JPH01319623A - Production of clean steel - Google Patents

Abstract

PURPOSE:To convert the nonmetallic inclusions contained in the steel so as to have a low melting point and to have easy stretchability and to prevent the disconnection of a steel wire rod for tire cords in a drawing stage and twisting stage by making combination use of an Si deoxidizing agent and an alkali metal compd. as a deoxidizing agent at the time of deoxidizing and cleaning the raw material molten steel for the above-mentioned steel wire rod. CONSTITUTION:The alkaline agent consisting of silicate such as Na2SiO3 or K2SiO3 or fluoride such as LiF or NaF is added together the composite deoxidizing agent of an Si system or Si-Mn or Si-Mn-Al system into the melt of the raw material high- carbon steel or under stirring of the molten metal by gas blowing from bottom blown tuyeres at the time of producing the steel wire rod for tire cords as the reinforcement material of the radial tires of automobiles. The residual nonmetallic inclusions of the Al2O3 system or SiO2 system, etc., in the steel which are plastically deformable are converted to the inclusions having the properties to be easily stretched in the working direction to form the wire rod at the time of hot rolling or drawing. The steel wire rod for tire cords is produced at a high yield without being disconnected by the presence of the inclusions at the time of the hot rolling and drawing of the steel stock.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention controls and rolls non-metallic inclusions generated by deoxidation treatment into a composition that is easily plastically deformed, thereby creating wire with excellent drawability and fatigue resistance. The present invention relates to a method for manufacturing clean steel that can provide steel materials, particularly high carbon steel wires.

[Prior Art] High carbon steel wire rods For example, steel wire rods for tire co-1 used as reinforcing materials for automobile radial tires are generally 5.5 m long.
It is manufactured by drawing mφ wire rod into high-strength ultrafine wire rod of 015 to 0.38 mmφ and then twisting the wire rods together.
Wire breakage is likely to occur in the manufacturing process, especially in the wire drawing process and the wire twisting process, resulting in a productivity rate of 1.

This results in a decline in quality, etc. One of the causes of wire breakage that is due to the material is the presence of non-metallic inclusions such as alumina-based hard inclusions mixed into the wire, and these non-metallic inclusions can shorten tie life and cause fatigue rupture of tire cords. It is also the cause.

In order to overcome this situation, various researches have been conducted on technologies to prevent the formation of non-metallic inclusions, especially alumina-based inclusions, and some practical technologies have also been developed. Is it the reduction of the amount of Al mixed into molten steel, as typified by the regulation of the amount of impurity Al in the agent?
Or, most of them were based on restrictions on the use of alumina-based refractory materials.

[Problem to be solved by the invention] However, even if the A1 strain mixed into molten steel is thoroughly reduced, it is not possible to completely prevent the mixing of A1, and trace impurities from ferroalloy raw materials etc. Contamination from slag adhering to ladles, contamination from impurities concentrated in the base metal, contamination from alumina-based refractories that must be used, etc. can be avoided. I can't come. Also, as the amount of A1, which is a deoxidizing element, is added, free oxygen increases, and it reacts with 81 in molten steel, making it easier to form 5in2 inclusions.This tendency becomes more pronounced as the steel becomes higher in Sl. Although the 5i02 inclusions thus generated are not as hard as alumina inclusions, they still cause deterioration of fatigue resistance because they are not stretched during hot rolling.

The present invention has been made in view of these circumstances, and it is possible to eliminate the adverse effects of non-metallic inclusions, particularly alumina inclusions, and to produce a steel material with excellent wire drawability and fatigue resistance. The present invention aims to provide a method for manufacturing.

[Means for Solving the Problems] According to the method of the present invention, when producing clean steel by adding a deoxidizing agent to molten steel, a mixture of an S1 deoxidizing agent and an alkali metal compound is used or a bottom blowing method is used. When producing clean steel by adding a deoxidizing agent to molten steel while stirring,
The gist of this method is that after adding the alkali metal compound to the bubble floating position of the bottom-blown gas, the Sl-based deoxidizing agent is added to the same position immediately.

[Function] Alumina-based and 5in2-based nonmetallic inclusions are hard inclusions as described above, or if they contain an alkali metal compound, their melting point decreases significantly and plastic deformability is greatly improved. Ru. That is, the nonmetallic inclusions containing the alkali metal compound can be drawn into a thin thread-like shape during hot rolling, and can be made into a form that is harmless to wire drawability and fatigue resistance.

Based on this knowledge, the present inventors have conducted various studies in an attempt to solve the above problem by adding an alkali metal compound to the molten steel deoxidizing process. However, many alkali metal compounds are unstable at high temperatures, and even if they are added directly to molten steel, it is difficult to incorporate them efficiently into nonmetallic inclusions. Therefore, the inventors of the present invention proposed including an alkali metal compound in the deoxidizing agent, and produced an S1 deoxidizing alloy containing an alkali metal. When molten steel is deoxidized using the Si-based deoxidizing alloy, the Si-based deoxidizing agent as well as the alkali metal compound can be smoothly dissolved into the molten steel, and the alkali metal is contained in the deoxidized product. was able to be contained smoothly.

However, in Sl-based deoxidizing alloys containing alkali metals, the boiling point of the alkali metals is low, so there is a drawback that there is a large evaporation loss of the alkali metals during melting, and the price of alkali metals is not cheap, so the cost of raw materials increases. There was a problem with this, and I felt that there was a need for further improvement.

The present invention was completed based on these circumstances, and as shown in the above structure, an S1 type deoxidizing agent and an alkali metal compound are used together in the deoxidizing treatment, thereby converting the deoxidized product into a composition containing an alkali metal. The gist of the invention is to control the As for the mode of combined use,
First, there is a case where a deoxidizing agent composition containing a Si-based deoxidizing agent and an alkali metal compound is used. In other words, during deoxidation, deoxidation products precipitate and grow using refractories and slag particles suspended in molten steel as nuclei, and also involve alumina inclusions floating in molten steel. Since the deoxidizing agent and the alkali metal compound are not supplied in a mixed state to the deoxidizing reaction point, the alkali metal can be incorporated into the deoxidizing product. On the other hand, alkali metal compounds have poor thermal stability, so if they are added alone to molten steel without any special measures, they cannot be efficiently incorporated into nonmetallic inclusions.

However, if the Si-based deoxidizing agent is dissolved in molten steel and an alkali metal compound is supplied in advance to the place where the deoxidizing reaction occurs, and then the S1-based deoxidizing agent is immediately introduced, then the Si-based deoxidizing agent is not necessarily dissolved. It turns out that it is not necessary to supply the agents in a mixed manner. For example, while molten steel is stirred with Ar bottom blowing, an alkali metal compound is added to the surface of the molten steel where Ar bubbles float to the surface, and the molten metal is suspended.If a Sl-based deoxidizing agent is immediately added to the same place, it becomes a Si-based deoxidizing agent. It was found that the molten alkali metal compound on the surface of the molten metal is dissolved in the molten steel, and the alkali metal can be efficiently contained in the alumina-based inclusions that are deoxidized products.

By supplying the Si-based deoxidizing agent and the alkali metal compound to the deoxidizing reaction point as described above, it is possible to form a deoxidized product with good plastic workability without particularly alloying the two in advance. The purpose can be achieved without causing evaporation loss of the alkali metal compound during the preparation of the deoxidizing agent.

Regarding the deoxidizing agent used in the present invention, the composition is not particularly limited as long as it is an S1-based deoxidizing agent, but the concept of Si-based deoxidizing of the present invention includes in addition to S1 deoxidizing, It also includes composite deoxidation and Si-Mn-A I composite deoxidation.
-Mn, Fe-3t.

Fe-A1 or the like may be used in a suitable combination. There are also no particular restrictions on the type of alkali metal compound.Among the alkali metal compounds, silicates (N a2 S i 03.
S i 03, etc.) or fluorides (LiF, NaF, etc.) are recommended.

[Example 2501- If [C
: 0.82%, Si: 0.25%, Mn: 0.50%
) 2401-n was melted and then deoxidized under the following conditions.

A mixture of 1500 kg of Fe-Mn, 1800 kg of Fe-3, and 300 kg of sodium silicate (N82 SiS103) was added in advance to a ladle, and FA steel was poured onto it from a converter. After finely adjusting the components using an RH degassing device, it was cast using a bloom continuous caster.

Example 2 Only Fe-Mn alloy (15
A mixture of 830 kg of Fe-3t alloy and 170 kg of thorium to be fluorinated was further added while performing arc heating and refining using an LF (molten steel heating ladle refining device). Thereafter, bloom continuous casting was performed in the same manner as in Example 1.

Example 3 Only Fe-Mn alloy (15
00 kg) was added, and a mixture of 200 kg of sodium silicate and 100 J of lithium fluoride was further added to the position where the bubbles of Ar for stirring rose using LF, and immediately Fe
-830 kg of 3t alloy was added. Thereafter, bloom continuous casting was performed in the same manner as in Example 1.

Comparative Example 1 Fe-Mn alloy 1500k was used when tapping steel from a converter to a ladle.
After adding g and 800 kg of Fe-3t alloy, vacuum degassing was performed using -RH, and continuous bloom casting was performed in the same manner as in Example 1.

Comparative Example 2 When steel is tapped from the converter to LF, Fe-Mn alloy y),
(tso okg) and roughly remove Fe-
After adding 830 kg of 3t alloy, continuous bloom casting was performed in the same manner as in Example 1.

Wire rods for tire coating with a diameter of 5.5 mm were produced from each of these blooms by hot rolling, and the size of inclusions in a cross section in the rolling direction at the central position in the length direction was measured using a microscope. The results are shown in Figure 1. or obtained. The size of the inclusions was evaluated based on the dimension in the direction perpendicular to the rolling direction, that is, the thickness. The measurement was carried out by taking 10 microscopic surfaces of 5.5 mm x 15 mm from each chassis of the above examples and comparative examples, and the average value was determined. Further, each chassis was measured three times. If the inclusions are easily stretched and their shape is controlled, they should be stretched like hot-rolled yarn and the thickness of the inclusions should be extremely small.

As shown in FIG. 1, no inclusions larger than 75 μm were observed in the example, and the inclusions were controlled to a substantially harmless size of 5.0 μm or less, whereas in the comparative example, the inclusions were 1.
Inclusions with a diameter of 0 μm or more were also observed, and it can be seen that the inclusions were changed into ones with a low melting point and easy to stretch by implementing the present invention. As a result of quantitative analysis of the inclusion composition using EPMA, the amount of inclusions in the comparative example was 0 to 2% in alkali metal compound amount (converted value), while in the example it was 4 to 24%.
(converted value).

[Effects of the Invention] According to the present invention, it is possible to stably and reliably control the shape of hard inclusions such as alumina-based inclusions and 5102-based inclusions, which are difficult to plastically deform even during hot rolling, into ones that have a low melting point and are easy to stretch. It comes. Thus, in steel for tire cords, it is possible to prevent wire breakage during the wire drawing and wire twisting steps, increase the life of the tie, and provide a tire coat with excellent fatigue resistance. Furthermore, it is possible to improve the fatigue resistance not only in tire coats but also in various steel plates and steel materials, and it is also possible to prevent deterioration of surface quality due to hard inclusions.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the distribution of the number of inclusions for each thickness of inclusions in Examples and Comparative Examples.

Claims (2)

[Claims] (1) When producing clean steel by adding a deoxidizing agent to molten steel, it is possible to control the composition of the deoxidized product to include alkali metals by using a mixture of a Si-based deoxidizing agent and an alkali metal compound. Characteristic clean steel manufacturing method. (2) When producing clean steel by adding a deoxidizing agent to molten steel while performing bottom blowing stirring, after adding an alkali metal compound to the bubble floating position of the bottom blowing gas, immediately add Si-based deoxidizer to the same place. A method for producing clean steel, characterized in that the composition of a deoxidized product is controlled to include an alkali metal by adding an agent.