CN113278762B - Ca alloying method in high-aluminum calcium sulfur composite free-cutting steel - Google Patents

Ca alloying method in high-aluminum calcium sulfur composite free-cutting steel Download PDF

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CN113278762B
CN113278762B CN202110526917.5A CN202110526917A CN113278762B CN 113278762 B CN113278762 B CN 113278762B CN 202110526917 A CN202110526917 A CN 202110526917A CN 113278762 B CN113278762 B CN 113278762B
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alloying
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steel
molten steel
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CN113278762A (en
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鲁金龙
龙鹄
余大华
丘文生
李至荣
刘栋
张志明
杨伟光
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SGIS Songshan Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0006—Adding metallic additives
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C22C33/06—Making ferrous alloys by melting using master alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

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Abstract

A Ca alloying method in high aluminum calcium sulfur composite free-cutting steel belongs to the field of steel smelting. The method comprises the following steps: converter or electric furnace smelting, LF refining, RH or VD vacuum treatment and continuous casting, which is characterized in that in the LF refining process, the end point Ca content is controlled; and after the vacuum treatment is finished, sequentially carrying out first Ca alloying, first Al alloying, second Ca alloying, S alloying and second Al alloying. Has the advantages of stable control of Ca in the alloying smelting process and the [ Ca ] in the molten steel cooling and pouring process]、[S]、[Al]Stable control of element content, Al easy to block water gap2O3And CaS inclusion is not easy to generate, a water gap is not easy to nodulate, and the castability is good.

Description

Ca alloying method in high-aluminum calcium sulfur composite free-cutting steel
Technical Field
The application relates to the field of steel smelting, in particular to a Ca alloying method in high-aluminum calcium sulfur composite free-cutting steel.
Background
The Ca-S composite free-cutting steel is a kind of composite free-cutting steel which is added with a small amount of Ca element on the basis of the S free-cutting steel, so that MnS inclusion which is easy to deform in the hot working process is converted into spindle-shaped (Ca, Mn) S inclusion, thereby further improving the cutting performance. In addition, the calcium-sulfur composite free-cutting steel can also obviously improve the anisotropy of mechanical properties caused by long-strip MnS inclusions in the sulfur free-cutting steel. At present, the calcium-sulfur series composite free-cutting steel is mainly applied to medium-carbon automobile steel with higher requirements on mechanical property and processability, such as: a pull rod, a control arm, a connecting rod and the like of the automobile.
Al element is not only a commonly used deoxidizing agent in the steel making process, but also a common alloy element in steel, and proper Al element and N element are combined, so that formed AlN can obviously refine grains, improve tissues and improve mechanical properties, and particularly nitriding parts with higher requirements on surface mechanical properties often have certain requirements on Al element in steel.
In recent years, the metallurgical field has made a lot of studies on the problem of castability of S-containing and Al-containing steel, since this steel simultaneously generates Al which is liable to block the nozzle during continuous casting2O3And CaS inclusions (chemical reaction: 2(CaO) +3[ Al)]+2[S]＝(Al2O3) + CaS), poor continuous casting castability. The aluminum-added calcium-sulfur composite free-cutting steel, in particular to high-aluminum calcium-sulfur composite free-cutting steel (high aluminum means more than 0.015wt percent of Al), not only has minimum requirements on the Al and S contents in the steel, but also requires certain Ca element in the steel, and further aggravates the risk of continuous casting water blocking (the chemical reaction is that [ Ca ] is used for the first time]+[S]CaS). Therefore, how to control [ Ca ] during cooling and pouring of molten steel]、[S]、[Al]The stability of the element content is not only for ensuring the chemical components of the final finished product, but also has important significance for the castability of continuous casting and the smooth production.
The patent 'a high-aluminum sulfur-containing calcium-controlling steel smelting process method' proposes LF refining high-alkalinity smelting, adding S before VD, then adding Al, then adding Ca after VD smelting, and smelting the high-aluminum sulfur-containing calcium-controlling steel by a method of adding Ca twice, however, the method comprises the following steps: 1) the S alloy is added firstly, the oxygen content in steel is increased, and then the Al addition process has overlarge Al oxidation and can form a large amount of Al2O3The impurities are removed from the mixture of the impurities,influence the purity and the castability of the steel; 2) the slag alkalinity in the LF smelting process is too high, S is easy to remove, and the S content cannot be stably controlled; 3) the Al content and the S content in the steel are kept consistent before and after the Ca wire is added for the second time after VD, and the difference with the actual experience is larger; 4) when S is added firstly and then Ca is added, CaS is directly generated in the molten steel and is easy to float upwards, the content of Ca in the molten steel cannot be ensured, and a water gap is easy to block.
In the patent of 'continuous casting production method of sulfur-containing aluminum-containing high-calcium steel', VD vacuum refining is broken, Al wires are fed into the steel firstly, then S wires are fed, and finally CaSi wires are fed to realize alloying. However, since Ca element in steel after CaSi wire is added exists mainly in molten state in molten steel, [ Ca ] and [ S ] cannot exist stably under thermodynamic conditions during casting, and CaS inclusion which is liable to block nozzle is formed. In addition, according to actual production experience, the contents of [ Ca ], [ S ] and [ Al ] in the cast steel are reduced to a certain extent, and the element content of a finished product (a continuous casting billet or a rolled material) cannot be ensured.
The patent 'free-cutting non-quenched and tempered steel and a manufacturing method thereof' provides a production method of free-cutting steel with Al, S and Ca, and provides a method for controlling the shape of MnS in the steel by controlling the S/Ca ratio.
The patent "Free-cutting steel for machining structured good machining in cutting by localized carbide tool" proposes to strictly control the contents or values of [ Al ], [ S ], [ Ca ], [ S ]/[ O ], [ Ca ] × [ S ], [ Ca ]/[ S ] and the like in steel to obtain a large amount of complex oxysulfide, thereby improving the cutting performance of steel. However: 1) the patent mainly aims at die casting products, and has no problem of castability; 2) the patent does not specify the smelting process and how to ensure the content of key elements.
It can be seen from the above known patents that, regarding the problems of castability and stability of control of content of key elements of high-aluminum calcium-sulfur composite free-cutting steel, the Ca cannot be stably controlled in the smelting process, the contents of the [ Ca ], [ S ] and [ Al ] elements in the processes of cooling and pouring molten steel cannot be stably controlled, and multi-furnace continuous casting cannot be realized in the actual production, and the difficulty is also high through the smelting processes of vacuum breaking, adding Al first, adding Ca, adding S, adding Al first and then adding calcium in refining, and the like.
Therefore, the invention is urgently needed to invent a Ca alloying method aiming at the high-aluminum calcium sulfur composite free-cutting steel, which can ensure the Ca stable control of the high-aluminum calcium sulfur composite free-cutting steel in the smelting process, realize the castability control of continuous casting and ensure the smooth production.
Disclosure of Invention
In order to solve the problems of the prior art, the present application aims to provide a method for alloying Ca in high-aluminum calcium sulfur composite free-cutting steel, which has the advantages of stable control of Ca in the alloying smelting process, and [ Ca ] in the molten steel cooling and pouring process]、[S]、[Al]Stable control of element content, Al easy to block water gap2O3And CaS inclusion is not easy to generate, a water gap is not easy to nodulate, and the castability is good.
In a first aspect, the present application provides a method for Ca alloying in a high aluminum calcium sulfur composite free-cutting steel, the method comprising: converter or electric furnace smelting, LF refining, RH or VD vacuum treatment and continuous casting, which is characterized in that in the LF refining process, the end point Ca content is controlled; and after the vacuum treatment is finished, sequentially carrying out first Ca alloying, first Al alloying, second Ca alloying, S alloying and second Al alloying.
In a second aspect, the present application provides an example of an alumino-calcium-sulfur composite free-cutting steel, which is prepared by the preparation method provided in the first aspect of the present application, and the main chemical components of the alumino-calcium-sulfur composite free-cutting steel comprise: c: 0.20wt% to 0.50wt%, Si: 0.15wt% -0.35 wt%, Mn: 0.60wt% -1.60 wt%, P: <0.020wt%, S: 0.020wt% -0.060 wt%, Al: 0.015wt% -0.030 wt%, Ca: 0.0015wt% -0.0035 wt%, N: 0.004-0.0012 wt%, and the balance of Fe and inevitable impurity elements.
The method for alloying Ca in the high-aluminum calcium sulfur composite free-cutting steel has the beneficial effects that:
the method controls the LF refining end pointThe content of Ca is that Ca alloying is carried out before Al alloying after vacuum treatment, so that the calcium element can generate oxide which is easy to be remained in molten steel as soon as possible. Then Al can be effectively avoided by two times of interval Al alloying and the second Ca alloying and S alloying between the two times of interval Al alloying2O3And a large amount of high-melting-point inclusions such as CaS. Through the matching control of the LF refining process and the vacuum treatment process and the control of the alloying sequence, the Ca in the smelting process can be stably controlled]、[S]、[Al]Element content, realizes Al easy to block water gap2O3And the generation of CaS inclusions is inhibited, and the nozzle is not easy to nodulate. The process of the invention is easy to operate, [ Ca ]]、[S]、[Al]The element content is controlled stably, the castability of the molten steel is good, and the smooth production is ensured.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.
FIG. 1 is a graph of the morphology of a typical sulfide in a material prepared in example 1 of the present application;
FIG. 2 is a graph of the morphology of a typical complex oxysulfide in a material prepared in example 1 of the present application;
FIG. 3 is a graph of the morphology of a typical sulfide in a material prepared in example 2 of the present application;
FIG. 4 is a graph of the morphology of a typical sulfide in a material prepared in example 3 of the present application;
FIG. 5 is a graph of the morphology of a typical sulfide in a material prepared in example 4 of the present application;
FIG. 6 is a graph showing the morphology of a typical sulfide in a material prepared in comparative example 1 of the present application;
FIG. 7 is a graph showing the morphology of a typical sulfide in a material prepared in comparative example 2 of the present application;
FIG. 8 is a graph of typical sulfide morphology in a material prepared according to comparative example 3 of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the examples of the present application clearer, the following examples are given for describing embodiments of the present application in detail, but it will be understood by those skilled in the art that the following examples are only for illustrating the present application and should not be construed as limiting the scope of the present application. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
In order to obtain the high-aluminum calcium sulfur composite free-cutting steel with qualified components, the smelting process is provided in the example, so as to be beneficial to the implementation of the scheme of the application by the technical personnel in the field.
The smelting process mainly comprises the following steps: converter or electric furnace smelting, LF refining, RH or VD vacuum treatment and continuous casting processes, and the specific process steps are as follows:
(1) converter or electric furnace smelting process: after smelting, the content of C in the molten steel meets the following requirements: 0.08 to 0.15wt%, for example: 0.08wt%, 0.09 wt%, 0.10 wt%, 0.11 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%; the temperature of the molten steel meets the following requirements: >1580 ℃, for example: 1590 deg.C, 1600 deg.C, 1610 deg.C, 1620 deg.C. Controlling the content of C in molten steel after smelting is finished, and avoiding the excessive high oxygen content of the molten steel after smelting is finished; the high enough molten steel temperature is beneficial to ensuring that the alloy is fully dissolved and the slag is melted as soon as possible.
(2) An LF refining procedure: after molten steel enters an LF refining furnace, the operations of rapid temperature rise, submerged arc, stirring, reasonable addition of a slag former in batches and the like are carried out to rapidly form white slag, and the content of oxygen and inclusions in the steel can be reduced by utilizing the strong reducibility of the white slag.
Further, in the middle of the LF smelting (the LF smelting process is divided into a front stage, a middle stage and a rear stage according to time, and is particularly divided according to the conventional process), if the Ca content in the molten steel is less than 0.0008wt%, a proper amount of Ca alloy is added, so that after the LF smelting is finished, the Ca content in the molten steel meets the following requirements: 0.0008wt% to 0.0015wt%, for example: 0.0008wt%, 0.0009 wt%, 0.0010 wt%, 0.0011 wt%, 0.0012wt%, 0.0013 wt%, 0.0014 wt%, 0.0015 wt%. The Ca content in the LF refining process is less than 0.0008wt%, the generation amount of stable Ca-containing liquid oxides in steel after Ca wires are added after vacuum breaking is reduced, and then CaS which has a high melting point and is easy to float and remove is generated with S elements in molten steel, so that the Ca content of finished products does not meet the requirement (<15 ppm). In addition, the excessive floating CaS causes the nozzle stopper to rise seriously, and the continuous casting heat is seriously influenced. Thus, the inventors found that: controlling the content of Ca in the molten steel to meet the following requirements after LF smelting is finished: 0.0008 to 0.0015 weight percent, which is favorable for stably controlling the content of Ca, inhibiting the accretion of a water gap and improving the continuous casting heat.
(3) RH or VD vacuum processing procedure: the RH or VD extreme vacuum (<67Pa) processing time is controlled according to 10-20 minutes. After the vacuum treatment is finished, first Ca alloying is performed, wherein the control range of the target Ca content is 0.0012-0.0020 wt%, and comprises the following steps: 0.0012wt%, 0.0013 wt%, 0.0014 wt%, 0.0015wt%, 0.0016 wt%, 0.0017 wt%, 0.0018 wt%, 0.0019 wt% and 0.0020wt%, so that low-melting-point liquid oxides are mainly generated in the molten steel and are not easy to float upwards, and the Ca element in the molten steel is ensured to exist in the molten steel mainly in the form of oxides but not in a dissolved state. Above this range, CaO oxides with high melting point are easily formed in the steel, and easily float up to enter slag phase, which is not favorable for Ca stabilization control; below this range, the amount of Ca alloy added in the later stage is too large, the stability of control is weakened, and alumina-based inclusions with high melting point are formed after Al is added.
Then carrying out first Al alloying, wherein the control range of the Al content is as follows: 0.005 to 0.020% by weight, for example: 0.005wt%, 0.006 wt%, 0.007 wt%, 0.008 wt%, 0.010 wt%, 0.011 wt%, 0.012 wt%, 0.013 wt%, 0.014 wt%, 0.015wt%, 0.017 wt%, 0.018 wt%, 0.019 wt%, 0.020 wt%. Sampling after homogenizing for 5 minutes, and carrying out second Ca alloying, wherein the control range of the Ca content is as follows: 0.0025 to 0.0035 weight percent, and excessive Ca alloy is added, so that the content of Ca in the steel cannot be ensured, and a large amount of CaS is generated in the steel to block a water gap; adding too low Ca alloy can not guarantee the Ca content of the final finished product. And performing S alloying after the second Ca alloying to ensure the content of S in the finished product. Finally, carrying out second Al alloying, wherein the control range of the Al content is as follows: 0.020wt% -0.035 wt%. After Al alloying, the soft stirring time is controlled according to 10-20 minutes.
After the vacuum treatment is finished, calcium alloying is carried out before Al alloying, then two times of interval Al alloying and second Ca alloying and S alloying are carried out between two times of interval Al alloying, and the proper calcium, aluminum and sulfur alloying system can effectively avoid Al2O3And a large amount of high-melting-point inclusions such as CaS. Through the matching control of the LF refining process and the vacuum treatment process and the control of the alloying sequence, the Ca in the smelting process can be stably controlled]、[S]、[Al]Element content, realizes Al easy to block water gap2O3And the generation of CaS inclusions is inhibited, and the nozzle is not easy to nodulate. The process of the invention is easy to operate, [ Ca ]]、[S]、[Al]The element content is controlled stably, the castability of the molten steel is good, and the smooth production is ensured.
(4) And (3) continuous casting process: the superheat degree of a tundish of a first furnace for continuous casting is controlled according to 32-40 ℃, and the superheat degree of the tundish of a continuous casting furnace is controlled according to 30-40 ℃. The number of continuous casting furnaces is 4 or more. During casting, the Ca element transformation behavior in steel with decreasing temperature is: calcium aluminate with a high CaO proportion (CaO proportion: 30 to 40 wt%, and more than the above range) → calcium aluminate with a low CaO proportion (CaO proportion: 0.5 to 20 wt%) → Al2O3+ CaS composite inclusions, Al2O3CaS is the main material for blocking the nozzle, thereby ensuring higher superheat degree of molten steel passing through the nozzle and reducing Al2O3And the generation of CaS is more beneficial to the stabilization control of the content of Ca and the smooth production.
The application example provides a high-aluminum calcium sulfur composite free-cutting steel which is prepared by the preparation method. The high-aluminum calcium sulfur composite free-cutting steel mainly comprises the following chemical components: c: 0.20wt% to 0.50wt%, Si: 0.15wt% -0.35 wt%, Mn: 0.60wt% -1.60 wt%, P:<0.020wt％，S：0.020wt％～0.060wt％，Al：0.015wt％～0.030wt％，Ca：0.0015wt％～0.0035wt％，N: 0.004-0.0012 wt%, and the balance of Fe and inevitable impurity elements. The main component of the composite oxysulfide core oxide in the steel is alumina or calcium aluminate with low CaO proportion, and the main component of the peripheral sulfide is (Ca, Mn) S, the number of the S is 30-100/mm2。
The method ensures that the final finished product comprises the following components: al: 0.015 to 0.030wt%, S: 0.020wt% -0.060 wt%, Ca: on the basis of 0.0015 to 0.0035 weight percent, the continuous casting of 4 furnaces and above can be realized, and the production efficiency and the economic benefit of the high-aluminum calcium sulfur composite free-cutting steel are greatly improved.
The Ca alloying method in the high Al-Ca-S composite free-cutting steel of the present application will be described in further detail with reference to the following examples.
Example 1
Provides a Ca alloying method of high-aluminum calcium sulfur composite free-cutting steel, the chemical components of which are shown in Table 1, and the Ca alloying method is prepared according to the following smelting method:
in the first step, 130 tons of top-bottom combined blown converter.
110 tons of molten iron and 20 tons of scrap steel are used as main raw materials, the C content in the molten steel is 0.10 wt% during tapping, and the temperature is 1603 ℃. Adding aluminum iron, carbon powder, ferrosilicon, ferromanganese, ferrochromium and slag charge in the tapping process.
And secondly, LF refining.
After the LF station, slag materials such as lime, a compound deoxidizer and the like are added for slagging operation. The content of [ Ca ] in the steel after LF refining is 0.0010 wt%.
And thirdly, RH vacuum smelting.
Keeping the pressure of the vacuum chamber at 67Pa for 15 minutes, firstly adding a Ca wire after the vacuum refining is finished and repressing, adding an Al wire after 3 minutes, and sampling after 5 minutes, wherein the molten steel comprises the following components of [ Ca ]: 0.0017 wt%, [ Al ]: 0.017 wt%, then Ca wire was added, 3 minutes later S wire was added, finally Al wire was added, 5 minutes later sampling, [ Ca ]: 0.0032 wt%, [ Al ]: 0.031 wt%. Stirring the mixture for 13 minutes by using weak argon, then lifting the mixture for pouring, wherein the molten steel comprises the following components (Ca): 0.0027 wt%, [ Al ]: 0.028 wt%, [ S ]: 0.035 wt%.
And fourthly, continuously casting.
The whole process adopts closed protective pouring to avoid secondary oxidation of molten steel. The superheat degree of the molten steel in the tundish is 39 ℃, the casting furnace is started, and the size of a casting blank is 320mm multiplied by 425 mm. The pouring time is 5 furnaces for normal production, and the total rising of the stopper rod curve is 4.2 mm.
Example 2
Provides a Ca alloying method of high-aluminum calcium sulfur composite free-cutting steel, the chemical components of which are shown in Table 1, and the Ca alloying method is prepared according to the following smelting method:
in the first step, 130 tons of top-bottom combined blown converter.
110 tons of molten iron and 20 tons of scrap steel are used as main raw materials, the C content in the molten steel is 0.12 wt% during tapping, and the temperature is 1590 ℃. Adding aluminum iron, carbon powder, ferrosilicon, ferromanganese, ferrochromium and slag charge in the tapping process.
And secondly, LF refining.
After the LF station, slag materials such as lime, a compound deoxidizer and the like are added for slagging operation. The [ Ca ] content in the steel after LF refining is 0.0009 wt%.
And thirdly, RH vacuum smelting.
Keeping the vacuum chamber pressure at 67Pa for 18 minutes, firstly adding Ca wires after the vacuum refining finishes repressing, adding Al wires after 3 minutes, and sampling after 5 minutes, wherein the molten steel comprises the following components of [ Ca ]: 0.0019 wt%, [ Al ]: 0.014 wt%; then Ca wire was added, after 3 minutes S wire was added, finally Al wire was added, after 5 minutes sampling, [ Ca ]: 0.0029 wt%, [ Al ]: 0.028 wt%, stirring with weak argon for 15 minutes, lifting and pouring, wherein the molten steel component before lifting is [ Ca ]: 0.0026 wt%, [ Al ]: 0.025 wt%, [ S ]: 0.032 wt%.
And fourthly, continuously casting.
The whole process adopts closed protective pouring to avoid secondary oxidation of molten steel. The superheat degree of the molten steel in the tundish is 33 ℃, the continuous casting furnace is adopted, and the size of a casting blank is 320mm multiplied by 425 mm. The pouring time is 5 furnaces for normal production, and the total rising of the stopper rod curve is 3.3 mm.
Example 3
Provides a Ca alloying method of high-aluminum calcium sulfur composite free-cutting steel, the chemical components of which are shown in Table 1, and the Ca alloying method is prepared according to the following smelting method:
in the first step, 130 tons of top-bottom combined blown converter.
110 tons of molten iron and 20 tons of scrap steel are used as main raw materials, the C content in the molten steel is 0.09 percent during tapping, and the temperature is 1602 ℃. Adding aluminum iron, carbon powder, ferrosilicon, ferromanganese, ferrochromium and slag charge in the tapping process.
And secondly, LF refining.
After the LF station, slag materials such as lime, a compound deoxidizer and the like are added for slagging operation. The content of [ Ca ] in the steel after LF refining is 0.0013 wt%.
And thirdly, RH vacuum smelting.
Keeping the vacuum chamber pressure at 67Pa for 16 minutes, firstly adding Ca wires after the vacuum refining finishes repressing, adding Al wires after 3 minutes, and sampling after 5 minutes, wherein the molten steel comprises the following components of [ Ca ]: 0.0016 wt%, [ Al ]: 0.009 wt%; then Ca wire was added, after 3 minutes S wire was added, finally Al wire was added, after 5 minutes sampling, [ Ca ]: 0.0034 wt%, [ Al ]: 0.027 wt%, stirring with weak argon for 13 minutes, lifting and pouring, wherein the molten steel component before lifting is [ Ca ]: 0.0029 wt%, [ Al ]: 0.025 wt%, [ S ]: 0.030 wt%.
And fourthly, continuously casting.
The whole process adopts closed protective pouring to avoid secondary oxidation of molten steel. The superheat degree of the molten steel in the tundish is 36 ℃, the continuous casting furnace is adopted, and the size of a casting blank is 320mm multiplied by 425 mm. The pouring time is 4 furnaces for normal production, and the total rising of the stopper rod curve is 3.9 mm.
Example 4
Provides a Ca alloying method of high-aluminum calcium sulfur composite free-cutting steel, the chemical components of which are shown in Table 1, and the Ca alloying method is prepared according to the following smelting method:
in the first step, 130 tons of top-bottom combined blown converter.
110 tons of molten iron and 20 tons of scrap steel are used as main raw materials, the C content in the molten steel is 0.10 wt% during tapping, and the temperature is 1602 ℃. Adding aluminum iron, carbon powder, ferrosilicon, ferromanganese, ferrochromium and slag charge in the tapping process.
And secondly, LF refining.
After the LF station, slag materials such as lime, a compound deoxidizer and the like are added for slagging operation. The content of [ Ca ] in the steel after LF refining is 0.0010 wt%.
And thirdly, RH vacuum smelting.
Keeping the vacuum chamber pressure at 67Pa for 18 minutes, firstly adding Ca wires after the vacuum refining finishes repressing, adding Al wires after 3 minutes, and sampling after 5 minutes, wherein the molten steel comprises the following components of [ Ca ]: 0.0018 wt%, [ Al ]: 0.014 wt%, Ca wire was then added, S wire was added after 3 minutes, Al wire was finally added, sampling was performed after 5 minutes, [ Ca ]: 0.0030 wt%, [ Al ]: 0.031 wt%. Stirring the mixture for 15 minutes by using weak argon, then lifting the mixture for pouring, wherein the molten steel comprises the following components (Ca): 0.0027 wt%, [ Al ]: 0.024 wt%, [ S ]: 0.038 wt%.
And fourthly, continuously casting.
The whole process adopts closed protective pouring to avoid secondary oxidation of molten steel. The superheat degree of the molten steel in the tundish is 36 ℃, the casting furnace is started, and the size of a casting blank is 320mm multiplied by 425 mm. The pouring time is 6 furnaces for normal production, and the total rising of the stopper rod curve is 6.7 mm.
Comparative example 1
Provides a smelting method of high-aluminum calcium sulfur composite free-cutting steel, the chemical components of which are shown in Table 1, and the high-aluminum calcium sulfur composite free-cutting steel is prepared according to the following smelting method:
in the first step, 130 tons of top-bottom combined blown converter.
110 tons of molten iron and 20 tons of scrap steel are used as main raw materials, the C content in the molten steel is 0.10 wt% during tapping, and the temperature is 1599 ℃. Adding aluminum iron, carbon powder, ferrosilicon, ferromanganese, ferrochromium and slag charge in the tapping process.
And secondly, LF refining.
After the LF station, slag materials such as lime, a compound deoxidizer and the like are added for slagging operation. The [ Ca ] content in the steel after LF refining is 0.0009 wt%.
And thirdly, RH vacuum smelting.
Keeping the vacuum chamber pressure at 67Pa for 15 minutes, adding Ca wires after the vacuum refining is finished and the re-pressing, adding no Al wires, and sampling after 5 minutes, wherein the molten steel comprises the following components of [ Ca ]: 0.0014 wt%, [ Al ]: 0.004 wt%; then Ca wire was added, after 3 minutes S wire was added and finally Al wire was added. Stirring the mixture for 15 minutes by using weak argon, then lifting the mixture for pouring, wherein the molten steel comprises the following components (Ca): 0.0022 wt%, [ Al ]: 0.029 wt%, [ S ]: 0.031 wt%.
And fourthly, continuously casting.
The whole process adopts closed protective pouring to avoid secondary oxidation of molten steel. The superheat degree of the molten steel of the tundish is 32 ℃, the plug rod obviously rises in the last furnace of the continuous casting furnace, the single furnace rises 8.7mm, the casting time normally produces 5 furnaces, and the whole casting time rises 13.9 mm. The size of the cast slab is "320 mm × 425 mm".
Comparative example 2
Provides a smelting method of high-aluminum calcium sulfur composite free-cutting steel, the chemical components of which are shown in Table 1, and the high-aluminum calcium sulfur composite free-cutting steel is prepared according to the following smelting method:
in the first step, 130 tons of top-bottom combined blown converter.
110 tons of molten iron and 20 tons of scrap steel are used as main raw materials, the C content in the molten steel is 0.13 wt% during tapping, and the temperature is 1586 ℃. Adding aluminum iron, carbon powder, ferrosilicon, ferromanganese, ferrochromium and slag charge in the tapping process.
And secondly, LF refining.
After the LF station, slag materials such as lime, a compound deoxidizer and the like are added for slagging operation. And after LF refining is finished. The content of [ Ca ] in the steel after LF refining is 0.0002 wt%, and Ca wires are not added in the process.
And thirdly, RH vacuum smelting.
Keeping the vacuum chamber pressure at 67Pa for 18 minutes, adding a Ca wire and then an Al wire after the vacuum refining finishes repressing, and sampling after 5 minutes, wherein the molten steel comprises the following components of [ Ca ]: 0.0011 wt%, [ Al ]: 0.012 wt%; then Ca wire was added, after 3 minutes S wire was added and finally Al wire was added. Stirring the mixture for 15 minutes by using weak argon, then lifting the mixture for pouring, wherein the molten steel comprises the following components (Ca): 0.0019 wt%, [ Al ]: 0.021 wt%, [ S ]: 0.031 wt%.
And fourthly, continuously casting.
The whole process adopts closed protective pouring to avoid secondary oxidation of molten steel. The superheat degree of the molten steel of the tundish is 33 ℃, the continuous casting furnace is adopted, the stopper rod rises to some extent, the single furnace rises by 8.2mm, the casting time produces 3 furnaces, and the stopper rod rises by 10.3mm in the whole casting time. The size of the cast slab is "320 mm × 425 mm".
Comparative example 3
Provides a smelting method of high-aluminum calcium sulfur composite free-cutting steel, the chemical components of which are shown in Table 1, and the high-aluminum calcium sulfur composite free-cutting steel is prepared according to the following smelting method:
in the first step, 130 tons of top-bottom combined blown converter.
110 tons of molten iron and 20 tons of scrap steel are used as main raw materials, the C content in the molten steel is 0.08 percent during tapping, and the temperature is 1604 ℃. Adding aluminum iron, carbon powder, ferrosilicon, ferromanganese, ferrochromium and slag charge in the tapping process.
And secondly, LF refining.
After the LF station, slag materials such as lime, a compound deoxidizer and the like are added for slagging operation. The content of [ Ca ] in the steel after LF refining is 0.0010 wt%.
And thirdly, RH vacuum smelting.
Keeping the pressure of the vacuum chamber at 67Pa for 17 minutes, adding a Ca wire and then an Al wire after the vacuum refining finishes and repressing, and sampling after 5 minutes, wherein the composition of molten steel is [ Ca ]: 0.0029 wt%, [ Al ]: 0.016 wt% and excessive calcium; because the Ca content is high and meets the target content requirement, the second Ca alloying is not carried out, an S line is added after 3 minutes, and the sampling is carried out after 5 minutes, wherein the molten steel comprises the following components of [ Ca ]: 0.0025wt%, [ S ]: 0.038 wt%; finally, an Al wire is added. Stirring the mixture for 15 minutes by using weak argon, then lifting the mixture for pouring, wherein the molten steel comprises the following components (Ca): 0.0018 wt%, [ Al ]: 0.022 wt%, [ S ]: 0.034 wt%.
And fourthly, continuously casting.
The whole process adopts closed protective pouring to avoid secondary oxidation of molten steel. The superheat degree of the molten steel of the tundish is 31 ℃, the continuous casting furnace is adopted, the stopper rod rises, the single furnace rises by 7.5mm, the casting is carried out for 3 furnaces, and the stopper rod rises by 9.7mm in the whole casting. The size of the cast slab is "320 mm × 425 mm".
TABLE 1 contents (wt%) of elemental chemical components in rolled materials of examples 1 to 4 and comparative examples 1 to 3
Element(s) C Si Mn P S Al Ca N
Example 1 0.40 0.21 1.55 0.014 0.034 0.026 0.0022 0.009
Example 2 0.41 0.20 1.57 0.011 0.032 0.023 0.0023 0.010
Example 3 0.35 0.24 0.82 0.011 0.027 0.022 0.0026 0.006
Example 4 0.48 0.24 0.75 0.014 0.036 0.019 0.0019 0.005
Comparative example 1 0.41 0.20 1.54 0.015 0.029 0.024 0.0014 0.010
Comparative example 2 0.36 0.25 0.80 0.017 0.027 0.018 0.0013 0.005
Comparative example 3 0.48 0.23 0.73 0.017 0.032 0.020 0.0011 0.005
It can be seen from comparative examples 1 to 4 and comparative examples 1 to 3 that:
the smelting process in the embodiments 1 to 4 meets the requirements of the invention, the rising amplitude of the stopper rod is small in the production process, the production is smooth, the continuous casting of 4 furnaces and above is realized, and the chemical components of the steel meet the requirements of Al: 0.015wt% -0.030 wt%, S: 0.020wt% -0.060 wt%, Ca: 0.0015 to 0.0035 weight percent.
In comparative example 1, no Al wire was added after the first Ca alloying, the production amount of calcium aluminate having a low melting point was small, the production amounts of CaO-based oxides and CaS having a high melting point were large, the Ca element loss was large, and the process control was unstable. In addition, in the pouring process, the diameter of a water gap is only about 10mm, the CaS in the molten steel can be enriched at the position of the water gap, even the water gap can be blocked, the CaS enriched at the position of the water gap is equivalently filtered and removed from the molten steel, the content of Ca in a finally obtained finished product is very low, the requirement is not met (<15ppm), and the stopper rod obviously rises.
In comparative example 2, the content of Ca in the LF refining process was low, and the end point Ca content was controlled without adding Ca lines, resulting in an LF outbound Ca content that did not meet the optimal content requirements of the invention. After the Ca line is added for the first time after vacuum repression, the content of Ca is low and is less than a target value, and the generation amount of stable Ca-containing liquid oxide in the steel is small; during the second Ca alloy, a large amount of Ca wires and the S element in the molten steel are supplemented to generate unstable CaS which is easy to float and remove, so that the Ca content of the finished product is low (<15 ppm). In addition, the generation of more CaS can cause the nozzle stopper to have stronger rising tendency, the stopper rises by 8.2mm in a single furnace, and the continuous casting heat number is reduced.
In the comparative example 3, the addition amount is too large during the first Ca alloying after the RH vacuum is finished, CaO oxides with high melting point are mainly generated in the molten steel, the oxides easily float up to enter a slag phase, and the requirement of the invention on the optimal content is not met. The content of [ O ] in the molten steel is sharply reduced due to the excessively high Ca content, Ca elements mainly exist in the molten steel in the form of CaS and are easy to float upwards, the Ca content control effect is poor, the Ca content of finished products is low (<15ppm), in addition, the generation of more CaS can cause a water gap stopper to have a stronger upward trend, the single furnace of the stopper rises by 7.5mm, and the continuous casting heat number is reduced.
The inclusions at the radius position of the aluminum-calcium-sulfur composite free-cutting steel rolled material 1/2 provided in examples 1 to 4 and comparative examples 1 to 3 were examined. The results show that:
in example 1: the rolled stock mainly comprises pure MnS and complex oxysulfide, and the appearance is shown in figure 1. The main component of the core of the composite oxysulfide is alumina or calcium aluminate with low CaO proportion, the main component of the periphery of the core of the composite oxysulfide is (Ca, Mn) S, the typical appearance of the core of the composite oxysulfide is shown in figure 2, and the number of the composite oxysulfide is 68/mm2。
In example 2: the rolled stock mainly comprises pure MnS and complex oxysulfide, and the appearance is shown in figure 3. The main component of the core of the compound oxysulfide is alumina or calcium aluminate, the main component of the periphery is (Ca, Mn) S, and the number of the compound oxysulfide is 72/mm2。
In example 3: the rolled stock mainly comprises pure MnS and complex oxysulfide, and the appearance is shown in figure 4. The main component of the core of the composite oxysulfide is alumina or calcium aluminate with low CaO proportion, the peripheral main component is (Ca, Mn) S, the number of the S is 64/mm2。
In example 4: the rolled stock mainly comprises pure MnS and complex oxysulfide, and the appearance is shown in figure 5. The main component of the core of the complex oxysulfide isAlumina or calcium aluminate with low CaO content, the outer main component of the alumina or calcium aluminate is (Ca, Mn) S, the number of the S is 39/mm2。
In comparative example 1: the rolled stock mainly comprises strip-shaped pure MnS and large-size composite oxysulfide, and the appearance is shown in figure 6. The main component of the core of the compound oxysulfide is calcium aluminate, the main component of the periphery of the core is (Ca, Mn) S, and the number of the compound oxysulfide is 24/mm2。
In comparative example 2: the strip-shaped pure MnS and the large-size composite oxysulfide are mainly contained in the rolled stock, and the appearance is shown in figure 7. The main component of the core of the compound oxysulfide is calcium aluminate, the main component of the periphery of the core is (Ca, Mn) S, and the number of the compound oxysulfide is 26/mm2。
In comparative example 3: the strip-shaped pure MnS is mainly used in the rolled material, and the appearance is shown in figure 8. The number of the composite oxysulfide is 11/mm2。
In conclusion, the method for alloying Ca in the high-aluminum calcium sulfur composite free-cutting steel provided by the application has the advantages that the Ca is stably controlled in the smelting process, and [ Ca ] is controlled in the molten steel cooling and pouring processes]、[S]、[Al]Stable control of element content, Al easy to block water gap2O3And CaS inclusion is not easy to generate, a water gap is not easy to nodulate, and the castability is good.
The foregoing is merely exemplary of the present application and is not intended to limit the present application, which may be modified or varied by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (7)

1. A method for Ca alloying in a high aluminum calcium sulfur composite free-cutting steel, the method comprising: converter or electric furnace smelting, LF refining, RH or VD vacuum treatment, continuous casting process, characterized in that, in the LF refining process, the control terminal Ca content satisfies: 0.0008wt% -0.0015 wt%; and after the vacuum treatment is finished, sequentially carrying out first Ca alloying, first Al alloying, second Ca alloying, S alloying and second Al alloying.
2. The method as claimed in claim 1, wherein in the LF refining process, if the Ca content of the molten steel in the middle of LF smelting is less than 0.0008wt%, Ca alloy is added, so that after the LF refining is finished, the Ca content in the molten steel satisfies the following conditions: 0.0008wt% to 0.0015 wt%.
3. The method of claim 1, wherein the target Ca content in the first Ca alloying is controlled in a range of 0.0012wt% to 0.0020wt%, and the target Ca content in the second Ca alloying is controlled in a range of 0.0025wt% to 0.0035 wt%.
4. The method of claim 1, wherein the target Al content in the first Al-alloying is controlled within a range of 0.005wt% to 0.020wt%, and the target Al content in the second Al-alloying is controlled within a range of 0.020wt% to 0.035 wt%.
5. The method according to claim 1, wherein in the converter or electric furnace smelting process, the content of C in the molten steel after smelting is satisfied: 0.08-0.15 wt%, and the temperature of molten steel is more than 1580 ℃.
6. An alumino-calcium-sulfur composite free-cutting steel, which is obtained by the method according to any one of claims 1 to 5, and which comprises, as main chemical components: c: 0.20wt% to 0.50wt%, Si: 0.15wt% -0.35 wt%, Mn: 0.60wt% -1.60 wt%, P: <0.020wt%, S: 0.020wt% -0.060 wt%, Al: 0.015wt% -0.030 wt%, Ca: 0.0015wt% -0.0035 wt%, N: 0.004-0.0012 wt%, and the balance of Fe and inevitable impurity elements.
7. The high-alumina calcium sulfur composite free-cutting steel as claimed in claim 6, wherein the main component of the composite oxysulfide core oxide in the steel is alumina or a low-CaO ratio calcium aluminate, and the main component of the peripheral sulfide is (Ca, Mn) S, and the number of the peripheral sulfide is 30 to 100/mm2。
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