of the vacuum refining treatment, the hydrogen content in the molten steel is 0.0001% to 0.00015%, and the nitrogen content in the molten steel is 0.0025% to 0.0050%. In this way, the hydrogen, nitrogen and inclusion contents in the molten steel can be further reduced, the surface cracking of the steel plate can be reduced, and the performance of the steel plate can be improved.

[0057] In some optional embodiments, the vacuum refining treatment includes washing the RH smelting furnace before smelting, and the washing meets the following conditions: the RH tank is washed with LF white slag molten steel, the temperature of the molten steel entering the RH tank is 1600°C~1650°C, the vacuum holding time is 15~20 minutes, and the components in the molten steel in the washing tank meet the following conditions: P≤0.02%, S≤0.005%, Ti≤0.005%.

[0058] In some optional embodiments, after the vacuum refining treatment, the method further comprises: calming the molten steel for ≥10 minutes and pouring it on a platform, and the temperature of the molten steel on the platform is 1517±2°C. During the calming process, the inclusions in the molten steel have more time to float to the surface of the molten steel and separate from the molten steel. This can significantly reduce the inclusion content in the steel, improve the purity of the steel, and improve the toughness and fatigue performance of the steel; hydrogen, nitrogen and other gases in the molten steel have more opportunities to escape, which can reduce defects such as pores and looseness.

[0059] The upper stage temperature of molten steel refers to the temperature of molten steel when it reaches the platform of the continuous casting machine for casting after refining and other treatments. In order to ensure that the molten steel has good fluidity and can be smoothly filled and solidified in the crystallizer, the upper stage temperature of the molten steel must be higher than the liquidus temperature. If the upper stage temperature is equal to or lower than the liquidus temperature, the molten steel may solidify prematurely during the casting process, resulting in problems such as nozzle blockage and surface quality defects of the ingot, affecting the normal continuous casting production. Therefore, controlling the upper stage temperature of molten steel within an appropriate range is conducive to improving the quality of continuous casting ingots and steel plates.

[0060] In some optional embodiments, in order to improve the protective effect of the mold slag, improve the quality of molten steel, and improve the lubrication performance of the mold slag, in the continuous casting process, the mold slag is controlled to include the following chemical components in terms of mass percentage: Na 2 O: 10.0% to 12.0%, Li 2O: 0.6% to 1.5%, F: 8.0% to 11.0%, CaO: 22.0% to 29.0%, SiO 2: 20% to 26.0%, the remainder being a main component carbonate component, the viscosity of the protective slag is controlled to be 0.05 to 0.160 Pa·s, and the melting temperature of the protective slag is controlled to be 860 to 920°C.

[0061] In some optional embodiments, in the continuous casting step, the thickness of the crystallizer copper plate is 15-25 mm, and the water volume of the wide copper plate of the crystallizer copper plate is 5000-5900 L / min. In this way, the cooling of the meniscus of the crystallizer can be slowed down and uniform, so that the cooling of the primary shell of the meniscus is uniform, and the generation of longitudinal cracks can be avoided.

[0062] In a second aspect, an embodiment of the present application provides a 65Mn high carbon steel, which is produced by the method described in the first aspect.

[0063] The hot-rolled hardness of the 65Mn high carbon steel in the embodiment of the present application is 240-270HB, and the elongation is 18% to 25%; the inclusions are small in size and less in content, and the problem of cold-rolled edge cracking is improved.

[0064] The hot-rolled hardness of high-carbon steel can be tested using the Brinell hardness HB scale. As an example, a hardened steel ball or carbide ball of a certain diameter (generally 10 mm) is pressed into the surface of the sample with a certain load (generally 3000 kg), and the load is removed after a specified time, leaving an indentation on the surface of the sample. The Brinell hardness value is the quotient of the load divided by the surface area of ​​the indented sphere.

[0065] Example

[0066] The following examples more specifically describe the disclosure of the present application, which are intended for illustrative purposes only, as it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0067] Example 1

[0068] This embodiment provides a method for producing 65Mn high carbon steel, which comprises the following steps: converter treatment, refining treatment, vacuum refining treatment and continuous casting treatment. The process flow chart of converter treatment-refining treatment-vacuum treatment-continuous casting treatment in the method for producing 65Mn high carbon steel is shown in FIG. Figure 1 shown.

[0069] 100t converter is charged with 75t molten iron, 25t scrap steel, and 75% molten iron ratio. The steelmaking model calculates the amount of ferrosilicon required to be added based on the composition, temperature, weight and scrap steel weight of the molten iron. The converter is set to a basicity of 3.0 according to the steelmaking model, and lime and light-burned dolomite are added for blowing. The chemical composition weight percentage of the final molten steel is C: 0.04%, P: 0.007%, Mn: 0.08%, S: 0.037%, and the temperature is 1595℃. The rest is Fe and unavoidable impurities. The final slag basicity is 3.2, and the slag washing lime and pre-melting refining are 2.0kg / t.

[0070] The weight of molten steel was 90.5t, and there was a clearance of 3.5 layers of bricks below the edge of the ladle brick tank. 500kg of lime and 200kg of refined slag were added, and the temperature was raised for 20 minutes. The temperature was measured at 1610℃, and about 10t of preheated scrap steel was added through the scrap steel baking device. The power was raised again, and the temperature was measured at 1604℃. The first batch of scrap steel was fully melted, and 8t of scrap steel was added. The clearance of 1.5 layers of ladle bricks below the edge of the ladle tank was emptied. After the scrap steel was added, the LF was refining and the temperature was raised. At the same time, 300kg of lime was added to make slag, and the deoxidizer was added to make slag white slag, and then stirred for desulfurization, and then alloyed. After the ingredients are qualified, they are fed into the pure calcium line for 230m. The weight percentage ratio of the sampled chemical composition is C: 0.66%, P: 0.013%, Si: 0.21%, Mn: 0.98%, S: 0.003%, Als: 0.025%, N: 0.0085%, and the rest are Fe and unavoidable impurities. The hydrogen is set at 8.1ppm, soft blowing is carried out for 10 minutes, and the temperature is measured at 1557℃ before leaving the station.

[0071] The molten steel is vacuum refined, the vacuum degree is 70Pa, and the argon flow rate of the riser is 140m 3 / h, cycle time 15min, measured hydrogen content 1.3ppm, detection C: 0.66%, P: 0.013%, Si: 0.21%, Mn: 0.98%, S: 0.003%, Als: 0.021%, N: 0.0045%. After the cycle is completed, the temperature of the molten steel is 1512℃, and the continuous casting is started after 11min of calming.

[0072] Process parameters: ingot entering furnace temperature is 870℃, molten steel superheat is 21℃, continuous casting speed is 3.9m / min, continuous casting secondary cooling water volume is 1.68L / (kg·min), continuous casting liquid core pressure is 5mm, ingot thickness is 65mm.

[0073] The physical and chemical performance indicators of the protective slag are basicity: 0.98, viscosity: 0.1Pa.s, melting point: 890℃, and the protective slag includes the following components in mass percentage: Na 2 O: 11.5%, Li 2 O: 1.02%, F: 10.1%, Cao: 25.12%, SiO 2:25.63%, the remainder is the main component carbonate component.

[0074] The crystallizer copper plate thickness is 19.5 mm, the crystallizer water flow rate is set at 5960 L / min, 500 L / min is manually subtracted, and the actual water flow rate is 5460 L / min.

[0075] The size of inclusions in the steel plate was tested according to GB / T-10561, and the results are shown in Table 1.

[0076] The elongation of the steel plate was tested according to GB / T-228, and the results are shown in Table 1.

[0077] Table 1

[0078]

[0079] The hot-rolled steel coil produced in Example 1 and the steel coil in the subsequent single-stand cold rolling process have no edge cracks.

[0080] Example 2

[0081] This embodiment provides a method for producing 65Mn high carbon steel, which includes the following steps: converter treatment, refining treatment, vacuum refining treatment and continuous casting treatment.

[0082] 100t converter is charged with 73t molten iron, 27t scrap steel, and 73% molten iron ratio. The steelmaking model calculates the amount of ferrosilicon required to be added according to the composition, temperature, weight and scrap steel weight of the molten iron. The converter is set to have a basicity of 3.0 according to the steelmaking model, and lime and light-burned dolomite are added for blowing. The chemical composition weight percentage ratio (wt%) of the final molten steel is C: 0.035%, P: 0.0071%, Mn: 0.078%, S: 0.039%, and the temperature is 1599℃. The rest is Fe and unavoidable impurities. The final slag basicity is 3.2, and the slag washing lime and pre-melting refining are 2.0kg / t.

[0083] The weight of molten steel was 90.2t, and there was a clearance of 4.0 bricks below the edge of the ladle brick tank. 500kg of lime and 200kg of refined slag were added. The power was turned on and the temperature was raised for 20min. The temperature was measured at 1608℃. About 13t of preheated scrap steel was added through the scrap steel baking device. The power was turned on again and the temperature was measured at 1609℃. The first batch of scrap steel was fully melted. 12t of scrap steel was added again, and there was a clearance of 1.5 bricks below the edge of the ladle tank. After the scrap steel was added, the LF was refining and the temperature was raised. At the same time, 300kg of lime was added to make slag. The deoxidizer was added to make the white slag, and then stirred for desulfurization, and then alloyed. After the ingredients are qualified, they are fed into the pure calcium line for 230m. The weight percentage (wt%) of the sampled chemical composition is C: 0.67%, P: 0.014%, Si: 0.20%, Mn: 0.99%, S: 0.003%, Als: 0.027%, N: 0.0095%, and the rest are Fe and unavoidable impurities. The hydrogen is set at 9.2ppm, and the soft blow is 10 minutes and the temperature is measured at 1558℃ before leaving the station.

[0084] The molten steel is vacuum refined, the vacuum degree is 70Pa, and the argon flow rate of the riser is 140m 3 / h, cycle time 16min, measured hydrogen content 1.2ppm, detected C0.67%, P0.014%, Si0.20%, Mn0.99%, S0.003%, Als0.024%, N0.0046%. After the cycle is completed, the temperature of the molten steel is 1513℃, and the continuous casting is started after calming for 10min.

[0085] Process parameters: ingot entering furnace temperature is 860℃, molten steel superheat is 25℃, continuous casting speed is 4.1m / min, continuous casting secondary cooling water volume is 1.65L / (kg·min), continuous casting liquid core pressure is 10mm, ingot thickness is 60mm.

[0086] The physical and chemical performance indicators of the protective slag are basicity: 0.90, viscosity: 0.09Pa.s, and melting point is 912℃. 2 O: 10.5%, Li 2 O: 1.1%, F: 11.4%. CaO: 23.24%, SiO 2 :25.82%, the remainder is mainly carbonate components.

[0087] The crystallizer copper plate thickness is 23 mm, the crystallizer water flow rate is set at 6240 L / min, 500 L / min is manually subtracted, and the actual water flow rate is 5740 L / min.

[0088] The inclusion size in the steel plate was tested according to GB / T-10561, and the results are shown in Table 2.

[0089] The elongation of the steel plate was tested according to GB / T-228, and the results are shown in Table 2.

[0090] Table 2

[0091]

[0092] The hot-rolled steel coil produced in Example 2 and the steel coil in the subsequent single-stand cold rolling process have no edge cracks.

[0093] Example 3

[0094] This embodiment provides a method for producing 65Mn high carbon steel, which includes the following steps: converter treatment, refining treatment, vacuum refining treatment and continuous casting treatment.

[0095] 100t converter is charged with 76t of hot metal, 24t of scrap steel, and 76% of hot metal ratio. The steelmaking model calculates the amount of ferrosilicon required to be added according to the composition, temperature, weight and scrap steel weight of hot metal. The converter is set to have a basicity of 3.0 according to the steelmaking model, and lime and light-burned dolomite are added for blowing. The chemical composition weight percentage of the final molten steel is C: 0.038%, P: 0.0091%, Mn: 0.068%, S: 0.027%, and the temperature is 1602℃. The rest is Fe and unavoidable impurities. The final slag basicity is 3.0, and the slag washing lime and pre-melting refining are 2.0kg / t.

[0096] The weight of molten steel weighed 91.2t, and there were 3 layers of bricks below the edge of the ladle brick tank. 500kg of lime and 200kg of refined slag were added, and the temperature was raised for 20min. The temperature was measured at 1610℃, and about 15t of preheated scrap steel was added through the scrap steel baking device. There was 1.5 layers of clearance of ladle bricks below the edge of the ladle tank. After the scrap steel was added, the LF refining was heated by electricity, and 300kg of lime was added to make slag. After adding deoxidizer to make slag, the white slag was stirred for desulfurization, and then alloyed. After the composition was qualified, it was fed into the pure calcium line for 240m. The weight percentage of the sampled chemical composition was C: 0.65%, P: 0.011%, Si: 0.24%, Mn: 0.1.02%, S: 0.003%, Als: 0.026%, N: 0.0084%, and the rest was Fe and unavoidable impurities. The hydrogen was set at 7.9ppm, and the temperature was measured at 1556℃ for 10min of soft blowing before leaving the station.

[0097] The molten steel is vacuum refined, the vacuum degree is 70Pa, and the argon flow rate of the riser is 140m 3 / h, cycle time 15min, measured hydrogen content 1.24ppm, detected C: 0.65%, P: 0.011%, Si: 0.24%, Mn: 1.02%, S: 0.003%, Als: 0.022%, N: 0.0041%. After the cycle is completed, the temperature of the molten steel is 1510℃, and the continuous casting is started after 13min of calming. The process parameters are the ingot furnace temperature of 855℃, the molten steel superheat is 18℃, the continuous casting speed is 4.1m / min, the continuous casting secondary cooling water volume is 1.67L / (kg·min), the continuous casting liquid core is pressed down by 10mm, and the ingot thickness is 60mm.

[0098] The physical and chemical properties of the protective slag are basicity 0.97, viscosity 0.11Pa.s, melting point 857℃, Na 2 O: 11.71%, Li 2 O: 1.29%, F: 10.2%, CaO: 24.8%, SiO 2: 25.56%, and the remainder is mainly carbonate components.

[0099] The crystallizer copper plate thickness is 21 mm, the crystallizer water flow rate is set at 6080 L / min, 500 L / min is manually subtracted, and the actual water flow rate is 5580 L / min.

[0100] The inclusion size in the steel plate was tested according to GB / T-10561, and the results are shown in Table 3.

[0101] The elongation of the steel plate was tested according to GB / T-228, and the results are shown in Table 3.

[0102] Table 3

[0103]

[0104] The hot-rolled steel coil produced in Example 3 and the steel coil in the subsequent single-stand cold rolling process have no edge cracks.

[0105] Example 4

[0106] This embodiment provides a method for producing 65Mn high carbon steel, which includes the following steps: converter treatment, refining treatment, vacuum refining treatment and continuous casting treatment.

[0107] 100t converter is charged with 73t molten iron, 27t scrap steel, and 73% molten iron ratio. The steelmaking model calculates the amount of ferrosilicon required to be added according to the composition, temperature, weight and scrap steel weight of the molten iron. The converter is set to a basicity of 3.0 according to the steelmaking model, and lime and light-burned dolomite are added for blowing. The chemical composition weight percentage of the final molten steel is C: 0.03%, P: 0.006%, Mn: 0.058%, S: 0.051%, and the temperature is 1591℃. The rest is Fe and unavoidable impurities. The final slag basicity is 3.0, and the slag washing lime and pre-melting refining are 2.0kg / t.

[0108] The weight of molten steel is 89.4t, and there is now a clearance of 4.5 layers of bricks below the edge of the ladle brick tank. 500kg of lime and 200kg of refined slag are added. The power is turned on and the temperature is raised for 20min. The temperature is measured at 1610℃. About 15t of preheated scrap steel is added through the scrap steel baking device. The power is turned on again to raise the temperature. The temperature is measured at 1616℃. The first batch of scrap steel has been fully melted. 15t of scrap steel is added again. There is a clearance of 1.5 layers of bricks below the edge of the ladle tank. After the scrap steel is added, the LF is refining and the temperature is raised. At the same time, 300kg of lime is added to make slag. The deoxidizer is added to make slag white slag and stirred for desulfurization, and then alloying is performed. After the ingredients are qualified, they are fed into the pure calcium line for 240m. The weight percentage ratio of the sampled chemical composition is C: 0.65%, P: 0.008%, Si: 0.26%, Mn: 0.1.05%, S: 0.003%, Als: 0.030%, N: 0.0092%, and the rest are Fe and unavoidable impurities. The hydrogen is set at 9.3ppm, and the soft blow is 10 minutes and the temperature is measured at 1559℃ before leaving the station.

[0109] The molten steel is vacuum refined, the vacuum degree is 70Pa, and the argon flow rate of the riser is 140m 3 / h, cycle time 15min, measured hydrogen content 1.24ppm, detected C: 0.65%, P: 0.008%, Si: 0.26%, Mn: 1.05%, S: 0.003%, Als: 0.022%, N: 0.0043%. After the cycle is completed, the temperature of the molten steel is 1509℃, and the continuous casting is started after 12min of calming. The process parameters are the ingot furnace temperature of 855℃, the molten steel superheat is 18℃, the continuous casting speed is 3.9m / min, the continuous casting secondary cooling water volume is 1.65L / (kg·min), the continuous casting liquid core is pressed down by 10mm, and the ingot thickness is 60mm.

[0110] The physical and chemical properties of the protective slag are basicity 0.88, viscosity 0.10Pa.s, melting point 861℃, Na 2 O: 11.43%, Li 2 O: 1.42%, F: 10.15%, CaO: 22.7%, SiO 2: 25.80%, and the remainder is mainly carbonate components.

[0111] The crystallizer copper plate thickness is 23.5 mm, the crystallizer water flow rate is set at 6280 L / min, 500 L / min is manually subtracted, and the actual water flow rate is 5780 L / min.

[0112]

[0113] The hot-rolled steel coil produced in Example 4 and the steel coil in the subsequent single-stand cold rolling process have no edge cracks.

[0114] Comparative Example 1

[0115] This comparative example 1 is different from Example 4. The production method of 65Mn high carbon steel in this comparative example adopts BOF-LF-CC production process, specifically converter treatment, refining treatment and continuous casting treatment.

[0116] 100t converter is charged with 94.6t of hot metal, 2.54t of scrap steel, and hot metal ratio of 86%. The steelmaking model is calculated based on the composition, temperature, weight and scrap steel weight of the hot metal. The converter is set to have a basicity of 3.0 according to the steelmaking model, and lime and light-burned dolomite are added for blowing. The chemical composition weight percentage ratio (wt%) of the final molten steel is C: 0.03%, P: 0.006%, Mn: 0.058%, S: 0.042%, and the temperature is 1620℃. The rest is Fe and unavoidable impurities. The final slag basicity is 3.0, and the slag washing lime and pre-melting refining are 2.0kg / t.

[0117] The weight of molten steel is 100.4t. LF refining adds 500kg lime and 200kg refined slag. Electricity is supplied to increase temperature. Deoxidizer is added to make slag. After obtaining white slag, it is stirred for desulfurization and then alloyed. After the composition is qualified, it is fed into the pure calcium line of 240m. The chemical composition weight percentage ratio of sampling is C: 0.655%, P: 0.012%, Si: 0.27%, Mn: 0.1.08%, S: 0.003%, Als: 0.030%, N: 0.0087%, and the rest is Fe and unavoidable impurities. Hydrogen is set at 7.8ppm. After soft blowing for 10min, the temperature is measured at 1522℃ before leaving the station. After calming for 12min, continuous casting is started.

[0118] Process parameters: ingot entering furnace temperature is 855℃, molten steel superheat is 18℃, continuous casting speed is 3.9m / min, continuous casting secondary cooling water volume is 1.65L / (kg·min), continuous casting liquid core pressure is 10mm, ingot thickness is 60mm.

[0119] The physical and chemical properties of the protective slag are basicity 0.896, viscosity 0.079Pa.s, melting point 840℃, Na 2 O: 14.2%, Li 2 O: 0.79%, F: 11.85%, CaO: 23.9%, SiO 2:26.67%, and the remainder is mainly carbonate components.

[0120] The crystallizer copper plate thickness is 23.5 mm, the crystallizer water flow rate is set at 6280 L / min, 500 L / min is manually subtracted, and the actual water flow rate is 5780 L / min.

[0121] The inclusion size in the steel plate was tested according to GB / T-10561, and the results are shown in Table 4.

[0122] The elongation of the steel plate was tested according to GB / T-228, and the results are shown in Table 4.

[0123] Table 4

[0124]

[0125] 32% of the hot coils produced in Comparative Example 1 had edge cracks, and the edge crack quality degradation rate of the subsequent single-stand cold rolling process reached 12.31%. Figure 3 The diagram of the steel coil edge crack produced by the converter treatment-refining treatment-continuous casting treatment process of the comparative example of the present application is shown in FIG. Figure 3 , 32% of the hot coils produced in Comparative Example 1 had edge cracks.

[0126] The scope of this application is not limited to this. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed in this application, and these modifications or replacements should be included in the protection scope of this application. Therefore, the protection scope of this application should be based on the protection scope of the claims.

Claims

1. A method for producing 65Mn high carbon steel, characterized in that: The method comprises the following steps: Converter treatment, including smelting molten iron in a converter by a single slag blowing process and adding scrap steel, wherein the molten iron ratio is 65% to 85%, the scrap steel ratio is 15% to 35%, and the slag basicity in the converter is 2.5-3.5; the carbon content in the molten steel is controlled to be 0.03% to 0.06% at the end of the converter treatment, and P < 0.012%; Refining treatment, including refining the molten steel and adding roasted scrap steel, when the temperature of the molten steel reaches 1580°C to 1620°C, adding the roasted scrap steel, the temperature of the scrap steel is 600°C to 800°C, and controlling the amount of scrap steel added to be below the edge of the ladle tank and at a height of 15t of molten steel; Vacuum refining treatment, including controlling the temperature of the RH refining furnace at 1552 to 1562°C, opening the main valve of the RH refining furnace and putting all pumps into operation, the ultimate vacuum cycle time ≥ 15min, the cycle time 20-25min; the circulation increases the argon flow rate of the molten steel by 100-150m 3 / h; Continuous casting treatment, continuously casting molten steel to obtain ingots, the water content of the secondary cooling zone of the continuous casting machine is 1.5-1.8L / (kg·min), and the continuous casting pulling speed is 3.6-4.5m / min; the ingots include the following chemical components in mass percentage: C: 0.62%-0.7%, Si: 0.17%-0.37%, Mn: 0.9%-1.2%, P≤0.018%, S≤0.004%, Als: 0.015%-0.06%, H: 0.0001%-0.00015%, N≤0.005%, and the balance is Fe and unavoidable impurity elements.

2. The method according to claim 1, characterized in that After the converter treatment, the method further comprises: adding 2.0 kg / t slag washing lime and 2.0 kg / t pre-melted refined slag respectively when tapping the converter.

3. The method according to claim 1, characterized in that The refining treatment includes controlling the final refining slag w(TFe)<1% and the final molten steel w(S)<0.004%.

4. The method according to claim 1, characterized in that The refining treatment includes: after the composition of the refined molten steel is qualified, the white slag is kept for 10 to 15 minutes and then calcium treatment is performed, the soft blowing time is ensured to be 8 to 15 minutes, and the outlet temperature is 1557±5°C.

5. The method according to claim 1, characterized in that At the end of the refining treatment, the hydrogen content in the molten steel is 0.0004% to 0.0013%, and the nitrogen content in the molten steel is 0.0040% to 0.013%; at the end of the vacuum refining treatment, the hydrogen content in the molten steel is 0.0001% to 0.00015%, and the nitrogen content in the molten steel is 0.0025% to 0.0050%.

6. The method according to claim 1, characterized in that The vacuum refining treatment includes washing the RH smelting furnace before smelting, and the washing meets the following conditions: the RH tank is washed with LF white slag molten steel, the temperature of the molten steel entering the RH tank is 1600°C to 1650°C, the vacuum holding time is 15 to 20 minutes, and the components in the molten steel for washing the tank meet the following requirements: P≤0.02%, S≤0.005%, and Ti≤0.005%.

7. The method according to claim 1, characterized in that After the vacuum refining treatment, the method further comprises: calming the molten steel for ≥10 minutes and then pouring the molten steel on a platform, wherein the temperature of the molten steel on the platform is 1517±2°C.

8. The method according to claim 1, characterized in that In the continuous casting process, the mold slag is controlled to include the following chemical components by mass percentage: Na2O: 10.0% to 12.0%, Li2O: 0.6% to 1.5%, F: 8.0% to 11.0%, CaO: 22.0% to 29.0%, SiO 2: 20% to 26.0%, the remainder being carbonate components, the viscosity of the protective slag is controlled to be 0.05 to 0.160 Pa·s, and the melting temperature of the protective slag is controlled to be 860 to 920°C.

9. The method according to claim 1, characterized in that: In the continuous casting step, the thickness of the crystallizer copper plate is 15-25 mm, and the water volume of the wide copper plate of the crystallizer copper plate is 5000-5900 L / min.

10. A 65Mn high carbon steel produced by the method according to any one of claims 1 to 9.

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