JPS6025486B2 - Method for manufacturing clean steel with low oxygen, sulfur, and nitrogen content - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing steel with extremely low oxygen, sulfur and nitrogen contents, clean workability and mechanical properties, particularly excellent rut resistance and little anisotropy.

It is well known that residual oxygen, sulfur, and nitrogen in carbon steel and alloy steel impair workability and mechanical properties. However, it is not possible to reduce the amount of oxygen, sulfur, and nitrogen sufficiently, so there are high chromium stainless steels that are difficult to process and have limited applications, and cobalt-based or nickel-based alloys that have poor rolling yields in hot rolling. . The inventors of the present invention first focused on the great deoxidizing power, desulfurizing power, and denitrifying power of calcium, and after deoxidizing the molten steel with aluminum, they further added calcium metal or calcium alloy to the molten steel. By adding it to strongly deoxidize and desulfurize,
We were able to produce steel with excellent workability. However, calcium has a high vapor pressure and evaporates at temperatures above 148,000, and evaporates immediately even when added to molten steel, so the yield that actually contributes to deoxidation and desulfurization is very low, and the price of calcium metal and its alloys is low. Due to its high cost, it still had technical and economical drawbacks. Therefore, in order to improve the above-mentioned drawbacks, the present inventors subsequently developed a melting furnace supported by a basic refractory containing Ca040% or more from Tokuka Sho 49-33778 and Samurai Gan Sho 49-$77y Karasuko. However, he invented a method for producing copper with excellent workability by adding aluminum or aluminum alloy to molten steel in a ladle in a vacuum or under an argon atmosphere to extremely reduce the oxygen and sulfur content in the molten steel. I applied.

However, according to the above invention, there are 0.0 peaks in the steel produced.
Since it is contained in an amount of 6 to 20%, there remains a problem in the ballability or anisotropy of the material depending on the steel type. The present invention improves the above-mentioned invention by the present inventors and makes it possible to extremely reduce the oxygen, sulfur, and nitrogen contents in steel, as well as to have extremely few nonmetallic inclusions, and to improve workability and mechanical properties, especially toughness. The purpose is to provide a method for producing clean steel with excellent anisotropy, without using solvents for molten steel in a container backed with a highly basic refractory containing 60% or more of Ca○. AI or A' and Tj, at least one of the rare elements under vacuum or an inert gas atmosphere other than nitrogen.
By adding seeds, after these additives combine with oxygen, nitrogen, etc. in molten steel and achieve deoxidation and denitrification of molten steel, remaining dissolved AI, Ti, and rare elements are removed from the refractory. At the interface between the refractory and molten steel, Ca○ in the refractory is reduced to generate Ca, which further reacts with oxygen, nitrogen, and sulfur remaining in the molten steel, and reacts with deoxidation product AI2Q and deoxidation product. The acid product Ca○ or the refractory component Ca○ existing on the surface of the refractory is combined to form a0 and AI2Q in the ladle with high desulfurization ability, and the series of reactions described above removes the molten steel. It was discovered that denitrification and desulfurization can be thoroughly carried out, and that the various reactions mentioned above can be reliably completed by containing predetermined amounts of Ca, Ti, and rare earth elements in the steel. With this knowledge, the present invention has been completed.

The target steel of the present invention contains ordinary elements C, Si, Mn, P, and S, including carbon steel containing 2% or less of C, and Ni, Cr, Co, and other elements in addition to the above ordinary elements to give special properties. W,
Special elements such as Mo, as well as those belonging to ordinary elements, are alloy steels in which they are added for the purpose of adding special properties beyond the content range of ordinary elements. The types of these alloy steels include low alloy steel (S for normal elements)
io. 5% or more, Mno. 8% or more, or Cuo. 2
There are high-strength, low-alloy steels, high-temperature, high-pressure, low-alloy steels, and low-alloy steels for the petroleum industry. Alloy steels (intermediate between alloy steel and stainless steel) include chromium steel, nickel steel, silicon steel, etc., and high alloy steels include high chromium stainless steel, chrome-nickel stainless steel, cobalt, and nickel-based alloy steels. Representative steel types of these carbon steels and alloy steels are shown in Tables 1 to 7. Table 1
Standard composition of low carbon steel pipe Table 2 Composition of high strength low alloy steel Table 3 Standard composition of low △ steel for high temperature and high pressure Table 4 Example of low alloy steel for petroleum industry Table 5 Ferritic and martensitic Japanese standard for fusen steel (JIS G 430s 4309,19
59) Types 21-24, 37, and 38 are Nio. 60%
It may contain the following.

Table 6 Ferritic and martensitic American Iron and Steel Institute type numbers P < 0.04 and S 0.03.
(Excluding free-cutting materials) Table 7 Austenitic high alloy steels In the present invention, the AI added to the molten steel can be added in the form of an aluminum alloy containing metal peaks.

Further, Ti, which is added in the same manner, can be added in the form of a titanium alloy containing Ti in addition to metal Ti. Furthermore, the rare earth element added in the same manner has an atomic number of 57.
The 15 nine elements from to 71 are 17 plus Sc and Y.
At least one of these elements, a misch metal consisting of these elements, or at least one of these elements
Although alloys containing seeds can be used, it is economically advantageous to use Ce, which has the largest amount among the rare elements and is relatively easy to separate, or Mitsushi metal, which is relatively inexpensive. A', Tj, and Ce are all elements that have a strong affinity with oxygen and nitrogen, and have conventionally been widely used for deoxidizing and denitrifying molten steel, but in the present invention,
New findings have been obtained in the treatment of molten steel using a predetermined amount of these metals in a refractory container with a high Ca content and in a vacuum or an atmosphere of an active gas other than nitrogen. Backing refractories that can be used in the present invention include crystalline lime, calcia refractories, and calcia refractories enriched with Ca○, and must be basic refractories containing 60% or more of Ca○. .

Table 8 shows examples of chemical components of refractories.
Table 8 Chemical composition of refractory materials In the present invention, when aluminum, or at least one of aluminum, titanium, and cerium is added to the molten carbon steel or alloy steel in a melting furnace or ladle under vacuum or argon atmosphere, Oxide-based nonmetallic inclusions as well as dissolved oxygen, nitrogen and sulfur in the molten metal react with aluminum, titanium or cerium to form e.g. AI203,
Ti○, Ce2Q, AIN, TIN, CeN, CeS,
Aluminum, titanium, or cerium that is present in excess while producing TiS2 etc. reduces Ca○ in the backed refractory to produce calcium.

In the vacuum treatment of molten steel, deoxidation by C occurs, and it is also known that a reaction between Ca in the refractory and C occurs as shown in the following equation. Ca00C=Ca(6) or KawajuC○(6) '11 In vacuum scouring, the lower the operating pressure and the greater the activity of C, the easier the reaction of formula '11 will proceed. However, V in molten steel
When an element having a strong affinity for C, such as a Ti group, a Ti group element, or a Cr group element, is present, the deoxidizing ability of C is considerably reduced. Therefore, it is thought that the reduction of Ca◯ by aluminum, titanium, or cerium that occurs in a vacuum or an argon atmosphere is based on the following reaction formula. 3Ca012AI =3Ca(g) or (,)10AI2Q
'21Ca○10Ti=Ca(8) or (1)10T
i○ (3'3Ca012Ce=3Ca(g
) or Kawaju Ce203 '4) Under atmospheric conditions, oxygen is absorbed into the molten steel, making it difficult to generate Ca○, and it is also impossible to leave calcium remaining in the molten steel.

In this way, the calcium produced by formulas {1) to [4} not only reacts with sulfur in the molten metal, but also reacts with oxygen and nitrogen that remain after deoxidation and denitrification with aluminum, titanium, or cerium, resulting in the following reactions. CaS, AI203, T
io, Ce208, AIN, Ca3N2, TIN, Ce
N, etc. can be generated. Ca(g) or (,)
10S=CaS [5}30214AI
=2ri203 [610212Ti=2Ti○ {7}
302 4Ce=2Ce203'
'8}Ti 10N=TIN'9'3Ca+2N=Ca
3N2 0Q mountain ten N=AIN
(11) Ce+N=CeN
(12)' Particularly when the amount of aluminum added is large in an argon atmosphere, the desulfurization ability as shown in A0 and Mt. 203 increases, and a molten birch layer is formed on the backing refractory surface, and cerium also directly participates in desulfurization. do.

As mentioned above, calcium has a high vapor pressure and evaporates at temperatures above 1480°C. Therefore, the molten metal is deoxidized by adding aluminum, titanium, or cerium using the conventional method, and then calcium or a calcium alloy is added to desulfurize it. However, according to the method of the present invention, calcium is separated from the molten metal and the backing refractory. Because it is reduced and produced over the entire contact surface, sufficient desulfurization, deoxidation, and denitrification can be carried out while evaporating and dissipating in the melt wound.

Also, unlike the conventional method, in the method of the present invention, the contact interface between calcium and the molten metal is large, so that some of the calcium can be alloyed with the metal elements in the molten metal, and its content can be reduced from 0.001 to 0. The fact that it can be reduced to .03% indicates that sufficient desulfurization, deoxidation, and denitrification can be carried out, and is a major feature of the method of the present invention. By the method of the present invention, oxygen in steel is reduced to 0.003% or less and sulfur is reduced to 0.0%.
10% or less, nitrogen content can be easily reduced to 0.010% or less, and copper with excellent workability and mechanical properties, especially grade, and less anisotropy can be produced. The reason why the Ca0 content of the back refractory is limited to 60% or more in the present invention is as follows.
In the case of basic refractories containing less than 60% Ca○, for example, Larnite refractories and dolomite refractories, the former contains a relatively large amount of Si02, while the latter contains a relatively large amount of Mg○, so Ca0 Since the activity of the refractory is low and there are many other impurity oxides, the melting point is lowered and it is more likely to be eroded, and the basicity of the melt formed on the surface of the backing refractory is low and the desulfurization ability is low. Basic refractories containing 60% L of Ca○ have a relatively small amount of deformation and expansion/contraction rate at high temperatures, and can be easily reduced by aluminum, titanium, cerium, etc. The Ca0 content in the basic refractory must be 60% or more, and it is particularly advantageous to use a refractory containing 80% or more Ca0 in the present invention.

In the present invention, the residual amount of aluminum in steel is reduced to 0.00
The reason for limiting the range to 5% to 0.0% is that if the residual amount of aluminum is less than 0.005%, the amount of large cave-ins of the desulfurization chamber formed on the surface of the refractory with hair, $a○・AI203, will be insufficient. This is because sufficient deoxidation, desulfurization, and denitrification conditions due to calcium cannot be satisfied, and on the other hand, steel with aluminum content exceeding 0.038% has colony-like nonmetallic inclusions rich in AI203. Since AI tends to remain and has an unfavorable effect on mechanical properties, particularly ballability and heterogeneity, the content of AI in molten steel must be within the range of 0.005% or more and less than 0.06%. In the present invention, the reason why the amount of added aluminum is limited to 0.10% or less is that although the added aluminum reduces Ca○ in the backing refractory and generates Ca, the remaining dissolved aluminum is converted into nitrogen. This is because it is necessary to reduce the amount of residual dissolved aluminum because it combines to form AIN and this AIN remains in the steel and cannot be denitrified. In relation to the setting of 0.038%, the amount added must be 0.10% or less.

In the present invention, the reason why at least one of titanium and rare earth elements in the steel is limited to 0.1% or less is that 0.1% or less is contained in the steel.
If the content exceeds 0.1%, it not only becomes economically expensive but also impairs mechanical properties, so it is necessary to limit the content to 0.1% or less.

In the present invention, calcium in steel is 0.001 to 0.0
The reason for limiting the range to 3% is that the calcium content is 0.0
If the oxygen content is less than 0.01%, the oxygen in the steel should be 0.003% or less.
It is not possible to keep sulfur below 0.010% and nitrogen below 0.010%, and on the other hand, if calcium remains in the steel in an amount exceeding 0.03%, workability and corrosion resistance deteriorate.
．． It is necessary to keep it within the range of 0.001% to 0.03%.

In the production method of the present invention, argon atmosphere means that the molten metal is treated by adding AI while blowing argon gas into the molten metal in an open furnace, closed furnace or ladle, or in a closed furnace or a closed ladle. The molten metal is treated by blowing N into the molten metal when argon gas is blown into the molten metal.

Example 1 Pure iron or iron - 30% in a high frequency vacuum induction melting furnace.

The alloy 4k9 was used in the melting experiment. Alumina was used for the Gaikanga, and Ca○, a first class reagent, was used as the backing refractory material.The material was ground to about 20 mesh and then put into a Kanga mold and compacted well. The hardened kanji was baked in an electric resistance furnace and immediately put to use. Each initial oxygen o: 0.
After vacuum melting pure iron or iron alloy molten metal containing approximately 0.04%, initial sulfur So = approximately 0.01%, and initial nitrogen No = approximately 0.01%, aluminum is melted at 0.1% in an atmosphere of argon pressure.
In an experiment in which 0.05% of titanium was added, the components of each ingot after agglomeration are shown in Table 9. As shown in the table, oxygen can be reduced to 0.002% or less, sulfur can be reduced to 0.003% or less, nitrogen can be reduced to 0.006% or less, and C
The residual amounts of a were 0.003% and 0.001%. Table 9 Example of chemical composition of pure ferro-alloy ingots 2. Laboratory melting of 4K9 of r-Fe alloy or 7. Mo-Fe alloy in O2 dish IL in 4. high-frequency vacuum induction melting furnace. I did it.

As in Example 1, a refractory material made from Ca○ was used as a backing material for Naikanka. Each initial oxygen 0o = 0.0
After vacuum melting each alloy molten metal with approximately 1%, initial sulfur So = approximately 0.008%, and initial nitrogen No = approximately 0.005%, use aluminum as a deoxidizing agent*0.08 or 0.03% as a final additive. 0 or 0.03% cerium was added under reduced pressure, and after 5 minutes it was cast into a 5-fold mold. The average chemical composition of these two types of ingots is as shown in Section 1. In all cases, remarkable deoxidation, desulfurization, and denitrification were observed, and edge cracking, which tends to occur during secondary hot working, did not occur, and the ductility and bending properties of the cold worked sheet materials were significantly improved. It has come to pass. Table 10 Chemical Composition Example 3 of Alloy Materials Using a high frequency vacuum induction melting furnace with calcia refractory material (84.6% Ca○) as the backing refractory, 500k93 charges of the equivalent material in SCM22 were melted.

As a final deoxidizing agent after melting, aluminum and titanium, ferrotitanium, or aluminum and Mitsushimetal are used as a final deoxidizing agent.
It was added under reduced pressure of 0-orr, and after 10 minutes it was cast into a 20-degree ingot. Table 11 shows the average chemical compositions of these three types of ingots. By adding aluminum and titanium, ferrotitanium, or aluminum and misch metal together, a clean pongee grain steel material with low oxygen, sulfur, and nitrogen content was obtained. In addition, the absorbed energy value of each charge in the impact test is 10k9・w/ at room temperature.
, and there was little dissimilarity (C/L 20.8), and a major improvement in steel quality was observed. Table 11 1 Example of weaving low gray purple alloy 4 For melting, a vacuum/pressure type high frequency induction melting furnace with an output of 1 arc W and a side ratio of 7 was used.

The production of the limestone panel was the same as in Example 1. Electrolytic iron is 8
The dissolved amount was defined as 0.00 m. When adding the deoxidizing agent, 0.1% aluminum was added under 1 atm of argon gas to a fly Azusa bath which had been subjected to vacuum treatment at 10 to 4 Tord Fahrenheit for about 1 minute after elution in vacuum. In addition, the initial oxygen content of molten iron is approximately 5
In 0Q starvation, initial sulfur was 0.008%, 0.023%, 0
．． Deoxidation, desulfurization, and demineralization were investigated by adding the above aluminum to three types of 14% molten metals. According to these results, after 1 minute, the oxygen content of each molten metal decreased to 0.003% or less, the sulfur content decreased to 0.010% or less, and the nitrogen content decreased to 0.010% or less, indicating remarkable deoxidation. , desulfurization,
Denitrification was achieved. According to the present invention, oxygen, sulfur,
A clean steel with extremely low nitrogen content and excellent mechanical properties and workability can be obtained.

Claims (1)

[Claims] 1. molten steel in a melting furnace or ladle backed with a basic refractory containing 60% or more of CaO, without using a solvent, in a vacuum or under an argon atmosphere, with an aluminum content of 0.1%
The CaO contained in the backing material is reduced by adding 0% or less, and the generated Ca deoxidizes, desulfurizes, and denitrifies the molten steel, and adds 0.005 to 0.038% of aluminum to the molten steel.
%, leaving 0.001 to 0.03% calcium remaining,
The steel is characterized by containing less than 0.003% of oxygen, less than 0.010% of sulfur, and less than 0.010% of nitrogen, which is clean with low content of oxygen, sulfur, and nitrogen, and has excellent workability and mechanical properties. A method for producing steel with excellent properties, especially toughness, and low anisotropy. 2 Aluminum 0.1% is melted into molten steel in a melting furnace or ladle backed with a basic refractory containing 60% or more of CaO without using a solvent under vacuum or argon atmosphere.
0% or less and one or two of titanium and rare earth elements to reduce CaO contained in the backing material, and the generated Ca deoxidizes, desulfurizes, and denitrifies the molten steel, and By leaving 0.005 to 0.038% of aluminum, 0.001 to 0.03% of calcium, and 0.1% or less of at least one of titanium and rare earth elements in the molten steel,
The steel is characterized by containing less than 0.003% of oxygen, less than 0.010% of sulfur, and less than 0.010% of nitrogen, which is clean with low content of oxygen, sulfur, and nitrogen, and has excellent workability and mechanical properties. A method for producing steel that has excellent properties, especially toughness, and low anisotropy.