JPH0551667A - Seacoast high weather-resistant steel - Google Patents

Abstract

PURPOSE:To manufacture a seacost high whether-resistant steel excellent in corrosion resistance by adding mixed preliminarily treated powder of iron powder and oxide to molten steel contg. a specified amt. of P and uniformly dispersing the fine powder of the oxide into the steel. CONSTITUTION:Preliminarily treated powder constituted of a kneaded material of the fine particles of oxide such as CaO having <1mum average particle size and iron powder having <200mum average particle size is added to molten steel having a compsn. contg., by weight, <0.1% C, 0.03 to 0.35% Si, <1.5% Mn, 0.05 to 0.15% P, <0.01% S, 0.005 to 0.07% Al and 0.0001 to 0.10% Ca, and the particles of the oxide having low specific gravity are stuck to the iron powder having high specific gravity, which is infiltrated into the molten steel, and the oxide particles having <5mum particle size are uniformly dispersed into the steel. By the effect of inhibiting the infiltration of Cl ions by P in the steel and the alkalinization of the surface of the steel by the oxide such as CaO and MgO, the seacoast high corrosion resistance weather-resistant steel excellent in corrosion resistance in a corrosive environment contg. a large quantity of Cl ions such as sea water can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high coast weather resistant steel having excellent corrosion resistance in steel structures such as bridges and buildings, particularly in a corrosive environment containing a lot of chloride ions such as in the coastal area.

[0002]

2. Description of the Related Art Conventionally, Cu represented by weathering steel,
In the case of a low alloy steel containing a small amount of P and the like, it is known that the rust film formed on the steel surface by exposure to the atmosphere becomes stable rust having a high anticorrosion function. However, the stable rust described above is unlikely to be formed in a salty environment such as the coastal area. this is,
In an environment with a lot of salt, p
This is because H tends to decrease. In other words, when corrosion of steel begins, the pH of the steel surface usually tends to decrease, but once the pH of the rust film or the interface with the rust decreases, the ring ratio of chlorine ions in the rust film increases, and Concentration occurs near the steel-rust interface, which results in the formation of a hydrochloric acid atmosphere, which begins to accelerate corrosion. At the same time, the decrease in pH increases the solubility of iron ions, creating a state in which the formation of stable rust, which is the source of the anticorrosion mechanism of corrosion resistant low alloy steel such as weather resistant steel, is prevented.

As described above, lowering the pH in the rust coating creates an unfavorable situation for steel materials in which the dissolution rate of iron is increased and at the same time the formation of stable rust is prevented, but in order to prevent this, A method of preliminarily dispersing a metal oxide for alkalizing the steel surface in the steel material and causing the metal oxide to act simultaneously with the corrosion reaction to prevent the formation of the above-described accelerated corrosion condition is considered to be effective. As an example of steel invented based on such an idea, Japanese Patent Publication No. 58-
There is a 25458 publication. According to this prior art, oxides of Be, Mg, Ca, Sr, and Ba are mentioned as the additive metal oxides in the steel that are intended to have an alkalizing action on the steel surface. By adding these oxides, even if the oxides are slightly dissolved together with the base iron, the base iron interface is kept at a high pH even under rusting, whereby corrosion is suppressed.

[0004]

However, as in the above-mentioned Japanese Patent Publication No. 58-25458, B is added to ordinary steel.
Although it has been found that it is effective to cause the metal oxide to act at the same time as the corrosion reaction by alkalizing the steel surface by containing one or more oxides of e, Mg, Ca, Sr and Ba, It is difficult to uniformly disperse a pure oxide in steel by the steelmaking technology of No. 1, and therefore it is the fact that it has not been put to practical use industrially.

[0005]

In the present invention, as a result of various studies to solve such problems, the average particle size is 1
By using the pretreated powder obtained by kneading the oxide particles having a particle size of not more than μm and the iron powder having an average particle size of not more than 200 μm, it is possible to sufficiently disperse the particles in the steel even in the present steelmaking technology. The gist of the invention is, in wt%, C: 0.1% or less Si: 0.03 to 0.35% Mn: 1.5% or less P: 0.05 to 0.15% S: 0 0.01% or less Al: 0.005 to 0.07% Ca: 0.0001 to 0.10% The balance is Fe and unavoidable impurities, and the oxide particles have an average particle size of 1 μm or less and the average particle size of 200 μm or less. In the coastal high weather resistance steel, the pre-treated powder obtained by kneading the iron powder is added to the molten steel having the above composition to uniformly disperse the oxide having a particle size of 5 μm or less.

The present invention will be described in detail below. In the present invention, the greatest feature is that the pretreated powder obtained by mixing and kneading the oxide particles and the metal powder is added to the molten steel. Therefore, first, to increase the specific gravity of oxide particles to facilitate addition to molten steel, and to achieve uniform dispersion in molten steel, use iron powder to attach oxide particles around iron powder. It is intended to increase the overall specific gravity.
That is, the oxide particles adhered around the iron powder are mechanically alloyed, that is, so-called iron powder and oxide particles are treated with high energy.
Mixing in a mill (attritor), mechanical compression, breaking,
The bonding is repeated to form a powder in which oxide particles are uniformly dispersed in the matrix. Therefore, it is necessary to perform a pretreatment in which the particle diameter of the iron powder, which is a metal powder, is regulated to 200 μm or less and the iron powder is mechanically attached to the surface. The reason why the particle size of the iron powder is regulated is that the upper limit of the average particle size of the iron powder is 200 μm or less because the oxide particles and the iron powder are likely to be non-uniformly mixed when the size is too large, because of the relationship with the oxide particles. I decided. In addition, the oxide particles were 1 μm or less. The reason for this is that even if some of the oxide particles agglomerate as a result of adding the pretreated powder mixed with iron powder and kneaded to the molten steel,
In order to uniformly disperse oxides of m or less, the thickness was 1 μm or less.

The reason why these oxide particles are directly added to the molten steel is that, unlike the sintered body of the alloy steel, the highly weather resistant thick plate product is continuously mass-produced. Also, the reason for adding as a mixed powder without adding the oxide particles alone is that the oxide particles aggregate to form a powder, and the volume is increased, and the specific gravity is smaller than that of molten steel. This is because if added, it floats and does not yield in the molten steel. Aggregated oxide particles were separated and mixed with iron powder to reduce the volume. The reason for selecting iron powder is that it does not separate and float when added to molten steel. Further, CaO and MgO are used as the oxide particles. CaO and M
The reason for using gO is that, as described above, the metal oxide that alkalizes the steel surface is dispersed in the steel material in advance and the metal oxide acts simultaneously with the corrosion reaction to prevent the formation of accelerated corrosion. is there. Therefore, the present invention is not limited to these two types, as long as the same effect is achieved.

[0008]

Next, in order to achieve the desired characteristics of the present invention, it is necessary to limit the amount of each constituent element to an appropriate range as described below. C: 0.10% or less C is an effective component for improving strength, but 0.1
%, The corrosion resistance deteriorates, so the upper limit is 0.1%.
And Si: 0.03 to 0.35% Si requires 0.03% or more for deoxidation, but if used in a large amount, the toughness of steel deteriorates, and if it exceeds 0.35%, corrosion resistance deteriorates. Therefore, the upper limit was set to 0.35%. Mn: 1.5% or less Mn is an element useful as a deoxidizing agent, a desulfurizing agent, and for obtaining an appropriate structure with improved strength and hot workability.
If it exceeds 1.5%, the strength is increased but the workability such as bending and the toughness are deteriorated, and particularly the weldability is deteriorated.
The upper limit was 5%.

P: 0.05 to 0.15% P is an essential element for preventing harmful chlorine ions from penetrating into the rust film and forming stable rust, and at least 0.05%. However, if the content exceeds 0.15%, the weldability deteriorates, so the upper limit was made 0.15% or less. S: 0.01% or less Since S is an element that deteriorates corrosion resistance, the allowable upper limit is 0.01%. Al: 0.005-0.07% Al is usually used as a deoxidizer 0.005-
The range was 0.07%. Ca: 0.0001 to 0.1% Ca is an effective element for improving the corrosion resistance, and the improving effect is effective if 0.0001% or more relative to the weight of steel is contained, but 0.1% If it exceeds 1.0, the workability and weldability deteriorate, so the Ca content is 0.0001 to 0.1%.
And

CaO has a function of alkalizing the steel surface. This CaO is dispersed in the steel in advance, and CaO acts at the same time as the corrosion reaction so that the pH of the steel surface becomes high.
The passivation film produced by densification is made denser to give stronger corrosion resistance. Due to this alkalinization, the average particle diameter of the oxide needs to be 5 μm or less in order to dissolve it in rust, and if it exceeds this, it becomes insoluble or non-uniformly dissolved, and its effect decreases. Further, MgO also behaves similarly to CaO.

[0011]

EXAMPLE A mixed powder was produced by placing iron powder and CaO powder in a container together with a tungsten carbide ball and mixing them with an attritor. Average particle size of iron powder at that time 100
~ 150μm, average particle size of CaO powder 0.1 ~ 0.5μ
m is mixed at a volume ratio of iron powder and CaO particles of 5 to obtain a pretreated powder. On the other hand, after the molten steel whose alloy composition has been adjusted in a high-frequency melting furnace having a capacity of 300 kg is deoxidized with Al, the pretreated powder is injected into the molten steel flow during casting by argon gas, and then the steel is discharged to the mold. The steels of the present invention at that time are shown in Table 1 together with comparative examples. 20m by hot rolling of steel ingots with these chemical components
A steel plate having a thickness of m was used and heat-treated in a usual manner. After that, three kinds of tests of a seawater immersion test, a soil burial test, and a semi-industrial zone air exposure test were conducted. The results are shown in Table 1 for corrosion rate,
It was indicated by pitting corrosion. As can be seen from Table 1, the steels of the present invention (1) to (10) have the corrosion rates of various exposure tests of the conventional steels (11) to (15), which is 100 steel.
It can be seen that the corrosion rate ratio of the steel of the present invention is very small. Regarding the pitting corrosion, when the presence or absence of pitting corrosion on the surface is examined, the steels of the present invention have almost no pitting corrosion and a small amount of thickness reduction. On the other hand, all the comparative steels were in a state where the unevenness was large and the corrosion was advanced.

[0012]

[Table 1A]

[0013]

[Table 1B]

(1) Seawater immersion test (0.5 years): After immersing in seawater, the rust of the test piece was removed, and after pickling with sulfuric acid containing inhibitor, the weight was measured and the corrosion weight loss was determined. (2) Soil burial test (1 year): Buried 30 cm below the ground,
Seawater was sprayed every 3 months, and after 1 year, the test piece was taken out, and the weight was measured after rusting and pickling, and the corrosion weight loss was obtained. (3) Semi-industrial zone atmospheric exposure test (0.5 years): The degree of corrosion progress was determined by increasing the amount of corrosion after exposure. (Note) Table 1 * 1: Corrosion rate: Corrosion ratio of the steel of the present invention when the corrosion rate of the conventional steel is 100. * 2: Pitting corrosion: Presence or absence of surface pitting corrosion. ⊚: Almost no pitting corrosion and slight metal loss. ◯: Good as a whole with some unevenness. X: Large unevenness and corrosion progresses and is defective.

[0015]

As described above, according to the coast-high weathering steel by oxide dispersion according to the present invention, compared with the conventional chloride-resistant alloy steel, saltwater-resistant seawater, coastal atmosphere, and soil. The weather resistance is extremely improved in the environment exposed to the atmosphere, and it is possible to disperse CaO uniformly in the steelmaking process easily at a low cost, and it is possible to mass-produce it. Is.

Claims (1)

[Claims] 1. By weight%, C: 0.1% or less Si: 0.03 to 0.35% Mn: 1.5% or less P: 0.05 to 0.15% S: 0.01% or less Al: 0.005-0.07% Ca: 0.0001-0.10% Oxide particles composed of the balance Fe and unavoidable impurities and having an average particle size of 1 μm or less and iron powder having an average particle size of 200 μm or less. A coast high weather resistance steel characterized in that the kneaded pretreated powder is added to the molten steel having the above-mentioned composition to uniformly disperse the oxide having a particle size of 5 μm or less.