CN107557531B - Barium alloy treated non-quenched and tempered steel sulfide inclusion control method - Google Patents
Barium alloy treated non-quenched and tempered steel sulfide inclusion control method Download PDFInfo
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Abstract
The application provides a method for controlling sulfide inclusions of non-quenched and tempered steel treated by barium alloy, which adopts barium alloy to control Al2O3Impurities are mixed for denaturation, and residual Al is caused while molten steel cleanliness is improved2O3The steel is distributed in a dispersed and uniform state and is used as a core for forming subsequent sulfide inclusions, the sulfur content of non-quenched and tempered steel is controlled to be 0.04-0.06%, continuous casting in 8 furnaces is realized under the condition that the sulfur content of the non-quenched and tempered steel is controlled by the Al, Ba and S content, the adding time and the method, the coarse system of the sulfide inclusions is less than or equal to 2.0 grade, and the fine system is less than or equal to 3.0 grade.
Description
Technical Field
The invention relates to the control of the composition, form and distribution of sulfide inclusions for improving the cutting performance in the production process of non-quenched and tempered steel, and belongs to the refining inclusion control technology in the field of ferrous metallurgy.
Background
The microalloy non-quenched and tempered steel is an ideal energy-saving and resource-saving economic new material, meets the requirements of development policies of the steel industry, and has wide economic and social benefits and market prospects. The method has wide application, and is mainly used for manufacturing various workpieces such as crankshafts, connecting rods, transmission shafts, steering knuckles and the like of automobiles and engineering machinery. The non-quenched and tempered steel for the automobile can reduce energy consumption and cost, reduce deformation and cracking caused by quenching in a quenching and tempering process, and realize light weight. In recent years, with the increase of automobile output and automobile holding capacity in China, the pressure of energy conservation and emission reduction is rapidly increased. However, the application of non-quenched and tempered steel for automobiles in China is not widespread, and the non-quenched and tempered steel only accounts for 7% of special steel for automobiles, while the non-quenched and tempered steel accounts for 33% in Japan. Under the condition that the current situation of energy shortage in China conforms to the international development trend, the expansion of the application of non-quenched and tempered steel in the industry of China has important significance.
In germany, sweden and japan, the research and application of non-quenched and tempered steel have been successful. China began to enter a line for researching and developing non-quenched and tempered steel in the 80 th century, but has obvious gap with China such as Japan and Germany in the aspects of standard level, stability of steel quality and the like, and influences the popularization and application of the non-quenched and tempered steel.
In order to improve the cutting processing performance of non-quenched and tempered steel for automobiles, a proper amount of sulfur (generally 0.035-0.08%) is added into the steel, so that the chip breaking during the cutting processing of products can be promoted, the service life of a cutting tool is prolonged, the surface smoothness of the products is improved, and the machining performance of steel products is improved. However, after rolling deformation, sulfides in steel are easy to generate thin and long manganese sulfide, and anisotropy of the mechanical properties of steel is caused, so that the precipitation of the sulfides in the steel is reasonably controlled to enable the sulfides to have proper shape, size, quantity and distribution, the method has important significance for improving the comprehensive properties of high-quality steel such as non-quenched and tempered steel, and the shape control of the sulfides is one of the difficult problems which are addressed by the metallurgical industry. Calcium treated sulfur containing non-quenched and tempered steels are currently the most studied and most commonly used method in industrial production. But the control means of the form and the size of the sulfide in the prior sulfur-containing non-quenched and tempered steel is limited, and the related mechanism research is lack of depth. Therefore, the research and development of the sulfide control technology for the solidification process of the sulfur-containing microalloy non-quenched and tempered steel for the automobile has wide market prospect and great social benefit.
At present, main research work is carried out around controlling the form and size of sulfide in steel, wherein the form of the sulfide is controlled by adding sulfide forming elements, and the sulfide is finely and dispersedly precipitated by controlling oxides serving as sulfide precipitation cores. Different researchers have conducted a series of studies on the problem from different angles, and the formation mechanism of sulfide and the influence of different process factors on the form of sulfide in steel are studied.
The method of improving the quality of steel by modifying sulfide inclusions by calcium-adding treatment of molten steel has been widely used in steel-making production. Document 7 describes an industrial comparative experimental study on the morphology of calcium-treated modified sulfides, and quantitatively analyzes the morphology and the component type of sulfides in rods. The results show that: the calcium treatment can form more complex sulfides in the steel, and the calcium content in the sulfides is improved, so that the aspect ratio of the sulfides is obviously reduced. Meanwhile, the research finds that the improvement of Mn/S is beneficial to improving the as-cast state and the distribution uniformity of sulfides in the bar; as the increase of Mn/S is beneficial to the spheroidization or spindle control of sulfide, the Mn/S under the experimental condition should be controlled to be about 40.
The influence of magnesium and magnesium-calcium treatment on the form of sulfides in non-quenched and tempered steel researches the influence of magnesium treatment and magnesium-calcium composite treatment on the form, size and distribution of sulfides in non-quenched and tempered steel, and shows that modification causes the as-cast sulfides to be converted from II type to III type and I type, so that the distribution of sulfides is improved, but the size is increased.
The study of rare earth metamorphic sulfides in "rules of action and optimal control of rare earth in steel" published in the university of Beijing science and technology "shows that in order to obtain high quality rare earth treated steel, the range of the appropriate RE/s ratio in steel must be controlled. The influence of the rare earth bowl magnesium composite modifier on inclusions in 55400 steel published in the university of inner Mongolia science and technology by RE-Mg composite modification treatment on sulfur-containing steel shows that the sizes of the inclusions are obviously reduced and the inclusions are uniformly distributed, and long strip-shaped easy-to-deform MnS inclusions are replaced by small-sized spherical and dispersedly distributed rare earth and magnesium composite inclusions. The grade of coarse sulfide in steel is obviously reduced, the grade of fine sulfide is increased, larger inclusions in steel are transformed into fine inclusions, and the size of the inclusions in steel is greatly improved.
The results of the smelting and forging experiments on the sulfur-containing non-quenched and tempered steel in the laboratory, which are published by "control of sulfide morphology in sulfur-containing non-quenched and tempered steel" of January, Chengweig, Mengkui show that the size and the number of sulfide inclusions in the steel are reduced and increased with the increase of the solidification rate of the steel; with the increase of the forging and pressing compression ratio, sulfide inclusions are cracked and become fine; the plasticity of the sulfide is the best when the alloy is forged at 950 ℃, the plasticity of the sulfide is better at 1250 ℃, and the plasticity of the sulfide is poorer between 1050 and 1150 ℃; as the holding time during heating is prolonged, the number of sulfide inclusions decreases and the size increases.
"research on development of non-heat-treated steel by applying oxide metallurgy" published in Henan metallurgy applies oxide metallurgy to the research on non-heat-treated steel, and it is confirmed that the size and amount of MnS can be adjusted by dispersing oxides in steel.
The research on the concept of controlling sulfides in steel by carrying out isothermal heat treatment on a YF45MnV steel continuous casting billet is provided by the influence of isothermal heat treatment on sulfides in YF45MnV steel published in the Material Heat treatment academic newspaper, and the research shows that the sulfides in the YF45MnV steel continuous casting billet can be controlled to be in a smaller size and an ideal shape (a spindle shape and a nearly spherical shape) by proper heat treatment parameters; coarse austenite after isothermal treatment can realize grain refinement through a subsequent deformation process.
The 'free-cutting non-quenched and tempered steel solidification process and MnS precipitation law in steel' published in the material heat treatment academic newspaper takes a typical free-cutting non-quenched and tempered steel type YF45MnV as a research object, thermodynamic calculation software is used for calculating and researching the precipitation behavior of steel, a Scheil-Gulliver model is used for calculating and simulating a solidification process which has obvious influence on the shape distribution of sulfides, and the segregation behavior of alloy elements in the solidification process is researched.
Theoretical analysis of elements controlling Ostwald ripening of manganese sulfide in Steel according to the theory of Ostwald ripening of the second phase in dilute solution, the influence of the relative content of sulfur and manganese elements in steel on the elements controlling Ostwald ripening of manganese sulfide in steel is analyzed and calculated. When the manganese content in the manganese-containing alloy steel, the low-alloy high-strength steel and the plain carbon steel is more than 0.17 percent, the control element of the Ostwald ripening process of manganese sulfide is sulfur.
The solute microsegregation model of the steel continuous casting process considers the thermodynamic conditions of/gamma phase transformation and MnS precipitation in the steel solidification process, establishes a solute microsegregation model coupling MnS inclusion precipitation, and analyzes the influence rule of steel type components, MnS inclusion precipitation and cooling rate on the high-temperature mechanical property of the steel solidification process.
A mathematical model for analyzing the change of the composition of non-metallic inclusions including sulfides was developed by controlling and utilizing micro-segregation and macro-segregation in the steel solidification process published in the annual meeting prosecution of iron and steel in 2007, and the critical point segregation size for preventing Mns from being precipitated in the continuously cast slab was indicated.
When the high-temperature mechanical properties of steel are studied, it is found that almost all sulfur in steel is re-dissolved at this time after the solution treatment at 1330 ℃, and S is re-precipitated as sulfide at grain boundaries as solidification proceeds, and the re-precipitation of S has a great influence on the plasticity of steel. CaS can be uniformly dissolved in MnS to form (Ca, Mn) S inclusions, the solid solution strengthening effect of CaS can increase the hardness of sulfide, and the hardness of sulfide is increased along with the increase of the content of sulfide.
Moreover, a large number of research results show that the size of manganese sulfide in the continuous casting billet influences the deformation behavior of the continuous casting billet in subsequent rolling. When the manganese sulfide is less than 5 μm, the shaping is reduced along with the reduction of the size; when it is less than 1 μm, manganese sulfide does not even deform during rolling. If the sulphides in the steel can be controlled to a smaller size before rolling, their deformation during the subsequent rolling will be greatly reduced.
In summary, the sulfide inclusion denaturation and solidification process is one of the most important processes for controlling sulfide composition, morphology and distribution. However, at present, the research on sulfide formation mechanism in the solidification process of sulfur-containing non-quenched and tempered steel is less, the control level is lower, and sulfur in steel mainly exists in II-type MnS in cluster distribution, so that the comprehensive performance of steel is poor, the requirements of domestic customers cannot be met, and a large amount of import is needed.
The invention develops a sulfide control technology based on barium alloy treatment on the basis of summarizing and analyzing the sulfide formation and control technology in sulfur-containing non-quenched and tempered steel for automobiles at home and abroad.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the prior art has the technical problems of low control level, poor comprehensive performance of steel, high S content, high impurity content, easy occurrence of nozzle nodulation in the continuous casting process and the like.
The technical scheme is as follows:
a method for controlling sulfide inclusions of non-quenched and tempered steel treated by barium alloy comprises the following steps:
the first step is as follows: smelting steel, and adding a final deoxidizer grain refining element into molten steel in the tapping process of a converter, wherein the final deoxidizer grain refining element is aluminum, and the addition amount of the aluminum is 0.01-0.05% of the mass of the molten steel;
the second step is that: adding barium alloy into the molten steel at the end of LF refining to the Al generated in the first step2O3Performing inclusion modification, wherein the addition amount of the barium alloy is 0.0001-0.03 percent of the mass of the molten steel;
the third step: after VD vacuum degassing, sulfide is added into the molten steel to form composite sulfide with oxide as core, and the addition amount of the sulfide is 0.01-0.08% of the mass of the molten steel.
As a preferred technical scheme of the invention: the sulfide adopts sulfur, iron sulfide, cored wires fed with sulfur or cored wires fed with iron sulfide.
As a preferred technical scheme of the invention: the barium alloy is SiBa core-spun yarn, SiCaBa core-spun yarn, SiAlBa core-spun yarn or SiCaAlBa core-spun yarn.
As a preferred technical scheme of the invention: the control range of the Al content in the steel treatment process is as follows: 0.01-0.05%, the control range of Ba content is: 0.0001-0.030%, the control range of S content is as follows: 0.01-0.08%.
As a preferred technical scheme of the invention: the addition time of the sulfide is more than or equal to 10min after the barium alloy is added.
Has the advantages that:
1. the barium alloy is added to carry out oxide inclusion modification treatment on the steel which is not added with sulfur, so that the cleanliness of the sulfur-containing non-quenched and tempered steel is improved, and the residual Al is refined and homogenized2O3The inclusion is taken as a formation core for forming sulfide inclusion.
2. By the technical measures of adding Ba first and then adding S and controlling the content of Ba to be 0.0001-0.030% and the content of sulfur to be 0.010-0.080%, the sulfur content is stabilized and the sulfide is denatured. And prevents nozzle clogging during continuous casting.
3. For C70S6BY steel, Al content of 0.015% was added during converter tapping, Ba content of 0.01% was added at the end of ladle refining in a theoretical amount, and S content of 0.065% was added after vacuum treatment. Finally, the effect that sulfide inclusions are less than 2 grades and the continuous casting is carried out for more than 8 furnaces is obtained.
4. For F45MnVS, aluminum deoxidation is adopted in the process of tapping through an electric furnace, the aluminum content is adjusted to 0.040-0.060% in the first sample of LF, and a silicon-calcium-barium cored wire of 2 m/ton steel is fed at the end of LF refining. After VD vacuum degassing, breaking vacuum and adding sulfur to 0.030-0.050%. Finally, the effect that sulfide inclusions are less than 2 grades and the continuous casting is carried out for more than 10 furnaces is obtained.
The specific implementation mode is as follows:
embodiments of the present invention are described in further detail below by way of specific implementations.
Example 1:
1) steel grade: C70S6BY
2) The process flow comprises the following steps: 100-ton converter smelting → LF refining + VD vacuum degassing → continuous casting 220 multiplied by 280 blank → heat preservation, cleaning → heating furnace heating → production of phi 70mm material → heat preservation → straightening → peeling → acid cleaning, cleaning → ultrasonic flaw detection → sampling inspection and analysis. Wherein aluminum is added in the tapping process of the converter, barium alloy is fed in after LF refining is finished, and residual Al is added while molten steel cleanliness is improved2O3The inclusions are denatured into oxide inclusion cores distributed in a dispersed manner, which serve as a basis for further forming oxide-cored sulfides, and the sulfides are added after VD vacuum degassing.
3) Essential point of process control
(1) Deoxidizer alloying of converter tapping
Adding aluminum to perform pre-deoxidation operation in the converter tapping process, wherein the specific adding sequence is as follows: ferrosilicon, silicomanganese, high chromium → aluminum → ferrosilicon → high nitrogen carburant → lime, the specific addition is as shown in the following table:
(2) refining and deoxidizing to adjust components, wherein the components of molten steel before barium alloy is added are as follows:
0.021% mass part of SiBa core-spun yarn, namely 1.5 m/ton steel is fed.
(3) Composition of refining slag in refining process
| Timing of sampling | SiO2 | FeO | Al2O3 | CaO | MgO | Alkalinity of |
| After VD | 14.45 | 1.1 | 26.9 | 44.96 | 6.31 | 3.55 |
| Before the hoist | 15.1 | 0.87 | 30.67 | 39.56 | 6.86 | 3.07 |
(4) Adjusting the sulfur content of steel smelting chemical components, and adjusting the molten steel components after sulfur content adjustment
And after VD vacuum degassing, adding a cored wire fed with sulfur to adjust the sulfur content to meet the technical agreement requirement of steel grade.
(5) Non-metallic inclusions in steel
(6) Gas content in steel
Example 2:
1) steel grade: f45MnV
2) The process flow comprises the following steps: 70-ton EAF converter smelting → LF refining + VD vacuum degassing → continuous casting 180X 240 billet → slow cooling/heat conveying → heating furnace heating → material production → slow cooling → straightening → finishing → ultrasonic flaw detection → inspection and warehousing. Wherein aluminum is added in the tapping process of the converter, barium alloy is fed in after LF refining is finished, and residual Al is added while molten steel cleanliness is improved2O3The inclusion denaturation is oxide inclusion core distributed in a dispersion way, which is used as the basis for further forming sulfide taking oxide as the core, and the sulfide is added after the barium alloy is added for more than or equal to 10 min.
3) Essential point of process control
(1) The alloy and aluminum contents were adjusted during refining by adding aluminum during tapping of the electric furnace for preliminary deoxidation as shown in the table below.
(2) Then 2.0 m/ton of Si-Ca-Ba core-spun yarn is fed. Followed by VD vacuum treatment. Composition of refining slag in refining process
| CaO | SiO2 | FeO | Al2O3 | MgO | Alkalinity of |
| 48.90 | 17.81 | 0.93 | 12.9 | 6.31 | 2.75 |
(3) Chemical composition of steel smelting, molten steel composition after regulating sulfur content
After vacuum treatment, according to the actual sulfur content in the steel, adding a cored wire fed with iron sulfide to adjust the sulfur content to the range required by the steel grade technical agreement.
(4) Non-metallic inclusions in steel
Claims (4)
1. A method for controlling sulfide inclusions of non-quenched and tempered steel treated by barium alloy is characterized by comprising the following steps:
the first step is as follows: smelting steel, and adding a final deoxidizer grain refining element into molten steel in the tapping process of a converter, wherein the final deoxidizer grain refining element is aluminum, and the adding amount of the aluminum is 0.01-0.05% of the mass of the aluminum in the molten steel;
the second step is that: adding barium alloy into the molten steel at the end of LF refining to the Al generated in the first step2O3Performing inclusion modification, wherein the addition amount of the barium alloy is 0.0001-0.03 percent of the mass of barium in the molten steel;
the third step: after VD vacuum degassing, sulfide is added into the molten steel to form composite sulfide with oxide as core, the addition amount of the sulfide is 0.01-0.08% of the mass of sulfur in the molten steel, and the addition time of the sulfide is more than or equal to 10min after barium alloy is added.
2. The method for controlling sulfide inclusions in non-quenched and tempered steel processed by a barium alloy according to claim 1, wherein the method comprises the following steps: the sulfide adopts sulfur, iron sulfide, cored wires fed with sulfur or cored wires fed with iron sulfide.
3. The method for controlling sulfide inclusions in non-quenched and tempered steel processed by a barium alloy according to claim 1, wherein the method comprises the following steps: the barium alloy is SiBa core-spun yarn, SiCaBa core-spun yarn, SiAlBa core-spun yarn or SiCaAlBa core-spun yarn.
4. The method for controlling sulfide inclusions in a barium alloy treated non-quenched and tempered steel according to claim 1, wherein: the control range of the Al content in the steel treatment process is as follows: 0.01-0.05%, the control range of Ba content is: 0.0001-0.030%, the control range of S content is as follows: 0.01-0.08%.
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