Method for producing high-cleanliness hot work die steel bloom through converter continuous casting machine

Abstract

The invention relates to a method for producing a high-cleanliness hot work die steel bloom through a converter continuous casting machine. The method comprises the following steps that S1, alloy baking is conducted; molten iron is subjected to desulfurization pretreatment, the S mass content of the desulfurized molten iron is smaller than or equal to 0.005%, oxide scale accounting for 4%-7% of the total loading mass is added into a dephosphorization converter firstly, then the desulfurized molten iron is added, 10 kg-20 kg of lime slag is added per ton of iron in the blowing process, and after duplex is finished, the semi-steel component mass content P is smaller than or equal to 0.025%, and the S mass content is smaller than or equal to 0.008%; s3, a duplex decarburization process; s4, tapping and alloying; s5, a refining process; and S6, a continuous casting process. The contents of residual elements P, S, Ti and Ca of the bloom are low, the cleanliness is high, the total oxygen content is low, the surface quality of the casting blank is excellent, and the production requirements of high-performance hot work die steel raw materials for electroslag are met.

Description

Technical Field

[0001] The invention relates to the production of hot working die steel, in particular to a production method of high-performance H13, XGYZ01, XG407 and other large square billets, and specifically to a method for producing high-cleanliness hot working die steel large square billets using a converter continuous casting machine. Background Art

[0002] H13, XGYZ01, XG407, etc. are representative steels of hot working die steel and are the most widely used hot working die steels. Hot working die steel, on the one hand, pursues lower cost as the goal of rolling products, suitable for some molds with low requirements. On the other hand, it pursues quality as the main forging material, mostly used for high-performance hot working molds such as die casting molds, forging molds and extrusion molds. Due to its large amount of alloy addition and low phosphorus and sulfur content requirements, most of them adopt the production process of electric furnace → refining outside the furnace → die casting / continuous casting → electroslag remelting → forging → heat treatment. Electric furnace production can solve the problem of large amount of alloy addition, but the content of impurity elements in the finished product is relatively high. The converter → die casting process can produce high-cleanliness ingots, but the yield rate is low and the cost is high. At present, it is mainly produced by converter → refining outside the furnace → continuous casting → electroslag remelting process. The above process mainly has the following problems: Because this type of steel has a large amount of alloy added, the tapping temperature must be increased to ensure alloy melting when using a converter. However, it is difficult to ensure that the P content of the finished product is ≤0.010% by increasing the tapping temperature. In order to ensure the desulfurization rate in the refining process and the total oxygen content of the finished product, aluminum must be added to the steel for deoxidation. After aluminum is added to the steel, a calcium treatment process will be used to ensure the pouring performance of the continuous casting machine. After calcium treatment, the cleanliness of the finished product will decrease and the inclusions will exceed the standard. Due to the high hardness of this type of steel, the continuous casting machine's steel drawing process is prone to problems such as ingot warping, difficulty in cutting, uneven cooling and cracking of the ingot.

[0003] In the publicly published literature on hot working die steel, Patent No. CN 113249547 A, a smelting method for high purity hot working die steel H13, does not describe how to ensure the phosphorus and sulfur content of the finished product under the premise of adding a high amount of alloy, and the patent also emphasizes not feeding calcium wire, but does not describe how to ensure the casting performance of aluminum-containing steel without feeding calcium wire; Patent application No. 202210713991.2 makes clear requirements on the temperature of the slow cooling pit for casting, but does not clearly explain how to reach the temperature of the slow cooling pit. This patent clearly states that the slow cooling pit is paved with hot billets of other steel grades in advance, and the top is pressed with hot billets; in addition, although the patent also clearly states that the billet drawing speed should be quickly increased to the target drawing speed after pouring, the purpose of speeding up in this patent is different. The purpose of speeding up in this patent is to prevent serious warping of billets at low drawing speeds, while the purpose of speeding up in the comparative patent is to avoid steel leakage; The refining method of electroslag steel for high-purity hot working die steel involved in Patent No. CN 106591681 A. After triple removal of iron water, the end-point composition is Si≤0.015%, P≤0.010%, S≤0.010%. Double slag operation is adopted in both converter and refining. High basicity slag system is used in refining. Low casting speed of 0.53 - 0.56 m / min is adopted in continuous casting.

[0004] The production method of H13 continuous casting billet involved in Patent No. CN 106011671 A. After desulfurization pretreatment of iron water, S in iron water ≤0.015%. Converter single connection process is adopted. High basicity slag system is used in refining. The finished product has P≤0.030% and S≤0.030%. The continuous casting speed is 0.4 - 0.6 m / min. The cast billet is placed in a slow cooling pit for 24 - 72 h of slow cooling. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for producing large bloom of high cleanliness hot working die steel by a converter continuous caster. The large bloom has low contents of residual elements P, S, Ti, Ca, high cleanliness, low total oxygen content, and excellent surface quality of the billet, meeting the production requirements of raw materials for high-performance electroslag hot working die steel.

[0006] The technical solution of the present invention: A method for producing large bloom of high cleanliness hot working die steel by a converter continuous caster, specifically including the following steps: S1 Alloy baking; S2 Double connection semi-steel smelting: After desulfurization pretreatment of iron water, the mass content of S in the desulfurized iron water ≤0.005%. First, add 4% - 7% of the total charged mass of scale in the dephosphorization converter, then pour in the desulfurized iron water. During the blowing process, add 10 kg - 20 kg of lime slag material per ton of iron. After the double connection ends, the mass content of P in the semi-steel is ≤0.025% and S is ≤0.008%; S3 Double connection decarburization process; S4 Steel tapping alloying; S5 Refining process: S6 Continuous casting process.

[0007] Preferably, for S1 alloy baking: Before production, put low-titanium high-carbon ferrochrome (titanium mass content ≤0.03%, 6% ≤ carbon mass content ≤ 10%) into a clean ladle without ladle edge. Use gas to bake the alloy, ensuring that the alloy baking temperature ≥600℃ before the alloy is put into use.

[0008] Preferably, in S2 double-vessel semi-steel smelting: the hot metal undergoes desulfurization pretreatment. After desulfurization, the S content in the hot metal is ≤0.005%, and the Ti content in the hot metal is not required. First, scale with a total charging ratio of 4%-7% is added into the dephosphorization converter. The scale is all produced from the production of aluminum-killed steel, with an S content ≤0.008%. Then, the desulfurized hot metal is charged. To avoid an increase in the sulfur content of the semi-steel after the double-vessel process, no other scrap is added into the dephosphorization converter except for the scale. The low-sulfur scale is relied on to control the initial temperature and provide a high-iron-oxide slag, ensuring the dephosphorization rate of the dephosphorization converter. During the blowing process, 10 kg - 20 kg of lime slag material is added per ton of iron, and no other slag materials are added. After the double-vessel process ends, the composition of the semi-steel is P ≤0.025% and S ≤0.008%. By using low-sulfur scale as the raw material for the double-vessel hot metal, the problem of the increase in the sulfur content of the double-vessel hot metal is solved. By smelting semi-steel, the problem of Ti in the hot metal being introduced into the molten steel is solved, which is more conducive to the smelting of low-Ti steel.

[0009] Preferably, in S3 double-vessel decarburization process: the semi-steel hot metal is charged into the decarburization converter. Since the silicon in the double-vessel hot metal has been oxidized and the temperature is insufficient, no scrap is added into the furnace. And after the double-vessel process, the Ti in the hot metal is completely oxidized, which is more conducive to the control of the Ti content in the molten steel. After the converter is charged with hot metal, ferromolybdenum is added into the furnace. To prevent ferromolybdenum from sticking to the furnace wall and not melting, ferromolybdenum is added after charging the hot metal. To ensure sufficient temperature in the furnace, 4 - 6 kg of ferrosilicon per ton of iron is added into the furnace for temperature raising and slag melting. During the blowing process, 20 kg - 30 kg of lime per ton of iron and 3 kg - 5 kg of fluorite per ton of iron are added. The end-point temperature is controlled at 1620℃ - 1660℃. Since the P and S contents of the double-vessel hot metal used are relatively low, it can be ensured that the end-point P ≤0.005% and S ≤0.010%. In S3, ferromolybdenum is added into the furnace through the scrap bucket after the converter is charged with hot metal, which can prevent ferromolybdenum from sticking to the furnace wall and not melting, and to ensure sufficient temperature in the furnace.

[0010] Preferably, in S4 tapping alloying: during the tapping process, aluminum is added into the ladle for deoxidation to ensure that the total aluminum content in the molten steel entering the LF is 0.020% - 0.040%. Then, silicomanganese alloy is added for alloying. During the period when 1 / 3 - 3 / 4 of the tapping amount of the converter is discharged, a low-alkalinity titanium-control refining synthetic slag and part of lime are added to control the final slag alkalinity R (CaO / SiO2) at 4.0 - 7.0. The weight percentage of the synthetic slag consists of the following components: CaO 30 - 50%, SiO2 10 - 15%, Al2O3 5 - 20%, MgO ≤3%. At the same time, TiO2 ≤0.1% and CaF2 ≤1% are controlled in the components, and the balance is inevitable impurities. The addition amount of the synthetic slag is 10 - 17 kg per ton of steel. After the tapping ends, low-titanium high-carbon ferrochrome (with a Ti content ≤0.03%) baked in the ladle is slowly poured into the ladle. The ladle containing the molten steel is ensured to have two bottom blows with good bottom-blowing effects. During the alloy pouring process, the ladle car is slightly started to shake the ladle to avoid alloy caking.

[0011] Preferably, S5 refining process: LF treatment, adding alloys to fine-tune the chemical composition during the refining process, adding aluminum particles to the slag surface during the early heating process to remove oxygen from the slag, the addition amount is 0.5-1.5kg / ton of steel, to improve the desulfurization efficiency, adding ferrosilicon powder to the slag liquid surface in the middle and late stages for diffusion deoxidation, reducing the slag basicity to avoid the increase of titanium content in the molten steel and promoting the adsorption of inclusions by the refining slag, the addition amount is 0.5-2.5kg / ton of steel, controlling the final slag R at 2.5-5.0, and the Al2O3 content should be controlled at 17-35%. The refining treatment time is 60-100min, promoting the adsorption of inclusions and desulfurization by the refining slag, and further removing the gas content in the steel through RH vacuum process treatment, and no calcium treatment is performed after the RH treatment. The residual elements of the finished product are P≤0.010%, S≤0.003%, Ti≤0.0020%, 0.010%≤Al≤0.020%, and the rest are H13 main element content and unavoidable impurity elements.

[0012] Preferably, S6 continuous casting process: electromagnetic induction heating is adopted for the tundish, the superheat of the tundish is stably controlled at 15-25°C, argon blowing is used for the stopper rod, and the argon blowing amount is adjusted to slight bubbling on the liquid surface of the crystallizer to ensure the argon blowing effect of the stopper rod, and less flow casting steel is used after pouring, and the pulling speed is quickly increased to 0.6-0.8m / min to avoid the billet head being tilted and damaging the equipment due to too low pulling speed, and the billet is difficult to cut due to its high strength. An iron powder blowing device is added at the billet cutting point to increase the cutting strength to ensure smooth cutting of the billet, and the large square billet is directly put into the slow cooling pit after cutting (the billet of the tail furnace of the upper pouring is put into the slow cooling pit for warming, the billet of the head furnace of the lower pouring is put into the slow cooling pit for warming, and the billet of the head furnace of the lower pouring is put on the H13 billet for pressing), the billet entering the pit temperature is ≥600°C, the large square billet is slowly cooled for 48h and then the cover is opened, and it is cooled to below 100°C and then taken out of the slow cooling pit.

[0013] Preferably, S6 continuous casting process: the treated molten steel is cast into a large square billet with an end face size of 280mm×325mm.

[0014] The production method provided by the present invention has the following advantages: The molten iron adopts ultra-deep desulfurization duplex molten iron, and the duplex process uses low-sulfur iron oxide scale as coolant. The steel-making temperature of the converter is reduced by alloy baking and the dephosphorization rate of the converter is increased. The refining process is controlled by high basicity in the early stage and low basicity in the late stage slag system, which can ensure that the residual elements P, S and Ti content of the finished product are low, which can improve the impact toughness of the material, improve hot brittleness and improve thermal fatigue performance.

[0015] The use of aluminum deoxidation calcium-free treatment technology and low-basicity titanium-controlled refining synthetic slag can ensure the desulfurization efficiency of the refining process and the ultra-low oxygen content of the finished product, reduce large-sized endogenous inclusions, and improve the purity of the steel.

[0016] By using electromagnetic induction to heat the tundish, long-period and low-flow steady casting can be achieved. Using iron powder as an auxiliary cutting means can ensure the smooth cutting of the billet, and the surface quality of the billet is excellent, enabling multi-furnace continuous casting and meeting the production requirements of high-performance hot work die steel raw materials for electroslag remelting.

[0017] 4. Through this process, high-performance hot work die steel for electroslag remelting with total oxygen content ≤ 12 ppm and DS-type inclusions ≤ 1.0 can be obtained.

[0018] The present invention solves the above problems existing in the production process of converter → secondary refining → continuous casting → electroslag remelting in the prior art, and produces high-performance die steel materials with ultra-low oxygen, high purity, uniform comprehensive properties of low phosphorus and sulfur contents, and good segregation degree. In the present invention, the control of technical parameters in the converter, refining, and continuous casting processes is quite different from that in the prior art. After desulfurization pretreatment, ultra-deep desulfurization of hot metal is achieved. Using iron oxide scale as a double-strand coolant avoids sulfur increase during the double-strand process. The converter adopts a full hot metal double-strand process to reduce the content of titanium and phosphorus in hot metal. High-quality low-titanium ferrochrome and ferrosilicon are used for deoxidation alloying. In the early stage of the refining process, high-alkalinity desulfurization is carried out, and in the later stage, low-alkalinity and low-controlled titanium are used to adsorb inclusions to ensure the castability without calcium treatment. The continuous casting machine uses a stopper rod to blow argon to improve the casting performance. Electromagnetic induction heating is used for the tundish to stably control the superheat, and the quality of the cast billet is controlled by increasing the casting speed and putting the cast billet into a slow cooling pit. It has the characteristics of low residual elements, high cleanliness, and excellent surface quality of the cast billet, meeting the production requirements of high-performance hot work die steel raw materials for electroslag remelting. Specific Embodiments

[0019] The production method provided by the present invention is further described below through examples.

[0020] A method for producing large bloom of high-cleanliness hot work die steel by a converter continuous casting machine, including alloy baking, double-strand semi-steel smelting, double-strand decarburization process, tapping alloying, refining process, and continuous casting process. Each process is described as follows: Example 1

[0021] The steps for producing the large bloom are as follows: The hot metal is subjected to desulfurization pretreatment, and the S content of the hot metal is 0.004%. The converter double-strand process is adopted. In the double-strand converter, iron oxide scale generated from 5.3% of the total charged aluminum-killed steel is added, and no scrap is added. During the blowing process, 17 kg of lime is added per ton of iron. The P content of the semi-steel hot metal in the converter is 0.021%, and the S content is 0.008%.

[0022] The semi-steel hot metal after the double-strand is poured into the decarburization converter. Ferrosilicon (4.8 kg / ton of iron) is added to the furnace through the scrap bucket for temperature raising and slag melting; ferromolybdenum is added to the furnace through the scrap bucket. During the blowing process, 26 kg of lime per ton of iron and 3.8 kg of fluorite per ton of iron are added. The end-point temperature is controlled at 1645 °C. The P content of the molten steel at the end of the furnace is 0.004%, and the S content is 0.008%.

[0023] During the tapping process, aluminum is added to the ladle for deoxidation. The total aluminum content in the molten steel in the LF furnace is 0.035%. Then, ferrosilicon manganese alloy is added for alloying. When 1 / 3 of the converter tapping amount is reached, a low-alkalinity titanium-controlled refining synthetic slag and part of the lime are added, and the final slag alkalinity R (CaO / SiO2) is controlled to be 5.2. The weight percentage of the refining synthetic slag consists of the following components: CaO 30 - 50%, SiO2 10 - 15%, Al2O3 5 - 20%, MgO ≤ 3%. At the same time, TiO2 ≤ 0.1% and CaF2 ≤ 1% are controlled in the components, and the balance is inevitable impurities. The addition amount of the synthetic slag is 15.8 kg / ton of steel. After the tapping is completed, low-titanium high-carbon ferrochrome (titanium content ≤ 0.03%) baked in the ladle (baking temperature ~605°C) is slowly poured into the ladle. The ladle containing the molten steel is ensured to have two bottom blows and good bottom blow effect. During the alloy addition process, the ladle car is slightly started to shake the ladle to avoid alloy caking.

[0024] During the early heating process of LF refining, 0.6 kg / ton of steel of aluminum pellets are added on the slag surface to remove the oxygen in the slag and improve the desulfurization efficiency; in the middle and later stages, ferrosilicon powder is added on the slag liquid surface for diffusion deoxidation to reduce the slag alkalinity and avoid the increase of titanium content in the molten steel. The addition amount of ferrosilicon powder is 0.51 kg / ton of steel, and the final slag R is 4.5 and the Al2O3 content is 32%. The refining treatment time is 95 min, and it is further processed by RH vacuum process to remove the gas content in the steel. After the RH treatment is completed, no calcium treatment is carried out. The content of residual elements P in the finished product is 0.010%, S content is 0.003%, Ti content is 0.0020%, Al content is 0.017%, and the rest are the main element content of the electroslag steel and inevitable impurity elements.

[0025] The treated molten steel is cast into a large billet with an end face size of 280 mm × 325 mm. The tundish is heated by electromagnetic induction, and the tundish superheat is 22°C. The stopper rod uses an argon-blowing stopper rod, and the argon-blowing amount is adjusted to make the liquid level in the mold slightly bubble to ensure the argon-blowing effect of the stopper rod. After starting the casting, the steel is poured with a small flow rate, and the casting speed is quickly increased to 0.78 m / min. A ferrous powder spraying device is added at the billet cutting place to increase the cutting strength and ensure the smooth cutting of the billet. After the large billet is cut, it is directly put into the slow cooling pit. (The tail furnace billet of the previous casting is put into the slow cooling pit for warming, the head furnace billet of the next casting is put into the slow cooling pit for warming, and the head furnace billet of the next casting is placed on the H13 billet for pressing the billet). The billet entering the pit temperature is 675°C. After the large billet is slowly cooled for 48 h, the cover is removed, and it is cooled to 83°C and taken out of the slow cooling pit.

[0026] The total oxygen content of the high-performance hot work die steel for electroslag obtained in this example is 10.1 ppm, and the DS type inclusion level is 0.5 level. Example 2

[0027] The production steps of the large billet are as follows: The hot metal undergoes desulfurization pretreatment, and the S content in the hot metal is 0.005%. The combined blowing process of a converter is adopted. In the combined blowing converter, scale generated from 7% of the total charged aluminum killed steel is added, and no scrap is added; 20 kg of lime is added per ton of iron during the blowing process; the P content in the semi-steel hot metal of the converter is 0.023% and the S content is 0.007%.

[0028] The semi-steel hot metal after the combined blowing is charged into the decarburization converter. Ferrosilicon (5 kg per ton of iron is used for temperature raising and slag melting) is added into the furnace through the scrap bucket; ferromolybdenum is added into the furnace through the scrap bucket; 30 kg of lime per ton of iron and 5 kg of fluorite per ton of iron are added during the blowing process. The end-point temperature is controlled at 1660 °C. The P content in the molten steel at the end of the furnace is 0.004% and the S content is 0.007%.

[0029] During the tapping process, aluminum is added into the ladle for deoxidation. The total aluminum content in the molten steel entering LF is 0.040%. Then ferrosilicon manganese alloy is added for alloying. When 1 / 3 of the tapping amount of the converter is reached, low-alkalinity titanium-controlled refining synthetic slag and partial lime are added to control the final slag basicity R (CaO / SiO2) to be 6.8. The weight percentage of the refining synthetic slag consists of the following components: CaO 30 - 50%, SiO2 10 - 15%, Al2O3 5 - 20%, MgO ≤ 3%. At the same time, TiO2 ≤ 0.1% and CaF2 ≤ 1% are controlled in the components, and the balance is inevitable impurities. The addition amount of the synthetic slag is 16.8 kg per ton of steel. After the tapping is completed, low-titanium high-carbon ferrochrome (titanium content ≤ 0.03%) baked in the ladle (baking temperature ~620 °C) is slowly poured into the ladle. The ladle containing the molten steel is ensured to have two bottom blows and good bottom blow effect. During the alloy pouring process, the ladle car is slightly started to shake the ladle to avoid alloy caking.

[0030] During the early heating process of LF refining, 1.2 kg of aluminum particles per ton of steel are added on the slag surface to remove oxygen in the slag and improve the desulfurization efficiency; in the middle and late stages, ferrosilicon powder is added on the slag liquid surface for diffusion deoxidation to reduce the slag basicity and avoid the increase of titanium content in the molten steel. The addition amount of ferrosilicon powder is 1.45 kg per ton of steel. The final slag R is 4.7 and the Al2O3 content is 32%. The refining treatment time is 95 min, and it is further processed by RH vacuum process to remove the gas content in the steel. No calcium treatment is carried out after the RH treatment. The residual element P content in the finished product is 0.010%, the S content is 0.003%, the Ti content is 0.0020%, and the Al content is 0.015%. The rest are the main element content of the electroslag steel and inevitable impurity elements.

[0031] The processed molten steel is poured into a large bloom with an end face size of 280 mm × 325 mm. The tundish is heated by electromagnetic induction, and the superheat of the tundish is 25°C. For the stopper rod, the argon blowing amount of the argon-blowing stopper rod is adjusted to make the liquid level in the mold slightly bubble to ensure the argon-blowing effect of the stopper rod. After starting casting, a small-flow casting method is adopted, and the casting speed is quickly increased to 0.76 m / min. A iron powder spraying device is added at the billet cutting position to increase the cutting strength and ensure the smooth cutting of the billet. After the large bloom is cut, it is directly put into the slow-cooling pit. (The tail furnace billets of the previous casting are put into the slow-cooling pit to warm up, and the head furnace billets of the next casting are put into the slow-cooling pit to warm up. The head furnace billets of the next casting are placed on the H13 billets for pressing.) The temperature of the billet entering the pit is 678°C. After the large bloom is slowly cooled for 48 h, the cover is removed, and it is cooled to 88°C and then taken out of the slow-cooling pit.

[0032] The total oxygen content of the high-performance hot work die steel for electroslag obtained in this example is 10.5 ppm, and the DS-type inclusion level is 0 level. Example 3

[0033] The production steps of the large bloom are as follows: The hot metal is pretreated for desulfurization, and the S content of the hot metal is 0.004%. The converter double-blank process is adopted. The scale generated from the aluminum-killed steel with a total charge of 4% is added to the double-blank converter, and no scrap is added. During the blowing process, 15 kg of lime is added per ton of iron. The P content of the semi-steel hot metal in the converter is 0.025%, and the S content is 0.006%.

[0034] The semi-steel hot metal after the double-blank is poured into the decarburization converter. Ferrosilicon (4 kg / ton of iron) is added to the furnace through the scrap bucket for temperature raising and slag melting; ferromolybdenum is added to the furnace through the scrap bucket. During the blowing process, 20 kg of lime per ton of iron and 3 kg of fluorite per ton of iron are added. The end-point temperature is controlled at 1620°C. The P content of the molten steel at the end of the furnace is 0.003%, and the S content is 0.005%.

[0035] During the tapping process, aluminum is added to the ladle for deoxidation. The total aluminum content of the molten steel entering the LF is 0.020%. Then, ferrosilicon manganese alloy is added for alloying. When 1 / 3 of the converter tapping amount is reached, a low-alkalinity titanium-controlled refining synthetic slag and part of the lime are added to control the final slag alkalinity R (CaO / SiO2) to be 4.3. The weight percentage of the refining synthetic slag consists of the following components: CaO 30 - 50%, SiO2 10 - 15%, Al2O3 5 - 20%, MgO ≤ 3%. At the same time, TiO2 ≤ 0.1% and CaF2 ≤ 1% are controlled in the components, and the balance is inevitable impurities. The addition amount of the synthetic slag is 10.4 kg / ton of steel. After the tapping is completed, the low-titanium high-carbon ferrochrome (titanium content ≤ 0.03%) baked in the ladle (baking temperature ~613°C) is slowly poured into the ladle. The ladle containing the molten steel is ensured to have two bottom blows and good bottom-blowing effects. During the alloy pouring process, the ladle car is slightly started to shake the ladle to avoid alloy caking.

[0036] During the early heating process of LF refining, 0.9 kg of aluminum particles per ton of steel are added to the slag surface to remove oxygen in the slag and improve the desulfurization efficiency. In the middle and late stages, ferrosilicon powder is added to the slag liquid surface for diffusion deoxidation to reduce the slag basicity and prevent the titanium content in the molten steel from increasing. The addition amount of ferrosilicon powder is 2.01 kg per ton of steel. The final slag has an R value of 2.6 and an Al2O3 content of 17%. The refining treatment time is 63 minutes, and the molten steel is further processed by the RH vacuum process to remove the gas content in the steel. No calcium treatment is carried out after the RH treatment. The residual element P content in the finished product is 0.009%, the S content is 0.003%, the Ti content is 0.0018%, and the Al content is 0.010%. The rest are the main element content of the electroslag steel and inevitable impurity elements.

[0037] The treated molten steel is cast into a large bloom with an end face size of 280 mm × 325 mm. The tundish is heated by electromagnetic induction, and the tundish superheat is 23°C. The argon flow rate of the argon blowing stopper is adjusted to make the liquid surface in the mold bubble slightly to ensure the argon blowing effect of the stopper. After starting casting, a small-flow casting method is used, and the casting speed is quickly increased to 0.8 m / min. A ferrous powder spraying device is added at the billet cutting position to increase the cutting strength and ensure smooth cutting of the billet. After the large bloom is cut, it is directly put into the slow cooling pit. (The tail furnace billets of the previous casting are put into the slow cooling pit for warming, the head furnace billets of the next casting are put into the slow cooling pit for warming, and the head furnace billets of the next casting are placed on the H13 billets for pressing). The billet entry temperature is 690°C. After the large bloom is slowly cooled for 48 hours, the cover is removed, and it is cooled to 85°C and taken out of the slow cooling pit.

[0038] The total oxygen content of the high-performance hot work die steel for electroslag obtained in this example is 9.3 ppm, and the DS type inclusion level is 0.5. Example 4

[0039] The production steps of the large bloom are as follows: The hot metal is pretreated for desulfurization, and the S content of the hot metal is 0.003%. The converter double-blank process is adopted. 6% of the scale generated from aluminum-killed steel is added to the double-blank converter, and no scrap is added. During the blowing process, 12 kg of lime is added per ton of iron. The semi-steel hot metal in the converter has a P content of 0.022% and an S content of 0.007%.

[0040] The semi-steel hot metal in the second half of the double-blank is poured into the decarburization converter. Ferrosilicon (5.8 kg per ton of iron) is added to the furnace through the scrap bucket for temperature raising and slag melting; ferro molybdenum is added to the furnace through the scrap bucket. During the blowing process, 22 kg of lime per ton of iron and 4.3 kg of fluorite per ton of iron are added. The end-point temperature is controlled at 1643°C. The P content of the molten steel at the end of the furnace is 0.005%, and the S content is 0.009%.

[0041] During the tapping process, aluminum is added to the ladle for deoxidation. The total aluminum content in the LF molten steel is 0.032%. Then, ferrosilicon manganese alloy is added for alloying. When 1 / 3 of the converter tapping volume is reached, a low-alkalinity titanium-controlled refining synthetic slag and partial lime are added. The final slag alkalinity R (CaO / SiO2) is controlled at 4.9. The weight percentage of the refining synthetic slag consists of the following components: CaO 30 - 50%, SiO2 10 - 15%, Al2O3 5 - 20%, MgO ≤ 3%. At the same time, TiO2 ≤ 0.1% and CaF2 ≤ 1% are controlled in the components, and the balance is inevitable impurities. The addition amount of the synthetic slag is 16.8 kg per ton of steel. After the tapping is completed, low-titanium high-carbon ferrochrome (titanium content ≤ 0.03%) baked in the ladle (baking temperature ~630°C) is slowly poured into the ladle. The ladle containing molten steel is ensured to have two bottom blows with good bottom-blowing effect. During the alloy pouring process, the ladle car is slightly started to shake the ladle to avoid alloy caking.

[0042] During the early heating process of LF refining, 1.0 kg of aluminum pellets per ton of steel are added on the slag surface to remove oxygen in the slag and improve the desulfurization efficiency. In the middle and late stages, ferrosilicon powder is added on the slag liquid surface for diffusion deoxidation to reduce the slag alkalinity and avoid the increase of titanium content in the molten steel. The addition amount of ferrosilicon powder is 2.4 kg per ton of steel. The final slag R is 4.8 and the Al2O3 content is 29%. The refining treatment time is 75 min, and it is further processed by the RH vacuum process to remove the gas content in the steel. No calcium treatment is carried out after the RH treatment. The residual element P content in the finished product is 0.009%, S content is 0.002%, Ti content is 0.0019%, Al content is 0.019%, and the rest are the main element content of electroslag steel and inevitable impurity elements.

[0043] The treated molten steel is cast into a large bloom with an end face size of 280 mm × 325 mm. The tundish is heated by electromagnetic induction, and the tundish superheat is 17°C. The stopper rod uses an argon-blowing stopper rod, and the argon-blowing amount is adjusted to make the liquid level in the mold slightly bubble to ensure the argon-blowing effect of the stopper rod. After starting casting, the steel is poured with a small flow rate, and the casting speed is quickly increased to 0.65 m / min. A ferrous powder spraying device is added at the casting blank cutting position to increase the cutting strength and ensure the smooth cutting of the casting blank. After the large bloom is cut, it is directly put into the slow-cooling pit. (The tail furnace casting blank of the previous casting is put into the slow-cooling pit to warm, the head furnace casting blank of the next casting is put into the slow-cooling pit to warm, and the head furnace casting blank of the next casting is placed on the H13 casting blank for pressing the blank). The casting blank entry temperature is 684°C. After the large bloom is slowly cooled for 48 h, the cover is removed, and it is cooled to 85°C and taken out of the slow-cooling pit.

[0044] The total oxygen content of the high-performance hot work die steel for electroslag obtained in this example is 9.5 ppm, and the DS type inclusion level is 1.0.

[0045] Comparative Example 1

[0046] The production steps of the large bloom are as follows: The hot metal undergoes desulfurization pretreatment, and the S content in the hot metal is 0.006%. The converter double-stage process is adopted. In the double-staged converter, scale generated from 4.5% of the total charged aluminum-killed steel is added, and no scrap is added. During the blowing process, 13 kg of lime is added per ton of iron. The semi-steel hot metal in the converter has a P content of 0.020% and an S content of 0.009%.

[0047] The semi-steel hot metal after the double-stage is poured into the decarbonization converter. Ferrosilicon (4.8 kg per ton of iron) is added into the furnace through the scrap bucket for temperature raising and slag melting; ferromolybdenum is added into the furnace through the scrap bucket. During the blowing process, 23 kg of lime per ton of iron and 3.1 kg of fluorite per ton of iron are added. The end-point temperature is controlled at 1650 °C. The P content of the molten steel at the end of the furnace is 0.005%, and the S content is 0.011%.

[0048] During the tapping process, aluminum is added into the ladle for deoxidation. The total aluminum content in the molten steel entering the LF is 0.033%. Then ferrosilicon manganese alloy is added for alloying. When 1 / 3 of the tapping amount of the converter is reached, low-alkalinity titanium-controlled refining synthetic slag and part of lime are added to control the final slag basicity R (CaO / SiO2) to be 5.3. The weight percentage of the refining synthetic slag consists of the following components: CaO 30 - 50%, SiO2 10 - 15%, Al2O3 5 - 20%, MgO ≤ 3%, and at the same time, TiO2 ≤ 0.1% and CaF2 ≤ 1% are controlled in the components, and the balance is inevitable impurities. The addition amount of the synthetic slag is 13 kg per ton of steel. After the tapping is completed, low-titanium high-carbon ferrochrome (titanium content ≤ 0.03%) baked in the ladle (baking temperature ~603 °C) is slowly poured into the ladle. The ladle containing the molten steel is ensured to have two bottom blows and good bottom-blowing effect. During the alloy pouring process, the ladle car is slightly started to shake the ladle to avoid alloy caking.

[0049] During the early heating process of LF refining, 1.1 kg of aluminum particles per ton of steel are added on the slag surface to remove oxygen in the slag and improve the desulfurization efficiency; in the middle and late stages, ferrosilicon powder is added on the slag liquid surface for diffusion deoxidation to reduce the slag basicity and avoid the increase of titanium content in the molten steel. The addition amount of ferrosilicon powder is 1.3 kg per ton of steel, and the final slag R is 3.5 and the Al2O3 content is 20%. The refining treatment time is 85 min, and it is further processed by the RH vacuum process to remove the gas content in the steel. No calcium treatment is carried out after the RH treatment. The residual element P content of the finished product is 0.009%, the S content is 0.004%, the Ti content is 0.0019%, and the Al content is 0.017%. The rest are the main element content of the electroslag steel and inevitable impurity elements.

[0050] The processed molten steel is poured into a large bloom with an end face size of 280 mm × 325 mm. The tundish is heated by electromagnetic induction, and the superheat of the tundish is 20°C. For the stopper rod, the argon blowing amount of the argon-blowing stopper rod is adjusted to make the liquid level in the mold slightly bubble to ensure the argon-blowing effect of the stopper rod. After starting casting, a small-flow casting method is adopted, and the casting speed is quickly increased to 0.72 m / min. A iron powder spraying device is added at the billet cutting position to increase the cutting strength and ensure the smooth cutting of the billet. After the large bloom is cut, it is directly put into the slow cooling pit. (The tail furnace billets of the previous casting are put into the slow cooling pit to warm up, and the head furnace billets of the next casting are put into the slow cooling pit to warm up. The head furnace billets of the next casting are placed on the H13 billets for pressing). The temperature of the billet entering the pit is 667°C. After the large bloom is slowly cooled for 48 hours, the cover is removed, and it is cooled to 78°C and then taken out of the slow cooling pit.

[0051] The total oxygen content of the high-performance hot work die steel for electroslag obtained in this example is 12.2 ppm, and the DS type inclusion level is 1.0 level.

[0052] Comparative Example 2

[0053] The production steps of the large bloom are as follows: The hot metal is pretreated by desulfurization, and the S content of the hot metal is 0.004%. The double-conversion process of the converter is adopted. The scale generated from the total charged 5.8% of aluminum-killed steel is added into the double-conversion converter, and no scrap steel is added. During the blowing process, 17 kg of lime is added per ton of iron. The P content of the semi-steel hot metal in the converter is 0.027%, and the S content is 0.007%.

[0054] The semi-steel hot metal after the double conversion is poured into the decarburization converter. Ferrosilicon (5.3 kg / ton of iron) is added into the furnace through the scrap steel hopper for temperature raising and slag melting; ferromolybdenum is added into the furnace through the scrap steel hopper. During the blowing process, 28 kg of lime per ton of iron and 4.5 kg of fluorite per ton of iron are added. The end-point temperature is controlled at 1637°C. The P content of the molten steel at the end of the furnace is 0.008%, and the S content is 0.008%.

[0055] During the tapping process, aluminum is added into the ladle for deoxidation. The total aluminum content of the molten steel entering the LF is 0.030%. Then ferrosilicon manganese alloy is added for alloying. When 1 / 3 of the tapping amount of the converter is reached, a low-alkalinity titanium-controlled refining synthetic slag and part of lime are added, and the final slag basicity R (CaO / SiO2) is controlled to be 6.2. The weight percentage of the refining synthetic slag is composed of the following components: CaO 30 - 50%, SiO2 10 - 15%, Al2O3 5 - 20%, MgO ≤ 3%. At the same time, TiO2 ≤ 0.1% and CaF2 ≤ 1% in the components are controlled, and the balance is inevitable impurities. The addition amount of the synthetic slag is 16.8 kg / ton of steel. After the tapping is completed, low-titanium high-carbon ferrochrome (titanium content ≤ 0.03%) baked in the ladle (baking temperature ~610°C) is slowly poured into the ladle. The ladle containing the molten steel is ensured to have two bottom blows and good bottom blow effects. During the alloy pouring process, the ladle car is slightly started to shake the ladle to avoid alloy caking.

[0056] During the early heating stage of LF refining, 0.7 kg of aluminum particles per ton of steel are added on the slag surface to remove oxygen in the slag and improve the desulfurization efficiency. In the middle and late stages, ferrosilicon powder is added on the slag surface for diffusion deoxidation to reduce the slag basicity and prevent the titanium content in the molten steel from increasing. The addition amount of ferrosilicon powder is 2.2 kg per ton of steel, and the final slag has an R value of 4.5 and an Al2O3 content of 27%. The refining treatment time is 97 minutes, and the molten steel is further processed by the RH vacuum process to remove the gas content in the steel. No calcium treatment is carried out after the RH treatment. The residual element P content in the finished product is 0.011%, the S content is 0.003%, the Ti content is 0.0018%, and the Al content is 0.013%. The rest are the main element content of the electroslag steel and inevitable impurity elements.

[0057] The molten steel treated is cast into a large bloom with an end face size of 280 mm × 325 mm. The tundish is heated by electromagnetic induction, and the tundish superheat is 24°C. For the stopper rod, the argon blowing amount of the argon blowing stopper rod is adjusted to make the liquid level in the mold bubble slightly to ensure the argon blowing effect of the stopper rod. After starting casting, the steel is poured with a small flow rate, and the casting speed is quickly increased to 0.78 m / min. A ferrous powder spraying device is added at the billet cutting position to increase the cutting strength and ensure the smooth cutting of the billet. After the large bloom is cut, it is directly put into the slow cooling pit. (The tail furnace billets of the previous casting are put into the slow cooling pit to warm, and the head furnace billets of the next casting are put into the slow cooling pit to warm. The head furnace billets of the next casting are placed on the H13 billets for pressing.) The billet temperature when entering the pit is 689°C. After the large bloom is slowly cooled for 48 hours, the cover is removed, and it is cooled to 89°C and taken out of the slow cooling pit.

[0058] The total oxygen content of the high-performance hot work die steel for electroslag obtained in this example is 11.3 ppm, and the DS type inclusion grade is 1.5.

[0059] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made in these embodiments without departing from the principles and spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A method for producing large billets of high-cleanliness hot work die steel by a converter continuous caster, characterized in that, It includes the following steps: S1 Alloy baking; S2 Twin-slag semi-steel smelting: The hot metal is pretreated by desulfurization. After desulfurization, the mass content of S in the hot metal is ≤0.005%. First, 4%-7% of the total charged mass of scale is added into the dephosphorization converter, and then the desulfurized hot metal is charged. During the blowing process, 10 kg - 20 kg of lime slag material per ton of iron is added. After the twin-slag process, the mass content of P in the semi-steel is ≤0.025%, and S is ≤0.008%; S3 Twin-slag decarburization process; S4 Steelmaking alloying; S5 Refining process: S6 Continuous casting process.

2. The method for producing large bloom of high-cleanliness hot work die steel by a converter continuous caster according to claim 1, characterized in that, The specific steps of S1 are as follows: Before production, low-titanium high-carbon ferrochrome is placed in a clean ladle without ladle edge. The mass content of titanium is ≤0.03%, and 6% ≤ the mass content of carbon ≤ 10%. The alloy is baked using gas. Before the alloy is put into use, the alloy baking temperature is ≥600°C.

3. The method for producing large billets of high cleanliness hot work die steel by a converter continuous casting machine according to claim 1, characterized in that, In S2, the scale added into the dephosphorization converter first is all the scale generated from the production of aluminum-killed steel, and the mass content of S in the scale is ≤0.008%.

4. A method for producing large billets of high-cleanliness hot work die steel by a converter continuous caster, characterized in that, The specific steps of S3 are as follows: The semi-steel hot metal is charged into the decarburization converter. After the converter is charged with hot metal, ferromolybdenum is added into the furnace. First, the hot metal is charged and then ferromolybdenum is added. 4 - 6 kg of ferrosilicon per ton of iron is added into the furnace. During the blowing process, 20 kg - 30 kg of lime per ton of iron and 3 kg - 5 kg of fluorite per ton of iron are added. The end-point temperature is controlled at 1620°C - 1660°C, and the end-point mass percentage of P is ≤0.005%, and S is ≤0.010%.

5. The method for producing large bloom of high cleanliness hot work die steel by a converter continuous caster according to claim 1, characterized in that The specific steps of S4 are as follows: During the steelmaking process, aluminum is added into the ladle for deoxidation. The total aluminum mass content in the LF molten steel is 0.020% - 0.040%. Then ferrosilicon manganese alloy is added for alloying. During the period when 1 / 3 - 3 / 4 of the converter steel output is reached, low-alkalinity titanium-controlled refining synthetic slag and lime are added to control the final slag basicity RCaO / SiO2 to be 4.0 - 7.

0. The synthetic slag consists of the following components by weight percentage: CaO 30 - 50%, SiO2 10 - 15%, Al2O3 5 - 20%, MgO ≤ 3%. At the same time, the mass content of TiO2 in the components is controlled to be ≤0.1%, and CaF2 is ≤1%. The balance is inevitable impurities. The addition amount of the synthetic slag is 10 - 17 kg per ton of steel. After the steelmaking is completed, the low-titanium high-carbon ferrochrome baked by the ladle is poured into the ladle. The mass content of titanium in the low-titanium high-carbon ferrochrome baked by the ladle is ≤0.03%.

6. A method for producing large billets of high cleanliness hot work die steel by a converter continuous caster, characterized in that, The specific steps of S5 are as follows: During the LF treatment refining process, alloys are added for fine-tuning of chemical components. During the early heating process, 0.5 - 1.5 kg of aluminum pellets per ton of steel are sprinkled on the slag surface to remove the oxygen in the slag. In the middle and late stages, ferrosilicon powder is added to the slag liquid surface for diffusion deoxidation, and the addition amount is 0.5 - 2.5 kg per ton of steel. The final slag R is controlled to be 2.5 - 5.0, and the mass content of Al2O3 is controlled to be 17 - 35%; The refining treatment time is 60 - 100 min. The RH vacuum process is used to further remove the gas content in the steel. After the RH treatment, no calcium treatment is carried out; The mass content of residual elements in the finished product is P ≤ 0.010%, S ≤ 0.003%, Ti ≤ 0.0020%, 0.010% ≤ Al ≤ 0.020%, and the rest are the main element content of H13 and inevitable impurity elements.

7. A method for producing large billets of high-cleanliness hot work die steel by a converter continuous caster, characterized in that, The specific steps of S6 are as follows: the tundish is heated by electromagnetic induction, the superheat of the tundish is stably controlled at 15 - 25 °C, the casting speed is increased to 0.6 - 0.8 m / min, an iron powder injection device is added at the billet cutting position, the bloom is directly put into the slow cooling pit after cutting, the last furnace billet of the previous casting is put into the slow cooling pit for warming, the billet entry temperature is ≥600 °C, the bloom is slowly cooled for 48 h and then the cover is removed, and it is taken out of the slow cooling pit after being cooled to below 100 °C.

8. A method for producing large billets of high-cleanliness hot work die steel by a converter continuous caster, characterized in that, In S6, the molten steel after being treated is cast into a bloom with an end face size of 280 mm × 325 mm.