GB2410252A - High-cleanliness steel and process for producing the same - Google Patents
High-cleanliness steel and process for producing the same Download PDFInfo
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- GB2410252A GB2410252A GB0509770A GB0509770A GB2410252A GB 2410252 A GB2410252 A GB 2410252A GB 0509770 A GB0509770 A GB 0509770A GB 0509770 A GB0509770 A GB 0509770A GB 2410252 A GB2410252 A GB 2410252A
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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
- C21C7/10—Handling in a vacuum
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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
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/06—Deoxidising, e.g. killing
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Abstract
A process for producing a high-cleanliness steel, comprising the steps of: subjecting a molten steel to oxidizing refining in an arc melting furnace or a converter; adding a deoxidizer to the molten steel in the furnace before tapping to deoxidize the molten steel; transferring the deoxidized molten steel to a ladle furnace to perform ladle refining; and then circulating the refined molten steel through a circulation-type vacuum degassing device to degas the molten steel.
Description
_ 24 10252
Description
HIGH-CLEANLINESS STEEL AND PROCESS FOR PRODUCING THE SAME
TECHNICAL FIELD
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The present invention relates to a high-cleanliness steel for use as steels for mechanical parts required to possess fatigue strength, fatigue life, and quietness, particularly, for example, as steels for rolling bearings, steels for constant velocity joints, steels for gears, steels for continuously variable transmission of toroidal type, steels for mechanical structures for cold forging, tool steels, and spring steels, and a process for producing the same.
Steels for use in mechanical parts required to possess fatigue strength and fatigue life should be high-cleanliness (low content of non-metallic inclusions in steels) steels.
Conventional production processes of these high-cleanliness steels include: (A) oxidizing refining of a molten steel in an arc melting furnace or a converter; (B) reduction refining in a ladle furnace (LF); (C) circulation vacuum degassing in a circulation-type vacuum degassing device (RH) (PH treatment); (D) casting of steel ingots by continuous casting or conventional ingot casting, and (E) working of steel ingots by press forging and heat treatment of steel products. In the process (A), scrap is melted by arc heating, or alternatively, a molten steel is introduced into a converter where oxidizing refining is performed, followed by the transfer of the molten steel to a ladle furnace.
The temperature, at which the molten steel is transferred, is generally a high temperature of about 30 C above to less than 100 C above the melting point of the steel. In the process (B), a deoxidizer alloy of aluminium, manganese, silicon, etc. is introduced into the ladle furnace, to which the molten steel has been transferred, where reduction refining is carried out by deoxidation and desulphurisation with a desulphuriser to regulate the alloying constituents. A generally accepted knowledge is such that the effect increased with increasing the treatment time.
In this process, a long time of more than 60 min is adopted, and the treatment temperature is generally 50 C above the melting point of the steel. In the RH treatment in the process (C), vacuum degassing is carried out in a circulation vacuum degassing tank while circulating the molten steel through the circulation vacuum degassing tank to perform deoxidation and dehydrogenation. In this case, the amount of the molten steel circulated is about to 6 times the total amount of the molten steel. In the process (D), the RH treated molten steel is transferred to a tundish where the molten steel is continuously cast into a bloom, a billet, a slab or the like. Alternatively, the molten steel from the ladle is poured directly into a steel ingot mold to cast a steel ingot.
In the process (E), for example, a bloom, a billet, a slab, or a steel ingot is rolled or forged, followed by heat treatment to prepare a steel product which is then shipped.
When steels having a particularly high level of cleanliness are required, in the above process, the cast steel ingot is provided as a raw material which is then subjected to vacuum re- melting or electroslag re-melting to prepare such steels.
In recent years, mechanical parts have become used under more and more severe conditions. This has lead to more and more severe requirements for properties of steel products, and steel products having a higher level of cleanliness have been required in the art. The above-described conventional production processes (A) to (E), however, are difficult to meet this demand.
In order to meet this demand, steel products have been produced by the vacuum re-melting or the electroslag resmelting. These methods, however, pose a problem of significantly increased production cost.
Under these circumstances, the present invention has been made, and it is an object of the present invention to provide steel products having a high level of cleanliness without relying upon the re-melting process.
DISCLOSURE OF THE INVENTIO
The present inventors have made extensive and intensive studies on the production process of high-cleanliness steels with a view to attaining the above object. As a result, they have found the cleanliness of steels can be significantly improved by the following processes.
The invention will be described. In the conventional process using a refining furnace, such as an arc melting furnace or a converter, melting and oxidizing refining are mainly carried out, for example, in the arc melting furnace or the converter, and the reduction period (deoxidation) is carried out in ladle refining furnace. On the other hand, the present invention is directed to a process for producing a high-cleanliness steel, comprising the steps of: subjecting a molten steel to oxidizing refining in an arc melting furnace or a converter; adding a deoxidizer including manganese, silicon, and aluminium (form of alloy of manganese, silicon, aluminium, etc. is not critical) in an amount of not less than 2 kg per ton of the molten steel to the molten steel in the same furnace before tapping to deoxidize the molten steel; transferring the deoxidized molten steel to a ladle furnace to perform ladle refining; and then circulating the refined molten steel through a circulation-type vacuum degassing device to degas the molten steel.
According to a preferred embodiment of the present invention, the molten steel is transferred to the ladle furnace in such a manner that the tapping temperature of the molten steel is at least 100 C above, preferably at least 120 C above, more preferably at least 150 C above, the melting point of the steel.
According to the present invention, preferably, the refining in the ladle furnace is carried out for not more than min. preferably not more than 45 min. more preferably 25 to min. The degassing subsequent to this step is generally carried out in a circulation-type vacuum degassing device in such a manner that the amount of the molten steel circulated is brought to not less than 5 times the total amount of the molten steel.
On the other hand, in the present invention, in the circulation-type vacuum degassing device, the amount of the molten steel circulated in the degassing is brought to at least 8 times, preferably at least 10 times, particularly preferably at least 15 times, larger than the total amount of the molten steel, and the degassing time is at least 25 min. The present invention embraces the high-cleanliness steel produced by the above production process.
According to the present invention, preferably, the content of oxygen in the steel is not more than 1O ppm. Preferably, when the content of carbon in the steel is less than 0.6% by mass, the content of oxygen in the steel is not more than 8 ppm.
Particularly preferably, in the case of C a 0.6% by mass, the oxygen content is not more than 6 ppm.
Preferably, in the steel according to the present invention, the number of oxide inclusions having a size of not less than Am as detected by dissolving the steel product in an acid, for example, oxide inclusions having an A1203 content of not less than 50t, is not more than 40, preferably not more than 30, more preferably not more than 20, per 100 g of the steel product.
In the steel of the present invention, for example, when the maximum inclusion diameter in 100 mm2 of the surface of the steel product is measured in 30 sites, the predicted value of the maximum inclusion diameter in 30000 mm2 as calculated according to statistics of extreme values is not more than 60 am, preferably not more than 40 m, more preferably not more than 25 m.
BRIEF DESCRIPTION OF THE DRAWINGS
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FIG. 1 is a diagram showing the oxygen content of products in 10 (heats) according to the process of the present invention using in-furnace deoxidation in the treatment of a molten steel of steel SUJ 2, and the oxygen content of products in 10 (heats) according to the conventional process wherein the in-furnace deoxidation is not carried out; FIG. 2 is a diagram showing the oxygen content of products in 10 (heats) according to the process of the present invention using in-furnace deoxidation in the treatment of a molten steel of steel SCM 435, and the oxygen content of products in 10 (heats) according to the conventional process wherein the in-furnace deoxidation is not carried out; FIG. 3 is a diagram showing the maximum predicted inclusion diameter according to statistics of extreme values in products in (heats) according to the process of the present invention using in- furnace deoxidation in the treatment of a molten steel of steel SUJ 2, and the maximum predicted inclusion diameter in products in (heats) according to the conventional process wherein the in- furnace deoxidation is not carried out; FIG. 4 is a diagram showing the maximum predicted inclusion diameter according to statistics of extreme values in products in (heats) according to the process of the present invention using in- furnace deoxidation in the treatment of a molten steel of steel SCM 435, and the maximum predicted inclusion diameter in products in 10 (heats) according to the conventional process wherein the in-furnace deoxidation is not carried out; FIG. 5 is a diagram showing the L1o life as determined by the thrust rolling service life test of products in 10 (heats) according to the process of the present invention using infurnace deoxidation in the treatment of a molten steel of steel SUJ 2, and the L1o life of products in 10 (heats) according to the conventional process wherein the in-furnace deoxidation is not carried out; and FIG. 6 is a diagram showing the Llo life as determined by the thrust rolling service life test of products in 10 (heats) according to the process of the present invention using in-furnace deoxidation in the treatment of a molten steel of steel SCM 435, and the L1o life of products in 10 (heats) according to the conventional process wherein the in-furnace deoxidation is not carried out.
A preferred production process of a high-cleanliness steel according to the invention comprises the following steps (1) to (5).
(1) A molten steel is subjected to oxidizing refining in an arc melting furnace or a converter. Subsequently, in the same furnace, a deoxidizer including manganese, silicon, and aluminium (form of alloy of manganese, silicon, and aluminium, etc. is not critical) is added in an amount of not less than 2 kg per ton of the molten metal, and, in some cases, a slag former, such as CaO, is simultaneously added to deoxidize the molten steel. The deoxidized molten steel is then transferred to a ladle. The deoxidation in a steel making furnace, such as an arc melting furnace or a converter, is a most important step in the present ! 6 invention. The deoxidation before the ladle refining, which has hitherto been regarded as unnecessary, to reduce the oxygen content to some extent before the ladle refining can finally realize the production of steels having low oxygen content.
(2) The molten steel transferred to the ladle is subjected to reduction refining and regulation of chemical composition in a ladle refining furnace.
(3) The molten steel, which has been subjected to reduction refining and regulation of chemical composition in step (2), is degassed by circulating the molten steel through a circulation- type vacuum degassing device, and, in addition, the chemical composition of the steel is finally regulated.
(4) The molten steel, which has been degassed and subjected to final regulation of the chemical composition in step (3), is cast into an ingot.
(5) The ingot is press forged into a product shape which is then optionally heat treated to provide a steel product.
In the preferred production process of a high-cleanliness steel according to the present invention, regarding step (1), wherein the molten steel is transferred to the ladle furnace, among the steps (1) to (5), while the molten steel is generally tapped at a temperature of about 50 C above the melting point of the steel, in the present invention, the molten steel is transferred at a temperature of at least 100 C above, preferably at least 120 C above, more preferably 150 C above, the melting point of the steel. By virtue of this constitution, the metal deposited around the ladle can be fully dissolved in the molten steel, and the slag can also be fully floated, whereby the separation and dropping of the metal and slag into the molten steel in an advanced refining state during the ladle refining, thereby increasing the oxygen content, can be prevented.
According to a preferred embodiment, in the ladle refining in the above step, while a refining time longer than 60 min is generally regarded as offering a better effect, in the present invention, the refining in the ladle furnace is carried out for not more than 60 min. preferably not more than 45 min. more preferably 25 to 45 min. and, regarding degassing in step (3), while it is a general knowledge that a degassing time of less than 25 min suffices for satisfactory results, that is, it is a general knowledge that satisfactory results can be obtained by bringing the amount of the molten steel circulated to about times the total amount of the molten steel, in the present invention, the amount of the molten steel circulated in the circulation-type degassing device is brought to at least 8 times, preferably at least 10 times, more preferably at least 15 times, larger than the total amount of the molten steel, to perform degassing for a long period of time, i.e., not less than 25 min. By virtue of this constitution, the time of ladle refining, wherein refining is carried out while heating, can be brought to a minimum necessary time, and, in the step of degassing not involving heating, the floating separation time for oxide inclusions can be satisfactorily ensured. This can prevent an increase in oxygen content caused by the contamination from refractories or slag on the inner side of the ladle refining furnace, and, at the same time, the formation of large inclusions having a size of not less than about 20 Em can be prevented. In the circulation-type vacuum degassing, particularly since a nozzle is dipped in the molten steel and only the molten steel is circulated, the slag on the upper surface of the molten steel is in a satisfactorily quiet state. Therefore, the number of oxide inclusions from slag into the molten steel is fewer than that during the reduction period process in the ladle refining furnace.
Therefore, in the pre-deoxidized molten steel, the adoption of a satisfactorily long degassing time can realize a significant reduction of even relatively small deoxidation products. In the present specification, this method is called short-time LF, long- time RH treatment or short LF, long RH treatment.
The present invention embraces a high-cleanliness steel produced by the above means.
According to a preferred embodiment, the high-cleanliness steel according to the present invention is a high-cleanliness steel, excellent particularly in rolling fatigue life, which is characterized in that the content of oxygen in the steel is not more than 10 ppm; preferably, when the content of carbon in the steel is less than 0.6% by mass, the content of oxygen in the steel is not more than 8 ppm; and, particularly preferably, in the case of C m 0.6% by mass, the oxygen content is not more than 6 ppm. It is generally known that lowering the oxygen content can contribute to improved rolling fatigue life. Among the steels produced by the production process according to the present invention, high-cleanliness steels having an oxygen content of not more than 10 ppm, preferably not more than 8 ppm in the case of C 0.6% by mass, stably exhibit excellent rolling fatigue life.
Further, according to a preferred embodiment, the steels produced according co che process of the present invention include highcleanliness steels possessing excellent rolling fatigue life and fatigue strength, which are characterized in that the number of oxide inclusions having a size of not less than 20 Am as detected by dissolving the steel product in an acid, for example, oxide inclusions having an A1203 content of not less than 50%, is not more than 40, preferably not more than 30, more preferably not more than 20, per 100 g of the steel product. This evaluation method for steel products reflects both the oxygen content and the maximum inclusion diameter in a predetermined volume. Regarding the fatigue strength, fatigue life, and quietness, in the case of steels having the same oxygen content, oxide inclusions having a certain large size are harmful, and, in particular, oxide inclusions having a size of not less than 20 Am are harmful.
Therefore, among the steels produced by the process according to the present invention, steels, wherein the number of oxide inclusions having a size of not less than 20 Am (for example, having an A12O3 content of not less than 50%) as detected by dissolving the steel product in an acid is not more than 40, preferably not more than 30, particularly preferably not more than 20, per 100 g of the steel product, are high-cleanliness steels having both excellent rolling fatigue life and excellent fatigue strength and, in addition, excellent quietness.
According to a preferred embodiment, the high-cleanliness steels according to the present invention further include high-cleanliness steels, which are excellent particularly in rotating bending fatigue strength and cyclic stress fatigue strength and are characterized in that, when the maximum inclusion diameter in 100 mm2 of the cross-section of the steel product is measured in 30 sites, the predicted value of the maximum inclusion diameter in 30000 mm2 as calculated according to statistics of extreme values is not more than 60 am, preferably not more than am, more preferably not more than 25 am. The cyclic stress fatigue strength and the fatigue limit are known to greatly depend upon the maximum inclusion diameter in a predetermined volume.
This is disclosed in Japanese Patent Laid-Open No. 194121/1999 of which the applicant is identical to that in the application of the present invention. High-cleanliness steels, wherein, for example, typically when the maximum inclusion diameter in 100 mm2 of the cross-section of the steel product is measured in 30 sites, the predicted value of the maximum inclusion diameter in 30000 mm2 as calculated according to statistics of extreme values is not more than 60 am, preferably not more than 40 Am more preferably not more than 25 m, stably exhibit excellent fatigue strength. In this case, the high-cleanliness steels have an oxygen content of not more than 10 ppm, preferably not more than 8 ppm in the case of C > 0.6t by mass, and a predicted value of maximum inclusion diameter of not more than 60 m, preferably not more than 40 m, more preferably not more than 25 am. The steels produced by the process according to the present invention are high-cleanliness steels possessing both excellent rolling fatigue life and excellent fatigue strength. While acid dissolution is a very timeconsuming, troublesome work, the above method, which, without steel product dissolution work, can observe a certain area under a microscope to statistically predict the maximum inclusion diameter, is advantageously simple. Further, particularly in fatigue created by cyclic stress of tensile compression, it is known that the maximum diameter of inclusions present at a site susceptible to failure is a great factor which governs the strength This method, which can statistically predict this maximum diameter, is advantageous
EXAMPLE
A molten steel was subjected to oxidizing refining in an arc melting furnace. In the same furnace, deoxidizers, such as aluminium and silicon, were then added to the refined molten steel to deoxidize the molten steel. The pre-deoxidized molten steel was transferred to a ladle furnace to perform ladle refining. The refined molten steel was then degassed in a circulation-type vacuum degassing device, followed by an ingot production process using casting. Steel products of JIS SUJ 2 and SCM 435 in 10 heats thus obtained were examined for the oxygen content of the products, the predicted value of the maximum inclusion diameter according to statistics of extreme values, and L1o service life by a thrust-type rolling service lift test. In the measurement of the predicted value of the maximum inclusion diameter, a test piece was taken off from a 65 forged material, the observation of 100 mm2 was carried out for 30 test pieces, and the maximum inclusion diameter in 30000 mm2 was predicted according to statistics of extreme values. In the thrust-type rolling service life test, a test piece having a size of 60 X 20 x 8.3T, which had been subjected to carburizing, quench hardening and tempering, was tested at a maximum hertz stress Pmax: 4900 MPa, followed by calculation to determine the L1o service life.
An example of the operation of oxidizing refining in an arc melting furnace or a converter followed by deoxidation in the same furnace (hereinafter referred to as ''in-furnace deoxidation"), that is, only infurnace deoxidation, according to the present invention for 10 heats of steel SUJ 2 is shown in Table 1.
As is apparent from Tables 1 to 8, for steel products produced according to the present invention wherein a molten steel produced in an arc melting furnace or a converter is subjected to in-furnace deoxidation in the same furnace, is transferred to a ladle furnace to perform refining, and is then circulated through a circulation-type vacuum degassing device to degas the molten steel, for steels produced using a combination of infurnace deoxidation + high-temperature tapping at a temperature above the conventional operation, i.e., melting point + at least 100 C., for steels produced using a combination of in-furnace deoxidation + short LF, long RH treatment wherein the operation time in the ladle furnace is shortened and, in addition, the RH quantity of circulation in circulation degassing (that is, amount of molten ( 11 steel circulated/total amount of molten steel circulated) is increased to satisfactorily perform degassing for a long period of time, and for steels produced using a combination of all the above treatments, that is, a combination of the in-furnace deoxidation + high-temperature tapping + short LF, long RH, can realize, for both steel types, SUJ 2 and SCM 435, lowered oxygen content of products and significantly decreased number of inclusions having a size of not less than 20 m. Further, as can be seen from Tables 1 to 8, for the examples of the present invention, regarding the cleanliness, all the steel products are evaluated as fair (A), good (O), or excellent, that is, are excellent high cleanliness steels. By contrast, as can be seen from Tables 9 and 10, for all the conventional examples, the cleanliness is evaluated as failure (X), and the conventional steel products cannot be said to be clean steels. In this connection, it should be noted that fair (I) is based on the comparison with good (O) and excellent ha) and, as compared with steels produced according to the conventional process involving no tapping deoxidation which is evaluated as failure (X), the steels evaluated as fair (I) have much higher cleanliness.
For the heats wherein the in-furnace deoxidation has been carried out, both the oxygen content and the predicted value of the maximum inclusion diameter are reduced by increasing TSH [(temperature at which molten steel is transferred to ladle refining furnace)-(melting point of molten steel)=TsH)] to improve the cleanliness. For the heats in which the in-furnace deoxidation has been carried out, regarding the relationship of the refining time in the ladle furnace with the oxygen content and the predicted value of the maximum inclusion diameter, when the refining time is not less than about 25 min. the oxygen content and the predicted value of the maximum inclusion diameter are satisfactorily lowered. The predicted value of the maximum inclusion diameter, however, increases with increasing the refining time. The reason for this is considered as follows. With the elapse of time, the melt loss of refractories in the ladle furnace is increased, the equilibrium of the slag system is broken, for example, as a result of oxidation due to the contact with the air, and the level of the dissolved oxygen goes beyond the minimum level of dissolved oxygen. Further, the relationship of the amount of molten steel circulated/total amount of molten steel in the circulation-type vacuum degassing device with the oxygen content and the predicted value of the maximum inclusion diameter, the effect of enhancing the cleanliness increases with increasing the amount of molten steel circulated, and is substantially saturated when the amount of molten steel circulated/total amount of molten steel is not less than 15 times.
It was confirmed that reducing the oxygen content and the predicted value of the maximum inclusion diameter results in improved Llo life. This indicates that steels produced by the process according to the present invention, which can reduce the oxygen content and the predicted value of the maximum inclusion diameter, have excellent fatigue strength properties such as excellent rolling fatigue life.
FIG. 1 is a diagram showing the oxygen content of products in lO heats in the production process according to the present invention wherein, in the treatment of a molten steel for steel SUJ 2, a molten steel is subjected to oxidizing refining in an arc melting furnace or a converter, a deoxidizer is then added to the same furnace before tapping to deoxidize the molten steel, and the deoxidized molten steel is transferred to a ladle furnace to perform ladle refining, and is then circulated through a circulation-type vacuum degassing device to degas the molten steel, and the oxygen content of products in lO heats in the conventional process wherein the in-furnace deoxidation is not carried out. In FIGS. l, 3, and 5, A1 shows data on the adoption of only in-furnace deoxidation according to the present invention defined in claim 15, A2 data on in-furnace deoxidation + high- temperature tapping according to the present invention defined in claim 2, A3 data on in-furnace deoxidation + short-time LF, long- time RH treatment according to the present invention defined in claim 3, A4 data on in-furnace deoxidation + high-temperature tapping + short-time LF, long-time RH treatment according to the present invention defined in claim 3, and conventional data on
prior art.
FIG. 2 is a diagram showing the oxygen content of products in lO heats in the production process according to the present invention wherein, in the treatment of a molten steel for steel SCM 435, a molten steel is subjected to oxidizing refining in an arc melting furnace or a converter, a deoxidizer is then added to the same furnace before tapping to deoxidize the molten steel, and the deoxidized molten steel is transferred to a ladle furnace to perform ladle refining, and is then circulated through a circulation-type vacuum degassing device to degas the molten steel, and the oxygen content of products in lO heats in the conventional process wherein the in-furnace deoxidation is not carried out. In FIGS. 2, 4, and 6, B1 shows data on The adoption of only in- furnace deoxidation according to the present invention defined in claim l, B2 data on in-furnace deoxidation + high- temperature tapping according to the present invention defined in claim 2, B3 data on in-furnace deoxidation + short-time LF, long- time RH treatment according to the present invention defined in claim 3, B4 data on in-furnace deoxidation + high-temperature tapping + short-time LF, long-time RH treatment according to the present invention defined in claim 3, and conventional data on the conventional process wherein the in- furnace deoxidation is not carried out.
FIG. 3 is a diagram showing the maximum predicted inclusion diameter of products determined according to statistics of extreme values in lO heats in the production process of the present invention using in-furnace deoxidation in the treatment of a molten steel for steel SUJ 2 accordingto claims l to 3, and the maximum predicted inclusion diameter of products in lO heats in the conventional process wherein the in-furnace deoxidation is not carried out.
FIG. 4 is a diagram showing the maximum predicted inclusion diameter of products determined according to statistics of extreme values in lo heats in the production process of the present invention using in-furnace deoxidation in the treatment of a molten steel for steel SCM 435 according to claims l to 3, and the maximum predicted inclusion diameter of products in lo heats in the conventional process wherein the in- furnace deoxidation is not carried out.
FIG. 5 shows data on L1o service life of products as determined by a thrust rolling service life test in lO heats in the production process of the present invention using in-furnace deoxidation in the treatment of a molten steel for steel SUJ 2 according to claims l to 3, and the L1o service life of products in lO heats in the conventional process wherein the in-furnace deoxidation is not carried out.
FIG. 6 shows data on L1o service life of products as determined by a thrust rolling service life test in lO heats in the production process of the present invention using in-furnace deoxidation in the treatment of a molten steel for steel SCM 435 according to claims l to 3, and the L1o service life of products in lO heats in the conventional process wherein the in-furnace deoxidation is not carried out.
As is apparent from the test results, it was confirmed that, for both steel SUJ 2 and steel SCM 435, the adoption of a method wherein a molten steel is subjected to oxidizing refining in an arc melting furnace or a converter, a deoxidizer is then added to the same furnace before tapping to deoxidize the molten steel, and the deoxidized molten steel is transferred to a ladle furnace to perform ladle refining, and is then circulated through a circulation-type vacuum degassing device to degas the molten steel, can significantly reduce both the oxygen content of the products and the predicted value of the maximum inclusion diameter and, according to the process of the present invention, the cleanliness is significantly improved and the L1o life as determined by the thrust rolling service life test is significantly improved. The addition of treatments to the process, that is, the addition of only in-furnace deoxidation according to the present invention as defined in claim l, the addition of in- furnace deoxidation + high-temperature tapping according to the present invention defined in claim 2, and the addition of infurnace deoxidation + short-time LF, long-time RH treatment according to the present invention as defined in claim 3 or the addition of in-furnace deoxidation + high-temperature tapping + short-time LF, long-time RH treatment according to the present invention defined in claim 3, can significantly improve all the oxygen content of products, the predicted value of the maximum inclusion diameter, and the Llo life as determined by the thrust rolling service life test.
The above examples demonstrate that the process according to the present invention can lower the oxygen content and the predicted value of the maximum inclusion diameter, and the L1o life is improved. This indicates that steels produced according to the process of the present invention, which can reduce the oxygen content and the predicted value of the maximum inclusion diameter, have excellent fatigue strength properties, such as excellent rolling fatigue service life.
As is apparent from the foregoing description, the present invention can provide a large quantity of steel products having a very high level of cleanliness without use of a re-melting process which incurs very high cost. This can realize the provision of high-cleanliness steels for use as steels for mechanical parts required to possess fatigue strength, fatigue life, and quietness, particularly, for example, as steels for rolling bearings, steels for constant velocity joints, steels for gears, steels for continuously variable transmission of toroidal type, steels for mechanical structures for cold forging, tool steels, and spring steels, and processes for producing the same, that is, can offer unprecedented excellent effect.
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a\ m o| r. in o m rid m N N 113. n la ' D D n n Do N D N R up u, n n.. lien nrD rn,,D. to U O to n _ n _ a r, N n _ a _ n D n a 0 r4 0 r, _ IJ 4 _ U N m n N D D 1 7 = _ ! Q -rD N 'D n D N a n a D -D N _ a _ u rl n N N N n n D N D _ a _:E n 0 0 n N-n N D tn 0 n _ u |a '9 1l |L:; . o Ol: D < a:: C: :_ tO4X Q:#& E., X o i X 1 Q o _ _ . t IJ - N _ K N -- r __ U _ _, o _ K N:) K ' O N O _ K N C e _ N o H. I I g d _ O _ O _ _ __ O jam O 4: to: _ _ 1 9 --r r _ n _ _ n _ r O h 5 n n r D r _ t rD r O _ D D D n r r v. D n O 3L r N D N r o D r O 0 n n r i N _ n ID _ O D n O 0 n D r n c D n _ _ a n r O li r n D d n _ D n _ r n r O 0 53 0 1' n r Ir n, n n nr' r D O r m n-- D _ n n - - n n o i- _ _ 2 0 - n n _ tn u r = i r n N r 0 O _ n t5 r n r use 0 N N O hi N n 0 n _ n_ rO _ N 0 O O C n n n n n N N Yl O H ID n N ' cn r D - _ 5 N O S: C, n N n N r O t-I >., C N a: 0 ol r0 = _ N O 0H _ cnr, 0: u' N O o: + :1i: o .. ! = 2 1 i, _ 0. _ _ _ r 0 _ rat _ O dR: I 'I _' U 5 a, n N n a, n _ N n n r4 N O , . t in! l, ::; - -- 22.. . ...
i. , . . - , Or r _ _ r N:p N O _ h @ _ r r _ N r o r _ tar w _ a O m n r 0 r _ _ Yost _. N' N n r == N -_ A r. cl rat n r_ r _ r r _ Al n b 7 {21 r r _ r _ N o _ oy 0 u, u 1- r a' r e Q .: i3 x-No, _ r o __ _ _ _ i w w _ r N 1 r r r N_ o _ = m _ _ x e r' r = = r _ $1} 1 11.1.,;>l:.l 1 1 a
- - - - - -
tn 1 n c n rat 8 C n 3 1 - n n r D r r _ A: c:- n 0 n c 9 n a n ':i Cry _ j 8 Ed n:o _ r n n n Cat _ ; u' r: r r, s N o r n 0 rr _ 8 n r r 0 r o n nr u, c 0 _ l8. r r-- n - r r _ __ O r U A r r 0 r n n r 0 _ c' ,4 c n _ u a, r A A =1 r _ c _ r _ n n 0 r' t t= ::1'; 2 4 _ O |_ _ N -- ' I I N X h 1{ l: . 0 _ lo _ _ e 0 e n n N N X O _; n _ rat C i n e n rot to NX I h n _ 0 Ir 7 ret vc n 0 e X -l 3Y,≈l 3l n N _ N IT T] :st _ - ! N n n N X _ n o 1- it An _ 0 a N 1: o N X n n rl In In n m N N X 0 rl m l o | In 0 In x in _ _ n N n n N N N X --1 O- T _ e r e N n n n N N X _; 4.
r o l O n u-' o -o 0 x 11 iIt,:, if l 3 10 |
Claims (7)
- CLAIMS: 1. A process for producing a high-cleanliness steel, comprisingthe steps of: subjecting a molten steel to oxidizing refining in an arc melting furnace or a converter; adding a deoxidizer to the molten steel in the furnace before tapping to deoxidize the molten steel; transferring the deoxidized molten steel to a ladle furnace to perform ladle refining; and then circulating the refined molten steel through a circulation-type vacuum degassing device to degas the molten steel.
- 2. The process according to claim 1, wherein the molten steel is transferred to the ladle furnace in such a manner that the temperature of the molten steel to be transferred is at least 100 C above the melting point of the steel.
- 3. The process according to claim 1, wherein the refining in the ladle furnace is carried out for not more than 60 min. and the degassing in the circulation-type vacuum degassing device is carried out for not less than 25 min.
- 4. A high-cleanliness steel produced by the process according to any one of claims 1 to 3.
- 5. The high-cleanliness steel according to claim 4, wherein the content of oxygen in the steel is not more than 10 ppm.
- 6. The high-cleanliness steel according to claim 4, wherein the number of oxide inclusions having a size of not less than 20 Am as detected by dissolving the steel product in an acid is not more than 40 per 100 g of the steel product.
- 7. The high-cleanliness steel according to claim 4, wherein the predicted value of the maximum inclusion diameter in 30000 mm2 as calculated according to statistics of extreme values is not more than 60 m.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000167089A JP2001342515A (en) | 2000-06-05 | 2000-06-05 | Highly clean steel and production method |
| JP2000167088A JP2001342516A (en) | 2000-06-05 | 2000-06-05 | Highly clean steel and production method |
| JP2000167087A JP2001342514A (en) | 2000-06-05 | 2000-06-05 | Highly clean steel and production method |
| JP2000167085A JP2001342512A (en) | 2000-06-05 | 2000-06-05 | Highly clean steel and production method |
| JP2000167086A JP4562244B2 (en) | 2000-06-05 | 2000-06-05 | Manufacturing method of high cleanliness steel |
| GB0500783A GB2406580B (en) | 2000-06-05 | 2001-06-05 | High-cleanliness steel and process for producing the same |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB0509770D0 GB0509770D0 (en) | 2005-06-22 |
| GB2410252A true GB2410252A (en) | 2005-07-27 |
| GB2410252B GB2410252B (en) | 2005-09-07 |
Family
ID=34743970
Family Applications (3)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0509771A Expired - Lifetime GB2410503B (en) | 2000-06-05 | 2001-06-05 | High-cleanliness steel and process for producing the same |
| GB0509770A Expired - Lifetime GB2410252B (en) | 2000-06-05 | 2001-06-05 | High-cleanliness steel and process for producing the same |
| GB0509772A Expired - Fee Related GB2410253B (en) | 2000-06-05 | 2001-06-05 | High-cleanliness steel and process for producing the same |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0509771A Expired - Lifetime GB2410503B (en) | 2000-06-05 | 2001-06-05 | High-cleanliness steel and process for producing the same |
Family Applications After (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0509772A Expired - Fee Related GB2410253B (en) | 2000-06-05 | 2001-06-05 | High-cleanliness steel and process for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| GB (3) | GB2410503B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2028285A1 (en) * | 2006-06-09 | 2009-02-25 | Kabushiki Kaisha Kobe Seiko Sho | Steel for high-cleanliness spring with excellent fatigue characteristics and high-cleanliness spring |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102808062B (en) * | 2012-07-19 | 2014-03-05 | 中国科学院金属研究所 | Method for controlling A segregation of steel ingots by purification of molten steel |
| CN114875197B (en) * | 2022-05-10 | 2023-11-14 | 江苏利淮钢铁有限公司 | Technological method for controlling inclusion types in steel to improve purity of molten steel |
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| US4544405A (en) * | 1983-09-02 | 1985-10-01 | M.A.N. Maschinenfabrik Augsburg-Nurnberg Aktiengesellschaft | Method of producing steels of great purity and low gas content in steel mills and steel foundries and apparatus therefor |
| EP0163784A1 (en) * | 1984-05-25 | 1985-12-11 | China Steel Corporation | Two stage deoxidation process in steel-making |
| JPS6396210A (en) * | 1986-10-09 | 1988-04-27 | Sumitomo Metal Ind Ltd | Pre-deoxidizing method in converter interior |
| EP0548868A2 (en) * | 1991-12-24 | 1993-06-30 | Kawasaki Steel Corporation | Method of refining of high purity steel |
| JPH10237533A (en) * | 1997-02-27 | 1998-09-08 | Sumitomo Metal Ind Ltd | Production of hic resistant steel |
| JP2000129335A (en) * | 1998-10-20 | 2000-05-09 | Nkk Corp | Production of extra-low sulfur steel excellent in cleanliness |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH01188619A (en) * | 1988-01-21 | 1989-07-27 | Nkk Corp | Method for rh vacuum degasification |
| JPH02179813A (en) * | 1988-12-28 | 1990-07-12 | Nippon Steel Corp | Method for refining molten metal into high purity and high cleanliness |
| JP2847774B2 (en) * | 1989-07-07 | 1999-01-20 | 住友金属工業株式会社 | Refining method of molten metal |
| JPH1192811A (en) * | 1997-09-12 | 1999-04-06 | Sumitomo Metal Ind Ltd | Refinement of molten metal |
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2001
- 2001-06-05 GB GB0509771A patent/GB2410503B/en not_active Expired - Lifetime
- 2001-06-05 GB GB0509770A patent/GB2410252B/en not_active Expired - Lifetime
- 2001-06-05 GB GB0509772A patent/GB2410253B/en not_active Expired - Fee Related
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4544405A (en) * | 1983-09-02 | 1985-10-01 | M.A.N. Maschinenfabrik Augsburg-Nurnberg Aktiengesellschaft | Method of producing steels of great purity and low gas content in steel mills and steel foundries and apparatus therefor |
| EP0163784A1 (en) * | 1984-05-25 | 1985-12-11 | China Steel Corporation | Two stage deoxidation process in steel-making |
| JPS6396210A (en) * | 1986-10-09 | 1988-04-27 | Sumitomo Metal Ind Ltd | Pre-deoxidizing method in converter interior |
| EP0548868A2 (en) * | 1991-12-24 | 1993-06-30 | Kawasaki Steel Corporation | Method of refining of high purity steel |
| JPH10237533A (en) * | 1997-02-27 | 1998-09-08 | Sumitomo Metal Ind Ltd | Production of hic resistant steel |
| JP2000129335A (en) * | 1998-10-20 | 2000-05-09 | Nkk Corp | Production of extra-low sulfur steel excellent in cleanliness |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2028285A1 (en) * | 2006-06-09 | 2009-02-25 | Kabushiki Kaisha Kobe Seiko Sho | Steel for high-cleanliness spring with excellent fatigue characteristics and high-cleanliness spring |
| EP2028285A4 (en) * | 2006-06-09 | 2011-04-20 | Kobe Steel Ltd | Steel for high-cleanliness spring with excellent fatigue characteristics and high-cleanliness spring |
| US8613809B2 (en) | 2006-06-09 | 2013-12-24 | Kobe Steel, Ltd. | High cleanliness spring steel and high cleanliness spring excellent in fatigue properties |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2410503B (en) | 2005-09-07 |
| GB0509770D0 (en) | 2005-06-22 |
| GB0509772D0 (en) | 2005-06-22 |
| GB2410253A (en) | 2005-07-27 |
| GB2410503A (en) | 2005-08-03 |
| GB0509771D0 (en) | 2005-06-22 |
| GB2410252B (en) | 2005-09-07 |
| GB2410253B (en) | 2005-09-14 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PE20 | Patent expired after termination of 20 years |
Expiry date: 20210604 |