JP2013044046A - Method for manufacturing high-clean steel - Google Patents

Abstract

Provided is a production method for stably producing a high clean steel having a relatively high Si concentration by an ESR method which is a method for producing a high clean steel with reduced non-metallic inclusions.
A method for producing a steel type containing s-Al as an additive element or impurity element and containing at least 1.0% to 2.0% by mass of Si, wherein the suspended consumable electrode 5 is a metal mold. The molten slag 6 in FIG. 2 is lowered from above and energized between the consumable electrode 5 and the metal mold 2 to melt the consumable electrode 5 in the vicinity of the upper surface of the molten slag 6 and the droplets are melted into the molten slag. In the ESR method of obtaining the steel ingot 9 of the steel type by passing the inside of the metal mold 2 and capturing in the vicinity of the bottom of the metal mold 2, the vicinity of the upper surface of the molten slag 6 is replaced with a mixed gas composed of an inert gas containing at least oxygen. To do.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a high clean steel with reduced non-metallic inclusions, and more particularly to a method for producing a high clean steel having a relatively high Si concentration.

  An ESR (Electro Slag Remelting) method is known as a steelmaking technique for obtaining highly clean steel with reduced non-metallic inclusions. A rod-shaped consumable electrode having a predetermined component composition is formed by forging, and dipped from the upper part of the molten slag in the metal mold while being suspended and gradually lowered. At this time, if current is applied between the consumable electrode and the metal mold, the tip of the consumable electrode is melted by resistance heating in the vicinity of the top surface of the slag, and the resulting droplet passes through the molten slag by gravity and accumulates at the bottom of the metal mold. To go. Since the droplets are highly purified and deposited by the molten slag-molten metal reaction, a highly clean steel ingot can be obtained.

  In such an ESR method, generally, an inert gas such as argon heavier than air is given to the top of the molten slag in order to prevent the oxidation of the molten slag and the unintentional incorporation of gas components into the molten slag. The slag is kept out of direct contact with air.

  Moreover, VSR (Vacuum electro slag remelting) method, which is one of the ESR methods, forms an outer shell that covers the upper part of the molten slag and makes it an airtight space so that the degree of vacuum in the space can be increased. Alternatively, a replacement atmosphere is provided and the atmosphere can be controlled with high accuracy. For example, Patent Document 1 discloses such an apparatus. Here, it describes that the degree of vacuum can be controlled within a range of 100 to 600 Torr, and the steelmaking process is performed while maintaining a pressure condition that does not substantially cause slag boiling.

が平衡することから説明をしている。すなわち、溶融メタルとして溶解した消耗電極の溶滴のうち、Ｓｉ成分は酸素と反応してＳｉＯ _２となって溶融スラグ側に取り込まれていく。すると、溶滴においては上記反応式が左方向に進み、脱酸が進行するのである。すなわち、Ｓｉ濃度が高い鋼種については比較的容易に低酸素化が達成可能である。他方、Ｓｉ濃度が低い鋼種については、逆に低酸素化が困難である。 By the way, a deoxidation process is important in steelmaking technology. Deoxidation in the ESR method is mainly due to the reaction of the Si component added to the consumable electrode as a deoxidizer. In this regard, Patent Document 2 describes the following molten slag-molten metal reaction on the slag surface:

Is explained from the equilibrium. That is, among the droplets of the consumable electrode dissolved as molten metal, the Si component reacts with oxygen to become SiO ₂ and is taken into the molten slag side. Then, in the droplet, the above reaction formula proceeds to the left, and deoxidation proceeds. That is, for a steel type having a high Si concentration, oxygen reduction can be achieved relatively easily. On the other hand, low oxygen reduction is difficult for steel types with low Si concentration.

  On the other hand, in Patent Document 2, regarding the manufacturing method of low silicon and low oxygen steel, the entire ESR apparatus is sealed to block the interior space from the atmosphere, and the atmosphere of the reaction system is set to an oxygen blocking atmosphere. In the above, the steel grade whose Si concentration was adjusted to 0.30% by weight or less was redissolved as a consumable electrode, and the Si concentration was 0.30% by weight or less and the oxygen concentration was cleaned to 0.002% by weight or less. It discloses that silicon and low oxygen steel can be obtained. Such ESR method is a kind of VSR method.

JP 2007-302954 A JP-A-7-233426

  A type of hot tool steel, such as DH31 (trade name) with a Si concentration of 0.3% by mass or less, can produce a highly clean steel ingot by the ESR method or the VSR method as described above. On the other hand, in the steel type having a Si concentration of about 1.0% by mass higher than DH31 (trade name), even if an attempt is made to produce a highly clean steel ingot by the ESR method or the VSR method, unevenness in mechanical characteristics is likely to occur. In particular, the variation in impact value was likely to increase.

  The present invention has been made in view of such a situation, and an object of the present invention is to achieve a high cleanliness with a relatively high Si concentration by the ESR method, which is a manufacturing method of high clean steel with reduced nonmetallic inclusions. It is providing the manufacturing method which manufactures steel stably.

  The present inventor has found that the cause of uneven mechanical properties is coarse alumina grains in the steel ingot. Aluminum in the steel ingot is inevitably contained when scrap is used in addition to being added for the purpose. Therefore, a method for suppressing the formation of coarse alumina particles by such aluminum was devised and introduced into the manufacturing method.

  That is, the production method according to the present invention is a method for producing a steel type containing s-Al as an additive element or impurity element and containing at least 0.7% to 2.0% Si by mass, and suspended consumption. An electrode is lowered from above into the molten slag in the metal mold and energized between the consumable electrode and the metal mold to melt the consumable electrode in the vicinity of the upper surface of the molten slag, and this droplet is passed through the molten slag. In the ESR method of obtaining a steel ingot of the steel type by capturing in the vicinity of the bottom of the metal mold after passing through, the vicinity of the upper surface of the molten slag is replaced with a mixed gas composed of an inert gas containing at least oxygen. .

  According to this invention, by replacing the vicinity of the upper surface of the slag with a mixed gas composed of an inert gas containing at least oxygen, s-Al contained as an additive element or impurity element can be oxidized and taken into the molten slag side. . Therefore, coarse alumina grains in the steel ingot can be suppressed, and highly clean steel having a relatively high Si concentration can be produced stably.

  In the above-described invention, a closed space may be formed above the molten slag, and the closed space may be replaced with the mixed gas. According to this invention, the amount of oxygen in the inert gas in the vicinity of the upper surface of the slag can be stabilized, so that coarse alumina grains in the steel ingot can be reliably suppressed, and a high clean steel with a relatively high Si concentration can be stably produced. It can be manufactured.

  In the above-described invention, an upper portion of the molten slag may be replaced with an inert gas and oxygen may be given into the closed space. According to this invention, the amount of oxygen in the inert gas in the vicinity of the upper surface of the slag can be easily adjusted, coarse alumina particles in the steel ingot can be reliably suppressed, and highly clean steel having a relatively high Si concentration can be stabilized. Can be manufactured.

  In the above-described invention, an airtight space may be formed above the molten slag, and the airtight space may be evacuated and then replaced with the mixed gas. According to this invention, the amount of oxygen in the inert gas in the vicinity of the upper surface of the slag can be easily adjusted, coarse alumina particles in the steel ingot can be reliably suppressed, and highly clean steel having a relatively high Si concentration can be stabilized. Can be manufactured.

  In the above-described invention, the steel types are mass%, C: 0.35 to 0.42%, Si: 0.80% to 1.20%, Mn: 0.25 to 0.50%, Cr: 4 .80 to 5.50%, Mo: 1.00 to 1.50%, V: 0.80 to 1.15%, s-Al: 0.007% or less, other inevitable impurity elements And the remaining Fe may be included. According to this invention, s-Al can be reliably oxidized and taken into the molten slag side, coarse alumina particles in the steel ingot can be suppressed, and highly clean steel with a relatively high Si concentration can be produced stably. It can be done.

It is a figure which shows the manufacturing apparatus used with the manufacturing method of this invention. It is a flowchart which shows the manufacturing method of this invention. It is a figure which shows the other manufacturing apparatus used with the manufacturing method of this invention. It is another flowchart which shows the manufacturing method of this invention.

[Example 1]
A method of manufacturing a high clean steel with reduced non-metallic inclusions according to one embodiment of the present invention, in particular, a method of manufacturing a high clean steel having a relatively high Si concentration will be described. First, the ESR device 1 (see FIG. 1) used in the manufacturing method will be described.

  As shown in FIG. 1, the ESR device 1 includes a water-cooled metal mold 2, a power source 3 connected thereto, an electrode holding unit 4 connected to the power source 3, and a valve 11 from an inert gas source 10. And an inert gas supply path 12 communicating with the upper part of the space in the metal mold 2. The ESR device 1 further includes a partition plate 7 so as to surround the consumable electrode 5 inside the metal mold 2. By the partition plate 7, the space inside the metal mold 2 is partitioned into an upper space 2a and a lower closed space 2b. The metal mold 2 is further connected with an oxygen supply path 15 that leads from the oxygen source 13 through the valve 14 to the closed space 2b. In other words, as described above, the ESR apparatus 1 is provided with the partition plate 7 newly provided in the normal ESR apparatus, thereby enabling supply of oxygen to the upper space 2a and the lower closed space 2b which are divided. It is.

  Next, the manufacturing method of the high clean steel using the above-mentioned ESR apparatus 1 is demonstrated. Note that the steel types suitable for production in this example include s-Al as an additive element or impurity element in a range of 0.007% or less by mass% and at least 0.7 to 2.0% by mass. % Steel containing Si. For example, in mass%, C: 0.35 to 0.42%, Si: 0.80% to 1.20%, Mn: 0.25 to 0.50%, Cr: 4.80 to 5.50% , Mo: 1.00 to 1.50%, V: Steel such as DHA1-A (trade name) having a component composition of 0.80 to 1.15%.

The steel used as the consumable electrode 5 has the same component composition as the above-described steel types, and it is preferable to make fine adjustments in consideration of effects such as deoxidation during refining. The consumable electrode 5 is a forged round bar made of such steel, but inevitably contains aluminum because scrap is used as a raw material. Therefore, it is preferable that the content of s-Al in the consumable electrode 5 is 0.010% or less in mass% so that the production of coarse alumina grains in the obtained steel ingot can be easily suppressed. Further, in the slag, for example, it can be a general basic slag _{CaF 2, Al 2 O 3,} CaO and the like as a main component. In this example, slag of CaF ₂ : 70% and Al ₂ O ₃ : 30% was used in terms of mass%.

  Referring to FIG. 2 together with FIG. 1, the slag is placed on the bottom of the metal mold 2 (S1). The consumable electrode 5 is suspended from the electrode holding part 4, and the lower end thereof is positioned so as to contact the slag (S2).

  At the same time, the valve 11 is opened to purge the space 2a and the closed space 2b in the metal mold 2 with an inert gas. In this embodiment, the inert gas is argon gas. Since there is a gap between the partition plate 7 and the consumable electrode 5, the closed space 2b is also purged with the inert gas. Further, the valve 14 is opened to supply oxygen into the closed space 2b. That is, the closed space 2b is purged with a mixed gas of an inert gas and oxygen having a predetermined partial pressure (S3). Thus, by providing the partition plate 7, the oxygen amount in the closed space 2b can be stabilized and the oxygen amount can be easily adjusted. Note that the inert gas may be supplied to the closed space 2b such that the inert gas supply path 12 communicates with the closed space 2b.

  The power is turned on to apply a predetermined voltage between the consumable electrode 5 and the slag, and the slag is melted by the resistance heating (S4). As a result, the lower end of the consumable electrode 5 is melted by resistance heating of the molten slag 6. As the consumable electrode 5 is dissolved, the position of the electrode holding portion 4 is controlled so that the consumable electrode 5 is gradually lowered from above and the tip of the consumable electrode 5 is always immersed in the vicinity of the surface layer of the molten slag 6 (S5). . The droplets generated as the consumable electrode 5 is dissolved are refined while passing through the molten slag 6. The refined droplets are captured by the molten pool 8 formed below the molten slag 6, cooled from the lower end and the periphery thereof to the metal mold 2 and solidified to gradually form the steel ingot 9 (S6). .

  In such refining, the space 2a is filled with an inert gas to block the inside of the metal mold 2 from the atmosphere, and the closed space 2b is filled with a mixed gas containing oxygen at a predetermined partial pressure, and the upper surface of the molten slag 6 is filled. A predetermined amount of oxygen can be supplied.

  The molten slag 6 is supplied with oxygen from a mixed gas, and can oxidize s-Al contained in a passing droplet and take it in. As a result, more s-Al can be taken into the molten slag 6 than when purged with an inert gas, so that the formation of coarse alumina grains in the steel ingot 9 can be suppressed. . Therefore, the mechanical properties of the steel ingot 9, in particular, the impact value can be stabilized, and highly clean steel having a relatively high Si concentration can be stably produced.

[Example 2]
Next, a VSR device 21 used in a method for producing highly clean steel with reduced non-metallic inclusions according to another embodiment of the present invention will be described.

  As shown in FIG. 3, the VSR device 21 includes a water-cooled metal mold 22, a power supply 23 connected thereto, an electrode holding unit 24 connected to the power supply 23, and a sealed space 22 a inside the metal mold 22. A furnace body upper part 22 ′ that allows the electrode holding part 24 to move up and down while being fixed to the upper part thereof. Further, the gas supply path 32 connected to the furnace body upper part 22 ′ from the inert gas source 30 to the sealed space 22 a through the valve 31, the control valve 42 and the dust by the oil rotary pump 40 and the roots type vacuum pump 41. A vacuum path 44 for depressurizing the sealed space 22a through the separator 43 is provided. An oxygen source 33 is further connected to the gas supply path 32 via a valve 34. In other words, as described above, the VSR device 21 can supply oxygen in a normal VSR device that performs ESR under reduced pressure.

  Next, a method for manufacturing steel by the VSR device 21 will be described. Note that the steel types suitable for production in this example include s-Al as an additive element or impurity element in a range of 0.007% or less by mass% and at least 0.7 to 2.0% by mass. % Steel containing Si. For example, high-clean steel such as DHA1-A (trade name) as in Example 1.

The steel used as the consumable electrode 25 has the same component composition as the above-described steel types, and it is preferable to perform fine adjustment in consideration of effects such as deoxidation during refining. The consumable electrode 25 is a forged round bar made of such steel. Further, as in Example 1, the s-Al content in the consumable electrode 25 is preferably 0.010% or less by mass%. In addition, as in Example 1, for the slag, for example, general basic slag mainly composed of CaF ₂ , Al ₂ O ₃ , CaO or the like can be used. In this example, slag of CaF ₂ : 70% and Al ₂ O ₃ : 30% was used in terms of mass%.

  4 together with FIG. 3, first, a slag is placed on the bottom of the metal mold 22 (S1). After fixing the furnace body upper part 22 'to the metal mold 22 so as to seal the inside, the consumable electrode 25 is suspended from the electrode holding part 24, and its lower end is positioned so as to contact the slag (S2).

  Subsequently, air is discharged from the sealed space 22a inside the metal mold 22 by the oil rotary pump 40 through the control valve 42, the pressure is reduced, and the pressure is further reduced by the roots type vacuum pump 41 (S3a).

  Subsequently, the valve 31 is opened, and the sealed space 22a in the metal mold 22 is purged with an inert gas. In this embodiment, the inert gas is argon gas. Further, the valve 34 is opened, oxygen is supplied into the sealed space 22a, and the sealed space 22a is purged with a mixed gas of an inert gas and oxygen having a predetermined partial pressure (S3b). As described above, once the vacuum is pulled and then purged with the mixed gas, the oxygen amount in the sealed space 22a can be easily adjusted.

  Subsequently, the power is turned on to melt the consumable electrode 25 to generate droplets, and the steel ingot 29 is formed while refining the droplets passing through the molten slag 26 (S4, S5, S6). Details are the same as those in the first embodiment, and a description thereof will be omitted.

  In such refining, the sealed space 22 a is filled with a mixed gas containing oxygen, and a predetermined amount of oxygen can be supplied to the upper surface of the molten slag 26.

  The molten slag 26 is supplied with oxygen from a mixed gas, and can oxidize s-Al contained in the passing droplets to be taken in. As a result, more s-Al can be taken into the molten slag 26 than when purged with only an inert gas, so that the formation of coarse alumina grains in the steel ingot 29 can be suppressed. it can. Therefore, the mechanical properties of the steel ingot 29, in particular, the impact value can be stabilized, and highly clean steel having a relatively high Si concentration can be stably produced.

  As described above, in steel types having a relatively high Si concentration, deoxidation can proceed rapidly in the molten slag, but this tends to cause a shortage of oxygen that can be used for the molten slag-molten metal reaction in the molten slag. . By actively supplying oxygen from the mixed gas to the molten slag, oxygen in the molten slag that tends to be deficient can be supplemented, and s-Al in the droplets passing through the molten slag can be actively oxidized. Conceivable. Since the produced alumina is large in size and easily floats, it is considered that it could be easily taken into the molten slag.

  In addition, it is considered that an excessive amount of oxide is generated in the steel ingot obtained when oxygen is excessively supplied to the molten slag, and on the other hand, if it is too small, it is considered that the effect of incorporating s-Al into the molten slag cannot be obtained. The amount of oxygen in the mixed gas is adjusted as appropriate.

  Further, oxygen may be mixed with an inert gas in advance and then supplied to the closed space 2b or the sealed space 22a.

  Up to this point, the representative embodiments according to the present invention and the modifications based thereon have been described, but the present invention is not necessarily limited thereto. Those skilled in the art will recognize a variety of alternative embodiments and modifications without departing from the scope of the appended claims.

1 ESR device 5, 25 Consumable electrode 6, 26 Molten slag 9, 29 Steel ingot 13, 33 Oxygen source 21 VSR device

Claims (5)

A method for producing a steel type containing s-Al as an additive element or impurity element and containing at least 0.7 to 2.0% Si by mass,
The suspended consumable electrode is lowered from the upper part to the molten slag in the metal mold and energized between the consumable electrode and the metal mold to melt the consumable electrode in the vicinity of the upper surface of the molten slag and In the ESR method for obtaining a steel ingot of the steel type by passing through the molten slag and then capturing near the bottom of the metal mold, the vicinity of the upper surface of the molten slag is replaced with a mixed gas composed of an inert gas containing at least oxygen. The manufacturing method characterized by this.   The manufacturing method according to claim 1, wherein a closed space is formed in an upper portion of the molten slag, and the inside of the closed space is replaced with the mixed gas.   The manufacturing method according to claim 2, wherein an upper portion of the molten slag is replaced with an inert gas and oxygen is given into the enclosed space.   The manufacturing method according to claim 1, wherein an airtight space is formed in an upper part of the molten slag, and the airtight space is evacuated and then replaced with the mixed gas. The steel grade is mass%,
C: 0.35-0.42%,
Si: 0.80% to 1.20%,
Mn: 0.25 to 0.50%,
Cr: 4.80-5.50%,
Mo: 1.00 to 1.50%,
V: 0.80 to 1.15%,
5. The production method according to claim 1, comprising s-Al: 0.007% or less and having a component composition containing other inevitable impurity elements and the balance Fe.

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