CN113699428A - Ti alloying process for reducing TP321 stainless steel seamless tube layering defect - Google Patents
Ti alloying process for reducing TP321 stainless steel seamless tube layering defect Download PDFInfo
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Abstract
The invention relates to the technical field of stainless steel smelting, and provides a Ti alloying process for reducing the layering defect of a TP321 stainless steel seamless tube, which comprises the following steps: providing crude molten steel by an electric arc furnace, blowing oxygen for decarburization by AOD, reducing by AOD ferrosilicon, deeply deoxidizing by AOD aluminum, and performing AOD for the first timeAnd (3) tapping after Ti alloying, performing secondary Ti alloying after calcium treatment in an LF refining furnace, taking out the LF refining furnace after the third Ti alloying, and performing die casting. The invention creates a three-step process in the titanium alloying process, the yield of the three-step Ti alloying is gradually improved, and TiO is reducedxThe generation of impurities effectively reduces large-size SiO in the stainless steel2‑Al2O3MnO-CaO and TiOxThe content of MnO inclusions is reduced, the layering defects in the stainless steel seamless tube are reduced, and the ultrasonic flaw detection qualification rate of the stainless steel seamless tube is improved.
Description
Technical Field
The invention relates to the technical field of stainless steel smelting, in particular to a Ti alloying process for reducing the layering defect of a TP321 stainless steel seamless tube.
Background
The austenitic stainless steel has the advantages of excellent corrosion resistance, formability, toughness in a wide temperature range and the like, is widely applied to industrial departments such as petroleum, nuclear industry, transportation, aerospace and the like and living goods industry, and the yield of the austenitic stainless steel accounts for about 70 percent of the total weight of the stainless steel. The Ti element is widely applied to the stainless steel, and mainly realizes the effects of stabilization, pinning, dispersion strengthening and the like by separating out TiN (C, N) particles with different sizes and uniform distribution, thereby further improving the corrosion resistance and the obdurability of the stainless steel. The TP321 is typical titanium-containing austenitic stainless steel, has more excellent high-temperature corrosion resistance than the conventional 304 austenitic stainless steel, does not need heat treatment after welding, and can be used for a long time at the temperature of a stainless steel sensitization area, thereby being widely applied to heat-resistant pressure-resistant pipelines of petroleum, natural gas, nuclear power and the like.
However, because Ti element has strong binding ability with O, S, N, C elements in molten steel, Al can be generated in the smelting process of the titanium-containing stainless steel2O3-MgO-TiOx、CaO·TiO2And a great variety of inclusions such as TiNMost of the substances are harmful, which have adverse effects on the smelting and quality of stainless steel, including agglomeration in a crystallizer, blockage of a continuous casting nozzle, scale defects on the surface of a stainless steel plate, and poor ultrasonic flaw detection caused by delamination defects. Researches find that the layering defect of TP321 stainless steel is mainly large-size SiO in the steel2-Al2O3MnO-CaO and TiOxThe MnO inclusion cluster is formed after rolling.
In order to control harmful impurities generated in the titanium-containing stainless steel smelting process and reduce adverse effects caused by titanium alloying, Chinese patent CN103225008A discloses a method for preventing agglomeration and nozzle nodulation in a crystallizer in the titanium-containing stainless steel smelting process, wherein the process route comprises electric smelting crude molten steel, AOD furnace refining, ladle refining and continuous casting, and creates favorable conditions for reduction mainly by improving the carbon content and the temperature of molten steel in an electric furnace; the aim of full deoxidation is achieved through reduction, and the yield of titanium is improved and stabilized; the flow of blowing and stirring is increased in the LF furnace, so that impurities in molten steel fully float upwards, secondary oxidation of continuous casting tundish is prevented, the temperature of molten steel in the tundish is increased, the molten steel is prevented from secondary pollution, caking and nozzle nodulation in a crystallizer are reduced, the continuous casting operation rate is effectively increased, and on-site and rolled waste products are reduced. Chinese patent CN104294005A discloses a method for smelting titanium-containing stainless steel, which is to carry out ladle treatment on molten steel after refining, mainly comprising slagging-off and re-slagging, Ti alloying after Al deep deoxidation and calcium treatment, aiming at carrying out secondary deep deoxidation on the molten steel, improving the yield of titanium, reducing the oxygen content in the molten steel, and reducing TiO in the molten steel2、CaO·TiO2And the impurities are contained, so that the nozzle nodulation probability in the continuous casting process is reduced, and the surface quality of the stainless steel in the rolling process is improved.
Disclosure of Invention
The problems existing in the prior art are as follows: in the above patents, Ti alloying is completed by one-time addition, when Ti alloying is carried out in an AOD refining furnace, Ti element reacts with deoxidation product and O element in molten steel to generate TiOxImpurities are included, the cleanliness of molten steel is reduced, and meanwhile, the yield of Ti alloy is low; after Al deep deoxidation in LF refining furnaceWhen the process is carried out, the reaction between Ti element and slag is violent, the fluctuation of the components of the molten steel is large, and the yield of Ti alloy is also lower. Meanwhile, related patents about the titanium-containing stainless steel layered defect control process are reported less.
The invention aims to overcome at least one of the defects of the prior art, and provides a Ti alloying process for reducing the layering defect of a TP321 stainless steel seamless tube aiming at the problem of unstable control of the layering defect of the TP321 stainless steel seamless tube at present, wherein a process route of 'an electric arc furnace +20t AOD refining furnace + LF refining furnace + die casting' is adopted, the components and the temperature of AOD molten steel entering the furnace are strictly controlled, and the peroxidation degree of the molten steel during oxygen blowing and decarburization is reduced; reasonably controlling the contents of Al and Ca elements in the molten steel in the Ti alloying process, and reducing MgO and Al2O3The content of inclusions; optimizing Ti alloying, and creating a three-step process, wherein the first Ti alloying is carried out after Al in the AOD refining furnace is deeply deoxidized, part of Ti elements are burnt to complete the slagging task of the LF refining furnace, the second Ti alloying is carried out after the Ca treatment of the LF refining furnace, the condition that the Ti element content in molten steel is not uniform due to the fact that the Ti alloy is added in place once is prevented, and the Ti element and part of Al which does not float upwards in time are reduced2O3The third Ti alloying before the LF refining furnace is out of the station makes the Ti content in the molten steel meet the target component, the yield of the three-step Ti alloying is gradually improved, and TiO is reducedxThe generation of impurities effectively reduces large-size SiO in the stainless steel2-Al2O3MnO-CaO and TiOxThe content of MnO inclusions is reduced, the layering defects in the stainless steel seamless tube are reduced, and the ultrasonic flaw detection qualification rate of the stainless steel seamless tube is improved.
The invention adopts the following technical scheme:
a Ti alloying process for reducing the layering defects of a TP321 stainless steel seamless tube comprises the following steps:
s1, providing crude molten steel by an electric arc furnace: controlling the components of the AOD molten steel entering the furnace and the temperature of the molten steel to set values;
s2, AOD oxygen blowing decarburization: adding lime and magnesia, controlling the end point w C not more than 0.06%; supplementing high-carbon ferrochrome and electrolytic manganese during the period;
s3, AOD ferrosilicon reduction: adding lime and ferrosilicon, introducing argon, and stirring; after reduction, slagging-off is thorough in the AOD furnace, and the residue amount is less than 20kg of ton steel;
s4, deep deoxidation of AOD aluminum; adding lime, fluorite and aluminum ingot, introducing argon, stirring, and controlling w [ Al ] in the molten steel to be 0.05-0.06%;
s5, tapping after the AOD is alloyed for the first time with Ti: adding ferrotitanium alloy, controlling w [ Ti ] in the molten steel to be 0.10-0.15%, controlling slag components, and mixing AOD slag steel;
s6, performing secondary Ti alloying after the LF refining furnace calcium treatment: after the LF enters the station, the temperature of the molten steel is increased; feeding a calcium wire into the molten steel by using a wire feeding machine, and blowing argon gas for stirring; then adding ferrotitanium alloy, and controlling w [ Ti ] in the molten steel to be 0.25-0.30%;
s7, taking out of the LF refining furnace after the third Ti alloying: adding ferrotitanium before LF, and adjusting the components of molten steel to meet the requirement that w [ Ti ] is 0.40-0.45%; adding a proper amount of lime, and adjusting slag components; transferring the ladle to a die casting platform;
s8, die casting: argon is adopted for protection in the whole process, and die casting protective slag is added to prevent secondary oxidation.
In step S1, w [ C ] in the AOD charged molten steel is controlled to be equal to or greater than 2.0%, w [ Si ] is 0.4 to 0.5%, w [ Mn ] is 0.8 to 0.9%, w [ Cr ] is 16.0 to 16.5%, w [ Ni ] is 9.5 to 10.0%, and the temperature of the molten steel is not lower than 1470 ℃, so as to create favorable conditions for the subsequent AOD oxygen decarburization and reduction.
In any of the above possible implementation manners, there is further provided an implementation manner, when the 20t AOD refining furnace is adopted, in step S2, 1500 ± 100kg of lime and 200 ± 50kg of magnesium oxide are added; during the period, 800 plus or minus 50kg of high-carbon ferrochrome and 60 plus or minus 5kg of electrolytic manganese are supplemented, so that the pressure for supplementing alloy and adjusting components in the reduction period is reduced.
In any of the above possible embodiments, there is further provided an embodiment in which, in step S3, lime is added in an amount of 300 ± 50kg and ferrosilicon is added in an amount of 450 ± 50kg to accelerate the melting of the ferrosilicon and the homogenization of the molten steel composition, and the argon gas flow rate is controlled to 10 to 15Nm m3Min, stirring for 8-12min, controlling W [ Si ] in molten steel]＝(0.3-0.5)％Promoting the reaction between ferrosilicon and slag and molten steel and SiO2Floating and removing the similar impurities; after the ferrosilicon reduction is finished, slagging-off in the AOD furnace needs to be thorough, and the residue is less than 20kg of steel per ton.
In any of the above possible implementation manners, there is further provided an implementation manner that in step S4, after the slag removal is completed, 300 ± 50kg of lime, 140 ± 10kg of fluorite, 150 ± 10kg of aluminum ingot and 10-15 Nm/Nm of argon gas flow are added to the slag3Min, stirring for 8-12min to speed the smelting of aluminum ingot and the homogenization of molten steel components and control W [ Al ] in molten steel]0.05-0.06%, promoting the reaction between aluminum ingot and molten steel, and promoting Al2O3Floating and removing the similar impurities to reduce the content of O element in the molten steel; the yield of Ti element in the titanium alloying process is improved.
In any of the above possible implementation manners, there is further provided an implementation manner, in step S5, after the deep deoxidation is completed, 65kg of ferrotitanium alloy is added into the furnace, and w [ Ti ] in the molten steel is controlled]0.10 to 0.15 percent; part of Ti element is burnt, so that the slag meets the component requirement: w (CaO) 50%, w (SiO)2)＝20％，w(Al2O3)15～20％，w(TiOx) 3-5%, and the slagging requirement of the LF refining furnace is met; after the component detection is qualified, mixing the AOD slag steel;
in step S6, after the LF arrives at the station, the power is transmitted to increase the temperature to more than 1600 ℃; then, a calcium wire is fed into the molten steel by a wire feeder, the feeding amount of pure calcium is 0.2-0.8 kg per ton of steel, and MgO & Al in the molten steel is reduced2O3The content of similar impurities; argon is blown and stirred for 8-12min to promote the floating removal of impurities; then adding 55 plus or minus 5kg ferrotitanium alloy to control w [ Ti ] in the molten steel]0.25-0.30 percent of the total content of Ti, and the Al which is not floated upwards in time partially and caused by overhigh content of Ti element is reduced2O3MgO-CaO oxide reaction due to the improved cleanliness of molten steel and the TiO content in the slagxThe yield of Ti element is further improved; the flow rate of argon gas is controlled to be 0.1-0.2 Nm3Min; promoting the homogenization of the components of the molten steel and the upward floating removal of the inclusion (Ti alloy is not suitable to be added in place once, preventing the non-uniform distribution of Ti element, reducing the Ti element and partial Al which does not float upwards in time2O3-MgO-CaO oxide reaction);
in step S7, adding 50 + -5 kg of ferrotitanium alloy before LF, and adjusting molten steel components to satisfy w [ Ti [ ]]0.40-0.45% of the total weight of the components; during LF refining, a proper amount of lime is added, and the slag components are adjusted to meet the following requirements: w (CaO) 55%, w (SiO)2)＝18％，w(Al2O3)12～18％，w(TiOx)<1 percent; after the components are qualified, the ladle is transferred to a die casting platform.
In step S8, when the temperature of the molten steel is reduced to 1510 ± 10 ℃, casting is started, and during the casting process, the whole process of the nozzle is protected by argon gas; the method adopts a lower pouring method die casting mode, and die casting protective slag is added at the bottom of the die, so that the secondary oxidation caused by the direct contact of molten steel and air is prevented.
In any of the possible implementations described above, there is further provided an implementation that in step S2, w [ Cr ] is ≥ 52%, w [ C ] is ≤ 10.0%, and w [ Si ] is ≤ 5.0%.
In any of the above possible implementations, there is further provided an implementation in which, in step S3, w [ Si ] in the ferrosilicon is 72.0 to 80.0%, and w [ Al ] is 2.0% or less.
In any of the possible implementations described above, there is further provided an implementation that, in steps S5, S6 and S7, w [ Ti ] ≦ 65.0-75.0%, w [ Si ] ≦ 3.50%, and w [ Al ] ≦ 6.0% in the ferrotitanium alloy.
The invention also provides a TP321 stainless steel seamless tube which is prepared by the Ti alloying process for reducing the layering defect of the TP321 stainless steel seamless tube.
The invention has the beneficial effects that: the three-step process in the titanium alloying process is originally created, wherein the first Ti alloying is carried out after the Al in the AOD refining furnace is deeply deoxidized, part of Ti elements are burnt to complete the slagging task of the LF refining furnace, and the second Ti alloying is carried out after the Ca treatment of the LF refining furnace, so that the uneven distribution of the Ti elements caused by the once adding of the Ti alloys in place is prevented, and the Ti elements and the Al are reduced2O3The third Ti alloying before the LF refining furnace is taken out of the station makes the content of Ti element in the molten steelThe target composition is satisfied.
Drawings
FIG. 1 is a schematic diagram showing the delamination defect of a TP321 stainless steel seamless tube.
FIG. 2 is a diagram showing a layered defect inclusion of a TP321 stainless steel seamless pipe; (a) the side surface of the delamination defect, and (b) the surface of the delamination defect.
Detailed Description
Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that technical features or combinations of technical features described in the following embodiments should not be considered as being isolated, and they may be combined with each other to achieve better technical effects. In the drawings of the embodiments described below, the same reference numerals appearing in the respective drawings denote the same features or components, and may be applied to different embodiments.
The embodiment of the invention provides a Ti alloying process for reducing the layering defect of a TP321 stainless steel seamless tube, which comprises the following steps:
s1, providing crude molten steel by an electric arc furnace: controlling the components of the AOD molten steel entering the furnace and the temperature of the molten steel to set values;
s2, AOD oxygen blowing decarburization: adding lime and magnesia, controlling the end point w C not more than 0.06%; supplementing high-carbon ferrochrome and electrolytic manganese during the period;
s3, AOD ferrosilicon reduction: adding lime and ferrosilicon, introducing argon, and stirring; after reduction, slagging-off is thorough in the AOD furnace, and the residue amount is less than 20kg of ton steel;
s4, deep deoxidation of AOD aluminum; adding lime, fluorite and aluminum ingot, introducing argon, stirring, and controlling w [ Al ] in the molten steel to be 0.05-0.06%;
s5, tapping after the AOD is alloyed for the first time with Ti: adding ferrotitanium alloy, controlling w [ Ti ] in the molten steel to be 0.10-0.15%, controlling slag components, and mixing AOD slag steel;
s6, performing secondary Ti alloying after the LF refining furnace calcium treatment: after the LF enters the station, the temperature of the molten steel is increased; feeding a calcium wire into the molten steel by using a wire feeding machine, and blowing argon gas for stirring; then adding ferrotitanium alloy, and controlling w [ Ti ] in the molten steel to be 0.25-0.30%;
s7, taking out of the LF refining furnace after the third Ti alloying: adding ferrotitanium before LF, and adjusting the components of molten steel to meet the requirement that w [ Ti ] is 0.40-0.45%; adding a proper amount of lime, and adjusting slag components; transferring the ladle to a die casting platform;
s8, die casting: argon is adopted for protection in the whole process, and die casting protective slag is added to prevent secondary oxidation.
Preferably, in step S1, the AOD is controlled to be fed into the molten steel in a range of w [ C ] not less than 2.0%, w [ Si ] not less than 0.4 to 0.5%, w [ Mn ] not less than 0.8 to 0.9%, w [ Cr ] not less than 16.0 to 16.5%, w [ Ni ] not less than 9.5 to 10.0%, and the temperature of the molten steel not less than 1470 ℃.
Preferably, when a 20t AOD refining furnace is adopted, 1500 plus or minus 100kg lime and 200 plus or minus 50kg magnesium oxide are added in the step S2; during the period, 800 plus or minus 50kg of high-carbon ferrochrome and 60 plus or minus 5kg of electrolytic manganese are supplemented.
Preferably, in step S3, lime 300 + -50 kg and ferrosilicon 450 + -50 kg are added, and the argon flow rate is controlled to 10-15Nm3Min, stirring for 8-12min, controlling W [ Si ] in molten steel]＝(0.3-0.5)％。
Preferably, in step S4, lime 300 + -50 kg, fluorite 140 + -10 kg, aluminum ingot 150 + -10 kg and argon gas flow rate is controlled to 10-15Nm3Min, stirring for 8-12min, controlling W [ Al ] in molten steel]＝0.05～0.06％。
Preferably, in step S5, the slag satisfies the composition requirement: w (CaO) 50%, w (SiO)2)＝20％，w(Al2O3)15～20％，w(TiOx)3～5％；
In step S6, after the LF arrives at the station, the power is transmitted to increase the temperature to more than 1600 ℃; then, a calcium wire is fed into the molten steel by a wire feeder, the feeding amount of pure calcium is 0.2-0.8 kg per ton of steel, and MgO & Al in the molten steel is reduced2O3The content of similar impurities; argon is blown and stirred for 8-12min to promote the floating removal of impurities; then adding 55 plus or minus 5kg ferrotitanium alloy to control w [ Ti ] in the molten steel]0.25 to 0.30% and the flow rate of argon gas is controlled to 0.1 to 0.2Nm3/min；
In step S7, adding 50 + -5 kg of ferrotitanium alloy before LF, and adjusting molten steel components to satisfy w [ Ti [ ]]0.40-0.45% of the total weight of the components; during LF refining, a proper amount of lime is added, and the slag components are adjusted to meet the following requirements: w (CaO) 55%, w (SiO)2)＝18％，w(Al2O3)12～18％，w(TiOx)<1％。
Preferably, in step S8, the casting is started when the temperature of the molten steel is reduced to about 1510 ℃.
Preferably, in step S2, w [ Cr ] is not less than 52%, w [ C ] is not more than 10.0%, and w [ Si ] is not more than 5.0%.
Preferably, in the ferrosilicon, w [ Si ] is 72.0-80.0%, and w [ Al ] is less than or equal to 2.0%.
Preferably, w [ Ti ] is 65.0-75.0%, w [ Si ] is less than or equal to 3.50%, and w [ Al ] is less than or equal to 6.0%.
The present invention will be further described below by way of comparative examples and specific examples.
Comparative example
(1) The electric arc furnace provides crude molten steel: the raw materials of the electric arc furnace comprise scrap steel and return materials, and the components of crude molten steel obtained by melting before tapping are shown in table 1, namely the components of AOD molten steel entering the furnace; after the AOD is put into the furnace, the temperature of the molten steel is detected to be 1480 ℃.
(2) AOD oxygen blowing decarburization: adding 300kg of lime and 50kg of magnesium oxide at the bottom of the AOD furnace, and slagging off after molten steel is put into the furnace and oxygen is blown for 3 min; adding 1500kg of lime and 200kg of magnesium oxide into the furnace, continuously adjusting the flow of oxygen-argon, blowing oxygen for decarburization, and supplementing 920kg of high-carbon ferrochrome during decarburization; after the completion of decarburization, the molten steel had the composition shown in Table 1.
(3) AOD reduction slagging-off: continuously blowing oxygen for decarburization for 6 min; then adding 250kg of ferrosilicon, 120kg of aluminum ingot, 85kg of electrolytic manganese and 300kg of lime into the furnace, and controlling the argon flow to be 15Nm3The melting of the alloy and the homogenization of the molten steel components are accelerated, the reaction between the ferrosilicon and the aluminum ingot and between the slag and the molten steel is promoted, and the floating removal of inclusions is promoted; and after 15min, slagging off in an AOD furnace.
(4) Tapping after AOD titanium alloying: after slagging off is finished, 42kg of micro-carbon ferrochrome, 30kg of ferrosilicon, 30kg of aluminum ingot, 40kg of ferrotitanium, 300kg of lime and 140kg of fluorite are added into the furnace, and the argon flow is controlled to be 15Nm3Min, accelerating the melting of the alloy and the homogenization of the components of the molten steel, and accelerating the slagging; after 4min, 360kg of ferrotitanium is added, AOD slag steel is mixed out after the component detection is qualified, and the components of AOD tapping molten steel are shown in Table 1.
(5) Steel ladle soft stirring: on the die casting platform, argon is blown into the ladle, and the flow of the argon is controlled to be 0.1-0.2 Nm3And/min, soft stirring to promote floating removal of the inclusion.
(6) Die casting and casting: when the temperature of the steel ladle molten steel is reduced to about 1510 ℃, casting is started; in the casting process, the whole process of the water gap is protected by argon; a lower pouring method die casting mode is adopted, and die casting protective slag is added at the bottom of the die, so that secondary oxidation caused by direct contact of molten steel and air is prevented; the composition of the molten steel before the end of casting is shown in Table 1.
Table 1 example 1 molten steel composition change in the smelting process,% by mass
| C | Si | Mn | P | S | Cr | Ni | Ti | Al | Ca | O | N | |
| AOD furnace | 0.96 | 0.88 | 0.85 | 0.03 | 0.012 | 15.6 | 9.5 | |||||
| After AOD decarburization | 0.11 | - | 0.52 | 0.03 | 0.01 | 16.6 | 10.4 | 0.048 | 0.016 | |||
| Before AOD tapping | 0.059 | 0.37 | 1.12 | 0.03 | 0.001 | 18.3 | 9.6 | 0.51 | 0.026 | 0.0007 | 0.0022 | 0.016 |
| Before the steel casting is finished | 0.057 | 0.4 | 1.12 | 0.03 | 0.002 | 18.5 | 9.6 | 0.46 | 0.023 | 0.0005 | 0.002 | 0.013 |
Examples
(1) The electric arc furnace provides crude molten steel: raw materials of the electric arc furnace comprise scrap steel and return materials, and the components of crude molten steel obtained after melting are shown in table 2, namely the components of AOD molten steel entering the furnace; the composition of the molten steel after the AOD is charged is detected to be 1475 ℃.
(2) AOD oxygen blowing decarburization: after molten steel is put into a furnace, adding 1500kg of lime, 200kg of magnesium oxide and oxygen-argon mixed blowing for decarburization, gradually adjusting the flow of the oxygen-argon and reducing the burning loss of Cr element in the decarburization process; during the period, 800kg of high carbon ferrochrome and 60kg of electrolytic manganese are supplemented; after the completion of decarburization, the molten steel had the composition shown in Table 2.
(3) AOD ferrosilicon reduction: adding 300kg of lime and 450kg of ferrosilicon into the furnace, and controlling the flow of argon to be 15Nm3Stirring for 10min to speed the smelting of ferrosilicon and the homogenization of molten steel components, promote the reaction between ferrosilicon and slag and molten steel and promote SiO reaction2Floating and removing the similar impurities; and after the ferrosilicon reduction is finished, slagging off in the AOD furnace.
(4) Deep deoxidation of AOD aluminum: after slagging off is finished, 300kg of lime, 140kg of fluorite and 150kg of aluminum ingot are added into the furnace, and the argon flow is controlled to be 15Nm3Stirring for 10min to accelerate the melting of aluminum ingot and the homogenization of molten steel components, promote the reaction between the aluminum ingot and the molten steel and promote Al2O3Floating up to remove the inclusion-like substances and reduce the content of O element in the molten steel.
(5) Tapping after AOD first Ti alloying: adding 65kg of ferrotitanium alloy, mixing AOD slag steel after the components are qualified, wherein the components of AOD tapping molten steel are shown in Table 2.
(6) And (3) performing secondary Ti alloying after calcium treatment of the LF refining furnace: after the LF enters the station, feeding a calcium wire into the molten steel by using a wire feeder, wherein the feeding amount of pure calcium is 0.2-0.8 kg per ton of steel; argon is blown and the mixture is stirred for 10 min; then adding 55kg of ferrotitanium alloy; the flow rate of argon gas is controlled to be 0.1-0.2 Nm3/min；
(7) And (3) taking out of the LF refining furnace after the third Ti alloying: adding 50kg of ferrotitanium alloy before LF, transferring the ladle to a die casting platform after the components are qualified, wherein the components of molten steel are shown in Table 2;
(8) die casting and casting: when the temperature of the steel ladle molten steel is reduced to about 1510 ℃, casting is started; in the casting process, the whole process of the water gap is protected by argon; a lower pouring method die casting mode is adopted, and die casting protective slag is added at the bottom of the die, so that secondary oxidation caused by direct contact of molten steel and air is prevented; the composition of the molten steel before the end of casting is shown in Table 2.
Table 2 example 2 molten steel composition change in the smelting process,% by mass
| C | Si | Mn | P | S | Cr | Ni | Ti | Al | Ca | O | N | |
| AOD furnace | 2.2 | 0.50 | 0.81 | 0.03 | 0.015 | 16.5 | 9.8 | |||||
| After AOD decarburization | 0.05 | - | 0.75 | 0.03 | 0.012 | 17.3 | 10.2 | 0.042 | 0.012 | |||
| Before AOD tapping | 0.052 | 0.43 | 1.06 | 0.03 | 0.002 | 18.6 | 9.9 | 0.13 | 0.056 | 0.0006 | 0.0023 | 0.011 |
| LF refining furnace outbound | 0.051 | 0.43 | 1.08 | 0.03 | 0.002 | 18.7 | 9.8 | 0.46 | 0.055 | 0.0028 | 0.0022 | 0.010 |
| Before the steel casting is finished | 0.05 | 0.45 | 1.08 | 0.03 | 0.002 | 18.7 | 9.9 | 0.44 | 0.052 | 0.0023 | 0.0018 | 0.0098 |
The embodiment adopts the Ti alloying process of the TP321 stainless steel seamless pipe delamination defect provided by the invention. Compared with the examples, the Ti alloying in the comparative example is added once before the tapping of the AOD furnace, the yield of ferrotitanium is low in the titanium alloying process, and the molten steel isHigh melting point SiO generated in2-Al2O3MnO-CaO and TiOxMnO inclusions are difficult to remove, and layering defects are formed in the processes of forging and tube penetrating, so that the ultrasonic flaw detection yield of the seamless tube is low. In the embodiment, the composition and the temperature of the AOD molten steel entering the furnace are strictly controlled, so that the pressure of the AOD in the processes of oxygen blowing, decarburization and reduction is reduced; the contents of Al and Ca elements in the molten steel are reasonably controlled, the content of O element in the molten steel is reduced, and the yield of ferrotitanium during titanium alloying is improved; adopts a three-step process of Ti alloying, improves the yield of Ti alloy, and reduces TiO contentxThe possibility of high-melting-point inclusions is reduced, the possibility of large-size inclusion cluster and layering defects is reduced, and the qualification rate of ultrasonic flaw detection of the stainless steel seamless pipe is improved from about 80% to over 95%.
The invention adopts the process route of 'electric arc furnace +20t AOD refining furnace + LF refining furnace + die casting', strictly controls the components and temperature of AOD molten steel entering the furnace, and reduces the peroxidation degree of the molten steel during oxygen blowing and decarburization; reasonably controlling the contents of Al and Ca elements in the molten steel in the Ti alloying process, and reducing MgO and Al2O3The content of inclusions; the three-step process for optimizing Ti alloying has the advantages that the yield of the three-step Ti alloying is gradually improved, and TiO is reducedxThe generation of impurities effectively reduces large-size SiO in the stainless steel2-Al2O3MnO-CaO and TiOxThe content of MnO inclusions reduces the layering defects in the stainless steel seamless tube, and the ultrasonic flaw detection qualification rate of the stainless steel seamless tube is improved (the first Ti alloying is completed before AOD steel tapping in order to meet the slag requirement of LF, the second Ti alloying is performed in order to reduce the condition that Ti elements are unevenly distributed due to the fact that Ti alloys are added in place once, so that the Ti elements react with oxide inclusions and slag, Ca wires are fed and argon gas is blown for stirring for 10min, the cleanliness of molten steel is improved, the reaction of the Ti elements and the oxides is reduced in the second Ti alloying, the third Ti alloying is added before an LF refining furnace is taken out of the station, the cleanliness of the molten steel is further improved, the reaction of the Ti elements and the oxides is further reduced, and the yield of the Ti alloys is further improved).
While several embodiments of the present invention have been presented herein, it will be appreciated by those skilled in the art that changes may be made to the embodiments herein without departing from the spirit of the invention. The above examples are merely illustrative and should not be taken as limiting the scope of the invention.
Claims (10)
1. A Ti alloying process for reducing the delamination defect of a TP321 stainless steel seamless tube, the process comprising:
s1, providing crude molten steel by an electric arc furnace: controlling the components of the AOD molten steel entering the furnace and the temperature of the molten steel to set values;
s2, AOD oxygen blowing decarburization: adding lime and magnesia, controlling the end point w C not more than 0.06%; supplementing high-carbon ferrochrome and electrolytic manganese during the period;
s3, AOD ferrosilicon reduction: adding lime and ferrosilicon, introducing argon, and stirring; after reduction, slagging-off is thorough in the AOD furnace, and the residue amount is less than 20kg of ton steel;
s4, deep deoxidation of AOD aluminum; adding lime, fluorite and aluminum ingot, introducing argon, stirring, and controlling w [ Al ] in the molten steel to be 0.05-0.06%;
s5, tapping after the AOD is alloyed for the first time with Ti: adding ferrotitanium alloy, controlling w [ Ti ] in the molten steel to be 0.10-0.15%, controlling slag components, and mixing AOD slag steel;
s6, performing secondary Ti alloying after the LF refining furnace calcium treatment: after the LF enters the station, the temperature of the molten steel is increased; feeding a calcium wire into the molten steel by using a wire feeding machine, and blowing argon gas for stirring; then adding ferrotitanium alloy, and controlling w [ Ti ] in the molten steel to be 0.25-0.30%;
s7, taking out of the LF refining furnace after the third Ti alloying: adding ferrotitanium before LF, and adjusting the components of molten steel to meet the requirement that w [ Ti ] is 0.40-0.45%; adding a proper amount of lime, and adjusting slag components; transferring the ladle to a die casting platform;
s8, die casting: argon is adopted for protection in the whole process, and die casting protective slag is added to prevent secondary oxidation.
2. The Ti alloying process for reducing the delamination defect of a TP321 stainless steel seamless tube as claimed in claim 1, wherein in step S1, the AOD is controlled to be added into the molten steel w [ C ] is not less than 2.0%, w [ Si ] is 0.4-0.5%, w [ Mn ] is 0.8-0.9%, w [ Cr ] is 16.0-16.5%, w [ Ni ] is 9.5-10.0%, and the temperature of the molten steel is not lower than 1470 ℃.
3. The Ti alloying process for reducing the delamination defect of a TP321 stainless steel seamless tube according to claim 1, wherein a 20t AOD finer is used, and in step S2, 1500 ± 100kg of lime and 200 ± 50kg of magnesium oxide are added; during the period, 800 plus or minus 50kg of high-carbon ferrochrome and 60 plus or minus 5kg of electrolytic manganese are supplemented.
4. The Ti alloying process for reducing the delamination defect of a TP321 stainless steel seamless tube according to claim 3, wherein in the step S3, lime 300 + -50 kg, ferrosilicon 450 + -50 kg and argon gas flow rate are controlled to 10-15Nm3Min, stirring for 8-12min, controlling W [ Si ] in molten steel]＝(0.3-0.5)％。
5. The Ti alloying process for reducing the delamination defect of the TP321 stainless steel seamless tube as claimed in claim 3, wherein in the step S4, lime 300 + -50 kg, fluorite 140 + -10 kg, aluminum ingot 150 + -10 kg and argon gas flow rate is controlled to 10-15Nm3Min, stirring for 8-12min, controlling W [ Al ] in molten steel]＝0.05～0.06％。
6. The Ti alloying process for reducing the delamination defects of the TP321 stainless steel seamless tube of claim 3,
in step S5, the slag satisfies the composition requirements: w (CaO) 50%, w (SiO)2)＝20％，w(Al2O3)15～20％，w(TiOx)3～5％；
In step S6, after the LF arrives at the station, the power is transmitted to increase the temperature to more than 1600 ℃; then, a calcium wire is fed into the molten steel by a wire feeder, the feeding amount of pure calcium is 0.2-0.8 kg per ton of steel, and MgO & Al in the molten steel is reduced2O3The content of similar impurities; argon is blown and stirred for 8-12min to promote the floating removal of impurities; then adding 55 plus or minus 5kg ferrotitanium alloy to control w [ Ti ] in the molten steel]0.25 to 0.30% and the flow rate of argon gas is controlled to 0.1 to 0.2Nm3/min；
In step S7, adding 50 + -5 kg of ferrotitanium alloy before LF, and adjusting molten steel components to satisfy w [ Ti [ ]]0.40-0.45% of the total weight of the components; during LF refining, a proper amount of lime is added, and the slag components are adjusted to meet the following requirements: w (CaO) 55%, w (SiO)2)＝18％，w(Al2O3)12～18％，w(TiOx)<1％。
7. The Ti alloying process for reducing the delamination defect of a TP321 stainless steel seamless tube as claimed in claim 1, wherein in step S8, the casting is started after the temperature of the molten steel is decreased to 1510 ± 10 ℃.
8. A Ti alloying process for reducing the delamination defect of TP321 stainless steel seamless tube according to claim 1 or 3 wherein in step S2 w [ Cr ] ≦ 52%, w [ C ] ≦ 10.0%, w [ Si ] ≦ 5.0%.
9. A Ti alloying process for reducing the delamination defect of a seamless tube of TP321 stainless steel as claimed in claim 1 or 4 wherein in step S3, w [ Si ] in Si-Fe is 72.0-80.0%, w [ Al ] is 2.0% or less.
10. A Ti alloying process for reducing the delamination defect of a TP321 stainless steel seamless tube as claimed in claim 1 wherein in steps S5, S6 and S7, w [ Ti ] ≦ 65.0-75.0%, w [ Si ] ≦ 3.50%, w [ Al ] ≦ 6.0% in said ferrotitanium alloy.
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