CN107488788A - A kind of special slag system and its preparation and application for being used to produce 17 4PH steel ingots - Google Patents

Abstract

A special slag system for producing 17-4PH steel ingots, the special slag system is composed of the following components by weight percentage: Al ₂ O ₃ : 26~28%, CaO: 25~27%, SiO ₂ : 4~5% , MgO: 5~6%, the balance is CaF ₂ ; its binary basicity CaO/SiO ₂ is 5~6.75; the melting hemisphere temperature of this special slag system is 1220~1250℃; 0.402~0.434Ω·cm. The viscosity at 1500°C is 0.0352~0.0359 Pa·s. The slag system of the present invention has low melting point, high resistivity, small viscosity change with temperature, good high-temperature plasticity, high alkalinity, low fluoride content, fast slag melting speed, and can meet the requirements of ingot-pulling electroslag remelting The requirements for the production of 17-4PH steel ingots by law can guarantee the internal quality and surface quality of 17-4PH steel ingots, and have the advantages of energy saving and environmental protection.

Description

A special slag system for producing 17-4PH steel ingot and its preparation and use method

technical field

The invention belongs to the field of iron and steel smelting, and in particular relates to a special energy-saving and environment-friendly slag system for producing 17-4PH steel ingots and a preparation and use method thereof.

Background technique

17-4PH alloy is a precipitation-hardening martensitic stainless steel. Due to its strong compressive strength, corrosion resistance and radiation resistance, it is widely used in aerospace turbine blades, offshore platforms, helicopter decks, nuclear fuel waste barrels, etc. field.

The composition of 17-4PH alloy is characterized by high content of Cr, Cu, Ni, Nb and other alloying elements, among which the Cr content is 15.0%~17.5%, the Ni content is 3%~5%, and the Cu content is 3%~5%. %, Nb content is 0.20%~0.45%. However, since the 17-4PH alloy contains a large amount of alloying elements such as Cu and Cr, the viscosity of the steel is relatively high, and the fluidity of the molten steel during the smelting process is very poor, which makes the solidification quality of the 17-4PH steel ingot poor and prone to cracking. Serious internal quality problems such as inclusions, shrinkage cavities, porosity, and segregation can easily cause surface quality problems such as surface wrinkles and slag grooves on the ingot. In view of the difficulty in the smelting process of this steel, the 17-4PH steel ingot is generally prepared by electroslag remelting method, which is because electroslag remelting method can realize the separation of pouring and solidification process, which can ensure the secondary refining of molten steel The purity of the molten steel can also ensure the compactness of the solidified structure of the steel ingot under the forced cooling of the water-cooled crystallizer. At the same time, the slag skin between the steel ingot and the crystallizer during the electroslag remelting process can play a better role in lubrication. Thereby ensuring the surface quality of the steel ingot. In order to ensure that the steel ingot has excellent internal quality and surface quality when electroslag remelting 17-4PH alloy, it is necessary to have a special pre-melted slag system suitable for this steel type. This slag system needs to meet the low melting point and high viscosity. low feature.

At present, the slag system required for steel production is basically a combination of Al ₂ O ₃ , CaO, SiO ₂ , MgO and CaF ₂ , but different ratios are suitable for the production of different steel ingots. For the production of 17-4PH alloy by the electroslag remelting method, the conventional slag system has high power consumption and low resistivity, which cannot meet the lubrication function, resulting in nodules, slag grooves, heavy skin and other surfaces on the surface of the steel ingot Quality defects. At the same time, the viscosity of traditional slag systems is prone to sudden changes with temperature changes within a certain temperature range. The above defects will affect the cost and quality of 17-4PH steel ingots.

Therefore, it is an urgent problem to develop a special slag system for producing 17-4PH steel ingot and its preparation and use method, so that it can meet the characteristics of energy saving, environmental protection, low melting point and low viscosity.

Contents of the invention

In view of the problems existing in the smelting of 17-4PH steel ingots and the requirements for the slag system, the purpose of the present invention is to provide a special slag system for producing 17-4PH steel ingots and its preparation and use method. The special slag system has a low Melting point, energy saving, and good fluidity. By adjusting the composition of the slag system, the melting point of the slag system is reduced and the electrical conductivity is increased. The rate of change of viscosity with temperature is small, and it has excellent high-temperature plasticity. Based on the traditional ingot-drawing slag system (60%CaF ₂ +20%CaO+20%Al ₂ O ₃ ), the present invention increases the proportion of CaO, the main purpose of which is to reduce the melting point of slag, so as to save energy and reduce consumption. Purpose; but after the amount of CaO increases, the slag easily absorbs moisture in the air to increase the hydrogenation of molten steel, so the proportion of MgO is also increased. This is because MgO will produce a dense film after melting, which can prevent moisture absorption. The increase of MgO will increase the viscosity of the slag and reduce the fluidity. In order to reduce the viscosity of the slag, the SiO ₂ content in the slag is increased. Another function of SiO ₂ is to increase the lubricity and high temperature strength of slag, which is conducive to the smooth progress of the ingot drawing process. Compared with the traditional ingot pumping slag system, the CaF ₂ content in the slag system of the present invention is lower, which reduces fluoride volatilization in the smelting process and reduces environmental pollution.

The object of the present invention is achieved like this: a kind of special-purpose slag system for producing 17-4PH steel ingot, the composition of this special-purpose slag system is _Al2O3 : ₂₆ ～28%, CaO: 25～27%, SiO ₂ : 4~5%, MgO: 5~6%, CaF ₂ content 34~40%, binary alkalinity between 5~6.75.

Preferably, the special slag is composed of the following components by weight percentage: Al ₂ O ₃ : 26.2%, CaO: 25.7%, SiO ₂ : 4.89%, MgO: 5.2%, and the balance is CaF ₂ ; The degree of CaO/SiO ₂ is 5.25.

Preferably, the special slag is composed of the following components by weight percentage: Al ₂ O ₃ : 27.8%, CaO: 26.9%, SiO ₂ : 4.1%, MgO: 5.9%, and the balance is CaF ₂ ; The degree CaO/SiO ₂ is 6.5.

The melting hemisphere temperature of this special slag system is 1220~1250℃.

The special slag is used to produce precipitation-hardening martensitic stainless steel 17-4PH steel ingot by ingot-pulling electroslag remelting method.

The specific slag system has a resistivity of 0.402~0.434Ω•cm at 1600°C and a viscosity of 0.0352~0.0359 Pa•s at 1500°C.

A method for preparing a special slag system for producing 17-4PH steel ingots, the preparation method includes the following steps: after mixing fluorite, quicklime, alumina, fused magnesia and silica in proportion, melting and stirring evenly, Melting at 1500~1560℃ for more than 40min.

Then pour it into a water-cooled slag tray made of steel plates, cool it to room temperature, and crush it to a particle size of 5-10mm to make a special slag system for the production of 17-4PH steel ingots with the above-mentioned composition content.

A method for using a special slag system for producing 17-4PH steel ingots. The method includes the following steps: first, bake the molten slag of the slag system of the present invention to 800°C and keep it warm for more than 10 hours; In the process, the baked special slag is heated to above 1600°C in the slag melting furnace and melted, and then refined for about 20 minutes, the liquid slag is poured into the crystallizer of the electroslag furnace, and the self-consumed electricity to be remelted The electrode is inserted into the crystallizer and then energized, so that the consumable electrode contacts the slag to form a energized circuit, and the smelting process of electroslag remelting is carried out at 17-4PH. After the electrode is melted and a molten pool is formed, the ingot extraction operation starts.

The experimental research shows that: when the slag contains 26%~28% Al ₂ O ₃ , CaO: 25~27%, SiO ₂ : 4~5%, MgO: 5~6%, CaF ₂ : 34~40% , which can not only ensure the high resistivity value of the slag, but also make the melting point of the slag system (that is, the temperature of the melting hemisphere) lower. The SiO ₂ content makes the slag have good high-temperature plasticity and strength, and it is not easy to break when the ingot is drawn, so that steel breakout and slag leakage accidents can be prevented, and the high alkalinity of the slag system inhibits the activity of SiO ₂ , can prevent the burning loss of easily oxidized elements. The content of CaF ₂ in this slag series is low and the content of Al ₂ O ₃ is high, so the resistivity is high, which is beneficial to reduce power consumption; the hemispherical temperature of this slag series is lower than that of ANF _{- 6} , 70%CaF ₂ ) is about 150°C lower (the hemispherical temperature of ANF-6 slag system is about 1400°C); the viscosity data of this slag system is also better than that of traditional ANF-6 slag, and the transition of viscosity with time is very smooth, Especially when the temperature reaches above 1400℃, the viscosity changes very little with the temperature. This kind of slag system can make the slag skin have a relatively stable friction coefficient and strength, so as to ensure the uniform and continuous thickness of the slag skin and improve the surface quality of the electroslag steel ingot. At the same time, it can reduce the phenomena of slag leakage and steel leakage caused by excessive slag skin friction during the ingot drawing process.

Compared with the prior art, the present invention has the following technical effects.

(1) Due to the high content of CaO and SiO ₂ , the slag system of the present invention has a lower melting point and better fluidity at the same temperature.

(2) It has the characteristics of "long slag" and good high-temperature strength, that is, the viscosity of the slag system does not change suddenly with the change of temperature within a certain temperature range, thus ensuring good high-temperature plasticity, and is suitable for ingot-type electroslag gravity furnace.

(3) Due to the high content of Al ₂ O ₃ , the resistivity of the slag system is high, and the melting point is low, and the slag melting speed is fast, which can have a good energy-saving effect.

(4) The high alkalinity can ensure the stability of easily oxidized elements in the remelting process.

(5) The content of calcium fluoride is low, which belongs to the low-fluorine slag system, which can reduce the volatilization of fluoride in the smelting process and reduce the harm to the environment.

Description of drawings

Figure 1 is a photo of the surface of an electroslag ingot produced by ingot-pulling electroslag remelting using the product of Example 1 of the present invention.

Figure 2 is a photograph of the surface of an electroslag ingot produced by ingot-pulling electroslag remelting using a traditional solid ingot pumping slag system.

Fig. 3 is the temperature-viscosity curve comparison chart of the slag system in the embodiment of the present invention and the traditional ingot pumping slag system and the traditional ANF-6 slag system; among the figure, S1 is the product of embodiment 1, and S2 is the product of embodiment 3, S3 is the traditional solid ingot pumping slag system, and ANF-6 is the traditional 70% CaF ₂ +30% Al ₂ O ₃ slag system.

detailed description

The fluorite used in the embodiment of the present invention is a high-purity fluorite block with a weight purity ≥ 98%.

The weight content of CaO in the lime used in the embodiment of the present invention is more than or equal to 92%.

The weight purity of Al ₂ O ₃ in the industrial alumina used in the examples of the present invention is ≥99%.

The weight purity of MgO in the fused magnesia used in the embodiment of the present invention is ≥98%.

The weight purity of _SiO2 in the silica used in the examples of the present invention is ≥98%.

Example 1.

High-purity fluorite block, lime, industrial alumina powder, fused magnesia and silica are used as raw materials. After mixing the prepared raw materials, electroslag furnace graphite electrode is used to slag. After all the materials are melted, the refining is continued for 40 minutes; then casting into a cast iron plate with a bottom thickness of 60mm, cooled and solidified to room temperature, crushed by a crusher, and screened out the part with a particle size of 5-10mm to obtain precipitation-hardening martensitic powder for the production of precipitation-hardening martensitic powder by the ingot-type electroslag remelting method. The pre-melted slag of the stainless steel 17-4PH steel ingot is packaged into a 10kg bag for use in the ingot pumping electroslag furnace.

The above special slag is composed of the following components by weight percentage: Al ₂ O ₃ : 26.2%, CaO: 25.7%, SiO ₂ : 4.89%, MgO: 5.2%, and the balance is CaF ₂ ; the binary basicity of the slag is CaO/ _SiO2 is 5.25.

Using the above-mentioned pre-melted slag in the 300kg multifunctional electroslag furnace test of the Institute of Special Steel Metallurgy, Northeastern University, first bake the slag of the slag system of the present invention to 800 ° C, and keep it warm for more than 10 hours; during the electroslag remelting process, Heat the baked special slag system to above 1600°C in the slag melting furnace and melt it, then refine it for about 20 minutes, pour the liquid slag into the crystallizer of the electroslag furnace, insert the consumable electrode to be remelted After the crystallizer is energized, the consumable electrode and the slag are in contact to form a energized circuit, and the smelting process of electroslag remelting is carried out at 17-4PH. After the electrode is melted and a molten pool is formed, the ingot extraction operation starts.

During electroslag remelting, the amount of pre-melted slag is calculated to ensure that the height of the slag pool is 260~280mm, which is 240~260kg/furnace steel, the voltage is 63~68V, the current is 18~20kA, and the melting rate is 800~970kg/h , the controlled casting speed of the smelting furnace used is 10~12 mm/min; the consumable electrode is produced by AOD furnace and rolled, with a diameter of Φ160mm; the size of the prepared electroslag ingot is Φ450mm, and the end steel ingot The surface quality is good, without slag grooves, nodules, heavy skin, wrinkles, slag inclusions and other defects, and the total weight content of non-metallic inclusions is reduced by 69%. The surface photo of the prepared electroslag ingot is shown in Figure 1.

1. Screening process of Al ₂ O ₃ content.

Based on the content of Example 1, the content of CaO, SiO ₂ , and MgO was fixed, and Al ₂ O ₃ with different content ( ₂₀ ~30%) was added, and the balance was CaF ₂ . The physical parameters of slag under _O3 content are shown in Table 1.

The results show that when the content of Al ₂ O ₃ is 26-28%, the resistivity and hemisphere temperature can meet the requirements of producing 17-4PH.

2. Screening of CaO content.

Based on the content of Example 1, the content of Al ₂ O ₃ , SiO _{2 , and} MgO was fixed, and CaO with different content (20~30%) was added, and the balance was CaF ₂ . The physical parameters of the slag are shown in Table 2.

The results show that when the CaO content is 25-27%, the resistivity is higher and the melting hemisphere temperature is lower, which can meet the requirements of energy saving and consumption reduction when smelting 17-4PH.

3. The screening process of SiO ₂ content.

Based on the content of Example 1, fix the content of Al ₂ O ₃ , CaO, and MgO, add SiO ₂ with different content ( ₂ ~6%), and the balance is CaF ₂ , and detect the resistivity and hemispherical temperature. See Table 3 for the physical parameters of the slag at different concentrations.

The results show that when the SiO ₂ content is 4-5%, it has good high-temperature plasticity and strength, which meets the requirements for the production of 17-4PH.

Example 2.

The pre-melted slag electroslag remelted 0Cr17Ni4Cu4Nb steel (namely 17-4PH) smelted in the above example 1 was used for production in a 1.5-ton electroslag furnace of an enterprise in Jiangsu.

During the electroslag remelting this time, the pre-melted slag was directly placed in the crystallizer of the electroslag furnace, and the solid slag starting process was adopted. The amount of slag used this time was 30kg, and the slag melting time was 30min. During smelting, the voltage is 57V-58V, the current is 6800A-7500A, the crystallizer specification is Ф330mm, and the electrode rod is a 205mm square rod forged by intermediate frequency furnace + refining furnace process. The actual remelting melts a 700kg steel ingot, and the melting time is 3 hours.

The surface quality of the finished electroslag ingot is good, without obvious defects such as slag grooves and nodules, and the content of S and P is low. Compared with the electrode material, the content of non-metallic inclusions in the electroslag ingot is reduced by about 65%.

Example 3.

Mix fluorite, quicklime, alumina, fused magnesia, and silica in proportion, melt and stir evenly, and melt at 1500~1560°C for 43 minutes; then pour it into a water-cooled slag pan made of steel plate, and cool to At room temperature, crush it to a particle size of 5-10mm to make a special slag system for the production of 17-4PH steel ingots with the above-mentioned composition content. Obtain low-pollution and energy-saving pre-melted slag for producing hollow ingots by ingot-pulling electroslag remelting, pack it into a 20kg bag, and use it in an electric slag furnace.

The above-mentioned special slag is composed of the following components by weight percentage: Al ₂ O ₃ : 27.8%, CaO: 26.9%, SiO ₂ : 4.1%, MgO: 5.9%, and the balance is CaF ₂ ; the binary alkalinity of the slag is CaO /SiO ₂ is 6.5.

The above pre-melted slag was used to produce electroslag remelting 17-4PH in an enterprise in Anhui. The slag melting process was started with liquid slag, that is, the graphite electrode first melted slag, and then replaced the metal electroslag to melt steel. The process during smelting is: voltage: 48V-52V; smelting current: 13000-13500A. Melting speed is controlled at 480kg/h～520kg/h.

According to experiments, the surface quality of electroslag ingots smelted by this slag system is good, without obvious defects such as slag grooves and nodules, and the content of S and P is low. Compared with the original electrode materials, the content of class A non-metallic inclusions in electroslag ingots The content of type B non-metallic inclusions is reduced by about 57%, and the content of type C non-metallic inclusions is reduced by about 65%.

Comparative example 1.

Mix fluorite, quicklime, alumina, fused magnesia, and silica in proportion, melt and stir evenly, and smelt at 1500~1550°C for 30 minutes; then pour it into a water-cooled slag pan made of steel plate, and cool to At room temperature, it is crushed to a particle size of 3-12mm to make the ingot slag system for traditional solid ingots.

The ingot slag system for traditional solid ingots is composed of the following components by weight percentage: Al ₂ O ₃ : 20%, CaO: 19.8%, CaF ₂ : 59%, and the balance is SiO ₂ .

Mix fluorite, quicklime, alumina, fused magnesia, and silica in proportion, melt and stir evenly, and melt at 1480~1570°C for 35 minutes; then pour it into a water-cooled slag pan made of steel plate, and cool to At room temperature, crush it to a particle size of 1-10mm to make ANF-6 slag system.

ANF-6 slag is composed of the following components by weight percentage: Al ₂ O ₃ : 29%, CaF ₂ : 70%, and the balance is SiO ₂ .

Example 1, Example 3, Ingot Slag System for Traditional Solid Ingots (60%CaF ₂ , 20%Al ₂ O ₃ , 20%CaO), ANF-6 (30% Al ₂ O ₃ , 70%CaF ₂ ) The physical parameters are shown in Table 4, and the viscosity in the range of 1300~1500°C is shown in Table 5.

The results show that the performance of Examples 1 and 3, that is, the slag system of the present invention is better than that of the traditional solid ingot slag system and ANF-6.

It can be seen from the above table that the viscosity of traditional solid ingot pumping slag system and ANF-6 slag changes greatly with temperature, and the curve is shown in Figure 3. The above test was repeated using the traditional solid ingot pumping slag system (60%CaF ₂ , 20%Al ₂ O ₃ , 20%CaO). The photo of the surface of the electroslag ingot produced is shown in Figure 2. The production experiment found that the surface quality of electroslag ingots smelted by traditional slag system is poor, with obvious defects such as slag grooves and nodules, and the total weight content of non-metallic inclusions is high.

Comparative example 2.

Mix fluorite, quicklime, alumina, fused magnesia, and silica in proportion, melt and stir evenly, and melt at 1500~1560°C for 43 minutes; then pour it into a water-cooled slag pan made of steel plate, and cool to At room temperature, crush it to a particle size of 5-10mm to make a special slag system for the production of 17-4PH steel ingots with the above-mentioned composition content. Obtain low-pollution and energy-saving pre-melted slag for producing hollow ingots by ingot-pulling electroslag remelting, pack it into a 20kg bag, and use it in an electric slag furnace.

The above special slag system is composed of the following components by weight percentage: Al ₂ O ₃ : 27.7%, CaO: 30%, SiO ₂ : 4.15%, MgO: 5.9%, and the balance is CaF ₂ ; the binary basicity of the slag is CaO /SiO ₂ is 7.2.

The above pre-melted slag was used to produce electroslag remelting 17-4PH in an enterprise in Anhui. The slag melting process was started with liquid slag, that is, the graphite electrode first melted slag, and then replaced the metal electroslag to melt steel. The process during smelting is: voltage: 52V; smelting current: 13000A. Melting speed is controlled at 4.35kg/min.

After experiments, the hydrogen content in the electroslag ingot reaches 4.3ppm, but the hydrogen content of the steel is required to be below 3ppm, which does not meet the quality requirements.

Through the comparison of Comparative Example 2, it can be concluded that when the CaO content is 25%-27% higher than the limit of the present invention, it will cause obvious moisture absorption during the smelting process, which is not conducive to the removal of hydrogen in the steel.

Comparative example 3.

Mix fluorite, quicklime, alumina, fused magnesia, and silica in proportion, melt and stir evenly, and melt at 1500~1560°C for 43 minutes; then pour it into a water-cooled slag pan made of steel plate, and cool to At room temperature, crush it to a particle size of 5-10mm to make a special slag system for the production of 17-4PH steel ingots with the above-mentioned composition content. Obtain low-pollution and energy-saving pre-melted slag for producing hollow ingots by ingot-pulling electroslag remelting, pack it into a 20kg bag, and use it in an electric slag furnace.

The above special slag system is composed of the following components by weight percentage: Al ₂ O ₃ : 27.5%, CaO: 20%, SiO ₂ : 4.12%, MgO: 5.9%, and the balance is CaF ₂ ; the binary basicity of the slag is CaO /SiO ₂ is 4.85.

The above pre-melted slag was used to produce electroslag remelting 17-4PH in an enterprise in Anhui. The slag melting process was started with liquid slag, that is, the graphite electrode first melted slag, and then replaced the metal electroslag to melt steel. The process during smelting is: voltage: 52V; smelting current: 13000A. Melting speed is controlled at 4.35kg/min.

The experimental analysis of the electroslag ingot after smelting shows that the A-type non-metallic inclusions in the steel are reduced by about 45%, the B-type non-metallic inclusions are reduced by about 30%, and the C-type non-metallic inclusions are reduced by about 35%. The effect of material is obviously lower than the slag system of the present invention.

Through the comparison of Comparative Example 3, it can be concluded that when the CaO content is lower than the 25%-27% defined in the present invention, it is not conducive to the removal of inclusions in the steel.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (6)

1. A special slag system for producing 17-4PH steel ingot, characterized in that the special slag system is composed of the following components by weight percentage: Al ₂ O ₃ : 26~28%, CaO: 25~27%, SiO ₂ : 4~5%, MgO: 5~6%, the balance is CaF ₂ , and the binary alkalinity is between 5~6.75. 2. A special slag system for producing 17-4PH steel ingot according to claim 1, characterized in that the melting hemispherical temperature of the special slag system is 1220~1250°C. 3. A special slag system for producing 17-4PH steel ingots according to claim 1, characterized in that the special slag system is used for the production of precipitation-hardening martensitic stainless steel 17 by ingot-pulling electroslag remelting -4PH steel ingot. 4. A special slag system for producing 17-4PH steel ingots according to claim 1, characterized in that the special slag system has a resistivity of 0.402~0.434Ω·cm at 1600°C, and a resistivity of 0.434Ω·cm at 1500°C The viscosity is 0.0352~0.0359 Pa·s. 5. a preparation method for producing the special-purpose slag system for producing 17-4PH steel ingot as claimed in claim 1, is characterized in that, this method preparation method comprises the steps: with fluorite, unslaked lime, aluminum oxide, fused magnesium Sand and silica are mixed in proportion, melted and stirred evenly, and smelted at 1500~1560°C for more than 40 minutes; Then pour it into a water-cooled slag tray made of steel plates, cool it to room temperature, and crush it to a particle size of 5-10mm to make a special slag system for the production of 17-4PH steel ingots with the above-mentioned composition content. 6. a method for using the special slag system for producing 17-4PH steel ingot as claimed in claim 1, characterized in that, the method for use comprises the steps of: first baking the molten slag of the slag system of the present invention to 800 ℃, and keep warm for more than 10h; in the electroslag remelting process, the baked special slag system is heated to above 1600℃ in the slag melting furnace and melted, and then refined for about 20min, and the liquid slag is poured into the electroslag furnace In the crystallizer, insert the consumable electrode to be remelted into the crystallizer and then energize, so that the consumable electrode and the slag are in contact to form a energized circuit, and carry out the smelting process of electroslag remelting 17-4PH, and form after the electrode is melted The ingot extraction operation starts after the molten pool.