JPH01116023A - Dephosphorizing agent for blowing into chromium steel - Google Patents

Abstract

PURPOSE:To easily dephosphorize Cr steel in a short time by using a dephosphorizing agent consisting of specified amts. of alkaline earth metal carbonate, alkali metal carbonate, alkaline earth metal and alkali metal halide and having a specified diameter. CONSTITUTION:A compsn. consisting of 60-100wt.%, in total, of 30-60wt.% alkaline earth metal carbonate and alkali metal carbonate and the balance alkaline earth metal and alkali metal halide with inevitable impurities is uniformly mixed, granulated, calcined and regulated to 1-0.2mm diameter. When the resulting dephosphorizing agent for blowing is used, Cr steel can easily be dephosphorized without increasing the viscosity of refining slag due to the oxidation of Cr or solidifying the slag.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dephosphorizing agent used in an injection dephosphorization method for Cr-containing steel, specifically steel containing 3% by weight or more of chromium.

[Conventional technology]

As a dephosphorization method for chromium-containing steel, a ``reductive dephosphorization method'' is known in which calcium phosphide is fixed and removed using a calcium-containing flux such as calcium metal or calcium carbide. r(1) contains 3.0% or more of Cr, and the C concentration is 0.
CaC of 0.5-5.0% of the amount of molten steel is added to chromium-containing molten steel whose 5ifi degree is adjusted to 0.5% or less.
2, 0.2-3.0% CaO, 0.03-0.3
% NaF and 0.05-0.5% NaffAlFc
A method for dephosphorizing chromium-containing steel, characterized by administering a flux consisting of and causing a reductive dephosphorization reaction. ' has been disclosed.

The following method is also known for dephosphorizing chromium-containing steel by the "oxidation refining method" using highly basic oxidizing slag.

(1) A method using barium oxide, which is a strongly basic oxide, as the main component, for example, in JP-A-62-112716, barium oxide or carbonic acid is added to a molten metal containing 30% by weight or less of Cr. Salt 30-70% by weight.

- 20 to 60% by weight of alkaline earth metal halides.

- A method for descaling a chromium-containing molten metal, characterized in that dephosphorization is carried out by adding a flux containing 1 to 20% by weight of an alkali metal carbonate as a main component. ' has been disclosed.

(2) Even more specific! A method aiming at preferential oxidation of phosphorus under two elemental partial pressure conditions, for example, JP-A-61-195912,
"When dephosphorizing and refining a molten iron alloy containing 3% by weight or more of chromium using a flux whose main components are oxides and/or carbonates and/or halides of metal elements, A flux whose components other than the compounds of iron, chromium, manganese, cobalt, molybdenum and nickel are expressed by the following formula (1) is used, and the oxygen partial pressure of the molten chromium-containing iron alloy during refining is determined by the following formula (2). A method for dephosphorizing a molten chromium-containing iron alloy, which comprises performing a refining process as part of the process.

0.80≦A≦0.95
...(1)-41600/T+8.60≦logP
O2≦-41600/T +10.10
...(2) Here, Δ=Σ(αi-Ai-Mi-ni-Zi)/Σ(Mi-
ni-Zi) Mi: Molar fraction of each component molecule ni: Number of metal elements forming one molecule of each component 21: Formal charge per each metal element A i: l/(1,
36(x i-0,26)) xi: Pauling's electronegativity of each metal element αi: The following constant determined by the compound form of each component molecule αi = 1.0 for oxides or carbonates αi = 1.0 for chlorides αi = 0, 9 When using a halide other than chloride, αi = 0, 7 po: Oxygen partial pressure of molten chromium-containing iron alloy during refining a
There is a disclosure of a method in which tm T: temperature 'K J.

[Problem that the invention seeks to solve]

However, in the above-mentioned reductive dephosphorization method, since calcium, which has a vapor pressure of 1 atm or more at steel-making temperature, reacts with phosphorus in the steel, loss due to evaporation of calcium is unavoidable, and the produced calcium phosphide and The problem is that phosphine, a toxic gas, is produced by reaction with atmospheric moisture and water, making it extremely difficult to stabilize the produced slag.

Furthermore, in the oxidative dephosphorization method using slabs based on highly basic barium oxide, etc., chromium oxide, iron oxide, etc. are required as oxidizing agents, and in order to suppress the oxidation of chromium, smelting under a low oxygen potential is required. and necessarily a few percent
The drawback was that it was limited to dephosphorization of custom-made high carbon, high chromium steel. There is also the problem that removing the slag requires a great deal of effort because of the increased viscosity or solidification of the slag due to the added chromium oxide and/or the produced chromium oxide.

c. Means for Solving the Problems] The present invention aims to solve the above problems and easily dephosphorize a wide range of chromium-containing steels from low chromium-low carbon steels to high chromium steels. As a result of intensive studies, this invention has been developed, and its main points are as follows.

(1) Alkaline earth metal carbonate (e.g. calcium carbonate or barium carbonate) is 30 to 60% by weight (hereinafter weight % is referred to as %) and the sum of alkaline earth metal carbonate and alkali metal carbonate is 60 to 60% by weight 100% and the remainder consists of alkaline earth metal halides (e.g. calcium fluoride, calcium chloride, barium chloride, etc.) and/or alkali metal halides and small amounts of unavoidable impurities (e.g. silicon oxide, iron oxide, etc.) Characteristic dephosphorizing agent.

The above composition needs to be mixed to a uniform composition and directly injected into the chromium-containing mixture, and for this purpose the following embodiment is desirable.

(2) A dephosphorizing agent in which all of the above compositions are made into powder of 0.15 nn or less, mixed uniformly, calcined at a temperature of 700°C or less, and the calcined mass is sized to 1 to 0.2 - .

(3) Alternatively, a dephosphorizing agent obtained by heating and melting the above composition above the melting point and above 800° C., and sizing to 1 to 0.2+ nm by, for example, an atomizing method or a mechanical crushing method.

[Effect]

The effects of each composition will be explained in detail below.

The oxidative dephosphorization reaction between phosphorus in steel and slag is as follows: 2[,P]+5(0)+(MxO)=(MxO-P,O
S) Here, [P]: Phosphorus in molten steel [O]: Oxygen in molten steel MxO: Represented by alkaline earth metal (x = 1) or alkali metal (x = 2) oxide, excluding phosphorus in steel For this purpose, supply of oxygen and a strong basic oxide for fixing the produced phosphorus oxide are essential, and for low chromium content steels of 31 or less, gaseous oxygen and/or iron oxide are used as the oxygen source.

Calcium oxide is commonly used as a basic oxide.
In the case of chromium-containing steel, chromium oxide or iron oxide was used as the oxidizing agent, and barium oxide, lithium oxide, and sodium oxide were used as the basic oxides. Furthermore, the dephosphorization reaction described above is advantageous because the reaction progresses toward the dephosphorization side when the humidity is low.

In the present invention, the basic principle is exactly the same as the dephosphorization reaction principle described above, but (1) an alkaline earth metal and an alkali metal carbonate are used as the base oxide and the oxidizing agent, and (2) the carbonate is added to the molten metal. By adding directly to.

The aim is to perform dephosphorization using carbon dioxide generated during the process of melting and decomposition of carbonates as an oxidizing agent and simultaneously generated active alkaline earth metal and alkali metal oxides as a base agent.

(3) The alkaline earth total oxides produced at this time, such as calcium oxide, oxide, and barium, are themselves strongly basic and have a phosphorus oxide fixing effect, but they are solid at steelmaking temperatures and are not sufficient when used alone. The reaction does not proceed.

Moreover, if the alkaline earth metal carbonate is 60% or more, solid oxides are generated in the generated slag, and the effect is reduced.

(4) For this reason, it is essential to lower the melting point by co-adding an alkali metal oxide, such as lithium oxide, sodium oxide, and potassium oxide, and this also reduces the phosphorus oxide fixing effect of the alkali metal oxide itself. Can be used.

However, alkali metal carbonates are expensive in terms of cost, and the generation of evaporated substances such as sodium carbonate due to thermal decomposition is significant, so it is necessary to keep the addition of alkali metal carbonates to the minimum necessary. The amount should remain below 30%.

(5) Furthermore, alkaline earth metals and/or alkali metal halides (e.g. barium chloride, calcium fluoride, lithium fluoride, sodium fluoride, etc.) are effective as melting point depressants for the alkaline earth metal oxides produced. However, it does not have a phosphorus oxide fixing effect by itself, and adding a large amount will result in a decrease in dephosphorization ability, so it must be kept to the minimum necessary amount, and should be kept at a maximum of 40% or less.

From the above effects, 30-60% alkaline earth metal carbonate and 60-100% alkaline earth carbonate + alkali metal carbonate.

and alkaline earth metals and/or alkali metal halides.

A composition consisting of

Note 1: For example, impurities such as silicon oxide, aluminum oxide, and phosphorous oxide significantly impair the dephosphorizing ability, and iron oxides such as iron oxide and chromium oxide act as oxidizing agents, but conversely lead to oxidation of chromium. Since these impurities are dangerous, they should be controlled to the lowest possible amount.

(6) In addition, in the present invention, phosphorus in steel is oxidized by carbon dioxide gas generated by decomposition of carbonates, and phosphorus oxide is reacted with nascent active alkaline earth metals and alkali metal oxides generated by decomposition. It is based on the principle of fixation, and adding it to the molten metal surface in the furnace as in normal refining has little effect, so it is preferable to add it directly into the molten metal, for example by blowing it with an inert gas. It is essential to add the composition of the present invention after sizing it into particles of 1 to 0.2+am.

(7) It is more desirable to use the composition of the present invention as a homogeneous composition by mixing and calcining or premelting, but in the case of calcining, the powders are mixed uniformly.

It is necessary to crush it to 0.15 m or less. During calcination or premelting, decomposition of carbonate may progress and reduce the amount of carbon dioxide as an oxidizing agent, and in the case of calcination, 7
It is necessary to limit the temperature to 00°C or lower, and even in the case of pre-melt to 800°C or lower.

〔Example〕

The present invention will be explained in detail with reference to Examples below.

(Example 1) In a 10 kg capacity atmospheric high frequency induction melting furnace, (A) 0.4%
C-5% Cr-0.03% P steel, and (B) 1.4%
Melt C-11% Cr-0.03% PM, 160
Table 1 shows the results when 50g of various fluxes were pulverized after being calcined at a low temperature and blown with Ar gas at a rate of 50g per 251kg of melt under conditions of 0-1500°C.

Note that the dephosphorization rates in Table 1 were calculated using the following formula.

Dephosphorization rate = (Initial P% - P% after blowing) / (Initial P%) X
100 Also, since all industrial grade raw materials were used as the raw materials for blending the flux, they contained a small amount of impurities.

As shown in Table 1, according to the method of the present invention, the reaction proceeds while the slag floats in the molten metal under sufficiently strong basic and weakly oxidizing conditions, making it possible to obtain a dephosphorization rate of 60% or more. can.

(Example 2) Test No. 2 (55% calcium carbonate-45% lithium carbonate system) and Test No. 5 (50% barium carbonate-10% Sodium carbonate - 40% barium chloride system) powder of 150 meshes (0.1 nm or less) was mixed and held at each temperature of 500 to 1000 ° C for 10 minutes,
Figure 1 shows the results of measuring the weight loss due to heating, that is, the amount of carbon dioxide released due to decomposition of carbonate.

As shown in FIG. 1, it was observed that all of them started melting at 750 to 800°C, and that carbon dioxide was rapidly released when heated above 800°C. For this reason, it can be seen that a temperature of 700° C. or lower is appropriate for calcination.

(Example 3) The same formulation as Test No. 2.5.6 in Table 1 was calcined or premelted under the conditions shown in Table 2.
Table 2 shows the test results when the particles were sized to a fine grain size and blown under the same conditions as in Example 1.

As shown in Table 2, conditions 2 of the present invention where the amount of carbon dioxide reduction is small
', 2', 5', and 6'' will improve the dephosphorization rate compared to mixed powder injection, but in the case of high-temperature premelt where most of the carbon dioxide is released, 2# and 6#' will significantly improve the dephosphorization rate. descend.

From the above, a suitable temperature is 700°C or less for calcining, and 800°C or less for premelt.

〔Effect of the invention〕

According to the method of the present invention, relatively inexpensive and strongly basic alkaline earth metal carbonates such as calcium carbonate and barium carbonate can be used extensively without increasing the viscosity of the refining slag due to chromium oxidation and without assimilation. It can easily dephosphorize chromium-containing steel in a matter of hours.

In the above "Detailed Description of the Invention", the explanation has been limited to carbon-chromium-phosphorus molten metal, but the invention is not limited to this, and tool steel,
Applicable to a wide range of materials such as stainless steel.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between heating temperature and weight reduction rate of flux according to the present invention.

Claims (1)

[Scope of Claims] 1 Alkaline earth metal carbonate is 30 to 60% by weight, and the sum of alkaline earth metal carbonate and alkali metal carbonate is 60 to 100% by weight, and the remainder is alkaline earth metal. A blown dephosphorizing agent for chromium-containing steel, characterized in that it is a composition consisting of an alkali metal halide and/or an unavoidable impurity, and has a particle size of 1 mm or less and 0.2 mm or more. 2 The composition described in item 1 is pulverized and mixed to a particle size of 0.15 mm or less, then calcined at 700°C or less to reduce the particle size to 1 mm or less.
．． A blown dephosphorizing agent for chromium-containing steel, characterized by having sized particles of 2 mm or more. 3. A blown dephosphorizing agent for chromium-containing steel, characterized in that the composition according to item 1 is melted at a temperature of not less than the melting point and not more than 800° C., and the particle size thereof is sized to be 1 mm or less and 0.2 mm or more.