Electroslag remelting method for smelting high-cleanliness hot-working die steel

Abstract

The invention discloses an electroslag remelting method for smelting high-cleanliness hot-working die steel in the field of steel smelting technology. The electroslag remelting slag system mainly includes the following chemical components in mass percentage: CaF2: 60%-65%, Al2O3: 20%-25%, CaO: 5-10%, MgO: 1-5%. The smelting process includes the following steps: firstly, slag is weighed according to the proportion, and the mixed slag is dried, then aluminum particles are mixed into the slag according to the mass fraction of 0.375%-0.450%, and finally the slag is filled and arc smelting is started. During the smelting process, aluminum particles and silicon calcium powder are added at regular intervals for deoxidation. The invention improves the basicity of the slag system and strengthens the desulfurization capacity of the slag system by adding appropriate amounts of CaO and MgO. When mixing the slag, adding appropriate amounts of aluminum particles and adding a certain amount of aluminum particles at regular intervals can produce stable oxide Al2O3 in the remelting process, effectively remove oxygen elements, improve the cleanliness of the hot-working die steel electroslag remelting product, and reduce the production cost.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting, and in particular to an electroslag remelting method for smelting high-cleanliness hot-working die steel. Background Art

[0002] At present, the hot working die steel mainly used in my country is the national standard H13 (4Cr5MoSiV1). The H13 series steel is C-Cr-Mo-Si-V martensitic hot working die steel, which is widely used in the manufacture of hot extrusion dies, die-casting dies, hot trimming dies, hot forging dies and hot stamping dies. During its use, it is subjected to physical and chemical effects such as wear, thermal fatigue, erosion, stress corrosion, and surface heat welding, so there are high requirements for its cleanliness and quality control. At present, in the traditional industrial smelting process, in order to further obtain high-cleanliness and uniform and dense steel ingots, the electroslag remelting process is used to reduce harmful elements and inclusions in the steel. However, the "37 slag" is generally used in the electroslag remelting process, that is, 30% Al2O3 and 70% CaF2 by mass fraction. Its disadvantage is that it is difficult to effectively reduce the oxygen and sulfur content in the molten steel and remove inclusions. At the same time, due to the high content of calcium fluoride in the slag, it is easy to volatilize during smelting production, pollute the atmosphere, and change the slag composition, reducing its stability. Summary of the invention

[0003] In order to overcome the above-mentioned deficiencies of the existing electroslag remelting of hot working die steel, the technical problem to be solved by the present invention is to provide a more environmentally friendly and efficient electroslag remelting method for smelting high-cleanliness hot working die steel.

[0004] The technical solution adopted by the present invention to solve its technical problem is:

[0005] The electroslag remelting method for smelting high-cleanliness hot-working die steel is characterized in that the electroslag remelting slag used for smelting mainly includes the following chemical components in mass percentage: CaF2: 60% to 65%, Al2O3: 20% to 25%, CaO: 5 to 10%, MgO: 1 to 5%, and the smelting process includes the following steps:

[0006] Step 1: Before smelting, weigh the slag according to the proportion and dry the mixed slag;

[0007] Step 2: After baking, aluminum particles are mixed into the slag system at a mass fraction of 0.375% to 0.450%;

[0008] Step 3: Fill the slag and start arc smelting, control the current of the electroslag remelting furnace between 7500 and 12000A, keep the current stable, the maximum current fluctuation does not exceed 700A, control the voltage between 50 and 60V, and the maximum voltage fluctuation does not exceed 10V;

[0009] Step 4. During the electroslag remelting process, add aluminum particles with a mass fraction of 0.042% to 0.052% and calcium silicon powder with a mass fraction of 0.021% to 0.026% every 4 to 6 minutes for deoxidation. The melting rate is controlled at 4.5 to 6.0 kg / min. The water temperature of the crystallizer is controlled between 40 and 60 degrees Celsius during smelting. After the smelting is completed, annealing and sampling are carried out to obtain a hot working die steel electroslag remelting product with low oxygen and low sulfur content.

[0010] Furthermore, the electrode rod base material for smelting mainly includes the following chemical components in mass percentage: C: 0.37%~0.43%, Si: 0.90%~1.20%, Mn: 0.30%~0.50%, P: ≤0.020%, S: ≤0.005%, Cr: 4.95%~5.50%, Mo: 1.20%~1.75%, V: 0.90%~1.10%, and the remainder of Fe and impurities.

[0011] Furthermore, the electrode rods need to be subjected to a tumbling treatment before smelting to remove the iron oxide scale on the surface of the electrode rods.

[0012] Furthermore, when the slag is weighed in step 1, the mass of the slag is 9.5% to 10% of the mass of the electroslag remelting electrode rod.

[0013] Furthermore, when the slag is dried, the baking temperature is 700-800° C. and the baking time is not less than 7 hours.

[0014] Furthermore, when the slag is filled in step three, the filling time is controlled within 30 to 50 minutes.

[0015] The beneficial effects of the present invention are:

[0016] 1. By providing appropriate slag composition and stable voltage and current, the high temperature stability of slag during electroslag remelting is enhanced, making it less likely to decompose and transfer oxygen to the molten steel;

[0017] 2. Adding appropriate amount of CaO and MgO increases the basicity of the slag system, promotes the transformation of sulfide inclusions, and enhances the desulfurization capacity of the slag system;

[0018] 3. Adding an appropriate amount of aluminum particles when mixing the slag and adding a certain amount of aluminum particles at regular intervals can produce stable oxide Al2O3 during the remelting process and effectively remove oxygen elements;

[0019] 4. By effectively removing oxygen and sulfur elements from the steel ingot, the cleanliness of the hot working die steel electroslag remelting product is improved, the content of harmful elements, gas elements and non-metallic inclusions in the steel is low, and the production cost is also reduced. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with embodiments.

[0021] The electroslag remelting method for smelting high-cleanliness hot-working die steel, wherein the electroslag remelting slag used for smelting mainly includes the following chemical components in mass percentage: CaF2: 60% to 65%, Al2O3: 20% to 25%, CaO: 5 to 10%, MgO: 1 to 5%, and the smelting process includes the following steps:

[0022] Step 1: Before smelting, weigh the slag according to the proportion and dry the mixed slag;

[0023] Step 2: After baking, aluminum particles are mixed into the slag system at a mass fraction of 0.375% to 0.450%;

[0024] Step 3: Fill the slag and start arc smelting, control the current of the electroslag remelting furnace between 7500 and 12000A, keep the current stable, the maximum current fluctuation does not exceed 700A, control the voltage between 50 and 60V, and the maximum voltage fluctuation does not exceed 10V;

[0025] Step 4. During the electroslag remelting process, add aluminum particles with a mass fraction of 0.042% to 0.052% and calcium silicon powder with a mass fraction of 0.021% to 0.026% every 4 to 6 minutes for deoxidation. The melting rate is controlled at 4.5 to 6.0 kg / min. The water temperature of the crystallizer is controlled between 40 and 60 degrees Celsius during smelting. After the smelting is completed, annealing and sampling are carried out to obtain a hot working die steel electroslag remelting product with low oxygen and low sulfur content.

[0026] Compared with the existing "37 slag" electroslag remelting process, this application reduces the content of CaF2 and Al2O3, and adds appropriate amounts of CaO and MgO to improve the slag system composition, which can increase the basicity of the slag system, promote the conversion of sulfide inclusions, and thus enhance the desulfurization capacity of the slag system; in addition, adding an appropriate amount of aluminum particles when mixing the slag, and adding a certain amount of aluminum particles at regular intervals in the subsequent smelting, can produce stable oxide Al2O3 during the remelting process, effectively removing oxygen elements; finally, with stable voltage and current, the high-temperature stability of the slag during the electroslag remelting process is enhanced, making it less likely to decompose and transfer oxygen to the molten steel. Through the combination of the above-mentioned multiple processes, this application can effectively remove oxygen and sulfur elements in the steel ingot, improve the cleanliness of the finished product of the electroslag remelting of hot working die steel, and reduce the content of harmful elements, gas elements and non-metallic inclusions in the steel, while controlling production costs.

[0027] For the electrode rod base material in the electroslag remelting process, the present application adopts the traditional electrode rod base material, which mainly includes the following chemical compositions by mass percentage: C: 0.37% to 0.43%, Si: 0.90% to 1.20%, Mn: 0.30% to 0.50%, P: ≤0.020%, S: ≤0.005%, Cr: 4.95% to 5.50%, Mo: 1.20% to 1.75%, V: 0.90% to 1.10%, and the balance is Fe and impurities. In order to avoid the introduction of oxygen elements, the electrode rod needs to be tumbled before smelting to remove the iron oxide scale on the surface of the electrode rod.

[0028] Before smelting, the following preferred options are also included:

[0029] When weighing the slag in step 1, the mass of the slag is preferably 9.5% to 10% of the mass of the electroslag remelting electrode rod, which is convenient for controlling the smelting efficiency and production cost. To ensure the drying effect of the slag, when drying the slag, the baking temperature is preferably 700 to 800°C, and the baking time is not less than 7 hours. When filling the slag in step 3, the filling time is controlled within 30 to 50 minutes to avoid inhaling too much impurities in the air for too long.

[0030] The present invention is further described below by means of specific examples.

[0031] Embodiment 1:

[0032] The high-end hot-working die steel electrode rod is smelted by electroslag remelting. The chemical composition of the hot-working die steel electrode rod base material for electroslag remelting is as follows by mass percentage: C: 0.39%, Si: 0.97%, Mn: 0.48%, P: 0.015%, S: 0.008%, Cr: 5.00%, Mo: 1.45%, V: 1.02%, and the rest is Fe and impurities. The electrode rod is tumbled before smelting to remove the oxide scale on the surface of the electrode rod, and the surface of the electrode rod is smooth and rust-free.

[0033] Before mixing the slag, the various raw materials of the slag were baked at a temperature of 760 degrees Celsius for 7.5 hours to completely remove the moisture in the slag. The mass of the slag is 9.6% of the mass of the electroslag remelting electrode rod. The composition of the electroslag remelting slag is calculated by mass percentage: CaF2: 65%, Al2O3: 25%, CaO: 5%, MgO; 5%.

[0034] After the baked slag system is stirred evenly, 0.380% of aluminum particles by mass are added, and the secondary stirring is performed to ensure that the aluminum particles are fully mixed into the slag, and then filling is performed, and the filling time is controlled within 45 minutes. After that, the arc is started and smelting begins. The current of the electroslag remelting furnace is controlled between 10000-10500A, and the current is kept stable. The maximum current fluctuation does not exceed 500A, and the voltage is controlled between 50-60V, and the maximum voltage fluctuation does not exceed 10V.

[0035] During the electroslag remelting process, 0.049% aluminum particles by mass are added for deoxidation and 0.022% calcium silicon powder by mass are added every 4 minutes. The melting rate is controlled at 5.5kg / min, and the water temperature of the crystallizer is controlled between 40-55 degrees Celsius during smelting. After the smelting is completed, annealing is carried out and sampling is performed to obtain a low-oxygen and low-sulfur hot working die steel electroslag remelting product. The finished electroslag ingot is sampled, and its oxygen content is 12ppm and its sulfur content is 7ppm. It is made into a metallographic sample and analyzed by ASPEX, and its oxide inclusions are 7.34 / mm 2 .

[0036] Embodiment 2:

[0037] The high-end hot-working die steel electrode rod is smelted by electroslag remelting. The chemical composition of the hot-working die steel electrode rod base material for electroslag remelting is calculated by mass percentage: C: 0.43%, Si: 0.96%, Mn: 0.35%, P: 0.018%, S: 0.010%, Cr: 5.03%, Mo: 1.55%, V: 0.97%, and the balance is Fe and impurities. The electrode rod is tumbled before smelting to remove the oxide scale on the surface of the electrode rod, and the surface of the electrode rod is smooth and rust-free.

[0038] Before mixing the slag, the various raw materials of the slag were baked at a temperature of 780 degrees Celsius for 8 hours to completely remove the moisture in the slag. The mass of the slag is 9.8% of the mass of the electroslag remelting electrode rod, and the electroslag remelting slag system is composed of CaF2: 64.5%, Al2O3: 24%, CaO: 7.5%, MgO; 4%.

[0039] After the baked slag system is stirred evenly, 0.415% of aluminum particles are added therein, and stirred twice to ensure that the aluminum particles are fully mixed into the slag before filling, and the filling time is controlled within 42 minutes. After that, the arc is started and smelting begins. The current of the electroslag remelting furnace is controlled between 7600-8200A, and the current is kept stable. The maximum current fluctuation does not exceed 600A. The voltage is controlled between 50-60V, and the maximum voltage fluctuation does not exceed 10V.

[0040] During the electroslag remelting process, 0.043% aluminum particles and 0.026% calcium silicon powder are added every 5 minutes for deoxidation. The melting rate is controlled at 4.8kg / min, and the water temperature of the crystallizer is controlled between 45-60 degrees Celsius during smelting. After the smelting is completed, annealing and sampling are carried out to obtain a low-oxygen and low-sulfur hot working die steel electroslag remelting product. The finished electroslag ingot is sampled, and its oxygen content is 10ppm and its sulfur content is 8ppm. It is made into a metallographic sample and analyzed by ASPEX, and its oxide inclusions are 5.58 / mm 2 .

[0041] Embodiment 3:

[0042] The high-end hot-working die steel electrode rod is smelted by electroslag remelting. The chemical composition of the hot-working die steel electrode rod base material for electroslag remelting is as follows by mass percentage: C: 0.44%, Si: 0.99%, Mn: 0.38%, P: 0.015%, S: 0.012%, Cr: 5.15%, Mo: 1.28%, V: 1.07%, and the balance is Fe and impurities. The electrode rod is tumbled before smelting to remove the oxide scale on the surface of the electrode rod, and the surface of the electrode rod is smooth and rust-free.

[0043] Before mixing the slag, the various raw materials of the slag were baked at 800 degrees Celsius for 8 hours to completely remove the moisture in the slag. The mass of the slag is 10% of the mass of the electroslag remelting electrode rod, and the electroslag remelting slag system is composed of CaF2: 63.9%, Al2O3: 24.1%, CaO: 8%, MgO; 4%.

[0044] After the baked slag system is stirred evenly, 0.446% aluminum particles are added therein, and stirred twice to ensure that the aluminum particles are fully mixed into the slag before filling, and the filling time is controlled within 37 minutes. After that, the arc is started and smelting begins. The current of the electroslag remelting furnace is controlled between 9800-10300A, and the current is kept stable. The maximum current fluctuation does not exceed 500A. The voltage is controlled between 50-60V, and the maximum voltage fluctuation does not exceed 10V.

[0045] During the electroslag remelting process, 0.050% aluminum particles and 0.023% calcium silicon powder are added every 6 minutes for deoxidation. The melting rate is controlled at 5.8kg / min, and the water temperature of the crystallizer is controlled between 55-60 degrees Celsius during smelting. After the smelting is completed, annealing and sampling are carried out to obtain a low-oxygen and low-sulfur hot working die steel electroslag remelting product. The finished electroslag ingot is sampled, and its oxygen content is 9ppm and its sulfur content is 5ppm. It is made into a metallographic sample and analyzed by ASPEX, and its oxide inclusions are 4.98 / mm 2 .

[0046] Comparative Example 1:

[0047] The high-end hot working die steel electrode rod is smelted by electroslag remelting. The chemical composition of the hot working die steel electrode rod base material for electroslag remelting is as follows by mass percentage: C: 0.44%, Si: 0.99%, Mn: 0.38%, P: 0.015%, S: 0.012%, Cr: 5.15%, Mo: 1.28%, V: 1.07%, and the balance is Fe and impurities.

[0048] Before mixing the slag, the various raw materials of the slag were baked at 800 degrees Celsius for 8 hours to completely remove the moisture in the slag. The mass of the slag is 10% of the mass of the electroslag remelting electrode rod, and the electroslag remelting slag system composition is calculated by mass percentage: CaF2: 69.4%, Al2O3: 30.6.

[0049] After the baked slag system is stirred evenly, arc is started and smelting begins. The current of the electric slag remelting furnace is controlled between 10000-10500A and the current is kept stable. The maximum current fluctuation does not exceed 500A. The voltage is controlled between 50-60V and the maximum voltage fluctuation does not exceed 10V.

[0050] During the electroslag remelting process, the melting rate is controlled at 5.8kg / min, and the water temperature of the crystallizer is controlled between 55-60 degrees Celsius during smelting. After the smelting is completed, annealing is carried out and sampling is performed to obtain the electroslag remelting product of low-oxygen and low-sulfur hot working die steel. The finished electroslag ingot is sampled, and its oxygen content is 29ppm and its sulfur content is 25ppm. It is made into a metallographic sample and analyzed by ASPEX. The oxide inclusions are 34.02 / mm 2 .

[0051] Comparative Example 2:

[0052] The high-end hot working die steel electrode rod is smelted by electroslag remelting. The chemical composition of the hot working die steel electrode rod base material for electroslag remelting is as follows by mass percentage: C: 0.44%, Si: 0.99%, Mn: 0.38%, P: 0.015%, S: 0.012%, Cr: 5.15%, Mo: 1.28%, V: 1.07%, and the balance is Fe and impurities.

[0053] Before mixing the slag, the various raw materials of the slag were baked at 800 degrees Celsius for 8 hours to completely remove the moisture in the slag. The mass of the slag is 10% of the mass of the electroslag remelting electrode rod, and the electroslag remelting slag system composition is calculated by mass percentage: CaF2: 69.4%, Al2O3: 30.6.

[0054] After the baked slag system is stirred evenly, arc is started and smelting begins. The current of the electric slag remelting furnace is controlled between 10000-10500A and the current is kept stable. The maximum current fluctuation does not exceed 500A. The voltage is controlled between 50-60V and the maximum voltage fluctuation does not exceed 10V.

[0055] During the electroslag remelting process, the melting rate is controlled at 5.8kg / min, and the water temperature of the crystallizer is controlled between 55-60 degrees Celsius during smelting. After the smelting is completed, annealing is carried out and sampling is performed to obtain the electroslag remelting product of low-oxygen and low-sulfur hot working die steel. The finished electroslag ingot is sampled, and its oxygen content is 25ppm and its sulfur content is 15ppm. It is made into a metallographic sample and analyzed by ASPEX. The oxide inclusions are 32.42 / mm 2 .

[0056] It can be seen from Examples 1-3 and Comparative Examples 1-2 that the present invention obtains a hot working die steel with low oxygen, low sulfur content and high cleanliness by providing a suitable electroslag remelting slag system and combining it with an appropriate deoxidation system, and the oxygen content is stably controlled to be less than 15ppm and the sulfur content to be less than 10ppm.

Claims

1. The electroslag remelting method for smelting high-cleanliness hot-working die steel is characterized by: The electroslag remelting slag used for smelting has the following chemical composition by mass percentage: CaF2: 60%~65%, Al2O3: 20%~25%, CaO: 5~10%, MgO: 1~5%. The smelting process includes the following steps: Step 1: Before smelting, weigh the slag according to the proportion and dry the mixed slag; Step 2: After baking, aluminum particles are mixed into the slag system at a mass fraction of 0.375% to 0.450%; Step 3: Fill the slag and start arc smelting, control the current of the electroslag remelting furnace between 7500~12000A, keep the current stable, the maximum current fluctuation does not exceed 700A, control the voltage between 50~60V, and the maximum voltage fluctuation does not exceed 10V; Step 4: During the electroslag remelting process, 0.042% to 0.052% aluminum particles and 0.021% to 0.026% calcium silicon powder are added every 4 to 6 minutes for deoxidation, the melting rate is controlled at 4.5 to 6.0 kg / min, and the water temperature of the crystallizer is controlled between 40 and 60 degrees Celsius during smelting. After the smelting is completed, annealing and sampling are performed to obtain a hot working die steel electroslag remelting product with low oxygen and low sulfur content; The electrode rod base material used for smelting includes the following chemical compositions in mass percentage: C: 0.37%~0.43%, Si: 0.90%~1.20%, Mn: 0.30%~0.50%, P: ≤0.020%, S: ≤0.005%, Cr: 4.95%~5.50%, Mo: 1.20%~1.75%, V: 0.90%~1.10%, and the balance is Fe and impurities.

2. The electroslag remelting method for smelting high-cleanliness hot-working die steel according to claim 1, characterized in that: Before smelting, the electrode rods need to be tumbled to remove the iron oxide scale on the surface of the electrode rods.

3. The electroslag remelting method for smelting high-cleanliness hot-working die steel according to claim 1, characterized in that: When the slag is weighed in step 1, the mass of the slag is 9.5% to 10% of the mass of the electroslag remelting electrode rod.

4. The electroslag remelting method for smelting high-cleanliness hot-working die steel according to claim 1, characterized in that: When the slag is dried, the baking temperature is 700~800℃ and the baking time is not less than 7 hours.

5. The electroslag remelting method for smelting high-cleanliness hot-working die steel according to claim 1, characterized in that: When filling the slag in step three, the filling time is controlled within 30 to 50 minutes.