Preparation method of large square blank for rolling high-carbon hard-line steel

Abstract

The invention provides a preparation method of a large square blank for rolling high-carbon hard-line steel, which comprises the following steps: firstly, carrying out converter semisteel smelting on a semisteel raw material, and tapping to obtain molten steel; then the molten steel obtained in the previous step is subjected to LF refining and RH vacuum treatment, and then continuous casting and crystallizer cooling are conducted to obtain a continuous casting blank with the section size being 360 mm * 450 mm; the continuous casting temperature ranges from 1490 DEG C to 1505 DEG C; and the cooling water amount of the crystallizer is 3300 to 3400 L / min. According to the method, bloom continuous casting production of the high-carbon hard wire steel is achieved, the high-homogeneity continuous casting blank is formed through innovative and scientific regulation and control of the continuous casting equipment technology, homogeneity regulation and control are strengthened through thermal diffusion and rolling extension, the high-quality blank is provided for rolling of the high-carbon hard wire steel, and the production efficiency is improved. And an important blank quality foundation is laid for wire rod rolling and drawing production of products such as steel strands.

Description

Technical Field

[0001] The invention belongs to the technical field of preparing large-size square billets for rolling high-carbon hard wire steel, and relates to a method for preparing large square billets for rolling high-carbon hard wire steel and a rolling process for high-carbon hard wire steel, and in particular to a method for preparing large square billets for rolling high-carbon hard wire steel. Background Art

[0002] High carbon hard wire steel is the main variety used to prepare high-strength cold-drawn steel wire. It is widely used in infrastructure construction and has important value for social development. For example, SWRH82B high carbon wire rod steel is the main raw material for the production of metal products such as prestressed steel wire, prestressed steel strand, high-strength steel wire and steel rope. Among them, the prestressed steel strand prepared with SWRH82B wire rod as raw material has been promoted and applied in my country's construction industry, and its development trend has continued to expand in recent years. In addition, the product is also widely used in marine engineering, energy engineering and water conservancy engineering. The product exhibits the characteristics of high strength, corrosion resistance, low relaxation and high toughness. Because its added value is greater than that of similar wire products, it is welcomed by the market industry.

[0003] At present, the main quality problem of this product is brittle fracture during drawing, and the main reasons include steel quality, uniformity of organizational properties and dimensional accuracy. For example, severe solute enrichment in the center will lead to abnormal microstructures such as martensite and secondary cementite in the product, which will seriously affect the drawing performance, and will cause problems such as wire breakage during drawing, affecting quality stability and smooth production. Each typical problem is generally controlled in different processes in the production process, and there are many series of studies on this product, mainly including product quality defect analysis and related control process technology research, such as a method for producing SWRH82B wire rod disclosed in patent CN109207837, a low-nitrogen SWRH82B steel smelting method disclosed in CN103667581, a method for controlling inclusions in the production of SWRH82B steel using a carbon-free ladle disclosed in CN108998626, and a dynamic light reduction process for continuous casting of prestressed steel SWRH82B large square billets disclosed in CN101648212.

[0004] However, the above-mentioned processes for the preparation of SWRH82B do not involve relevant research on steel billets. Moreover, with the continuous expansion of high-carbon hard wire steel SWRH82B in practical applications and the demand of production enterprises for improved production efficiency, the existing high-carbon hard wire rolling billets are mostly produced by continuous casting of small square billets. Not only is the production process inefficient, but if the production efficiency is only improved by increasing the drawing speed, there will be quality problems such as aggravated central segregation and poor removal of non-metallic inclusions, which can no longer meet the needs of further development. Therefore, the industry's research and production technology for large-size steel billets is more urgent. However, generally speaking, in continuous casting production, as the cross-section increases, the segregation tendency of the billet will increase, among which the central macroscopic segregation problem becomes more prominent, and the accompanying semi-macroscopic point segregation will also increase.

[0005] Therefore, how to find a more suitable preparation process for high-carbon hard wire steel SWRH82B square billet to solve the above-mentioned technical problems existing in the existing process, especially the preparation process for large-section billets, has become one of the urgent problems to be solved by many front-line researchers in the industry. Summary of the invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing large square billets for rolling high-carbon hard wire steel and a rolling process for high-carbon hard wire steel. The preparation method provided by the present invention can stably and efficiently produce continuous casting billets with a cross-sectional size of 360mm×450mm, thereby providing high-quality billets for the preparation of high-carbon hard wire steel, and the preparation method has simple process, good controllability, strong operability, and is more suitable for industrial promotion and application.

[0007] The present invention provides a method for preparing a large square billet for rolling high-carbon hard wire steel, comprising the following steps:

[0008] 1) After the semi-steel raw material is smelted in a converter, molten steel is obtained by tapping;

[0009] 2) The molten steel obtained in the above steps is subjected to LF refining and RH vacuum treatment, and then continuously cast and cooled in a crystallizer to obtain a continuous casting billet with a cross-sectional size of 360 mm×450 mm;

[0010] The continuous casting temperature is 1490-1505°C;

[0011] The cooling water volume of the crystallizer is 3300-3400 L / min.

[0012] Preferably, the semi-steel raw material is a semi-steel raw material for preparing high-carbon hard wire steel;

[0013] The grades of the high carbon hard wire steel include SWRH82B;

[0014] The mass content of S in the semi-steel raw material fed into the converter is less than or equal to 0.015%;

[0015] The tapping temperature is greater than or equal to 1650°C;

[0016] The mass content of C in the molten steel is less than or equal to 0.08%.

[0017] Preferably, argon is blown online during the steel tapping process, and a slide plate is used to block the slag to control the amount of slag discharged during the steel tapping process;

[0018] The slag amount in the steel tapping process is specifically that the thickness of the converter slag layer is less than or equal to 80 mm;

[0019] Ferrosilicon deoxidation, active lime and aluminum wire are also added during the steel tapping process;

[0020] Alloying is performed during 1 / 3 to 2 / 3 of the steel tapping process.

[0021] Preferably, the grade of the ferrosilicon is FeSi75;

[0022] The amount of ferrosilicon added is 500-520kg;

[0023] The amount of active lime added is 450-500 kg;

[0024] The feeding amount of the aluminum wire is 110-150m.

[0025] Preferably, the LF refining is specifically adding active lime and quartz sand to perform LF electric heating refining;

[0026] In the LF refining, the amount of active lime added is 100-150 kg;

[0027] In the LF refining, the amount of quartz sand added is 250-300 kg;

[0028] The basicity of the refined slag from the LF refining is 2.0-2.5.

[0029] Preferably, 15-20 kg of aluminum particles are also added to the LF refined slag;

[0030] The outlet temperature of the LF refining is 1590-1600°C;

[0031] The vacuum pressure of the RH vacuum treatment is less than or equal to 3 mbar;

[0032] The RH vacuum treatment time is 12 to 13 minutes;

[0033] The RH vacuum treatment is 1530-1545°C.

[0034] Preferably, the liquidus temperature of the continuous casting is 1465°C;

[0035] The temperature difference between the inlet and outlet water of the cooling water of the crystallizer is 4.2-4.6°C;

[0036] The secondary cooling water volume of the crystallizer is 0.32-0.35 L / kg 钢 ;

[0037] The electromagnetic stirring current intensity of the crystallizer is 400-420A;

[0038] The electromagnetic stirring current intensity at the solidification end of the crystallizer is 300-320A;

[0039] The continuous casting pulling speed is 0.52-0.58 m / min.

[0040] The present invention provides a rolling process for high carbon hard wire steel, comprising the following steps:

[0041] The high carbon hard wire steel ingots are stacked and slowly cooled, and then heated, and then water-cooled to reduce the surface temperature of the ingots, and then rolled to obtain high carbon hard wire steel;

[0042] The cast billet is a continuous casting billet prepared by the preparation method described in any one of the above technical solutions.

[0043] Preferably, the slow cooling temperature of the stacking slow cooling is 500-800°C;

[0044] The stacking slow cooling time is 8 to 15 hours;

[0045] The heating temperature is 850-1000°C;

[0046] The heating time is 2 to 3 hours.

[0047] Preferably, high-pressure water descaling is performed during the water cooling process;

[0048] The water cooling reduces the surface temperature of the casting to 600-650°C;

[0049] The rolling process is performed in 5 passes;

[0050] The rolling reduction ratios of the five passes are 35%, 30%, 20%, 10% and 5% respectively;

[0051] The cross section of the high carbon hard wire steel after rolling is 200 mm×200 mm.

[0052] The present invention provides a method for preparing large square billets for high carbon hard wire steel rolling, comprising the following steps: firstly, semi-steel raw materials are subjected to converter semi-steel smelting, and steel is tapped to obtain molten steel; then, the molten steel obtained in the above steps is subjected to LF refining and RH vacuum treatment, and then continuous casting and crystallizer cooling are performed to obtain continuous casting billets with a cross-sectional size of 360mm×450mm; the temperature of the continuous casting is 1490-1505℃; and the cooling water volume of the crystallizer is 3300-3400L / min. Compared with the prior art, the present invention particularly designs a method for preparing large square billets for high carbon hard wire steel rolling with specific control parameters, by controlling the parameters of the molten steel tapped from the converter smelting, the parameters of the LF refining and the RH vacuum treatment, and then combining the specific casting control, especially the control process and parameters of the crystallizer, thereby preparing high-quality large-size continuous casting billets of 360mm×450mm, which further reflects the high efficiency of large-section continuous casting and the advantages of regulating and controlling the organizational properties. The present invention realizes the continuous casting production of large square billets of high-carbon hard wire steel, forms highly homogeneous continuous casting billets through innovative and scientific regulation of the continuous casting equipment process, and further performs heating and rolling control, and strengthens homogeneity regulation through heat diffusion and rolling ductility, thereby providing high-quality billets for the rolling of high-carbon hard wire steel, laying an important billet quality foundation for the drawing production of products such as wire rod rolling and steel strands, and playing an extremely critical role in especially overcoming the contradiction between quality and efficiency of high-strength hard wire.

[0053] Experimental results show that, by adopting the preparation method provided by the present invention, high-quality production of large-section continuous casting billets for high-carbon hard wire steel rolling is successfully achieved, the center segregation level of the billet is significantly improved, and the center C segregation degree of the billet for rolling wire rod is controlled at 1.03-1.05 as a whole, which lays an important homogenization foundation for the control of wire rod microstructure and performance, and promotes high-level control of low-grade cementite at the center grain boundary of the wire rod. DETAILED DESCRIPTION

[0054] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention rather than limiting the patent claims of the present invention.

[0055] All raw materials of the present invention have no particular limitation on their sources, and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0056] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses industrial pure steel or high carbon hard wire steel of conventional purity in the field of casting and rolling.

[0057] The brands and abbreviations of all raw materials of the present invention are conventional brands and abbreviations in the art. Each brand and abbreviation is clear and definite in the field of its related use. Those skilled in the art can purchase them from the market or prepare them by conventional methods according to the brands, abbreviations and corresponding uses.

[0058] The present invention provides a method for preparing a large square billet for rolling high-carbon hard wire steel, comprising the following steps:

[0059] 1) After the semi-steel raw material is smelted in a converter, molten steel is obtained by tapping;

[0060] 2) The molten steel obtained in the above steps is subjected to LF refining and RH vacuum treatment, and then continuously cast and cooled in a crystallizer to obtain a continuous casting billet with a cross-sectional size of 360 mm×450 mm;

[0061] The continuous casting temperature is 1490-1505°C;

[0062] The cooling water volume of the crystallizer is 3300-3400 L / min.

[0063] The invention firstly smelts semi-steel raw materials in a converter, and then taps out the steel to obtain molten steel.

[0064] In the present invention, the semi-steel raw material is preferably a semi-steel raw material for preparing high carbon hard wire steel.

[0065] In the present invention, the grade of the high carbon hard wire steel preferably includes SWRH82B.

[0066] In the present invention, the mass content of S in the semi-steel raw material fed into the converter is preferably less than or equal to 0.015%, more preferably less than or equal to 0.012%, and more preferably less than or equal to 0.010%.

[0067] In the present invention, the steel tapping temperature is preferably greater than or equal to 1650°C, more preferably greater than or equal to 1680°C, and more preferably greater than or equal to 1700°C.

[0068] In the present invention, the mass content of C in the molten steel is preferably less than or equal to 0.08%, more preferably less than or equal to 0.05%, and more preferably less than or equal to 0.04%.

[0069] In the present invention, argon is preferably blown online during the steel tapping process, and a slide plate is used to block the slag to control the amount of slag in the steel tapping process.

[0070] In the present invention, the amount of slag in the steel tapping process is preferably such that the thickness of the converter slag layer is less than or equal to 80 mm, more preferably less than or equal to 70 mm, and more preferably less than or equal to 60 mm.

[0071] In the present invention, ferrosilicon deoxidation, active lime and aluminum wire are preferably added during the steel tapping process.

[0072] In the present invention, alloying is preferably performed at 1 / 3 to 2 / 3 of the steel tapping process, more preferably at 2 / 5 to 3 / 5, and even more preferably at 9 / 20 to 11 / 20.

[0073] In the present invention, the grade of ferrosilicon is preferably FeSi75.

[0074] In the present invention, the amount of ferrosilicon added is preferably 500-520 kg, more preferably 504-516 kg, and more preferably 508-512 kg.

[0075] In the present invention, the amount of active lime added is preferably 450-500 kg, more preferably 460-490 kg, and more preferably 470-480 kg.

[0076] In the present invention, the feeding amount of the aluminum wire is preferably 110-150 m, more preferably 118-142 m, and more preferably 126-134 m.

[0077] In the present invention, the molten steel obtained in the above steps is finally subjected to LF refining and RH vacuum treatment, and then continuously cast and cooled in a crystallizer to obtain a continuous casting billet with a cross-sectional size of 360 mm×450 mm.

[0078] In the present invention, the temperature of the continuous casting is 1490-1505°C, can be 1493-1502°C, can be 1496-1499°C.

[0079] In the present invention, the cooling water volume of the crystallizer is 3300-3400 L / min, can be 3320-3380 L / min, can be 3340-3360 L / min.

[0080] In the present invention, the LF refining is preferably performed by adding active lime and quartz sand to perform LF electric heating refining.

[0081] In the present invention, in the LF refining, the amount of active lime added is preferably 100-150 kg, more preferably 110-140 kg, and more preferably 120-130 kg.

[0082] In the present invention, in the LF refining, the amount of quartz sand added is preferably 250-300 kg, more preferably 260-290 kg, and more preferably 270-280 kg.

[0083] In the present invention, the basicity of the refined slag from LF refining is preferably 2.0 to 2.5, more preferably 2.1 to 2.4, and more preferably 2.2 to 2.3.

[0084] In the present invention, 15 to 20 kg of aluminum particles are preferably added to the LF refined slag, more preferably 16 to 19 kg of aluminum particles are added, and more preferably 17 to 18 kg of aluminum particles are added.

[0085] In the present invention, the outlet temperature of the LF refining is preferably 1590-1600°C, more preferably 1592-1598°C, and more preferably 1594-1596°C.

[0086] In the present invention, the vacuum pressure of the RH vacuum treatment is preferably less than or equal to 3 mbar, more preferably less than or equal to 2 mbar, and more preferably less than or equal to 1 mbar.

[0087] In the present invention, the RH vacuum treatment time is preferably 12 to 13 minutes, more preferably 12.2 to 12.8 minutes, and more preferably 12.4 to 12.6 minutes.

[0088] In the present invention, the temperature of the RH vacuum treatment is preferably 1530-1545°C, more preferably 1533-1542°C, and more preferably 1536-1539°C.

[0089] In the present invention, the liquidus temperature of the continuous casting is preferably 1465°C.

[0090] In the present invention, the temperature difference between the inlet and outlet water of the cooling water of the crystallizer is preferably 4.2-4.6°C, more preferably 4.25-4.55°C, more preferably 4.3-4.5°C, more preferably 4.35-4.45°C.

[0091] In the present invention, the secondary cooling water volume of the crystallizer is preferably 0.32 to 0.35 L / kg. 钢 , more preferably 0.325 to 0.345 L / kg 钢 , more preferably 0.33 to 0.34 L / kg 钢。

[0092] In the present invention, the electromagnetic stirring current intensity of the crystallizer is preferably 400-420A, more preferably 404-416A, and more preferably 408-412A.

[0093] In the present invention, the electromagnetic stirring current intensity at the solidification end of the crystallizer is preferably 300-320A, more preferably 304-316A, and more preferably 308-312A.

[0094] In the present invention, the continuous casting speed is preferably 0.52 to 0.58 m / min, more preferably 0.53 to 0.57 m / min, and more preferably 0.54 to 0.56 m / min.

[0095] The present invention provides a rolling process for high carbon hard wire steel, comprising the following steps:

[0096] The high carbon hard wire steel ingots are stacked and slowly cooled, and then heated, and then water-cooled to reduce the surface temperature of the ingots, and then rolled to obtain high carbon hard wire steel;

[0097] The cast billet is a continuous casting billet prepared by the preparation method described in any one of the above technical solutions.

[0098] In the present invention, the slow cooling temperature of the stack slow cooling is preferably greater than or equal to 500° C., more preferably greater than or equal to 550° C., more preferably greater than or equal to 600° C., or 500-800° C., or 550-750° C., or 600-700° C. Specifically, the stack slow cooling temperature in the present invention is the temperature of the ingot during the slow cooling, which can ensure that the harmful gas elements are relatively fully diffused and removed.

[0099] In the present invention, the stack slow cooling time is preferably greater than or equal to 8 hours, more preferably greater than or equal to 10 hours, more preferably greater than or equal to 12 hours, or 8 to 15 hours, or 9 to 14 hours, or 10 to 13 hours.

[0100] In the present invention, the heating temperature is preferably 850 to 1000°C, more preferably 890 to 970°C, and even more preferably 920 to 940°C.

[0101] In the present invention, the heating time is preferably 2 to 3 hours, more preferably 2.2 to 2.8 hours, and more preferably 2.4 to 2.6 hours.

[0102] In the present invention, high-pressure water descaling is preferably performed during the water cooling process.

[0103] In the present invention, the water cooling lowers the surface temperature of the casting billet preferably to 600-650°C, more preferably to 610-640°C, and even more preferably to 620-630°C.

[0104] In the present invention, the number of rolling passes is preferably 5.

[0105] In the present invention, the rolling reduction ratios of the five passes are preferably 35%, 30%, 20%, 10% and 5% respectively.

[0106] In the present invention, the cross section of the high carbon hard wire steel after rolling may be 200 mm×200 mm.

[0107] See Table 1, which shows the steel composition (mass percentage %) of high carbon hard wire steel SWRH82B.

[0108] Table 1

[0109] C Si Mn P S Cu Fe other 0.79～0.86 0.15～0.35 0.6～0.9 ≤0.03 ≤0.03 ≤0.20 margin National Standard

[0110] The present invention is to complete and refine the overall technical solution, better ensure the microstructure, composition and performance of large-size square billets of high-carbon hard wire steel, and further improve the stability and efficiency of the preparation of large square billets of high-carbon hard wire steel. The above-mentioned method for preparing large square billets for rolling high-carbon hard wire steel and a rolling process for high-carbon hard wire steel can specifically include the following contents:

[0111] The invention provides a process for preparing billets for rolling high-carbon hard wire steel, the process flow of which is: converter semi-steel smelting--LF electric heating refining--RH vacuum treatment--360mm×450mm cross-section large square billet continuous casting--stacking slow cooling--heat diffusion--large temperature gradient and large reduction rolling.

[0112] The technical parameters involved in each process are as follows: (1) the semi-steel [S]% entering the converter is ≤0.015%; the converter end target [C]% is <0.08%, and the tapping temperature is ≥1650°C; argon is blown online during the tapping process, and the amount of slag in the tapping process is strictly controlled by using a slide plate to block the slag, and the thickness of the slag layer in the converter is controlled within 80 mm; 500-520 kg of ferrosilicon is added for deoxidation; alloying is performed during 1 / 3 to 2 / 3 of the tapping process; 450-500 kg of active lime is added during the tapping process; and 110-150 m of aluminum wire is fed into the small platform.

[0113] (2) LF electric heating refining: Active lime and quartz sand are added before refining heating, where the amount of active lime added is 100-150 kg, the amount of quartz sand added is 250-300 kg, the basicity of the refined slag is controlled at 2.0-2.5, and 15-20 kg of aluminum particles are added to the slag. The LF outlet temperature is controlled at 1590-1600℃.

[0114] (3) RH vacuum treatment: vacuum degree ≤ 3 mbar, treatment time 12 ~ 13 min, complete alloy composition fine-tuning, composition reaches the target requirements, vacuum exit temperature is controlled at 1530 ~ 1545 °C.

[0115] (4) It is extremely critical that the casting temperature of the 360mm×450mm cross-section large square billet is controlled at 1490~1505℃ (liquidus temperature 1465℃); the crystallizer cooling water volume is 3300~3400L / min, and the inlet and outlet water temperature difference is 4.2~4.6℃; the secondary cooling water volume is 0.32~0.35L / kg 钢; The electromagnetic stirring current intensity of the crystallizer is 400~420A, the stirring current frequency is 2.4Hz, the electromagnetic stirring current intensity at the end of solidification is 300~320A, and the current frequency is 7.0Hz; the continuous casting pulling speed is 0.55±0.03m / min.

[0116] Specifically, after the above technical solution obtains the continuous casting large square billet with better homogeneity, the process control of the following steps is continued:

[0117] (1) Slow cooling of the ingot stacking requires the slow cooling temperature to be ≥500℃ for more than 8h.

[0118] (2) After the stacking and slow cooling, the ingot is promptly sent to the heating furnace, heated to 850-1000°C and kept warm for 2-3 hours.

[0119] (3) After the ingot leaves the heating furnace, high-pressure water is used to descale the ingot and the surface temperature of the ingot is rapidly reduced to 600-650°C to form a temperature gradient distribution with external cooling and internal heating, and large reduction rolling is performed.

[0120] (4) Rolling is performed for a total of 5 passes to a section of 200 mm × 200 mm, and the rolling reduction ratio of each pass in the rolling sequence is set as 35%, 30%, 20%, 10%, and 5% in sequence.

[0121] In addition to the above key technical points which must be implemented as required, the present invention requires that other continuous casting system processes be implemented in a conventional manner.

[0122] The above content of the present invention provides a method for preparing a large square billet for rolling high-carbon hard wire steel and a rolling process for high-carbon hard wire steel. The method for preparing a large square billet for rolling high-carbon hard wire steel with specific control parameters specially designed by the present invention controls the parameters of the molten steel discharged from the converter, the LF refining and the RH vacuum treatment parameters, and combines specific casting control, especially the control process and parameters of the crystallizer, so as to prepare a high-quality 360mm×450mm large-size continuous casting billet, which further reflects the high efficiency of large-section continuous casting and the advantages of microstructure and performance regulation. The present invention realizes the continuous casting production of large square billets of high-carbon hard wire steel, forms high-homogeneity continuous casting billets through innovative and scientific regulation of continuous casting equipment and process, and further performs heating and rolling control, and strengthens homogeneity regulation through heat diffusion and rolling extension, so as to provide high-quality billets for rolling of high-carbon hard wire steel, and lays an important billet quality foundation for the drawing production of products such as wire rod rolling and steel strands, especially for breaking through the contradiction between high-strength hard wire quality and efficiency.

[0123] Experimental results show that, by adopting the preparation method provided by the present invention, high-quality production of large-section continuous casting billets for high-carbon hard wire steel rolling is successfully achieved, the center segregation level of the billet is significantly improved, and the center C segregation degree of the billet for rolling wire rod is controlled at 1.03-1.05 as a whole, which lays an important homogenization foundation for the control of wire rod microstructure and performance, and promotes high-level control of low-grade cementite at the center grain boundary of the wire rod.

[0124] In order to further illustrate the present invention, a method for preparing a large square billet for rolling high-carbon hard wire steel and a rolling process of high-carbon hard wire steel provided by the present invention are described in detail below in combination with embodiments. However, it should be understood that these embodiments are implemented on the premise of the technical scheme of the present invention, and detailed implementation methods and specific operating procedures are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following embodiments.

[0125] Example 1

[0126] This embodiment is a steel mill using the method of the present invention to produce 200mm×200mm cross-section SWRH82B high carbon hard wire steel rolling billets.

[0127] The process technology flow is: converter semi-steel smelting - LF electric heating refining - RH vacuum treatment - 360mm×450mm cross-section large square billet continuous casting - stacking slow cooling - uniform heat diffusion - large temperature gradient and large reduction rolling.

[0128] The key technologies involved in the present invention are specifically implemented as follows: (1) The semi-steel [S]% entering the converter is controlled at 0.011%; the converter end point [C]% is 0.07%, and the tapping temperature is 1650°C; argon is blown online during the tapping process, and the amount of slag in the tapping process is strictly controlled by using a slide plate to block the slag, and the thickness of the slag layer in the converter is controlled at 75mm; 520kg of ferrosilicon is added for deoxidation; alloying is performed during 1 / 3 to 2 / 3 of the tapping process; 500kg of active lime is added during the tapping process; and 150m of aluminum wire is fed into the small platform. (2) LF electric heating refining: active lime and quartz sand are added before refining heating, wherein the amount of active lime added is 150kg, the amount of quartz sand added is 300kg, the basicity of the refined slag is controlled at 2.5, and 15kg of aluminum particles are added to the slag. The LF outlet temperature is controlled at 1600°C. (3) RH vacuum treatment: vacuum degree ≤ 3mbar, treatment time 13min, complete alloy composition fine-tuning, composition reaches target requirements, vacuum exit temperature is controlled at 1545℃. (4) It is extremely critical that the casting temperature of 360mm×450mm cross-section large square billet is controlled at 1490~1500℃ (liquidus temperature 1465℃); the crystallizer cooling water volume is 3350L / min, achieving an inlet and outlet water temperature difference of 4.4℃; the secondary cooling water volume is 0.35L / kg 钢; The crystallizer electromagnetic stirring current intensity is 420A, the stirring current frequency is 2.4Hz, the electromagnetic stirring current intensity at the end of solidification is 320A, the current frequency is 7.0Hz; the continuous casting pulling speed is 0.55±0.03m / min.

[0129] After the above steps have been completed to obtain a continuous casting bloom with good homogeneity, the following steps of process control are continued:

[0130] (1) The ingots are stacked and slowly cooled, and the slow cooling temperature is required to be 600-800℃ for 9 hours. (2) After the stacking and slow cooling, the ingots are promptly sent to the heating furnace, heated to 850-920℃ and kept warm for 3 hours. (3) After the ingots leave the heating furnace, high-pressure water is used to descale the ingots while rapidly lowering the surface temperature of the ingots to 600-650℃ to form a temperature gradient distribution with external cooling and internal heating, and large reduction rolling is performed. (4) A total of 5 rolling passes are performed to a section of 200mm×200mm, and the rolling reduction ratio of each pass in the rolling sequence is set to 35%, 30%, 20%, 10%, and 5% respectively.

[0131] In addition to the above key technical points which must be implemented as required, the present invention requires that other continuous casting system processes be implemented in a conventional manner.

[0132] The 200mm×200mm cross-section SWRH82B high-carbon hard wire steel rolling billet obtained in Example 1 of the present invention was subjected to drill sample segregation chemical inspection. Under the Φ4mm scale condition, the C element segregation degree of the center line of the billet was 1.04-1.05, and the proportion of cementite graded ≤2.0 at the center grain boundary of the rolled wire rod was 100%, and the proportion of graded ≤1.0 reached 83%.

[0133] Example 2

[0134] This embodiment is a steel mill using the method of the present technical invention to produce 200mm×200mm cross-section SWRH82B-2 high-strength hard wire steel rolling billets.

[0135] The process technology flow is: converter semi-steel smelting - LF electric heating refining - RH vacuum treatment - 360mm×450mm cross-section large square billet continuous casting - stacking slow cooling - uniform heat diffusion - large temperature gradient and large reduction rolling.

[0136] The key technologies involved in the present invention are specifically implemented as follows: (1) The semi-steel [S]% entering the converter is controlled at 0.006%; the converter end point [C]% is 0.06%, and the tapping temperature is 1670°C; argon is blown online during the tapping process, and the amount of slag in the tapping process is strictly controlled by using a slide plate to block the slag, and the thickness of the slag layer in the converter is controlled at 63mm; 500kg of ferrosilicon is added for deoxidation; alloying is performed during 1 / 3 to 2 / 3 of the tapping process; 450kg of active lime is added during the tapping process; and 130m of aluminum wire is fed into the small platform. (2) LF electric heating refining: active lime and quartz sand are added before refining heating, wherein the amount of active lime added is 150kg, and the amount of quartz sand added is 280kg, the basicity of the refined slag is controlled at 2.3, and 17kg of aluminum particles are added to the slag. The LF outlet temperature is controlled at 1590°C. (3) RH vacuum treatment: vacuum degree ≤ 3mbar, treatment time 12min, complete alloy composition fine-tuning, composition reaches target requirements, vacuum exit temperature is controlled at 1534℃. (4) It is extremely critical that the casting temperature of 360mm×450mm cross-section large square billet is controlled at 1492~1500℃ (liquidus temperature 1465℃); the crystallizer cooling water volume is 3350L / min, achieving an inlet and outlet water temperature difference of 4.4℃; the secondary cooling water volume is 0.32L / kg 钢 ; The crystallizer electromagnetic stirring current intensity is 400A, the stirring current frequency is 2.4Hz, the electromagnetic stirring current intensity at the end of solidification is 300A, the current frequency is 7.0Hz; the continuous casting pulling speed is 0.55±0.03m / min.

[0137] After the above steps have been completed to obtain a continuous casting bloom with good homogeneity, the following steps of process control are continued:

[0138] (1) The ingots are stacked and slowly cooled, and the slow cooling temperature is required to be 600-800℃ for 8.5 hours. (2) After the stacking and slow cooling, the ingots are promptly sent to the heating furnace, heated to 950-1000℃ and kept warm for 2-3 hours. (3) After the ingots leave the heating furnace, high-pressure water is used to descale the ingots while the surface temperature of the ingots is quickly reduced to 630-650℃ to form a temperature gradient distribution with external cooling and internal heating, and large reduction rolling is performed. (4) A total of 5 rolling passes are performed to a section of 200mm×200mm, and the rolling reduction ratio of each pass in the rolling sequence is set to 35%, 30%, 20%, 10%, and 5% respectively.

[0139] In addition to the above key technical points which must be implemented as required, the present invention requires that other continuous casting system processes be implemented in a conventional manner.

[0140] The 200mm×200mm cross-section SWRH82B high-carbon hard wire steel rolling billet obtained in Example 2 of the present invention was subjected to drill sample segregation chemical inspection. Under the Φ4mm scale condition, the C element segregation degree of the center line of the billet was 1.04-1.05, and the proportion of cementite graded ≤2.0 at the center grain boundary of the rolled wire rod was 96%, and the proportion of graded ≤1.0 reached 68%.

[0141] Example 3

[0142] This embodiment is a steel mill using the method of the present technical invention to produce 200mm×200mm cross-section SWRH82B-2 high-strength hard wire steel rolling billets.

[0143] The process technology flow is: converter semi-steel smelting - LF electric heating refining - RH vacuum treatment - 360mm×450mm cross-section large square billet continuous casting - stacking slow cooling - uniform heat diffusion - large temperature gradient and large reduction rolling.

[0144] The key technologies involved in the present invention are specifically implemented as follows: (1) The semi-steel [S]% entering the converter is controlled at 0.008%; the converter end point [C]% is 0.07%, and the tapping temperature is 1660°C; argon is blown online during the tapping process, and the amount of slag in the tapping process is strictly controlled by using a slide plate to block the slag, and the thickness of the slag layer in the converter is controlled at 70mm; 510kg of ferrosilicon is added for deoxidation; alloying is performed during 1 / 3 to 2 / 3 of the tapping process; 500kg of active lime is added during the tapping process; and 120m of aluminum wire is fed into the small platform. (2) LF electric heating refining: active lime and quartz sand are added before refining heating, wherein the amount of active lime added is 140kg, and the amount of quartz sand added is 250kg, the basicity of the refined slag is controlled at 2.1, and 16kg of aluminum particles are added to the slag. The LF outlet temperature is controlled at 1590°C. (3) RH vacuum treatment: vacuum degree ≤ 3mbar, treatment time 13min, complete alloy composition fine-tuning, composition reaches target requirements, vacuum exit temperature is controlled at 1540℃. (4) It is extremely critical that the casting temperature of 360mm×450mm cross-section large square billet is controlled at 1496~1505℃ (liquidus temperature 1465℃); the crystallizer cooling water volume is 3370L / min, achieving an inlet and outlet water temperature difference of 4.5℃; the secondary cooling water volume is 0.335L / kg 钢 ; The crystallizer electromagnetic stirring current intensity is 420A, the stirring current frequency is 2.4Hz, the electromagnetic stirring current intensity at the end of solidification is 320A, the current frequency is 7.0Hz; the continuous casting pulling speed is 0.55±0.03m / min.

[0145] After the above steps have been completed to obtain a continuous casting bloom with good homogeneity, the following steps of process control are continued:

[0146] (1) The ingots are stacked and slowly cooled, and the slow cooling temperature is required to be 500-700℃ for 15 hours. (2) After the stacking and slow cooling, the ingots are promptly sent to the heating furnace, heated to 950-1000℃ and kept warm for 2-2.5 hours. (3) After the ingots leave the heating furnace, high-pressure water is used to descale the ingots while the surface temperature of the ingots is quickly reduced to 630-650℃ to form a temperature gradient distribution with external cooling and internal heating, and large reduction rolling is performed. (4) A total of 5 rolling passes are performed to a section of 200mm×200mm, and the rolling reduction ratio of each pass in the rolling sequence is set to 35%, 30%, 20%, 10%, and 5% respectively.

[0147] In addition to the above key technical points which must be implemented as required, the present invention requires that other continuous casting system processes be implemented in a conventional manner.

[0148] The 200mm×200mm cross-section SWRH82B high-carbon hard wire steel rolling billet obtained in Example 3 of the present invention was subjected to drill sample segregation chemical inspection. Under the Φ4mm scale condition, the C element segregation degree of the center line of the billet was 1.03-1.05, and the proportion of cementite graded ≤2.0 at the center grain boundary of the rolled wire rod was 97%, and the proportion of graded ≤1.0 reached 70%.

[0149] The above implementation examples illustrate that after adopting the present invention, high-quality production of high-carbon hard wire steel rolling billets is successfully achieved, the center segregation level of the billets is significantly improved, and the center C segregation degree of the billets for rolling wire rods is overall controlled at 1.03 to 1.05, which lays an important homogenization foundation for the control of wire rod microstructure and performance, and promotes high-level control of low-grade cementite at the center grain boundary of the wire rod.

[0150] The above is a detailed introduction to a method for preparing a large square billet for rolling high carbon hard wire steel and a rolling process for high carbon hard wire steel provided by the present invention. The principle and implementation method of the present invention are described in detail using specific examples. The description of the above embodiments is only used to help understand the method and its core idea of ​​the present invention, including the best mode, and also enables any technician in the field to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for preparing a large square billet for high carbon hard wire steel rolling, characterized in that: The following steps are involved: 1) After semi-steel raw materials are smelted in a converter, molten steel is obtained by tapping; 2) The molten steel obtained in the above steps is subjected to LF refining and RH vacuum treatment, and then continuously cast and cooled in a crystallizer to obtain a continuous casting billet with a cross-sectional size of 360 mm×450 mm; The continuous casting temperature is 1490-1505°C; The cooling water volume of the crystallizer is 3300-3400 L / min.

2. The preparation method according to claim 1, characterized in that: The semi-steel raw material is specifically a semi-steel raw material for preparing high-carbon hard wire steel; The grades of the high carbon hard wire steel include SWRH82B; The mass content of S in the semi-steel raw material fed into the converter is less than or equal to 0.015%; The tapping temperature is greater than or equal to 1650°C; The mass content of C in the molten steel is less than or equal to 0.08%.

3. The preparation method according to claim 1, characterized in that: Argon is blown online during the steel tapping process, and a slide plate is used to block the slag to control the amount of slag discharged during the steel tapping process; The slag amount in the steel tapping process is specifically that the thickness of the converter slag layer is less than or equal to 80 mm; Ferrosilicon deoxidation, active lime and aluminum wire are also added during the steel tapping process; Alloying is performed during 1 / 3 to 2 / 3 of the steel tapping process.

4. The preparation method according to claim 3, characterized in that: The grade of the ferrosilicon is FeSi75; The amount of ferrosilicon added is 500-520kg; The amount of active lime added is 450-500 kg; The feeding amount of the aluminum wire is 110-150m.

5. The preparation method according to claim 1, characterized in that: The LF refining specifically includes adding active lime and quartz sand to perform LF electric heating refining; In the LF refining, the amount of active lime added is 100-150 kg; In the LF refining, the amount of quartz sand added is 250-300 kg; The basicity of the refined slag from the LF refining is 2.0-2.

5.

6. The preparation method according to claim 1, characterized in that: 15-20 kg of aluminum particles are also added to the LF refined slag; The outlet temperature of the LF refining is 1590-1600°C; The vacuum pressure of the RH vacuum treatment is less than or equal to 3 mbar; The RH vacuum treatment time is 12 to 13 minutes; The RH vacuum treatment is 1530-1545°C.

7. The preparation method according to claim 1, characterized in that: The liquidus temperature of the continuous casting is 1465°C; The temperature difference between the inlet and outlet water of the cooling water of the crystallizer is 4.2-4.6°C; The secondary cooling water volume of the crystallizer is 0.32-0.35 L / kg 钢 ; The electromagnetic stirring current intensity of the crystallizer is 400-420A; The electromagnetic stirring current intensity at the solidification end of the crystallizer is 300-320A; The continuous casting pulling speed is 0.52-0.58 m / min.

8. A rolling process for high carbon hard wire steel, characterized in that: The following steps are involved: The high carbon hard wire steel ingots are stacked and slowly cooled, and then heated, and then water-cooled to reduce the surface temperature of the ingots, and then rolled to obtain high carbon hard wire steel; The cast billet is a continuously cast billet prepared by the preparation method according to any one of claims 1 to 7.

9. The rolling process according to claim 8, characterized in that: The slow cooling temperature of the stacking slow cooling is 500-800°C; The stacking slow cooling time is 8 to 15 hours; The heating temperature is 850-1000°C; The heating time is 2 to 3 hours.

10. The rolling process according to claim 8, characterized in that: High-pressure water descaling is performed during the water cooling process; The water cooling reduces the surface temperature of the casting to 600-650°C; The rolling process is performed in 5 passes; The rolling reduction ratios of the five passes are 35%, 30%, 20%, 10% and 5% respectively; The cross section of the high carbon hard wire steel after rolling is 200 mm×200 mm.