CN111748747B - Ultralow-silicon ultralow-aluminum semi-boiling steel and smelting method - Google Patents
Ultralow-silicon ultralow-aluminum semi-boiling steel and smelting method Download PDFInfo
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Abstract
An ultra-low silicon and ultra-low aluminum semi-boiling steel comprises the following components in percentage by weight: c: 0.003-0.005%, Si is less than or equal to 0.01%, Mn: 0.22-0.30%, Alt is less than or equal to 0.002%, P is less than or equal to 0.015%, S is less than or equal to 0.009%, N: 0.0035-0.0070%, and simultaneously requiring: less than or equal to 0.050 percent of Cu, less than or equal to 0.030 percent of Ni, less than or equal to 0.040 percent of Cr, less than or equal to 0.010 percent of Sn, less than or equal to 0.020 percent of As and less than or equal to 0.010 percent of Ca; smelting: KR desulfurization; smelting in a converter; RH vacuum treatment; casting into a blank; and conventionally performing post-processing. By optimizing the components and the smelting process, the content of free oxygen in the end-point molten steel is 0.0010-0.0020%, Alt is less than or equal to 0.002%, nitrogen is 0.0038-0.0058%, and carbon is 0.0030-0.0050%, and the smelting components are stable, and the casting blank quality is good.
Description
Technical Field
The invention relates to semi-boiling steel and a smelting method, in particular to ultra-low silicon and ultra-low aluminum semi-boiling steel and a smelting method.
Background
The ultra-low silicon and ultra-low aluminum semi-boiling steel is applied to the steel for the fins of the condenser. The product requires the thickness specification to be 1.2-5 mm, the tensile strength to be 290-350 Mpa and the yield strength to be 190-280 Mpa. In addition to the strength described above, the steel post-processed surface is coated with aluminum, which can cause delamination of the steel sheet if the Alt in the steel is higher than the aluminum coating. In addition, the steel plate needs to be welded for pipe making, and the steel plate also needs to have good weldability. Further, extremely low silicon is required because a high silicon content decreases the density of the steel, promotes the growth of columnar grains in the steel, reduces the plasticity, and also decreases the weldability of the steel, generates low-melting-point silicates during welding, and increases the fluidity of slag and molten metal, causing a spattering phenomenon, which affects the welding quality. Thus, the requirements for silicon and aluminum are low.
In practical production, from the smelting process, smelting molten iron into molten steel in a converter is an oxidation process, the molten steel smelted in the converter has strong oxidizing property, and the molten steel needs to be deoxidized by adding a deoxidizer. The common deoxidation method of the molten steel is as follows: one is deoxidation with ferrosilicon, and the result is that the molten steel contains a high percentage of silicon by mass; the other is deoxidation with aluminium alloy, as a result of which the aluminium content of the steel is relatively high. It is difficult to obtain extremely low silicon and aluminum simultaneously. And is one of the problems that those skilled in the art are studying.
Controlling Alt in steel not to be too high, and requiring Alt to be less than or equal to 0.002%. As the RH vacuum treatment needs to add aluminum for deoxidation, the Alt is ensured to be less than or equal to 0.002 percent, the free oxygen in the molten steel cannot be less than 0.0010 percent, otherwise the Alt can exceed 0.002 percent, and the subsequent aluminum coating processing quality is influenced. And the free oxygen in the molten steel cannot be too high, if the free oxygen in the molten steel is too high, the liquid level of a molten steel crystallizer can fluctuate too much in the casting process, the casting blank is easy to generate defects of air holes and the like, and the quality of the casting blank cannot be ensured. Therefore, the control of free oxygen in molten steel cannot exceed 0.0020 percent, which is also another technical problem.
Carbon is an element that directly affects the plasticity, toughness, weldability, and the like of steel, and is also the most effective element for improving the strength of steel. The tensile strength and yield strength of the steel increase with increasing carbon content, which reduces elongation and impact toughness, and corrosion resistance.
The main roles of nitrogen in steel are solid solution strengthening and age precipitation strengthening, which improves the macrostructure of steel, makes it dense and solid, and increases strength. Too low a nitrogen content results in insufficient strength of the steel, and too high a nitrogen content results in reduced toughness and weldability of the steel.
After retrieval:
the Chinese patent application No. CN201710064843.1 discloses a smelting method of low-silicon low-aluminum low-oxygen steel, and the components of the low-silicon low-aluminum low-oxygen steel in percentage by mass are as follows: less than or equal to 0.05 percent of C, less than or equal to 0.05 percent of Si, less than or equal to 0.05 percent of Mn, less than or equal to 0.002 percent of Al, less than or equal to 0.002 percent of O, less than or equal to 0.003 percent of N, less than or equal to 0.010 percent of P, and less than or equal to 0.010 percent of S; the smelting mode is that molten iron is pretreated to deeply remove S, a converter boils to discharge steel, RH deoxidization and weak argon blowing are carried out; the method comprises the following specific steps: (1) in the hot metal pretreatment, lime and passivated magnesium metal powder are sprayed into the hot metal according to the condition of the hot metal, and the hot metal S is removed to be less than 0.0020 percent; thoroughly skimming slag after desulfurization, wherein the temperature of molten iron after skimming is more than 1260 ℃; (2) adding iron in a converter, and adopting a single slag method for smelting if the molten iron P is less than or equal to 0.08%; if the P content in the molten iron is more than 0.08 percent, smelting by a double-slag method; tapping in a converter boiling manner, controlling the tapping C to be 0.065-0.08%, and simultaneously ensuring that the oxygen activity in steel is 500-600 ppm during tapping; if the oxygen activity in the steel is more than 600ppm, feeding an aluminum wire after the furnace, and controlling the oxygen activity of molten steel in the tank to be 500-600 ppm; controlling Mn in tapping below 0.05%, P below 0.009%, and tapping temperature above 1665 ℃; (3) after tapping, the steel ladle is transported to an RH station, and enters a vacuum mode after entering the station and measuring the temperature, and in order to ensure the carbon deoxidation capability and effect, the time of RH vacuum degree below 0.2kPa is not less than 20 min; then, determining oxygen and adding aluminum, controlling the oxygen activity at 40-60 ppm, then breaking the gap, then feeding Ca-Fe wire, and stopping wire feeding when the content of Ca in the steel reaches 10-25 ppm; and after the wire feeding is finished, performing weak argon blowing operation, wherein the weak argon blowing time is more than 10min, and then directly pouring on a machine. Although the document does not increase the production cost and prolong the production rhythm, the document can lower the aluminum and the oxygen, can reduce the total oxygen and is beneficial to the purification of steel. However, in the document, as lime and a modifier are not added in tapping to modify the molten steel top slag, the oxygen activity is 40-60 ppm after RH vacuum treatment, the oxygen activity is higher, the liquid level of a molten steel crystallizer fluctuates too much in the casting process, and the casting blank is easy to generate air holes and other defects. And the Ca-Fe wire feeding operation is carried out after the vacuum is finished, because the oxygen activity is higher, the oxidability of the molten steel and the steel slag is strong, Ca is easy to oxidize when the Ca-Fe wire feeding operation is carried out, the oxidation reaction violently turns over the molten steel surface, the molten steel is easy to be secondarily oxidized, and impurities are generated to influence the purity of the molten steel.
The document with Chinese patent application number CN201810898692.4 discloses a method for controlling free oxygen in ultra-low carbon and low aluminum steel, and the production process comprises the following steps: pretreating molten iron: blowing desulfurization powder into molten iron, removing slag completely, and transferring the molten iron to a converter for smelting when the weight percentage of sulfur in the molten iron is less than or equal to 0.003%; smelting in a converter: adding the desulfurized molten iron into a converter, and blowing oxygen to reduce carbon to smelt into molten steel, wherein the oxygen blowing time is 15-18 min; adding a slagging material in the smelting process of the converter, tapping into a steel ladle when the weight percentage of carbon in molten steel in the converter is less than or equal to 0.06%, the weight percentage of oxygen in the molten steel reaches 0.05-0.09%, and the temperature of the molten steel reaches 1680-1720 ℃, and tapping by adopting slag stopping; after molten steel enters an argon blowing station, adding 2-5 kg/t of steel lime and 0.5-1.5 kg/t of steel slag modifier, and stirring for 2-5 min by bottom blowing argon; and (3) vacuum refining in an RH furnace: carrying out vacuum circulating decarburization and deoxidation in an RH vacuum refining furnace, testing the oxygen content in molten steel after 5-10min of decarburization, adding a first batch of deoxidizer when the weight percentage content of oxygen is more than 0.04%, and adding a second batch of deoxidizer for deoxidation when the weight percentage content of carbon in steel is less than or equal to 0.003% and the weight percentage content of oxygen is less than or equal to 0.04%; when the chemical component content in the molten steel and the temperature of the molten steel reach target values, the treatment process is finished; and (5) standing for 15-25 min, and transferring the molten steel to a continuous casting process. In the RH refining final steel, the weight percentage of free oxygen is controlled to be 0.002% -0.005%, and the weight percentage of Als is less than or equal to 0.003%. The oxygen activity is higher, the liquid level of the molten steel crystallizer can fluctuate too much in the casting process, and the casting blank is easy to generate air holes and other defects.
In summary, the following steps: in the technical field, the content of free oxygen in molten steel after the vacuum finishing of ultra-low silicon, ultra-low aluminum and RH is high at present. The reasons why ultra-low silicon cannot be obtained are: on one hand, silicon is not thoroughly oxidized in the steelmaking process, and certain residue exists; on the other hand, the phenomenon that the steel slag returns silicon into the molten steel in the refining process due to no slag modification or poor modification effect cannot be effectively inhibited. Because the silicon content is high, the density of the steel is reduced, the plasticity of the steel is reduced, and the welding performance of the steel is reduced.
The aluminum content and the free oxygen content in the molten steel are in opposite corresponding relation, the free oxygen content cannot be lower than 0.0010 percent if ultra-low aluminum is obtained, the free oxygen content is higher than 0.0020 percent, and pores are easy to generate in the continuous casting process. At present, the content of free oxygen in steel cannot be accurately controlled in the technical field, because a balance point of the content of aluminum and the content of free oxygen in steel is not found, the contradiction between the content of aluminum in steel and the content of free oxygen cannot be effectively solved, namely, the content of aluminum in steel is high but the content of free oxygen is low, although pores are not easily generated, the content of aluminum is high, and the requirement of a user for coating aluminum on the surface in the later processing cannot be met; or the content of aluminum in the steel meets the requirement and the content of free oxygen is high, so that the liquid level of a crystallizer in the casting process of the molten steel fluctuates too much, and the casting blank is easy to generate defects of air holes and the like.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the ultralow-silicon and ultralow-aluminum semi-boiling steel and the smelting method, wherein the content of free oxygen in end-point molten steel is 0.0010-0.0020%, Alt is less than or equal to 0.002%, the content of nitrogen is 0.0038-0.0058%, and the content of carbon is 0.0030-0.0050%, and the ultralow-silicon and ultralow-aluminum semi-boiling steel has stable components and good casting blank quality and meets the requirements of higher-end users.
The measures for realizing the aim are as follows:
the ultra-low silicon and ultra-low aluminum semi-boiling steel comprises the following components in percentage by weight: c: 0.003-0.005%, Si is less than or equal to 0.01%, Mn: 0.22-0.30%, Alt is less than or equal to 0.002%, P is less than or equal to 0.015%, S is less than or equal to 0.009%, N: 0.0035-0.0070%, and simultaneously requiring: less than or equal to 0.050 percent of Cu, less than or equal to 0.030 percent of Ni, less than or equal to 0.040 percent of Cr, less than or equal to 0.010 percent of Sn, less than or equal to 0.020 percent of As, less than or equal to 0.010 percent of Ca, and the balance of iron and inevitable impurities.
Preferably: the content of C is 0.0034-0.0046 wt%.
Preferably: the weight percentage content of N is 0.0045% -0.0070%.
Preferably: the weight percentage content of Si is less than or equal to 0.0095 percent.
A method for smelting ultra-low silicon and ultra-low aluminum semi-boiling steel comprises the following steps:
1) KR desulfurization, duration: slagging-off not less than two times, namely slagging-off before and slagging-off after, and requiring the retention time between slagging-off twice not less than 5 min; the exposed surface is not less than 90%; s in the desulfurized molten iron is less than or equal to 0.001 percent;
2) smelting in a converter by top-bottom combined blowing; when smelting is finished, controlling the free oxygen in the molten steel to be 0.045-0.075%; when tapping: firstly, no alloy is added; secondly, adding lime and 40 aluminum modifiers into the top slag according to the proportion of 2.5-3.5 kg/ton steel and 0.75-1.45 kg/ton steel;
3) RH vacuum treatment
The RH vacuum treatment is carried out in two stages under the condition of not blowing oxygen:
the first stage is as follows: the treatment time is 10-15 min; the driving gas is argon with a flow rate of 135-145 m3H; keeping the vacuum degree not more than 0.133kpa for 5-10 min; at the end of this phase: the carbon content is 0.0015 to 0.0030 percent, the free oxygen content in the molten steel is 0.025 to 0.045 percent, and the nitrogen content is 0.0020 to 0.0030 percent;
and a second stage: the treatment time is 12-15 min; the driving gas is nitrogen with the flow rate of 146-165 m3H; controlling the vacuum degree at 0.5-0.95kpa, and keeping the vacuum degree for 11-14 min;
determining the free oxygen content in the molten steel before Al addition according to the oxygen determination value;
amount of added aluminum WAlCalculated according to the following formula:
WAl＝1.125（O%-0.0010%）* Wsteel*1000/R*η*WSteelThe unit: kg/ton steel;
in the formula: r-represents the yield of Al, unit: percent;
WsteelThe amount of molten steel expressed in unit: ton;
o-represents the free oxygen content in the molten steel before the addition of aluminum, in wt.%;
ηAlaluminum purity of Al added, unit: percent;
and adding a carburant according to the proportion of 0.015-0.040 kg per ton of steel after the aluminum is added and the circulation is carried out for 3 minutes;
the end of the vacuum treatment requires: finally, the content of free oxygen in the molten steel is 0.0010-0.0020%, Alt is less than or equal to 0.002%, nitrogen content is 0.0038-0.0058%, and carbon content is 0.0030-0.0050%;
4) pouring into a blank
In the continuous casting process: argon is not blown into the tundish, and argon is not opened in the whole casting process; controlling the superheat degree of the tundish at 20-35 ℃; the blank drawing speed is 1.1-1.3 m/min;
5) the subsequent steps are carried out conventionally.
Preferably: when smelting is finished, the free oxygen in the molten steel is 0.045-0.065%.
Preferably: the end of the vacuum treatment requires: the content of free oxygen in the final molten steel is 0.0010-0.0016%, Alt is less than or equal to 0.0016%, nitrogen content is 0.0038-0.0047%, and carbon content is 0.0030-0.0046%.
Mechanism and action of each element and main process in the invention
Carbon (C): is an element which directly affects the strength, plasticity, toughness, welding performance and the like of steel. The carbon content is the most effective element for improving the strength of the steel, the tensile strength and the yield strength of the steel are improved along with the increase of the carbon content, but the elongation and the impact toughness are reduced, the corrosion resistance is also reduced, and in order to ensure that the steel plate obtains good comprehensive performance, if the content is lower than a limited value, the tensile strength of the steel can not reach 290Mpa, and the yield strength can not reach 190 Mpa. On the other hand, if the content is higher than the limited value, the steel has extremely low content of deoxidizing elements such as Si and Al, and the deoxidation is incomplete, so that the molten steel contains free oxygen. Oxygen precipitated when molten steel is solidified in the continuous casting process is easy to react with carbon to generate CO subcutaneous bubbles. In order to prevent the generation of the subcutaneous bubble defect, the carbon is controlled, that is, the carbon-oxygen concentration product is controlled not to be excessively high, and the generation of the carbon-oxygen reaction can be suppressed without generating the subcutaneous bubbles. On the other hand, the tensile strength and the yield strength of the carbon are over-standard due to over-high carbon, which is not beneficial to subsequent processing of users. The content of C in the present invention is preferably 0.0034% to 0.0046%.
Silicon (Si): silicon is high in harm to reduce the density of steel, and silicon can promote the growth of columnar crystals in the steel and reduce the plasticity. Silicon can reduce the weldability of steel, because silicon has a stronger binding capacity with oxygen than iron, and easily generates low-melting-point silicate during welding, increases the fluidity of slag and molten metal, causes a splash phenomenon, and affects welding quality. The steel grade of the invention is fin steel for welded pipe application, so the lower the silicon is, the better the silicon is, the Si content is controlled to be less than or equal to 0.010 percent, and the Si content is preferably controlled to be less than or equal to 0.0095 percent.
Manganese (Mn): the manganese-containing steel can improve the strength of steel, can be infinitely dissolved with iron, and has relatively small influence on plasticity while improving the strength of the steel, so that the manganese is widely applied to a reinforcing element in the steel. The Mn content of the present invention is preferably 0.22% to 0.30%.
Aluminum (Alt): when the content of Alt is limited by the invention, brittle alumina inclusions are easily generated, the impact resistance and fatigue resistance of steel are reduced, the oxidation of a steel plate is promoted, and the hot workability, welding performance and cutting processability of the steel are influenced. Because the later-stage processing surface of the steel is coated with aluminum, if the Alt in the steel is high, the aluminum coating processing is layered, and the aluminum coating processing quality effect is influenced.
Phosphorus (P): p has a certain effect of improving corrosion resistance, but is an element easy to segregate, generates serious segregation in the local part of steel, reduces plasticity and toughness, and is extremely harmful to low-temperature toughness, so that P is controlled to be less than or equal to 0.015 percent.
Sulfur (S): s is a harmful element in steel, is easy to combine with manganese to generate MnS inclusion, reduces the low-temperature impact toughness of the steel, is easy to segregate and enrich in the steel, reduces the corrosion resistance of the steel, and controls the S to be less than or equal to 0.009 percent, preferably the S to be less than or equal to 0.005 percent.
Nitrogen (N): the main functions of nitrogen in steel are solid solution strengthening and aging precipitation strengthening, which can improve the macroscopic structure of steel, make it compact and firm and improve the strength. If the nitrogen content is less than the value defined in the present invention, the strength of the steel is insufficient, but if it is more than the defined value, the toughness and weldability of the steel are lowered. Therefore, the N element in the steel is controlled to be 0.0035 to 0.0070 percent.
According to the invention, when smelting is finished, the free oxygen in the molten steel is controlled to be 0.045-0.075%; when tapping: firstly, no alloy is added; secondly, lime is added into the top slag according to 2.5-3.5 kg/ton steel, 40 aluminum modifier is added into the top slag according to 0.75-1.45 kg/ton steel, the free oxygen in the molten steel is controlled to be too low and too high, the oxygen deficiency is reduced, the RH vacuum carbon-oxygen reaction is insufficient, and the RH vacuum decarburization is not facilitated. The free oxygen in the molten steel is higher than the oxidability of the molten steel and steel slag, and the difficulty of accurately controlling the content of the free oxygen after RH finishing is very high. The alloy is not added during tapping so as to avoid the alloy from being oxidized and have low yield. The modifier is adopted to carry out slag modification on top slag deoxidation in the tapping process, because the affinity of aluminum and oxygen is higher than that of silicon and oxygen, namely the oxygen-deprivation capacity of aluminum is higher than that of silicon, the slag is occupied by aluminum, the transmission of silicon in molten steel to the slag can be inhibited, the silicon content in the slag is very low, the silicon content caused by the silicon return of the steel slag to the molten steel in the subsequent refining process is avoided, and thus the extremely low silicon component can be obtained.
The invention carries out RH vacuum treatment in two stages in the stage of RH vacuum treatment under the condition of not blowing oxygen, and the requirements are as follows:
the first stage is as follows: the treatment time is 10-15 min; the driving gas is argon with a flow rate of 135-145 m3H; keeping the vacuum degree not more than 0.133kpa for 5-10 min; at the end of this phase: the carbon content is 0.0015 to 0.0030 percent, the free oxygen content in the molten steel is 0.025 to 0.045 percent, and the nitrogen content is 0.0020 to 0.0030 percent; and a second stage: the treatment time is 12-15 min; the driving gas is nitrogen with the flow rate of 146-165 m3H; controlling the vacuum degree at 0.5-0.95kpa, and keeping the vacuum degree for 11-14 min; because the main task of the first stage is to utilize the carbon-oxygen reaction to deeply decarbonize,harmful gases and impurities are removed, and the purity of molten steel is ensured, so the control parameters of the vacuum degree, the processing time and the vacuum degree maintaining time of the RH vacuum first stage are required to be set as above. Argon is used as driving gas under the vacuum degree condition, because the denitrification capability of RH vacuum circulation molten steel is far greater than the nitrogen circulation nitrogen increasing capability, nitrogen cannot be increased in the molten steel at the stage. The main task of the second stage is to further remove the impurities on one hand, and on the other hand, nitrogen is added to the molten steel by adopting nitrogen circulation, the nitrogen adding speed of the molten steel under the vacuum degree condition is 0.00015-0.00020%/min, and the nitrogen adding time of the molten steel is controlled to achieve the standard requirement of the nitrogen addition of the molten steel according to the nitrogen adding speed by combining the nitrogen content in the molten steel of the first stage, so the parameters are set as above.
And the amount of added aluminum W at this stageAlCalculating according to the formula: wAl＝1.125（O%-0.0010%）* WSteel*1000/R*η*WSteelBecause the free oxygen content in the steel is O% after the RH vacuum carbon-oxygen reaction is complete; the target oxygen amount in the molten steel is set to be 0.0010%, the setting of the target oxygen amount is critical, and the lower limit value is taken because the free oxygen content is controlled to be 0.0010% -0.0020% after RH vacuum is finished, so that the residual oxygen in the steel slag is fully considered, and the lower limit value is a critical value obtained through a plurality of tests. The rest of the aluminum reacts with oxygen 2AL +3O = AL2O3Amount of molten steel W based on mass fraction of aluminum and oxygenSteelContent of aluminum R, yield of aluminum etaAlThe above calculation formula is derived as conventionally known.
The invention is characterized in that in the continuous casting process: the tundish does not blow argon, and argon is not opened in the whole casting process because the free oxygen content in the steel is 0.0010% -0.0020%, the steel is different from the killed steel and belongs to semi-boiling steel, the liquid level fluctuation of the crystallizer in the casting process is larger than that of the killed steel, if the tundish blows argon, the argon is opened in the whole casting process, the liquid level fluctuation is increased, the boiling is intensified, and the casting blank is easy to generate air holes and other defects.
Compared with the prior art, the invention optimizes the components and the smelting process to ensure that the content of free oxygen in the end-point molten steel is 0.0010-0.0020%, Alt is less than or equal to 0.002%, nitrogen is 0.0038-0.0058%, and carbon is 0.0030-0.0050%, and the smelting components are stable, the casting blank quality is good, and the requirements of higher-end users are met.
Detailed Description
The present invention is described in detail below:
table 1 is a list of values of chemical components of each example and comparative example of the present invention;
table 2 is a table of the main process parameters and the result values for each example of the present invention and comparative example.
Each example was produced according to the following procedure:
1) KR desulfurization, duration: slagging-off not less than two times, namely slagging-off before and slagging-off after, and requiring the retention time between slagging-off twice not less than 5 min; the exposed surface is not less than 90%; s in the desulfurized molten iron is less than or equal to 0.001 percent;
2) smelting in a converter by top-bottom combined blowing; when smelting is finished, controlling the free oxygen in the molten steel to be 0.045-0.075%; when tapping: firstly, no alloy is added; secondly, adding lime and 40 aluminum modifiers into the top slag according to the proportion of 2.5-3.5 kg/ton steel and 0.75-1.45 kg/ton steel;
3) RH vacuum treatment
The RH vacuum treatment is carried out in two stages under the condition of not blowing oxygen:
the first stage is as follows: the treatment time is 10-15 min; the driving gas is argon with a flow rate of 135-145 m3H; keeping the vacuum degree not more than 0.133kpa for 5-10 min; at the end of this phase: the carbon content is 0.0015 to 0.0030 percent, the free oxygen content in the molten steel is 0.025 to 0.045 percent, and the nitrogen content is 0.0020 to 0.0030 percent;
and a second stage: the treatment time is 12-15 min; the driving gas is nitrogen with the flow rate of 146-165 m3H; controlling the vacuum degree at 0.5-0.95kpa, and keeping the vacuum degree for 11-14 min;
determining the free oxygen content in the molten steel before Al addition according to the oxygen determination value;
amount of added aluminum WAlCalculated according to the following formula:
WAl＝1.125（O%-0.0010%）* Wsteel*1000/R*η*WSteelThe unit: kg/ton steel;
in the formula: r-represents the yield of Al, unit: percent;
WsteelThe amount of molten steel expressed in unit: ton;
o-represents the free oxygen content in the molten steel before the addition of aluminum, in wt.%;
ηAlaluminum purity of Al added, unit: percent;
and adding a carburant according to the proportion of 0.015-0.040 kg per ton of steel after the aluminum is added and the circulation is carried out for 3 minutes;
the end of the vacuum treatment requires: finally, the content of free oxygen in the molten steel is 0.0010-0.0020%, Alt is less than or equal to 0.002%, nitrogen content is 0.0038-0.0058%, and carbon content is 0.0030-0.0050%;
description of the drawings: the vacuum treatment stage can carry out twice aluminum adding according to the requirement, and the aluminum adding amount in each time is according to WAl＝1.125（O%-0.0010%）* WSteel*1000/R*η*WSteelCalculating to obtain;
4) pouring into a blank
In the continuous casting process: argon is not blown into the tundish, and argon is not opened in the whole casting process; controlling the superheat degree of the tundish at 20-35 ℃; the blank drawing speed is 1.1-1.3 m/min;
5) the subsequent steps are carried out conventionally.
TABLE 1 ingredient lists (wt%) of inventive examples and comparative examples
TABLE 1
TABLE 2 List of the main process parameters of the examples of the invention and the comparative examples
TABLE 2-1
Tables 2-2
Tables 2 to 3
In tables 2 to 3, the amount of aluminum W added each timeAlAccording to the formula WAl＝1.125（O%-0.0010%）* WSteel*1000/R*η*WSteelAnd (4) calculating.
The reason for adding aluminum for the second time is that the actual oxygen content in the molten steel is higher than the theoretical oxygen content due to the fact that the oxygen transmission amount of the steel slag into the molten steel is higher than the theoretical oxygen content or due to the fact that the oxidizing environment in an RH vacuum chamber is stronger. The second aluminum adding adjustment is based on the situation of free oxygen content in the steel measured after the first aluminum adding, and the values of other parameters are the same as those in the calculation of the first aluminum adding amount.
Tables 2 to 4
The specific examples are merely illustrative and not limitative of the embodiments of the present invention.
Claims (3)
1. A method for smelting ultra-low silicon and ultra-low aluminum semi-boiling steel comprises the following steps:
1) KR desulfurization, duration: slagging-off not less than two times, namely slagging-off before and slagging-off after, and requiring the retention time between slagging-off twice not less than 5 min; the exposed surface is not less than 90%; s in the desulfurized molten iron is less than or equal to 0.001 percent;
2) smelting in a converter by top-bottom combined blowing; when smelting is finished, controlling the free oxygen in the molten steel to be 0.045-0.075%; when tapping: firstly, no alloy is added; secondly, adding lime and 40 aluminum modifiers into the top slag according to the proportion of 2.5-3.5 kg/ton steel and 0.75-1.45 kg/ton steel;
3) RH vacuum treatment
The RH vacuum treatment is carried out in two stages under the condition of not blowing oxygen:
the first stage is as follows: the treatment time is 10-15 min; the driving gas is argon with a flow rate of 135-145 m3H; keeping the vacuum degree not more than 0.133kpa for 5-10 min; at the end of this phase: the carbon content is 0.0015 to 0.0030 percent, the free oxygen content in the molten steel is 0.025 to 0.045 percent, and the nitrogen content is 0.0020 to 0.0030 percent;
and a second stage: the treatment time is 12-15 min; the driving gas is nitrogen with the flow rate of 146-165 m3H; controlling the vacuum degree at 0.5-0.95kpa, and keeping the vacuum degree for 11-14 min;
determining the free oxygen content in the molten steel before Al addition according to the oxygen determination value;
amount of added aluminum WAlCalculated according to the following formula:
WAl＝1.125（O%-0.0010%）* Wsteel*1000/R*ηAl *WSteelThe unit: kg/ton steel;
in the formula: r-represents the yield of Al, unit: percent;
WsteelThe amount of molten steel expressed in unit: ton;
o-represents the free oxygen content in the molten steel before the addition of aluminum, in wt.%;
ηAlaluminum purity of Al added, unit: percent;
and adding a carburant according to the proportion of 0.015-0.040 kg per ton of steel after the aluminum is added and the circulation is carried out for 3 minutes;
the end of the vacuum treatment requires: finally, the content of free oxygen in the molten steel is 0.0010-0.0020%, Alt is less than or equal to 0.002%, nitrogen content is 0.0038-0.0058%, and carbon content is 0.0030-0.0050%;
4) pouring into a blank
In the continuous casting process: argon is not blown into the tundish, and argon is not opened in the whole casting process; controlling the superheat degree of the tundish at 20-35 ℃; the blank drawing speed is 1.1-1.3 m/min;
5) carrying out post-working procedures according to the conventional method;
the ultra-low silicon and ultra-low aluminum semi-boiling steel comprises the following components in percentage by weight: c: 0.003-0.005%, Si is less than or equal to 0.01%, Mn: 0.22-0.30%, Alt is less than or equal to 0.002%, P is less than or equal to 0.015%, S is less than or equal to 0.009%, N: 0.0035-0.0070%, and simultaneously requiring: less than or equal to 0.050 percent of Cu, less than or equal to 0.030 percent of Ni, less than or equal to 0.040 percent of Cr, less than or equal to 0.010 percent of Sn, less than or equal to 0.020 percent of As, less than or equal to 0.010 percent of Ca, and the balance of iron and inevitable impurities.
2. The method for smelting an ultra-low silicon, ultra-low aluminum and semi-boiling steel as claimed in claim 1, wherein: when smelting is finished, the free oxygen in the molten steel is 0.045-0.065%.
3. The method for smelting an ultra-low silicon, ultra-low aluminum and semi-boiling steel as claimed in claim 1, wherein: the end of the vacuum treatment requires: the content of free oxygen in the final molten steel is 0.0010-0.0016%, Alt is less than or equal to 0.0016%, nitrogen content is 0.0038-0.0047%, and carbon content is 0.0030-0.0046%.
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